RT-PCR detection of lentiviruses in milk or mammary secretions of sheep or goats from infected flocks.

In this study we evaluated a reverse transcriptase polymerase chain reaction (RT-PCR) technique for detecting lentiviral infection in milk or mammary secretions from small ruminants. Initial observations on seven goats infected with cloned caprine arthritis-encephalitis virus (CAEV) showed that RT-PCR on milk cells is as reliable as coculture for detecting viral infection, and is quicker and simpler. With a suitable choice of redundant primers followed by a semi-nested amplification, it proved possible to detect the virus in milk samples from naturally infected French sheep (8/8) or goats (9/9), and viral sub-groups could be identified by hybridization with discriminatory probes. All seropositive animals gave positive amplifications, as did one seronegative goat from a contaminated herd, suggesting greater sensitivity for RT-PCR. None of eight goats from a long-established seronegative herd ever gave a positive RT-PCR amplification. This technique provides a simple means for rapidly identifying potentially infectious animals and for epidemiological investigations, as long as the primers are selected according to the genetic structure of the local viral population.