PNEUMONIC PLAGUE

KARL F. MEYERGeorge William Hooper Foundation, University of California Medical Center, San Francisco, California

The primary pneumonic plague outbreaks inOakland in 1919 and Los Angeles in 1924 consti-tute good points of reference for epidemiologicalobservations and experimental studies on thisform of plague. Retrospective analysis of themreveals some still unanswered questions.

In the Oakland outbreak (24), a man wenthunting in the hills of Contra Costa County inApril 1919 and perhaps took home a squirrel forfood. He fell ill about 4 days later, having anaxillary bubo and a secondary pneumonia.Another man living in the same house contractedplague and in turn passed it directly or indirectlyto 12 others. All of the patients died, plus twophysicians and two nurses. Confusing clinical andbacteriological observations raise some doubtthat plague was the cause of death of one of thenurses. The disease was first taken to be in-fluenza, but the diagnosis was changed afterbipolar bacilli were seen in smears from the lungand after animal inoculation tests in one case.Plague was not found among 6,000 rats trappedsoon afterward, but infected squirrels were dis-covered in the area where the man had hunted.The weather was warm and dry.As reported on the Los Angeles outbreak (9),

in October 1924 a Mexican woman died after anillness of 4 days. Her husband and nurse becameill and both died. The cause of death of the hus-band was given as "double lobar pneumonia."Within 2 days, 32 cases of pneumonic plague,all fatal, were discovered in persons living in thehouse and in friends and relatives who hadvisited the home of the first patient, who prob-ably had had a secondary plague pneumonia.Among them were four children 10 years old orless, one woman of 50, a priest, a nurse, and anambulance driver who helped transport the pa-tients. Bubonic plague had been diagnosed inother patients in the area, and plague bacilliwere found in commensal rats that had in allprobability contracted it from squirrel fleas. Theclimate was not unusual.The clinical histories, autopsy reports, and

cultures of the plague strains isolated from tenof the victims did not indicate where the first

patient contracted the infection nor preciselyhow it spread.

Similar epidemics had been observed in India(50) and in Manchuria in 1910-1911 and 1920-1921. According to the classical account ofSticker (56, 57), pneumonic plague was first seento be associated with bubonic plague in the 14thcentury. In few accounts is it clear whether thepneumonia was primary or secondary and towhat extent it was contagious. By the middle ofthe 16th century it was noticed that pneumonicoutbreaks were preceded by bubo pest.From the earliest time the question of how

plague spreads has been the foremost one. Atfirst this was a very simple question, and forlack of specific information the principle of iso-lation was applied if possible. So far as thepneumonic form is concerned, the question re-mains largely unanswered even though manyempty spaces in general knowledge of plague andits spread, especially the bubonic form, have beenfilled.

In a valuable collection of letters at the Uni-versity in Basel, Switzerland, between the human-ists and Paracelsists dealing with plague in 1563-1564, a significant, simple, still tenable conceptof spread is spelled out (23). J. Crato, in a letterdated 1565 and addressed to Theodor Zwinger,wrote that transmission of pneumonic plague isdue to inhalation of plague seminaria in theexpired air of plague patients who exhale theplague contagium and disperse it in the air. Thesignificance of the concept, that pneumonicplague is airborne, was not realized because inthe depopulating epidemics that gave it thename of Black Death, pneumonia was subordi-nate in the spread of plague in Europe. Proce-dures to test this concept became available onlyduring the most recent pandemic and the greatManchurian pneumonic plague epidemics of1910-1911 with 60,000 deaths. Their extremeinfectivity under climatic and living conditionsfavorable to spread are well documented (68).The pneumonic form was first bacteriologicallyproved by Childe (6) in cases in Bombay in 1896.

Strong and Teague (58) and Strong, Crowell,249

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

KARL F. MEYER

and Teague (59) furnished the first experimentalevidence to support Crato's theory of spread.After exposing plates of agar through the wardsin the neighborhood of patients and before pa-tients during and between coughing spells, theysaw that more plague bacilli were disseminatedinto the air during coughing than during talkingor breathing. They did not measure the maximaldistance but estimated that droplets might bepropelled several yards. Little was known 50years ago about the behavior of airborne dropletsor the existence of droplet nuclei. Variation inthe humidity of the air was recognized as a fac-tor, and the effects of atmospheric dryness andcold were seen in experiments. Cold, high relativehumidity, and the presence of mucus in sputumwere believed to prevent droplets from drying orsettling quickly. At the International PlagueConference (21) in Mukden in 1911, where thesefindings were reported, the conclusion was reachedthat since in many cases transmission has followedclose approach to or actual contact with a pa-tient and since the wearing of an efficient anti-microbial mask protects, pneumonic plague is anaerial infection.Some disagreed, believing that plague bacilli

are introduced orally, through kissing or withfingers soiled with feces of plague-infected fleasor during handling of plague-infected wildrodents. Laboratory infections, for example, inthe Allgemeine Krankenhaus in Vienna, sup-ported this idea. An animal caretaker handlingguinea pigs with cutaneous lesions contractedpneumonic plague, which rapidly spread to hisphysician and then the physician's nurse (36),as did the Los Angeles outbreak. It was thoughtto have been the funeral of the first victim thatthoroughly saturated these demonstrative peoplewith Pasteurella pestis. Dust contaminated withthe feces of plague-infected rodents or beddingsoiled with the sputum of pneumonic plaguepatients was believed to produce primary lunginfection. True, direct contact may spread theinfection, but the air seems to be the usualconveyor of pneumonic plague among humanbeings.

Although this infection has an unequaled repu-tation for contagion, there have been circum-stances in which patients with secondary pneu-monia or with pneumonic plague neither initiatednor continued epidemics. Why an occasionalpatient with a terminal pneumonia suddenly

begins to infect contacts approaching him orbreathing the same air also remains a puzzle;perhaps exhalation of the organisms is not con-stant. Furthermore, the early studies on plagueby the Indian Plague Commission (20) wereexplicit in indicating that the relationship be-tween inhalation of plague bacilli into the respira-tory tract and the supervention of primary plaguepneumonia is not necessarily direct.Some unusual character of the infecting or-

ganism was suspected to be responsible for thepneumonic character; during this immediatepostmicroscopic period the organism was themajor preoccupation. Neither serological norcultural differences that would enable predictionof clinical effects have been detected amongplague strains. Enhanced specific tropism forlung tissue cannot be revealed by any knowntechnique. Secondary lung manifestations are byno means usual in animals inoculated percu-taneously or subcutaneously with strains freshlyisolated from the sputum or lung tissue frompneumonic plague patients; guinea pigs havesuccumbed quickly, showing septicemia andmoderate adenopathy within 3 to 4 days. Freshlyisolated strains from bubonic plague patientshave had the same effects. On the other hand,almost all rodents infected cutaneously withplague bacilli, whether from pneumonic or bu-bonic plague, show disseminated foci of broncho-pneumonia when they survive longer than 6 days.They show tendencies to pulmonary localizationeven if the skin is merely denuded and notscarified; this is true particularly when the issueof the fatal infection is delayed (8). Neitherexalted virulence nor pneumotropism accountedfor the characteristics of the Oakland and LosAngeles episodes.

