Bovine neosporosis is the most frequently diagnosed cause of bovine abortion in many countries in Europe and worldwide. It is caused by the protozoan parasite Neospora caninum. The economic impact of the disease involves significant losses due to abortion, premature culling, reduced milk yield and reduced post weaning weight. A recent study conducted at Moredun using aborted bovine foetal tissues, collected from across Scotland, showed that 26% were positive for Neospora caninum.
Cattle may become infected by the ingestion of oocysts shed by infected dogs (horizontal transmission) or through parasite migration during pregnancy to the foetus from persistently infected dams (vertical transmission). Cattle infected with the parasite are 3-7 times more likely to abort than uninfected cattle. Vertical transmission of the parasite is very efficient and infected animals may pass the parasite to their offspring over several generations and in successive pregnancies.
Contributory factors involved in disease pathogenesis include, stage of gestation when parasitaemia and infection of the placenta occur, the maternal immune response, the foetal immune response and potentially genetic variation between different parasite isolates.
Although, host-parasite interactions are relatively well understood, there is no available vaccine in Europe to protect against abortion and information for farmers on how best to control the disease is limited. Research at Moredun has focussed on understanding the host-parasite relationship at different stages of gestation using experimental infection of pregnant cattle. This has helped our understanding of the pathogenesis of disease and the various functions of the maternal immune response (protective versus harmful) and the contribution of foetal immune responses to protection against disease.
Experimental infection of naïve cattle prior to pregnancy will protect against a challenge administered at mid-gestation, causing vertical transmission in a control group of cattle. These experiments, conducted at Moredun, suggest that vaccination may be a feasible option to control the disease in naïve animals.
An important factor with bovine neosporosis is the large numbers of animals born congenitally infected with N. caninum that have no clinical symptoms at birth. Whether these congenitally infected animals pose a higher risk of developing disease in their offspring compared with naïve animals infected horizontally, is not fully understood.
There is a need to develop more sensitive diagnostic tests to allow the accurate detection of infected and carrier animals. Neospora outbreaks are mostly diagnosed by pathological examination of aborted foetuses, foetal serology and maternal serology. Detection methods depend heavily on the condition of the aborted foetus when it is submitted for diagnosis. Assessments of Neospora infections of herds or prevalence rates within herds are done by testing for Neospora specific antibodies. However, antibody titres in persistently infected animals fluctuate and this may lead to negative diagnostic results. This means that a negative result is no guarantee that the animal is not infected with Neospora. Better diagnostic tests are essential for farmers who are trying to either maintain a Neospora free herd when they are replacing stock or when they need to make decisions if and how they can eliminate the parasite from their herd.
The role of dogs in the lifecycle of Neospora caninum was discussed in an edition of Landward, broadcast on BBC Two Scotland on 7th December 2012:
Neospora also featured during a BBC Radio Scotland programme on the problem of dog fouling. Please click below to listen to Moredun's Professor Lee Innes and Nigel Miller, President of the NFUS being interviewed for the piece:
Not a Member?
Moredun membership allows you to keep up to date with the latest advances in livestock health. You can join or renew your Moredun membership online.
Not a Member?
Keep up to date with Moredun's latest research advances by becoming a member now. Join now