Page 1498 - Small Animal Internal Medicine, 6th Edition

1470 PART XIV Infectious Diseases

TABLE 95.1
VetBooks.ir Ehrlichia spp., Anaplasma spp., and Rickettsia spp. of Primary Significance to Dogs or Cats PRIMARY CLINICAL

SMALL
GENUS AND SPECIES ANIMAL HOST CELL TROPISM PRIMARY VECTOR SYNDROMES

Anaplasma Dog and cat Granulocytotropic Ixodes spp. Fever, polyarthritis
phagocytophilum
Anaplasma platys Dog and cat Thrombocytotropic Rhipicephalus sanguineus Fever, thrombocytopenia,
uveitis
Ehrlichia canis Dog and cat Monocytotropic Rhipicephalus sanguineus; Fever and diverse
Dermacentor variabilis manifestations
Ehrlichia chaffeensis Dog and cat Monocytotropic Amblyomma americanum, Subclinical; unclear in
Dermacentor variabilis natural infections
Ehrlichia ewingii Dog and cat Granulocytotropic Amblyomma americanum Polyarthritis, fever,
meningitis
Rickettsia rickettsii Dog and cat Dermacentor spp., Amblyomma Fever and diverse
americanum, Rhipicephalus manifestations
sanguineus

FIG 95.2
Suppurative changes consistent with polyarthritis induced by
Ehrlichia canis, E. ewingii, or Anaplasma phagocytophilum
infection in dogs.

FIG 95.1
Anaplasma phagocytophilum morulae in a neutrophil of an mild and nonspecific. The morulae cannot be distinguished
experimentally infected cat. from those of E. ewingii, but the geographic range of the
infections varies between the organisms; the travel history
can help rank the differentials (see the Canine granulocytic
Diagnosis ehrlichiosis section in this chapter).
Morula of A. phagocytophilum can be detected in neutrophils There are multiple serum antibody tests around the world.
of some clinically affected dogs, so infection can be strongly The most common point-of-care assay that detects antibod-
suspected after performance of a complete blood count ies against A. phagocytophilum (SNAP 4Dx Plus, IDEXX,
(CBC) or evaluation of synovial fluid from a joint tap (see Westbrook, ME) also detects antibodies against A. platys.
Fig. 95.2). Other CBC abnormalities recognized in some Many other service laboratories offer A. phagocytophilum
dogs include thrombocytopenia, hemolytic anemia (rarely), antibody testing (Moroff et al., 2014). Antibody assay results
leukopenia, eosinopenia, lymphocytosis, and monocytosis. can be falsely negative in acute cases, so a convalescent test
Reported biochemical panel and urinalysis abnormalities are 2 to 3 weeks later may be required to confirm exposure. If