General information
The Heterobilharzia americana TaqMan real-time qPCR is a highly sensitive and specific molecular assay for detection of H. americana DNA directly from canine fecal samples.
The analytical sensitivity of the assay is 1.5 eggs per gram of feces (60% reproducibility) and 3 eggs per gram of feces (100% reproducibility). Diagnostic sensitivity is 98.2% in feces from dogs with H. americana eggs observed by fecal sedimentation. Both analytical and diagnostic specificities are 100%. Analytical specificity was assessed by testing ten non target species including Alaria sp., Ancylostoma sp., Cystoisospora ohioensis, Eimeria sp., Taeniidae, strongylid-type eggs, Trichuris vulpis, Giardia sp., Sarcocystis sp., and Toxocara canis.
Additional information about this assay can be found in the 2026 open access article describing the validation and optimization of the TaqMan fecal PCR.
For this test, we require 1 gram of fresh feces. A paired fecal saline sedimentation test could also be employed and is recommended prior to initiation of therapy in an infected dog. For storage and shipping, samples should be refrigerated and can be stored for up to one week prior to shipment. Freeze-thaw cycles are discouraged as this could damage parasite DNA. Fresh samples are preferred. Please ship samples overnight with a gel ice pack Monday-Thursday as the lab is unable to accept shipments on weekends or holidays.
Turnaround: 1-2 business days after receipt of samples.
General information about Heterobilharzia americana
Heterobilharzia americana is a trematode parasite that causes canine schistosomiasis and is closely related to Schistosoma species that infect humans. In the United States, infections have traditionally been considered endemic along the Gulf Coast and southern Atlantic states associated with the limited range of the required intermediate snail host for the life cycle of the parasite (see more below). However, an increasing number of cases have now been reported in newly established endemic regions such as California, Arizona, and Utah. Ongoing prevalence work at the TAMU GI lab suggests that infected dogs may be found across a wide range of the United States. However, the specific location of where a dog became infected is rarely known in most cases and many dogs travel across the country.
Transmission occurs when free-swimming cercariae, one of the life stages of the parasite shed from an infected snail, penetrates the skin of a dog during contact with a contaminated freshwater source. Freshwater sources include ponds, lakes, rivers, or irrigation ditches; however, there are reports of infected dogs that lack a history of swimming suggesting that intermittent standing water in yards may also pose risk for infection. After skin penetration, immature parasites migrate through tissues and the bloodstream, pass through the lungs, and mature in the liver before establishing as reproductive pairs in the mesenteric vasculature. Adult worms produce eggs that migrate to the intestinal lumen to be passed via feces into the environment or become lodged in tissues such as the intestinal wall, liver, spleen, pancreas, and mesenteric lymph nodes. The presence of eggs in tissues induces a granulomatous inflammatory response, leading to fibrosis and organ dysfunction. Granulomas are a hallmark of disease and are responsible for many of the systemic and clinicopathologic abnormalities observed in infected dogs.
Clinical signs and clinicopathologic findings
Clinical signs of canine schistosomiasis are variable, and some dogs may remain asymptomatic. Common symptoms include diarrhea, hematochezia, weight loss, inappetence, vomiting, lethargy, and polydipsia. Clinicopathologic abnormalities may be variable or even absent in asymptomatic infection. Hyperglobulinemia, hypoalbuminemia, hypercalcemia, and elevations in liver enzymes may be found on a chemistry panel. Complete blood count may reveal eosinophilia, anemia, or thrombocytopenia. Hypercalcemia has been documented in a small percentage of infected dogs and may be severe when present. The exact mechanism of hypercalcemia is complex, varies amongst infected dogs, and is not yet well understood. Canine schistosomiasis should be included on the differential list for dogs with compatible clinical signs, hypercalcemia of unclear origin, residence in or travel to endemic regions, and access to freshwater.
