Sequence and phylogenetic analyses of an Indian isolate of orf virus from sheep

The authors describe the isolation and identification of orf virus (ORFV) from an outbreak in a flock of sheep at Mukteswar, Uttarakhand, India, in 2009. The causative agent, ORFV was successfully isolated in primary lamb testes cells and identified using a semi-nested diagnostic polymerase chain reaction (PCR) and sequence and phylogenetic analyses of immunogenic envelope protein (B2L) coding gene. The affected animals showed characteristic proliferative skin lesions around the mouth and on nostrils and, in a few animals, lesions were also noticed on the tongue irrespective of age and sex. The morbidity, mortality and case fatality rates observed were 6%, 45% and 13%, respectively. Clinical samples were initially screened by counter immuno-electrophoresis and the serum neutralisation test; further positive skin scabs were tested with diagnostic PCR and virus isolation was performed on primary or secondary lamb testes cultures. Sequencing and phylogenetic analyses of the sheep isolate based on the B2L gene revealed that the isolate was closest to a goat isolate retrieved from an outbreak at the same geographic location in 2000. Furthermore, it also showed close genetic similarities with other Indian isolates reported earlier. Regular and systematic investigation of outbreaks is necessary to monitor the disease in susceptible populations. The development of rapid diagnostic methods as well as effective vaccine to control this infection not only from India but also other parts of the world is called for.