Another explanation was that the strains fromwild rodents were particularly likely to causesecondary lung involvement. The epidemiologicalevidence, however, is not convincing. In theUnited States, except for the two mentionedoutbreaks, pneumonic plague has not beenobserved. Most cases of wild rodent origin haveoccurred singly, and secondary pulmonary com-plications have been inconspicuous. Furthermore,pneumonic plague is the usual form in Mada-gascar and Indonesia, where ordinary domesticrats form the reservoir.With the introduction of the biotest, the use of

flea inoculations, to locate wild rodent plague foci

250 [VOL. 25

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

PNEUMONIC PLAGUE

in California, it was noted that macroscopic lunglesions were not uncommon in test animals. Atfirst this observation was considered significant,but it was soon observed that plague bacilliwhich resided in domestic fleas produced lunglesions as readily as those in wild rodent fleas.This was particularly noticeable in guinea pigswhich died after the sixth day. On artificialcultivation, this apparent pneumotropism waslost except when the dose was reduced and thedisease in the guinea pigs was prolonged.

Investigators of the Oakland epidemic firstthought it to be a highly virulent form of in-fluenza. This recalled the idea of certain Indianplague workers, the German Plague Commission(14) in 1898 and 1907, and Calmette and Salim-beni (5) that some visible or ultramicroscopicvirus might be associated with P. pestis andthat this mixed infection might account for thepneumonic type.The physician who had seen the patient in

Oakland who was the crux of the outbreak hadmade the diagnosis "influenza." There were stillresiduals of pandemic influenza in the earlymonths of 1919; but since it had disappeared bythe time of the epidemic, the cases of fatal so-called "influenza" aroused doubts among thehealth officials. At that time, procedures forconclusive diagnosis of viral respiratory infec-tions had not yet been devised. The incidence ofrespiratory infection in Los Angeles in October1924 was low and not exceptional in the Mexicanpopulation in the area around the plague focus.Particular attention was paid to this since in theyears just before White (63) and Nicolle andGobert (40) had insisted on a close connectionbetween influenza and pneumonic plague. How-ever, extensive epidemiological observationslend little support to the idea that other patho-gens encourage the development of pneumonicplague. Seasonal occurrence of influenza inMadagascar did not increase pulmonary com-plications in plague outbreaks. McCrumb andhis colleagues (34) failed to obtain serologicalevidence that influenza viruses were involved inthe pathogenesis of the cases of pneumonicplague they studied in Madagascar. Perhapsviruses other than influenza virus might makepneumonic plague highly infectious (54) in therare case in which they coexist, but it wouldseem unwise to doubt the infectiousness ofpneumonic plague alone. The house epidemics

described by Tieh and others (60) illustrate thispoint. Of course the same factors may encouragethe development and spread of respiratory infec-tion in general.Pneumonic epidemics, then, do not seem to be

attributable to any peculiar property of the bacil-lus, to any particular rodent or flea species, norto mixed infection. Their spread depends more onextrinsic factors which bring the parasite andhost together than on intrinsic factors in either.

It seems more reasonable to assume theirorigin in a source that usually has disappearedby the time the pneumonic outbreak erupts, i.e.,a patient with severe, prolonged bubonic plaguewho has full-blown secondary pneumonia, whocoughs and expectorates copiously, and whobehaves like the "cloud baby" recently describedin staphylococcal infections (12). Epidemiologicalinquiry may be crippled by the circumstance thatno stable witnesses survive to give informationabout this patient. Pathological investigationsmay be handicapped because in many areasautopsy is not permitted. The few cases in whichthe clinical course could have been observed tookplace before the development of precise methodsof measurement and observation.

In the Oakland outbreak, one salient point hasnot been emphasized, namely, that a physiciancalled in consultation, impressed by the painfulaxillary swelling, had incised and then reopenedit on two occasions within 4 days. The surgicalmanipulations of the axillary bubo may havedetached thrombi -loaded with bacilli and thesemay have become emboli in the lung.

In the former German colony in West Africa,a patient coming down' with bubonic plaguetraveled from infected Dar es Salaan into theinterior to his home village, stopping and talkingwith villagers along the way. During the first 3days he passed through four villages, through twosettlements on the fourth and fifth days, andfinally reached his home village, where he died.Eleven cases of primary pneumonic plaguemarked his trail, eight contracted on the fourthand fifth days of his journey, and three in hisvillage (K. F. Meyer, personal observation, un-published).

Investigators of the Manchurian epidemictraced outbreaks to a traveler with secondaryplague pneumonia proceeding from an infectedto an uninfected place. Again in 1946, the epi-

2511961]

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

KARL F. MEYER

demic described by Tieh and other observers(60) in Mukden began with a visit.

Petrie and Todd (42), while studying plaguein Egypt, also noticed that travelers are particu-larly likely to develop marked secondary lunginvolvement. They suggested the interestingexplanation that in the dry desert a high satura-tion deficiency of the air causes evaporation ofmoisture from the pulmonary mucous membrane,disposing it to secondary pneumonia.,

Just 2 years ago inMd r another travel-ing plague patient distributed the organismswhich caused an epidemic (4).Once the news of a plague epidemic circulates,

the usual reaction is flight, an old problem inplague control, and the dying victim may wantto return home. Some of those who flee are alreadyinfected but have no symptoms. There are un-doubtedly factors in this flight effort, such asexposure, xhalustion, and change of environment,that might aggravate the illness and favor respira-tory complications. There is no detailed knowl-edge of this patient: whether excretion of plaguebacilli takes place, in all cases, whether this excre-tion is intermittent, or of the true nature of theresponsible exposure. Corresponding facts arenot known of the recipient: the minimal infectivedose, susceptiilityi, exposure, and climaic con-ditions which might favor respiratory infections.Social customs participate, especially those con-cerning reunion, impending death, death, andinterment.

All the more serious outbreaks reported haveoriginated under circumstances particularlyfavorable to infections through the respiratorytract. In the Manchurian epidemics, gros over-crowding in badly ventilated underground innswith tightly shut doors and windows probablycharged the air with great concentrations ofdroplets of microbe-laden moisture ejected fromthe lungs during coughing. Strong and asso-ciates (58, 59) mentioned that the cloud of con-densed vapors issuing from the mouth duringexpiration was seen to extend a distance of 30cm. During the International Plague Conferencein 1911, it was recognized that pneumonic plagueis contracted indoors most commonly.That pestilential air is a vehicle of infection was

known long before microorganisms could beseen. By analogy with other respiratory infec-tions, the inhalation airborne disease theory wasadopted for pneumonic plague without considera-tion of the concept of infectious droplets advanced

by Fltigge at the beginning of this century. Onegroup of epidemiologists and pathologists insistedthat P. pesti. is directly inhaled into the airpassages. Others argued that the primary infec-tion is in the tonsils and that the lungs are onlysecondarily infected by bacilli carried by theblood. The first group reasoned that severepneumonic plague is caused by entry of theOrganisms through the lower parts of the respira-tory tract. There is an element of truth on bothsides.

