Demonstration of sites of latency of infectious laryngotracheitis virus using the polymerase chain reaction.

Mature laying chickens were inoculated intratracheally with a field strain of infectious laryngotracheitis (ILT) virus. Tracheal swabs were collected regularly from all birds for virus culture. At various times post-inoculation, pairs of birds were killed and tissues removed for detection of virus products using conventional tissue homogenization and culture, organ culture, indirect immunofluorescence (IF) and also the polymerase chain reaction (PCR). The latter was used to detect a DNA sequence from the ILT virus thymidine kinase gene. Following inoculation the birds developed mild respiratory disease with clinical signs characteristic of ILT from 3 to 10 days post-inoculation. Trachea and turbinate tissues were virus-positive as determined by virus isolation, organ culture, IF and PCR on day 4 post-inoculation. After recovery from the acute phase, virus shedding initially ceased, then intermittent, low level shedding was recorded for five of the six remaining birds. In an attempt to locate sites of latency, pairs of birds were sampled at 31, 46 and 61 days post-inoculation. Virus was not detected in upper respiratory tract or ocular tissues by conventional techniques, or in the trigeminal, proximal and distal ganglia. All tissues were also negative by PCR, except for the trigeminal ganglia of five of the six birds. All PCR-positive birds had previously shed ILT virus intermittently between days 19 and 59 post-inoculation. As we did not detect viral DNA in any of the other tissues sampled from clinically recovered birds, we conclude that the trigeminal ganglion is the main site of latency of ILT virus.