Chagas disease, a chronic parasitic infection that can damage the heart, is widespread in the US and is a frequent cause of sudden cardiac death but often goes undiagnosed by physicians, the American Heart Association has warned.
More than 300 000 people in the US each year are infected by the protozoan causing Chagas disease, Trypanosoma cruzi, the association warned in a scientific statement in the journal Circulation.1 About a third of infected people eventually develop overt heart disease because of the damage done by the parasite. A further 10% develop chronic neurological or gastrointestinal complications.
The vector is the bloodsucking triatomine insect or kissing bug, a name given because of its tendency to bite the face, especially around the mouth. The bite itself does not transmit the parasite, but the insect often defecates immediately afterwards, and scratching can rub the faeces into cuts or mucus membrane, causing infection.
The acute phase of infection may cause no symptoms or non-specific flu-like symptoms. Cardiomyopathy is detected only years or decades later. The first symptom is often heart failure or a heart attack that occurs years after infection.
Testing donated blood indicates that between 5.5% and 7.5% of infections in the US are locally acquired. T cruzi has been in North America for centuries, infesting raccoons, coyotes, and other mammals. However, transmission from insects to humans remains comparatively rare in the US, said Sheba Meymandi, director of the Center of Excellence for Chagas Disease at Olive View-UCLA Medical Center in Los Angeles. She leads a project that has offered twice monthly free screening for Chagas for 10 years, finding and treating over 300 patients.
“Americans are less susceptible for the same reasons that they are less prone to mosquito-borne diseases like dengue: they tend to live more indoor lives, with air conditioning,” said Meymandi. She added, “Further south you see high rates among rural people, especially where adobe walls and thatched roofs provide homes for the bugs.”
The particular species of triatomine bug that predominates in the US “has better toilet habits—they tend to move after feeding and defecate somewhere else,” she said.
Some infections in the US are caused by blood transfusion and organ donation, and there are congenital cases. But most of the cases that Meymandi has identified are among immigrants who were infected in their home countries years previously.
About 95% of blood donations and most donated organs in the US are now screened for Chagas. In Britain and Canada, donated blood is screened if the donor questionnaire shows Latin American origin or travel history.
T cruzi infects about 1.5 million people in Brazil and 1.2 million in Argentina, and more than a million people in South America have Chagas related heart disease. But doctors there are trained to look out for it, whereas in northern countries it often “slips below physicians’ radar,” said Meymandi.
Chagas disease also has a foothold in Europe, particularly in Spain, where at least 42 000 people are infected.2
In 2017 the Los Angeles screening programme found 59 confirmed cases among 4755 residents born in Latin America, a rate of 1.2% that supports the US Centers for Disease Control and Prevention’s estimate of 300 000 cases nationwide. “If anything that’s an underestimate,” said Meymandi, who believes that less than 1% of infected people are receiving treatment.
There are partially effective treatments, benznidazole and nifurtimox, but they work less well in long established infections. “If you detect Chagas when there’s already cardiomyopathy, it’s often too late,” said Meymandi.
“If there’s one thing I would urge physicians to do, it’s to make sure that all of your patients who come from Latin America are screened at least once,” she concluded.