Plague seems to be contracted in many caseswhen the infectee comes within close range of thecoughing infector. Since the frequency of coughand the quantity of bacilli sprayed undoubtedlyvary from case to case, and probably from timeto time in the same case, depending on the natureand severity of the respiratory involvement, theinfectiousness of pneumonic plague patients alsoprobably varies greatly. Early in the infection,when the patient coughs little and plague bacilliin the expectorations are few or even absent, heis not likely to be highly dangerous.

Patients, suffering from a confusing form ofsepticemia or bubonic plague acquired throu.ghthe respiratory tract, in which cough is an insig-nificant symptom, are not infectious. This wasfirst mentioned in 1922 when Wu Lien-Teh,Chun, and Pollitzer (67), reported on 34 autop-sies of victims of plague in the Harbin area duringthe second Manchurian epidemic. In nine cases(eight adults and one child 2 years old) no pneu-monic lesions of any sort were seen, but conges-tion and edema of the lungs, slight reaction inthe fauces, larynx, and trachea, and in somecases cervical buboes were observed. Theythought that in this group P. pestis enteredthrough the respiratory tract, without suggestingthe exact site of invasion, and gave rise to plaguesepticemia without true pneumonia. To makeallowance for this possibility, they suggested theterm "pulmonary plague," but this directs atten-tion to the lungs rather than the upper part ofthe respiratory tract. In three of nine autopsiesin the Los Angeles epidemic, pulmonary con-solidation was not seen but there were hemor-rhagic edematous lesions in the tonsils, epiglottis,and vocal cords.One further distinction must be made: It is

conceivable that this form of plague could alsoarise from flea bites on the neck.An explanation of this unusual form and the

better known pneumonic form began with the

252 [VOL. 25

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

PNEUMONIC PLAGUE

work of Wells and Wells (62) and many otherson aerial infection with droplets and dropletnuclei. The wide differences in behavior betweenlarge and small droplets is obviously significantin these forms of plague. The term "dropletinfection" is rarely, if ever, mentioned, even inthe current plague literature. The classical experi-ments of Jorge in 1905 and Strong and Teague(58), exposing petri dishes at varying distancesfrom a coughing pneumonic plague patient,measured only coarser particles. On first thought,it might seem that such particles would enter therespiratory tract and be deposited at resistantsites as in other bacterial pneumonias. But theupper part of the respiratory tract is furnishedwith no known defense against P. pestis. Thesmaller the particles the more likely they are tobe inhaled and lodge in the highly susceptiblelung itself.

Given a heavy concentration of organisms perunit volume of air and prolonged exposure in thispestilential air, inhalations of particles of differentsizes begin the invasion through the deepest partsof the respiratory tract, the bronchioles, andpulmonary -alveoli. Perhaps only the largerparticles can lodge in the upper respiratory tractand give rise to tonsillar or to septicemic plague.

So far as the influence of climate is concerned,the California outbreaks cast doubt on the ideathat pneumonic plague occurs only in coldweather when a low water deficit of the atmos-phere presumably enables the sputum dropletsto float in the air for a considerable time. Thedisease has been observed in countries withwarm or even hot climates where these conditionsdo not exist. The circumstances favoring aerialinfection are immediate proximity to the in-fector, overcrowding, and diverse social factors.Customs as, for example, in Los Angeles wherea prolonged burial ceremony was held withmany people attending, promoted exchange ofthe bacilli.

Until quite recently the diagnosis of pneumonicplague was virtually a death sentence; the mor-tality rate was nearly 100%. Until 1946, onlynine recoveries were reported (60). Even in thepast, however, isolation of the patients andsegregation and careful observation of their con-tacts shortened the outbreaks. Prophylacticchemotherapy of contacts with sulfonamides inMadagascar and in other areas with tetracyclinesand prompt treatment of the patients withstreptomycin or tetracyclines arrested the spread

of a pneumonic outbreak in progress for 3 weeks(17, 64).

EXPERIMENTAL PLAGUE INDUCED THROUGHRESPIRATORY TRACT

Ever since the pathobacteriological diagnosis ofhuman primary pneumonic plague in December1896 by Childe (6), numerous attempts havebeen made to reproduce this form of plague inexperimental animals and success has varied.The first experiments were on primates, but itseems better to begin with those on laboratoryrodents.

Guinea PigsIntranasal and intratracheal infection. In 1899

at the Institute Pasteur, Batzaroff (3), on theadvice of Roux, introduced a cotton swab chargedwith virulent plague bacilli into the nostrils ofguinea pigs and reported that this produced abronchopneumonia which, according to Nattan-Larrier and Richard (39), resembled humanprimary pneumonic plague. This mode provednot always so successful in the hands of otherexperimenters. Kolle (25) modified it by instillingthe bacilli into the buccal cavity, the nose, orthe conjunctival sac. Only a few guinea pigs gotpneumonia; the others died from cervical bubonicplague and septicemia. Either the direct intra-tracheal inoculation of a suspension of 50,000,000P. pestis (2) or intranasal instillation of a suspen-sion of virulent bacilli into the nostril of guineapigs anesthetized with barbiturates (35) hasproduced a model of pneumonic plague. From200 to 700 P. pestis are flushed into the deeperrespiratory passages by this latter simple tech-nique. This experimental lung infection, with itsbroncholymphatic, pneumonic, and terminalsepticemia phases, resembles the human typehistologically. Intranasal infection is consideredadequate for testing immunization and treat-ment (13, 37). Some guinea pigs infected by thesemethods have transmitted the infection to normalcagemates. This is not usual, however, even ifthe animals are fed wet carrots and cabbage, asstipulated by Batzaroff.

Bacterial clouds. Under the influence of studieson pulmonary tuberculosis, Martini (31, 32) andsubsequently Strong et al. (59) exposed guineapigs to sprays of suspended plague bacilli inspecially constructed glass cages. Over 25% ofthe animals so exposed had lesions of pneumoniaat autopsy; the remaining 75% had cervical

2531961]

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

KARL F. MEYER

adenitis, tracheobronchitis, and rapidly fatalsepticemia. The only explanation that could beoffered at that time was that superficial inspira-tion and the position of the larynx of the guineapig prevented the organisms from penetratinginto the bronchioles and air sacs. Once the in-fluence of aerosol particle size on respiratoryinfections was known, Druett and his associates(10) conducted careful studies and explained thetwo forms of plague originating in the respiratorytract of the guinea pig. They develop accordingto the size of the infected particles presented tothe host.

