January 26, 2013

vet. Dr. M. Sayedain. Jaffery


The word “VACCINE”, with us seems to have acquired the status of some mythical  elixir. It is considered  to be the end-all & be-all of disease control, a sort of panacea, hence we have placed our entire trust in its basket that is very fragile. May be this is the reason why the variety & volume of Live and Inactivated Vaccines, imported as well as  manufactured locally and consumed  here is the largest of what might be available or used anywhere else. Despite (or may be because of) excessive and indiscriminate application of assorted vaccines obtained from just anywhere, the state of flock-health continues to be the prime source of worry while the virulence, pathogenicity and epizootiological ecology of the infectious agents manifests no appreciable abatement.The antiquated Newcastle disease is as vibrant as ever, rather it  appears to be rejuvenating !


Before adoption of  an highly  intensive system to  raise  Hybrid chicken, in order to produce fertile Eggs, day-old Chicks, table Eggs and  tender Meat on commercial scale, there were only few infectious diseases like the Newcastle disease, fowl Pox  and  Borreliosis, etc,  encountered periodically in the native Fowl i.e., the desi murgh.  which used to be a part of traditional backyard flocks in almost every household. Today we have every infectious & non-infectious  problem (you name it, we have it) in our Hybrid chicken commonly known as  farm ki murghi.

We rather, also sometimes face new  emerging diseases, like the Adenovirus infection that was first  identified in Broiler chicks at Angara Goth ( a village on the out-skirts of Karachi). It did not exist anywhere else except in Pakistan. (Angara disesase reported in the prestigious Text-book  “Diseases of Poultry”, 10th edition, 1997, pp-119-22, published by AmericanAssociation of Avian Pathologists). While this disease has been controlled or eradicated elsewhere, here in the country of it origin, the Angara disease has unfortunately entrenched itself firmly in our epizootiological ecosystem and is now threatening to involve Layer birds as well. Main reason of our failure to contain the relatively mild adeno-virus, lies in the  hit-or-miss  application of the home-brewed “chutney” vaccines.

2- Basic philosophy of using a Vaccine is to incite a bio-phylactic phenomenon  within the body through training the haemopoietic system of the recipient to recognise the invader and save its identity in its memory, so that  the body is not taken unaware in the event of subsequent invasion by the actual pathogen of same ilk. Since the body is already tuned by vaccination to identify the specific invader, it brings into operation quite a complex  mechanism of defense that  protects the body from damages ensuing after subsequent  invasion by the same foreign invader. If otherwise, a body is left untrained, non-vaccinated, and has no record in its memory process of  the  identity of  disease causing agent, it will prove susceptible to the infection and suffer from disease along-with all its  consequences  & sequellae.

Once the proficiency of  identifying the invader is acquired by the body, the defensive response is automatically switched on, while the body does not even feel the attack or its counter-reactionary response aimed at  neutralization of the alien. Thus, the subsequent field exposure to actual pathogen , results in boosting up of the defensive  potential and the body may acquire solid & long-lasting immunity specific against that particular pathogen it was trained to identify.

In most cases such a  reaction  is highly explicit and of very narrow spectrum because the immunity holds good precisely for that particular invader against which it was induced. For example, a body trained to recognize  ND virus through ND vaccination will remain vulnerable to the attack by viruses other than Newcastle Disease. In some cases this specificity is so narrow that it will work only against that specific type or sub-type of the infectious agent against which it was produced, viz, some viruses like those of Infectious Bronchitis and Influenza,  have more than one antigenic type, hence vaccination is not effective for a different antigenic genre  of the same virus. Such a propensity offers serious problems for Immunisation procedures which have to be taken care of by developing  vaccines for each separate strain, type  or subtype  of the  same virus..


Classical response of a body to vaccination is also not so simple or straight forward. This attribute is subject to  innumerable factors that influence the ultra-delicate  physio-chemistry of the body and  bio-kinetics of  the antigen.

3-For example,

a)     state of  physiological health of the  recipient of  the vaccine,

b)    level of residual passive or active immunity present in the body,

c)     standard of nutrition, balanced according to the demand of the bird,

d)    quantum  of  left-over remnants or residue of mycotoxins and potent drugs in the body,

e)     potability, volume, temperature and  availability of drinking water,

f)      nature, extent and type of Stress-inducing factors in the environment,

g)     specification of  live vaccine and its inoculums prepared prior to use,

h)    criterion of inactivated or oil-emulsified vaccines  and their stability,

i)       method & route of administering the vaccine,(ocular,oral,parental, etc)

j)       presence of concurrent disease, (clinical, non-clinical, occult, etc)


After receiving a vaccine, particularly the live one, an otherwise healthy bird may sometimes show a sort of local or generalized short-lived  reactions, such as momentary dullness, listlessness, transient conjunctivitis, ephemeral pyrexia, diarrhea, momentary nervousness, quick-ebbing swelling or dry pock-marks at the site of injection, etc, etc. Some such signs would often suggest that the vaccine was well taken by the defensive system of the bird. Sometimes the reaction to a live vaccine may be manifest as a simulation of disease, which  in fact may not be true disease. Enlarged  Bursa of  Fabricius after administration of  “hot” vaccine against bursal disease and nervous or respiratory  signs following mesogenic ND vaccine (or at times even lentogenic vaccine) may be rare but are not uncommon  post-vaccinal  responses. In such instances careful observation is however, called for to distinguish a positive response which is beneficial, from the negative backlash  which can be damaging.


Such easily ignorable demeanour in flock are, most of the time, either not identified or disregarded by the farmer. However, appearance of some odd observations not distinctly explainable may induce marked disturbance in state of health or render the body vulnerable to ailments with untoward consequences. Total  absence of  such  low-key  and  temporary behaviour in

the flock immediately after vaccination might be  mis-construed as an inadequacy of  the  immuno-competence  of  birds or  impotence of  vaccine.

4- Factors such as Feed intake or assimilation of nutrients from feed and the rate of their conversion into healthy growth, live-ability  or productivity of the flock, may often appear to be below optimum without any apparent reason. In such instances attention of the farmer gets unnecessarily occupied and concerned about one or  the other disease, (which may not be there) and its treatment (which may not be indicated), whereas the reality might only be a reflection of some adverse reaction of vaccine or its wrong application. Bluish-black comb or enormously swollen head can be encountered after faulty injection of an oil-emulsified vaccine, which though gradually dissolves, becomes a source of severe distress for the bird. Acute conjunctivitis after un-hygienically administered intra-ocular vaccine might often result in the loss of affected eye. The chick may be lost due to gangrenous dermatitis of the wing when subjected to improper wing-web inoculation. Severe respiratory signs may crop up after aerosol vaccine spray where contaminated water was used. Expected positive response to the  otherwise high-quality vaccine can be rendered negative, where carelessness is allowed to creep in any step of   vaccination procedures, viz, storage and transportation etc, of the sensitive biologic.


In order to  achieve sustained performance,  in terms of  Live-ability, Health, Rate of Growth,  Feed Conversion Ratio (FCR),  Productivity true to the potential of  the Hybrid chicken and of course Return on Investment , etc, it therefore becomes highly imperative that correct concepts be developed about Vaccine, Vaccination, Immunisation and Immunity. These terms, so commonly used, are not synonymous and call for elucidation and correct awareness by each & every Stake-Holder/Entrepreneur in the various inter-dependant sub-sectors/components of the fast developing Industrial complex of Chick, Egg, & Meat Production Technologies.



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