A study conducted at the University of Georgia Poultry Diagnostic and Research Center and funded by the U.S. Poultry and Egg Association has revealed new insights into infectious laryngotracheitis (ILT).

The study found that combination live Newcastle disease and infectious bronchitis vaccines interfered with the immunity produced by tissue-culture-origin ILT. Both tissue-culture- and chick-embryo-origin ILT vaccines depressed antibody response to infectious bronchitis and Newcastle disease, suggesting mutual interference.

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The ILT virus designated strain 63140 persists in the trachea longer than a U.S. Department of Agriculture standard challenge strain. The incubation period for the prevalent North Georgia field strain is only two to three days. There is a high degree of correlation between antibody title level against ILT and the geographic distribution of the infection in North Georgia. Protection is adversely affected when dilution of vaccine viruses is carried out.

The emergence of strain GA63140 ILT has resulted in significant losses in the regional broiler industry. Health professionals involved with egg production flocks should be aware of the variants of this strain, which require diligent application of chick-embryo-origin vaccine. The protective ability of ILT vector vaccine has yet to be determined.