Particles smaller than 1 A initiate broncho-pneumonia, which leads to septicemia and death.Large particles, 10 to 12j tin diameter, apparentlydeposited in the region of the head, penetrate thelocal epithelium and, through the afferent lym-phatics, lead to septicemia much sooner thanwhen organisms are deposited on the bronchialor alveolar wall. Septicemia arising from theprimary focus in the cervical lymph nodes causedinfection of the lung but no pneumonia.The respiratory tract of the guinea pig (a nose

breather) prevents particles larger than 4 1Afrom reaching the lungs, and in neither form ofthe disease is the cellular picture that of primarypneumonic plague in man. In this respect thepneumonic lesions produced by this method differfrom those after intranasal or intratrachealinoculation.The British workers also made cross-infection

studies. Twelve animals exposed to 7 LD5o ofsingle organisms were housed with 12 controls.Cross infection occurred in about 18% of thecontrol animals. Although erratic, the infectionswere more likely when the initial disease wasprimary pneumonia. Interestingly, the cross-infected animals suffered from the form charac-teristic of that following exposure to large particleclouds, i.e., septicemia but no pneumonia. Sincethis form is only occasionally contagious, itcannot establish epizootics.

Several Russian workers, Korobkova (27),Y. N. Rall, and V. P. Smirov (cf. Pollitzer (46)),also tried but failed to produce primary pneu-monic plague in guinea pigs as well as in sisels andmarmots by inhalation. Their contact infectionswvere probably attributable to the same type ofinfection as that observed by British workers. Theparticle size used in these experiments is not givenin the papers.

The guinea pig is unsuitable for experimentalepidemiological study of primary pneumonicplague, but since the respiratory infection isusually much more severe than the cutaneous orsubcutaneous infection, it is most useful in theevaluation of vaccines and the study of immunity.

MiceExperimental respiratory infection in the

laboratory mouse has been achieved either byexposure to aerosols (19, 31, 51-53) or by intra-nasal instillation. Animals so infected have beensacrificed at intervals and the development ofthe pneumonia has been followed in serial micro-scopic sections.

Inhalation of infected particles produced lesionsquite similar to those of human primary pneu-monic plague. The process began in the alveolarsepta with intense cellular infiltration, followedby massive hemorrhage and edema, bacterialmultiplication in the blood vessels, and progres-sive extension into adjacent lobules of lung tissue.

After instillation, the early lesions were in thebronchi, and peribronchial masses of bacteriaappeared before cellular infiltration in the alveoli.As the inflammatory reaction progressed, thepneumonic lesions at the time of death resembledthose of human primary pneumonic plague.

In the study of immunity and chemotherapy,the mouse is adequate, but few attempts toaccomplish cross infection have succeeded. Occa-sionally a contact mouse, exposed to a group ofsix infected by inhalation, would die of septicemiawith a few isolated pneumonic infarcts.

In the early inhalation experiments by Martini(31) 19 mice were exposed to infective spray butonly 4 that died had lesions of pneumonia. Thespray, generated with a Paroleine sprayer (Bur-roughs Wellcome), consisted of particles ofvarious sizes. Meyer and Larson (38), in numer-ous experiments using a Wellstype atomizer,exposed large series of mice in closed chambersfor 3 min. to clouds containing 800,000 to 1,600,-000 plague bacilli per liter. These particles werealso of different sizes. The infections resultingfrom these exposures were variable. Some 65%of the mice died with lesions of lobular lobarpneumonia, 17 % with cervical buboes andpneumonic infarcts, 14% with cervical buboes,and 4% with septicemia and no visible buboes.In other tests, over 60%/ died with lesions ofsepticemia and cervical buboes, only 20% awith

254 [VrOL. 25

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

PNEUMONIC PLAGUE

primary pneumonia. Probably the particle sizesdiffered in the different experiments. Applyingthe observations of Druett and associates (10),the large particles impinged on the mucosa of thenose and upper respiratory tract and gainedentrance into the lymph channels leading tobuboes in the cervical lymph nodes, or they in-vaded the blood stream without primary localiza-tion in lymph tissue.Mice with this form of plague are poor in-

fectors. They too are nose breathers. Theirrespiratory tract successfully prevents largeparticles exhaled by the animal with pneumoniafrom reaching the lung of the contact, so a con-

tinuous infection chain cannot be maintained.The mouse is not satisfactory for study of pneu-monic plague.

Other Rodents

Plague has been produced in small and largemarmots (Arctomys bobac, Spermophilus citellus)by exposing them in a special wooden box for 5to 10 min to a spray of P. pestis in saline (22, 65,66). The mortality rate was 100%, but only 5 of13 tarabagans and sisels suffered from primarypneumonic plague, the remainder from primarysepticemia. This resembles the type of diseaseobserved in Manchuria in 1920-1921, with in-volvement of the tracheobronchial lymph nodesand few lesions in the lung parenchyma. Whenthe marmots were kept in a central compartmentand were surrounded with cages holding contacts,those with pneumonia did transmit the septicemictype. The incubation time was short. Exposureto the marmot infected by inhalation was con-

tinuous since the wire netting holding the infectorand the contacts allowed aerial transmission.Nevertheless, transmission was quite variable.In one experiment three of ten; in another, afterexposure for 4 to 6 days, seven of nine contactscontracted plague; the report does not statewhether all the contacts contracted primarypneumonic or bubonic septicemia plague. Thelatter had not been recognized in 1916 when theexperiments were made. According to recentreports by Russian workers (Rall, 1958; Smirnov,1956; cf. Pollitizer (46)) primary pneumonicplague did not develop in marmots or sisels keptin close contact with ainmals suffering fromsecondary plague pneumonia.Experiments with rabbits have given con-

tradictory results. Batzaroff (3) and Calmette

and Salimbeni (5) had successful results withnasal swabbing. Tsurumi (61) claimed successwith various methods. At the Hooper Founda-tion, pneumonic lesions have been produced byinoculating directly into the lung with a syringe,a procedure originally used by Shibayama onguinea pigs. Significant is the statement byMartini (31) that not pneumonic plague butsepticemia results when rabbits receive P. pestisby inhalation.

MonkeysShortly after Childe's work, studies to repro-

duce pneumonic plague in experimental animalswere undertaken, and it is probably not coinci-dence that primates were first chosen. Threeseparate instances of spontaneous plague out-breaks in monkeys had just then been observed inIndia by Clemow in 1900 (7). Commenting on thepropagation of plague in Hurdwar, Hankin (18)described his observations on a primate thatdied shortly after it had been brought to hislaboratory. Nasal secretions contained innumera-ble bacilli that looked like P. pestis, and theyproduced plague in rats. Subsequently the organsof the primate yielded the plague bacillus, butunfortunately an autopsy report is not available.After having seen the intolerable conditionsunder which monkeys were living during theepidemic, Hankin suspected that inhalation ofdust infected with P. pestis caused the fatal infec-tion in the monkey.

Experiments with monkeys of different generaand species have been undertaken since, and theindividual susceptibility to parenteral infectionhas varied.

