Veterinarians Warn Of Deadly, “Revolting” Parasite Sickening Dogs
Alarming new research from a top Texas vet about a parasitic menace has NYC's Animal Medical Center warning vets and owners to be on the lookout.

Once treated as a Gulf Coast oddity, Heterobilharzia americana, the parasite that causes canine schistosomiasis, is forcing a nationwide rethink and redrawing of maps following a presentation of new research.

When I noticed “canine schistosomiasis” on the agenda for a veterinary conference I attended in June in Seattle, my stomach dropped. No pun intended.

Schistosomiasis is a devastating, parasitic disease spread through feces-infested water in far-flung corners of the developing world. At least that’s the people perception of the disease.

I had studied schistosomiasis as an undergraduate at Brown in a course called, “The Burden of Disease in Developing Countries.” What was “schistosomiasis” doing on the agenda at a veterinary conference in Seattle – and what was “canine” doing next to it? My anxiety level grew when I arrived for Dr. Kathleen Aicher’s talk at the Seattle Convention Center in June at the American College of Veterinary Internal Medicine (ACVIM) annual forum – often where the most consequential, talked about research is unveiled – and saw images of Labradors on the cover slide of her PowerPoint. 

The Bad News From Seattle, From A Top Vet

A veterinary internist and assistant professor at Texas A&M University’s Veterinary Medical College, Dr. Aicher told audience members she and her team were “astounded’ by the prevalence numbers they were uncovering, both in “high risk” and in “low risk” populations of Labradors. But before we get to a discussion of Dr. Aicher’s prevalence data, let’s unpack what she and her team have uncovered with respect to geography. For decades, H. americana was regarded largely as a parasite of the Gulf Coast and southern Atlantic states, where compatible freshwater snails complete part of its life cycle. Now, said Dr. Aicher, researchers had documented infections well beyond that traditional range, including outbreaks in Utah and California. Dr. Aicher said dogs from still more states have tested positive through Texas A&M University’s Gastrointestinal Laboratory, although she underscored that the location of a dog at testing did not establish where it became infected.

“I suspect that even since I’ve made this map, there are other dogs that have been positive,” she said. “I think this could be everybody’s problem.”

(Dr. Aicher declined to make slides or data from the lecture in Seattle available for publication, but TCR has included a single grainy photo taken by the reporter with an iPhone and will continue to follow-up.)

It is absolutely possible that a dog could be diagnosed with schistosomiasis here in New York,” Dr. Ann Hohenhaus wrote this week on the blog she publishes for the Schwarzman Animal Medical Center.

On top of the expanded map, Dr. Aicher says the risk profile for the parasite may be misunderstood or evolving due to climate change. For example, there are positive test results of the low-risk “bench” Labrador who are not known to swim in freshwater sources. Dr. Aicher said her team has found infected dogs with no known history of regular swimming or water training. In an endemic area, she said, exposure may be as ordinary as stepping into a flooded backyard.

In fact, the most surprising and telling cases may be the dogs  with no known exposures to swimming or freshwater sources – apart from, perhaps, their backyards.  In an interview with The Canine Review after the forum, Dr. Aicher described two French bulldogs from the Houston suburbs who had “never left their backyard — and they both were infected.”

Dr. Aicher said dogs standing in water in their backyards after heavy rain was the team’s best explanation, but the account does not establish the precise site of infection without environmental testing. It does, however, illustrate why “Does your dog swim?” may be an inadequate screening question. This is also where global warming could account for disease spread. Nonetheless, Dr. Aicher says the disease may be present in parts of the country where veterinarians are not yet testing for it.

Dogs are moved around the country in ways clinicians may not know or realize. Families take pets on vacation. Sporting dogs travel to competitions and hunting grounds. Rescue dogs are transported from Gulf states to northern shelters.

“There are dogs all over the country…that are being tested and found to be positive,” she told TCR.

Dr. Aicher said her laboratory has received positive samples from dogs in Wisconsin and Ohio whose veterinarians had no known travel to historically endemic areas. Those reports are important signals, she explained, but they do not by themselves prove established local transmission. Confirming that requires finding the parasite’s life cycle in the environment, including a compatible infected snail.

California Findings

That kind of confirmation came in California in 2023.

In 2023, Los Angeles County health officials issued an animal health advisory after 11 dogs from Los Angeles, Orange and Riverside counties were diagnosed with canine schistosomiasis between 2018 and 2023. All had visited the Colorado River before diagnosis. One died.

University of California, Riverside researchers later collected more than 2,000 snails near Blythe, California and identified H. americana in two snail species. They wrote about their findings in a peer reviewed paper. The finding tied infected dogs, capable snail hosts and the parasite to the same location.

Canine Schistosomiasis In NYC?

