Chagas Disease (CD) is a neglected tropical parasitic disease endemic to Latin American countries but is becoming a global health problem, affecting people in other parts of the world, including Canada and US due to migration. Approximately 15 million people are affected worldwide and over 100 million are at risk. People in endemic countries are infected primarily by vector borne transmission through the triatomine bug. Other modes of transmission include blood transfusion, organ transplantation and congenital transmission. Two of the seven reported cases of transfusion-transmitted CD in North America were reported in Canada in 1989 and 2000, raising concerns about the spread of CD in Canada. In 2010, Canada implemented donor blood screening for CD.
CD is a lifelong disease and is divided into acute, intermediate and chronic phases. The acute phase begins shortly after infection. Although largely asymptomatic, it is accompanied by massive parasite replication. In fact, parasites are visible in the blood 1-2 weeks post infection. Only 10-20% of infected individuals show specific symptoms such as muscle pain, splenomegaly and hepatosplenomegaly, making diagnosis of CD difficult. Some infected individuals recover from symptoms without treatment but can still progress into the intermediate phase, which lasts for years, characterized by an absence of evident tissue damage and organ dysfunction. If undetected in the acute phase, diagnosis becomes difficult with the currently available diagnostic methods, as parasites are no longer detectable in the blood. The chronic phase is triggered by the migration of parasites to the heart muscle tissues and digestive tract. About one third of infected individuals progress into the chronic phase and develop digestive and cardiac complications, resulting in chronic chagasic cardiomyopathy that leads to sudden death. Other complications in the chronic phase include mega syndromes in the colon and esophagus.
CD is caused by the obligate intracellular protozoan parasite trypanosoma cruzi (T. cruzi). In endemic regions of the world, T. cruzi is most commonly transmitted to the host by the triatomine bug when the bug, containing circulating infective forms of the parasite, takes a blood meal off the human host and defecates infective parasites at the bite site, which can also enter the host through the mucosal membrane and are able to invade all nucleated cells in the host.
The current control measures and diagnosis methods for CD are limited and include improved housing and spraying insecticides, aimed at lowering death rate before T. cruzi develops resistance to the insecticides. Although these have shown some effectiveness in controlling CD, given the large pool of primary hosts for CD, it is difficult to maintain a T. cruzi-free environment and therefore, complete control is not possible. The current treatment for CD is based on two drugs, benznidazole (BZL) and nifurtimox (NF), that interfere with cellular processes of T. cruzi. However, they are toxic both to T. cruzi and to cells in the human body, causing severe discomfort to the host, such as anorexia and digestive manifestations. Both drugs have been used sparingly because of their limited success in treatment; in fact, T. cruzi infection is not eliminated in 83.5% of acute cases after treatment and does not prevent the onset of severe heart lesions. The treatment outcome differs depending on disease phase, treatment duration, and dose of drug, age and geographic location of infected individuals. The diagnostic methods currently being used include serology, PCR and blood smear, but neither is reliable to accurately inform or monitor clinical status and provide information about treatment efficacy. Progress is still ongoing in this field.
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