What Makes Bats The Perfect Hosts For So Many Viruses?
The study is “an important piece of the puzzle in
understanding why viruses [from bats] may be emerging and impacting people and
other animals,” says Kevin Olival, a disease ecologist with EcoHealth Alliance
in New York City, who wasn’t involved in the research
“There’s a lot we can learn from bats about
their immune system and take some of that information to think about our own
health and developing our own therapeutics” against viruses, he says.
Scientists have pinpointed
bats as potential sources of several viral outbreaks in humans. Insect-eating
bats may have been the source of the 2014–16 Ebola outbreak in
West Africa (SN: 12/31/14).
Egyptian fruit bats (Rousettus aegyptiacus)
harbor Marburg virus, a hemorrhagic virus related to Ebola. Other bat species
are reservoirs of SARS-like coronaviruses, possibly including one that sparked an ongoing outbreak in China (SN: 1/24/20)
The virus originated in bats and then jumped to humans, perhaps through other animals
The Marburg virus and some
strains of the Ebola virus can kill up to 90% of humans infected. India’s
Kerala state has just faced an outbreak of the Nipah virus and seventeen people
have died so far. This may seem like a small number, but only one of the eighteen
people infected survived. For a number of these viruses hosted by bats, there
is no known cure or vaccine, which means that doctors can only offer supportive
treatment while the patient’s immune system fights off the virus.
Bats’ immune defenses may be why their viruses can be so deadly to people
When it comes to viruses, ones from bats are weirdly deadly — at
least to humans. The mammals can carry many viruses with the potential to cause
serious diseases in people, including rabies, Ebola, Nipah, severe acute
respiratory syndrome, or SARS, and others. Bats rarely get sick from those
viruses. Why these pathogens tend to be so dangerous when they infect other
animals has been a mystery. Previous work suggests that a bat’s immune system
is especially adapted to tolerate viruses, thanks in part to its ability to
limit inflammation..
Now a study using cells grown
in a lab hints that to counter a bat’s immune defenses, these viruses have
gotten good at spreading rapidly from cell to cell. That means that when they
get into animals without a similarly strong immune system, the viruses are
particularly adept at causing serious damage, researchers report February 3 in
eLife...
Researchers
at the University College Dublin have also
shown that bat macrophages can rapidly mount a robust antiviral response whenever
a pathogen is detected, but compared to the immune response of a mouse, the bat
immune system can quickly reverse their response by releasing anti-inflammatory cytokines.
Other
researchers have suggested that bats’ super-tolerance might have something to
do with their ability to generate large repertoires of naïve antibodies, or the
fact that when bats fly, their internal temperatures are increased to around 40
deg C (104 deg F), which is not ideal for many viruses. Only the viruses that
have evolved tolerance mechanisms survive in bats. These hardy viruses can
therefore tolerate human fever. What is a good thing for bats is a bad thing
for humans.
So, what can we do to prevent future
outbreaks of bat viruses? We certainly cannot create
vaccines and drugs for all these emerging pathogens. However, there is a need
to study the interactions between bats, humans and domestic animals and
identify factors that are making bats come into contact with humans and
domestic animals, and try to do something about it.
