Avian metapneumovirus (aMPV), previously referred to as turkey rhinotracheitis,1 is an emerging viral pathogen in poultry, responsible for a highly contagious disease particularly in chickens and turkeys.2 Although aMPV infection often involves the respiratory tract, it can also affect the oviduct, contributing to reduced egg production.3 Birds of any age are susceptible to aMPV infection, and secondary infection with bacteria such as Escherichia coli, Bordetella, and Pasteurella can complicate the situation, resulting in a condition known as swollen head syndrome (SHS), with adverse impact on infected animals.3-5

aMPV was rst described in South Africa in 1978, but the disease rapidly spread to other regions in Europe and Asia2,4 and more recently in the Americas (United States, Brazil, and Mexico).6-10 The only countries reported as aMPV free are Australia and Canada.11 aMPV belongs to the family Paramyxoviridae and is further divided into four subtypes. Subtypes A and B were identied in South Africa and Europe, subtype C in Asia and the United States, and subtype D was detected in France.2,10,12-16 In Latin America, only subtypes A and B have been described, mainly in Brazil and Mexico.6-8,17

aMPV is a member of the genus Metapneumovirus, subfamily Pneumovirinae, family Paramyxoviridae.1 Apart from the subfamily Pneumovirinae, the family Paramyxoviridae contains a second subfamily Paramyxovirinae. While the subfamily

Pneumovirinae comprises two genera (Metapneumovirus and Pneumovirus), the subfamily Paramyxovirinae encompasses seven genera (Aquaparamyxovirus, Avulavirus, Ferlavirus, Henipavirus, Morbillivirus, Respirovirus, and Rubulavirus).