Mutations may have saved brown howlers from yellow fever virus
Exposure to a past virus may have selected for variations in their immune genes, maybe aided in their survival

Date:
August 12, 2020
Source:
University of Utah
Summary:
From 2007 to 2009, a devastating yellow fever virus outbreak nearly
decimated brown and black and gold howler monkey populations at
El Parque El Pin~alito in northeastern Argentina. An international
research team tested if howlers who survived the outbreak had any
genetic variations that may have kept them alive. In brown howlers,
they found two mutations on immune genes that resulted in amino
acid changes in the part of the protein that detects the disease.



FULL STORY ==========================================================================
At the start of her 2008 field season at El Parque El Pin~alito in
the Misiones province in northeastern Argentina, Ilaria Agostini knew
something was terribly wrong. Agostini has studied Misiones' two howler
monkey species since 2005 - - brown (Alouatta guariba clamitans) and
black and gold (A. caraya) howlers.

Both lived at relatively low densities in the park, but still existed
in one of the most continuous, well-preserved remnants of habitat known
as the Atlantic Forest. She knows them better than anyone in the world.


==========================================================================
But the treetops were silent, void of the booming chorus for which the
howler monkeys are named.

"At the beginning, I found one dead monkey. Then in two hours, another
one. In all my team and I found 14 dead howlers," said Agostini, a
biologist at the Instituto de Biologi'a Subtropical of Argentina. "That
first day, we started to suspect it was yellow fever." From 2007
to 2009, a devastating yellow fever virus outbreak nearly decimated
El Pin~alito's howler monkey populations. The brown and black and
gold howlers are extremely susceptible to the disease that enslavers
introduced to the Americas. In the last few years, logging activity has progressively affected the howlers' habitat and brought humans closer to wildlife, increasing the risk of virus transmission from the loggers to
the howlers. When laboratory analyses confirmed that the monkey's died
from yellow fever, health authorities vaccinated human populations to
prevent further transmission. By then, the damage was done.

"Our howler groups just disappeared from the park. We found almost
no signs of a presence until 2014 -- six years after the outbreak,"
Agostini said.

A recent United Nations report predicts that more diseases that spread
from animals to humans, such as COVID-19, will emerge due to habitat destruction.

The flip-side -- human disease spreading to animals -- is also true. How
will increased virus transmission affect wild animal populations? The
yellow virus outbreak in El Parque El Pin~alito provided a natural
laboratory to investigate.



==========================================================================
In a study led by the University of Utah, an international research team
tested whether howler monkeys who survived the yellow virus outbreak had
any genetic variations that may have kept them alive. The article was
published online on June 25, 2020 in the American Journal of Physical Anthropology.

In 2017, Nicole Torosi, postdoctoral researcher at Rutgers University
and then a doctoral student at the University of Utah, joined Agostini
in El Pin~alito to search for any living brown or black and gold
howlers. They eventually counted nine brown howlers and two black
and gold howlers. Torosin sequenced the genomes of liver samples that Agostini's team had collected from monkeys who died before the outbreak,
right after the outbreak, and she extracted DNA from the poop of those
who had survived.

"We saw many more dead black and gold howler monkeys than brown howlers
after the outbreak," said Torosin, postdoctoral researcher at Rutgers University. "We wondered if there were genetic differences that may have
helped the brown howlers survive somehow." The scientists focused on
two immune genes that detect the type of single- stranded RNA viruses to
which yellow fever virus belongs. The genes, toll-like receptor (TLR)
7 and TLR 8, recognize and destroy the invading viruses in both humans
and non-human primates.

The team found no genetic variants present at higher rates in the
surviving monkeys than in the deceased ones. However, in comparing the
two species, they found three mutations in the DNA sequence of the brown
howler individuals. Two of these mutations result in amino acid changes
in the part of the protein that detects the disease. In a companion study published in Molecular Phylogenetics and Evolution, Torosin found that
the changes were positively selected in the brown howler population.



==========================================================================
"If the amino acid sequence is different, then the protein is different,
and that could affect the entire downstream response to dealing with the virus," said Torosin. "Maybe that's why more brown howlers survived."
The researchers hypothesize that the brown howlers were exposed to a
different virus in the past that selected for the mutations and may have
helped them deal with yellow fever virus. Torosin's next steps are to
do an immune test for the two species by exposing cells to the virus to
see what the responses are in a controlled environment "With COVID-19,
we've seen how a virus that originated in China can spread across the
world. Here, humans brought a virus to primates that have evolved
without exposure to it for tens of millions of years and it nearly
wiped them out," said co-author Timothy Webster, anthropologist at the
U. "We're interacting with species in new ways that are creating new
immune challenges, both for humans and for other species." Rebuilding
the chorus There are still howler monkeys in the park, but they need
time to recover and reorganize into groups -- if they're not wiped by
another outbreak, which is a real possibility, Agostini said. In order
to document their progress, Agostini and her team of Proyecto Caraya'
Rojo, together with the NGO Asociacio'n Civil Centro de Investigaciones
del Bosque Atla'ntico (CeIBA), came up with a new way of tracking --
by recording their calls using wildlife acoustic recorders.

"Just looking for them in the forest isn't efficient. They're so elusive,
and live at such low densities, you can go days without finding them,"
she said.

"Recording their vocalizations could be very useful for howlers. They
give these very loud calls."

========================================================================== Story Source: Materials provided by University_of_Utah. Original written
by Lisa Potter.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Nicole S. Torosin, Timothy H. Webster, Herna'n Argibay, Candelaria
Sanchez Fernandez, Hebe Ferreyra, Marcela Uhart, Ilaria Agostini,
Leslie A. Knapp. Positively selected variants in functionally
important regions of TLR7 in Alouatta guariba clamitans with yellow
fever virus exposure in Northern Argentina. American Journal of
Physical Anthropology, 2020; 173 (1): 50 DOI: 10.1002/ajpa.24086 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200812153639.htm

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