Molecular Identification of Neospora caninum Infection in Aborted Fetuses of Sheep, Cattle, and Goats in Mazandaran Province, Northern Iran

Bovine infectious abortion: a systematic review and meta-analysis

The aim of the present systematic review and meta-analysis was to identify the main infectious agents related to bovine abortion worldwide in the period between 2000 and 2022. First, we investigated the global prevalence of infectious agents related to bovine abortion. For this analysis, only 27 articles detected of a wide panel of agents were included. The random effects model revealed that the estimated prevalence of the abortifacient agents in bovine abortion was 45.7%. The heterogeneity among studies was high, but Egger's test showed that there was no publication bias, even though the total number of samples analyzed in these articles was variable. There was no significant effect of the year of the study publication on the estimated prevalence, although an increasing trend was observed over time, possibly due to the implementation of new diagnostic techniques. Then, we analyzed the prevalence of the main transmissible agents in bovine abortion. For this analysis, 76 studies that analyzed 19,070 cases were included. Some infectious agent was detected in 7,319 specimens, and a final diagnosis was reached in 3,977 of these, when both the infectious agent and compatible histopathological changes were detected. We found that Neospora caninum was the most detected agent (22.2%), followed by opportunistic bacteria (21.4%), Chlamydiaceae family (10.9%) and Coxiella burnetii (9.5%). Regarding viral agents, bovine herpes virus type 1 and bovine viral diarrhea displayed similar prevalence rates (approximately 5%). After considering the description of specific histopathological changes, our analyzes showed that N. caninum was a confirmed cause of abortion in 16.7% of the analyzed cases, followed by opportunistic bacteria (12.6%) and Chlamydia spp. (6.8%); however, C. burnetii was only confirmed as a cause of abortion in 1.1% of the cases. For all agents, the heterogeneity among studies was high, and the subgroup analyzes discarded the diagnostic method as the cause of such heterogeneity. This study provides knowledge about the global prevalence of the different infectious agents related to bovine abortion, the most coming of which is N. caninum. In addition, this review reveals the existing deficiencies in the diagnosis of bovine abortion that must be addressed in the future.

Ovine Neosporosis: The Current Global Situation

Simple Summary

This review summarizes the current global situation of Neospora caninum infection in sheep by referring to all of the available descriptions of natural ovine neosporosis to date, focusing on epidemiology, clinical signs, lesions, and diagnosis. The data suggest that ovine neosporosis is more prevalent than currently thought, that it has increased in the last few decades, and that it should now be considered in the differential diagnosis when investigating abortion in sheep.

Abstract

In the past 20 years, Neospora caninum infection in sheep has been reported in at least 31 countries worldwide from all sheep-rearing continents (Europe, Asia, the Americas, Africa, and Oceania), and its role as an abortifacient agent is becoming more evident. Most studies of ovine neosporosis have focused on its epidemiology, based primarily on serological analysis, with only a few studies investigating the actual presence of the parasite by PCR and/or IHC. Individual seroprevalence rates were highly variable between countries, and even between regions within the same country, ranging from 0.0% to 67.4% positive. Furthermore, most of the studies were not directly comparable due to differences in experimental designs, sample sizes, husbandry systems, ecological factors, and serological tests (e.g., IFAT, ELISA, MAT, Western blot). The latter, along with the scarcity of studies on the relevance of N. caninum as an abortifacient agent, may bias the perception of the importance of this disease. This review summarizes the situation of N. caninum infection in sheep using all available published studies describing natural ovine neosporosis. The epidemiology shows that ovine neosporosis is found worldwide, and it poses a relevant risk to the sustainability of sheep flocks.

The Global Prevalence of Neospora caninum Infection in Sheep and Goats That Had an Abortion and Aborted Fetuses: A Systematic Review and Meta-Analysis

Neospora caninum (N. caninum) can be a potential factor causing a significant rate of miscarriages in small ruminants (sheep and goats) worldwide. Therefore, the present study aimed to determine the global status of N. caninum in sheep and goats that had an abortion and aborted fetuses. Five English databases (PubMed, ScienceDirect, Web of Science, Scopus, and ProQuest) were searched for relevant scientific articles published from their inception until November 4, 2021. Finally, 21 studies conducted on sheep (1,671 aborted fetuses and 935 abortive sheep) and 10 studies on goats (130 aborted fetuses and 80 abortive goats) were included for the final meta-analysis. A random-effects meta-analysis model was used to estimate the pooled prevalence with 95% confidence intervals (CIs). Moreover, sensitivity analysis, publication bias test, and quality assessment were performed in this study. The pooled prevalence of N. caninum in aborted fetuses of sheep and goats globally was estimated to be 15% (95% CI: 9-21%) and 7% (95% CI: 2-12%) using molecular methods. Besides, the seroprevalence of N. caninum was estimated to be 17% for aborted fetuses of sheep. The overall prevalence rate of N. caninum infection in sheep that had an abortion was 3%. The present results show a relatively high prevalence of N. caninum infection in sheep that had an abortion and aborted fetuses compared to goats. Therefore, further studies using different diagnostic techniques to more accurately estimate the rate of infection in sheep and goats may help provide adequate control measures and strategies to reduce the rate of abortion in sheep and goats and reduce economic damage to the livestock industry. This study was registered at the International Prospective Register of Systematic Reviews (PROSPERO; code: CRD42020216694).