Introduction

A retrovirus infection of chickens, turkeys, ducks, geese, and quail with morbidity up to 25%, usually higher in females than males. A gradual increase in mortality and poor growth in broilers may be the main signs. Transmission is lateral and possibly transovarian, and the infection can be spread by mosquitoes or in contaminated Marek's disease vaccines. There is an incubation period of 5-15 days.

Signs

• There may be no obvious signs.
• Diarrhoea.
• Leg weakness.
• Marked stunting when Marek's disease vaccine is contaminated.

Post-mortem lesions

• Neoplastic lesions in liver, spleen and kidney.
• Sometimes nodules in intestine and caecae.
• Sometimes enteritis and proventriculitis (especially in broilers infected with contaminated Marek's disease vaccine).

Diagnosis

Pathology, chick inoculation.

Treatment

None.

Prevention

Formal control programmes have not been documented as the condition is sporadic and relatively self-limiting. Avoidance of contamination of live vaccines is the main control measure practised.