Scientists Step Closer To New Treatments For River Blindness
The larval stage of Onchocerca ochengi used in the vaccine.
(Image source: University of Liverpool)
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.
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.
Source: University of Liverpool. April 2006.
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