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Chagas Disease (Trypanosomiasis) |
Etiologic agent = Trypanosoma cruzi
American trypanosomiasis is caused by infection with Trypanosoma
cruzi. This uniflagellate protozoan is primarily transmitted
by reduviid or so-called "kissing" bugs (e.g., Triatoma
spp. and Rhodnius spp.).
- Chagas disease is distinct from the more renowned "African
trypanosomiasis" or "sleeping sickness." African
trypanosomiasis is caused by infection with T. brucei gambiense
or T. brucei rhodesiense and is transmitted by the infamous
"tse-tse fly" (Glossina).
Transmission:
Reduviid
bugs live in the burrows or nests of wild animals, and in
dark, sheltered areas of human homes. They particularly like to
inhabit mud/adobe houses in Latin America.
- Like the sandfly vectors of leishmaniasis, reduviid bugs
are also most active at night.
- Transmission of T. cruzi occurs by a unique mechanism
in which the reduviid bugs are attracted to CO2
in exhaled breath, and then after finding their host this way,
they create a wound while feeding and then defecate into the
wound. However, dogs can also be infected by vector contamination
of existing wounds, by ingestion of the tissues of wild animal
hosts, by ingestion of the reduviid bugs themselves and transplacentally
or through the milk.
- Twelve species of Triatoma occur in the U.S. However,
these strains are not as effective as the Latin American reduviids
in causing infection by fecal contamination of bite wounds (due
to delayed defection relative to feeding activity). However,
it is possible that any reduviid bug can serve as a source of
infection for dogs when they eat the bugs.
- Congenital transmission and transmission via organ transplantation
and blood transfusion have also been reported in humans, with
at least 9 such cases in the U.S. Hence, therre are plans to
develop a blood donor screening program to begin as early as
2004.
Epidemiology:
Chagas disease is quite rare in both dogs and people in the
U.S., but is of increasing concern because of emigration to the
U.S. from endemic areas of Central and South America. In Latin
America, as with Leishmania, DOGS ARE AN IMPORTANT
RESERVOIR HOST FOR TRYPANOSOMA CHAGASI.
- A recent study that modeled Chagas disease in Argentina (Cohen
and Gurtler, 2001) found that people could "greatly reduce
the risk of human infection by excluding domestic animals, especially
infected dogs, from bedrooms."
- Sixteen to eighteen million people are estimated to be infected
in Central and South America, with 50,000 people estimated to
die from Chagas disease each year.
- It is also estimated that 25,000-100,000 Latin American immigrants
in the U.S. are infected.
- In the U.S., Chagas disease has been documented in dogs in
Louisiana, Texas, Oklahoma, South Carolina andVirginia, where
a bitch and 8 out of 9 of her puppies were infected.
- Focal areas in the U.S. may have seropositivity rates in
dogs up to 86%.
- This hemoflagellate can also be found in various wild animal
species in the U.S., including raccoons, armadillos and opossums.
There is currently no vaccine available against Chagas disease,
although a DNA-based vaccine has shown promise in a mouse-model
system.
One very unique new approach to control of American trypanosomiasis
is to release reduviid bugs that harbor a transformed bacteria.
This is a species of bacteria that is normally an essential symbiont
and nutritionally required by the reduviid bug. But in this case,
the bacteria also expresses an enzyme that kills the trypanosomes
within the reduviid bug's gut. It does not, however, harm the
reduviid bug itself. (See Conte, J.E., Jr., 1997 and Beard et
al., 1998)
For trivia buffs- which
famous evolutionary biologist is purported to have died of Chagas
disease?
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