Review of the Food-borne Zoonoses Research ... - ARCHIVE: Defra

Project code: OZ0404
Project title: Bovine neosporosis: the evaluation of zoonotic risk
and the development of evidence-based control
strategies
Start date (dd/mm/yy): 01/11/2002
End date (dd/mm/yy): 31/12/2005
£242,267.00
Total cost:
Affiliation: University of Liverpool
Abstract of research
The newly recognised protozoan parasite Neospora caninum has recently emerged as a
major cause of disease in cattle and dogs worldwide (1). In cattle, research by various
international groups, including our own laboratory in a previous DEFRA funded research
project (Contract CSA 3618, 1996 - 1999), has shown the importance of the infection in
the etiology of abortion and the significance of vertical transmission in its epidemiology.
This project concentrated on the recently discovered oocyst stage of N. caninum. It
sought to improve rational control measures in cattle by determining if, and under what
circumstances, oocysts could infect pregnant cattle and cause disease, what risk factors
exist and how likely are oocysts to infect the environment. The existence of
environmental contamination by oocysts also creates a potential zoonotic hazard which
was evaluated in a large scale human serological study.
The project failed to find any evidence of exposure to infection in over 3700 human
serum samples rigorously selected and examined by two assays. The results show that
the risk of human infection in the UK is extremely low and that millk and meat from UK
cattle can be regarded as safe in this respect.
In cattle, the project showed that oocyst infection in pregnancy can lead to abortion in
cattle if exposure occurs around mid-pregnancy but not if it occurs early or late in
pregnancy. However, exposure at 210 days in pregnancy led to high rates of congenital
infection in healthy calves. Thus oocyst infection is likely to be extremely important in
maintaining the basic reproductive rate of the parasite at >1 by creating infected females
which are then presumed to endogenously transplacentally infect all their offspring.
Review Summary
Overall the project has generated some important findings, specifically the lack of
evidence for human infection and zoonotic transmission, and the lack of associated
evidence that dogs were a major source of oocyst infection to cattle. Also important was
that although oocysts can infect pregnant cows and cause abortion or congenital
infection, epidemiological risk factors suggested that the likelihood of this occurring was
low.
The results of this research have clearly answered the policy question on zoonotic risk
and have shown that, if a zoonotic risk to humans exists in the UK, it is very low. The
69