New African buffalo study provides insight into persistence of highly contagious pathogens

A new study from Oregon State University on foot-and-mouth disease in buffaloes in South Africa could help explain how certain highly contagious pathogens can persist and become endemic in a population, long after they are they burned their initial pool of sensitive topics. hosts.

The results, published in Science Magazine, are particularly relevant as the world’s human population draws closer to the second anniversary of the COVID-19 pandemic, and researchers and policymakers face the reality that the virus is not going away anytime soon.

The study raises the same question that many are now asking about COVID-19, said lead author Anna Jolles, professor of epidemiology at OSU’s Carlson College of Veterinary Medicine with a dual appointment to the College of Science. After responding to the disaster situation, what happens next?

“Is there a way to really limit the infection after it becomes endemic?” she said. “A study in a lab can’t answer that, because it’s a population-wide question, and in the lab you don’t have whole animal populations and all the variation among hosts, pathogens or the environment. Searching for wild hosts is one way to get a glimpse of how this might unfold. “

Co-authors of the article include OSU Assistant Professor Brianna Beechler and Associate Professor Jan Medlock.

Foot-and-mouth disease does not cause serious illness in buffaloes, but when it spreads to cattle and other hoofed species, it can cause painful sores in the mouth and on the feet. It does not infect humans.

The study examined the mechanisms of transmission of three main strains of the foot-and-mouth disease virus among buffalo herds in Kruger National Park in South Africa: SAT1, SAT2 and SAT3. Researchers tested blood and tissue samples from a wild herd every two to three months from 2014 to 2017 and observed the dynamics of infection in a captive group of buffaloes at shorter time intervals for six month.

“A lot of studies and a lot of press on highly contagious pathogens focus on the ‘forest fire’ stage, when the pathogen passes through the population and people are trying to predict how far it will go and what fraction of it. the population will be infected in the epidemic stage, “Jolles said.” But once that wildfire stage has passed, then where does this pathogen go? This is what we are focusing on. “

The researchers were basically trying to think like a virus: what is the best way for a pathogen to spread within a given buffalo population, and how does it survive lean periods when there are very few hosts susceptible to infect?

Since foot-and-mouth disease is so contagious, almost all buffaloes in the regions where it occurs contract local strains of the virus and acquire some level of immunity fairly early in their life. But young calves are susceptible to infection after around 4-6 months when they lose their maternal immunity, so transmission among severely infected young buffaloes was the main route investigated by researchers. After buffaloes recover from acute infection, some keep the virus in their tonsils, where it can lie dormant for months. The second route of transmission, which the researchers speculated would be less effective, was through these carrier animals.

The buffalo birth season lasts almost six months, so it was previously thought that it would be possible for the virus to remain in the most recent calves of the past year long enough to infect calves born earlier the following year. . However, the results of this study showed that foot-and-mouth disease would not persist in buffalo populations with only this mode of transmission “infantile infection”.

And unlike previous studies which found almost no evidence of carrier transmission, the OSU study documented carrier transmission among two out of three strains, SAT1 and SAT3, albeit at a rate about 100 times lower than the rate. of acute transmission among actively infected animals. Researchers have found that even this low rate of carrier transmission allows SAT1 and SAT3 to persist.

SAT2 seems to work differently. Even though it is transmitted quickly during acute infection, it works “pathetically poorly” on carrier transmission, Jolles said. Researchers have yet to determine exactly how the strain persists. It has a high mutation rate, so they hypothesize that, like the flu in humans, it could change so much and so quickly that the buffalo’s immune system no longer recognizes the virus.

While buffalo herds may be geographically confined, the global human population is more interconnected than ever before, Jolles said, making it easier for pathogens to become endemic and persist in the long term.

“This pandemic was not an unexpected thing, in a general sense,” she said. “You would expect other pathogens to spread through human populations. We’re so wide open for that; there are so many of us and we’re so well connected, it really is a giant playground for them. Pathogens.”

Due to the size of the population, Jolles said it would be very difficult to prevent the persistence of a virus like COVID-19 around the world, but public health interventions can help limit transmission and endemicity. at local level.