Avian metapneumovirus infection in turkeys: a review on turkey rhinotracheitis

Avian metapneumovirus (aMPV) is a major respiratory pathogen in poultry worldwide, causing an acute and highly contagious infection of the upper respiratory tract in turkeys (turkey rhinotracheitis) and many other avian species, including chickens (swollen head syndrome). Since its first description in late 1970s in South Africa, 6 subtypes (A, B, C, D, and 2 new subtypes) have been identified. Infected animals develop local and systemic immunity. However, maternal derived antibodies do not correlate with protection. In intensive flocks, infection spreads rapidly between birds. Wild birds can be infected and they are suggested as probable links. Affected turkeys exhibit nonspecific symptoms and lesions dominated by an acute inflammation of the upper respiratory tract. The virus can induce a decrease in egg production and poor eggshell quality that cause huge economic losses to the poultry industry. Diagnosis of aMPV infection is performed by ELISA tests and molecular methods (RT-PCR). Application of rigorous biosecurity and vaccination programs are crucial and effective for the control of turkey rhinotracheitis. Different types of vaccines are used, with satisfactory protection offered by live attenuated and inactivated vaccines. In addition, new vaccines are being developed and tested which seem to give convincing results.