MALARIA IN MEXICO C. Johnson

'Mr. Johnson was a graduate student at the University of Mi nnesota when he d id the research for this paper.

The traditional picture of Mexico, at least to the average tourist, is never complete without a peon, in sombrero and serape, sleeping in the noonday sun, or putting off to manana whatever physical exertion is required. Actually, when seriously considered, this pic­ture is found to be a myth, no more representative of the Mexican than the traditional cowboy or gangster image is of the American . What is interesting in the image of the peon, however, is that he is an excellent example of a population debilitated by malaria.

To most North Americans, the exis­tence of endemic malaria in an indus­trialized, modern nation is unthinkable -it is considered to be a lowland trop­ical disease of undeveloped nations. As recently as 1957, however, it was in Mexico the leading cause of death from infectious disease, accounting for 519.6 deaths per million population, far exceeding such killers as tubercu­losis (302.1 per million), influenza (270.9 per million), dysentery (188.6 permillion) and typhoid (117.8 permil­lion).1 Doubly interesting is the fact that, by that year, both smallpox and yellow fever had been vanquished, evidence of the progress of modern medicine in Mexico. Since 1957, ma­laria also has declined in its toll in human lives, but a question is raised of how extensive that toll may have been historically.

28

Population D ecline in Mexico

The phenomenal decline of the na­tive population of Mexico in the years following the Spanish Conquest is a matter of record. The cause of the de­cline has been a subject of controversy, but examination of the literature avail­able seems to indicate that disease played a major role. The problem is­how much of the decline may be at­tributed to malaria?

No actual figures are available on the population of the Valley of Mexico before the Conquest and during the early years of the colonial regime. Many estimates have been made, but only recently have they been based on such records as tributary lists or taxa­tion data. Such is the case with the estimates of the Berkeley school;2

Estimated Year Population

1519 25,200,000 1532 16,800,000 1548 6,300,000

1568 2,650,000 1580 1,900,000 1595 1,375,000 1605 1,075,000

Opinions as to the lowest point of the decline vary-sufficient data are not yet available-but there is general agreement that it was some time in the seventeenth century.

In th ei r studies of population de­cline, Borah and Cook divide Mexico into ten ecologically-unique regions, grouped as either Highland or Low­land. Comparing subtotals, they note that, while the total population of Mexico was declining at a rate of about 3% to 6% per year, the rate of decline was nearly twice as great in Lowlands as in Highlands. They interpret this dif­ference as being disease-related. By extending this type of analysis to the

29

individual regions, interesting differ­ences are revealed between them, as well as between Highlands and Low­lands. (Tables 1 and 2) Mapping the rates of decline suggests that no single disease could have been responsible for the decline, but a series of diseases, affecting different areas at different times, or with different degrees of se­verity (Maps 1 to 4).

The data obtained also reveal that recovery began in some regions during the late sixteenth century-areas along the Pacific Lowlands with some asso­ciated highlands (i.e., Nayarit, Colima, Jalisco, Guerrero, and part of Michoa­can), plus the northern Atlantic Low­lands (i.e., parts of Tamaulipas, San Luis Potosi, and Hidalgo, and northern Veracruz). In southern Veracruz, how­ever, population appears to have sta­bilized briefly about mid-century (1568-1580), and then resumed the decline (1580-1595). This suggests the introduction of a new disease at that time in the area around the chief port of colonial Mexico.

Characteristics of Malaria

Research into the epidemiology of malaria reveals that, of the four species of Plasmodia, three are found in Mex­ico. All may be fatal, especially if un­treated or if treated with inadequate quinine therapy. Falciparum malaria, which is not usually recognizable by the classic chills and fever, may kill within a few hours. Repeated attacks of the milder vivax malaria also may kill. Under epidemic conditions, as when introduced into a non-immune population, pernicious malaria (partic­ularly falciparum) is more common, and large numbers of people of all ages may be killed in a relatively-short outbreak. During such epidemics, there may be intestinal complications or hemorrhaging, but death is most often due to cerebral involvement, so