Intratracheal instillation. The Austrian PlagueCommission reported that primary pneumonicplague developed in a monkey which took a deepbreath after a suspension of P. pestis had beenintroduced into its mouth (1). Wyssokowitz andZabolotny (69), Polverini (47), and Zabolotny(70) easily produced the pneumonic form byintroducing suspensions of plague bacilli with theaid of a catheter into the trachea of anesthetizedprimates.To evaluate antimicrobial drugs or vaccines,

McCrumb, Larson, and Meyer (33) and Ehren-krantz and Meyer (11) administered a diluted,agar-grown culture by direct laryngoscopythrough a hard rubber catheter into monkeysunder barbiturate anesthesia. Pneumonic infec-

2551961]

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

KARL F. MEYER

tion was established with as few as 120 to 270organisms in Macacus rhesus and Cynomolgusphilippinensis. Individual variations were over-come when 1,000,000 to 100,000,000 were in-stilled. The monkeys were asymptomatic for 1to 3 days. Fever was the first indication of activeinfection. Roentgen evidence of pneumonitisappeared soon after the onset of fever, and thepneumonitis progressed. The infection terminatedfatally on the fifth to eighth day, usually accom-panied by septicemia.

This method was chosen because it madecertain that the organisms reached the lung; itrequired no complicated equipment and had beenused by the most qualified experimental patholo-gist, L. Schmidt, in his extensive studies on thechemotherapy of experimental tuberculosis. Itwas not chosen to study the details of the develop-ment of pneumonic plague nor to illuminate themode of introduction. It has obvious shortcom-ings. Anesthesia may disturb pulmonary function,adding a provocative factor. Intubation maylocalize the lesions or create a portal of entry.The inoculum in a fluid medium might for sometime supply the organisms with a pabulum unap-proachable by the defense mechanism of thehost.

Nevertheless, the gross and microscopic lesionsproduced by the intratracheal and inhalationprocedures are quite similar except that bytracheal instillation the organisms are introducedinto the bronchi and terminal bronchioles ratherthan the air sacs. Thus the genesis of the lesionsis the same as that in guinea pigs infected byintratracheal instillation.

Inhalation. In an effort to learn the pathogene-sis of pneumonic and primary septicemic plague,Strong and Teague (58) put 55 Philippine mon-keys in closed glass cages. They sprayed virulentplague bacilli suspended in saline for 2 to 3 mininto the air the monkeys breathed. All the animalsso exposed contracted plague. Unfortunatelydetails are not given, but the statement that"the primary point of infection may be not onlythe lungs but also the mucous membranes of themouth and throat" suggests the possibility of thenonpneumonic form. Under the influence ofKoulecha's view (29) that pneumonic plague isprimarily septicemia and that the lungs becomesecondarily involved by way of the blood, theysearched for a portal of entry in the upper respira-tory tract. They found changes in the tonsils

only if the bacilli had been placed on the posteriorpart of the throat with a glass rod. But in a finalstatement they concluded that primary septi-cemia sometimes takes place and death mayoccur, although rarely before lesions are visible inthe lungs or lymph nodes.By exposing unanesthetized primates to in-

fectious aerosols with measured doses in a specialexposure apparatus, Speck and Wolochow (55)studied experimental pneumonic plague inMacacus rhesus. The LD5o, determined here forthe first time, was about 20,000 inhaled cells.The clinical and laboratory findings were similarto those of others (11, 33).

Incidental to their work with guinea pigs,Druett and his colleagues (10) made some experi-ments with monkeys, using single-organismclouds and particles 12 A, in diameter. Bothproduced lobar pneumonia although the diseasetook longer to develop after exposure to largeparticles.

Contact cross infection. At the InternationalPlague Conference in iMukden and in his book,Zabolotny (71) noted as early as 1897 that mon-keys given Haffkine or other vaccines contractedlung infection when left in the same cage withinfected animals. One monkey treated pro-phylactically with antiplague serum also becameinfected when similarly exposed.

Girard and Robic (15) and Robic (48, 49)succeeded in a single experiment in bringingabout cross infection among a group of nine"maki," Madagascar lemurs (Propithecus spe-cies). Three lemurs were inoculated by the con-junctival or nasal route with two drops of a brothculture of virulent P. pestis. On the third daythereafter, two of the animals died, and on thefifth day the third died, all with lesions of typicalpneumonic plague. Of the six lemurs in closecontact in the box with the infected, five diedwithin 4 or 5 days, invariably within 24 to 48 hrafter showing signs of illness. None coughed butthree of the five had mucopurulent nasal dis-charge teeming with plague bacilli that provedhighly virulent for guinea pigs. Dissection of theneck disclosed enlarged hemorrhagic cervical andsubmaxillary lymph nodes and septicemia. Thesixth lemur escaped the cross infection; althoughit was held in the contaminated cage, it did notacquire plague. Robic considered the infectionin the contacts to be a form of "peste pulmonaire"serially transmitted by the infective mucous

256 [VOL. 25

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

PNEUMONIC PLAGUE

discharge. The upper respiratory tract or theeyes may have served as the portal of entry. Thisexperiment is also valuable in that it shows thehigh susceptibility of lemurs to plague.At the Hooper Foundation (38) healthy pri-

mates were exposed to cagemates with frankclinical pneumonia produced by the same methodas that used by McCrumb and co-workers (33).In several experiments monkeys with fever anddefinite roentgenographic evidence of pneumoniawere placed in a cage divided in two compart-ments which made bodily contact impossible butallowed free passage of the exhaled air. The ex-posure time ranged from less than 1 day to thetime the infected primate survived after thehealthy one was introduced.

In 36 exposure experiments, 23 of the contactsdied of plague, on the average 7 to 7 days afterthe beginning of exposure. Nineteen contractedcervical bubonic septicemia and only three devel-oped pneumonic plague. Monkeys exhalingplague bacilli were selected for the experiments.Blood agar plates were held 4 to 5 in. from themonkey's mouth for 30 to 60 sec. In every in-stance in which the plates contained over 20organisms, the contact monkey contractedplague. The contagiousness was roughly corre-lated with the number of bacilli exhaled and totalexposure time. Most of the infectors were severelyill and most of them coughed, but the extent ofthese indications was not measured because itwas impossible to observe the animals all thetime.

