Neosporosis

Neospora caninum

In some areas, such as north coast of New South Wales, Neospora caninum is thought to be responsible for more than 30% of all abortions in cattle. Initial investigations in North Queensland dairy herds estimate that about 26% of cattle are infected with this parasite. A recent research project on 3,700 beef cattle from 25 management groups across Queensland has shown that Neospora caninum was present in all herds.

Cattle, dogs

The egg producing stage of the life cycle of Neospora caninum occurs in the intestine of wild or domestic dogs. Eggs passed in the faeces of dogs may be ingested by an intermediate host, such as cattle. When the foetal membranes or aborted foetus are eaten by dogs, the parasite will infect the dogs which in turn shed eggs and the life cycle is complete.

Abortion due to Neospora usually occurs between 4–7 months of gestation, but may occur at any time from 3 months to term. Foetuses aborted before 3 months may not be observed, so the role of Neospora at this stage of gestation is not known.

Infected calves may be born showing incoordination and paralysis of the limbs but this is uncommon. Adult cows have no clinical signs of illness following infection.

Within a herd, abortion due to Neospora can be sporadic (low numbers of abortion occasionally) or it may occur as an abortion storm (large number of animals abort within a short period of time), which could be as much as 33% of the breeding herd aborting within a few months. Whether or not an abortion will occur in an infected animal is determined by a number of factors (i.e. the virulence of the strain, the health status and genetic susceptibility of the host and stage of pregnancy when infected).

Most common impacts are:

• abortion and sick calves
• decreased milk yield and weight gains.

In a 2011 study, it was shown that there is a 3–4 times increase in risk of abortion in infected dairy cattle compared to those that are not infected. Recent research has shown that there is no significant difference in reproduction performance between infected and uninfected beef herds.

Some properties may have more than half their cattle infected with the parasite and never encounter any reproductive problems, and then experience an abortion storm where annual abortion rates of 15–20% occur. Although the triggers for these abortion storms are not known, events that suppress the cow's immune system are being investigated (immunosuppressant toxins – which can occur in mouldy fodder – and bovine pestivirus have been suggested).

Researchers in the United States have reported a 5% decrease in milk production in infected first-lactation dairy heifers and decreased weight gains in infected beef cattle.

Study in 1997 showed that the economic impact of N caninum infection in cattle has been estimated at A$85 million per annum for the dairy and $25 million for the beef cattle industry in Australia. The true costs are probably higher, since these calculations only take account of abortion outbreaks.

It has yet to be investigated whether congenitally infected pups produce eggs or if a dog is capable of gaining a second infection after the first one has cleared.

There are 2 major ways of transmission for cattle.

Dog-to-cow (horizontal transmission)

The first is from dog-to-cow via ingestion of dog faeces or contaminated pasture. This kind of infection of a non-pregnant cow results in immunity and will not affect reproductive performance. If the cow is infected during pregnancy, the calf will be infected.

Cow-to-calf (vertical transmission)

The second route of infection is from cow-to-calf during pregnancy. Calves that do not abort are mostly born clinically normal but infected (persistently infected) and will have a 95% chance of giving birth to infected progeny without a dog-to-cow route being involved.

It has been shown that vertical transmission, especially from the persistently infected cattle, is the major route of infection and cycling of the parasite within herds. Recent research demonstrated there was evidence of low rates of dog-to-cow transmission at 70% of the groups. It is highly unlikely that the parasite is transmitted by contact, sexually or through the milk.

Diagnosis of abortion as a result of Neosporosis is best made by a veterinary laboratory through the examination of the aborted foetus for microscopic lesions.

It is important to collect aborted foetuses, chill them (not freeze them) and submit them to the laboratory as soon as possible.

To avoid leptospirosis and Q fever, use protective gloves, seal in plastic bags and refrigerate.

You can contact Biosecurity Queensland to request a test for the detection of antibodies in blood, but this should be conducted as part of a strategic sampling of the herd.

Treatment

There is currently no drug therapy available to treat Neosporosis in cattle.

Control

Limit the access of farm and wild dogs to infectious material, such as aborted foetuses, stillborn calves and afterbirth, and prevent exposure of dog faeces to pastures and stored feed.

Ensure you clean the afterbirth (placentas and/or foetuses) as afterbirth from even non-aborting animals may contain parasites that are infectious to dogs and cattle.

Controlling dog-to-cow transmission

Controlling dog-to-cow transmission alone is not effective enough. Reducing wild dog population in extensive grazing situations may reduce the dog-to-cow infection rate and the infrequent incidence of increased abortions, but it is unlikely to reduce the prevalence of infection as transmission is mainly from cow-to-calf during pregnancy.

Controlling cow-to-calf transmission

On properties with a low rate of dog-to-cow transmission, it may be possible to breed the parasite out of a herd by:

• not including infected cows in the breeding herd
• not breeding replacement heifers from infected cows.

A blood test can help determine which animals are infected, and may be especially useful for studs and pre-purchase testing.

Vaccination

A vaccine is currently available in the United States. However, the vaccine was not capable of preventing vertical transmission of Neospora in cattle and its effectiveness in preventing abortions is still under review.