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Water-borne parasites: Improving detection and treatment in canines

Water is such a major part of our daily lives that the thought of a water-borne parasite is enough to make anyone worry. However, researchers at Texas A&M University are working to understand parasite infection and discover possible preventions and treatments.

Karen Snowden, a professor of veterinary pathobiology at the College of Veterinary Medicine & Biomedical Sciences, and her graduate student, Jessica Rodriguez, are studying Heterobilharzia americana, a waterborne flatworm trematode parasite commonly thought to affect wildlife, and which can also infect dogs and horses. Reported cases of canine infection are on the rise, but researchers are unsure why.

“We examined medical records from 238 dogs diagnosed with Heterobilharzia americana in Texas over the past 22 years,” Rodriguez said. “Dogs can show nonspecific symptoms like diarrhea, vomiting, weight loss, and decreased appetite.  In many cases, dogs were diagnosed only after undergoing surgery and biopsy.  We hope to increase veterinarians’ awareness of this parasite so that more dogs are diagnosed with non-invasive tests and before they become very ill.”

The eggs of this parasite hatch when they come into contact with fresh water and quickly penetrate a specific type of aquatic snail, where they then multiply before leaving to search for a warm-blooded host. The larvae, as they are called at this point, stay in the water until an appropriate host comes along, at which point they latch onto that animal and burrow through the skin, infecting the body systemically as they travel to the lungs, the liver (where they mature), and eventually the veins of the abdominal organs. There, the male and female flatworms mate and produce eggs. Most eggs are carried to the intestinal wall, where they erode their way into the intestines to be passed in the feces and begin the cycle again.  Some eggs are carried to the liver where they cause inflammation and disease in dogs.

Although this particular parasite is not considered a human pathogen, it is closely related to several other parasites that do affect humans. In an innovative, One Health approach, Rodriguez is using what is known about treatment of the human disease to suggest a better diagnostic test, and potentially, a treatment for dogs with the similar parasite. Any treatments or preventions found work well for dogs, moreover, could then go the other direction and be applied to human medicine.

“We can easily apply a One Health concept spanning human and veterinary medicine while studying the parasite, H. americana,” Snowden said.  “We are proving that a test designed to detect the closely related human parasite, Schistosoma, will also diagnose this local animal parasite.  In turn, the Heterobilharzia parasite can be developed as a animal model to study the globally important human Schistosoma parasite, testing new drugs and understanding disease processes with less human risk in a research setting.”

Another example of this diversity of parasites is Cryptosporidium, a type of protozoan that can cause gastrointestinal problems, such as severe watery diarrhea, in humans and other vertebrate animals. Crypto, as the parasite is often called, is spread in the fecal-oral fashion, most commonly through drinking contaminated water.

Humans often become infected when they accidently swallow a little bit of contaminated water as they are swimming.  As crypto is resistant to many powerful disinfectants, including chlorine, even treated swimming pools and water parks can be dangerous. Furthermore, when crypto gets into the sources drinking water sources (such as rivers, lakes, or wells), it can be difficult to destroy all of the parasites. The biggest officially recorded crypto outbreak was in Milwaukee, Wisconsin, in 1993 when it infected 403,000 people after one of the city’s two water purification plants was contaminated, probably with runoff from cattle pastures.

Cryptosporidiosis, the disease caused by this parasite, is found worldwide and is one of the top four diarrheal pathogens in infants and toddlers in developing countries. It can be a life-threatening condition for immune compromised individuals, and there is no approved treatment for them, and crypto is thought to have killed about 100,000 people in 2010. However, Dr. Guan Zhu, another professor in VTPB, studies parasite metabolism in order to find possible drug targets. He and his team recently discovered a treatment that reduced the parasite load by up to 90 percent, offering hope that a drug might soon be developed to treat human and animal cases.

“Cryptosporidium is a classic example of One Health pathogen as it infects both humans and animals and affects environments by contaminating drinking and recreational waters,” Zhu said. “Our research focuses on understanding what happens inside this tiny parasite at molecular and biochemical levels. Our ultimate goal is to develop effective therapeutics by targeting the essential molecules in the parasite.”