CHICAGO (Reuters) Feb 09 - Closantel, an older drug used to treat a parasitic liver disease in animals, may prove effective at combating river blindness in humans, a major cause of infection-related blindness, U.S. researchers said on Monday.
Transmitted by blackflies breeding along fast-flowing tropical waterways, river blindness is an eye and skin disease caused by the filaria worm, which infects more than 37 million people in Africa, Central and South America and Yemen.
The researchers said closantel, used to fight liver fluke in cattle and sheep, showed promise at disrupting the life cycle of the filaria worm.
"We think this finding holds terrific potential for the treatment of river blindness, one of 13 recognized neglected tropical diseases," said Dr. Christian Gloeckner, a postdoctoral fellow at the Scripps Research Institute in La Jolla, California, whose study appears in Proceedings of the National Academy of Sciences.
The finding may be especially important because the parasite that causes river blindness, or onchocerciasis, is starting to develop resistance to ivermectin (Mectizan), the only drug widely available to treat it.
In humans, the adult female filaria worm produces thousands of baby or larval worms that spread throughout the body. When they die, they cause a strong immune system response that can destroy surrounding tissue.
The current study builds on research suggesting that targeting chitin, which forms a protective outer layer during the parasite's larval stage, may offer a new target. This outer covering must be degraded by digestive enzymes during a molting phase for the organism to develop.
The trick was to find an existing drug that might block the enzymes.
The team searched a library of more than 1,500 drug compounds at Johns Hopkins University in Baltimore for one that might target a digestive enzyme specific to the parasite.
They found four -- but only one, closantel, appeared to be potent enough.
To test it, a team led by Dr. Sara Lustigman at the Lindsley F. Kimball Research Institute at the New York Blood Center exposed larvae to increasing concentrations of closantel and found it completely prevented molting.
Dr. Gloeckner said in a statement that the findings suggest closantel or a chemically similar drug could be a "promising alternative or adjunct therapy in combination with ivermectin for the treatment of onchocerciasis."
Proc Natl Acad Sci USA 2010.
