Jan. 5, 2000 CSIRO research into controlling worms in sheep is in the frontline contributing to the battle against the devastating human disease, river blindness.
With backing from the World Health Organisation (WHO), Dr Leo Le Jambre of CSIRO Animal Production is working to prevent the potential threat of drug resistance in the parasitic worms.
Dr Le Jambre says current drugs used to control the human parasites could be threatened by similar resistance problems to those seen in sheep parasites, which already endanger the livelihoods of Australian farmers.
The roundworm parasite Onchocerca volvulus that causes river blindness (onchocerciasis) is spread by the bite of the black fly. It causes years of suffering with potential blindness and severe skin itching such that social life, work, education and socio-economic development are affected.
Some 18 million people are infected with the parasite and a further 80 million are at risk. Most of these infected people live in Africa.
"Ivermectin is the only drug that is used on a large scale for the control of onchocerciasis. This same drug is extensively used to control worm parasites in sheep and already cases of ivermectin resistance are being reported by Australian producers," Dr Le Jambre says.
"Development of resistance to ivermectin by the Onchocerca parasite could seriously hamper the progress of the River Blindness Control Programmes.
"In order to detect any ivermectin resistance, should it appear, WHO is keen to develop the appropriate tools to monitor the human use of the drug.
"In Australia, internal worm parasites are a major health problem in grazing livestock. They cost the sheep industry at least $200 million per year, including $80 million in the cost of chemical treatments.
"Despite the range of drugs available for livestock use, the worms have developed widespread resistance to two of the three broad-spectrum drug families and are now showing resistance to the one remaining group, the avermectins," says Dr Le Jambre.
"We need early warning of the appearance of resistant worms. If we can pin down the genes responsible for resistance then we can develop early warning systems," he explains.
"This has been achieved for some drug families but not yet for ivermectin and this is the push of the current work at CSIRO Animal Production which is being supported by WHO."
"Our studies have already shown that ivermectin resistance in sheep worms is inherited as a dominant trait. Resistance develops faster when it is inherited as a dominant trait, as all the worms which carry the gene will be resistant."
"Our aim, as contributors to WHO's research effort, is to have the first DNA assay for ivermectin resistance in the River Blindness parasite available within three years."
"Availability of a robust test to detect ivermectin resistant genes will not only benefit humans with onchocerciasis, but it will benefit sheep producers."
"This will have immediate application in Australia with better worm management procedures based on the early detection of drug resistance," adds Dr Le Jambre.
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