Chagas disease in Texas: new surveillance data

NEW ORLEANS – Researchers have reported high rates of Trypanosoma cruzi, the parasite responsible for Chagas disease, in two studies conducted in Texas on wild dogs and in refuge, suggesting that the pathogen is more widespread in the local environment than is commonly thought.

However, another study presented here was good news for Texan hunters: the survey data indicated frequent potential exposure to the transmitting insect. T. cruzino more than 1,000 hunters tested had been infected.

The results of the three studies were reported during a poster session at the annual meeting of the American Society of Tropical Medicine and Hygiene.

Dogs and T. cruzi

Chagas disease affects about 8 million people worldwide, including about 300,000 in the United States. Yet, it tends to go unnoticed in this country, perhaps because it is still generally considered a tropical disease.

Similarly, although T. cruzi is known to infect dogs and cause serious diseases, it is not one of the parasitic organisms that US veterinarians regularly screen.

To better understand infection rates in dogs, researchers at Texas A & M University in College Station, led by Sarah Hamer, DMV, Ph.D., conducted two studies: one on shelter dogs in seven places in the state and another on pet dogs from poor countries. semi-rural communities called "colonias" in the lower Rio Grande Valley.

In the shelter dog study presented by Carolyn Hodo, DMV, Ph.D., researchers tested 608 dogs T. cruzi and four other vector-borne pathogens (including Dilofilaria immitis heartworm). Rates of T. cruzi ranged from 5.5% in Fort Worth to 29.5% in San Antonio; the overall average was 18.1%.

Hodo and colleagues noted that these percentages were comparable to those observed for D. immitis, which is systematically examined in the United States, which suggests that it would make sense to do the same thing for T. cruzi. In addition, while the dog heartworm is not a human health problem, Chagas disease certainly is. Hodo said dogs are "useful as sentinels for vector-borne diseases".

In this case, she said MedPage today, this certainly applies, since the vector of T. cruzi – what's called huggers – requires many blood meals and is just as likely to feed on humans as dogs. A large number of infected dogs is a sign that T. cruzi is also widespread in the environment.

The colonia study, presented by Italo Zecca, MPH, showed even higher prevalences in which 231 dogs from seven communities were tested. Seroprevalence for T. cruzi 20.0% to 55.9%, with an overall average of 35.5%. While many shelter dogs in Hodo's study came from homes where they would have been mostly kept indoors, most of the colonies' dogs live on the outside.

However, the researchers noted that the gross numbers of both studies should be interpreted with caution. In the colonia study, molecular PCR tests were only positive in 3.9% of dogs. Zecca and colleagues have indicated that positive PCR results "may signal an acute infection or that dogs are more likely to be infectious to the vectors". But specificity for T. cruzi serological tests are known to be well below 100%.

Risk for hunters

This issue was also addressed in the hunter study, reported by Sarah Gunter, PhD, of Baylor College of Medicine in Houston. Serologic testing of 1,093 people identified as hunters yielded positive results in 23 cases – but none was confirmed by the CDC's "baseline" test for Chagas, Gunter said.

This was "good news," she said, as the 1,093 survey participants said they were frequently exposed to situations and environments that were prone to infection. Most respondents knew nothing about Chagas disease and few took steps to reduce their risk.

Participants were asked a number of questions about possible contact with bedbugs or the blood of potentially infected animals.

• Majorities reported the following:
• Spend the night in the open air or in tents or cabins
• See kissing insects during the hunt
• Never / rarely using an insect repellent
• Never / rarely wear gloves to dress animals

More than 90% reported having been in contact with deer and 72% with wild pigs, two known reservoirs of T. cruzi. Only 40% said they heard about Chagas disease.

Gunter said MedPage today that public health be taught primarily to hunters about Chagas disease and what they can do to minimize risks. She noted that the state's Department of Parks and Wildlife (which facilitated this study) is organizing training programs in which such education could easily be included. This training is mandatory for all hunters born after September 2, 1971.

2018-10-31T18: 00: 00-0400