Vaccination, a vexed issue for small poultry farmers

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Marek’s disease

Marek’s disease is a severe debilitating and often terminal viral disease affecting chickens. Infected birds become emaciated with drooping wings and may develop paralysis in one or both legs. Tumours may also develop within the bird’s internal organs.

Marek’s disease is invariably a lot worse that it normally appears because only a small proportion of the birds in an infected flock may show these symptoms and die.  However, the majority of birds will have ‘unsymptomatic’ infection and although appearing outwardly normal, they will be shedding virus particles in huge quantities for the rest of their life on the farm. Only a small percentage of birds within an infected flock will show typical symptoms and die. 

When a virus shedding bird is introduced onto a farm where the disease has never occurred before high mortality rates are quickly seen. Once infected with the virus a farm is, for all practical purposes, contaminated forever. Generally speaking, broiler birds encounter fewer problems from Marek's disease than do layers, simply because they spend less time on the farm.

However, the good news for small poultry producers is that vaccination against Marek's disease is highly effective provided it is carried out in the correct way. This particular vaccination is most correctly and efficiently done at the hatchery to one day old chicks. It is therefore easier all round for the producer to order already vaccinated chicks from the hatchery.

Otherwise, it is essential to ensure vaccination of all new birds on the day of their arrival on farm. Marek’s vaccine will not be completely effective if a bird has already been exposed to the disease for more than a few days prior to vaccination.  Marek’s vaccine is sold frozen for administration under the skin at the back of the bird’s neck. Label instructions must be followed to the letter for vaccination to be successful.

Fowl pox

Fowl Pox is caused by yet another highly infectious virus (the pox virus) affecting both chickens and turkeys. Fowl pox is strictly a disease of birds and entirely unrelated to the human illness called chicken pox. The disease typically causes round and firmly adhering scabs on any un-feathered areas of the bird’s skin, together with fever (high temperature) and a drastic fall in feed consumption, resulting in slow growth rates and reduced egg production.

Sometimes, the disease may cause inflammation in the mouth and trachea causing affected birds, which cannot eat. The virus is spread from bird to bird through the bites of blood-sucking insects or through wounds and scratches inflicted by birds on each other while fighting.

Though seriously debilitating and often fatal, fowl pox is easily prevented by vaccination. Vaccine is introduced directly into the skin by using a two-pronged metal needle previously dipped in the vaccine. All birds on the farm should be vaccinated at one time with yearly booster vaccinations recommended.

Newcastle disease

Newcastle disease is the most important of a wide range of respiratory diseases that cause devastating losses in both commercial flocks and village chickens. This virus disease, which is a major constraint on the productivity and survival of village chickens, can be controlled by the use of vaccines.

Some Newcastle disease vaccines deteriorate after storage for one or two hours at room temperature, which clearly makes them unsuitable for use in village situations where the vaccine may need to be transported for hours or in some cases days at ambient temperature.

The I-2 Newcastle disease vaccine, which has been specifically developed for local or regional poultry production is more robust under higher temperature conditions. It is described as a thermostable vaccine which requires long-term storage in the refrigerator.

However, this I-2 vaccine will not deteriorate as quickly as the traditional vaccines during transportation into the field. 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.

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