It’s one of the most insidious diseases you’ve never heard of, but Chagas is here in California and 29 other states across the U.S.

It kills more people in Latin America than malaria each year, and researchers think roughly 300,000 people in the U.S. currently have it but are unaware.

That’s because the illness tends to lie dormant for years, only making itself known when its victim keels over via heart attack, stroke or death.

Chagas disease is caused by the parasite Trypanosoma cruzi, which lives in a bloodsucking insect called the kissing bug. There are roughly a dozen species of kissing bugs in the U.S. and four in California known to carry the parasite. Research has shown that in some places, such as Los Angeles’ Griffith Park, about a third of all kissing bugs harbor the Chagas parasite.

It’s why a team of epidemiologists, researchers and medical doctors are calling on the World Health Organization and Centers for Disease Control and Prevention to label the disease as endemic, meaning consistently present, in the U.S. They hope that will bring awareness, education, dialogue and potentially public health investment to a disease that has long carried a stigma, falsely associated with poor, rural migrants from bug-infected homes in far-off tropical nations.

“This is a disease that has been neglected and has been impacting Latin Americans for many decades,” said Norman Beatty, a medical epidemiologist at the University of Florida and an expert on Chagas. “But it’s also here in the United States.”

“We had a kid from the Hollywood Hills who got it,” said Salvadore Hernandez, a cardiologist with Kaiser Permanente in Northern California. He said the patient had not traveled out of the country and probably got it in his leafy, affluent neighborhood, where kissing bugs are prevalent.

The parasite has also been detected in local wildlife, including wood rats, skunks and mice in Griffith Park, as well as bats, raccoons and black bears in other parts of the state.

“Kissing bugs are pretty equal opportunity when it comes to who they take a blood meal from,” said Sarah Hamer, an epidemiologist at Texas A&M University’s School of Veterinary Medicine and Biomedical Sciences, listing off a variety of animals, such as ocelots, bobcats, coyotes, birds, reptiles and amphibians.

“That means the reservoir for T. cruzi is pretty large,” she said.

California has the largest number of people in the U.S. infected with Chagas disease — between 70,000 and 100,000. That’s mostly because the state is home to so many people from countries where the disease is endemic. But it’s also because the parasite and vector live here, meaning some of those cases could be home-grown.

A small study by the state’s Department of Public Health, for instance, found that 31 of 40 human cases reported to the state between 2013 and 2023 — about 78% — were acquired in other countries. For the remaining cases, health officials couldn’t rule out local transmission.

Chagas is not a reportable disease in California, which means the state does not require physicians and health systems to report and investigate it, as it does with influenza, Lyme and malaria. However, it is reportable in Los Angeles and San Diego counties; Los Angeles was the first county in the state to mandate reporting of the disease.

Between 2019 and 2023, health officials confirmed about 18 cases of Chagas disease in L.A. County, “although many more cases likely go undiagnosed,” the department wrote in a statement. It said most of the identified cases were infected internationally, but some appear to be locally acquired.

Gabriel Hamer, an entomologist at Texas A&M, said that confirmed human cases in the U.S. represent “just the tip of the iceberg” and that nobody really knows how many people actually have the disease. “There’s no standardized reporting system. There’s no active surveillance.”

Most people find out they have the disease only after trying to donate blood, said Hamer.

Janeice Smith, a retired teacher in Florida, discovered she had it in 2022 after receiving a letter from her local donation center telling her she’d tested positive and should go see a physician.

Smith now runs a nonprofit to increase awareness of Chagas, which she said she probably got in 1966 when her family went to Mexico for vacation. She had returned home with a swollen eye and high fever, and was hospitalized for several weeks. No one found out what caused her symptoms until almost six decades later.

Hamer said proteins in the kissing bugs’ saliva can cause acute reactions, such as swollen limbs, eyes and anaphylaxis, all unrelated to the disease-carrying parasite.

But it’s the longer-term or chronic effects that cause the most harm. And because the disease is not well known, and its symptoms are often indistinguishable from other forms of cardiac and organ damage, it’s likely many people are showing up to their doctors’ offices with heart arrhythmia, a swollen esophagus, seizures and stroke, without ever being screened.

“The disease is definitely underdiagnosed,” said Hernandez, the Kaiser cardiologist. “If we screened for it and caught it early, most patients could be cured. The problem is we don’t, and people end up dying or requiring terrifically expensive care,” including organ transplants and surgery.

Anti-parasitic medications can be used to stop disease progression.

Chagas is also prevalent in dogs who show similar clinical signs, heart failure or arrhythmias.

“We’ll see these acutely infected, usually young dogs that might be puppies, or dogs less than 1 or 2 years of age that are really adversely affected. And then we would have dogs that would come in older, and they might be in heart failure,” said Ashley Saunders, a Texas A&M veterinary cardiologist.

She said dogs often acquire the disease by eating the bugs, which give a much higher “dose” of the parasite than a few bug poops in a cut.