Abortion bug is spreading fast in dairy cattle
By Sue Rider
VETS are investigating a new parasite that causes abortion in cattle.
Veterinary investigation centres recorded a 4.2% incidence of the bug, known as neospora, in aborted foetuses over a six-month period ending January 1995.
First discovered in the UK about 12 months ago (News, Mar 29, 1994), it is now thought to be more common in aborting cattle in Britain than leptospirosis. Evidence suggests 5-10% of all abortions in the national dairy herd are caused by neospora. That represents some 2000 dairy cows – twice the number that abort due to leptospirosis.
Studies have also found neospora in the USA, New Zealand, Australia, Japan, South Africa, Canada, Sweden and the Netherlands.
It causes abortion at any stage of pregnancy and is said to be similar to the parasite which causes toxoplasmosis, and abortion, in sheep.
But evidence from Liverpool University suggests that unlike toxoplasma, neospora can infect cattle permanently, causing repeat abortions and reduced fertility.
US research also suggests it is possible that cows infected once can go on to produce a live calf that will also be infected.
Spread of infection from cow to calf is currently the only known mode of transmission. But it is suspected the parasite has a carnivorous host which could spread infection to cattle from its faeces. It is not clear whether it is bird or animal. Vets do not know how to prevent or control infection.
"Neospora is a far bigger threat than leptospirosis," says the universitys Prof Alexander Trees. "Because it is vertically transmitted it blights breeding stock."
Vets advise producers with unusually high levels of abortion in their herd to seek a thorough vet examination of the foetus.
Like toxoplasma, neospora could potentially infect humans, with pregnant women most at risk, though vets have no evidence of this.