Incubation period days

Period of communicability Bugs become infected after 8-10 days and remain so for life, which lasts about 2 years. Infected persons have circulating trypanosomes in the acute and early chronic stages of the disease,

Short stumpy form

Trypomastigote

Fig. 15.18. Different forms of the trypanosomidae.

and this may persist in small numbers for the life of the individual.

Occurrence and distribution Chagas' disease is found throughout Central America and in most countries of South America. Considerable progress has been made in controlling the disease, Uruguay being declared free of infection in 1997, Chile in 1999 and Brazil in 2000. Argentina and Venezuela will probably be declared free very soon.

Control and prevention The methods of control are to reduce the number of bugs that can come into close proximity with humans and the reservoirs of disease. These requirements are both satisfied by improvements to housing. Unfortunately, trypanosomiasis is a disease of poverty, and building new and better houses is rather impractical in this segment of the population. If assistance can be given, then proper foundations and cement walls will not only deny a place for

the bugs to live, but also prevent rats and armadillos from making their burrows underneath them. Even with existing houses, much can be done by applying a layer of mud plaster to walls and erecting a simple ceiling. Where cost prohibits any of these methods, residual insecticides can be sprayed on the walls and ceilings. This can effectively be carried out as a control programme using a similar methodology to malaria.

First a pyrethrum spray is administered, which draws the bugs out of their hiding places and marks the infected houses. In the attack phase, a residual insecticide is sprayed on all houses in an infected locality (not just to infested houses). A second spraying is made 90 days after the first, to houses where bugs have been found either in the preliminary or attack phase. Spraying continues at this time interval until the number of infested houses falls below 5%. Maintenance is achieved by regular house searches, instituting focal spraying when re-infestation is discovered.

The use of pyrethroid fumigant cans which release insecticide when lit, and insecticidal paints are simpler methods than residual spraying.

An alternative is to protect the individual from being bitten by the use of ITMN (see further under malaria discussed previously).

The dog is probably the most important domestic reservoir and householders should question the value of maintaining such animals if they are proving a threat to the health of the family. Good hygiene, trapping and poison will keep down rats. Control of the wild reservoir is unlikely to be successful.

In areas of high endemicity, screening of blood donors is required and gentian violet can be added to the blood.

Treatment Nifurtimox and benznidazole are effective in the acute and early chronic phase of the disease.

Surveillance Regular monitoring of houses for signs of infestation or re-infestation should be maintained (see above).

Semi-domestic cycle

Domestic cycle

Fig. 15.20. Transmission cycles of American trypanosomiasis.

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