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CANINE INFLUENZA VIRUS
INFECTION
At Issue:
Earlier this year,
numerous television and newspapers reports addressed, in only ways that the
media can do this, recent research findings that confirmed the fact the equine
influenza virus ‘jumped’ species and had infected dogs. [Primary Investigators: Dr. P. Cynda Crawford, University of Florida,
College of Veterinary Medicine, Gainesville, FL; Dr. Ed Dubovi, Cornell University, College of
Veterinary Medicine, Ithaca, NY.]
What’s
more, these reports cited concerns of widespread respiratory disease affecting,
and even killing, dogs. And then…is
this the forerunner of the impending avian influenza outbreak that (maybe)
threatens humans throughout the world??
Will pet dogs threaten human health???
NOT QUITE!
The Facts:
The Clinical Disease: In January 2004 (correct…2004), an
outbreak of respiratory disease occurred in 22 racing greyhounds at a Florida
racetrack. Two clinical syndromes were
reported:
1. a mild cough, with fever, lasting 10-14 days with
subsequent recovery (14 dogs), and…
2. peracute death associated with extensive lower
respiratory tract hemorrhage (8 dogs…36%) involving the lungs, mediastinum, and
pleural space. Histology of the lungs
revealed suppurative bronchopneumonia as well as bronchiolitis, and
tracheitis.
In a summary statement to the CDC, Dr.
Crawford points out that canine influenza is NOT a highly fatal disease,
indicating that 80% of infected dogs develop nasal discharge, cough, mild fever
and recover spontaneously. Several
others will show NO CLINICAL SIGNS whatsoever.
What makes this disease particularly problematic, clinically speaking,
is the fact that it is contagious from dog-to-dog. Susceptibility rates, obviously, are very
high.
Co-infection with other viruses and/or
bacteria have not been studied. CIV infection in a dog with concurrent
bacterial infection (B. bronchiseptica would be a likely candidate!) of
the lower respiratory tract could pose a significant health threat to the
affected dog(s).
Mortality in dogs is estimated to be from
6% to 8%. In clinical practice, this
number may be much lower.
The Conclusion: Identification of infected dogs in widespread geographical
locations from 2003 to 2005, support the conclusion that a single virus
transmission event from horses to dogs occurred. What’s more, horizontal spread of the adapted
virus from dog to dog was documented.
Virus Identification: After considerable research, it was (recently) confirmed that
interspecies transmission of an entire equine influenza A (H3N8) virus
(documented as a cause of equine respiratory disease for over 40 years) to the
dog [ie, the virus sequence corresponds
with the H3 immunoglutinen and the N8 neurominidase subtype]. What’s more, investigators at U of FL
examined archival lung tissue from greyhounds that died from hemorrhagic
bronchopneumonia in March 2003. Sequence
analyses of virus isolated from lungs indicated that viruses had infected
greyhounds prior to 2004. Further studies comparing the equine and
canine influenza viruses have shown that only 4 amino acid changes
differentiate the two viruses.
Seroprevalence in Racing Greyhounds:
From January to May 2005, blood from 96 dogs at 7 Florida racetracks was
collected (acute and convalescent samples).
100% were seropositive. 100% of
dogs (n = 25) in West Virginia racetracks were seropositive. Ten dogs in Wisconsin were also
seropositive.
Occurrence of Canine Influenza in Dogs: Blood samples collected from 70 dogs with respiratory disease in
shelters in Florida and a variety of veterinary practices in Florida and New
York City showed 97% were positive for antibody to the influenza virus (ie,
past exposure). This study demonstrated
that canine influenza virus infection was not unique to the greyhound breed. Today, approximately 30 States and the District
of Columbia have confirmed infections in dogs...shelter-housed dogs
predominate.
Transmission: Experimental studies in dogs suggest that virus will persist in
the nasal cavity and oropharynx of challenged dogs and suggests that shedding
is possible. Dog-to dog transmission
could occur via large aerosolized droplets from the upper respiratory tract,
fomites, or direct mucosal contact.
Clinical Diagnosis of Canine Influenza
Virus: Serology (acute and convalescent antibody
titers-approx $20 per sample) is the primary tool used to establish a diagnosis
in dogs. Several laboratories offer
serology testing (antibody titers) as a diagnostic test. HOWEVER, it must be noted that the
clinical disease is short...about 10 days to 2 weeks, and the period of virus
shedding is even shorter...about 8 days. It is therefore highly unlikely that
the infection can be ‘diagnosed’ prior to the time the disease spontaneously
resolves.
Treatment: Supportive care with a broad spectrum
antimicrobial is indicated to manage the risk of secondary bacterial
bronchopneumonia (suggest: doxycycline,
amoxicillin-clavulanic acid, azithromycin, or a fluoroquinolone). The accumulation of fluid in the pleural
space, although regarded a grave prognostic sign, should be removed via
thoracocentesis. Care should be taken to
properly dispose of materials (endotracheal tubes, catheters, needles,
syringes, oxygen tubing, etc.).
Vaccine: In July 2009, the first vaccine for CIV
was released (Intervet Schering-Plough).
This is a killed, adjuvanted vaccine licensed (conditional) for use
in dogs only. It is important to
understand that while the vaccine has been shown to mitigate the severity of
clinical signs in challenged dogs and reduce the shedding of virus following exposure,
the vaccine does not prevent infection nor does it prevent shedding.
Vaccinated dogs, following experimental challenge, may still develop clinical
signs.
Considering infection risk (very low)
among individual household pet dogs, routine vaccination with the CIV vaccine
is not recommended. Indications for
vaccination are perhaps best left to shelter-housed dogs where the threat of
infection is clearly higher. AT ISSUE
FOR SHELTERS...at least 2 doses of this killed vaccine are required to
induce an immune response. In the
typical shelter setting, most dogs do not even reside in the facility long
enough to derive any benefit from vaccination.
Zoonotic potential: There is NONE. Although the authors of this study
added: “evidence of canine influenza
infection in pet dogs, a primary companion animal for humans, raises the
possibility that dogs may provide a new source for transmission of novel
influenza A viruses to humans. “ ….there
is absolutely no evidence even suggesting that dog-to-human transmission
has occurred….nor does it suggest that zoonotic transmission will occur.
The
canine influenza virus is so close to the equine influenza virus, 4 amino
acids, (and the equine influenza virus has NEVER infected humans in 40 years),
investigators have indicated that the canine influenza virus may even be LESS
likely than the equine virus to infect humans.
Recent concerns
over the human influenza type A viruses that have also jumped species and
subsequently infected humans: avian
(H5N1) and swine (H1N1), has fueled concerns over the ability of the CIV to
infect humans. Owners should be assured
that there is no evidence whatsoever that dogs have the ability to transmit CIV
to humans.
Updated August 2009
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