Abstract
Chagas disease (CD), also known as American trypanosomiasis, is a vector-borne protozoal zoonotic disease that is endemic to much of Latin America and parts of the southern United States.1,2 The etiologic agent is Trypanosoma cruzi and its vector is a triatomine reduviid bug, also known as a kissing bug.1 In 2013, CD was designated a reportable disease in Texas.3,4 Although research indicates the wood rat (Neotoma micropus) is the most common host animal for T. cruzi in Texas, infections have also been documented in dogs, coyotes, opossums, armadillos, cattle, horses, and sheep.5 Dogs are the predominant domestic reservoir for CD in many endemic areas. In Texas, 537 cases of canine CD were confirmed between 1993 and 2007.6 The triatomine vector releases infective metacyclic trypomastigotes onto the skin of a mammalian host. These then enter the host through rubbing or scratching of the bite wound or through permissive mucosal or conjunctival surfaces.1 Infection can also occur from ingestion of infected bugs. Clinical signs vary in the acute, latent, and chronic phases.4 Clinical signs in dogs in the acute phase include lethargy, lymphadenopathy, pale mucous membranes and hepatosplenomegaly. The latent phase can be prolonged with clinical signs appearing to regress. Chronic phase signs include right-sided cardiac dysfunction, arrhythmias, ascites, pleural effusion, and hepatomegaly, although sudden death was the most common presentation at any phase in one Texan study.7,8
Trypanosomes were seen on a blood smear during a physical examination of a two-year-old intact male Pacific walrus (Odobenus rosmarus divergens) currently at SeaWorld San Antonio and on temporary loan from the Wildlife Conservation Society's New York Aquarium. Acute and convalescent serum was submitted for indirect fluorescent antibody (IFA) testing (using canine Ig) at the Texas A&M Veterinary Medical Diagnostic Laboratory. Results were 1:80 and 1:320. Other samples for PCR testing were submitted to the Texas A&M Department of Veterinary Integrative Biosciences and another offsite laboratory for PCR and lytic antibody testing. Results were positive for infection.
There is no preventative vaccine available or approved antitrypanosomal treatment in the United States. The two commonly used drugs outside of the US are benznidazole and nifurtimox. These drugs are available in the US in some circumstances, exclusively for human use, through investigational protocols with the CDC. Current treatment focuses on the chronic phase clinical signs of heart failure and arrhythmias. Vector control is the most effective method of prevention in Latin America.9
Acknowledgements
The authors wish to thank LTC (Dr.) Douglas Owens of the US Army Institute of Surgical Research, Lisa Auckland of Texas A&M University, and all of the SeaWorld San Antonio team members for their support, especially the Laboratory, Animal Care, and Training staff.
* Presenting author
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