1 Oct 2021
Pirbright researchers studied what happens to foot-and-mouth disease between outbreaks and how it is able to maintain itself in a population once the initial infection is over.
Joshua Silverwood
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Image: Pixabay
A new study undertaken by scientists at a Surrey research institute and a South African national park has shone light on how foot-and-mouth disease (FMD) persists.
Researchers representing a joint coalition of The Pirbright Institute, Kruger National Park and the Onderstepoort Veterinary Institute in South Africa, as well as Oregon State University in the US, have been working to understand how FMD continues to persist in the wildlife reservoir of African buffalo.
The aim was to work out what the virus was doing between outbreaks and how it was able to maintain itself in a population once the initial “wildfire” infection was over.
FMD is extremely contagious and able to infect entire buffalo populations in areas where it is circulating, providing some level of immunity in young animals. This immunity wanes considerably at around four to six months of age when young calves lose their maternally derived antibodies, making them susceptible to infection.
Researchers focused on this as a primary path of transmission in the study, as well as investigating a second transmission route via carrier animals.
The study found that in the primary transmission group all naive animals became infected and became carriers. Unlike previous studies, the researchers were able to show that carrier transmission does occur, but at a rate considerably lower than in primary infection.
Scientists used mathematical models to establish that none of the strains would be able to persist in populations from one birthing season to another if the buffalo didn’t become carriers and, therefore, that “childhood infection” alone is not sufficient to explain how the virus becomes endemic.
Simon Gubbins, head of transmission biology at The Pirbright Institute, said: “Why does a virus that spreads so rapidly – R numbers greater than 20 or more have been reported – need to persist at low levels?
“Our work shows this long-term carriage in the reservoir host allows the virus to persist in an immune population until new susceptible animals become available.”
Pirbright director Bryan Charleston added: “It is also clear from our previous research that new virus variants are produced during this long-term carriage.
“Another important finding from this study is that some viruses transmit efficiently from carriers, but other strains of the virus do not. Buffalo sometimes mix with farmed cattle causing outbreaks of disease, in other cases there is no transmission.
“Our work suggests one of the reasons for this difference depends on the virus variant the buffalo are carrying.”
