Possible P–Q Type Variation in Infectious Laryngotracheitis Virus

Abstract

FROM an outbreak of acute infectious laryngotracheitis in South Australia¹ a strain of virus was isolated which proved to be highly resistant to neutralization by antisera in the pock neutralization test. On intratracheal inoculation into susceptible birds, it gave rise to typical acute infectious laryngotracheitis in about four days, produced a typical vaccination reaction when given by the cloacal route and gave rise to antibodies fully active against a type infectious laryngotracheitis virus. On primary isolation it showed some degree of resistance to neutralization by its homologous and other infectious laryngotracheitis antisera, but after storage for eight months in the ‘dry ice’ refrigerator it was almost completely resistant to neutralization by all available antisera (see table). Prior to this outbreak, infectious laryngotracheitis was not known to be present in South Australia despite a careful watch being kept, and no spread of the typical explosive epidemic form of the disease in other flocks has followed this outbreak. A survey of hens throughout South Australia showed that, at the time of isolation of this strain, about 50 per cent of the flocks had birds with demonstrable infectious laryngotracheitis antibodies in their sera.