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Recently Avian metapneumovirus (AMP) infection was diagnosed in turkeys and broilers in North Carolina.  This virus is responsible for swollen head syndrome (SHS) in broilers and has been recognized as a clinical entity for over 45 years in various broiler production areas in the World. Although Koch’s postulates confirm that the AMP virus is pathogenic, clinical presentation and severity are influenced by intercurrent infection with other pathogens and environmental conditions.

In the Republic of South Africa where SHS was first described, the condition is both seasonal and regional.  Outbreaks were initially observed in broiler flocks on the highland (5,000-foot) inland  plateau during the harsh winter characterized by cold and dry conditions.  Outbreaks were associated with immunosuppression, at the time caused by emerging variants of infectious bursal disease.  Metapneumovirus resulted in a transient upper respiratory infection with obvious conjunctivitis and involvement of the Harderian gland.  Irritation caused mildly affected birds to  scratch at their eyelids. This resulted in superficial abrasions and lacerations of the periorbital region with introduction of fecal material carrying STEC from litter into the ocular adnexa. Within days, a flock aged from 20 to 30 days of age would progress from mild respiratory signs to severe cellulitis of the periorbital and head region with symblepharon and death due to dehydration. In severe case mortality could rise to 30 percent of the flock through to harvest with severe runting of affected survivors.

Fortunately, there are both serologic and antigen detection systems available in the U.S. at numerous laboratories to assist diagnosticians. 

• The University of Georgia Poultry Disease Research Center (PDRC) offers an rt PCR assay for subtypes A, B and C of AMP.  Virus isolations are also available to conduct virus characterization.  The PDRC requests submission of whole heads, or tracheas, that must be collected  at an initial stage of an outbreak to avoid secondary bacterial contamination.  Specimens should be submitted by Express Next Day delivery on ice
• The BioChek ELISA and the IDEX ELISA will detect antibodies to subtypes A and B and both are available at diagnostic laboratories operated by the Universities of Delaware, Purdue, Minnesota and Iowa State. 
• rt PCR is available from AviServe, Iowa State University, NVSL, PDRC, South Dakota State University, University of Minnesota, the Pennsylvania Diagnostic Laboratory and the University of Delaware.

Practitioners involved in egg production should consider conducting serologic surveys on flocks to determine the extent of AMP exposure. The results would be especially instructive for flocks that have experienced high mortality due to avian coryza. This is predicated by observations that in the past two years, the mortality and impact on egg production due to avian coryza has become more severe, suggesting a concurrent pathogen exacerbating the impact of infection with the primary bacterial pathogen.

Dr. Jose Linares of CEVA Animal Health has prepared an overview with images of lesions associated with infection. This informative contribution can be accessed by clicking on to the link.

Avian Metapneumovirus – Diagnostic Labs that can test for aMPV