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RABIES, WILDLIFE - USA (07): (ARIZONA) BAT VARIANT
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A ProMED-mail post
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International Society for Infectious Diseases
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Date: 15 Nov 2009 release
Source: AVMA.org [edited]
<http://www.avma.org/onlnews/javma/nov09/091115m.asp>
Foxes, skunks spreading bat rabies variant in Arizona
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Authorities are monitoring the adapted rabies virus during a record year
for rabies cases. In response to a recent outbreak of an adapted bat rabies
viral variant in terrestrial mammals, skunks in Arizona were trapped,
vaccinated, and released. Foxes and skunks in northern Arizona are
spreading an adapted version of a rabies virus variant associated with
bats. The state is also enduring a 2nd consecutive record year for rabies
cases in animals.
More than 200 animals in the state tested positive for rabies in the 1st 9
months of 2009, including dozens of foxes and skunks that were infected
with a bat virus variant that has adapted and spread among those
terrestrial mammals. By contrast, only 176 rabid animals were discovered in
all of 2008.
Craig Levy, an epidemiologist and the manager of the vectorborne disease
program for the Arizona Department of Health Services, said southern
Arizona has historically had reservoirs of the gray fox rabies strain and
the south-central skunk variant, and the state has multiple bat virus
variants. But in 2001, the state had an unusual outbreak of rabies among
skunks in Flagstaff, which is in northern Arizona.
"We never saw rabid skunks that far north in Arizona," Levy said. "So we
knew something was out of whack, and we had those skunks variant-typed to
find out what type of virus we were talking about. And it turns out that
the skunks were transmitting big brown bat variant, but it was going skunk
to skunk to skunk."
A scientific report in the August 2006 issue of Emerging Infectious
Diseases, "Bat-associated rabies virus in skunks," states that 19 skunks in
Flagstaff were confirmed to be infected with a bat-associated rabies virus
variant in 2001. "This is the largest recorded cluster of bat RABVV (rabies
virus variant) infection in terrestrial mammals," the report states.
"Investigation of this novel outbreak showed evolution in action with the
emergence of an RABVV that successfully adapted from Chiroptera to
Carnivora." The report also states the variant reappeared in 5 skunks and a
fox in 2004. By late 2008, foxes were transmitting the variant to other
foxes, Levy said.
"We may have some evolution occurring right before our eyes as we see a
different virus variant circulating very efficiently within the wrong
host," Levy said.
Rabies virus variants are genetically distinct strains, and information
from the CDC indicates those variants are typically maintained in a single
reservoir host species.
A 2009 circular from the US Geological Survey National Wildlife Health
Center, "Bat rabies and other lyssavirus infections," states that, after
transmission of a variant from its reservoir host to an atypical or
aberrant host species, "a dead-end infection usually results because the
maladapted atypical host quickly dies before the virus can be transmitted
further."
"Identification of variants that infect atypical hosts, such as humans,
usually points to a particular natural reservoir host species, such as a
species of carnivore or bat, as the source of human infection," the report
states.
David Bergman, the state director of USDA Wildlife Services in Arizona,
said a higher human population in the state, an increase in recreational
activity in the state, and increased rabies awareness are connected with
the record number of reported rabies cases. Bergman said it is concerning
that terrestrial wildlife is transmitting rabies near Flagstaff for the 1st
time in 40 years.
Part of the overall rise in rabies cases is related to a normal cycle of
infections, said Dr Charles E Rupprecht, chief of the rabies program of the
national Centers for Disease Control and Prevention. But the outbreak of a
bat rabies variant among terrestrial mammals in Arizona is unusual.
As people create comfortable human habitats in the desert, wildlife thrives
in the same areas, Dr Rupprecht said. Skunks are grassland animals that do
not typically live in high densities in deserts, he said, but construction
of golf courses near Flagstaff gave them room to thrive, and high
population density likely is related to the adaptation of the rabies virus
variant associated with brown bats.
The adapted variant is now demonstrating how viruses adapt and emerge, Dr
Rupprecht said. And there is a risk that, if it is truly adapted to fox
species, it could spread into the Navajo Nation and cause an outbreak in
unvaccinated dogs.
