Veterinary Type Culture, National Research Centre on Equines, Sirsa Road, Hisar, Haryana-125001.
Camelpox is highly infectious disease of camels caused by Camelpox virus (CMLV). CMLV also has public health significance as possibility of Orthopoxviruses such as variola (VARV), vaccinia (VACV), Cowpox (CPV), monkeypox and taterapox, emerging or re-emerging as a threat to human health as the proportion of the world's population that is immunologically naive for OPVs is increasing. Transmission of CMLV in human has been reported earlier on the basis of clinical symptoms and first conclusive CMLV zoonosis has been reported recently in India which proves the zoonotic nature of the disease. Hence, it is prudent to study the virulence associated genes which has significance in host-tropism. The central region of CMLV genome is highly conserved and encodes proteins for viral replication while the terminal regions are variable and encode proteins responsible for virulence of virus. One of these terminal genes named 176R encodes a 57 kDa protein which shows sequence similarity to mammalian schlafens (m-slfn). An ortholog of m-slfn was found in Orthopoxviruses which is named as viral schlafen (v-slfn). Only limited structural and functional studies of v-slfn gene have been carried out to understand the specific role of this gene. In the present study, we have characterized the schlafen gene of the Camelpox virus isolated from recent outbreak-2009 at Barmer and Jaisalmer, district of Rajasthan. The Barmer outbreak was associated with the human infection. The characteristic pock-like lesions in camels were distributed over the hairless parts of the body, whereas clinical manifestations such as papules, vesicles, ulceration and finally scabs were confined over fingers and hands of camel handlers and attendants. Clinical samples such as skin scabs/swabs and blood collected from affected animals. The disease was confirmed by detection of CMLV-specific antigen and antibodies by counter immunoelectrophoresis (CIE) and serum neutralization test (SNT) which was later confirmed upon virus isolation in Vero cell culture, and amplification of 243 bp product of CMLV-specific ankyrin repeat protein (C18L) gene. Genomic DNA was purified from isolated virus and subjected to amplification of schlafen gene using specific designed primers. The amplified gene was cloned and sequenced. Sequence analysis of this gene revealed that the Open reading frame (ORF) was 1509bp encoding 502 amino acid residues. In order to find out the homology, the sequence of the gene was compared with other sequences in databases using BLAST software. Comparative analysis showed maximum homology of 95–99% at nucleotide level with variola virus followed by vaccinia, rabbitpox, ectromalia, cowpox and monkeypox viruses. Sequence analysis revealed that this is truncated in all the available variola and vaccinia viruses. We observed single point mutation (S34P) in slfn protein sequence in comparison to available two CMLV isolates (Mongolian & Kazakthan). However, further studies are required to elucidate the specific role of this change in virulence and their possible interactions with the host immune response. The phylogenetic analyses showed that slfn genes of Indian isolates clustered along with all CMLV isolates and showed close relationship with variola and vaccinia viruses. We have analyzed schlafen gene of CMLV to find out any changes which may have some role in virulence and to correlate phylogenetically with the available sequences worldwide as this gene plays a critical role in the modulation of the innate and adaptive immune responses imposed by host by interfering immune defense mechanisms. This is the first report of schlafen gene analysis of Indian isolates of CMLV. The present study would help in further understanding of molecular mechanism that govern the species tropism of poxvirus– host relationships that need to be overcome to initiate zoonotic poxvirus infections in non-evolutionary hosts as outbreak of CMLV was associated with human infection.
