In his lab in the University of Vermont’s Stafford Hall, Christopher Huston, M.D., associate professor of medicine and infectious disease expert, and his team are growing cultures of a deadly, microscopic intestinal parasite in the tiny wells of a plate about the size of a smartphone. Into each of the 384 wells in each plate, they use the pins on a transfer tool to deliver 384 different drugs.
Huston has been searching for a better way to treat an infection called cryptosporidiosis caused by the parasite Cryptosporidium, also known as “crypto.” He has developed a series of tests for drug compounds in hopes of finding one that can successfully impede the parasite, which attaches to the intestinal lining and causes malnourishment and diarrhea that eventually can lead to dehydration and death.
Crypto is the leading cause of waterborne disease in the U.S. and an alarmingly serious problem in many developing countries, where the parasitic infection is the second most-common cause of life-threatening diarrheal disease in infants. Stopping it is a priority for the Bill & Melinda Gates Foundation, which learned of the problem through its Global Enteric Multi-Center Study (GEMS) of gastrointestinal diseases in Africa and South Asia.
Most commonly spread through water, making it particularly dangerous in areas without proper sewage or water-treatment systems, crypto is also a challenge in developed countries like the U.S., because it’s resistant to chlorine. A 1993 outbreak resulting from crypto contamination of Milwaukee’s drinking water sickened more than 400,000 people and killed 69.
The Gates Foundation, which funded the University of Toronto and other sites to develop drug treatments for malaria and tuberculosis several years ago, learned of the extent and gravity of crypto through the GEMS study. The organization wondered whether drugs found to fight malaria might also work on this parasite. Having no experience with crypto, the Toronto researchers steered Gates and approximately $100,000 of their grant funding to Huston.
To date, treatment involves the drug nitazoxanide, but it has little effect on children and those with compromised immune systems, Huston says. “In malnourished little kids, it’s quite a lousy drug.”
He has worked with crypto both in the lab and real life. Dairy cattle carry one of the two main species of the parasite that can spread to people, and Huston saw an infected female patient who lived on a dairy farm.
In order to test the impact of more than 300 drug compounds per assay plate on crypto, “We use a little robot at the end of 48 hours to fix them and stain them,” Huston says. Computers analyze pictures taken with an automated microscope, showing the parasites as little colored dots.
Relying on the University of Toronto’s library of compounds, he and his team hope to find drug-like compounds known to inhibit protein targets (for example, enzymes) that malaria needs and which might similarly suppress crypto, Huston says. So far, he has had no “hits” with the Toronto cache.
His team has had more success with a broader library of drug-like chemicals – all of which impede malaria growth, but not necessarily thru known mechanisms – from the Medicines for Malaria Venture, a not-for-profit research center based in Geneva, Switzerland. Huston’s team screened those compounds in a separate “assay,” or trial, and about three percent were active against crypto, he says.
They have used those compounds against crypto in mice, as well as in the lab cultures, and are scaling up the project to run tests on sick calves, Huston says. He hopes ultimately that their work will lead to an effective drug.
“Even if none of our candidates work, the chances that somebody finds something with our assay that makes it (into drug development) are quite good,” Huston says. “I’m pretty confident that something will come of our efforts.”