The following is from a fax from Dr. Rupprecht of the Centers For Disease
Control in Atlanta.
 
Pathogenesis of Bat Rabies Virus Variants in Domestic Ferrets
 
M. Niezgoda  D.J. Briggs  J.S. Shaddock  C.E. Rupprecht
Centers for Disease Control & Prevention, Viral and Zoonosis Branch,
Atlanta, GA
Thomas Jefferson University, Department of Microbiology and Immunology,
Philadelphia, PA.
Kansas State University, College of Veterinary Medicine, Manhattan, KS.
 
The domestic ferret is increasing in popularity as a pet in the United
States, raising critical questions for public health officials responsible
for the management of ferret bites to human beings, in regards to the
potential risk for rabies.  Although the first licensed rabies vaccine was
approved for use in domestic ferrets in 1990, healthy vaccinated ferrets
that bite human beings may, based on review of the case report, be routinely
euthanatized and examined for rabies, rather than be held and observed.
Current recommendations result largely from the lack of information on
ferret response to rabies virus infection.  Neither clinical signs nor a
determination of virus secretion in salvia prior to clinical signs are well
documented.  As a continuation of studies investigating the pathogenesis of
rabies in domestic ferrets, preliminary studies investigated ferret response
using virus variants associated with North American bats.  Ferrets received
virus by intermuscular inoculation and were held for a minimum observation
period of 120 days.  Ferrets were observed daily, and weekly samples
included swabs of the oral cavity, body weights, rectal temperatures, and
blood for serology.  Twelve ferrets received a virus variant associated with
the big brown bat (Epiesicus fucus) at concentrations that ranged from 104.1
to 103.4 MICLD50.  Nine of 12 ferret were euthanatized with severe clinical
signs of rabies.  Mean incubation period was 20 days (range 16 to 22 d).
Mean morbidity period was 3 to 4 days (range 2 to 6 d).  Additionally, 12
ferrets received a rabies virus variant associated with the Brazilian free
tailed bat (Tadarida brasiliensis) at concentrations that ranged from 104.7
to 103.7 MICLD5O.  Ten of 12 ferrets were euthanized with severe clinical
signs.  Mean incubation period was 23 days (range 10 to 44 d).  Mean
morbidity period was 2 to 3 days (range 1 to 3 d).  Common clinical signs of
rabies included ataxia, paresis, paraparesis, and paralysis.  Ferrets
receiving the big, brown rabies virus variant had additional signs of
lethargy, fever, and cachexia.  One ferret from this group was aggressive.
Ferrets receiving the Brazilian free tailed bat rabies virus variant had
additional signs of vocalization and the majority of rabid ferrets had
aggressive behavior.  To date, nearly half of the ferrets receiving the big
brown bat rabies virus variant had detectable rabies virus neutralizing
antibodies at the time of euthanasia, and one survivor seroconverted,
whereas, no ferret from the group given the Brazilian free tailed bat rabies
virus variant was seropositive at euthanasia, and similarly 1 survivor
seroconverted, In ferrets receiving the big brown bat rabies virus variant,
rabies virus was isolated from the salivary glands of 2 of 9 ferrets
euthanatized with severe clinical signs and one of these shed virus in their
saliva (concomitant with clinical signs), whereas, virus was isolated from
the salivary gland of only 1 ferret given the Brazilian free tailed bat
rabies virus variant and no rabies virus was detected in saliva.  To
adequately ensure the publics health, continuing studies must be completed
before any changes in ferret rabies control recommendations can be
considered.
[Posted in FML issue 2102]