Chagas disease is a vector-borne protozoan illness endemic to most Latin American countries.  Risk is greatest in those with long-term domestic exposure to the Triatomine bug, which nests in thatched roofing and the cracks of adobe or unfinished brick.  Transmission occurs when the bug feeds on human blood during the night and defecates the underlying pathogen, Trypanosoma cruzi, into the bite wound.

Chagas disease is divided into 2 phases:

• The acute phase (8-12 weeks after transmission) is characterized by circulating trypomastigotes that are detectable on blood microscopy.  Most patients are asymptomatic, but a minority develop nonspecific symptoms (eg, fever, malaise, anorexia) and inflammation/swelling at the site of inoculation (eg, eye swelling following conjunctival inoculation).

• The chronic phase begins when the immune system eliminates circulating parasitemia, leading to resolution of acute symptoms.  Patients subsequently develop a prolonged asymptomatic phase ("indeterminate form"), whereby serology is positive for T cruzi, but there are no symptoms, signs, detectable parasitemia, or indications of end-organ damage.  After 1-3 decades, a minority of those with asymptomatic chronic infection develop end-organ disease of the heart or gastrointestinal system.

Chronic Chagas cardiomyopathy is the most common complication of Chagas disease.  It is thought to be caused by chronic, low-grade, parasite-mediated myocarditis, which leads to the progressive destruction of cardiac fibers and subsequent cardiac fibrosis.  Common complications include biventricular heart failure, cardiac arrhythmias (particularly ventricular arrhythmias), and ventricular aneurysm with intracardiac thrombus (leads to thromboembolic disease/stroke).

(Choice A)  Treponema pallidum has an affinity for the aortic wall and can cause ascending aortic aneurysms (syphilitic aortitis) in patients with tertiary syphilis.  Diagnosis is made with serology; treponemes are not visible on standard microscopy.

(Choice B)  Neurocysticercosis, which is caused by the larval stage of the pork tapeworm Taneia solium, is characterized by the formation of multiple calcified brain lesions that may result in seizures and/or focal neurologic signs several years after transmission.  Diagnosis is made with imaging and serology, not blood microscopy.

(Choice D)  Lyme disease is a tick-borne illness caused by Borrelia burgdorferi.  Early localized disease is characterized by a migrating erythematous, bull's-eye rash (erythema migrans) and nonspecific symptoms.  Months or years later, patients can develop late manifestations, such as large joint arthritis or Lyme encephalopathy.  B burgdorferi is a spirochete and cannot be seen on standard blood microscopy.

(Choice E)  Schistosomiasis is transmitted to humans who swim or bathe in fresh water contaminated with cercariae from infected snails.  The fluke matures in the liver and spreads to the mesenteric vessels, where it releases eggs that can cause end-organ inflammation and fibrosis (eg, periportal liver fibrosis).  Diagnosis is made by identifying eggs in urine or stool, not on blood microscopy.

Educational objective:
Chagas disease is a protozoal illness that is endemic to Latin America.  Patients in rural areas are at greatest risk when their houses harbor the vector (Triatome bug) in adobe walls or thatched roofs.  Acute infections are often asymptomatic, but patients can develop Chagas cardiomyopathy (eg, heart failure, ventricular arrhythmias, ventricular aneurysms) several decades later.