Ectromelia virus (ECTV) is a zoonotic viral disease whose natural host is the mouse. It belongs to the Poxviridae family of the genus Orthopoxvirus and is among the species of Vaccinia virus. It has a linear, double-stranded DNA genome that is 209,771 bp. The virion is gram-negative and appears in large, oval structures with a dimension of approximately 140 X 220 nm. (1.,2.)
Characteristics of the host
What host/s is/are involved? Is there host specificity? Are there secondary reservoirs?
The host of ECTV is Mus musculus, better known as the mouse (book). While all mice are susceptible to the infection, clinical disease and mortality of mice is dependent upon virus and mouse strain. Mice strains highly susceptible to ECTV include A, CBA, C3H, DBA/2, and BALB/c while those that appear to be most resistant to infection include C57BL/6 and C57BL/10. The infection is not commonly seen among commercial colonies of mice but rather in research laboratories that exchange mouse tissues, live mice, transplantable mouse tumors, and mouse sere (book, Chen, estaban).
The natural reservoir of ECTV is unknown but it is suggested that wild mice may be involved as ECTV has a narrow host range infecting only certain species of mice (CHen). In laboratory studies, wild mice species including Mus caroli, Mus cookii, and Mus cervicolor popaeus are highly susceptible to experimental infection than other species of mice (book).
What kind of interaction do host and symbiont have? How is the host affected by the relationship? How does the host acquire and transmit the symbiont? Is the interaction obligate or facultative?
The skin is the natural route of the infection, believed to be through abrasions in the skin. The virus can be transmitted through direct contact with an infected mouse or contaminated bedding. Replication occurs in the epidermis layer of the skin. It then spreads from the release of virual progeny from the initial infected site which results in spread to the lymph nodes, blood stream, and central target organs the spleen and the liver. 
Molecular Insights into the Symbiosis
Describe molecular/genetic studies on the symbiosis. The poxvirus family is characterized by a similar organization of highly conserved essential genes mostly involved in the replication of the virus in the center and unique genes involved in virus-host interactions in the terminal regions.
Ecological and Evolutionary Aspects
What is the evolutionary history of the interaction? Do particular environmental factors play a role in regulating the symbiosis? The original strain of ECTV, the Hampstead strain, was first discovered in a laboratory-mouse colony in 1930 by Marchal in England who called it "infectious ectromelia" (book). Since it's discovery, other ECTV strains have been isolated from various outbreaks around the world, with different disease severity.These include the Moscow, Hampstead and N1H79 strains, which are the most thoroughly studied and understood. Of these recognized strains, Moscow is the most virulent and infectious (book, chen, esteben).
Describe two findings on the symbiosis published within the last two years.
1. Chen, N et al. (2003). The genomic sequences of ectromelia virus, the causative agent of mousepox. Virology. 1: 165-86.
2. Esteban, D. and Buller, L. (2005). Ectromelia virus: the causative agent of mousepox. Virology. 86: 2645-2659.
Edited by [Elizabeth Stanley], students of Grace Lim-Fong
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