Poultry is one of the most vibrant commercial sector which is playing a vital role to
bridge the gap between supply and demand of animal protein foods to cater for its ever
increasing human population 2.1 per cent annually in Pakistan (Sahota et al. 2003).
Vaccination is one of the most effective way to prevent the poultry birds from the
specific diseases. Disease producing microorganisms can be classified smallest to largest as
viruses, bacteria, fungi, protozoa and parasites. All, except the viruses are sensitive to drugs
when outbreaks occur. Vaccination is basically the introduction of a specific biological substance
(antigen) into the bird to stimulate the antibodies formation or immunity to a particular disease.
Usually the biological substance is avirulent the live disease organisms, which are capable to
protect the bird against the particular disease by producing an immune response. Presence of
these organisms (antigen) in the blood stimulates the body's defense mechanism to produce
antibodies that neutralize the disease causing organisms when the bird is exposed to them
(Kamboh et al. 2009).
A danger of such type of live vaccines is that the live microbes can back mutate to a
virulent form. While, dead vaccines that contain whole killed (usually by formalin or phenol)
microbes are safe. They may contain little or no extraneous material and therefore tend to
produce fewer adverse effects (Palombo and Semple 2001). The vaccines that contain dead
organisms are safe with respect to residual virulence and are easy to store, since organisms are
already dead. While live vaccines may possess residual virulence for the animal by reversion of
avirulent organisms to fully virulent type or spread to nonvaccinated animals. Dead vaccines
have very little risk of ‘alive’ contamination, while live vaccines always run the risk of
contamination with unwanted organisms; for instance, outbreaks of reticuloendotheliosis in
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chickens in Japan and Australia have been traced to contaminated Marek’s disease vaccine
(Tizard 1995).
Avian Influenza viruses typically produce Syndromes ranging from asymptomatic
infection to respiratory disease and drops in egg production to severe, systemic disease with near
100% mortality (Olsen et al. 2002). Avian influenza initially was recognized as a highly lethal,
systemic disease (i.e., highly pathogenic). HPAI was known by various name including fowl
plague, fowl pest etc. Avian Influenza viruses are classified in the family orthomyxoviridae,
genus influenza virus A (Garten et al. 2009). Avian influenza viruses can be categorized into
four clinical groups:1) highly virulent, 2) moderately virulent, 3) mildly virulent, and 4)
Avirulent (Swayne and Suarez 2000). Avian Influenza further sub type based on serologic
reaction of HA and NA surface glycoproteins. Fifteen sub types of HA and nine sub types of
NA are recognized (Swayne and Suarez 2000). MP AI viruses in domestic poultry produce
clinical sign reflect abnormalities in the respiratory, digestive, urinary and reproductive organs
(Allwright et al. 1993). To date, naturally occurring highly virulent influenza A viruses that
produce acute clinical disease in chickens, turkeys and other birds of economic importance have
been associated only with the H5, H7 and H9 subtypes. Influenza A viruses of subtype H9 are
now considered to be wide spread in poultry and have demonstrated the ability to infect humans
(Fedorko et al. 2006).
To date, all outbreaks of the highly pathogenic form have been caused by influenza A viruses
of the subtypes H5 and H7. The disease is transmitted horizontally by direct contact through
contamination. There is little or no evidence of vertical transmission (egg-borne infection).
However, eggshell surfaces can be contaminated with the virus (Potima 2007). Wild and
domesticated water fowl is the major natural reservoir of influenza A viruses. Representatives of
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3
all of the different subtypes of avian influenza A virus have been isolated from birds, particularly
from aquatic species such as ducks, geese, and gulls (Karasin et al. 2000). Wild birds such as
geese, ducks and game birds; they can be carriers of even highly pathogenic strain H5N1
shedding the virus in their feces without clinical signs of disease.
Thus, the present study was carried out to examine the viral contamination (Influenza A
virus) in poultry vaccines manufactured locally and imported from different countries of the
world in Pakistan. The findings of the study have helped us to see the Avian Influenza A virus
contamination in vaccines which are used in field conditions and also help to evaluate the purity
of vaccines. The RT-PCR based technology has been described for the detection of different
RNA viruses such as Newcastle disease virus etc. (Payne et al. 1981) revealed contamination of
vaccines with ALVs, specifically in two Marek´s vaccines, which confirms that these agents are
potential contaminants of viral vaccines applied in poultry. This assay has meant a considerable
advance due to a higher sensitivity and specificity upon differentiating the subgroups compared
with ELISA. It is quicker test for detection of RNA viruses than the viral isolation, which
requires until 10 days and it needs detection by ELISA for the identification result.