The project on village chicken production in Hwedza district, Zimbabwe, was initiated in cooperation with the Korea Program for International Cooperation in Agricultural Technology (KOPIA) and the Scientific and Industrial Research and Development Centre (SIRDC). It is also a collaboration in working together with small holder farmers at village level and Agritex. This initiative will improve indigenous chicken production by increasing poultry health management, nutrition, hatchability, growth rates, meat yield per bird, and reduce mortalities throughout the production cycle– thus improving farmers’ incomes through indigenous chicken production. With such improvements, household consumption and income will be greatly increased. Poultry vaccines are widely applied to prevent and control contagious poultry diseases. Their use in poultry production is aimed at avoiding or minimising the emergence of clinical diseases at farm level, thus in turn increasing production.
Vaccines and vaccination programmes vary broadly in regard to several local factors (e.g. type of production, local pattern of disease, costs and potential losses) and are generally managed by the poultry industry. The financial losses caused by the major epidemic diseases of poultry (avian influenza and Newcastle disease) have been enormous for the entire poultry production value chain. Vaccination should also be applied in the framework of poultry disease eradication programmes at national or regional levels under the official supervision of public Veterinary Services, especially Newcastle disease which is a notifiable disease in Zimbabwe.
Herd immunity protection against the clinical form of the disease is effective at an individual level, whereas the reduction of both susceptibility and infectivity also benefits the entire poultry population in the vaccinated flock/area. The positive effect on a vaccinated population known as ‘herd immunity’ may be defined as; the reduced probability of an individual (bird or flock) becoming infected whenever it is part of a vaccinated population. Herd immunity is important at two levels:
- Flock level: if a single bird in a vaccinated flock is not immunised, it has a chance of becoming infected which is inversely proportional to the level of protection achieved by the other vaccinated and immunised birds in the same flock;
- Country/region/compartment level: the higher the prevalence of vaccinated flocks in the vaccination area, the lower the probability of infection in unvaccinated flocks located in the same country/area/compartment.
In order to optimise the ‘herd immunity’ effect in a vaccination area, in this case Hwedza Chishaka village, it is of the utmost importance to target the bird species with the highest susceptibility to any given infection. The protection of the most susceptible poultry species serves to lower both the risk of disease introduction and the infectious pressure in the environment, thus reducing the risk of a massive spread of the infection to unvaccinated poultry farms situated in the vaccination zone. With an aggressive vaccination approach we have adopted reducing disease pressure in the community.
Tips for Successful Vaccination
If a vaccine is mishandled or improperly used, it may result in vaccination failure. Vaccines are labelled with instructions for use. If the entire flock is not vaccinated properly, the disease may spread. Newly hatched chicks have some passive immunity passed down from the mother through the egg. Vaccination of chicks at less than 10 days of age often does not produce uniform or lasting immunity. Therefore, vaccine stock should be rotated, as vaccines can deteriorate over time. Vaccines come with a date of expiration, thus any expired product should be discarded.
Each vaccine is designed for a specific route of administration, and only the recommended route should be used.
Sick birds should not be vaccinated, and vaccines should be protected from heat and direct sunlight. As most vaccines are living, disease-producing agents, they must be handled with care. When using the drinking-water method of vaccination, the water should be free of sanitizers and chlorine, as live-virus vaccines are readily destroyed by these chemicals. After vaccinating, all opened containers should be burnt or disinfected to prevent the accidental spread to other poultry species.
An important part of the procedure is to ascertain whether the vaccine has worked, or been “taken”. A good example of this is the fowl pox vaccine, which is administered by a wing stab. Within 7 to 10 days after vaccination, a “take” should appear at the vaccination site. This is in the form of a small pimple, one half to one centimetre in diameter. If the take is larger and has a cheesy core, it indicates that contaminants have been introduced either with the vaccine or with dirty vaccinating equipment. A check for takes would involve inspecting approximately 100 birds for every 10,000 vaccinated.
Failure to find evidence of success could be because of:
- Faulty technique resulting in the vaccine not being introduced into the vaccination site.
Faulty vaccine – too old or not stored or mixed correctly.
- It would be unusual but not impossible for the vaccine to be faulty from manufacture.
The birds are already immune, i.e. the immune system has already been triggered as a result of parental (passive) immunity, previous vaccination or other exposure to the causal organism.