In recent years there have been increased reports of ORFV infections in sheep, goats, wild animals, and humans worldwide [5, 10, 12, 19, 20, 24–27]. The clinical features of the infected animals varied from subclinical to multiple lesions around the lips, mouth, muzzle, nostrils, teats, and oral mucosa and occasionally within the buccal cavity esophagus, stomach, intestine, or the respiratory tract [3–5, 24, 27]. Recently genital lesions  and multifocal cutaneous infections  were also reported. However, virus isolation and characterization is seldom achieved in China. In this outbreak, the lesions were located around the mouth, muzzle, and the upper and lower eyelids (Figure 1). These are classical clinical signs and strong evidence of an orf virus infection.
The identity of NA1/11 strain was confirmed by Western blot, electron microscopy, amplification of specific genes from viral DNA by PCR, and DNA sequencing. Western blot analysis revealed four strong reactive protein bands and six weak bands detected by sheep ORFV antiserum (Figure 3). Furthermore, a 39 kDa protein was detected in the NA1/11 viral protein blot using a Mab A3 against ORFV-Jilin ORFV059 protein , suggesting a cross reaction between the two different isolates and providing a tool for ORFV epidemiological surveillance and diagnosis.
The observed shape of NA1/11 virus was similar to the typical ovoid-shape of orf virus and the specific PCR products from the genomic DNA of the isolated virus confirmed our diagnosis of orf infection from this sheep herd. In China, from 2005 to 2006, ORFV outbreaks occurred in the provinces of Inner-Mongolia, Guangxi, Shanxi, Fujian, Jilin, Jiangsu and Beijing, and the government strengthened the vaccination program to control this disease . However, in 2010, Jilin and Hubei provinces reported outbreaks of ORFV infected sheep herds [5, 12]. In 2011, we found an outbreak in sheep herds in Nongan, northeast China. Because of the persistence or repetition of ORFV infections, it is very difficult to eliminate this virus. ORFV infection is considered a re-emerging disease in China and other countries [24, 25].
In the ORFV genome, ORFV011, 059, 109, 110 and 132 genes have distinct functions for orf virus infections and pathogenesis. The ORFV011 gene encodes the major envelope immunogenic protein , while the ORFV059 gene encodes an immunodominant protein and plays a role in virus maturation and adsorption . Both of these proteins are conserved and are used for orf detection, molecular characterization, and phylogenetic analysis [5, 28]. ORFV109 and 110 encode envelope type II glycoproteins, which are expressed in inter- and extracellular enveloped virions . The ORFV132 protein is an apparent homolog of the mammalian vascular endothelial growth factor (VEGF) family and plays an important role in the development of lesions induced by the orf virus . These three genes are highly variable. According to the phylogenetic relationships based on the ORFV011, NA1/11 clustered with two Chinese strains, Xinjiang and Gansu, isolated from Northwest China, and was close to the Brazilian strain MT-05, American strain OV-IA82 and New Zealand strain NZ2. Usually phylogenetic analysis indicates a hypothetical origin of virus strains; the results presented here suggest that the OV-IA82 and NZ2 strains were introduced into China, but it is difficult to determine the route through which the new strains entered into China. Theoretically, the diversity of viral sequences is linked to viral strain differences, or other factors such as flock immunity, genetic susceptibility, or method of exposure. This implies that we may use the NZ2 strain, which is licensed and widely used in Europe  to vaccinate sheep herds and reduce ORFV outbreaks in China. We propose that the phylogenetic analysis of parapoxvirus should use entire genomic sequences to obtain more precise results.
Our results indicated that the nucleotide sequences similarities (or distances) among different ORFV strains are divergent (Figure 8 and 9). We hypothesize that the genetic differences among ORFV virus strains mainly relate to geographic location and animal host. However, as the variables are non-metric, the nMDS results need further complete genome comparisons to understand fully the genetic diversity and epidemiology of this complex group of viruses.