Benifiting poultry by EGG-adapted Gumboro vaccine

The deadly “Gumboro” disease of chicken is caused by a virus, which results into immuno-compromising in the birds and leading to great economic losses. The disease can now be controlled by a locally developed egg-adapted live as well as inactivated vaccines thus benefiting the country by saving the foreign exchange with regards to WTO scenario.

Livestock and poultry play a major role in the economy of Pakistan. Out of total deaths in poultry, 20% are due to infectious bursal disease (Gumboro) alone. The disease causes increased carcase condemnation rates. The infectious bursal disease commonly known as Gumboro is an acute, highly contagious viral infection of young chickens, which spreads very rapidly by contact with sick birds. The virus has a great affinity for the lymphoid tissue as its primary target. with special predilection for the bursa of Fabricious (BF), which is responsible for maturation of immune system of the birds. The economic importance of the disease is manifested in two ways i.e. direct and indirect losses. The direct losses are in the form of high mortality. Indirect losses are due to acquired immunodeficiency or immuno-suppression, impaired growth and poor performance. Furthermore, the increased use of antibiotics and chemicals to fight against opportunistic (secondary) infections is a major concern for human health. Gumboro virus is resistant to many disinfectants and environmental factors, and remains infectious for at least four months in the poultry house environment. Because of the resistant nature of Gumboro virus, once a poultry house becomes contaminated, the disease tends to recur in subsequent flocks.

The Gumboro virus does not affect humans: The immune system is that part of the body which fights infectious disease micro-organism by producing specialized cells, lymphocytes, which secret specialized large protein molecules, antibodies. These attack infectious micro-organisms preventing them from entering, multiplying and damaging parts or cells of the body. Early recruitment of the immune cells occurs in the Bursa of Fabricius and the Thymus. If the virus damages both of them in young chickens, then this organ will not be capable of programming sufficient numbers of lymphocytes. Thus, the chickens will experience reduced immune system capabilities (immunosuppression). The severity of the disease is directly related to the number of susceptible cells; therefore, the highest age susceptibility is between 3-6 weeks. Chickens infected with Gumboro virus shed the virus in their faeces thus contaminating the feed, water and poultry house litter. Other chickens in the house become infected by ingesting the virus and can easily be transmitted among the farms by people, equipment and vehicles.

The majority of field infections are sub-clinical which are economically more important. Diseased birds have poor body weight gain and high feed conversion ratios with high mortality and excessive reactions to respiratory vaccines. Clinical signs of disease include dehydration, trembling, ruffled feathers, vent pecking, and depression. On necropsy, the principle lesions are found in the bursa of Fabricius (BF).

Diagnosis of IBD involves consideration of the flocks’ history, and of the clinical signs and lesions. Clinical signs alone are sometimes not sufficient to make a final diagnosis, but when combined with gross lesions, it is possible to arrive at a preliminary diagnosis. Confirmation of diagnosis should be accomplished by virus isolation or detection of viral antigens in tissues from suspected cases.

Keeping in view the current situation, the author adapted local Gumboro virus on chicken embryo for the preparation of an egg-adapted vaccine in the Biotechnology Laboratory, Department of Veterinary Microbiology, University of Agriculture, Faisalabad. Gumboro virus from field outbreaks was collected and purified from seven different areas of Pakistan. No differences were observed among all the different isolates collected from the Pakistani outbreaks in respect of polypeptide pattern, number and molecular weights but both differed from polypeptide maps of live commercial Gumboro vaccines.

Highest titre of antibodies against Gumboro disease virus as measured by indirect hemagglutination test was achieved in groups receiving locally prepared vaccine. Protection percentage was found maximum in groups receiving egg-adapted Gumboro vaccine prepared from local virus (98%).

In second part of the study, different adjuvants (chemical substances, which are supposed to enhance and prolong the vaccine performance) were used to prepare different egg-adapted Gumboro vaccines and protection level for each vaccine was assessed by challenge with virulent Gumboro virus. In another experiment the above mentioned an egg-adapted Gumboro vaccines were tried with liposomal and imuunostimulatory complexes (ISCOMs) as adjuvants by giving one or two shots of vaccines. Immune response was higher and protective with egg-adapted Gumboro vaccine prepared in positively charged form of liposomal vaccine and ISCOMs. It is concluded that vaccination with egg-adapted Gumboro vaccine prepared in liposome or ISCOMs adjuvants is the most suited way to immunize the birds against Gumboro virus. In present studies this combination proved safe and best for immunization of chicken without immunosuppression.