Real-time PCR assay to identify variants of Vaccinia virus: implications for the diagnosis of bovine vaccinia in Brazil

Abstract

Naturally occurring infections of Vaccinia virus (VACV) have been recognized in Brazil during the past 10 years. Human Brazilian Vaccinia virus (BVV) infections typically occur as a zoonosis transferred from affected dairy cows to their handlers. Outbreaks have caused notable economic losses to the rural community in the region. The origins of BVV are unclear but previous analyses have shown that at least two distinct clades of BVV exist. The aim of this study was to develop a rapid and inexpensive process for identification and differentiation of BVV that should facilitate epidemiological and ecological investigations including the improved diagnosis of Brazilian Orthopoxvirus infections. A SYBR green quantitative real-time polymerase chain reaction (PCR) targeting the hemagglutinin gene was developed to identify different populations of BVV, VACV vaccine strains used in Brazil during the smallpox eradication campaign (Vaccinia Lister (VACV-LIS) and New York City Board of Health (VACV-NYCBH)), and currently available vaccines (VACV-NYCBH DRYVAX and VACV-NYCBH Acambis 2000). Three primer combinations (one to amplify many orthopoxviruses including all vaccinia viruses described so far; one to differentiate BVV from vaccine strains (VACV-LIS, VACV-NYCBH DRYVAX and VACV-NYCBH Acambis 2000); and one to differentiate BVV clades) were designed to work at the same annealing temperature and reaction conditions. In addition, these methods were able to detect orthopoxvirus viral DNA in lesion biopsy material without the need for DNA extraction.