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Bird Flu Situation In Nepal & Diagnosis Services Available
in Central AnimalDisease Investigation Laboratory
Dr.Kedar KarkiInfluenza is an acute contagious viral disease
which occurs in both man and lower
animals dates back centuries and even in Hippocrates' era. It is
known by severalnames like influenza (man), swine influenza (pig),
equine (horse) or avian influenza(birds)in various species of
animals and man. Human influenza was found to becaused by virus in
England in 1933, although it was first identified in pig
three`years earlier. The current interest of the bird flu or avian
influenza or fowl plaguewas shown to be caused by a virus in the
early 1955. From 1997 to 2004, severalcases of bird flu have been
reported in Hong Kong, China, Belgium, Netherlands,Vietnam,
Cambodia, Taiwan, Indonesia and recently in Thailand and Pakistan
leadingto death of several people and slaughter of Millions of
chickens. So far no case hasbeen reported in India.The causative
agent:
The influenza Virus belongs to group which is a RNA virus and is
of three types A, B,and C on the basis of nucleoprotein (NP) and
matrix protein (M) present in the coreof the virion. Out of these
three, the only type A is widely distributed in populationand has
zoonotic importance. The virus is of 100-120 nm in diameter and
enclosed inan envelope which contains protein spike haemagglutinin
(H) and the enzymeneuraminidase (N). The H and N peplomer
determines sub type specific antigenicityand broadly grouped as H1,
H2, H3, ... and N1, N2, N3,.... An abrupt or majorchange in the
composition of H and N antigens with in a group is called
antigenic'shift' where as antigenic 'drift' is the minor change
even a change in a single aminoacid of the H antigen. The single
stranded RNA genome occurs as eight separatemolecules, most of
which code for a single protein. Because of segmented genome,
genetic reassortment can occur in cells infected with two
different strains ofinfluenza A virus. This reassortment occurs in
nature and is an important source ofgenetic variability and thus
epidemics and epizootics. The strains of type Ainfluenza virus are
classified on the basis of animal origin, the place of
origin;strain number and year of isolation viz. A/chick/Germany?
N/49 (H10N7). Thechange of strains which involves mutated 'hot'
spots in protein moiety areresponsible for by-passing immunological
defences and infection.Animals Susceptible: Influenza virus affects
human and a wide varieties of animalslike swine, equine, avain
species such as chickens, turkey, duck, quail and wildbirds. The
virus also causes disease in cattle and other domestic ruminants.
Wildmammals such as ferrets, mink, mice, gibbons, baboons and
monkeys are also
susceptible to infection. The disease has also been reported
from aquatic animalssuch as whales are seals.
Mode of Transmission: Bird flu spreads through nasal,'
respirtory and othersecretions and faucal excretions of infected
bird. Uncooked or half cooked poultryproducts such as chicken and
eggs may spread the disease. Person to persontransmission generally
does not occur but may occur through the respiratory routeand close
human contact such as crowds, enclosed places etc. Several
influenza A
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strains can coexist in the same population and one individual
can be simultaneouslyaffected with two strains and reassortment of
the two strains form newer strainwhich may be more virulent than
previous one and spread the disease.
Direct transfers of a swine strain and an avian strain from
animals to man, withresultant clinical illness, have been
demonstrated, but such transmissions have beenobserved very rarely.
Some strains of human influenza virus can easily infect pigunder
natural condition The disease in man affects chiefly and the swine
virus caninfect man. In the respiratory system resulting chill,
1976, the soldier of new Jerseyinfected fever, earache, myalgia,
anorexia, believed to be fsneezing, nasalobstruction, sore throat
and cough. Pnemonic complications like bronchitis,pneumonia and
nervous, cardiac signs, conjunctivitis, diarrhoea and vomiting
mayalso be seen. with swine strain were modified form of the virus
of the 1918pandemic throughout the world.Avian strain can infect
mammals in nature and thusprovide a bridge between the vast
reservoir of avian infections and man. Wildmigratory birds may
spread the disease from one place to other. The isolation of
the
virus from duck ponds revealed that the water may also be a
possible route oftransmission. Influenza virus isolated from
aquatic animals such as wheals and seals,was found antigenically
similar to that of classical fowl plague virus. Workersassociated
with the seals were infected with the disease. These all provide
theinstance of avian strain of virus causing disease in mammals
including man.
Incubation Period : 1-3 days
Clinical Features: The disease in man affects chiefly the
respiratory systemresulting chill, fever, headache, myalgia,
anorexia, sneezing, nasal obstruction, sorethroat and cough.
Pnemonic complications like bronchitis, pneumonia and
nervous,cardiac signs, conjunctivitis, diarrhoea and vomiting may
also be seen. In animals
the. symptoms are almost similar to man. The disease spreads
rapidly in swine herd.In horses, along with respiratory problems
strangles, conjunctivitis and othercomplications have been found.
Infected birds manifest cough, sneezing, sinusitis,lacrimation,
oedema of head and neck and sometimes diarrohea and centralnervous
system involvement. In wild birds and fowls the influenza virus
isprincipally an intestinal infection rather than respiratory one
and sometimes goesunnoticed and they are the reservoir of the
virus. Acute haemorrhagic pneumoniais the post mortem finding in
seals.Diagnosis:Clinical diagnosis possible due to variability of
signs and the resemblance withother respiratory diseases.
Serological tests like HA, HI, CFT, AGPT and ELISA may
be done but are not much useful because of their frequent
infectionswith a multiplicity of serotypes. Virus isolation is
essential to establish the
cause of an outbreak. The isolation can be done in developing
chick embryo andcell culture in chick embryo fibroblast and canine
kidney cell line. Rapid test isalso available in CVL.Prevention and
Control:
