Molecular Detection and Surveillance of Zoonotic Abortive Agents in Small Ruminants in Tunisia: Epidemiology and Risk Factors

Every year, farmers in Tunisia watch their flocks of sheep and goats with a quiet anxiety. When a pregnant animal loses its young, it is often dismissed as a sad but normal part of life, a routine loss that requires no further thought. Yet, behind this silence lies a complex web of invisible threats. Many of the microbes that cause these losses are not just dangerous to animals; they are zoonotic, meaning they can jump from livestock to humans, posing a dual risk to the economy and public health. For decades, the true scope of this problem in Tunisia remained hidden because the tools used to investigate these losses were limited. Traditional methods could tell researchers that an animal had been exposed to a disease in the past, but they could not confirm if a specific infection was actively causing a current abortion. Without knowing exactly which germ was at work, it is impossible to stop the spread effectively.

To solve this puzzle, a team of researchers from the Tunisian Ministry of Agriculture and the Institut Pasteur de Tunis launched a comprehensive investigation. They set out to replace guesswork with precise molecular detection, scanning for five specific pathogens known to cause reproductive failure: bacteria like Brucella, Coxiella burnetii, Chlamydia, and Salmonella, as well as the parasite Toxoplasma gondii. Over a period spanning from July 2020 to February 2023, the team worked across twenty-four governorates, collecting biological samples from 159 abortion cases on 83 different farms. They gathered vaginal swabs, blood, and fetal tissues, treating each sample with advanced laboratory techniques that act like a highly sensitive searchlight, capable of finding the genetic fingerprints of these germs even when they are present in tiny amounts.

The results revealed a landscape far more active and interconnected than previously understood. The study found that at the herd level, more than sixty percent of the farms involved had at least one of these dangerous pathogens circulating. It was not just a matter of one germ causing one problem; the researchers discovered that nearly a quarter of the infected herds were dealing with co-infections, where two or even three different pathogens were attacking the animals simultaneously. The most common culprits were Brucella and Chlamydia, each found in nearly a quarter of the positive cases, followed by Toxoplasma and Coxiella. Salmonella was rare, appearing in only a tiny fraction of cases. This high rate of mixed infections suggests that the environment on these farms is teeming with multiple threats, making the job of keeping animals healthy even more difficult.

The timing and location of these losses also told a clear story. The data showed a distinct seasonal rhythm, with abortion cases peaking during the autumn and winter months and dropping significantly in the summer. This pattern aligns with the natural reproductive cycle of the animals, where pregnancies reach their most vulnerable stages during the cooler seasons. Geographically, the problem was not spread evenly across the country. The northern and central regions, where farming is more intensive and animal populations are denser, bore the brunt of the infections, while western areas saw far fewer reported cases. In some central governorates, all five of the studied pathogens were found to be circulating at the same time, creating a perfect storm of risk for the local livestock.

Perhaps the most actionable finding of the study concerned how farmers manage their herds. The researchers identified a powerful link between vaccination and disease prevention. Animals that had not been vaccinated against brucellosis were far more likely to suffer from infectious abortions than those that had been protected. The data indicated that the absence of this specific vaccine was the strongest predictor of infection, suggesting that a simple, established preventive measure could drastically reduce losses. Conversely, the study noted a surprising pattern regarding neighboring farms: when abortion was reported on nearby properties, the risk for a specific farm seemed to decrease. The authors suggest this might not mean the disease is less dangerous, but rather that the threat of neighbors being sick makes farmers more vigilant, leading them to adopt better hygiene and biosecurity practices that inadvertently protect their own flocks.

The study also clarified how to best catch these germs when they strike. The researchers found that the type of sample collected and the speed of collection mattered immensely. Vaginal swabs proved to be the most reliable tool, maintaining high detection rates even if collected several days after the abortion occurred. In contrast, blood samples became much less reliable after ten days. This insight is crucial for veterinarians and farmers, as it means that even if an animal loses its young and the event is not reported immediately, a simple swab can still provide a definitive diagnosis. By combining these molecular tools with better timing and a focus on vaccination, the study offers a clear path forward. It moves the conversation from accepting abortion as an inevitable tragedy to viewing it as a manageable health issue, providing the scientific foundation needed to protect both the livelihoods of Tunisian farmers and the health of the people who depend on them.