Human cowpox: presentation and investigation in an era of bioterrorism

Development of real-time PCR assay for specific detection of cowpox virus

Background

The number of recorded human cowpox cases are recently increasing. The symptoms caused by cowpox virus (CPXV) in a number of human cases are close to the symptoms characteristic of the orthopoxviral human infections caused by monkeypox or smallpox (variola) viruses. Any rapid and reliable real-time PCR method for distinguishing cowpox from smallpox and monkeypox is yet absent.

Objectives

The aim of this study was to develop a quick and reliable real-time TaqMan PCR assay for specific detection of cowpox virus and to determine the sensitivity and specificity of this method.

Study design

Based on aligned nucleotide sequences of orthopoxviruses, we found a virus-specific region in the CPXV genome and selected the oligonucleotide primers and hybridization probe within this region. The specificity of the developed method was tested using a panel of various orthopoxvirus (OPV) DNAs. The sensitivity was determined using the recombinant plasmid carrying a fragment of CPXV DNA and genomic DNA of the CPXV strain GRI-90.

Results

The analytical specificity of this method was determined using DNAs of 17 strains of four OPV species pathogenic for humans and amounted to 100%. The method allows 6 copies of plasmid DNA and 20 copies of CPXV DNA in the reaction mixture to be detected.

Conclusion

A quick and reliable TaqMan PCR assay providing for a highly sensitive and specific detection of CPXV DNA was developed.

[Human infection by the cowpox virus in the microregion of Itajubá, state of Minas Gerais: case report]

The authors report three human cases of cowpox infection, among farm workers who were manually milking infected cows, in the microregion of Itajubá, Minas Gerais. The diagnostic techniques used were: isolation of samples similar to the vaccinia virus, from skin lesion secretions; polymerase chain reaction; electronic microscopy; and antibodies for Orthopoxvirus in the patients' blood.