New research shows that in sub-Saharan Africa the virus
responsible for foot and mouth disease (FMD) moves over relatively short
distances and the African buffalo are important natural reservoirs for
the infection. The study, published in mBio®, the online
open-access journal of the American Society for Microbiology, sheds
light on how the type of FMD virus called SAT 2 emerged in sub-Saharan
Africa and identifies patterns of spread in countries where SAT 2 is
endemic.
"The data suggest that the common ancestor of all SAT 2 was in
[African] buffalo. It's very clear that historically infections have
moved from buffalo to cattle," says corresponding author Matthew Hall of
the University of Edinburgh in Scotland.
Foot and mouth disease (FMD) is devastating to livestock all over the
world, but it's a particular problem in Africa, where wildlife that
harbor the virus are thought to pass it on to their domesticated
cousins.
FMD strikes cloven-hoofed animals, presenting as a high fever,
blistering in the mouth and feet, decline in milk production in females,
and weight loss. Although most animals recover over the course of
months, some die of complications from the disease. In wild buffalo, the
disease is very rarely symptomatic and animals can be persistently
infected for a period of several years. The SAT 2 serotype of the virus
is endemic in sub-Saharan Africa, but it has crossed the Sahara and
caused outbreaks in North Africa and the Middle East between 1990 and
2012.
In the hopes they could eventually predict future outbreaks, Hall and
his colleagues wanted a better picture of the diversity of SAT 2
viruses in sub-Saharan Africa and how they move around from one location
to another. They used 250 genetic sequences of the VP1 section of the
genome from SAT 2 isolates taken from all over sub-Saharan Africa and
tracked the appearance of the various unique 'topotypes' over the
region.
Hall says the patterns in which the topotypes appear in different
places gives strong support to the idea that the virus is spread by
infected hosts in land movements over relatively short distances. What's
more, African buffalo are an important "maintenance host," meaning they
maintain a reservoir of the virus that can re-infect domesticated
animals after time and culling has ended an outbreak among livestock.
The relationships between the 250 sequences also indicate that it's
possible the original source of the SAT 2 viruses that are now found in
wild and domesticated animals was African buffalo.
To Hall, these results indicate that genetic tracking of viruses has a
lot of potential for making inferences about viral spread and heading
off future outbreaks.
"We showed that we can demonstrate [virus movement] using genetic
data. It's a tool that can be used for that kind of inference. In cases
where less is known, this is a valid way of going about answering the
questions," says Hall.
Going forward, Hall says he plans to apply a similar approach to
studying serotype O FMD viruses in Africa, Asia, and South America to
identify links between different animal populations. "It's good to know
the reason it spreads," says Hall. "It could be quite a contribution to
eradication or control efforts
No comments:
Post a Comment