Patricia L. Dorn
Associate Professor & Dean's Distinguished Teaching Professor
A
Brief
Summary
of Chagas
Disease
and its
Natural
Transmission
in the
U.S.
First human case of insect-transmitted Chagas parasite found in Louisiana
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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 only 20-30% of infected people will eventually develop the disease.
Seventeen 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 , and Triatoma 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 possums, armadillos, wood rats and squirrels. Animals usually acquire the parasite by eating the bugs.
In the summer of 2006, we discovered the first ever human case of insect-transmitted Chagas parasite in Louisiana and the sixth ever in the U.S. Previously there had only been five reported cases of insect transmission of the Chagas parasite to humans in the United States . Three of these cases occurred in Texas 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.
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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. 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 elsewhere about 30 min. later.
A blood screening test was just approved by the FDA. In December of 2006 widespread screening of blood donations for the Chagas parasite has revealed levels much higher than was previously appreciated (1/4,655 positive blood units), especially in areas with large Hispanic populations.
For additional information:
First
human
case of
insect
transmission
of Chagas
parasite
identified
in Louisiana
Patricia
Dorn,
Ph.D.
Loyola
University
New Orleans
dorn@loyno.edu
(504)
865-3672
Dawn
Wesson,
Ph.D.
Tulane University
Health Sciences
Center
Wesson@tulane.edu
15 November 2006
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Did you know that Chagas disease is a leading cause of heart disease in Latin America? Chagas disease is endemic to parts of Mexico and Central and South America where 11-13 million people are infected with the parasite. So far, only five cases of insect transmission of the parasite that causes the disease have been reported in the U.S. We have recently discovered the first reported human case of insect transmission of the Chagas parasite in Louisiana.
The Chagas parasite is carried by insects commonly called kissing bugs because they feed at night and tend to feed on the face, usually uncovered at night. In addition to heart disease, the Chagas parasite causes megasyndrome (enlargement of intestines and esophagus) in South America.
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Chagas disease began as a zoonosis, that is, it is found in many forest animals and is maintained in a forest cycle moving between the wild mammals and insects in many areas of the Americas, including the United States. The parasite is found in the feces of the kissing bug and a person may become infected if he or she is contaminated by the parasite-containing feces. This usually happens while the kissing bug takes a blood meal. The kissing bug defecates during the blood meal and leaves a drop of parasite-contaminated feces on the person’s skin. The person unknowingly scratches the bite, introducing the parasite into the bite wound or into mucous membranes such as the eyes, nose or mouth. One can also become infected if one receives a blood transfusion or organ transplant from an infected person or congenitally (from mother to child during pregnancy or birth). Some people have been infected from food or drink contaminated with parasite feces, usually when the bugs were accidentally crushed in the ingested product.
Called the silent killer, Chagas rarely shows symptoms following infection and in fact, symptoms usually take 10-20 years to develop during which time the person is unaware he/she is infected. Even for people who harbor the parasite only 20-30% will actually develop Chagas disease. However, if they do develop Chagas disease, it is quite serious and usually fatal. Treatment is only usually effective within the first couple of months following infection when most people don’t know they are infected. In the U.S. the only obtainable medication has troubling side effects and is only available under an investigational drug protocol through the Centers for Disease Control and Prevention (CDC). There is currently no vaccine available against this disease.
An active zoonotic cycle has likely been present in the U.S. for thousands of years. We have several species of kissing bugs and many carry the Chagas parasite. Studies done in the late 1980s and early 1990s showed that ~40% of the opossums and armadillos and ~2-5% of dogs in Louisiana have the Chagas parasite. Ongoing studies in collaboration with Dr. Malone and colleagues at the LSU School of Veterinary Medicine show higher rates in dogs (up to 30%) in some foci in LA. Animals usually acquire the parasite by eating the kissing bugs.
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People in the U.S. rarely contract the Chagas parasite from the kissing bugs. Four cases have occurred in infants, three in Texas and one in Tennessee. The fifth case occurred in a 56-year-old woman in California. Why so few people become infected in the U.S. is not entirely clear. However, the most important reason is likely that we don’t tend to live in houses that provide good habitat for the kissing bugs and that the kissing bugs can get into at night (when they feed). The other is that apparently the behavior of the bugs found in the U.S. means that they transmit the parasite only poorly. 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 the parasite-laden feces elsewhere about 30 min. later. So, most people living in the U.S. are not at risk for contracting the disease from insects.
However, there is growing concern about an increasing risk for transmission of the parasite through blood transfusions or organ transplants. The Blood Products Advisory Committee of the US Department of Health and Human Services has recommended universal screening of all donors for the Chagas parasite since at least 1989, while blood screening for Chagas is mandatory in nearly all Latin American countries. So far the numbers in the U.S. remain small: 10 total cases, 5 each for transfusion and solid organ transplant transmission although it is clear that we are only seeing the tip of the iceberg. Two cases of transmission by organ donation were reported just this year in Los Angeles. Hundreds of thousands of people have immigrated into the U.S. from highly endemic areas in Latin America and it was estimated in 2002 that more than 100,000 immigrants to the U.S. have the parasite and don’t know it. Finally, once the appropriate agencies have worked out how to manage the potentially thousands infected that may be uncovered by screening, it now appears that the FDA is on the verge of approving and implementing a screening test. So although the risk of contracting Chagas from insects is low in the U.S., the risk of contracting Chagas by blood transfusion or organ transplant remains unknown but is likely increasing due to changing donor demographics. The launching of mandatory, universal blood and organ screening for the Chagas parasite in the U.S. is welcome news indeed.