Los Angeles County Veterinary Public Health reports 11 cases of canine schistosomiasis (the liver trematode, Heterobilharzia americana) in dogs from 3 Southern California counties: Los Angeles, Orange, and Riverside between 2018-2023.
All 11 dogs had been swimming in the Colorado River before being diagnosed.
Southern California has not been known to be enzootic for the parasite. The Heterobilharzia americana parasite is known to be enzootic in North Carolina, South Carolina, Georgia, and the Gulf Coast states including Florida, Louisiana, and eastern Texas.
The geographic range for this parasite may be increasing, as small numbers of cases have also been reported from Oklahoma, Kansas, Indiana, and Utah. These 11 cases in dogs that visited the Colorado River suggest that the range may be expanding further, although this has not yet been confirmed.
Infection is acquired from direct contact with fresh water containing the free-swimming life stage of the Heterobilharzia americana Freshwater snails serve as the intermediate host. The parasite is not transmitted directly between dogs or from dogs to humans.
The disease in dogs has a very gradual, insidious onset, initially causing lethargy, loss of appetite, and weight loss. Gastrointestinal signs such as vomiting, and diarrhea are common. Without treatment, cases progress to severe liver and intestinal disease, and can be fatal.
This parasite is known to cause a self-limiting dermatitis in humans (“swimmer’s itch”).