VACCINATION OF HYDATIDOSIS DISEASE
Hydatid disease is the common terminology for cysts of the dog tapeworm parasite, Echinococcus granulosus. Cysts slowly grow in grazing animals that have eaten eggs of the tapeworm, and become infective to dogs after 2-5 years.
The life-cycle is completed when dogs eat infective cysts. Humans become accidentally infected with the tapeworm eggs, and suffer hydatid disease because after 5-10 years the growing cysts often interfere with normal functioning of the liver of lung, or other organs where the parasite has lodged.
Hydatid disease is common throughout the world where pastoralism is practiced, and is particularly common in populations where education and hygiene are limited. The control procedures used to eliminate Echinococcosis from Iceland, the Falkland Islands, Tasmania and New Zealand are not sufficiently effective in continental environments.
A vaccine to protect grazing animals against infection is an additional control method that focuses on grazing animals instead of the dog. Most grazing animals are already vaccinated against a parasitic disease can fit into normal farm practice.
A cDNA library was created from E. granulosus oncosphere mRNa, and screened with antibody affinity-purified from a protein molecule which on SDS-PAGE existed as a doublet at 23 and 25kDa (Health and Lawrence, 1996). A number of clones were selected, expressed in the pGEX system (Smith and Johnson, 1988) and tested in New Zealand.
One clone, Eg 95, was the most effective (Light-owlers et al., 1996) and all our work subsequently has used this clone.
This paper described laboratory and field testing of the vaccine produced in bulk in Escherichia coli. Sheep and goats in Xinjiang Uygur Autonomous Province of China and in Chubut Province of Argentina where hydatid disease is endemic, were either given E. granulosus eggs orally, or were naturally challenged by grazing naturally-infected environments. Sheep and cattle in New Zealand were maintained in a quarantine environment and were given E. granulosus eggs orally.