TABLE 1

DECLINE OF POPULATION (by regions)

Population Population Percentage of Pre-Conquest 1532 Pre-Conquest

Region (mi ll ions) (millions) Population

10.9 7.99 73.3 II 2.8 1.53 54.6 Iia } 1.9 .88 {

.17 46.3 III .71 IV 1.7 1.56 91.8 V .8 .68 85.0

VI } 4.6 2.10 { .86 45.7 VII 1.24 VIII 1.3 1.03 73.1

IX } 1.2 1.07 { .46 89.2 X .61

Total 25.2 16.87 67.1

Source : Woodrow Borah and Sherburne F. Cook, " The Aboriginal Population of Central Mexico on the Eve of the Spanish Conquest," Ibero-Americana : 45 (Berkeley and Los Angeles : University of California Press, 1963), p. 157.

TABLE 2

DECLINE OF POPULATION IN HIGHLANDS (A ) AND IN LOWLANDS IN COASTAL REGIONS (B)

(by regions)

Percentage of Percentage of Percentage of Percentage of 1532 Population 1568 Population 1580 Population 1595 Population

Remaining Remaining Remaining Remaining Region in 1568 in 1580 in 1595 in 1605

A Highlands I 21.3 72.1 62.5

Iia 18.1 68.7 90.9 IV 14.2 67.0 97.3

VIII 18.0 85.6 60.2 IX 17.5 80.2 140

Subtotal 19.8 73.1 69.9 75.7

B Lowlands in Coastal Regions II 4.8 56.7 109.5

III 5.3 84.2 56.2 V 9.9 82.3 66.0

VI 7.4 68.7 77.2 VII 9.1 56.1 110.9

X 9.9 34.4 195.2 Subtotal 7.4 62.6 94.1 89.9 Total 16.7 71.5 72.5 78.3

30

)

o 10:) E4 E""9

5c'lle in '.!iles

31

SURVP.TAL ~ TE

0:'" POPULA '!'ION IN COLONIAL !O~EXICO

20:) I

13:v Regions

Prp.conqup.st t o 1532

IT:] [IIJ ,...,-, L.:..-'..J

ITZJ &\'SI

Man 1

Least decline - 99 .0 to 99.9% 713 .0 to 87 .9% 73 . 0 to 77 . 9% 50.0 to 59 .9%

~.Iost decline hO . f) to hc}.9% £J

" )

~ ( ) L. . .,

I c._ . 1'"

i~·· - · \ . C ~ ~ i . ( "I. ." . .-J , . \ r

/ - ~ ~ ' \ ") i 'l ~

I / I 1

.,- ) \ ../ I" ! ,... . 6 ; (

", ' • c.. ~ -'\ ~ . I c... II ""I 1[: ' - .

'\). I " ~j" '- . . " . Iil' ._. ii " , .--' J! I I ~/ . . '\ .

I' . . ~ . -' " J II . "1. f I 1" ' --. .

~ -' (_. " 1" . '1 .. -... . -- ~ I ) .. ~

. I ·1 r ·...}

I l ~rr

I I . :IX. . I - I I " . , ,

~~I VIII .. -W

. (

\1.1 11 . :EtA h, IIlliI I I . . . . _IE: 1:::. ..... I . . . ~Df I I' I . ..

• ... I - flj ...

I I I I1iiW , I I I I I I "'1: , . \ 1111 I I I

" I I ' I N II I I W I I I 1\

I I I \I I '--1[11 1111 I ~ I ~ I . t-

I ..,;,

'1L l ,!!! ---.....

