Chagas' Disease: Transmission

Transmission occurs chiefly via infected bugs. These large insects like to bite sleeping humans at night (a mosquito net gives protection). They have a sharp proboscis which at rest is folded below the head like a jack-knife. When biting they inject anticoagulants and an anaesthetic substance into the wound. Since this makes their bite quite painless (kissing bugs), people seldom wake up and several bites may take place unnoticed in the course of one night. The parasite is not inoculated directly by the bite, as Chagas initially thought. In 1913 Brumpt showed that the parasite is found in the faeces of the insect. While the animals suck blood, they defecate. By scratching, a bitten person can bring the faeces into the bite wound or rub them into the conjunctiva. The parasites multiply in humans and appear in the blood. The cycle is completed when a subsequent bug drinks infected blood. In the bug the parasite undergoes further changes and after 2 to 3 weeks is excreted with the faeces during a subsequent bite. It is estimated that the risk per bite by an infected Triatoma is one in a thousand. The existence of a totally different infection route was demonstrated in animals and is assumed in some human cases. Food or drink infected with the faeces of infected bugs or containing dead bugs may lead to infection in experimental animals. It is not known whether this also occurs in humans, and how common oral transmission then is. Congenital infection (1 to 2 % risk) and transmission via blood transfusion also occur (poor people often sell their blood). Transmission via transfusion is particularly important in urban zones. The risk of infection after an infected blood transfusion is estimated at one in five. There are sporadic cases of accidental contamination of laboratory staff (finger prick, aerosol) and after organ transplantation.

Category: Medicine Notes