Canine schistosomiasis

Overview

What is Canine schistosomiasis?

Canine schistosomiasis is an infectious disease caused by the parasitic flatworm Heterobilharzia americana that infects dogs. The flatworm can also infect wildlife and cause schistosomiasis in animals such as raccoons (the natural host), bobcats, mountain lions, rabbits, deer, coyotes and other animals. Animals are infected by swimming or wading in fresh waters contaminated with the flatworm.

Public Health/Human Concern:

Infected dogs or animals with Canine schistosomiasis do not pose a zoonotic risk to people, meaning they cannot spread the disease to humans. Aquatic snails carrying the flatworms that cause schistosomiasis in humans are a different species than the flatworms that affect animals. The flatworms affecting humans are not found in the United States.

How is Canine schistosomiasis transmitted to dogs/animals?

The lifecycle is complex and involves several stages:

1. Animals infected with Heterobilharzia americana, shed flatworm eggs in their feces. Raccoons are the natural host to these parasites, but dogs, coyotes, bobcats, horses, deer, and rabbits can also shed eggs.
2. These eggs hatch when in contact with water, releasing the first larval stage, called miracidia. This larval stage infects freshwater snails (Galba cubensis,most commonly). Inside the snail, the larva transforms into the next stage, called cercariae.
3. The cercariae leave the snail and are free living in freshwater
4. Dogs and other animals are infected when they swim or wade in the infected water and cercariae penetrate their skin, potentially leading to skin inflammation. The cercariae then migrate to the liver and lungs.
5. In the dog’s liver, the cercariae mature into adult flatworms. They then migrate to intestinal blood vessels to mate. The flatworms lay eggs that travel to the intestines to be released in the feces, and the cycle begins again.
6. The parasite is not transmitted directly between dogs or from dogs to humans.

Life cycle of Heterobilharzia americana. Courtesy Anil Baniya, PhD, Connor Goldy, Department of Nematology at the University of California, and Jiranun Ardpairin, Department of Microbiology and Parasitology, Faculty of Medical Science, Naresuan University, Phitsanulok, Thailand

What are the symptoms in dogs?

The disease in dogs has a very gradual (slow) onset, initially causing lethargy, loss of appetite, and weight loss. Gastrointestinal signs such as vomiting and diarrhea are common. Other signs reported include coughing, increased gut sounds, and an increase in drinking and urination. Without treatment, cases progress to severe liver and intestinal disease and can be fatal.

What can I do to prevent this in dogs?

The only prevention measure is for dogs to avoid direct contact with bodies of freshwater that are known to contain the parasite.

Where can the flatworm Heterobilharzia americana be found?

It was previously considered to be confined to the Gulf Coast and southern Atlantic states, but the range is expanding to new areas in the Southwest. 

What is the treatment for dogs?

If you have a pet that is experiencing symptoms similar to Canine schistosomiasis, it is recommended you reach out to your veterinarian to determine best course of action for testing and treatment.

Guidance for Veterinarians:

Heterobilharzia americana, is not detected by routine fecal screenings and the clinical signs of schistosomiasis in dogs can mimic many other diseases. There are no preventives to reliably protect dogs from contracting the parasite in freshwater environments so raising awareness for dog owners and veterinary medical communities is essential for early detection and effective management of the disease. When taking a medical history, veterinarians should ask about exposure to freshwater bodies and travel.

Veterinarians are also strongly encouraged to learn more about the parasite, including how to order fecal PCR testing, and to consider Heterobilharzia The following sites may be helpful in offering more information:

Sources:

Animal Health Advisory: Heterobilharzia americana (canine schistosomiasis) confirmed in 11 dogs in three Southern California Counties (LA, Orange and Riverside)

Companion Animal Parasite Council – Canine Schistosomiasis https://capcvet.org/guidelines/schistosomiasis

2021 – Graham et al. Heterobilharzia americana infections in dogs: A retrospective study of 60 cases (2010-2019) – case series from Texas (enzootic area) https://onlinelibrary.wiley.com/doi/full/10.1111/jvim.16127

2019 Animal Health Alert about 2 Canine Schistosomiasis cases in LA County: http://publichealth.lacounty.gov/vet/docs/AHAN/AHAN_Schisto_03122019.pdf