Patricia Dorn, Ph.D.
A Brief Summary of Chagas Disease and its Natural Transmission
in the United States
First human case of insect-transmitted Chagas parasite found in Louisiana
Chagas disease is caused by a parasite called Trypanosoma cruzi. The parasite is carried by Reduviid bugs commonly called cone-nosed bugs or kissing bugs because they feed at night so tend to feed on the face, usually uncovered at night.
The parasite is found in the feces of the bug and the person may become infected if he or she is contaminated by the parasite-containing feces. One can also become infected by blood transfusion, organ transplant or congenitally (from mother to child during pregnancy or birth) or by food or water contaminated with bug feces. Rarely, and usually in children, there may be symptoms shortly following infection (called the acute phase). Usually symptoms (heart disease in the U.S., Mexico and Central America ) take 10-40 years to develop (during the chronic phase) and 20-40% of infected people will eventually develop the disease, and most will die of congestive heart failure.
Ten species of kissing bugs are known to occur in the United States, the most significant of which are Triatoma gerstaeckeri in Texas and New Mexico, T. rubida and T. protracta in Arizona and California, and T. sanguisuga, which is more widely distributed across the southeastern United States. The distribution of the parasite encompasses the southern states from California to Florida and in the East northward to Maryland. Significant numbers of wild animals are infected including opossums, armadillos, wood rats and squirrels. Animals usually acquire the parasite by eating the bugs.
In the summer of 2006, we discovered the first human case of insect-transmitted Chagas parasite in Louisiana and the sixth ever in the United States. Of the previous five cases, three occurred in Texas in infants, two in 1955 and the other in 1983. The fourth case occurred in a 56-year-old California woman in 1982. The fifth case occurred in rural Tennessee in 1998 in an 18-month-old child. The bug was found in the child's crib, and the infection was detected by PCR and treated during the acute stage. Another case of an infant in Texas is currently under investigation.
There are several reasons that likely explain why so few people become infected in the U.S. The most important is that we don't tend to live in houses that provide good habitat for the bugs and that the bugs can get into at night. The other is that apparently the behavior of the bugs found in the U.S. means that they transmit the parasite only poorly. Kissing bugs in the U.S. prefer to stay in the wild areas and only move into houses in the summer months, attracted by light. And rather than defecating and depositing the parasite on the skin during the blood meal (as happens in Mexico and Central and S. America), the bugs here take the blood meal, leave the host and defecate later, away from the host. See our recent article on the behavior and infection rates in SW bugs (SA Klotz et al. 2009 Acta Tropica 111:114-118).
The U.S. blood supply began to be screened for the Chagas parasite in 2007. Already there are significant numbers of infected blood units identified. See the AABB web site for this information.
For additional information:
Click here for The Centers for Disease Control and Prevention's web site with detailed information about Chagas disease, its transmission and treatment.
AABB Biovigilance Web site - blood screening results in the U.S.
Evaluation and treatment recommendations for the U.S., see: C. Bern, et al. (2007) "Evaluation and Treatment of Chagas Disease in the United States: A Systematic Review" JAMA 298 (18) 2171-2181.
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The contents of this communication are the sole responsibility of Patricia Dorn and do not necessarily represent the opinions or policies of Loyola University New Orleans.