By Isabel Keane

Up to 100,000 Californians have been infected with a potentially fatal disease — without even knowing it.

Chagas disease, caused by a parasite that lives inside so-called “kissing bugs,” has been reported in California and 29 other U.S. states.

The illness, which has potentially infected between 70,000 and 100,000 California residents, lies dormant for years, only making itself known when victims suffer serious cardiac issues, including heart attacks or strokes.

There are roughly a dozen species of the blood-sucking kissing bugs in the U.S., and four are found in California. Some Los Angeles hotspots, including Griffith Park, are teeming with bugs infected with the Chagas disease parasite. A third of all kissing bugs at the famous park and observatory carry the parasite, and the disease has been detected in local wildlife, including wood rats, skunks and mice, according to the report.

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

Due to its prevalence in the U.S., researchers are now calling on the World Health Organization and Centers for Disease Control and Prevention to classify the disease as endemic, which means it is consistently present.

California has more residents who have been infected with Chagas disease, which is caused by the parasite Trypanosoma cruzi, than any other state, in part due to there being so many residents who come from countries where the disease is endemic, according to the report. A study by California’s Department of Health found that 31 of 40 human cases reported between 2013 and 2023 were acquired in other countries. Officials could not rule out local transmission for the remaining cases.

While the disease was once only found in more rural parts of Mexico and Central and South America, it is now present in at least 30 U.S. states. About 8 million people globally and an estimated 280,000 in the U.S. have Chagas disease without even knowing it, according to the CDC.

Doctors and physicians are not required to report cases of the disease in California, as they would have to for other diseases such as influenza, Lyme and malaria, meaning cases are likely vastly underreported. Gabriel Hamer, an entomologist, even said that confirmed human cases in the U.S. represent “just the tip of the iceberg,” and that no one truly knows the true total.

“There’s no standardized reporting system. There’s no active surveillance,” Hamer said.

According to Hamer, many people only discover they have Chagas after trying to donate blood.

Chagas can cause acute reactions, including swollen limbs, eyes and anaphylaxis, though its longer-term effects, such as seizures or strokes, are much more dangerous.

Other symptoms include fever, feeling tired, body aches, headaches, rash, a loss of appetite, diarrhea, vomiting and eyelid swelling. These symptoms may be mild but would appear in the first weeks or months after infection, according to the CDC.

The disease, while curable if antiparasitic treatment is provided early on, can often lead to sometimes fatal cardiac issues, including heart attacks or strokes.