Advanced Genetic Tools Revamp Search for Drugs to Treat Cryptosporidium

Genetically engineered modifications to genome of the diarrhea-causing parasite Cryptosporidium are expected to expedite research towards vaccine and drug development to prevent or cure infection by this pathogen.

Recent studies into the global causes of severe diarrhea in young children have identified the protozoan parasite Cryptosporidium as the second most important diarrheal pathogen after Rotavirus. Cryptosporidium is also an opportunistic pathogen in the contexts of human immunodeficiency virus (HIV)-caused AIDS and organ transplantation.

There is no vaccine against Cryptosporidium and only a single [US] Food and Drugs Administration approved drug—nitazoxanide—that provides no benefit for either malnourished children or immunocompromised patients. Cryptosporidiosis drug and vaccine development are limited by a lack of systems for continuous culture, good animal models, and molecular genetic tools.

Investigators at the University of Georgia (Athens, USA) have applied CRISPR/Cas technology to the Cryptosporidium problem. Since 2013, the CRISPR/Cas system has been used in research for gene editing (adding, disrupting, or changing the sequence of specific genes) and gene regulation. By delivering the Cas9 protein and appropriate guide RNAs into a cell, the organism's genome can be cut at any desired location.

The investigators reported in the July 15, 2015, online edition of the journal Nature that by applying this methodology they had introduced a reporter gene into the parasite that caused it to emit light that could be observed under a microscope for in vivo and in vitro drug screening. To isolate stable transgenic organisms with this gene they developed a mouse model that delivered sporozoites directly into the intestine. They also established and optimized transfection of C. parvum sporozoites in tissue culture for in vivo selection for aminoglycoside drug resistance.

"One of the biggest obstacles with Cryptosporidium is that it is very difficult to study in the lab, and that has made scientists and funders shy away from studying the parasite," said senior author Dr. Boris Striepen, professor of cellular biology at the University of Georgia. "We think that the techniques reported in this paper will open the doors for discovery in Cryptosporidium research, and that will, in turn, lead to new and urgently needed therapeutics."

"Now that we have overcome these initial hurdles, we have a great opportunity to move forward much faster," said Dr. Striepen. "There is need, there is opportunity and now there is technical ability, so I think we may have reached a turning point in the fight against this important disease. There are enormous libraries of chemicals available now, and some of these chemicals may work as a treatment for Cryptosporidium and this technology will help us find them much more rapidly."

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