Neosporosis - Cattle

Description

Caused by the protozoan parasite Neospora caninum and is the commonest cause of abortion in dairy cattle. Neospora caninum is similar to Toxoplasma gondii and although the complete life cycle of the protozoa is unknown, the dog has been found to be the definitive host.

Stillborn calves can be born from infected dams and congenitally infected calves may be born with encephalomyelitis. Abortion usually occurs between 5-7 months of gestation but can occur as early as 3 months. Most cases of infection occur via vertical transmission however animals can become infected from their mothers milk, by eating food and water contaminated with dog faeces containing 'Neospora caninum oocysts, or from cow to cow.

Signalment

Neospora has been documented to infect cattle both beef and dairy, sheep, goats and dogs. There is no age predilection.

Diagnosis

The histological appearance of lesions on an aborted fetus can be enough to confirm a diagnosis. Additionally antibodies to the protozoa can be identified via serological methods.

Clinical Signs

Often infected cattle present with no clinical signs other than abortion.

Calves can be born with encephalomyelitis causing various neurological signs such as paresis, decreased reflexes and ataxia.

Repeat abortions are often reported in affected animals due to a persistent infection.

Laboratory Tests

An indirect fluorescent antibody test can be used to detect antibodies from samples and an ELISA is available which will also detect antibodies. A PCR method to identify antigen is currently under development

Pathology

Non-suppurative encephalitis is most commonly seen in aborted foetuses. Additionally non suppurative myocarditis, myositis and widespread non suppurative infiltrates in other organs are often found. Tissue cysts will be present and can be identified.

Hepatitis may also be found in epidemic abortions.

Signs of placentitis will be evident on inspection of the placenta.

Treatment

Dogs should not be allowed access to calving cows, placental membranes and aborted or dead calves

Dogs should also be stopped from defecating in cattle feeding areas.

Seropositive cattle should be identified and culled and none of their progeny should be bred from.

Seronegative cattle should be selected for breeding.

Vaccination is possible but only in the USA. It is a killed protozoal vaccine for healthy, pregnant cows and is given in the first 3 weeks of pregnancy and then every 3-4 weeks during gestation. Revaccination with 2 doses should be undertaken during each subsequent pregnancy.