Detection of Vaccinia virus during an outbreak of exanthemous oral lesions in Brazilian equids.

REASONS FOR PERFORMING STUDY: In August 2014, an outbreak of oral exanthematous disease in equids was reported in Brazil, affecting 11 donkeys and 3 mules.

OBJECTIVES: To investigate if Vaccinia virus (VACV) was the aetiological agent in this outbreak.

STUDY DESIGN: Investigation of clinical cases using serological, molecular and phylogenetic approaches.

METHODS: To analyse the presence of neutralising antibodies against VACV, samples were submitted in triplicate to a plaque-reduction neutralisation test (PRNT50% ). On the basis of previous studies which detected VACV DNA in sera, we submitted extracted DNA samples to different polymerase chain reaction (PCR) platforms targeting Orthopoxvirus (OPV) genes (C11R, A56R and A26L). The PCR products were directly sequenced in both orientations using specific primers and capillary electrophoresis. The alignment and phylogenetic analysis of the A26L and A56R nucleotide sequences (maximum likelihood) were prepared with the obtained nucleotide fragments.

RESULTS: Serological and molecular data suggested VACV as the aetiological agent. The neutralising antibodies against OPV were detected in 5 (55.5%) of the equids, with titres ≥40 neutralising u/ml. Based on the results obtained from all PCR platforms, all samples were positive for OPV: 9 (100%) for A56R, 4 (44.4%) for C11R and 3 (33.3%) for A26L. The alignment of the nucleotide sequences of the A26L and A56R fragments revealed that the samples were highly similar to the homologous genes from other Brazilian VACV Group 1 isolates (98.8% identity on average). Furthermore, both the A26L and A56R sequences showed signature deletions also present in the sequences of Group 1 VACV isolates from Brazil.

CONCLUSIONS: Our data raises questions about the role of equids in the chain of VACV epidemiology. The surveillance of equids in VACV-affected areas worldwide is relevant.