[FEL-L] Avian influenza: An emerging feline threat?
GemOJungle at aol.com
GemOJungle at aol.com
Sat Sep 30 07:56:27 CDT 2006
Avian influenza: An emerging feline threat? (Update)
Until recently, it was thought that cats couldn't get the flu. But the new
strain of avian influenza first seen in Asia and now arriving in Europe can—
and does—infect cats.
<PUBLICATIONDATE Jun 1, 2006 <AUTHOR> By: _Margaret C. Barr, DVM,
PhD_ (http://www.vetmedpub.com/vetmed/author/authorInfo.jsp?id=22910)
Veterinary Medicine
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Margaret C. Barr, DVM, PhD
College of Veterinary Medicine
Western University of Health Sciences
Pomona, CA 91766
Editors' note: This is an excerpt of a peer-reviewed article that originally
ran in Veterinary Medicine's October 2005 issue. It has been updated to
include information about the continued spread of avian influenza in cats.
HISTORICALLY, cats have been considered to be resistant to influenza virus
infections. Cats can be experimentally infected with human H3N2 virus, but the
infection is usually subclinical.1 Although cats live in close contact with
people, feline influenza outbreaks have not been recognized. Whether
human-to-cat transmission is possible is unknown, but it clearly has not been
associated with disease in the past. However, we now know that cats can—and do—
become infected with the H5N1 strain of avian influenza virus.
Reported cases in nondomestic and domestic cats
In December 2003, two tigers and two leopards in a zoo in Thailand died
after exhibiting signs of fever and respiratory distress.2 The animals had been
fed fresh poultry carcasses from a local slaughterhouse. Although the
diagnosis had not been made at the time, chickens in the area were dying of H5N1
influenza virus infections. Postmortem examination of tissues from the tigers and
leopards revealed fibrinous pneumonia, multifocal hemorrhage in internal
organs, and encephalitis. Immunohistochemistry, reverse transcriptase-polymerase
chain reaction testing, and virus isolation confirmed a diagnosis of H5N1
avian influenza virus infection. The virus was virtually identical to the
strain that was circulating in chickens at the time of infection. All the animals
had been vaccinated with an attenuated feline panleukopenia virus vaccine
two weeks before their illness. Although there was no evidence of panleukopenia
virus-induced disease, immunosuppression associated with the vaccine may
have contributed to the severity of the influenza in these cats.2
Domestic cats in Thailand have also been infected with the H5N1 virus.3,4 In
February 2004, a group of 15 cats living near an affected poultry farm
became ill. According to news reports, three of the cats had been tested for avian
influenza by researchers at Thailand's Kasetsart University, with two cats
having positive results at that time. Fourteen of the 15 cats had died, and
the last cat was very ill. The method of influenza transmission in these cats
was unknown. During the same month, another cat in Thailand became ill five
days after eating a pigeon carcass.5 The cat was initially febrile and
depressed and then developed convulsions and ataxia before it died two days after
the onset of illness. H5N1 influenza virus antigen was detected by
immunohistochemistry in brain, heart, lung, liver, kidney, and spleen samples from this
cat. Virus isolates from the cat were almost identical to isolates from
infected pigeons and chickens in the same region.
A second outbreak of H5N1 avian influenza in nondomestic cats occurred in
October 2004 in a tiger zoo in Thailand.6 Initially, the cats likely became
infected by ingesting raw infected bird carcasses. Tigers infected later in the
outbreak were probably infected by cat-to-cat transmission because they were
fed cooked poultry beginning a few days after the first tigers became ill.
Clinical signs in affected tigers included respiratory distress, a
serosanguineous nasal discharge, neurologic signs, and high fever. Leukopenia,
thrombocytopenia, and elevated liver enzyme activities were common laboratory
findings. Most of the animals had severe lung congestion and hemorrhage. Infection
with H5N1 avian influenza virus was confirmed in several animals by using
immunohistochemistry, virus isolation, or both techniques. Twenty-nine tigers died
during the first week of the outbreak, and a total of 147 of the zoo's 441
tigers either died or were euthanized during the three weeks after the first
tigers became ill.
In February 2006, a domestic cat in Germany was infected with H5N1 avian
influenza virus, probably by ingesting an infected wild bird. This case was
quickly followed by the detection of three H5N1-positive cats in Austria.7
Several H5N1-infected swans were found in the same regions as the infected cats.
In response, the European Standing Committee on the Food Chain and Animal
Health (SCFCAH) issued recommendations for veterinarians and pet owners. The
statement recommended inspecting and testing sick or dead cats that might have
had contact with wild birds, reporting suspected cases to appropriate
authorities, and preventing contact between pet cats and wild birds. It also
recommended the same procedures for dogs. The SCFCAH report emphasized that the risk
of avian influenza virus infections in cats remains low, and the risk of
cat-to-human transmission is even lower at this time.8 <PRIMARY>
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Avian influenza: An emerging feline threat? (Update)
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Avian influenza: An emerging feline threat? (Update)
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Experimental inoculation of domestic cats
In addition to these outbreaks, researchers have demonstrated the
susceptibility of domestic cats to H5N1 avian influenza virus.9 Unlike in previous
studies with other influenza virus strains, cats developed severe respiratory
disease after exposure to H5N1 virus by ingestion, intratracheal inoculation,
or contact with experimentally infected cats. Intratracheal inoculation of
three cats resulted in fever beginning Day 1 after exposure and in decreased
activity, conjunctivitis, and labored breathing by Day 2 after exposure. One
cat died on Day 6. Pathologic findings included focal pulmonary
consolidation and diffuse alveolar damage. Two cats housed with these infected cats and
three cats fed virus-infected chicks also developed similar clinical signs
and pathology. Infection with H5N1 avian influenza virus was confirmed in all
these cats by virus isolation from pharyngeal swabs and by
immunohistochemistry on lung tissue.
