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Canine Chagas' disease: update (Proceedings)

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Nov 01, 2010

OVERVIEW
     • Caused by the zoonotic hemoflagellate protozoan parasite Trypanosoma cruzi.
     • Infection occurs when infected feces of a vector (Triatominae, commonly called kissing or assassin bugs) are deposited in a wound (bite site of vector) or mucous membrane, or when a dog eats an infected vector (shown to occur in opossums and raccoons). Raccoons fed infected meat do not get infected so dogs probably not infected by eating meat from intermediate hosts in which the organism is sequestered in muscle. Transmission by contaminated blood transfusion also occurs.
     • Endemic (in both humans and pets) in South and Central America.
     • Most cases in dogs in the USA seenTexas, but also Louisiana, Oklahoma, South Carolina, and as far north as Virginia. Infected vectors and reservoir hosts also reported in the western (California, New Mexico), southern (Florida, Georgia) and southeastern (North Carolina, Maryland) states.
     • Six endemic human cases reported in the USA, the last in a Louisiana woman after Hurricane Katrina.
     • After local multiplication at site of entry (5 days post-infection - DPI), hematogenous spread occurs to most organs but mainly the heart (and much less extent, brain). Organisms become intracellular, multiply, then rupture out into the circulation to produce maximal parasitemias (14 DPI) associated particularly with acute myocarditis and, less commonly, diffuse encephalitis.
     • Parasitemias wane (sub-patent by 30 DPI), antibody titers rise (detectable by 26 DPI), and the dog enters a protracted asymptomatic period (can last for months to years) if he survives the acute myocarditis. During this time, there is progressive and insidious development of myocardial degeneration and eventual dilative cardiomyopathy of unknown pathogenesis.
     • Some isolates from dogs in the USA don't seem very pathogenic and just lead to very high antibody titers without disease.

SIGNALMENT
     • Commonly seen in young (acute form - usually under 2 years) but reported in old dogs (chronic form), hunting breeds, more often in males (dogs likely to contact vectors or reservoir hosts)
     • Cats can become infected, but no case has been reported in North America.

CLINICAL SIGNS
Two syndromes - acute (myocarditis or encephalitis in young dogs) or chronic (dilative cardiomyopathy in older dogs)

Historical Findings
Acute
     • Sudden death
     • Lethargy, depression, anorexia
     • Diarrhea
     • Weakness
     • Exercise intolerance
     • Mild to severe CNS dysfunction (like distemper)
     • Ataxia, seizures

Chronic
     • Weakness
     • Exercise intolerance
     • Syncope
     • Sudden death

Physical Examination Findings
Acute
     • Generalized lymphadenopathy
     • Signs of both left and right heart failure
     • Tachycardia with or without arrhythmias
     • Neurologic signs, weakness, ataxia, chorea, seizures (indistinguishable from distemper)

Chronic
Sustained or paroxysmal tachycardia

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS
     • Cardiomyopathy
     • Congenital cardiac defects
     • Traumatic myocarditis
     • Distemper
     • Toxoplasmosis
     • Neosporosis