Sl' l1 'TI7AL qATE OF POPULATION IN COLONIAL ~ICO

9y ~egions

1532 to 1568

HE Over 20% ( Leas t decline)

EH3 15. 0 to 19.9% 0 100 200 M 9.0 to l u . 9% E4 F3 F"1 I

SC'll e in }Ul es ~ Under 9t (Greatest decline)

tJ

V.an 2

32

33

.J"

I )

i~ ' - " . \ . { i. ' , \

._ . ,/ :r'\ /' (

,-'

SU:PTI7AL ~ATE OF POPULATION IN COIDNIAL MEXICO

'3y ttegions

o 100 200

1568 to 1590

m 78 . 0 to 87.9% (Least decline) o 60. 0 to 72 .9~ m 50.0 to 59 .9%

Scale in Miles a 30.0 to 39.9% ( Greatest decline)

lJ

Map 3

\ )

r o-. • . , \

f' . . \ . I ". \

. ?\ / I

.--- \ <;

(

\

--- . ~ . l.'" '\, ." ~.-

(

SURnVAL ltATE OF POPULATION IN COWNIAL MEXICO

o 100 200 E3 F?"3 E3 I

Scale in Miles

3y ~e~ions

1580 to 1595

D [L] ~ l.!....:....:J

EZl W2l

Over 100% 88 .0 to 99.9% (Least decline) 71.0 to 77 .9% 60 .0 to 72 .9'1, 50.0 to 59 .9% (Greatest

decline )

Man 4

34

...

L

that the disease may resemble enceph­alitis or meningitis. Thi s fact leads to a suspicion that the puzzling death of Ponce de Leon could have been due to malaria. The puzzle then becomes why the epidemic spread no further than the hundred persons stated to have been on the ship involved.

Origin and Diffusion of Malaria

Historically, malaria was common around the Mediterranean. The Atlas of Diseases3 shows Plasmodium vivax (tertian malaria) as above average in prevalence in this area, and Plasmo­dium fa/ciparum below average. In Africa, however, P. falciparum is above average, and P. viva x below average in prevalence, partly the result of a ge­netic immunity to the latter, found only in certain groups of Negroes and in some hill people of India. Such re­sistance indicates the process of nat­ural selection operating over a long period of time, hence long association with the disease. Africa is, therefore, the probable source area of malaria, with P. vivax representing the earliest form of the disease.

The outbreak of an epidemic re­quires only: (-I) a non-immune popu­lation ; (2) a source of disease orga­nisms (in the case of malaria, gameto­cytes) which may initially be small; (3) a vector (in the case of malaria, any of numerous species of anopheline mos­quitos). All three factors appear to have been present in the New World. The migration of small groups of peoples across the Siberian land bridge during glacial ages would effectively screen out diseases such as malaria in which temperature is a crucial factor in the development of both the parasite and the vector. This argues for the exis­tence in America of a non-immune population. Records of the Spanish Conquest show that the first Negro reached Mexico as early as 1520 with

35

Narvaez' army, so it is probable that sources of different gametocytes (from Spain and from Africa) were present, at least sporadically, from the date of the Conquest or very soon after. The distribution of anophelines therefore becomes the critical factor to trigger epidemics of malaria in the NewWorld.

Vectors of Malaria

In the laboratory, many species of mosquitoes may be made to carry dis­ease organisms, but, under natural conditions, they may not do so. A spe­cies must first of all be widespread and exist in large numbers to be important as a vector. Distribution of anophe­lines is limited by ocean barriers, each species tending to be restricted to a si ngle continent unless a land bridge exists, such as that between North and South America. Most species are neo­tropical, but a few are found in north­ern latitudes or high altitudes, and these are obviously of great interest in a study of the Mexican Plateau.

The Atlas of Diseases locates the Mexican species as follows: in Yuca­tan and the southern lowlands, Ano­pheles pseudopunctipennis p., and A. darlingi ; on the Gulf Coast, A. quadri­maculatus, and A. albimanus; on the plateau, A. pseudopunctipennis, and A. aztecus (a subspecies of the series maculipennis). Komp (4) adds to these A. crucians, and A. atropos. Russell et al (5) add A. argyritarsis and A. puncti­macula (extending from southern Mex­ico to Argentina), and A. freeborni (which extends from the west coast of Canada to Northwest Mexico).

