Unvaccinated Goats as Sentinel Animals for foot-and-mouth disease virus surveillance at the Wildlife– Livestock Interface: Serological and Molecular Evidence
A three-year surveillance study in India demonstrates that unvaccinated goats effectively serve as sentinel animals for detecting silent Foot-and-Mouth Disease virus circulation at wildlife–livestock interfaces, evidenced by declining serological and molecular markers of natural infection alongside increasing protective immunity in vaccinated bovines.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Foot-and-mouth disease is a highly contagious viral illness that affects animals with split hooves, such as cattle, buffalo, sheep, and goats. The virus causes fever and painful sores in the mouth and on the feet, leading to severe suffering and massive economic losses for farmers. In India, where millions of cattle and buffalo are raised, the government runs a rigorous vaccination program to protect these animals. The vaccines are effective at preventing the visible signs of the disease, but they do not always stop the virus from circulating quietly within a herd. When vaccinated animals get infected, they often show no symptoms, making it difficult for veterinarians to know if the virus is still present. To solve this, scientists look for specific markers in the blood that indicate a natural infection occurred, separate from the effects of the vaccine. However, in areas where wild animals and livestock share the same grazing lands, tracking this silent virus is particularly difficult.
In a three-year study conducted in the forests of central India, researchers explored a new way to monitor the virus at the edge where wildlife and domestic animals meet. The study focused on two tiger reserves, Sanjay Dubri and Bandhavgarh, where villagers let their livestock graze near wild herds of deer and other animals. While the cattle and buffalo in these villages received regular vaccinations, the goats did not. Because goats were not vaccinated, any sign of infection in them would be a clear, unambiguous signal that the virus was active in the environment. The research team treated these unvaccinated goats as sentinels, or early warning systems, to detect the virus even when the vaccinated cattle appeared healthy.
The scientists collected blood samples from thousands of animals between 2021 and 2023. They tested the blood for two types of antibodies. One type appears after an animal receives a vaccine or gets infected, while the other type appears only after the animal's body fights off a natural infection. In the vaccinated cattle, the researchers found that the protective antibodies from the vaccine were increasing over time, showing the program was working. However, they also found the infection-only antibodies in many of these cattle, proving that the virus was still circulating despite the vaccinations. In the unvaccinated goats, the results were even more telling. The goats showed clear evidence of natural infection, with a significant number testing positive for the infection markers. This confirmed that the virus was moving through the population, infecting animals that had no protection from vaccines.
The study also looked for the virus itself in the fluid from the animals' throats. In the first year of the study, nearly half of the goats that had been exposed to the virus were actively shedding it. By the third year, this number had dropped significantly, mirroring a similar decline seen in the cattle. This parallel drop suggested that as the herd immunity in the cattle grew stronger through repeated vaccinations, the overall amount of virus in the environment decreased. The researchers managed to isolate the virus from two cattle samples in 2023 and analyzed its genetic code. They found it belonged to a specific lineage of the virus that has been circulating in India since 2019. Although they could not sequence the virus from the goats, the fact that the goats were infected at the same time and place as the cattle strongly suggested they were part of the same transmission chain.
The findings suggest that unvaccinated goats can serve as a powerful tool for disease surveillance. In areas where vaccination makes it hard to spot the disease in cattle, the goats act as a sensitive indicator, revealing the presence of the virus when it might otherwise go unnoticed. The study did not find evidence of the virus jumping from wild animals to livestock, but it did confirm that the virus persists in the landscape where domestic and wild animals interact. By monitoring these unvaccinated animals, health officials can get a clearer picture of whether the virus is truly under control or if it is still hiding in the population. This approach offers a practical way to strengthen disease control programs, ensuring that even when clinical signs disappear, the virus does not remain undetected.
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