Last July, in EID Journal: Shelter Dogs as Sentinels for Trypanosoma cruzi – Texas, we looked at a unique seroprevalence study looking for the parasite that causes Chagas disease. Left untreated, this infection can progress to serious chronic conditions over years or decades, which can include cardiac and intestinal complications.
There are an estimated 300,000 individuals in the United States believed infected with Chagas. Many do not know they are infected, and nearly all are believed to have acquired the infection in Central or South America. Although primarily vectored by infected triatomine bugs, the infection can also be acquired through:
- congenital transmission (from a pregnant woman to her baby);
- blood transfusion;
- organ transplantation;
- consumption of uncooked food contaminated with feces from infected bugs; and
- accidental laboratory exposure.
The past couple of years has shown some evidence that autochthonous transmission in the United States may be more common than previously thought.
The CDC reports there are 11 species of triatomine bugs that have been found the southern United States. Up until recently, there was little concern over contracting Chagas disease from triatomine bugs in North America, as they were believed to rarely take blood meals from humans.
In 2012, in an EID Journal Dispatch, researchers found that 38% of (an admittedly small sample) of triatomine bugs tested in Arizona and California had fed on human blood.
Lori Stevens , Patricia L. Dorn, Julia Hobson, Nicholas M. de la Rua, David E. Lucero, John H. Klotz, Justin O. Schmidt, and Stephen A. Klotz
A high proportion of triatomine insects, vectors for Trypanosoma cruzi trypanosomes, collected in Arizona and California and examined using a novel assay had fed on humans. Other triatomine insects were positive for T. cruzi parasite infection, which indicates that the potential exists for vector transmission of Chagas disease in the United States.
And last year we saw evidence of a rare, locally acquired Chagas infection (see Autochthonous Transmission of Trypanosoma cruzi, Louisiana).
Which brings us to a new study, published yesterday in the EID Journal, that similarly finds a surprisingly high percentage of human blood meals among T. sanguisuga (aka `Eastern Bloodsucking Conenose’ ), sampled in Louisiana.
Volume 20, Number 12—December 2014
Etienne Waleckx1 , Julianne Suarez, Bethany Richards, and Patricia L. Dorn
To evaluate human risk for Chagas disease, we molecularly identified blood meal sources and prevalence of Trypanosoma cruzi infection among 49 Triatoma sanguisuga kissing bugs in Louisiana, USA. Humans accounted for the second most frequent blood source. Of the bugs that fed on humans, ≈40% were infected with T. cruzi, revealing transmission potential.
Chagas disease, caused by the parasite Trypanosoma cruzi, is mainly transmitted to humans and other mammals by blood-sucking insects called triatomines (also known as kissing bugs). In the United States, 24 species of wild mammals have been found to be naturally infected with T. cruzi, but only a few (<25) autochthonous cases of vectorial transmission to humans have been described (1,2). This number is probably an underestimate, and there is concern that vectorial transmission to humans in the United States may increase because of the following factors: 1) loss of sylvan blood sources because of habitat destruction, forcing the bugs to seek other (possibly human) blood sources; 2) climate change that could extend the range of the vectors northward; and 3) introduction of parasites by migrants from disease-endemic countries (3–5). Among the 11 triatomine species in the United States, the most widely distributed and the only 2 found in Louisiana are Triatoma lecticularia and T. sanguisuga (5). Bugs of the species T. sanguisuga are responsible for the first described autochthonous case of T. cruzi transmission in Louisiana (6), but little is known about their feeding habits in natural conditions. To evaluate the risk for Chagas disease (based on human/vector/parasite contact) and determine the feeding behavior of T. sanguisuga bugs, we molecularly identified the blood meal sources and T. cruzi infection in T. sanguisuga kissing bugs.
Our results indicate that T. sanguisuga kissing bugs pose an epidemiologic threat to humans and animals in Louisiana. Human/vector/T. cruzi contact is frequent; 55% of bugs were infected, of which nearly 40% had fed on humans.
For now, local acquisition of Chagas disease in the United States appears rare, although it is also likely an under-reported disease. With changes to our climate and increased incursion of humans into areas where wildlife (and triatomine bugs) may carry this parasite, the possibility exists that its incidence will increase with time.