Page 1554 - Small Animal Internal Medicine, 6th Edition

1526 PART XIV Infectious Diseases

rate in Virginia was 1%. Although some cats in Mexico are can also be used to amplify T. cruzi DNA from tissues or
known to be seropositive, clinical disease in cats has not been blood, and positive test results prove infection. Trypomas-
VetBooks.ir characterized (Longoni et al., 2012). tigotes can be cultured from blood or grown by bioassay
in mice.
The organism has three life stages: trypomastigotes (flag-
ellated stage found free in blood), amastigotes (nonflagel-
lated intracellular form), and epimastigotes (flagellated form Treatment
found in the vector). When infected kissing bugs defecate Nifurtimox has been prescribed for Chagas disease, but it is
during feeding, epimastigotes enter the vertebrate host, toxic and not readily available in the United States. In a
infect macrophages and myocytes, and transform into amas- recent study of allopurinol for the treatment of T. cruzi infec-
tigotes. Amastigotes divide by binary fission until the host tion in an experimentally infected mouse model, a positive
cell ruptures, releasing trypomastigotes into the circulation. response was noted. Thus treating clinically affected dogs
The vector is then infected by ingesting trypomastigotes with allopurinol as described for Leishmania may be prudent.
during a blood meal. Transmission can also occur transpla- In recent studies, administration of benznidazole or ravuco-
centally by vector ingestion, blood transfusion, or ingestion nazole lessened parasitemia but did not prevent infection in
of infected tissues or milk. Coinfection with parasites like dogs (Diniz Lde et al., 2010; Kratz et al., 2018; Santos et al.,
Ancylostoma caninum may potentiate T. cruzi infection 2012). Administration of the statin, simvastatin, at 20 mg PO
(Enriquez et al., 2016). Peak parasitemia occurs 2 to 3 weeks q24h lessened cardiac dysfunction over time in an experi-
after infection, causing acute disease. Disease in dogs is pri- mentally infected dog, likely from the immune modulating
marily a cardiomyopathy that develops from parasite- effects of the drug (Melo et al., 2011). Whether the same
induced damage to myocardial cells or immune-mediated benefits will be recognized in naturally infected dogs remains
reactions. to be proven. DNA vaccines for use as therapy also show
promise (Quijano-Hernandez et al., 2008). Glucocorticoid
Clinical Features therapy may improve survival of infected dogs. Therapy for
Exercise intolerance and weakness are nonspecific present- arrhythmias or heart failure should be instituted as needed.
ing complaints that relate to myocarditis or heart failure Most dogs that survive acute infection develop dilative car-
during acute infection. Generalized lymphadenopathy, diomyopathy. Survival time in 11 dogs ranges from 0 to 60
pallor, tachycardia, pulse deficits, hepatomegaly, and abdom- months.
inal distension can be detected on physical examination.
Anorexia, diarrhea, and neurologic signs occasionally occur. Zoonotic Aspects and Prevention
Dogs that survive acute infection can present for evaluation Infected dogs can serve as a reservoir of T. cruzi for vectors,
of chronic dilative cardiomyopathy. In 537 dogs in Texas and blood from infected dogs can be infectious to human
that were confirmed serologically or by histopathology, the beings (Travi, 2018). Vector control is the primary means
primary clinical abnormalities included anorexia, ascites, of prevention. In one study, use of deltamethrin-treated
cardiac conduction disturbances, cardiomegaly, lethargy, collars reduced Triatoma infestans feeding success on
and respiratory difficulties (Kjos et al., 2008). In another dogs (Reithinger et al., 2005; Travi, 2018). However, treat-
study of 11 dogs with chronic infection, right-sided cardiac ment with fipronil does not provide adequate protection
disease, conduction disturbances, ventricular arrhythmias, (Gürtler et al., 2009; Amelotti et al., 2012). Dogs should
and supraventricular arrhythmias were most common be kept from other reservoir hosts, such as opossums, and
(Meurs et al., 1998). should not be fed raw meat. Potential blood donors from
endemic areas should be serologically screened. For blood
Diagnosis donor programs, high-risk breeds (e.g., Foxhounds) or dogs
Common clinicopathologic abnormalities include lympho- from endemic areas should be screened for T. cruzi infec-
cytosis and increased activities of liver enzymes and creatine tion by serology or PCR assays, and positive dogs should
kinase. Thoracic radiographic, abdominal radiographic, be excluded from the program (Wardrop et al., 2016).
and echocardiographic findings are consistent with cardiac Experimental vaccine studies in dogs have been shown to
disease and failure but are not specific for trypanosomiasis. lessen parasitemia and potential for development of Chagas
The primary electrocardiographic findings are ventricular disease.
premature contractions, heart block, and T-wave inver-
sion. Definitive diagnosis is based on organism demon- Suggested Readings
stration. Trypomastigotes (one flagellum, 15-20 µm long) Babesiosis
can be identified during acute disease on thick blood film Annoscia G, et al. A new PCR assay for the detection and differ-
or buffy coat smears stained with Giemsa or Wright stain. entiation of Babesia canis and Babesia vogeli. Ticks Tick Borne
The organism is sometimes detected in lymph node aspi- Dis. 2017;8:862.
rates or abdominal effusions. Histopathologic evaluation of Baneth G. Antiprotozoal treatment of canine babesiosis. Vet Para-
cardiac tissue usually reveals myocarditis (98%) and amasti- sitol. 2018;254:58.
gotes (82%) are often identified (Kjos et al., 2008). Serologic Birkenheuer AJ, et al. Babesia gibsoni infections in dogs from
assays can be used to prove exposure to T. cruzi. PCR assays North Carolina. J Am Anim Hosp Assoc. 1999;35:125.