Dear Editor,rnEctromelia virus(ECTV)is a large double-stranded DNA virus belonging to the genus Orthopoxviruses in the family Poxviridae.It is the causative agent of mousepox,which is a lethal,acute toxic disease with high mortality rate in most strains of laboratory mice.It was first discovered in 1930 when mice were first used as animal models(Marchal 1930).It has long been enzootic in laboratory mouse colonies in Europe,Japan,and China,and later spread to USA(Fenner 1981;Esteban and Buller 2005).To date,there are four ECTV strains with complete genome sequences deposited in GenBank.ECTV strain Hampstead(ECTV-Ham)was the first discovered strain from a laboratory mouse colony in London(Marchal 1930).ECTV strain Moscow(ECTV-Mos)derived from Moscow was considered more virulent than ECTV-Ham based on animal experiments(Andrewes and Elford 1947).ECTV strain Naval(ECTV-Nav)was isolated from an outbreak at the Naval Medical Research Institute in Bethesda,MD(Dick et al.1996).ECTV strain culture-col-lection ATCC VR-1431(ECTV-ATCC)was isolated from throat swabs of six individuals who were suffering from erythromelalgia in rural China in 1987.This virus was referred as erythromelalgia-associated poxvirus as indicated by serological tests and viral morphology(Zheng et al.1992).By next generation sequencing in 2012,the virus was finally identified a new ECTV strain closely related to strains ECTV-Mos and ECTV-Nav(Mendez-Rios et al.2012).