Imaging abnormalities
Some dogs infected with H. americana may have classic changes observed with abdominal imaging. Diffuse mineralization outlining the walls of the intestines may be observed via abdominal radiographs. Heterogenous small intestinal wall layering or pinpoint hyperechoic foci in the small intestine, liver, or mesenteric lymph nodes may be observed with ultrasound. These changes may be found both in dogs with and without clinical symptoms. A lack of observed imaging abnormalities does not exclude the possibility of infection.
Diagnosis
Traditional diagnosis relies on identification of H. americana eggs in feces using fecal saline sedimentation or detection of eggs in biopsies of affected tissues. Fecal sedimentation is not routinely performed in clinical practice due to the time-consuming nature of the test and expertise required to accurately identify eggs. The TAMU GI Lab TaqMan real-time PCR assay provides a sensitive and specific alternative for detection of H. americana DNA directly from feces.
Treatment
There are currently no FDA-approved veterinary drugs specifically labeled for the treatment of canine schistosomiasis. Treatment protocols are off label and are based on published clinical experience as well as extrapolation from treatment in people with schistosomiasis. Praziquantel in combination with fenbendazole is commonly used in both “high dose” and “low dose” protocols described in more detail in this link. Doses of praziquantel and fenbendazole are prescribed at higher doses and in longer duration than as labeled for other parasites. Treatment regimens may need to be repeated based on follow-up diagnostic testing. Owners of large-breed dogs should be advised that achieving effective praziquantel doses may require many tablets depending on formulation and veterinarians should consider the use of a commercially available Biltricide® 600mg tablet. Based on reports of transient and severe bone marrow suppressions documented in some dogs following treatment for H. americana, owners should be advised to stop treatment immediately and consult their veterinarian if this is suspected. Combination products containing praziquantel (such as Drontal Plus®) are not recommended as they may also contain febantel, a pro-drug of fenbendazole. Using this product to achieve the desired praziquantel dose will provide excessive fenbendazole to the dog, particularly if used in combination with a separate dose of fenbendazole. Veterinarians should use products that contain praziquantel exclusively such as Droncit®, Biltricide®, or compounded praziquantel. Follow-up testing is recommended to assess treatment response.
Further reading
Aduku, F., Gookin, J. L., Suchodolski, J. S., Poellmann, L. J., Luksovsky, J. L., Verocai, G. G., … & Aicher, K. M. (2026). Optimization and validation of a TaqMan real-time PCR for the detection of Heterobilharzia americana in dog feces. Veterinary Parasitology, 110712. Doi: https://doi.org/10.1016/j.vetpar.2026.110712
Aicher, K., & Poellmann, L. (2025).Diagnosis and treatment of Heterobilharzia americana infection in dogs. Today’s Veterinary Practice, March/April, 24–29.
Baniya, A., Goldy, C.J., Ardpairin, J., Achi, P., Chang, Y.W., Adrianza, R.C., Vitta, A., Dillman, A.R., 2024. Canine schistosomiasis in the west Coast: Heterobilharzia americana in two natural intermediate hosts found in the Colorado River, California. Pathog. (Basel, Switzerland). https://doi.org/10.3390/pathogens13030245
Cook, A.K., 2022. Schistosomiasis in the United States. Vet. Clin. North Am. – Small Anim. Pract. 52, 1283–1303. https://doi.org/10.1016/j.cvsm.2022.06.009
Graham, A.M., Davenport, A., Moshnikova, V.S., Gilmour, L.J., Fabiani, M., Bishop, M.A., Cook, A.K., 2021. Heterobilharzia americana infection in dogs: a retrospective study of 60 cases (2010-2019). J. Vet. Intern. Med. 35, 1361–1367. https://doi.org/10.1111/jvim.16127
Loker, E.S., Dolginow, S.Z., Pape, S., Topper, C.D., Alda, P., Pointier, J.P., Ebbs, E.T., Sanchez, M.C., Verocai, G.G., DeJong, R.J., Brant, S. V., Laidemitt, M.R., 2021. An outbreak of canine schistosomiasis in Utah: acquisition of a new snail host (Galba humilis) by Heterobilharzia americana, a pathogenic parasite on the move. One Heal. 13, 100280. https://doi.org/10.1016/j.onehlt.2021.100280
