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Swollen Head Syndrome
Other Names: Avian Metapneumovirus
Swollen head syndrome (SHS) is an acute, highly contagious upper respiratory tract infection of poultry. SHS is caused by infection with the avian metapneumovirus (AMPV), a type of pneumovirus which is classified into four subtypes (A, B, C, and D). Other diseases associated with this virus include turkey rhinotracheitis (TRT) and avian rhinotracheitis (ART). AMPV was first reported in South Africa in 1978, in a flock of turkeys. It quickly spread to other regions, affecting poultry worldwide.
The typical clinical signs seen in chickens infected with the virus include swelling of the periorbital and infraorbital sinuses, particularly around the eye, coupled with mild conjunctivitis. SHS has similar clinical signs as several other viruses, especially Newcastle disease and APMV-3, avian influenza virus, and infectious bronchitis virus. There is also several different bacteria and Mycoplasma species that cause similar clinical signs to that seen in chickens with SHS.
The only way to know for sure that a bird has SHS is by isolation and identification of AMPV in tests conducted at a veterinary diagnostic laboratory. Testing is performed on the nasal secretions or tissue scrapings, taken from the sinus and turbinates of chickens during the early stages of infection. The various tests available include real-time polymerase chain reaction (RT-PCR) (used to detect viral RNA in secretions), immunohistochemistry (on formalin-fixed tissues), and enzyme linked immunosorbent assay (ELISA) or serum neutralization (to detect pneumovirus-specific antibodies in the blood).
The virus spreads primarily by direct contact with infected birds or indirect contact through contaminated feed, water, fomites or personnel.
Case 1: Swollen head syndrome in a Chickens From 50 commercial broiler flocks included in a study concerning respiratory disease, signs of swollen head syndrome (SHS) were shown in eight. Postmortem examination was performed in eight birds showing signs of SHS from each flock. The trachea and head from each bird were collected for laboratory investigation. An enzyme-linked immunosorbent assay (ELISA) was used for the detection of viral and avian mycoplasma antigens in the trachea, and bacteriologic examinations were performed from the infraorbital sinuses of the infected birds. According to the ELISA results, the most frequently detected antigen in the trachea was Mycoplasma synoviae (six flocks, 75%), followed by infectious bronchitis virus (IBV) (five flocks, 62.5%), avian adenovirus (four flocks, 50%), avian reovirus (three flocks, 37.5%), Mycoplasma gallisepticum (one flock, 12.5%), and Newcastle disease virus (NDV) (one flock, 12.5%). Turkey rhinotracheitis (TRT), infectious laryngotracheitis, and avian influenza viral antigens were not detected. Experimental assays for characterization of NDV and IBV isolates showed that they were strains of low virulence (evidently vaccine strains). Bacteriologic examinations from the infraorbital sinuses of the affected birds resulted in the isolation of Escherichia coli (seven cases, 87.5%) and Staphylococcus spp. (one case, 12.5%). It is evident that TRT virus did not play a causal role in SHS in commercial broiler flocks in Greece, but in this condition, other viruses (IBV, NDV), mycoplasmas, or bacteria may be involved, and environmental conditions seem to be essential to the occurrence and severity of the disease. Ref