Page 1545 - Small Animal Internal Medicine, 6th Edition

CHAPTER 98 Polysystemic Protozoal Infections 1517

Ticks should be controlled, and cats in endemic areas Clinical Features
should be housed during periods of peak tick activ- Although subclinical infection is common, both H. america-
VetBooks.ir ity. Cytauxzoon felis has been shown to be transmitted clinical illness without concurrent immune deficiency. Clini-
num and H. canis can be primary pathogens, resulting in
by A. americanum between 36 and 48 hours after feeding
cally affected dogs have been in all age groups, but disease is
(Thomas et al., 2018). An imidacloprid/flumethrin collar
was effective at blocking transmission by A. america- most commonly recognized in puppies. Fever, weight loss,
num in one experimental study (Reichard et al., 2013). and severe hyperesthesia over the paraspinal regions are
Known C. felis-positive cats should not be used as blood common findings. Anorexia, pale mucous membranes from
donors, and cats to be used as blood donors in endemic anemia, depression, oculonasal discharge, meningoencepha-
areas should be shown negative by PCR assay (Wardrop lomyelitis, and bloody diarrhea occur in some dogs. Cutane-
et al., 2016). ous lesions consisting of a pruritic swelling were described
in one dog (Little and Baneth, 2011). Clinical signs can be
intermittent and recurrent.
HEPATOZOONOSIS
Diagnosis
Etiology and Epidemiology Neutrophilic leukocytosis (20,000-200,000 cells/µL) with a
Hepatozoonosis in dogs is caused by the protozoal agents left shift is the most common hematologic finding for dogs
Hepatozoon canis and Hepatozoon americanum. In North infected with H. americanum. Thrombocytopenia is unusual
America, H. americanum predominates, is transmitted by unless co-infection with Ehrlichia canis, Anaplasma spp., or
Amblyomma maculatum (Gulf Coast tick), and is most Leishmania spp occurs. Normocytic, normochromic, nonre-
common in the Texas Gulf Coast, Mississippi, Alabama, generative anemia is common and is likely from chronic
Georgia, Florida, Louisiana, and Oklahoma. In Africa, inflammation. Increased activity of alkaline phosphatase but
southern Europe, and Asia, H. canis predominates and is not creatine kinase occurs in H. americanum–infected dogs.
transmitted by R. sanguineus (brown dog tick). In South Hypoalbuminemia, hypoglycemia, and, rarely, polyclonal
America, H. canis is transmitted by R. sanguineus and A. gammopathy occur in some dogs. Periosteal reactions from
ovale. Hepatozoon canis can also be transmitted transpla- the inflammatory response directed at tissue phases in
centally. Cystozoites are an infectious stage of Hepatozoon muscle can occur in any bone except the skull, are most
spp. that form in the tissue of paratenic hosts like rabbits, common in young dogs, do not occur in every case, and are
mice, and some rats and can initiate infection in dogs not pathognomonic for hepatozoonosis. Definitive diagnosis
after predation (Johnson et al., 2009a,b). In one study of is based on identification of gamonts in neutrophils or
614 dogs with suspected hepatozoonosis in the United monocytes in Giemsa or Leishman stained blood smears or
States, the prevalence rates for H. americanum, H. canis, by demonstration of the organism in muscle biopsy sections.
or both were 27.2%, 2.3%, and 2.3%, respectively (Li et al., However, the organisms can be detected in the blood of
2008). healthy dogs and cats. Serologic tests are available in some
At least three Hepatozoon species can be detected in countries and because the tissue phases are not cleared, posi-
the blood of cats in Europe (Díaz-Regañón et al., 2017; tive test results suggest that the dog is infected. However,
Giannelli et al., 2017), and the organism can be amplified because subclinical infection can occur, presence of serum
from ticks removed from cats (Duplan et al., 2018). The antibodies does not prove the clinical manifestations are
routes of transmission and clinical disease associations are from Hepatozoon spp. infection. PCR assays are now avail-
currently unclear, but the cats are commonly co-infected able in some laboratories, and positive results confirm infec-
with feline leukemia virus or feline immunodeficiency tion (Li et al., 2008; Modrý et al., 2017). Quantitative PCR
virus. assay results may be used to follow treatment responses in
Vertebrate hosts develop macrogametes and microga- the future.
metes in neutrophils and monocytes after infection by a Hep-
atozoon spp. The tick ingests the organism during a blood Treatment
meal and oocysts develop. After a dog ingests an infected No therapeutic regimen has been shown to eliminate H.
tick, sporozoites are released and infect mononuclear phago- canis or H. americanum infection from tissues. However,
cytes and endothelial cells of the spleen, liver, muscle, lungs, clinical disease resolves rapidly with several drug proto-
and bone marrow, and ultimately form cysts containing mac- cols. For treatment of H. americanum, the combination of
romeronts and micromeronts. Micromeronts develop into trimethoprim-sulfadiazine (15 mg/kg PO q12h), pyrimeth-
micromerozoites, which infect leukocytes and develop into amine (0.25 mg/kg PO q24h), and clindamycin (10 mg/kg
gamonts. Tissue phases induce pyogranulomatous inflam- PO q8h) for 14 days is highly successful in the acute stage
mation, resulting in clinical disease. Glomerulonephritis or (Macintire et al., 2001). Use of decoquinate (10-20 mg/kg
amyloidosis may occur as a result of chronic inflammation q12h) with food lessens the likelihood of recurrence of clini-
and immune complex disease. Infected dogs can serve as cal disease and prolongs survival time. Imidocarb dipro-
a source of infection for ticks for months to years (Ewing pionate (5-6 mg/kg intramuscularly or subcutaneously)
et al., 2002). administered once or twice 14 days apart is the drug of