Age affected: 3-30 weeks. Broilers develop problems from 5-8 weeks and breeder pullets at 10-18 weeks of age.
Causes: Double stranded RNA reovirus.
Effects: Incubation period is 9-13 days. Birds are down on the hocks and have stunted growth, are reluctant to move and have an uneven gait. Swollen tendons above and below the hocks and a ruptured gastrocnemius muscle are also seen.