Sequencing parasites may control river blindness

Professor Warwick Grant researches the nematode parasite, or worm, that causes onchocerciasis, or river blindness

Around 35 million people are currently battling onchocerciasis, or river blindness. One in 40 of these infected people will suffer vision impairment because of the infection, which is the second leading cause of preventable blindness in sub-Saharan Africa.

Professor Warwick Grant is an expert on the nematode parasite, or worm, that causes the disease. “Adult worms are up to 80 centimetres long, live under the skin, and produce thousands of offspring every day,” he explains. “The tiny baby worms are able to move through the body and into the cornea, causing severe dermatitis and eye damage.”

The disease is transmitted by black flies that live near flowing water, such as rivers and streams. “When a black fly takes a blood-based meal from an infected person, it will also ingest baby worms, which are passed on to and infect the next person the fly bites,” says Grant.

Onchocerciasis has, historically, been managed by vector control and the antiparasitic drug, Ivermectin, which was originally developed to treat heartworm in dogs. But drug resistance is becoming a problem.

Backed by funding from the National Institutes of Health, Grant and his collaborators are genome sequencing parasites to identify why some respond to drugs, and others do not. That information, says Grant, “is buried in its genome, its complete set of DNA.”

Grant and his team have sequenced hundreds of nematode genomes to determine the status of the parasite population. This information will be used to develop better diagnostic tools.

“When control programs encounter difficulties eradicating onchocerciasis, the problem may be one of drug compliance, or it may be a result of drug resistance. Our work will determine what the problem is and provide advanced warning if drug resistance is starting to emerge.”

Grant has devoted much of his career to this research, which began with a desire to understand the “sophisticated biology of nematode parasites” and has evolved into a commitment to help control the disease.

“This research might help 35 million people, almost as many as those affected by HIV,” he says. “If I had another scientific life to live, I’d want to continue my work on onchocerciasis.”