DETECTION OF FOOT-AND-MOUTH-DISEASE BY REVERSE TRANSCRIPTION-POLYMERASE CHAIN-REACTION AND VIRUS ISOLATION IN CONTACT SHEEP WITHOUT CLINICAL SIGNS OF FOOT-AND-MOUTH-DISEASE

Two non-vaccinated sheep were experimentally infected with FMDV and on e day later 4 other sheep were brought in contact, Although the contac t sheep showed no clinical signs, serology indicated that all sheep be came infected. Various secretion samples, taken over a period of at le ast one month, and various tissue samples were examined for the presen ce of FMDV by RT-PCR and by virus isolation. FMDV was most often found in saliva (mouth swabs), followed by nasal secretion and sera. Faecal material, wool and milk were less suitable. The period of detection w ith the highest frequency of positive isolations was between 2 to 4 da ys pi for the infected sheep and between 5 to 10 days pc for the conta ct animals. It was established that in subclinically infected sheep, w ith a very low amount of virus present, FMD viral RNA could be detecte d by a sensitive RT-PCR-ELISA although virus isolation and standard RT -PCR remained negative, Moreover there was some evidence of active spr eading of FMDV from the contact sheep to two sentinel pigs, This indic ates that serologically positive contact sheep without clinical signs may be considered as a danger for the transmission of FMDV.