Scientists step closer to new treatments for river blindness

Veterinary scientists in Liverpool have found that some African cattle have natural immunity to a parasite, similar to that which causes river blindness in humans.

These new findings, by scientists at the University’s Faculty of Veterinary Science and the Liverpool School of Tropical Medicine, indicate that it may be possible to vaccinate humans against River Blindness. The disease causes blindness in thousands of people in some of the poorest countries in the world, particularly in West and Central Africa.

River blindness, or onchocerciasis, is caused by a parasitic worm and leads to severe itching of the skin and lesions of the eye which can result in blindness. The parasite is spread by black flies which breed in rivers and deposit the larvae of the worm into the person they bite. The disease develops over a long period of time, particularly in young adults, eventually preventing them from working and farming and hence feeding themselves and rearing their families.

Professor Sandy Trees, at the University’s Faculty of Veterinary Science, said: “Onchocerciasis has been the target of major international efforts to control and ultimately eradicate it, but it still presents a huge burden to health in many impoverished countries. To see if a vaccine is feasible for the disease we looked at whether immunity exists naturally and whether it can be induced.”

The team investigated immunity in cattle infected with a very closely related worm – Onchocerca ochengi – that causes lumps to appear on the animal’s skin but does not cause blindness or illness. Examining infected cattle in Cameroon, the team found that some cows naturally develop resistance to Onchocerca ochengi.

They also showed that cattle which were normally susceptible to infection could be successfully immunised using a vaccine composed of minute parasite larvae, weakened by a controlled dose of radiation in the laboratory. After two years of natural exposure to infected black flies, the number of worms in vaccinated cattle was far lower than in unvaccinated animals.

Professor Trees added: “Although the immunisation method that we tested in cattle would not be suitable for human use, this research provides the first proof that immunisation against onchocerciasis is possible and hence it may be feasible to protect humans from the parasite using some form of vaccination.”

There is currently no safe drug available to cure the disease fully as treatments only kill the young Onchocerca volvulus worms and not the adults. Researchers are now looking to further understanding of how some cattle develop natural immunity when some do not, which will assist in targeting potential treatments for River Blindness.

The research, funded by the Edna McConnell Clark Foundation, is published in Proceedings of the National Academy of Sciences of the USA and can be viewed at http://www.pnas.org/current.shtml