References
Neospora in UK cattle
Abstract
Neosporosis was first identified in the 1980s and has since become well established as an endemic disease of cattle and a significant cause of abortion. Neospora caninum is an obligate, intracellular, protozoal parasite that relies on intermediate and definitive hosts to complete its lifecycle. Neospora infection leaves cattle three to thirteen times more likely to abort than a healthy animal. Calves may be born alive but be latently infected owith Neospora or have obvious defects. Disease transmission can be horizontal, when cattle ingest feed contaminated with infected dog faeces that results in latency or exogenous transplacental infection, or vertical when latent infection recrudesces, producing a congenitally infected calf. Testing involves serology or direct testing if abortion material is available. Serology can provide a presumptive diagnosis when carried out near in time to an abortion event. Eradicating the disease involves identifying infected cows and infected family lines through serology and removing these individuals from the herd. This approach takes time because seropositive cows do not always return positive tests, and in a herd with a high seroprevalence it is not economically viable to remove large numbers of animals.
Infections caused by Neospora caninum were first described relatively recently, having first been identified in dogs in 1984 (Bjerkås et al, 1984), differentiated from Toxoplasma gondii in 1988 (Dubey et al, 2007) and identified in dairy cattle in New Mexico in 1989 (Thilsted et al, 1989). During the past 30 years, neosporosis has become well established as an endemic disease of cattle in many countries and a significant cause of abortion in cattle. It is an obligate intracellular protozoal parasite, which relies on both intermediate and definitive hosts to complete its lifecycle. The impact of neosporosis on health, welfare and economics of farming systems is being recognised via control programmes implemented by milk suppliers (Sainsbury Plc, 2021) and farm assurance schemes (Red Tractor, 2022).
The main clinical presentation in Neospora-positive cattle is abortion from 5–7 months of gestation and can occur as early as 4 months (McAllister, 2016). Seropositive cows are three to thirteen times more likely to abort without any concurrent signs in the dams (Hall et al, 2005; Wouda et al, 1998). Aborted fetuses can be fresh, autolysed or mummified (Figure 1), depending on the time between fetal death and expulsion of fetal material (McAllister, 2016). If calves are born alive, they may be clinically normal, latently infected (but apparently normal) or have obvious defects. These defects can include being born prematurely, noticeably small, ataxic, recumbent, having poor conscious proprioception and/or reduced patellar reflexes (Figure 2) (McAllister, 2016). Dams may subsequently suffer from retained fetal membranes or metritis, as they would with any abortion.
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