Navajo Nation borders the outbreak zone
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Dr Scott C Bender, senior tribal veterinarian for the Navajo Nation
Veterinary Program, said the Navajo Nation has not identified infection
with a terrestrial rabies variant in a dog since the 1940s, but the nation
typically has one or 2 bats test positive for rabies yearly. The nation is
slightly larger than West Virginia and extends into Arizona, New Mexico,
and Utah.
The Navajo Nation's border is also 10 miles from Flagstaff, and high desert
country is the only barrier, Dr Bender said. The nation's residents
frequently travel to Flagstaff to adopt cats and dogs. He and the nation's
other veterinarian have frequently vaccinated dogs against rabies, and the
Indian Health Service hosts an annual rabies clinic, but estimates indicate
only between 5 per cent and 15 per cent of owned dogs on Navajo land are
vaccinated.
Dr Bender said his office has been investigating the use of oral rabies
vaccines in feral and semiferal dogs as well as the use in dogs of a birth
control vaccine developed for use in deer. The research has included pen
and field trials of the available rabies vaccine and oral rabies vaccine
baits, and at press time he expected some of the results would be presented
at the International Conference on Rabies in the Americas in October [2009]
in Quebec City.
Dr Bender said it is fascinating to watch the virus's proliferation in
foxes and skunks prove some theories about adaptation correct. He said it
is likely similar to the time when lyssaviruses such as rabies 1st jumped
from a bat into a terrestrial mammal.
But the fascination is accompanied by concern, Dr Bender said, and his
program is monitoring for outbreaks and performing research to reduce the
risk dogs will become infected and potentially expose people to the virus.
Any positive tests for the virus would be followed by a community
vaccination clinic and, likely, a reduction in the feral dog population.
Outbreak centered in Flagstaff
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Coconino County, the northern Arizona county that includes Flagstaff, had
through early October [2009] identified 32 rabid animals, including 22
foxes and 5 skunks. Levy said he thinks the vast majority of the foxes and
all the other animals had the big brown bat rabies virus variant.
The adapted virus is transmitted the same way as other rabies strains, and
there is no indication it is more infectious, Levy said. Treatment for
humans or animals exposed to the strain would be the same as for any other
rabies exposure. "It's still rabies virus and probably being transmitted by
way of animal bites or saliva exposures," Levy said.
The Department of Agriculture's Wildlife Services, the Coconino County
Health Department, the Arizona Department of Health Services, local animal
control officials, the Arizona Game and Fish Department, and partners on
Indian lands have worked together on surveillance and wildlife vaccination,
Levy said.
The county health department imposed quarantine zones to make sure pets
were vaccinated and people obeyed leash laws, Levy said.
Wildlife Services was involved in the distribution in July [2009] of more
than 130 000 vaccine baits, mostly by air, to create herd immunity in
foxes, Bergman said. The air drops of oral rabies vaccine were the 1st in
the state, and the baits were dropped within about 15 miles of every known
rabies case in the Flagstaff area. About 110 skunks were also trapped,
vaccinated, and released. The oral rabies vaccine baits do not work on skunks.
Increased surveillance and laboratory testing have been used to monitor the
virus variant's prevalence and distribution, Levy said, and the adapted
rabies virus variant appears to still be isolated to northern Arizona.
Health authorities have recorded an above-average number of rabies cases in
animals in the rest of the state, but Levy said, "A lot of our rabies
activity in our terrestrial mammals is all driven by natural animal
population fluctuation."
--
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ProMED-mail
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[Arizona can be located using the HealthMap/ProMEDmail interactive map at
<http://healthmap.org/r/007G>. - CopyEd.EJP]
[see also:
Vaccinia, human, oral rabies vaccine - USA: (PA) 20091105.3825
Rabies, bat, human - USA: (IN) 20091028.3733
Rabies, canine - USA (02): (AL) 20091002.3438
Rabies, bovine, feline - USA (02): (CO) 20091001.3415
Rabies, raccoon - USA (02): (VA) 20090920.3309
Rabies, equine, human exposure - USA: (CO, TX) alert 20090918.3276
Rabies, wildlife - USA (06): (FL) human exposure 20090915.3239
Rabies, feline, human & canine exposure - USA: (ME) 20090911.3208]
....................tg/ejp/sh
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