Evidence for Virus Population Heterogeneity in the Sheep and Goat Pox Vaccine Strain 0240

Sheep and goat pox vaccine strain 0240 was characterized. We designed a pair of primers flanking 3 ORFs including thymidine kinase (tk) gene of Kenya sheep-1. Polymerase chain reaction (PCR) was performed and PCR products of approximately 908 base pair (bp) in size were obtained for all cloned plaques and the vaccine strain. Lamb testicle (LT) DNA (negative control) as expected did not produce any PCR products. PCR products were digested with Ssp1 and Dra1 restriction enzymes and analyzed using agarose gel and polyacrylamide gel electrophoresis (PAGE), respectively. Generation of the expected banding pattern following digestion confirmed virus identity. The analysis revealed the presence of restriction fragment length polymorphisms (RFLPs) between some plaques at temperatures of 33?C and 37?C and the vaccine strain. An in vitro recombination experiment was performed for the 0240 vaccine strain, which revealed its viral sequence heterogeneity. The pattern of heat inactivation indicated the presence of at least two virus populations differing in heat sensitivity. In conclusion, these experiments indicated the presence of two different virus populations.