Komp ' s classification shows A. quadrimacu/atus, A. maculipennis, A. crucians, A. pseudopunctipennis, and A. eiseni in a closely-related group, and A. albimanus, A. argyritarsis, and A. darlingi in different series of an­other sub-genus of anophelines. Any of these can be vectors of malaria. They

are not equally abundant, however, so that the most likely vectors in Mexico are A. aztecus, A. quadrimaculatus, A. pseudopunctipennis, and A. albima­nus. As these are all domestic mos­quitoes, their distribution would ac­count for the presence of the disease everywhere in Mexico, which was in fact the case.

Boyd6 has noted that the ecology of anophelines varies among species. These differences explain some of the peculiarities of malaria. A. albimanus, believed to be the single most impor­tant vector, is highly adaptable, but not found over 3000 feet elevation, gener­ally breeding below 1300 feet (400 meters) . It tends therefore to extend inland along river valleys. A marked reduction in its numbers is noted dur­ing the dry season in Mexico. In the areas where A. albimanus is the vector, therefore, malaria tends to occur dur­ing the rainy season.

Anopheles quadrimaculatus is be­lieved to be the vector of malaria on the Gulf Coast from around Tuxpan north into the southern United States. This mosquito appears to be inhibited by high temperatures.

Anopheles pseudopunctipennis, the principal vector in highland areas, also appears to sp read along river valleys, is distributed throughout the moun­tains from the southwest United States into South America, and inhabits most of the area between Sierra Madre Oc­cidental and Oriental. It appears to prefer mountain streams which are not being flushed out by heavy rains and is responsible, therefore, for outbreaks of malaria during the dry season, and, obviously, for most of the incidence of the disease in arid and semi-arid areas.

One characteristic that A. albimanus and A. pseudopunctipennis have in common is their preference for resting high on the inside of palm-leaf-thatch

roofs. This habit makes both danger­ous as vectors, because of the proxim­ity of victims.

The last major vector of malaria in Mexico is Anopheles aztecus, a variety (or sub-species) of A. maculipennis. This species is not as particular as most mosquitoes about clean water, and, therefore, tends to replace A. pseudo­punctipennis around populated areas such as Mexico City. It breeds in ca­nals, irrigation channels, and pools containing algae and protozoa, and has been found surviving even under ice. This species is believed to be re­sponsib le for malaria around Xochi­miico, where clinical histories have been recorded since 1875.

Anophelines are not noted for long­distance flights, but may be dispersed for considerable distances downwind. Wind velocities at sunset and sunrise, when mosquitoes fly, may therefore be important factors in malaria. Con­versely, by creating waves, wind action may be destructive to anophelines in the aquatic stage.

The individual susceptibility to ma­laria of different species of Anopheles varies, and some seem to be more sus­ceptible to one species of Plasmodia, e.g., A. crucians seems to carry P. fal­ciparum. Species which have been in­fected experimentally in the laboratory do not always seem to transmit malaria in nature. This suggests that a period of adjustment or adaptation is neces­sary before a vector can transmit infec­tion efficiently. If this is so, the lapse of time between the arrival of the first Spanish conquistadores and the first outbreak of malaria, as well as the strange death of Ponce de Leon, may be explained (i.e., the disease was con­tracted elsewhere by all the people on the ship, but did not spread further because, in Mexico, no vector was yet adapted to the disease organism).

36

....

Physical Factors in The Incidence of Malaria

The most malarious area in Mexico is reported to be the south, but the disease occurs in highlands and arid areas as well as on the coast and in the rainforest. Official rates have been listed as: for the entire Republic, 140.7; Distrito Federa l, 6.16; Michoacan, 9.43; Chihuahua, 12 .55; Tabasco, 502.29; Oaxaca, 563.02. In 1939, an average figure, covering the period from 1922 to 1938, was set for mor­bidity at 576 per 100,000 population ; for mortality, 145.5 per 11 ,000,000 population?

