Enhancing farmer awareness: Vertical transmission of Neospora caninum in aborting cattle and the value of diagnostics tools

Abstract

The protozoan parasite Neospora caninum is an important cause of abortion in cattle. Infection occurs horizontally by ingestion of oocysts shed by canids or vertically, from an infected dam to the foetus, and may result in abortion, stillbirth, or the birth of subclinically infected offspring. We estimated the occurrence of N. caninum infections in cattle farms with repeated abortions in the canton of Grisons, Switzerland, by serological and molecular methods and investigated risk factors for infection. From March 2021 to March 2022, all available samples (serum/placenta/foetal brain) from cattle, which aborted during this period, were submitted to the Cantonal Veterinary Laboratory for mandatory abortion diagnostic and were additionally tested for N. caninum antibodies (ELISA), or DNA (real-time PCR). Two questionnaire surveys were conducted i) to collect farm and husbandry data for risk factor analysis, and ii) to assess the impact of diagnosis in positive farms and the outcome of control measures. Overall, 488 cattle from 356 farms were tested (488 sera, 247 placentas, 98 foetal brains). Seroprevalence at animal level was 11.3 % (54/488), whereas at herd level it was 14.0 % (50/356). Eighteen (69 %) out of 26 placentas from seropositive dams were PCR-positive. Vertical transmission was confirmed by PCR on foetal brain in 87 % (13/15) of seropositive dams from which this sample was available. All placenta and foetal samples from seronegative cattle were PCR negative. The response rates of the first and second questionnaires were satisfactory with 40.4 % (659/1632) and 46 % (23/50) responding farms, respectively. Due to the low prevalence of infection, no risk factors could be inferred. The second survey revealed that owners of positive farms appreciated the surveillance of N. caninum and requested increasing awareness among dog walkers about the contamination of pastures with dog faeces and the provision of subsidies for prevention and control measures.