September 13, 1996. Copyright, 1996, Graphic News. All rights reserved

FUNGUS COULD ELIMINATE RIVER BLINDNESS
By Laura Spinney, Science Editor

EMBARGOED UNTIL 11.30 FRIDAY 13 SEPTEMBER

LONDON, September 13, Graphic News - Fungi could replace pesticides to prevent the spread of African river blindness in developing countries, a biologist told the British Association's annual science meeting in Birmingham today.

River blindness is widespread in tropical sub-Saharan Africa and in Central and South America. It is caused by a nematode worm which is transmitted to humans via an intermediate host fly - the buffalo gnat - and its symptoms include an itching skin rash and blindness if the worm invades the optic nerve. Pesticides are currently used to destroy buffalo gnat populations, but not only can these chemicals damage the environment, there is also the danger that the insects will develop a resistance to them.

One alternative to using pesticides is to exploit natural predator-prey or host-parasite relationships to keep insect numbers at bay. Dr Stephen Moss of the University of Portsmouth has investigated the feasibility of such biocontrol in the case of river blindness by studying the relationship between the buffalo gnat and a parasitic fungus which infects it.

A group of fungi called Harpellales which grow to no more than a few cells in length occur naturally in the gut of buffalo gnats during their larval stage. Until recently they were thought to cause no harm to their host, but Moss's lab studies have shown that some species of these fungi can invade the ovarian tissue of the adult fly and either completely or partially replace the eggs. When the fly goes to deposit its eggs, it deposits the spores of the fungus instead. In some places, up to 40 per cent of adult buffalo gnats can be infected with the fungus, says Moss. He has not yet discovered how the fungus transfers itself from the gut of the larva to the adult's ovaries. But when the host-parasite relationship is completely understood, it should be possible to alter the balance of that relationship so that the parasite infects more of its gnat hosts, thus preventing them from reproducing successfully.

'Why biocontrol is not used extensively is because there are lots of balances to get right,' says Moss. If the host is wiped out completely, there is a danger that its niche will be filled by another, more dangerous species. But unlike pesticides, Harpellale fungi are host-specific, so they do not affect any other species. They will also be cheaper to use and do not leave harmful residues in rivers or soil.

Sources: British Association Annual Festival of Science