Swimmer's itch in dogs doesn't reflect on your pet's aquatic abilities. The skin lesions -- early symptoms of swimmer's itch -- result from infestation by the larvae of a freshwater flatworm parasite called Heterobilharzia americanum. This larvae has only a 24-hour life cycle, but can do a lot of damage to any dog it infects. Exposure risk is highest during the summer and in waters in the southern United States.
Heterobilharzia Americana Infection
Once the Heterobilharzia americana larvae find its host -- any warm-blooded animal, but primarily raccoons and various types of canines -- it burrows into the skin. It next heads to the lungs, and from there travels through veins leading to organs in the abdomen. In these organs, the larvae mature into flatworms and lay eggs. The eggs go into the intestinal wall and eventually pass out through feces. Some eggs remain, and these end up in other organs, especially the liver, usually causing serious symptoms. An infected dog can't transmit the parasite to another canine. Transmission occurs only with exposure to water containing the larvae.
Swimmer's Itch Symptoms
Along with skin lesions, symptoms of swimmer's itch include vomiting, diarrhea, which may contain blood, appetite and weight loss, anemia, drooling, excessive drinking and urination, and lethargy. The symptoms become worse over time, especially the diarrhea. Severely affected dogs might develop liver disease.
Diagnosis and Treatment
Symptoms of swimmer's itch resemble other conditions, so your dog may have to undergo fairly extensive testing to rule out other issues. Often, the dog's blood work appears normal, although he's quite sick. His blood calcium and blood protein levels could be high, which indicates exposure to Heterobilharzia americanum. When taking your dog's history, tell your vet if your pet has been swimming in any water bodies. For a definite diagnosis, your vet might send a fresh fecal sample from your dog's loose stool to a laboratory for testing.
Once diagnosed, your vet might treat your dog with a high dosage of the dewormers praziquantel or fenbendazole for several days. During this period, your dog may have to stay in the veterinary hospital. In many dogs, this mega-deworming results in a cure, or at least symptom cessation. In other canines, the treatment makes little or no difference. If the dog doesn't respond to treatment and remains very ill, euthanasia may be the only option.
The best way to prevent swimmer's itch is by keeping your dog out of water, especially natural water bodies such as ponds, canals, lakes and swamps. If you are hiking out near water and your dog does jump in, have a towel handy. Wipe him down thoroughly as soon as he exits the water. That helps minimize his chances of infection, as the larvae don't enter the skin until the water droplets dry up.
- Companion Animal Parasite Council: Canine Schistosomiasis Heterobilharzia Americana
- Animal Care Clinic: Ask the Experts
- Texas A&M University Veterinarian Medicine: Fecal PCR Test for Canine Schistosomiasis
- University of Sydney Centre for Veterinary Education: Heterobilharzia Americana
- Pet MD: Flatworm Parasite (Heterobilharzia) in Dogs
Jane Meggitt has been a writer for more than 20 years. In addition to reporting for a major newspaper chain, she has been published in "Horse News," "Suburban Classic," "Hoof Beats," "Equine Journal" and other publications. She has a Bachelor of Arts in English from New York University and an Associate of Arts from the American Academy of Dramatics Arts, New York City.