Autopsies were exceptionally thorough. In theabsence of pulmonary consolidation, the entireupper respiratory tract was dissected. Two formsof plague originating in the respiratory tract wereseen. Nineteen contracted cervical, bubonic,septicemic plague, and three developed pneu-monic plague with no lesions in the upper respira-tory tract. Serial sections indicated that theplague bacilli had entered the upper respiratorytract through the lymphatic tissues of Waldeyer'sring in the oropharynx. The afferent lymphaticscarried them to the regional lymph nodes andinduced primary buboes, and septicemia followedrapidly. This form was not contagious. Pneu-monic plague developed after inhalations ofexhaled particles into the tissues of the terminalbronchioles and alveoli. Only one contact withprimary pneumonia passed on the infection toanother contact, but here again it took the

cervical, bubonic, septicemic form and the chainwas broken.The influence of particle or droplet size and

whether the nose-breathing primates receivedthe infective dose through the nasal passageremain to be learned. The normal clearing mecha-nism would bring the organisms into the oro-pharynx and in contact with lymphatic tissueswell suited for multiplication of plague bacilli.These observations are disappointing because

they indicate that an epizootic, pneumonic formof plague can probably not be reproduced inprimates. On the other hand they explain someobservations in the Los Angeles epidemic andthe so-called nonpneumonic or pulmonary typeof lung pest recorded by Wu Lien-Teh et al. (67)and by Pollitzer and Li (45) in 1920-1921 inHarbin.

Probably the entire respiratory tract of mancan serve as a portal of entry for plague bacilliin the pestilential air.

IMMUNIZATION

At the International Plague Conference inMukden in 1911, Zabolotny reported some experi-ments on monkeys, summarized in the statementthat these animals could be protected againstlung infection only by repeated high doses ofagar-grown vaccines. In his opinion, it was muchmore difficult to vaccinate against respiratorythan bubonic plague. Strong and Teague (58)later vaccinated large numbers of guinea pigs andmonkeys by subcutaneous injection of a living,attenuated plague culture and later exposed themto infection by inhalation; an equal number ofunvaccinated and vaccinated animals wereexposed at the same time in each series. Of thevaccinated guinea pigs, 75% survived the expo-sure; many of the unimmunized animals died notof primary pneumonia but of primary bubonicinfection of the cervical nodes and of secondarysepticemia and sometimes secondary pneumonia.Only very few died of primary pneumonic plague.Nonimmunized monkeys exposed to inhalationalmost all died of primary pneumonic infection.Only about 10% of the vaccinated animals sur-vived infection by inhalation. A committee ofthat Conference summarized its opinions: (i) thatthe statistical evidence points to the conclusionthat some degree of protection is conferred againstbubonic plague by the use of vaccines, (ii) butexperience during the 1910-1911 epidemic does

25719611]

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

KARL F. MEYER

not allow any definite conclusion about the valueof prophylactic inoculation against plaguespneumonia, and (iii) that inhalation experiment)on animals (guinea pigs, white rats, monkeysshould be carried on to find out which vaccinecan best be used against pneumonic plague.These conclusions have been amply confirmed

in the course of mass vaccination with livingattenuated plague vaccines in Indonesia (41) andMadagascar (16). An appreciable immunity wasobtained when vaccination was repeated.

Living or killed organisms or antigen in aqueoussuspension customarily administered by the sub-cutaneous or cutaneous route in two inoculationshave rarely protected more than 10% of theanimals against inhalation infection. Repeatedinoculations of killed organisms or envelopeantigen with alum synergist or adjuvants haveprotected 90 to 100% of guinea pigs and monkeysagainst inhalation infections. In the course ofthese experiments, marked lung involvement wasregularly found in the absence of spleen and liverlesions when partly immune animals died fromthe pulmonary challenge after prolonged illnesses.

Pokrovskaia and Kaganova (43) and Pok-rovskaia et al. (44) attributed this lack of im-munity to "a weakly developed reticulo-endo-thelium and to little permeability for antibodiesof the lung tissues" and attempted to increasethe production of clasmatocytes by causing theanimals to inhale living vaccine strains (E.V. ofGirard and Robic and a Russian strain A.1\I.P.).These and other Russian workers (26, 28) com-bined repeated respiratory immunization and asubcutaneous inoculation and reported highresistance to cloud infection with virulent plaguebacilli in small series of guinea pigs and monkeys.Three subcutaneous inoculations of the livevaccine protected 85.7 %, and four inhalationvaccinations prevented pneumonic plague in66.7% of the guinea pigs. The doses of organismsused in challenge infections were large: 25,000,000for the nasal instillation, 250,000,000 for theinhalation.At the Hooper Foundation such experiments

on guinea pigs and mice yielded similar results.Any systemic immunization with living or

killed vaccines that have produced solid im-munity against bubonic infection has conferredappreciable resistance against respiratory infec-tion. Formalin-killed virulent plague bacillicoated with alum or incorporated in an adjuvant

given intramuscularly in two doses, followed byone booster dose 1 to 3 months later, has stimu-lated antibodies and complete resistance againstan inhalation infection in experiments at theHooper Foundation and elsewhere (30). Spacingof individual inoculations and the total period ofvaccination are at least as important as the totaldose of the immunizing agent. Active immunityagainst pneumonic plague has been attained withlive or killed adjuvant vaccine if the basic im-munity stimulated by two inoculations 30 daysapart is intensified by a subcutaneous boosterinoculation in the 19th week, to such an extentthat most of the vaccinated primates have sur-vived an intratracheal infection with 40,000virulent P. pestis; the controls succumb within4 days with clinical lesions of pneumonic plague.One of six vaccinated primates showed shadowsin the thoracic roentgenograms and slight eleva-tion of temperature, but it survived.

In experimental studies (i) local immunizationof the respiratory tract has not been required toprotect guinea pigs and primates against pneu-monic plague, (ii) the necessary immunity hasbeen obtained by intramuscular injection ofkilled or live plague bacilli provided they arecoated with alum or incorporated in adjuvantsand followed by a booster inoculation, (iii) vac-cines in aqueous suspension have produced a low-grade immunity, (iv) active immunity againstpneumonic plague has not been induced withtwo inoculations within 2 weeks, (v) the basicimmunity obtained with adjuvant vaccine hashad to be reinforced with a booster shortly beforeexposure, (vi) the immunity has declined after 3months, and to revive it, systematic reinoculationhas been required, and (vii) the state of im-munity has been shown in serum antibody levels.Present procedures of immunization of managainst plague with aqueous vaccines, accordingto serum antibody determinations, are essentiallyineffective against pneumonic plague.

Experimental pulmonary plague, whethersecondary to bubonic plague or primary pneu-monic plague, may well serve as a perfect modelto elucidate the pathogenesis of this unique air-borne infection, particularly if the infection anddisease could be consistently reproduced. Variousspecies of primates should be tested to learnwhich is most suitable for animal-to-animal pas-sage. The biophysical laws governing exhalationof P. pestis in sputum droplets and transfer to

258 IVOL. 25

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

PNEUMONIC PLAGUE

new hosts could then be learned. It is reasonableto suspect that the half-life of the plague bacilliin sputum droplets may differ from that in arti-ficial moist particles created by new instrumentsfrom suspensions of cultured organisms or tissueslurries. A blood-containing excretion consistingof enormous masses of living and dead bacilliprobably contains toxic substances that mayinfluence the deposition in the upper or muco-ciliary escalator of the lower respiratory tract.

LITERATURE CITED

1. ALBRECHT, H., AND A. GHON. 1960. Bacterio-logische untersuchungen uber die PestBacillus. Denkschr. Kaiserl. Akad. Wiss.66:581-827.

