Canine Influenza virus (CIV)
Domestic dogs have for
centuries been considered refractory to infection by influenza A viruses. But following reports of transmission of
influenza virus H3N8 sub-type from horses to dogs in the state of Florida/USA in
2004, this theory has so far been challenged. H3N8 influenza A sub-type which
usually afflicts horses, has been associated with outbreaks of a fatal
respiratory disease in Racing Greyhound dogs (fatality rate of 36%). This cross species transmission of H3N8 virus has been related to the proximity of Race-horses
to racing Greyhounds which enabled this virus (H3N8) to infect the dogs.
Most of these dog
infections are mild and are followed by a prompt clinical improvement. H3N8 Canine Influenza Virus (CIV) infections
spread among canine population (both racing greyhounds and pet dogs) of the
USA, without association with outbreaks of equine influenza, supporting a
possible horizontal transmission among dogs.
H3N8 CIV isolates now form
a single group of viruses that are molecularly and epidemiologically distinct
from currently circulating H3N8 equine influenza virus (EIV) in the USA. As the H3N8 CIV is a relatively novel pathogen in
the canine population, dogs lack natural immunity against the virus.
All dogs, regardless breed or age, are therefore susceptible to H3N8 CIV infection and the virus has been shown to rapidly spread within dog populations.
All dogs, regardless breed or age, are therefore susceptible to H3N8 CIV infection and the virus has been shown to rapidly spread within dog populations.
About 80% of infected
animals develop clinical signs upon infection whereas 20-25% develops
subclinical infection, but also shed and transmit the virus. Outbreaks can
occur when clinically normal carriers come into contact with a naïve
population.
The highest risk for
exposure to CIV occurs in communal facilities where dogs are housed and/or
placed in the following conditions:
·
high population density;
·
Indoor (closed-air) environments, such
as racing kennels, dog shows, agility events, animal shelters, kennel boarding
and training facilities, veterinary clinics, pet day-care centers, pet stores,
and pet grooming salons.
Additionally, stressful
situations, - such as travel, prolonged endurance exercise in severe weather,
and exposure to harsh terrain -, might increase the risk for influenza
infection in dogs.
Currently, canine
influenza (CI) caused by H3N8 is considered an endemic disease in metropolitan
areas of the North-eastern and Western regions of the USA, and has been confirmed in Korea, China and Thailand resulting in high morbidity (80%) and low mortality (1-5%) in the dog population. CIV infection
is not considered a seasonal flu and dog infections can occur year-round.
CIV is transmitted by direct contact, through aerosols generated by coughing and sneezing and by
indirect contact through fomites contaminated with respiratory secretions and
by people handling septic animals.
The incubation period
is usually less than five days, with the highest shedding occurring before the development
of clinical signs. CIV replicates in the respiratory epithelium, causing
tracheitis, bronchitis and bronchiolitis. As a result, the defense mechanisms
of the respiratory tract become severely compromised, predisposing to secondary
infections by bacteria or mycoplasma.
Dogs of all ages seem
to be equally susceptible to CIV-associate pneumonia.
Most dogs develop a mild form of the disease, characterized by persistent fever for one to four days (>39.4°C), depression, apathy, anorexia, sneezing, nasal and ocular discharge.
The cough is usually non-productive and persists for 10 to 30 days. Most dogs eradicate the infection and recover clinically within two weeks.
Most dogs develop a mild form of the disease, characterized by persistent fever for one to four days (>39.4°C), depression, apathy, anorexia, sneezing, nasal and ocular discharge.
The cough is usually non-productive and persists for 10 to 30 days. Most dogs eradicate the infection and recover clinically within two weeks.
The clinical
presentation of CIV infection is similar to that observed in “kennel cough” or
infectious tracheobronchitis. CI diagnosis therefore requires laboratory
confirmation, usually virus isolation, RT-PCR and/or testing of paired serum
samples by hemagglutination inhibition (HI).
Treatment consists
mainly of supportive care, including antibiotics for secondary bacterial
infections and hydration.
Preventive measures
include isolation of sick dogs and decontamination of premises with Quaternary
ammonium compounds or sodium hypochlorite. Contact of horses with dogs should be avoided
during outbreaks of equine influenza.
Vaccination of dogs against H3N8 CIV has been authorized in the USA since 2009, but vaccination should be restricted to animals that travel to high-risk areas experiencing canine or equine influenza. Vaccination significantly reduces virus shedding and the severity and duration of clinical disease, including the incidence and severity of lung damage.
Vaccination of dogs against H3N8 CIV has been authorized in the USA since 2009, but vaccination should be restricted to animals that travel to high-risk areas experiencing canine or equine influenza. Vaccination significantly reduces virus shedding and the severity and duration of clinical disease, including the incidence and severity of lung damage.
By:
Dr. Moses Bwana
Post-grad Student at the University of Nairobi
Department Pathology,Microbiology and Parasitology
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