Recent advances in understanding the epidemiology of Neospora caninum in cattle

INTRODUCTION: Neospora caninum is the most frequently diagnosed cause of ca ttle abortion in New Zealand and is an important pathogen worldwide. The pa rasite has been found in aborted bovine foetuses and in puppies with neurol ogical disease. Recent developments have provided new insights into the epi demiology of the disease that are reviewed in this article. TRANSMISSION: Transplacental infection is of major importance in the spread of N. caninum overseas. Most congenital infections result in the birth of apparently healthy calves. Seroepidemiological studies indicate introduced point-source infections are also likely, as do investigations of abortion o utbreak in cattle herds attributed to N. caninum. Horizontal transmission i s an important determinant of the stability of infection prevalence in a he rd. Two potential sources of horizontal transmission that have recently bee n reported are: via a canine definitive host and; cow-to-calf transmission through pooled colostrum or milk Transmission parameters for the organism h ave been estimated using mathematical modeling, to explore the epidemiology and options for control of N. caninum infection in dairy cattle in the abs ence of precise epidemiological data. LIFE-CYCLE: Seroepidemiologic studies, combined with the knowledge that dog s can be a definitive host, provide evidence supporting a dog-cattle life-c ycle. The importance of dogs in the epidemiology of bovine neosporosis is n ot yet clear. It is likely that N. caninum oocysts in dog faeces could serv e as a source of infection for cattle and recent studies have shown that th e canine and bovine isolatesflare the same organism. Infection of cattle or ally exposed to oocysts has been demonstrated experimentally but not in nat ure. It is not known if other wild carnivores may serve as definitive hosts of N. caninum. CONCLUSION: Despite active research for over a decade, very little is known about the mechanisms of transmission of N. caninum. Vertical transmission is well documented but horizontal spread and the pathogenesis of abortion f rom this disease need further investigation. It is evident that, even with a very high probability of vertical transmission, some form of horizontal t ransmission is required for the disease to persist in a herd.