2. BABLET, J., AND G. GIRARD. 1934. Lesionshistologiques dans la peste pulmonaireprimitive exp6rimentale du cobaye. Ann.inst. Pasteur 52:155-165.

3. BATZAROFF. 1899. La pneumonie pesteuseexp6rimentale. Ann. inst. Pasteur 13:385-405.

4. BRYGOO, E. R., AND M. GONON. 1958. L'6pid6-mie de peste pulmonaire de Doany en octo-bre 1957. Arch. inst. Pasteur Madagascar26:124-138.

5. CALMETTE, A., AND A. T. SALIMBENI. 1899. Lapeste bubonique; 6tude de l'6piddmie d'-Oporto en 1899. Ann. inst. Pasteur 13:865-936.

6. CHILDE, L. F. 1898. The pathology of plague.(Abstr.) Brit. Med. J. 2:858-862.

7. CLEMOW, F. G. 1900. Remarks on plague inthe lower animals. Brit. Med. J. 1:1141-1146.

8. CONNAL, A. 1927. Annual report of the MedicalResearch Institute. Annual Med. & Sani-tary Rept. Nigeria, 1927. App. A, p. 1-46.

9. DicKiE, W. M. 1926. Plague in California1900-1925. Proc. Conf. State and Prov.Health Authorities North America 21:30-78.

10. DRUETT, H. A., J. M. ROBINSON, D. W.HENDERSON, L. PACKMAN, AND S. PEACOCK.1956. Studies on respiratory infection. II.The influence of aerosol particle size on in-fection of the guinea pig with Pasteurellapestis. J. Hyg. 54:37-48.

11. EHRENKRANZ, N. J., AND K. F. MEYER. 1955.Studies on immunization against plague.VIII. Study of three immunizing prepara-tions in protecting primates against pneu-monic plague. J. Infectious Diseases 96:138-144.

12. EICHENWALD, H. F., 0. KOTSEVALOV, AND L.A. FASSO. 1960. The "cloud baby": an ex-

ample of bacterial-viral interaction. A. M.A. J. Diseases Children 100:161-173.

13. FAVAREL, R. 1949. Agglutination de Pasteu-rella pestis par le serum des pesteux (pestebubonique et peste pulmonaire). Bull. soc.pathol. exotique 42:335-338.

14. German Plague Commission. 1899. Berichtuber die Tatigkeit der zur Erforschung derPest im Jahre 1897 nach Indien entsandlenKommission, erstattet von Gaffky. Arb.kaiserl. Gesundh. 16:283-284.

15. GIRARD, G., AND J. ROBIC. 1941. Pneumoniepesteuse exp6rimentale. Arch. inst. PasteurTananarive. Ann~e 1940:32-34.

16. GIRARD, G., AND J. ROBIC. 1942. L'6tat actuelde la peste a Madagascar et la prophylaxievaccinale par le virus-vaccin E. V. Bull.soc. pathol. exotique 35:42-49.

17. GONON, E. R., S. RAKOTOMIHAMINA, AND

C. H. RAZAFIMANDIMBY. 1958. L'6pidemiede peste pulmonaire de Doany en octobre1957. Th6rapeutique et prophylaxie. Arch.inst. Pasteur Tananarive 26:134-138.

18. HANKIN, E. H. 1898. La propagation de lapeste. Ann. inst. Pasteur 12:705-762.

19. HERBERT, D. 1947. Streptomycin in experi-mental plague. Lancet 252:626-630.

20. Indian Plague Commission. 1905. Report onplague investigations in India. 5:91.

21. International Plague Conference, Mukden,Manchuria. 1912. Report of the InternationalPlague Conference, held April 1911. Bur.Printing, Manila. 483 p.

22. JETTMAR, H. M. 1923. Erfahrungen uber diePest in Transbaikalien. Z. Hyg. Infektions-krankh. 97:322-329.

23. KARCHER, J. 1956. Theodor Zwinger und seineZeitgenossen. Episode aus dem Ringen derBasler Xrzte um die Grandlehren der Medi-zin im Zeitalter des Barocks. Studien zurGeschichte der Wissenschaften in Basel,III. Helbing und Lichtenhahn, Basel. 75 p.

24. KELLOGG, W. H. 1920. An epidemic of pneu-monic plague. Am. J. Public Health 10:599-605.

25. KOLLE, W. 1901. Bericht uber die Thatigheitin der zu Studien uiber Pest eingerichtetenStation des Instituts fur Infectionskrank-heiten 1899-1900. Z. Hyg. Infektionskrankh.36:397-421.

26. KOROBKOVA, E. I., AND A. KRAINOVA. 1939.Essais l'immunisation contre la peste pul-monaire avec le vaccin EV. Vestnik mikr.epidem. i parazitol. 18:223-235. (In Russian,summary in French.)

27. KOROBKOVA, E. I. 1940. Sur la sensibilite descobayes a la peste dans les conditions de

20591961]

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

KARL F. MEYER

cohabitation avec des animaux pesteux.Vestnik mikr. epidem. i parazitol. 18:239-243. (In Russian, summary in French.)

28. KOROBKOVA, E. I. 1956. Zhivaia protivochum-naia vaktsina. Medgiz, Moskva. 205 p.

29. KOULECHA, G. S. 1912. Morbid anatomy, p.151. In Report of the International PlagueConference in Mukden, 1911.

30. LAWTON, W. D., G. M. FUKUI, AND M. J.SURGALLA. 1960. Studies on the antigens ofPasteurella pestis and Pasteurella pseudo-tuberculosis. J. Immunol. 84:475-479.

31. MARTINI, E. 1901. Ueber Inhalationspest derRatten. Z. Hyg. Infektionskrankh. 38:332-342.

32. MARTINI, E. 1902. Ueber die Wirkung desPestserums bei experimenteller Pestpneu-monie an Ratten, Mausen, Katzen, MIeer-schweinchen und Kaninchen. Klin. Jahrb.10:137-176.

33. MCCRUMB, F. R., JR., A. LARSON, AND K. F.MEYER. 1953. The chemotherapy of experi-mental plague in the primate host. J. In-fectious Diseases 92:273-287.

34. MCCRUMB, F. R., JR., S. MERCIER, T. H.CHEN, K. F. MEYER, AND K. GOODNER. 1955.Studies on the antibody patterns in pneu-monic plague patients. J. Infectious Diseases96:88-94.

35. MEYER, K. F., S. F. QUAN, AND A. LARSON.1948. Prophylactic immunization and spe-cific therapy of experimental pneumonicplague. Am. Rev. Tuberc. 57:312-321.

36. MEYER, K. F. 1952. Historical notes on dis-infected mail. J. Nervous Mental Disease116:523-554.

37. MEYER, K. F., S. F. QUAN, F. R. MCCRUMB,JR., AND A. LARSON. 1952. Effective treatmentof plague. Ann. N. Y. Acad. Sci. 55:1228-1274.

