infectious disease of feline blood

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PROCEEDINGS OF THE

NORTH AMERICAN VETERINARY CONFERENCE

VOLUME 20

JANUARY 7-11, 2006

ORLANDO, FLORIDA

SMALL ANIMAL EDITION

Reprinted in the IVIS website (http://www.ivis.org) with the permission of the NAVC.For more information on future NAVC events, visit the NAVC website at www.tnavc.org
http://www.ivis.org/http://www.ivis.org/


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Small Animal Hematology______________________________________________________________________________________________

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INFECTIOUS DISEASE OF FELINE BLOOD

John W. Harvey, DVM, PhD, Diplomate ACVPCollege of Veterinary Medicine

University of FloridaGainesville, FL

HEMOTROPHIC MYCOPLASMOSIS(HAEMOBARTONELLOSIS)

Hemotrophic mycoplasmas are gram-negative,nonacid-fast, bacteria that attach to the external surfaceof erythrocytes. Damage caused by parasite attachmentand immune-response by the host result in increasederythrocyte destruction and anemia. Hemotrophicmycoplasmas were classified as rickettsia in the genusHaemobartonellaor the genus Eperythrozoon for manyyears; however, results from sequencing of the 16SrRNA gene indicate that these parasites are closelyrelated to mycoplasmas. Consequently theHaemobartonellaand Eperythrozoongenera have beendiscarded and organisms in these genera were moved to

the genus Mycoplasma. Hemoplasmas has beenproposed as a trivial name for these hemotrophicmycoplasmas.

Although preweaning cats have been recognized withhemotrophic mycoplasmosis, most cases occur in adultanimals. Risk factors reported to be associated with thevisual identification of hemoplasma organisms in bloodinclude anemia, clinical signs of illness, cat-biteabscesses, FeLV-positive status, roaming outdoors, andage


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in 2 to 3 days. Dyspnea generally develops late in thecourse of the disease. Splenomegaly may be palpable.Experimental animals inoculated with infected blood ortissues rarely live more than 3 weeks after inoculation,and cats are usually dead within a week after clinicalsigns of illness are observed.

Laboratory FindingsIn the terminal stages of the disease, most cats will

have icteric plasma. The PCV may be in the low 30's butis usually in the 20's or upper teens. Reticulocyte countsare not increased in response to the anemia. Catsbecome thrombocytopenic during late stages of disease.Coagulation tests may be prolonged or remain normal.Elevations in ALT, BUN, and glucose are frequentlymeasured and serum protein is variably decreased.White blood cell counts are variable, but leukopeniagenerally develops terminally. Parasitemia occurs late inthe disease. When routinely-stained blood films areexamined, organisms appear in erythrocytes either asrounded "signet ring" bodies 1 to 1.5 microns in diameter

or as bipolar, oval or "safety pin" bodies 1 by 2 microns.The cytoplasm of the protozoan stains a light blue, whilethe nucleus appears red to purple. In the late stages ofthe disease, up to 25% of erythrocytes may containprotozoa, but parasites may be absent.

If parasites are absent or their identification isequivocal, schizonts may be identified in bone marrowaspirate smears. A PCR-based test for the nuclear smallsubunit (NSS) of the Cytauxzoon rRNA gene has beendeveloped, but it is of limited use in the diagnosis ofacutely ill animals, because the test results wouldgenerally not be available in time to effectively treat theanimal. Similarly, a serologic assay for antibodies usinga microfluorometric immunoassay can identify animals

that have survived the infection, but may not identifyacutely infected animals.

Therapy and PrognosisNearly all untreated cases in domestic cats are fatal,

although a less virulent strain has been reported in arestricted area of northwestern Arkansas andnortheastern Oklahoma. In this area, cats have survivedwithout specific treatment and 4 asymptomatic cats werediscovered by bleeding healthy cats in households with

ill cats. Treatment for cytauxzoonosis may be efficaciousif infected animals are recognized early. Therapy shouldinclude imidocarb dipropionate (Imizol) or diminazeneaceturate (2 mg/kg IM given twice with a 3 to 7 dayinterval), atropine (0.05 mg/kg SC) given prior to eachimidocarb treatment, heparin (150 U/kg SC q8h) withtapered decrease in dosage after the second imidocarbtreatment, fluid therapy, and a blood transfusion ifneeded.

References

1. Harvey JW. Hemotrophic mycoplasmosis. In:Greene CE, 3

rded. Infectious Diseases of the Dog

and Cat. Philadelphia: W.B. Saunders; 2005:inpress.

2. Meinkoth JH, Kocan AA. Feline cytauxzoonosis. VetClin North Am Small Anim Pract. 2005;35:89-101.

3. Messick JB. Hemotrophic mycoplasmas(hemoplasmas): a review and new insights intopathogenic potential. Vet Clin Pathol. 2004;33:2-13.

4. Willi B, Boretti FS, Cattori V et al. Identification,molecular characterization, and experimentaltransmission of a new hemoplasma isolate from acat with hemolytic anemia in Switzerland. J ClinMicrobiol. 2005;43:2581-2585.

5. Woods JE, Brewer MM, Hawley JR, Wisnewski N,Lappin MR. Evaluation of experimental transmission

of Candidatus Mycoplasma haemominutum andMycoplasma haemofelis by Ctenocephalides felis tocats. Am J Vet Res. 2005;66:1008-1012.

infectious disease of feline blood

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