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 Bird flu or Avian Influenza, is
a contagious disease of animals caused by viruses that normally
infect only birds and, less commonly, pigs. While all bird species
are thought to be susceptible to infection, domestic poultry
flocks are especially vulnerable to infections that can rapidly
reach epidemic proportions.
ETIOLOGY
Classification of the causative agent
Virus family Orthomyxoviridae, genus Influenzavirus A, B. To
date, all highly pathogenic isolates have been influenza A viruses
of subtypes H5 and H7
Resistance to physical and chemical action
Temperature : Inactivated by 56oC/3 hours; 60oC/30 min.
pH : Inactivated by acid pH
Chemicals : Inactivated by oxidising agents, sodium dodecyl sulphate,
lipid solvents, B-propiolactone
Disinfectants : Inactivated by formalin and iodine compounds
Survival : Remains viable for long periods in tissues, feces
and also in water
EPIDEMIOLOGY
• Highly contagious
Hosts
• Highly pathogenic avian influenza isolates have been obtained
primarily from chickens and turkeys
• It is reasonable to assume all avian species are susceptible
to infection
Transmission
• Direct contact with secretions from infected birds, excretion
especially feces
• Contaminated feed, water, equipment and clothing
• Clinically normal waterfowl and sea birds may introduce
the virus into flocks
• Broken contaminated eggs may infect chicks in the incubator
Sources of Virus
• Feces, respiratory secretions
• Highly pathogenic viruses may remain viable for long period
of time in infected feces, tissues and water.
Occurrence
Apathogenic and mildly pathogenic influenza A viruses occur
worldwide. Highly pathogenic avian influenza A (HPAI) viruses
of the H5 and H7 HA subtypes have been isolated occasionally
from free-living birds in Europe and elsewhere. Outbreaks due
to HPAI were recorded in Pennsylvania, USA in the years 1983-1984.
More recent outbreaks have occurred in Australia, Pakistan and
Mexico. There is evidence that H5 viruses of low pathogenicity
may mutate and become highly pathogenic. HPAI infections are
very rarely seen, and should not be confused with viruses of
low pathogenicity, which may also be of H5 or H7 subtypes.
DIAGNOSES
Incubation period is 3-5 days
Clinical diagnosis
• Severe depression, inappetence
• Drastic decline in egg production
• Facial edema with swollen and cyanotic combs and wattles
• Petechial hemorrhages on internal membrane surfaces
• Sudden deaths (mortality can reach 100%)
• Virus isolation needed for definitive diagnosis
Lesions
Chickens
• Lesions may be absent in cases of sudden death
• Severe congestion of the musculature
• Dehydration
• Substaneous edema of the head and neck area
• Severe congestion of conjunctiva, sometimes with petechia
• Excessive mucous exudate in the lumen of the trachea,
or severe haemorrhagic tracheitis
• Petechia on the inside of the sternum, on the serosa and
abdominal fat, serosal surfaces and in
the body cavity
• Severe kidney congestion, sometimes with urate deposits
in the tubules
• Hemorrhages and degeneration of the ovary
• Hemorrhages on the mucosal surface of the proventriculus,
particularly at the juncture with the gizzard
• Hemorrhages and erosions of the gizzard lining
• Hemorrhagic foci on the lymphoid tissues in the intestinal
mucosa
The lesions in turkeys are similar to those in chickens, but
may not be as marked. Ducks infected with HPAI and excreting
the virus, may not show any clinical signs or lesions.
Differential diagnosis
• Acute fowl cholera
• Velogenic Newcastle disease
• Infectious laryngotracheitis
• Infectious Bronchitis
LABORATORY DIAGNOSIS
Procedures
Identification of the agent
• Inoculation of 9-11 day-old embryonated chicken eggs
followed by:
a. demonstration of hemagglutination
b. immunodiffusion test to confirm the presence of influenza
A virus
c. subtype determination with monospecific antisera
d. strain virulence evaluation: intravenous pathogenicity index
(IVPI) in 4-8 week-old chickens
Serological tests
• Hemagglutination and hemagglutination inhibition tests
• Agar gel immunodiffusion
Samples
Identification of the agent
• Tracheal and cloacal swabs (or feces) from live birds
or from pools of organs and feces from dead birds
Serological tests
• Clotted blood samples or serum
TREATMENT
No specific treatment
Sanitary prophylaxis
a. Avoidance of contact between poultry and wild birds, particularly
waterfowl
b. Avoidance of the introduction of birds of unkown health status
into a flock
c. Control of human traffic
d. Proper cleaning and disinfection procedures
e. Practice an “all in-all out” system in the poultry
farm
In outbreaks
a. Slaughtering of all birds
b. Disposal of carcasses and all poultry products
c. Cleaning and disinfection
d. Allow at least 21 days before restocking
Medical prophylaxis
In the past, it has been considered counterproductive to vaccinate
against HPAI as some vaccinated individuals may, nonetheless,
become infected and shed virulent virus. However, in the recent
outbreaks in Pakistan and Mexico, inactivated vaccines have been
employed to combat rapidly spreading disease.
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