As described in the article “Poultry Vaccinations – An Insurance Policy” the fight to protect chickens against the most devastating viruses is a continuous one. Viral diseases are best prevented by vaccinating chickens to trigger an immune response; while this doesn’t eliminate the virus from the farm, it does act to prevent the worst reactions in your chickens. The virus is present, but not able to do its ‘job’ attacking your chickens.
Vaccination in the hatchery at one day old stimulates an immune response, which in turn builds up antibodies against the target virus while inherited maternal antibodies are losing their effectiveness. The vaccines used at Gale’s Agro Products include those designed to give protection against:
Marek’s Disease (Broilers and Layers)
First identified in 1907, this virus is commonly found in chickens around the world. It is highly contagious, spreading in the dust and dander being shed by infected birds, and can survive for long periods in the poultry house. Young chickens are very susceptible to infection, resulting in reduced growth performance and increased mortality. The virus can also compromise the bird’s immune system (immunosuppression) which leaves them at risk of contracting other secondary diseases which may already be present in the poultry house but not a risk to strong, healthy birds. There are several strains of this virus, some of which are more severe. There is no cure – prevention by vaccination, as well as a good biosecurity program, are the best defenses against Marek’s disease.
This virus has not been shown to transmit vertically from hen to chick (through hatching eggs). It is usually transmitted from one infected bird to another in close proximity to each other.
Infectious Bursal Disease, IBD or Gumboro Disease (Broilers and Layers)
Another very contagious virus that has caused huge economic damage to the global poultry industry, IBD usually affects birds younger than 17 weeks old. It causes, among other things, immunosuppression which can lead to secondary infections of other diseases. Chickens between 3 to 6 weeks old appear to be most susceptible, and will suffer from sudden increases in mortality, loss of appetite, huddling, and even diarrhea. Once a poultry house has been exposed to IBD it is very difficult to get rid of. Post mortem symptoms are very specific, usually a swollen organ called the “bursa of Fabricus” but also swollen kidneys and blood clots in the breast and thigh muscles.
Like Marek’s, IBD has not been shown to transmit vertically from parent to child – instead, infected birds drop faeces in their house litter where uninfected birds scratch and peck, becoming infected through oral ingestion. A good vaccination program combined with strong biosecurity measures – including good disinfection and long rest periods – are the best defense against IBD.
Newcastle Disease (Broilers and Layers)
Newcastle Disease Virus (NDV) affects bird species in varying degrees. Chickens appear to be the most severely affected, while waterfowl seem less susceptible. Wild birds, including the migratory birds that stop to feed in Caribbean islands every year, may carry strains of NDV without having strong symptoms. They can shed virus through their faeces and through respiratory droplets, both of which are picked up by indigenous bird species like pigeons which then fly around (and sometimes into) poultry houses.
There is no cure once birds are infected, however vaccination can reduce the severity of the response. Symptoms in unvaccinated birds can begin as soon as 2 days after infection, and may include muscle tremors, drooping wings or even paralysis; torticollis (star gazing), clear discharge from the mouth, and sudden death. Less severe infections can result in sneezing and coughing, diarrhea and depression. The severity of this disease and the lack of treatment mean that in many cases, NDV infected flocks are culled and incinerated to prevent further spread of the virus.
Vertical transmission pathways have not been clearly identified, and NDV infections are thought to most likely be transmitted from bird to bird. Vaccination and a strong biosecurity program are very important, including preventing wild birds from entering your poultry house.
Fowl Pox (Turkeys and Layers)
Fowl Pox is another world-wide virus affecting poultry negatively. There varying degrees of ‘fowl pox’ starting with the less aggressive skin lesions (“pox”) on un-feathered skin but progressing to lesions on internal organs and respiratory pathways. The virus develops slowly in poultry, often taking 2 to 8 weeks from infection to recovery – luckily the lesser strains do not usually cause high mortality. The virus can be spread from bird to bird through skin contact but in the Caribbean the most common source of initial infection appears to be mosquito bites. When mosquitoes bite an infected bird they can transmit the virus to birds in the same house or in nearby houses.
Once infected, birds can be treated with antibiotic skin treatments to prevent secondary bacterial infections but there is no treatment for the virus itself. Turkeys appear to be more likely to have higher mortality after a pox infection than layers, however layers will also experience reduced egg-laying and therefore prevention is important to avoid economic losses with both types of bird.
Fowl Pox is best managed with vaccination combined with removing mosquito habitats near to your poultry house.
