Parasite takes Toll on Cattle

22 April 2002

A new study funded by the Wellcome Trust biomedical research charity has been launched to discover how a parasite, that lies dormant in a cow's brain, causes thousands of spontaneous calf abortions.

The parasite, Neospora caninum, which was first identified in dogs, is believed to be responsible for around 6,000 abortions annually in the UK and many more around the world.

The disease can cause financial problems for farmers and in the most severe cases force them out of business.

The new study being led by Dr Diana Williams and colleagues at the Liverpool School of Tropical Medicine and Faculty of Veterinary Science, is aimed at revealing exactly how the parasite causes abortions and will hopefully eventually lead to a vaccine being developed.

Peter Rudman, Veterinary and Public Health Advisor at the National Farmers' Union said : "Any research which sheds light on the way this killer works will be invaluable for farmers who are under attack from all quarters in the current harsh climate."

Dr Williams, a lecturer in veterinary parasitology, said Neospora caninum infection was a "timebomb" for many farmers: "They may select a particular family of cows not knowing that they have the disease because there are no outward signs," she said. "And even those that are infected do not always suffer abortions. So they will breed and pass on the disease to their offspring who will do likewise.

"But then, for whatever reason, some of them will have abortions which can hit their owners very hard, especially when you think that one cow can be worth £1,500. We have worked with some farmers over the years who have been forced out of business through it. There is no cure or vaccine so the animals have to be culled.

"The disease has been prevalent for some years but there are still some farmers who do not know about it."

Neospora caninum was first seen in Norwegian dogs in 1984 and identified in the UK in 1989. It is estimated to be responsible for around 13% of all dairy cattle abortions in this country and is also prevalent in North and South America, Europe, Africa, Australia and New Zealand. It also affects beef herds but much less is known about the disease in beef cattle.

The parasite lies dormant in the host cow's brain, causing it no ill-health, but seems to be activated once pregnancy occurs, spreading through the body and passing through the placenta into the foetus.

Dr Williams and her colleagues are looking at two possible theories. The first hypothesis works on the basis that as the mother tries to control the ever-increasing parasites the delicate balance between foetal and maternal immune systems is disrupted.

"Since it's obviously in the mother's interest not to be killed by the activation of the parasite we think the foetus loses the battle and dies, leading to abortion.

"But there is another suggestion that the foetal immune system only develops during the second half of pregnancy. This would mean a foetus exposed to parasites very early on has no way of controlling their growth and it could be the invasion into the foetus as opposed to the mother's immune response which is causing the abortion."

The parasite is normally passed from mother to calf but Dr Williams said there is an outside chance it could also be transmitted through dog faeces.

Dr Williams will be assisted by Dr Peter Kaiser from the Institute of Animal Health in Compton, Berkshire and Dr David Bainbridge from the Royal Veterinary College in London.

Notes to editors:
The Wellcome Trust is an independent, research-funding charity, established under the will of Sir Henry Wellcome in 1936. The Trust's mission is to foster and promote research with the aim of improving human and animal health. For more information, visit www.wellcome.ac.uk

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