POVERTY AND THE ERADICATION OF CHAGAS DISEASE

PARASITES

Chagas disease, or American trypanosomiasis, is a parasitic disease affecting much of Latin America. It is caused by the protozoan parasite Trypanosoma cruzi, which was discovered by Carlos Chagas in 1909, and is transmitted by Reduviid insects, the vector of the disease. An estimated 16 to 18 million people are infected with T.cruzi, and of those infected, approximately 50,000 will die each year [2]. In addition, it is the leading cause of heart disease in Latin America [9] and represents the third largest tropical disease burden after malaria and schistosomiasis [4].

http://www.uta.edu/chagas/html/histCarl.html

There are two phases of the disease, an acute stage and a chronic stage. The acute phase typically lasts 4-8 weeks, and only occurs in about 1-2% of people infected. Symptoms of the acute stage include: a swelling and reddening of the bite location, particularly if it is near the eye (Romaña’s sign), enlarged lymph nodes, fever, fatigue, rash and enlarged liver or spleen. In rare cases, the acute phase can also lead to death, especially in young children. There is often an asymptomatic latency period that can last from months to years. The chronic stage of the disease is characterized by cardiac and digestive problems. The cardiac symptoms include irregular or rapid heartbeats, heart failure, and cardiac arrest. Intestinal problems can result from enlarged esophagus and intestines that lead to swallowing difficulties and constipation. Some patients also suffer from damage to their nervous systems, resulting in sensory impairment and diminished tendon jerks.

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The life cycle of T. cruzi begins when the metacyclic form of the trypomastigote enters the bloodstream of the mammal host. The trypomastigote reproduces in the cells to form amastigotes, which are released into the bloodstream when the cell dies. Some of these amastigotes reinfect new cells and others transform into trypomastigotes and stay in the bloodstream. The next stage of the life cycle occurs when triatomines ingest the trypomastigotes by feeding on infected hosts. The trypomastigotes reproduce asexually in the digestive tracts of the vectors, and are transmitted through the feces of the triatomines.

Life cycle of Trypanosima cruzi. Source: CDC

The insect vectors of Chagas disease are from the Reduviidae family and Triatominae subfamily. The species of triatomine that is responsible for the majority of Chagas disease transmission is Triatoma infestans, although many other species act as vectors across Latin America, such as Triatoma dimidiate and Rhodnius prolixus s in Honduras. The most common mode of transmission is vectorial transmission, which occurs most often when vectors become domesticated to human dwellings. They infest houses by living in cracks and holes in the wall, roofing made of palms, or animals dwellings adjacent to the house. The nocturnal insects then feed on humans at night, infecting them with the parasite. The vectors can also infect numerous other animal reservoirs. These reservoirs include both sylvatic species such as opossums, armadillos, marsupials, rabbits, and rats and domestic animals such as dogs and cats. In addition to infection by vector bites, the two other major modes of transmission are transfusion of infected blood and congenital transmission.

Chagas Disease can be diagnosed through identification of the parasite from microscopic examination of a drop of fresh anticoagulated blood or from blood smears. Indirect methods that allow multiplication of the parasite in the insect vector (xenodiagnosis) or in culture medium (hemoculture) can also be used but are less sensitive. Other diagnostic techniques include serological tests for T .cruzi specific antibodies and molecular diagnosis with PCR. Treatment to eliminate the parasite includes administration of benznidazole and nifurtimox, although these drugs can have toxic side effects.

 


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