MAREK’S DISEASE

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Causative Agent(s)

Herpesvirus (serotype 1 is most virulent), DNA virus. Chickens are the most important natural host (quail can also be infected). One of the most ubiquitous avian infections.

The virus is highly contagious, matures into infectious enveloped form in the epithelium of the feather follicle, and is then released into the environment. Can survive for months in poultry house litter. Chickens infected by inhalation. Once infected, chickens are carriers for long periods of time.

Clinical Presentation and Epidemiology

Asymmetric progressive paresis, leading to complete paralysis of one or more extremities. May see a transient paralysis syndrome (ataxic for several days), probably due to vasogenic brain oedema. Acute outbreaks characterized by depression and death. With a more prolonged course, can see nonspecific signs such as weight loss, paleness, anorexia, and diarrhoea.

Diagnostic Considerations

Necropsy findings. Diagnostic sample of choice is buffy coat (includes lymphocytes which contain the virus). Most widely used medium for primary isolation is chicken kidney cell tissue culture.

Management and Treatment

No treatment, but some birds may show spontaneous regression of lesions, and recovery.

Control relies on vaccination (usually with turkey herpesvirus, serotype 3) done at hatching time, strict sanitation, breeding for genetic resistance.