Rice University and the University of Texas Medical Branch (UTMB) at Galveston have collaboratively created a new medical diagnostic that is highly sensitive to the diarrheal disease cryptosporidiosis. Cryptosporidiosis are parasites that are common causes of prolonged diarrhea. The parasite is common in the United States, with an estimated 750,000 cases of cryptosporidiosis-caused diarrhea occurring each year, but only about 5% of cases are actually diagnosed. The low diagnostic rate is due to the fact that current methods of detection are slow and insensitive. Additionally, the parasite plagues developing countries, where 20% of childhood diarrheal deaths are due to cryptosporidiosis. It can be impractical to use high-technology diagnosis equipment in developing countries because it is expensive and usually requires electricity to operate. However, Rebecca Richards-Kortum, director of the Rice 360˚: Institute for Global Health Technologies, commented that the Rice/UTMB diagnostic offers, “A rapid, affordable, accurate point-of-care test could greatly enhance care for the under-served populations who are most affected by parasites that cause diarrheal illness.”
A. Clinton White, director of the Infectious Disease Division at UTMB, knew Richards-Kortum had the know-how to make a diagnostic tool, and he had a strong background in the disease. “I’ve been working with cryptosporidium for more than 20 years, so I wanted to combine her expertise in diagnosis with our clinical interest,” White said. The resulting test uses recombinase polymerase amplification (RPA) to detect trace amounts of DNA from cryptosporidiosis in patients’ stool. First, the parasitic DNA is purified; then, it is combined with RPA primers and enzymes that amplify the DNA to measurable levels. Finally, the amplified product is flowed over a detection strip to yield a positive or negative reading. “If the pathogen DNA is present, these primers will amplify it billions of times to a level that we can easily detect,” said Zachary Crannel, a graduate student at Rice’s BioScience Research Collaborative who published an article detailing the test in Analytical Chemistry.
The test is improved over the current tests for a number of reasons. The Rice test can detect the presence of just one parasite in a stool sample, and current tests might give a positive result if thousands of the parasite are present. Also, the Rice test requires limited equipment (RPA enzymes are shelf-stable up to a year, and the test is run at room or body temperature), but the current tests require special equipment (including microscopes, fluorescent tags, or thermal cyclers). Finally, the Rice test is low-cost and may be adapted for use in detecting other parasites, such as giardia, that cause intestinal disease.
Importantly, the test works. It was used to correctly discern between infected and control mice 27 out of 28 times and yielded 21 out of 21 successes when it was used with human stool. This is great news because “in the most recent global burden-of-disease study, diarrheal disease accounts for the loss of more disability-adjusted life years than any other infectious disease, and cryptosporidiosis is the second leading cause of diarrheal illness,” said Crannell. The test might be able to prevent another outbreak, such as the one that sickened 400,000 people in Greater Milwaukee in 1993, by quickly diagnosing the problem so that patients can be treated efficiently.