Concerns over an H5N1 influenza pandemic
Although human cases have been sporadic to date and efficient
human-to-human spread has not yet occurred, concerns about a potential H5N1 influenza
pandemic continue to rise. For the first time since the current H5N1 influenza
outbreak began in 2003, migratory birds appear to be spreading the highly
pathogenic avian influenza virus to domestic birds in countries along their
migratory routes. The virus has now been detected in birds in at least 32
countries.10 Despite this explosive spread in birds, little more than 200 human
cases of H5N1 influenza have been confirmed during the current outbreak; most
of these cases can be traced to direct contact with sick or dead birds or
their feces.
However, fears of an avian influenza pandemic remain because of the ability
of influenza viruses to mutate and change or expand their host range.
Influenza viruses carry their genes on eight separate segments; infection of a
single host cell with two different influenza viruses can result in a new virus
strain by packaging segments from both parent viruses in a single virus
particle (genetic reassortment). If such a reassortment resulted in enhanced
transmission between people, a pandemic might occur.10
The veterinarian's role in influenza surveillance
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1. Genetic reassortment of influenza viruses may lead to additional species
being involved in transmission.
The H5N1 influenza outbreaks in domestic and nondomestic cats point to this
virus's potential as a feline pathogen. Although poultry and wild ducks are
the virus's primary reservoir, several species of songbirds are also
susceptible to infection.11 These bird populations could serve as a conduit of
human infection through feline intermediaries. With each genetic reassortment of
the influenza viruses, species barriers become less effective (Figure 1). It
therefore seems reasonable for veterinarians to consider including
influenza as a differential diagnosis in cats with respiratory and neurologic
disease. Prompt recognition of avian influenza in any susceptible population of
animals will help control its spread and decrease the chance of another
devastating influenza pandemic.
If you suspect avian influenza in any species, contact the Animal Health
Diagnostic Center, College of Veterinary Medicine, Cornell University (phone:
607-253-3900; e-mail: _diagcenter at cornell.edu_ (mailto:diagcenter at cornell.edu)
) for testing information. Report cases of avian influenza to local or state
public health departments or the county veterinarian.
Although guidelines for handling infected pets have not been established,
human infection-control precautions recommended by the Centers for Disease
Control and Prevention can be adapted for use in companion animals. Use
stringent hygienic care (including using gloves, gowns, and masks) when handling
potentially infected animals, and maintain these animals under isolation
conditions until testing is completed or for 14 days after the onset of clinical
signs.
Treatment of influenza virus infection in cats would probably be based on
supportive care. Influenza antiviral agents have not been tested in cats, so
their safety and efficacy are unknown. The use of antiviral drugs such as
oseltamivir or zanamivir in nonhuman species is discouraged because of concerns
that circulating strains of influenza might develop resistance to these
drugs. In fact, the extralabel use of anti-influenza drugs in poultry has been
banned by the FDA.12
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1. Hinshaw VS, Webster RG, Easterday BC, et al. Replication of avian
influenza A viruses in mammals. Infect Immun 1981;34:354-361.
2. Keawcharoen J, Oraveerakul K, Kuiken T, et al. Avian influenza H5N1 in
tigers and leopards. Emerg Infect Dis 2004;10:2189-2191. Available at:
_www.cdc.gov/ncidod/EID/vol10no12/04-0759.htm_
(http://www.cdc.gov/ncidod/EID/vol10no12/04-0759.htm) . Accessed May 23, 2006.
3. Care urged after bird flu infected feline found. China Daily. Available
at: _www2.chinadaily.com.cn/english/doc/2004-02/20/content_307975.htm_
(http://www2.chinadaily.com.cn/english/doc/2004-02/20/content_307975.htm) . Accessed
March 29, 2005.
4. The World Health Organization Communicable Disease Surveillance &
Response (CSR). Avian influenza (H5N1)—update 28: reports of infection in domestic
cats (Thailand), situation (human) in Thailand, situation (poultry) in Japan
and China. 20 February 2004. Available at:
_www.who.int/csr/don/2004_02_20/en/_ (http://www.who.int/csr/don/2004_02_20/en/) . Accessed Sept. 15, 2005.
5. Songserm T, Amonsin A, Jam-on R, et al. Avian influenza H5N1 in
naturally infected domestic cat. Emerg Infect Dis 2006;12:681-683.
6. Thanawongnuwech R, Amonsin A, Tantilertcharoen R, et al. Probable
tiger-to-tiger transmission of avian influenza H5N1. Emerg Infect Dis
2005;11:699-701. Erratum in: Emerg Infect Dis 2005;11:976. Available at:
_www.cdc.gov/ncidod/EID/vol11no05/05-0007.htm_
(http://www.cdc.gov/ncidod/EID/vol11no05/05-0007.htm) . Accessed March 29, 2005.
7. Butler D. Can cats spread avian flu? Nature 2006;440:135.
8. European advice on H5N1 avian influenza in cats. Vet Rec 2006;158:314.
9. Kuiken T, Rimmelzwaan G, van Riel D, et al. Avian H5N1 influenza in
cats. Science 2004;306:241.
10. Avian influenza fact sheet (April 2006).Wkly Epidemiol Rec
2006;81:129-136.
11. Perkins LE, Swayne DE. Varied pathogenicity of a Hong Kong-origin H5N1
avian influenza virus in four passerine species and budgerigars. Vet Pathol
2003;40:14-24.
12. Avian influenza backgrounder. Available at:
_www.avma.org/public_health/influenza/avinf_bgnd.asp_
(http://www.avma.org/public_health/influenza/avinf_bgnd.asp) . Accessed May 15, 2006.
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