Temperature appears to be the sin­gle most important climatic factor, since the optimum condition for de­velopment of the parasi te in a mos­quito is 25 °C (45 ° F) for P. vivax, 30°C (54° F) for P. falciparum, and 22 ° C (39.6 ° F) for P. malariae. With lowered temperature, the time variable for de­velopment of the parasite increases, so that factors which affect temperature (i.e., winds, altitude, cold currents) will affect the occurrence of malaria, possi­bly even extend the period of develop­ment beyond the life expectancy of the vector.

The effects of wind and rainfall have already been noted, so that it is ob­vious how climatological factors may determine the type and number of mosquitoes in an area, their life expec­tancy, and the extent of their dispersal. However, since different species are adapted to different conditions of the natural environment, there is usually a vector present in Mexico which may transmit malaria.

Human and Cultural Factors in The Incidence of Malaria

Man is the only known carrier of malaria parasites. His movements are thus important in the spread of the

37

disease, through pilgrimages, work patterns, migrations, trade missions, even holiday travel , and the subse­quent pattern of disease should sug­gest such movements. In Mexico, the predominant types of malaria are: on the p lateau, P. vivax; in Yucatan and the adjacent lowlands, P. falciparum (though both of these plus P. malariae appear in each area). Tertian malaria (P. viva x), endemic in Spain, is believed to have been brought to America by the conquistadores, this being at least partly responsible for the rapid initial disappearance of the aborigines of the coast and Caribbean islands. Malignant malaria (P. falciparum) appears to have come to the New World later, from Af­rica, with the importation of increasing numbers of Negro slaves. The distribu­tion appears to corroborate this theory, as Negroes were more frequently em­ployed on plantations in lowland areas.

Man's activities provide new breed­ing areas for the vectors of malaria by deforestation, the breaking of ground for agriculture, irrigation, or the con­struction of such reservoi rs as fish and mill ponds, or even stock-watering tanks.

Various cu l tural habits are also con­tributory. Examples cited in the Atlas of Diseases include the type of housing (e.g., on the ground or on piles), cook­ing facil ities (indoors or out), and the proximity of domestic animals which might be alternate victims. The use of screening, repe ll ents, and insecticides in modern industrial countries is im­portant, but the conservatism of prim­itive peoples may lead to rejection of such modern innovations. Human at­titudes are thus crucia l to the inci­dence of malaria.

The selective nature of diseases in Mexico is one basis of the Black Leg­end (i.e., the theory of deliberate ex­termination). Examination of the inci­dence of malaria reveals something

I I I

else. Early sources refer to the host of insects encountered, but we cannot be certain that the people of Colonial Mexico were aware of the capacity of vectors as carriers of disease. In the sources examined, only GageS refers to the use of pabelfons. The extent of such use of mosquito nets or mosqui­teras is not known, but their origin dates back to the canopea of the Ro­man Empire. Since the Romans were aware of the connection between mosquitos and malaria, when they drained marshes, it is probable that the Spaniards also knew.

Among the Indians, the one known custom which would have discouraged mosquitoes- the continual censing with copal that was practiced on the teocalfi and elsewhere- was banned by the Spaniards. Thus the incidence of disease tended to be increased in one group and decreased in the other by cultural practices, above the differ­ences produced by centuries of expo­sure to disease in the Mediterranean and Africa on the one hand and Ameri­ca on the other, with no immunity at all .

Conclusions

In nature, there is no immune state for malaria, although it has been in­duced experimentally. This is partly due to the large number of strains­there appears to be no limit9-and immunity gained from an infection by one strain gives no protection from others, or, indeed, from the same strain after a lapse of time. The sole excep­tion appears to be the genetic resis­tance associated with the abnormal blood type S (i.e. , the sickle-cell trait).

In Spain and in Africa, where it ap­parently originated, malaria is endemic because of long exposure of the popu­lation. In the New World, exposure of a non-immune population would re­sult in the outbreak of epidemic as

soon as a vector was capable of trans­mitting the disease. At least two such epidemics seem probable-one of ter­tian malaria, one of malignant-but there could also have been an epidem­ic of quartan (P. ma/ariae) as it may easily be masked by the more obvious symptoms and severity of the other types.

