Comparison of F-, G- and N-based RT-PCR protocols with conventional virological procedures for the detection and typing of turkey rhinotracheitis virus

Fifty-six reverse transcriptions followed by a polymerase chain reaction (RT-PCR) were developed and/or assessed to detect and to type turkey rhinotracheitis virus (TRTV). Twenty-seven primers corresponding to sequences either common to both A and B viruses, or type-specific were respectively defined in the fusion (F), attachment (G) and nucleocapsid (N) proteins genes. Only one N-based RT-PCR detected 21/21 TRTVs isolated in four countries since 1985. Molecular typing (RT-PCR) and antigenic typing (ELISA) showed that TRTV strains antigenically related either to the 3BOC18 (UK/85/1) or to the 86004 (Fr/86/1) viruses belonged to the A or B genomic type respectively. Neither typing approach allowed assignment of two 1985 French isolates (Fr/85/1 and Fr/85/2) to either type A or B, these strains might thus belong to a third type. RT-PCR assays on tracheal and nasal swabs sampled during experimental and field infections significantly outperformed concurrent virus isolation in tissue culture and ELISA: G- and N-based RT-PCRs detected more positive samples than conventional methods. Molecular and serological results were concordant and demonstrated that all the recent French field viruses belonged to type B. Thus, N- and G- based RT-PCR are respectively specific and sensitive tools for rapid diagnosis and typing of TRTV in field samples.