RIGHT David Black and Miriam Hedley of Paragon Vet Group.


is infected for the fi rst time by consuming food or water contaminated with Neopspora oocysts as a result of it being contaminated with dog faeces.


The parasite circulates in the blood and again crosses over into the placenta and foetus. This pattern of disease seems to manifest as abortion storms on farms that were not previously affected and is often explained by infection having arrived from the outside at a given time, such as through contaminated feed or water. The outcome of Neospora infection is affected by the stage of pregnancy when the cow was fi rst exposed to the parasite.infected.


When a cow is early in pregnancy the foetus dies and the cow will abort or reabsorb so nothing may be seen, except a cow expected to be in calf returning to heat. But, when a cow is infected in mid pregnancy, disease results either in abortion or calves born early or with severe problems.


And when a cow is infected in late pregnancy it is less likely to be fatal as the foetus has a more mature im- mune system. The calf is likely to be born healthy, but it will be infected.


This last point demonstrates how congenitally infected heifers, when used for breeding, will pass Neospora on to the next generation and so the parasite is able to persist and spread on a farm. Animals infected via contaminated feed or water during early to mid gestation will usually abort. However, in herds where a high degree of infection already exists and the cow is already infected when she becomes preg- nant, infection is readily passed on to the calf, but abortion is much less common. It is thought that in these cows, the parasite does not leave the tissue cyst and circulate in the blood stream until the second half of pregnancy. At which point the calf’s immune system is able to cope with the infection. Diagnosis of Neospora can be diffi cult. As discussed above, very early foetal infection can result in reabsorp- tion of the foetus and the cow returns to service. This may give the appearance of infertility. Several animals returning to service in what would be mid-cycle is suggestive of early foetal death and potentially neosporosis. Later abortions provide a better chance of diagnosis. It is important that in these cases, the foetus and at least part of the placenta, alongside a blood sample from the dam is taken to the lab as soon as possible. The fresher the sample the greater the chance of a diagnosis.


The placenta and foetal brain are examined for signs of damage caused by the parasite or the parasite itself. A blood sample from the dam is not particularly useful alone. A positive result only indicates that the cow has been exposed to Neospora, not when, so it cannot be defi nitively given as the cause of that particular abortion. However, in conjunction with testing on the foetus and placenta the result can be much more meaningful. Unfortunately there is currently no treatment for Neospora and no vaccine licensed for use in Europe.


THE JOURNAL FEBRUARY 2015 101


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