Study on African buffalo offers insights on persistence of highly
contagious pathogens

Date:
September 30, 2021
Source:
Oregon State University
Summary:
A new study on foot-and-mouth disease among buffalo in South Africa
could help explain how certain extremely contagious pathogens are
able to persist and reach endemic stage in a population, long after
they've burned through their initial pool of susceptible hosts.



FULL STORY ==========================================================================
A new Oregon State University study on foot-and-mouth disease among
buffalo in South Africa could help explain how certain extremely
contagious pathogens are able to persist and reach endemic stage in
a population, long after they've burned through their initial pool of susceptible hosts.


==========================================================================
The findings, publishing in ScienceMagazine, are particularly relevant as
the world's human population is closing in on the two-year anniversary
of the COVID-19 pandemic, and researchers and policymakers are facing
the reality that the virus is not going away anytime soon.

The study raises the same question that many are asking now about
COVID-19, said lead author Anna Jolles, an epidemiology professor in
OSU's Carlson College of Veterinary Medicine with a dual appointment in
the College of Science. After responding to the disaster situation, what happens next? "Is there any way of really limiting the infection after
it becomes endemic?" she said. "A study in a lab can't answer that,
because this is a question at the population scale, and in the lab you
don't have whole animal populations and all the variation among hosts, pathogens or the environment. Looking in wild hosts is one way to get
insights into how this can play out." Co-authors on the paper include OSU assistant professor Brianna Beechler and associate professor Jan Medlock.

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



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

"A lot of studies and a lot of press on very contagious pathogens focus on
the 'wildfire' stage, when the pathogen is running through the population
and people try to predict how far it will go and what fraction of the population will become infected in the epidemic stage," Jolles said. "But
once that wildfire stage has passed, then where does that pathogen
go? That's what we're focusing on." Researchers were essentially trying
to think like a virus: What's the best way for a pathogen to spread within
a given buffalo population, and how does it survive the lean times when
there are very few susceptible hosts to infect? Because foot-and-mouth
disease is so contagious, almost all buffalo in regions where it is
present contract the local strains of the virus and achieve some level
of immunity fairly early in life. But young calves are susceptible to
infection after around 4-6 months of age when they lose their maternally derived immunity, so transmission among acutely infected young buffalo
was the primary pathway researchers analyzed. After buffalo recover from
acute infection, some retain virus in their tonsils, where it can lie
dormant for months. The second transmission route, which researchers hypothesized would be less effective, was via these carrier animals.

Buffalo birthing season lasts nearly six months, so it was previously
thought that it might be possible for the virus to remain in the
latest-born calves of the past year long enough to infect the earliest
born calves the following year. However, results from this study showed
that foot-and-mouth disease would not persist in buffalo populations
with only this "childhood infection" pattern of transmission.



==========================================================================
And contrary to past studies that 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 less than the rate of acute transmission among actively infected
animals. Researchers found that even this low rate of carrier transmission allows SAT1 and SAT3 to persist.

SAT2 appears to work differently. Even though it transmits quickly
during acute infection, it performs "pathetically poorly" on carrier transmission, Jolles said. Researchers have yet to pin down exactly how
the strain persists. It has a high mutation rate, so they hypothesize
that similar to the flu in humans, it might change so much and so rapidly
that buffalos' immune system no longer recognizes the virus.

While buffalo herds can be geographically contained, the global human population is more interconnected than ever before, Jolles said, so it's
easier for pathogens to become endemic and persist long-term.

"This pandemic was not an unexpected thing to happen, in a general
sense," she said. "One would expect other pathogens to spill into human populations. We're so wide open for it; there are so many of us and we're
so well connected, it's really a giant pathogen playground." Due to
population size, Jolles said it will be very hard to prevent persistence
of a virus like COVID-19 globally, but public health interventions can
help limit transmission and endemicity at the local level.

========================================================================== Story Source: Materials provided by Oregon_State_University. Original
written by Molly Rosbach. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Anna Jolles, Erin Gorsich, Simon Gubbins, Brianna Beechler,
Peter Buss,
Nick Juleff, Lin-Mari de Klerk-Lorist, Francois Maree, Eva
Perez-Martin, O.L. van Schalkwyk, Katherine Scott, Fuquan Zhang,
Jan Medlock, Bryan Charleston. Endemic persistence of a highly
contagious pathogen: Foot- and-mouth disease in its wildlife
host. Science, 2021; 374 (6563): 104 DOI: 10.1126/science.abd2475 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210930160449.htm

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