Chickens are susceptible to many infectious diseases. One of the most important of these is the viral disease known as Newcastle disease, which causes devastating losses in both commercial and village chickens. Reducing losses of large numbers of village chickens to virulent Newcastle disease is an essential first step to improving their productivity. Newcastle disease can be controlled by the use of vaccines. There are many Newcastle disease vaccines suitable for use in commercial chickens. These are available on the international market. The I-2 Newcastle disease vaccine has been developed for local or regional production and use in controlling Newcastle disease in village chickens. Many Newcastle disease vaccines deteriorate after storage for one or two hours at room temperature. This makes them unsuitable for use in villages where the vaccine may need to be transported for hours or in some cases days at ambient temperature. The I-2 Newcastle disease vaccine is more robust and is known as a thermostable vaccine. Thermostable vaccines still require long-term storage in the refrigerator. However during transportation of the vaccine to the field, the vaccine will not deteriorate as quickly as the traditional vaccines. Evaporative cooling provided by wrapping the vaccine in a damp cloth will be adequate for maintaining the viability of the vaccine during transportation to remote villages. However if it is stored in direct sunlight or allowed to reach high temperatures (above 37°C) for more than a few hours it too will deteriorate and be unsuitable for use as a vaccine. Immunity to Newcastle disease virus Chickens that survive infection with virulent Newcastle disease virus develop a long lasting immunity to further infection with Newcastle disease virus. The basis of this immunity is: 1. Circulating antibodies. 2. Secreted antibody producing mucosal immunity. 3. Cell mediated immunity. Newcastle disease virus of low virulence induces similar immune responses without causing severe disease. This is the basis of vaccination. Live vaccines These vaccines are made with virus that is alive and able to infect cells. Strains of virus of low or moderate virulence are used. They mimic natural infection and induce all three immune responses. Killed vaccines The ability of the virus to infect cells has been destroyed by treatment with a chemical, radiation or heat. These vaccines invoke only a circulating antibody response.
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