A protozoan has become the focus of significant international concern because of its connection with abortion and congenital infection in dairy and beef cattle populations around the world.

According to Dr John Ellis of the Molecular Parasitology group, Neospora caninum infection is common in cattle and dogs in Australia. Annual losses to the Australian dairy and beef industries caused by this parasite have been estimated at $100 million each year.

"Infected adult cattle rarely become ill and do not show any clinical signs of disease," said Dr Ellis. "However, cattle infected by N. caninum are associated with abortion, which in turn leads to increased culling, reduced milk yield and a reduction in value of female breeding cattle."

"In NSW, where the problem has been most extensively studied, abortion due to N. caninum is estimated at 1-5% annually on most dairy farms, but is occasionally reported to be as high as 20% per annum."

A high proportion (approximately 95%) of infected cows infects their offspring. It is also believed that post-natal infection occurs and is responsible for "abortion storms", where a high percentage of cattle abort in a short time.

Dogs are suspected, but not confirmed, of being able to transmit the parasite to cattle. In dogs, the main clinical sign of infection with N. caninum is neuromuscular disease, leading to paralysis of the hind limbs, especially in young puppies.

"Control measures may include protection of feed from dogs (in order to reduce faecal contamination), eliminating the practice of feeding raw offal from slaughtered cows or calves to dogs, and preventing or limiting access of dogs to cattle grazing areas," said Dr Ellis.

Dr Ellis suggested that serological tests may be needed to identify cattle exposed to the parasite, and that while selective culling strategies could be applied, this may be impractical in herds with high levels of infection.

"A better application of serological testing may be in the selection of replacement stock," said Dr Ellis. "A farmer can know the serological status of cows or calves before purchase."

"A test which can accurately predict a Neospora-induced abortion is still required so that cows at risk can be identified early in pregnancy. This would help a veterinarian apply clinical amelioration to enable carriage of foetuses to term which would otherwise have been aborted."

Infections in dogs (if caught early enough) may be treated with drugs, but this therapy is not considered practical for cattle. Vaccines for the control of N. caninum are not available, and no studies on vaccine development for N. caninum have yet been commissioned in Australia.

Serological evidence for human infection by N. caninum has been recently reported from the USA. No studies on prevalence of N. caninum in humans have yet been commissioned in Australia.

"This is a good example of our lack of knowledge about potentially damaging parasites even in domestic species," said Dr Ellis. "It is clear that a great deal of research into N. caninum is required."