Health Editor’s Note: The tropical disease, Chagas, is caused by a parasite which is passed from animals to humans with an insect as the intermediary. Currently Chagas is only found in the Americas and has an acute and chronic phase which if left untreated will give a lifelong infection. During the acute phase parasites will be found in the blood. Symptoms are fever and swelling around the site where the parasite entered through mucous membrane and/or the skin.
The Trypanosoma cruzi parasite is responsible for this disease with infection mostly occurring through contact with the feces of an infected “kissing bug”, triatomine bug, which is a blood sucker that feeds on animals and humans. After someone has the disease it can be spread from mother to unborn baby, blood transfusions, organ transplantation of an infected organ, contaminated food or drink, or during a laboratory accident.
During the day the tratomine bug hides in crevices of roofs and walls comes out at night and feeds on blood. While a person is sleeping, it tends to feed on the face, hence the term “kissing bugs.” After they ingest blood they will defecate on the person. The T. cruzi parasites are found in the feces that are left at the bite site. These bites usually itch and are scratched and the parasites are able to enter the host through the wound or through contact with mucous membranes, especially the conjunctiva of the eye. Once inside the parasite invades cells where they multiply and are released into the blood stream.
Chagas disease is mostly found in Mexico, Central American, and South America and thrives where homes are made out of thatched roofs and mud walls. Most Americans who have this disease has gotten it from outside the U.S.
Acute infections can cause severe inflammation of the heart muscle or the lining of the brain and/or brain. After the initial acute phase, many people will experience a time when they have no symptoms, but still have parasites in the blood. Twenty to 30% of those infected will develop life-threatening issues during their lifetime. Others will remain without symptoms and not develop symptoms of the disease.
The chronic form of the disease will include a dilated heart that cannot pump well, abnormalities of the heart rhythm that can lead to sudden death, or a dilated colon or esophagus that will cause problems with passing stool or eating…..Carol
Chagas Disease in Texas: New Surveillance Data
High Rates in Dogs Point to Environmental Presence
Written by John Gever Managing Editor,MedPage Today
This article is a collaboration between MedPage Today® and: Infections Diseases Society of America
NEW ORLEANS — Researchers reported high rates of Trypanosoma cruzi, the parasite responsible for Chagas disease, in a pair of studies on free-running and shelter dogs in Texas, suggesting that the pathogen is more prevalent in the local environment than commonly thought.
But there was good news for Texas hunters in another study presented here: although survey data indicated frequent potential exposure to the insect that transmits T. cruzi, not one of more than 1,000 hunters tested had been infected.
Results of the three studies were reported during a poster session at the American Society of Tropical Medicine and Hygiene annual meeting.
Dogs and T. cruzi
Chagas disease affects some 8 million people worldwide, including about 300,000 in the U.S. Yet it tends to fly under the radar 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 illness, it is not among the parasitic organisms that U.S. veterinarians routinely screen for.
To get a better handle on rates of infection in dogs, researchers at Texas A&M University in College Station under Sarah Hamer, DVM, PhD, conducted two studies: one in shelter dogs at seven locations across the state, and another in pet dogs from poor semi-rural communities called “colonias” in the lower Rio Grande valley.
In the shelter dog study, presented by Carolyn Hodo, DVM, PhD, the researchers tested 608 dogs for T. cruzi and four other vector-borne pathogens (including the Dilofilaria immitis heartworm). Rates of T. cruzi ranged from 5.5% in Fort Worth to 29.5% in San Antonio; the overall mean was 18.1%.
Hodo and colleagues noted that these percentages were comparable to those seen for D. immitis, which is routinely screened in the U.S., suggesting that it would make sense to do the same for T. cruzi. Moreover, whereas dog heartworm is not a human health concern, Chagas disease certainly is. Hodo said dogs are “useful as sentinels for vector-borne disease.”
In this case, she told MedPage Today, it certainly applies, since the vector for T. cruzi — so-called kissing bugs — requires many blood meals and are just as likely to feed on humans as on dogs. Large numbers of infected dogs are a signal that T. cruzi is also highly prevalent in the environment.
Even higher prevalences were seen in the colonia study, presented by Italo Zecca, MPH, in which 231 dogs from seven communities were tested. Seroprevalence for T. cruzi ranged from 20.0% to 55.9%, with an overall average of 35.5%. Whereas many of the shelter dogs in Hodo’s study came from people’s homes where they would have been primarily kept indoors, most dogs in colonias live outdoors.
However, the raw numbers in both studies should be interpreted cautiously, the researchers noted. In the colonia study, PCR molecular tests were positive in only 3.9% of the dogs. Zecca and colleagues indicated that positive PCR results “may signal acute infection or dogs that are more likely to be infectious to vectors.” But specificity for T. cruzi serological tests is known to fall well short of 100%.
Risk to Hunters
That issue also cropped up in the study of hunters, reported by Sarah Gunter, PhD, of Baylor College of Medicine in Houston. Serological testing of 1,093 individuals identifying themselves as hunters yielded positive results in 23 — but none were confirmed with the CDC’s “gold standard” testing for Chagas, Gunter said.
That was “good news,” she said, given that survey responses from the 1,093 participants indicated frequent exposures to situations and environments where infection could occur. Most respondents knew nothing about Chagas disease and few took steps to reduce their risk.
Participants were asked a number of questions related to likely contact with kissing bugs or blood from potentially infected animals.
- Majorities reported the following:
- Staying overnight in the open or in tents or cabins
- Seeing kissing bugs while hunting
- Never/rarely using insect repellent
- Never/rarely wearing gloves when field dressing animals
More than 90% reported contact with deer and 72% with feral hogs, both of which are known reservoirs for T. cruzi. Only 40% said they had heard of Chagas disease.
Gunter told MedPage Today that it should be a public health priority to educate hunters about Chagas disease and what they can do to minimize risk. She noted that the state’s Parks and Wildlife Department (which facilitated the current study) conducts training programs in which such education could be easily included. This training is mandatory for all hunters born after Sept. 2, 1971.
American Society of Tropical Medicine and Hygiene
Source Reference: Hodo C, et al “Canine sentinels of vector-borne disease in Texas, USA: High-risk dogs infected with diverse agents including Trypanosoma cruzi, but little evidence of Borrelia burgdorferi” ASTMH 2018; Abstract 1548.
American Society of Tropical Medicine and Hygiene
Source Reference: Zecca I, et al “Companion dogs living in underserved communities along the US Mexico-border serve as reservoir hosts for Trypanosoma cruzi, an increasing public health threat” ASTMH 2018; Abstract 1992.