SWOLLEN HEAD SYNDROME 

  Etiology
Swollen Head Syndrome (SAS) is a multifactorial condition involving the sequence of immune suppression (IBD, MD, CA) followed by exposure to a respiratory virus (IB, TRT, NCD) and terminating in E. coli cellulitis of the tissue surrounding the eyes. Related pneumoviruses including turkey rhinotracheitis virus causing tracheitis and sinusitis in turkeys and swollen heads in broiler breeders is accepted as a precipitating agent of SHS in broilers. Outbreaks of facial cellulitis have been diagnosed in California without evidence of TRT infection which is exotic to the USA. Environmental stress (low temperature and humidity, or high dust and ammonia levels) due to inadequate ventilation or climatic extremes exacerbates the prevalence and severity of SHS. Pathogenic E. coli strains, usually introduced through drinking water are responsible for the subcutaneous facial cellulitis which is characteristic of SHS.

Occurrence and Economic Significance
The condition occurs in southern Africa, Southeast Asia, and Latin America, especially in high-density broiler growing areas. Regionally, SHS often shows a seasonal occurrence. Losses due to primary mortality may attain 10% to 20% of the flock. Subsequent bacterial septicemia and airsacculitis which occurs approximately 10 - 14 days after the onset of acute facial cellulitis may result in additional mortality of up to 20% of survivors of the acute outbreak.

Transmission
The immune suppressive and respiratory agents are transmitted by direct and indirect contact and usually are associated with defects in biosecurity, especially on multiple-age farms. Pathogenic E. coli or other opportunistic pathogens including Ornithobacterium rhinotracheale can be introduced through contaminated water and litter. 

Clinical Signs
Under commercial conditions SHS is characterized by acute onset of morbidity involving up to 10% of the flock in broilers aged 14 - 30 days.

Affected birds show ocular discharge and conjunctivitis progressing to periorbital swelling. Terminally, eyes are closed and enlargement of the head is evident.

Pathology
Subcutaneous accumulation of viscous sero-purulent exudate, which becomes caseous in chronic cases.

Acutely affected birds may show tracheal hyperaemia and pulmonary congestion. Chronic cases show caseous airsacculitis, perihepatitis and peritonitis. Bursal and thymic atrophy consistent with previous IBD and CA infection respectively may be present.

Diagnosis
The obvious gross lesion comprising subcutaneous cellulitis of the head is highly suggestive of SHS. Attempts to isolate and identify primary and secondary pathogens should be carried out.

Serologic profiling of flocks is necessary to determine the pattern of maternal antibody decline and the response to either vaccination or field challenge with respiratory and immunosuppressive agents.

Treatment
Administration of water soluble antibiotics including fluoroquinolones will produce a transitory decline in flock mortality. Losses frequently resume after withdrawal of medication. Antibiotics should be used in accordance with the manufacturer's instructions and statutory restrictions relating to the withholding period should be observed. Medication should demonstrate a positive benefit:cost ratio. Improper or prolonged use of antibiotics will result in emergence of drug-resistant E. coli. In small-scale operations acute cases can be salvaged by transfer to small pens where food and water are available and birds can be treated with antibiotic and protected from persecution by the remainder of the flock.

Prevention
Chlorination of drinking water to 2 ppm and installation of closed (nipple) drinking systems are recommended.

Alleviation of obvious managemental deficiencies and environmental factors will reduce the intensity of respiratory stress.

Appropriate vaccination programs are required to prevent immunosuppressive and respiratory viral diseases.

Breeders can be vaccinated with commercial pneumovirus vaccines available in Europe. Attempts at immunization of broilers have not been successful.

Information provided by a Handbook from:
AMERICAN SOYBEAN ASSOCIATION

Gander Gab/Perfect Pets

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©2004