Swollen Head Syndrome

(Dikkop [Thick head], Facial cellulitis)

Swollen head syndrome is an acute, infectious respiratory disease of chickens characterized by periorbital swelling, swollen lacrimal glands, sneezing, and variable mortality. It affects broiler chickens at 4-6 wk of age, broiler parents, and commercial layers, and has been reported in southern Africa, the Netherlands, the UK, and other countries.

Etiology:
There is strong evidence that swollen head syndrome is caused by a mixed infection of the avian pneumovirus responsible for turkey rhinotracheitis ( Avian Bordetellosis , Turkey Rhinotracheitis) and secondary adventitious bacteria (usually Escherichia coli ) that invade the subcutaneous facial tissues and result in the swollen head. However, there is also evidence that the primary cause, at least in some areas, is a coronavirus serotypically distinct from other infectious bronchitis ( Infectious Bronchitis) serotypes. Other respiratory agents, including Newcastle disease virus, paramyxovirus-3, avian influenza virus, infectious bronchitis virus, and Haemophilus paragallinarum (infectious coryza) may cause respiratory disease and egg production problems that are not dissimilar.
Clinical Findings and Lesions:
The initial signs are sneezing followed by reddening and swelling of the lacrimal glands and swelling of the periorbital tissues, which extend over the head and down to the intermandibular wattle area over the next 24-36 hr. Birds scratch their face with their feet. Death may occur at this stage, or later after progression to a generalized polyserositis. The disease course is 5-10 days. Affected birds show petechiation to severe congestion of the turbinate mucosa and lacrimal glands, and when skin is removed from the swollen head, purulent and edematous subcutaneous cellulitis is revealed. Generally, the trachea is unaffected.

Adult chickens may also be affected, but the signs are less severe—mild respiratory disease followed by a small portion of the affected flock showing markedly swollen heads. Other signs include torticollis, disorientation, and general depression. In layers, egg production usually drops significantly.

Diagnosis:
This is based on typical signs, supported by identification of the virus from the trachea, lungs, viscera, nasal exudate, and scrapings of the sinus tissue. Samples must be taken from birds showing early signs of infection, and virus culture must be perfomed within hours to ensure successful recovery of the virus. Primary isolation is best performed in tracheal organ culture or embryonated turkey or chicken eggs; subsequently, the virus can be cultivated in cell cultures.

The virus can be identified by electron microscopy or serology. Similar clinical signs have been seen with other respiratory viruses such as Newcastle disease virus and avian coronaviruses. Viral and bacterial isolation can differentiate between these diseases.

Treatment and Control:
Turkey rhinotracheitis vaccine is available, but no specific coronavirus vaccine is commercially available. The disease is exacerbated by poor management practices such as inadequate ventilation, overstocking, poor litter conditions, and poor general hygiene. Antibiotics reduce the severity of the disease somewhat, presumably by controlling secondary bacteria.
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