Page 1553 - Small Animal Internal Medicine, 6th Edition

CHAPTER 98 Polysystemic Protozoal Infections 1525

most seronegative cats would shed the organism if infected. N. caninum infection by serologic testing, and response to
If owners are concerned that they may have toxoplasmosis, an anti-Toxoplasma drug. Interpretation of serum, aqueous
VetBooks.ir they should see their physician for testing. humor, and CSF antibody and PCR test results is as dis-
cussed for toxoplasmosis in cats.
CANINE TOXOPLASMOSIS Treatment
Clindamycin hydrochloride (10-12 mg/kg PO q12h) has
Etiology and Epidemiology been used most frequently for treatment of canine toxoplas-
Dogs do not produce T. gondii oocysts like cats, but they can mosis by the author. Trimethoprim-sulfa (15 mg/kg PO
mechanically transmit oocysts after ingesting feline feces. q12h) is an alternative protocol. Treatment should be con-
The tissue phases of T. gondii infection occur in dogs and can tinued for a minimum of 4 weeks. Ponazuril at 20 mg/kg PO
induce clinical disease. Approximately 20% of dogs in the q24h for 28 days was used successfully to treat a dog with
United States are seropositive for T. gondii antibodies (Levy suppurative keratitis and necrotizing conjunctivitis (Swinger
et al., 2011). Before 1988, many dogs diagnosed with toxo- et al., 2009). If uveitis is detected, topical glucocorticoid
plasmosis based on histologic evaluation were truly infected treatment should also be used.
with Neospora caninum (see Neosporosis section). Transpla-
cental infection occurs in dogs with both T. gondii and N. Zoonotic Aspects and Prevention
caninum. In one study of 41 stillborn puppies, 78.6% were Dogs do not complete the enteroepithelial phase of T. gondii
positive for T. gondii (Taques et al., 2016). Toxoplasma gondii but can mechanically transmit oocysts after ingesting feline
strains from dogs in Brazil were shown to be from four dif- feces. Like all other warm-blooded vertebrates, dogs are
ferent genotypes of which all were proven to be virulent to infected by the ingestion of sporulated oocysts or tissue
mice (da Silva et al., 2017). cysts. Repeated infection can occur in dogs, and it appears
that venereal infection can also occur (Arantes et al., 2009;
Clinical Features Taques et al., 2016). Toxoplasmosis in dogs can be prevented
Respiratory, gastrointestinal, or neuromuscular infection by not allowing dogs to be coprophagic and to feed only
resulting in fever, vomiting, diarrhea, dyspnea, and icterus cooked meat and meat by-products.
occurs most commonly in dogs with generalized toxoplasmo-
sis. Generalized toxoplasmosis is most common in immuno-
suppressed dogs such as those with canine distemper virus AMERICAN TRYPANOSOMIASIS
infection or those receiving cyclosporine to prevent rejection
of a transplanted kidney. Neurologic signs depend on the Etiology and Epidemiology
location of the primary lesions and include ataxia, seizures, Trypanosoma cruzi is a flagellate that infects many mammals
tremors, cranial nerve deficits, paresis, and paralysis. Dogs and causes American trypanosomiasis. The disease is diag-
with myositis present with weakness, stiff gait, or muscle nosed primarily in South America, but multiple cases have
wasting. Rapid progression to tetraparesis and paralysis with been detected in dogs of North America. Trypanosoma
lower motor neuron dysfunction can occur. One study asso- caninum is a new species identified in dogs in Brazil (Madeira
ciated T. gondii antibodies with polyradiculoneuritis in dogs et al., 2014). Continued work is needed to determine the
(Holt et al., 2011). Some dogs with suspected neuromus- prevalence of this agent in the United States and to define
cular toxoplasmosis probably have neosporosis. Myocardial the clinical importance of the agent. Trypanosoma cruzi is
infection resulting in ventricular arrhythmias occurs in molecularly diverse, but isolates from California have been
some infected dogs. Dyspnea, vomiting, or diarrhea occurs shown to be similar to those of Latin America and so are
in dogs with polysystemic disease. Retinitis, anterior uveitis, likely of being capable of inducing disease (Shender et al.,
iridocyclitis, and optic neuritis occur in some dogs with 2016). The triatomine vectors (reduviid [kissing] bugs) of
toxoplasmosis, but they are less common than in cats. Cuta- T. cruzi are common in parts of the United States including
neous disease has also been reported. Texas and California and frequently live in homes and dog
kennels (Curtis-Robles et al., 2018). Even though infected
Diagnosis reservoir mammals (dogs, cats, raccoons, opossums, arma-
As in cats, clinicopathologic and imaging abnormalities are dillos) and vectors are found in the United States, infection in
not specific. Hyperglobulinemia can occur in dogs with dogs or people is rare; this may relate to differences in vector
chronic infection (Yarim et al., 2007). Increased protein con- behavior and sanitation standards in the United States. In
centrations and mixed inflammatory cell infiltrates occur in one study in Texas, the number of serologically positive dogs
dogs with CNS toxoplasmosis. increased between 1987 and 1996 (Meurs et al., 1998). Fox-
Demonstration of the organism associated with inflam- hounds infected with Leishmania spp. are commonly shown
mation in tissues or exudates can lead to a definitive diagno- to be co-infected with T. cruzi (Duprey et al., 2006). In a
sis. More commonly an antemortem diagnosis is based on the study of 860 dogs in Tennessee, 6.4% had positive serum
combination of appropriate clinical signs, exclusion of other antibody titers suggesting exposure was common (Rowland
likely etiologies, positive serum antibody tests, exclusion of et al., 2010). In another smaller study, the seroprevalence