These characteristics of malaria ap­pear to fit into the observed pattern of decline - recovery - decline of popula­tion during the sixteenth century in Mexico. The outbreak of fever re­ported in Yucatan in 1527 was prob­ably malaria (not yellow fever, as re­portedL and it seems probable that it was one of the many diseases which broke out in Mexico just before and after 1532. Malaria was probably the great epidemic which followed Guz­man 's expedition to the west. Certainly malaria was established on the Gulf Coast in 1536, as, in that year, Zumar­raga wrote the Council of the Indies regarding the need for hospitals on the highway from Veracruz to Mexico City. From 1599 to 1618, one source10

reports yellow fever in Yucatan, but most others believe this disease to have made its initial appearance con­siderably later, in 1648.11 It is prob­able, therefore, that this epidemic was the first appearance of malignant ma­laria (P. fa/ciparum), since slaves were being imported in the late sixteenth century. Following this outbreak, dis­ease appeared on the plateau at Xochimilco, in 1601, in a pattern typical of malaria.

Translated, the Aztec term cocoliztli means merely painful fever. Because of the tendency of the Aztec language to describe qualities rather than specif­ics, this name, which appears frequent­ly in the literature, seems to have been applied to different diseases at differ­ent times. It is probable that malaria was an important member of this

38

...

..

group. The fact that it does not seem to have been recognized by the Span­iards may be ascribed to the changed pattern of the disease, which had been

FOOTNOTES

I I ) World Heal lh Organizalion, Annual Epidemio logi­cal and Vital Statistics, 1957 (Geneve : 1960).

(2) Sherbu rne F. Cook and Woodrow Borah, " Indian Population of Cenlral Mexico 1531-1610," Ibero­Americana : 44 (Berke ley and Los Angeles : Universily of California Press , 1%0). Woodrow Borah and Sherburne F. Cook, " The Ab­original Population of Centra l Mexico on Ihe Eve of the Spanish Conquest," Ibero-Americana : 45 (Berke ley and Los Angeles : University of California Press , 1963). Woodrow Borah and Sherburne F. Cook, " The Pop­ulation of Central Mexico in 1548," Ibero-Ameri­cana: 43 (Berkeley and Los Angeles : University of California Press, 1960).

(3) American Geographical Society, Atlas of Diseases (New York).

(. ) W. H. W. Komp, "The Classification and Identifi­cation of (he Anopheles Mosquitoes of Mexico, Central America , and the West Indies," A Sympo­sium on Human Malaria , ed. Forest Ray Moulton (Washington : American Association for the Ad­vancement of Science, 1941) .

39

produced by the interaction of factors -a non-immune population, different vectors, and the different physical and climatic characteri sti cs of Mexico.

(5) Paul F. Russe ll , Luther S. West, Reginald D. Man­we ll , and George MacDonald, Practical Malariology (London: Oxford University Press, 1963).

(0 ) Mark F. Boyd (ed.), Malariology (Philadelphia and London: W. B. Sau nders Company, 1949).

(7) Ernest Carroll Faust, " The Distribution of Malaria in North America , Mexico, Centra l America , and the West Indies," A Symposium on Human Malaria, ed. Forest Ray Moulton (Washington : American As­sociation for the Advancement of Science, 1941) .

(S) Thomas Gage, Travels in the New World, ed. J. Eric S. Thompson (Norman : University of Oklahoma Press, 1958) .

(' ) W . B. Redmond, " Immunity to Human Malaria : Characteristics of Immun ity," A Symposium on Hu­man Malaria , ed. Forest Ray Moulton (Washington : American Association for the Advancement of Sci­ence, 1941).

(101 Gordon Schendel , Medicine in Mexico (Austi n and London : University of Texas Press, 1968) .

(1 1) George Cheever Sha ttuck, The Peninsula of Yuca­tan: Medical, Biological, Meteoro logical and Socio­logical Studies (Washington: Carnegie Institute, 1933) .