Swollen head syndrome: clinical observations and serological examinations in West Germany

Swollen Head Syndrome (SHS) affects both broiler and broiler breeders and has become a problem in many countries. Clinical signs similar to those described in SHS conditions have been observed in northern Germany with the disease observed mostly in chicken broilers between 4 and 5 weeks of age and in broiler breeders between 24 and 36 weeks of age. The mortality rate in broilers has been variable from negligible to 5%. In broiler breeders, the symptoms were accompanied with a drop in egg production reaching 2-3% after 1 to 2 weeks. 422 Serum samples from 21 broiler flocks were examined for the presence of antibodies to TRT-virus using indirect ELISA tests. Antibodies were detected in 2 flocks which suffered from SHS, but not in 2 flocks showing respiratory manifestations nor in 17 apparently healthy flocks. The results obtained from testing 178 serum samples from 10 breeder flocks revealed that antibodies to TRT-virus were present in one flock with SHS signs as well as in 6 apparently healthy flocks. In addition, no antibodies were found in sera collected from 3 flocks--one with SHS and respiratory disease history; one recovered from respiratory infection and one without disease history. Examination of paired serum samples from 3 breeder flocks that suffered from typical SHS-signs collected at the onset of the disease and during the convalescent stage, as well as sera from one broiler and one breeder flocks that showed respiratory manifestations, showed that there are significant increases in the number of positive sera in the flocks with SHS symptoms. The other flocks remained free from TRT antibodies.