Every year, the American College of Veterinary Internal Medicine (ACVIM) holds a multi-specialist forum. At this meeting, oncologists, large- and small-animal internal medicine specialists, neurologists, cardiologists and nutritionists gather to exchange ideas about best practices in veterinary care and hear about the latest research topics in our field.
With so many presentations, no one can attend every interesting talk. But during breaks and mealtimes, we share what we have learned throughout the day. This blog post about an emerging disease of dogs, schistosomiasis, was inspired by a conversation I had in the exhibit hall at this year’s ACVIM Forum in Seattle with friends who attended a presentation on the topic.
What is canine schistosomiasis?
Schistosomiasis is caused by a parasitic flatworm or fluke, Heterobilharzia americana. The natural host of H. americana is the raccoon, but dogs can be infected if they swim in freshwater contaminated with the young flatworms.
The life cycle of this parasite is, frankly, revolting. 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.
Where does canine schistosomiasis occur?
Most reported cases of canine schistosomiasis have been along the Gulf Coast, particularly in Texas and Louisiana. Dogs in the southeastern United States and along the lower Colorado River are also at risk.
At the Schwarzman Animal Medical Center, we see rescue dogs imported from the South that may bring diseases uncommon to our geographic area, such as heartworms, canine transmissible venereal tumor and American trypanosomiasis.
Dogs from New York also travel south in the winter and could become infected with H. americana while visiting warmer climates. Given these travel patterns, it is absolutely possible that a dog could be diagnosed with schistosomiasis here in New York.
What clinical signs does a dog with schistosomiasis have?
Since the flatworms affect the intestines, common signs include weight loss, diarrhea—sometimes with blood—vomiting, and elevated liver and calcium levels are common. Bloodwork may also show an increased number of eosinophils, a type of blood cell associated with parasitic infections.
X-rays and ultrasound may show an enlarged spleen, liver or lymph nodes. The flatworm eggs cause inflammation which can lead to calcification of the intestinal walls, which may also be visible on x-rays or ultrasound.
How can my veterinarian diagnose schistosomiasis?
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.
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.
For very sick dogs, biopsies of the intestinal wall, liver or lymph node will identify the flatworms.
How can I prevent my dog from getting schistosomiasis?
Because dogs become infected through exposure to contaminated freshwater—but not the ocean—the best prevention is keeping your dog out of freshwater ponds, lakes, streams and other bodies of water in areas where the parasite may occur.
Can schistosomiasis be treated?
Yes. Your veterinarian can prescribe medications to treat schistosomiasis, but early diagnosis is critical for successful treatment. If your dog has traveled to the South or has spent time in freshwater and develops persistent gastrointestinal signs, be sure to tell your veterinarian about that travel and water exposure.