At New York City’s Schwarzman Animal Medical Center, one of the world’s leading veterinary nonprofit teaching hospitals, senior vet Dr. Ann Hohenhaus, who is a personal friend and mentor and publishes the hospital’s blog, is posting this week on canine schistosomiasis. She notes that she was inspired by a conversation that occurred in the conference exhibit hall at ACVIM following Dr. Aicher’s talk (during which I unloaded my anxiety about the worms and found a sympathetic audience). Click here to head to AMC’s blog.

“The life cycle of this parasite is, frankly, revolting,” Dr. Hohenhaus writes this week on the AMC blog. “The young flatworms penetrate a dog’s skin and migrate through the lungs into the blood vessels of the liver, where they mature and mate. The adult flatworms lay eggs that migrate into the intestine and are ultimately shed into the feces. If infected feces reach freshwater, the eggs hatch and infect snails. Inside the snail, the parasites mature into free-swimming flatworms, ready to infect another host.”

The canine disease should not be confused with human schistosomiasis, a major neglected tropical disease caused by related blood flukes. H. americana is primarily an animal parasite. In people, exposure to animal schistosome larvae may cause cercarial dermatitis, or “swimmer’s itch,” rather than the systemic canine disease described here. Another key distinction: in people, schistosomiasis is a disease of poverty.

“Diagnosis is frequently delayed due to lack of awareness,” Dr. Aicher said in her presentation. She is imploring veterinarians around the country to learn about the disease and start to test for it.

A 2026 study by Dr. Aicher and Texas A&M colleagues reported that a newly developed fecal PCR test had 98.2% accuracy (the authors disclosed that several of them, including Dr. Aicher, are paid employees of the Texas A&M GI Lab, which offers the test for a fee).

“A regular fecal sample will not pick up schistosomiasis, so your veterinarian will need to request a special fecal test. The best option is a DNA test, which looks for H. americana DNA in a fecal sample,” Dr. Hohenhaus says. “Your veterinarian simply sends your dog’s feces to a laboratory that offers H. americana PCR testing. The test is very sensitive and can detect as few as three flatworm eggs in a gram of feces—about the size of a raisin.”

While reporting this story, I grew so anxious about my own Labrador, my primary veterinarian in New York, who had also attended the Seattle conference – and, like Dr. Hohenhaus, had to listen to me carry on about the worms long after Dr. Aicher concluded her talk – eased my own fears by submitting Nellie’s fecal sample for testing at Dr. Aicher’s shop.

The result was negative and, because Nellie has chronic soft stool and suspected irritable bowel disease, Nellie’s pet insurance carrier, Trupanion, paid for the test. I note that Trupanion covered the test because if a client has insurance or is “OCD” like this reporter,  veterinarians everywhere should keep the test in mind. I’m glad we ruled it out for Nellie.

Dr. Aicher declined to confirm the case counts by state as of press time and would not answer questions about the New York tri-state, but in our interview, she noted that she spoke recently in Greenwich, Connecticut and would be overjoyed if veterinarians in the surrounding area starting adding HA to their lists of diagnostic differentials.

‘Astounding’ Prevalence Numbers

“In our low-risk Labrador retrievers,” Dr. Aicher said, referring to what she described as “patients who didn’t spend time swimming or training in water,” “we were very surprised to find 8.3% [prevalence].” Dr. Aicher’s Texas prevalence study was still enrolling dogs when she spoke in Seattle in June. She used the term “apparent prevalence,” cautioning against applying findings from selected populations to all dogs. Still, some of the results are especially telling, she says, particularly that the researchers have identified confirmed infections in dogs with no known so-called risk factors.

“We were astounded by our high risk counts that nearly 28% of these dogs were positive for Heterobilharzia, which was more than double their prevalence for other intestinal parasites.”

The Labrador Behind The Project

It was Drake, an 8-year-old chocolate Labrador retriever patient from the Houston area who “grabbed me and forever changed my career,” she told TCR. The research fund, The Drake Project, is named for the dog, who succumbed to complications from the disease.

“It was sort of a ‘never again, let’s learn something more about this’” moment, she said.

No Easy Treatment

There is no approved preventive medication that reliably protects dogs from H. americana, although Dr. Aicher told TCR she dreams of the day when HA is added to routine parasite prevention drugs for dogs. For now, treatment generally combines high-dose protocols of praziquantel, the drug used to treat the disease in humans, and fenbendazole, often at doses or durations outside their approved labels. The drugs can clear infection, but there have been reports of adverse events.

Awareness

Unlike human schistosomiasis, where poverty and infrastructure remain the most central challenges, Dr. Aicher says she views awareness as the key challenge in the dog version. Veterinary medicine does not yet know the parasite’s full range or presence, she noted. But thanks to Dr. Aicher, her colleagues — and Drake — at least more veterinarians will be on the lookout.