Tuesday, August 21, 2012
Insect-Borne Infections in South America: Chagas Disease
María Inés Guaia, Argentina
Chagas disease is the most important parasitic disease in Latin America, and the third most important infectious disease in the region, only after AIDS and tubeculosis. According to WHO figures, an estimated 10 million people are infected worldwide, and more than 25 million are at risk, most of them in Latin America.
This disease is caused by the parasite Trypanosoma cruzi, a flagellate protozoan, which is most often transmitted to men and other animals by an insect vector commonly named ‘vinchuca’. Vinchuchas are blood-sucking insects of the family Reduviidae, subfamily Triatominae.
The transmission generally happens at night, when the bugs emerge to feed. Unfortunately, vinchucha often take to dining on human blood. They bite humans, ingest their blood and immediately defecate liquid feces on the wound. The infection occurs if the Tripanosoma cruzi parasites in the insect feces enter the organism through mucous membranes or breaks in the skin. This is more likely to happen if the bitten person, likely asleep and unaware, scratches or rubs the feces into the bite wound.
Blood transfussions, infected organ transplants and mother-to-child exchanges during pregnancy are other, less common, avenues for transmission. In rare cases, Chagas has been transmitted through consumption of uncooked food contaminated with feces from infected bugs, or even accidental laboratory exposure.
The incubation phase of the disease lasts about a week. Following it, the disease evolves in three stages:
Acute phase: During the first 20 to 30 days, there may be inflammation in the place of bite, with local redness and temperature. Trypanosomas can be seen moving just by examining a drop of infected blood with the microscope.
Intermediate or latent phase: This is a variable period during which symptoms are absent. It can last for many years; generally, for the rest of an infected person’s life. The existence of parasites can be confrimed by observing antibodies in a blood test.
Cronic phase: The last phase depends on the severity of the case. This phase ussually starts 10 to 20 years after the infection. In many cases, patients realise they have the disease in this stage. Symptomes related to the affected organ/s (most commonly heart, colon or esophagus) arise. The most common alteration is the dilation of the organ/s involved. Chagasig cardiopathy is the most common cause of cardiac impairment and sudden death in the endemic zones of South America. It develops as right cardiac impairment and conduction dysfunctions.
Chagas is mainly a disease of the poor. The substandard housing conditions in which millions of people in LatinAmerica live provide plenty of cracks and holes in which the vinchuca can nest and develop confortably. Crowding and poor hygienic conditions also facilitate the proliferation of the bug.
The Chagas disease problem should not only be addressed from a medical and sanitary point of view, but also as a socioeconomic and infrastructural issue.