During the calving season, I unfortunately have had to investigate some abortion issues on farms.
The cause of abortion in a few cases has been identified as Neospora.
In this article, I have decided to explore Neospora, and what we can do to minimise its effect.
Neosporum caninum is a protozoan parasite of animals. It is a major cause of abortion in cattle and can be isolated from an aborted foetus.
It is identified in a large number of foeti submitted to the regional laboratories every year.
The dog is the definitive host for the parasite, which means the reproductive stage of the parasite occurs in the intestinal cells of the dog, and the eggs pass out in its faeces.
If the eggs are ingested by the cow, this will continue the life cycle of the parasite.
Once a cow ingests the eggs, referred to as horizontal transmission, it releases rapidly growing and motile tachyzoites.
These tachyzoites are attacked by the cow’s immune system, and convert to slow-growing bradyzoites, which can encyst in the cow’s muscle, nervous system, or placenta.
Calves born to previously infected cows are at risk of becoming infected, due to encysted bradyzoites being activated during pregnancy.
This is vertical transmission, and up to 80% of calves out of infected cows are infected as well.
This is the most common way an infection is maintained on a farm.
Abortions are the result of direct infection of the calf in the womb, or damage to the placenta.
Abortion can be from a newly acquired infection (horizontal transmission), or a re-occurrence within a persistently infected cow (vertical transmission).
Infected cows have an increased risk of abortion, with abortion storms seen on some farms.
Abortion is generally seen at 3-8 months of gestation, with mummification also seen.
Infected calves can be born weak, and neurological signs can also be seen, such as slow to rise, or a poor suck.
Foetal deformities can also be attributed to neospora infection.
Studies have indicated that milk production and milk solids of infected animals can also be affected.
There is no indication that bulls are a risk of spreading neospora.
The definitive host, dogs or foxes, can show anything from no clinical signs to symptoms such as diarrhoea, pneumonia, skin disease and neurological signs.
Testing for neospora is quite straightforward.
Bulk milk ELISA is helpful for surveillance at a herd level. In a herd with no infection, or seronegative, an increase in bulk tank ELISA will indicate recent infection.
Individual blood testing of all breeding animals is required to identify which animals are infected, as this will affect control strategy decisions.
The daughters of sero-positive animals should also be tested.
Your vet is best placed to help devise an on-farm control policy.
A control strategy to reduce vertical transmission, cow-to-calf, may include the following options:
Embryo transfer of high genetic merit embryos from a sero-positive cow to a seronegative recipient can protect a foetus from being born infected.
The best policy will depend on infection rate on the farm, as well as the genetic value of the animals in question.
It is essential to keep aborted foetuses and all placentas away from dogs and foxes.
Cattle feed must be securely stored away from dogs, cats and wildlife.
It is however, impossible to keep dog or fox droppings away from pasture.
Rodent control is also important, as they may also be a risk in the spread of neospora.
There is no vaccine currently available in Ireland.
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