38. MEYER, K. F., AND A. LARSON. 1960. Thepathogenesis of cervical septicemic plaguedeveloping after exposure to pneumonicplague produced by intratracheal infectionin primates, p. 1-12. Proc. Symposium Dia-mond Jubilee Haffkine Inst., Jan. 10-14,1959, Bombay, India.

39. NATTAN-LARRIER, L., AND L. RICHARD. 1931.Les lesions histologiques de la peste pul-monaire primitive. Bull. soc. pathol. exo-tique 24:388-394.

40. NICOLLE, C., AND E. GOBERT. 1924. Considera-tions gendrales sur la peste pulmonaire etsur sa nature. A propos de quelques petitsfoyers de cette forme de peste observes enTunisie. Arch. inst. Pasteur Tunis 13:212-225.

41. OTTEN, L. 1941. A live plague vaccine and theresults. Mededeel. Dienst VolksgezondheidNed.-Indie 30:61-110.

42. PETRIE, G. F., AND R. E. TODD. 1924. A reporton plague investigations in Egypt. (Abstr.)Trop. Diseases Bull. 21:875-876.

43. POKROVSKAIA, M. P., AND L. S. KAGANOVA.1945. Cytological method for the study of theimmunity mechanism. Medicine USSR(Soc. Cultural Relations with ForeignCountries), no. 10, p. 3.

44. POKROVSKAIA, M. P., I. G. MAKARENKO, N.A. KRASKINA, N. I. BRAUIDE, M. D. PRIAD-KINA, AND N. M. JUTOROVA. 1959. Significanceof cytochemical investigations in the studyof immunobiological problems. Zhur. Mi-krobiol. Epidemiol. Immunobiol. 30:5-11.

45. POLLITZER, R., AND C. C. Li. 1943. Some ob-servations on the decline of pneumonicplague epidemics. J. Infectious Diseases72:160-162.

46. POLLITZER, R. 1960. A review of recent litera-ture on plague. Bull. World Health Organi-zation 23:313-400.

47. POLVERINI, C. 1911. La peste. Giorn. realesoc. ital. igiene 23:145, 193.

48. ROBIC, J. 1941. Del' emploi du "Maki" commeanimal d'experience a Madagascar. Sonint6ret dans l'6tude de la peste. Bull. soc.pathol. exotique 34:246-249.

49. ROBIC, J. 1942. Peste experimentale du MIaki.Arch. inst. Pasteur Tananarive Anne6 1941,23-25.

50. SIMPSON, W. J. 1905. A treatise on plaguedealing with historical, epidemiological,clinical, therapeutic and preventive aspectsof the disease. Cambridge Univ. Press,Cambridge. 490 p.

51. SMITH, P. N., J. MCCAMISH, J. SEELY, ANDG. M. COOKE. 1957. The development ofpneumonic plague in mice and the effect ofparalysis of respiratory cilia upon the courseof infection. J. Infectious Diseases 100:215-222.

52. SMITH, P. N. 1959. Pneumonic plague in mice:gross and histopathology in untreated andpassively immunized animals. J. InfectiousDiseases 104:78-84.

53. SMITH, P. N. 1959. Pneumonic plague in mice:modification of the infection by antibodyagainst specific components of Pasteurellapestis. J. Infectious Diseases 104:85-91.

54. SOKHEY, S. S. 1960. Discussion, p. 12. Proc.Symposium Diamond Jubilee HaffkineInst., Jan. 10-14, 1959, Bombay, India.

55. SPECK, R. S., AND H. WOLOCHOW. 1957. Studieson the experimental epidemiology of respira-

260 [VOL. 25

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from

PNEUMONIC PLAGUE

tory infections. VIII. Experimental pneu-monic plague in Macacus rhesus. J. Infec-tious Diseases 100:58-69.

56. STICKER, G. 1908. Abhandlungen aus derSeuchengeschichte und Seuchenlehre. I.Band: Die Pest. 1. Teil: Die Geschichte derPest. A. Topelmann, Giessen. 478 p.

57. STICKER, G. 1910. Abhandlungen aus derSeuchenlehre. I. Band: Die Pest. 2. Teil:Die Pest als Seuche und als Plage. A. Thpel-mann, Giessen. 542 p.

58. STRONG, R. P., AND 0. TEAGUE. 1912. Studieson pneumonic plague and plague immuniza-tion. VI. Bacteriology. Philippine J. Sci.7:187-202.

59. STRONG, R. P., B. C. CROWELL, AND 0. TEA-GUE. 1912. Studies on pneumonic plagueand plague immunization. VII. Pathology.Philippine J. Sci., Sect. B. Philippine J.Tropical Med. 7:203-221.

60. TIEH, T. H., E. LANDAUER, F. MIYAGAWA, G.KOBAYASHI, AND G. OKAYASU. 1948. Pri-mary pneumonic plague in Mukden, 1946,and report of 39 cases with 3 recoveries. J.Infectious Diseases 82:52-58.

61. TSURUMI, M. 1924. Recherches sur la pestepulmonaire. Bull. offic. internat. d'hyg.publique 16:1369-1391.

62. WELLS, W. F., AND M. W. WELLS. 1936. Air-borne infection. J. A. M. A. 107:1698-1703.

63. WH1TE, F. N. 1923. The prevalence of epidemicdisease and port health organisation and

procedure in the Far East. PublicationDept. League of Nations, Geneva. 179 p.

64. World Health Organization, Expert Com-mittee on Plague. 1959. Third report. WorldHealth Organization Tech. Rept. Ser. No.165. 42 p.

65. Wu LIEN-TEH, AND F. EBERSON. 1917. Trans-mission of pulmonary and septicaemicplague among marmots. J. Hyg. 16:1-11.

66. Wu LIEN-TEH, AND H. M. JETTMAR. 1925-1926. A systematic experimental study ofthe pathology of pneumonic plague in thetarabagan and sisel (suslik). North Man-churian Plague Prevention Service Reports1925-1926. 5:1-26.

67. Wu LIEN-TEH, J. W. H. CHUN, AND R. POL-LITZER. 1922. Clinical observations upon thesecond Manchurian plague epidemic, 1920-1921. Natl. Med. J. China 8:225-255.

68. Wu LIEN-TEH. 1926. A treatise on pneumonicplague. League of Nations Health Organiza-tion, Geneva. 466 p.

69. WYSSOKOWITZ, V. K., AND D. K. ZABOLOTNY.1897. Recherches sur la peste bubonique.Ann. inst. Pasteur 11:663-669.

70. ZABOLOTNY, D. K. 1907. The plague, epidem-iology, pathogenesis and prophylaxis; ob-servations and inxestigations. St. Peters-burg. 94 p.

71. ZABOLOTNY, D. K. 1915. La peste pneumoniqueen Mandchourie. Petrograd.

19611 261

on Novem

ber 16, 2020 by guesthttp://m

mbr.asm

.org/D

ownloaded from