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Neospora

Two studies carried out by Moredun and SAC detected Neospora caninum in 22.9% of cattle abortions in the UK, which makes it the most common cause of abortion in the UK.

The parasite is shed in dogs faeces and is picked up by cattle from contaminated water or feed.  Routine dog wormers have no effect on the parasite and many dogs show no signs of infection.

Infection spreads (as tachyzoites) to other tissues in the cow, and if pregnant to the placenta, where damage to the placenta or transmission vertically through the placenta to the fetus can occur. This can result in abortion either as a result of primary damage or the immune mediated inflammatory response of the cow (Maley et al., 2003).

The tachyzoites can transform into bradyzoites (a  ‘dormant’ stage), which remain latent until the immune system of the cow is suppressed.  If this happens then infection can return.  Bradyzoites in tissue cysts can be consumed by dogs so it is important to stop dogs from eating fallen stock or after-birth.

If a non-pregnant animal is infected they become persistently infected.  This means that when they do become pregnant there may be early embryonic death due to recrudescence of the infection. 

Infection or recrudesce in the middle trimester can result in abortion or the birth of a weak or brain damaged live calf (characterised by incoordination).

Infection in the last trimester will result in a seropositive weak or brain damaged calf or a normal calf. It is important to note that  apparently healthy calves can be born to infected dams.  These calves are however, infected and are seropositive to N. caninum antibodies so may abort when they are older.

Transmission by dogs has been considered of relatively minor importance but a Dutch study showed that seropositivity to N. caninum in farm dogs was strongly correlated with a high prevalence of N. caninumantibodies in the cattle. (Wouda et al., 1999).

Dogs that have close contact with cattle and that are fed raw bovine meat are at greater risk of being seropositive

Effects on production

It has been estimated that around 6000 cattle abortions per year may be attributable to N. caninum

Most abortions occur sporadically but occasionally abortion storms may occur, where rates may reach 60%.  It is possible for cattle that have previously aborted due to Neospora infection to have a repeat abortion. 

Infection is thought to reduce milk production in adult dairy cows through its effects on fertility.  Cows which have aborted often produce a lower milk yield and are more likely to suffer retained fetal membranes (Duffield et al., 2001).   An increase in involuntary culling due to abortion can also lead to losses. Neospora infections in young calves have been reported to cause neuromuscular disease and may affect growth rate of finishing animals (Barling et al., 2001).

 Diagnosis

An ELISA is commercially available and used routinely in the UK to test serum samples for Neospora-specific antibodies.   All serological results should be interpreted with caution as antibody levels have been reported to fluctuate so consistent results from multiple tests should ideally be used if making decisions on culling (Haddad et al., 2005).

Barling, K. S. Lunt, D. K. Snowden, K. F. Thompson, J. A. (2001) Association of serologic status for Neospora caninum and postweaning feed efficiency in beef steers. Journal of the American Veterinary Medical Association. 219: 9, 1259-1262.

Wouda W. Dijkstra, T. Kramer, A. M. H. Maanen, C. van. Brinkhof, J. M. (1999) Seroepidemiological evidence for a relationship between Neospora caninum infections in dogs and cattle. International Journal for Parasitology. 29: 10, 1677-1682.

Farm Animal — Last updated on March 14, 2011