The Kiss of Death: Chagas' Disease in the Americas


Nocturnal Predators: Triatoma infestans and other Triatomine species

Triatoma infestans

triatomine infestans, or a vinchucaTriatoma infestans is a nocturnal predator that blood feeds on mammals while they are asleep. It is about one inch (2.5 cm) long, has two pairs of long, bent legs attached to an oval-shaped abdomen. A third pair of legs act like arms that are attached to the trapezoidal thorax near its protruding bulbous eyes. A proboscis (slender, needle-like projection) extends from the anterior head that is used to pierce skin and suck blood - a vampire-bug.

T. infestans is yellow-orange with black marking on top of its abdomen. top view of a vinchucaMales are larger than females. Their wings are thin, transparent, and cover the top of the abdomen. Only adults have wings, which are inefficient for flying but effective for gliding and mounting their mate during sex. Triatomines prefer nesting in roofs and ceilings, where they glide down upon sleeping humans. They are directed towards humans and other warm-blooded creatures by radar-like heat sensors in their antennas. Triatomines glide over 100 meters assisted by air currents. Gliding enables triatomines to travel throughout communities, colonizing house after house.

Blood suckers

diagram of the infection cycle through a vinchucaT. infestans is an instinctual blood sucker. It needs blood meals to pass through five instar stages to become an adult when it grows wings, copulates, and reproduces. Blood provides T. infestans with a protein- and lipid-rich diet. Heat sensors and pheromones (hormones deposited upon humans by previous predators) direct T. infestans to sleeping people. Detecting a food source, they probe the warm skin for underlying fluids with their proboscis and sense adenosine triphosphate, ATP, and other engorgement indicators. Coated with an anesthetic and anticoagulant, the proboscis pierces the skin and leisurely sucks up to 300 mg in sometimes 30 minutes. T. infestans is a glutton. After feeding, the abdomen of the engorged bug triggers peristalsis, and vinchucas defecate and deposit T. cruzi in the feces at the site of the wound. T. infestans exchange feces and parasites for blood. It ingests up to seven times its weight and has difficulty crawling away so slowly that awakened sleepers catch it - smashing them and leaving a brown splotch, a telltale sign to wary guests not to sleep there.

The development of T. infestans

Female triatomines develop into the adult stage before males do. After males emerge as adults, they inseminate females. Females are inseminated shortly after molting and can produce viable eggs for one year after copulation. In 10 to 20 days, females lay eggs. Females lay from 80 to 100 eggs, each ivory colored and half the size of a grain of rice. Adult T. infestans live an average of 8 to 16 months Their life span in Bolivia is 3 years and they lay an average of 240 eggs. Their eggs are valued by peasants who interpret them as signs of fertility. Girls put vinchuca eggs in tiny baskets and pretend that they are chicken eggs. Educational programs are changing peasants' perception of vinchucas eggs. Triatomines readily spread from the countryside to cities by transport of vinchuca eggs unknowingly carried in cargo.

Triatomines pass through 5 instar or growth stagethe instars of vinchucass, from birth and to adulthood. At all stages, triatomines are fast crawlers. Nymph stages take anywhere from 4 to 24 months, depending upon the availability of blood meals - needed to pass on to the next stage. During these stages they are able to feed up to 12 times their body weight. Fifth-stage instars are particularly dependent on blood meals to transform into adults, characterized by developing wings. Because flying takes a lot of energy, T. infestans is efficient, developing them only to reproduce and to colonize other areas. Triatomines usually take their blood meals after 7 days, but are able to live for months without feeding.

Vinchucas are not born with T. cruzi. As they feed throughout their early nymph stages, they become more susceptible to picking up T. cruzi, and incidents of infected bugs rise with age. Many become infected by the third instar stage. The infection rate of humans determines the infection rate of vinchucas. The higher the infection rate of a host population, such as in a house, the higher the infection rate is for T. infestans. Instars are small and superb crawlers. They hide in mattresses and bus seats where they can bite humans. They also crawl under mosquito netting and into sleeping bags, making it difficult to stop them.

Feeding at night

T. infestans are nocturnal and photosensitive. They hide during the day, coming out to feed and reproduce at night. Cracks of walls, mattresses, and clothing provides dark safety until nighttime, when they scurry about in search for meals.

Other infecting species

Triatoma infestans is the species most responsible for Chagas' disease in Bolivia, and accounts for 97% of the cases. The remaining 3% of Chagas' disease are caused by T. guasyana, T. melanocephala, T. oswaldoi, and T. venosa. This latter triatomines are primarily sylvatic and spread chagas among the wild animals it preys on. With the depletion of wild animals and their habitats in the Andes and Amazon, the threat of these triatomines spreading to urban areas becomes another threat.

In South America, Triatomine species responsible for Chagas' disease are, in order of importance, Triatoma infestans, Rhodnius prolixus, Panstrogylus megistus, Triatoma brasiliensis, Triatoma sordida, and Triatoma dimidiata. In Central America and Panama, the chief vector is Rhodnius pallescans. The primary reason for their abundance is that they have adopted domiciliary habits.

 

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