Disease prevention is better than cure. Chickens should be kept in optimum conditions to help prevent problems arising, and should be regularly inspected to enable you to detect issues early in their progression.
This can be controlled in commercial situations with a vaccination for day-old chicks. It is caused by a herpes virus, and spread in feather dander, which can spread for miles on the wind. It matures and becomes infectious in the feather follicles, and is then released back into the dander. Once in the environment it remains infectious for at least a year. Carrier birds can shed virus while showing no signs of infection.
Marek’s Disease causes development of tumours in the nervous system, resulting in paralysis of legs, wings and head, and usually death due to suffocation or dehydration. Surviving birds will be carriers and at risk of repeated bouts of disease.
As birds get older they develop some degree of resistance, and have a degree of immunity for 1 month of age. The best way to reduce levels of disease is regular cleaning of the poultry house to remove as much dander as possible.
Mycoplasma (Chronic Respiratory Disease)
This is a serious respiratory diease, and poultry are often sub-clinically affected, the diease only becoming apparant when the bird is faced with another challenge. Mycoplasma gallisepticum is spread through eggs, by aerosol droplets and direct contact. It causes chronic respiratory disease, with birds sneezing, coughing and producing nasal discahrge. Affected birds may become droopy and lethargic, have a reduced appetite and lose weight. Antibiotics can be effective at treating this disease.
Stress often plays apart in infections becoming apprant, either when moving birds, or with unfavourable conditions, including poor ventilation.