Issue 25 Autumn 2006
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Vaccines for Gut Roundworm Infections of Sheep and Cattle Almost all grazing ruminants become infected with damaging gut round worms. These are nearly always dealt with by treating the livestock with drugs, called anthelmintics, which provide effective control if combined with appropriate pasture management. Unfortunately strains of worms resistant to these drugs have evolved and are spreading inexorably. Alternative means of worm control are being sought, one possibility being by vaccination. There are no commercially available vaccines for any round worm species of any host including man. In the last 15 years scientists at Moredun and elsewhere discovered that if proteins were extracted from the surface of the intestinal cells of blood–sucking Haemonchus contortus and used to immunise sheep, then these animals were successfully vaccinated against this important worm. When the worms fed they ingested antibodies the immunised sheep had synthesised in their blood. These antibodies bound to the parasite gut, fatally impairing worm digestion. Trials performed in collaboration with Australian scientists suggested that a Haemonchus vaccine of this type would be highly effective under field conditions in New South Wales, a part of the world where this parasite is rife and where drug resistance is a very serious problem. Unfortunately Haemonchus and the other gut round worm species of ruminants can’t be cultured in the laboratory and can only be obtained from infected animals, a procedure far too costly for making a commercially viable vaccine. The solution is to use biotechnology to engineer micro-organisms to synthesise the precise worm vaccine proteins required cost effectively. Although this procedure has been successfully adopted in Australia for vaccines against cattle ticks and tapeworms, so far no-one has made it work satisfactorily for round worms. Scientists at Moredun are therefore concentrating on overcoming this problem and several promising leads are being pursued. Meanwhile, parallel efforts have focused on trying to get the same vaccine principle adapted for non blood feeding species; the ones which are more important in temperate climes such as exist in the UK. Recent results have been highly encouraging for Ostertagia ostertagi, the most important cattle worm, but curiously the same principle did not work for its sheep equivalent, Teladorsagia circumcincta.
Haemonchus contortus; globally the most important parasite species of small ruminants.
In this Issue E coli infections ………… 3 Patron praises Moredun’s work ………… 3 Protecting your flock from disease ……………
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Moredun’s Viral Surveillance Unit ………
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Roadshow Dates ………
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