Mousepox

Mousepox, an infectious disease of mice, caused by a virus. The virus is known as ectromelia virus, part of the family of poxviruses that also includes variola virus, which causes smallpox in humans. Although closely related to smallpox, mousepox does not affect humans, infecting only certain strains of mice maintained in laboratories for biomedical research. Because the disease is capable of killing large numbers of mice in lab colonies, outbreaks can disrupt research. Reports of mousepox outbreaks, while common in Europe, have become relatively rare in the United States.

After gaining entry to an uninfected mouse, primarily through breaks in the skin, the ectromelia virus multiplies rapidly. It first affects the liver and spleen, then spreads to the skin, lymph nodes, liver, and other organs, where it causes tissue death. In acute cases, infected mice display a hunched appearance, with swelling of the face and extremities. The virus can also cause a skin rash followed by lesions or ulcerations on the skin. The discomfort created by these wounds may cause the infected mice to gnaw on their skin, even to the point of amputating their own limbs.

Infected mice shed the virus from their skin lesions and from urine and feces, passing on the infection to other mice. There is no treatment for mousepox, but mice can actually be protected by being given the vaccine for smallpox. Smallpox and mousepox are so similar that mice have served as an experimental model in which researchers study infection and immune system reaction to smallpox.

Mousepox has been at the center of controversy since 2001, when a team of researchers in Australia, using the techniques of biotechnology, accidentally created a “supervirus” version of the disease. Hoping to create a genetically engineered sterility treatment to control the mouse population, the researchers spliced a gene for an immune system molecule known as interleukin-4 (IL-4) into the virus. When injected into mice, the altered virus had the unexpected effect of suppressing the normal immune response, allowing the mousepox strain to kill all of the infected mice.

In 2003, building on the work of the Australian scientists, a team of researchers led by an American microbiologist used the IL-4 molecule to create another, equally lethal artificial form of the mousepox virus. The altered virus was able to kill mice that had previously been vaccinated against mousepox. The researchers also investigated and reported strategies for killing the “supervirus.” These measures included using a combination of antiviral compounds and smallpox vaccine.

Research into supervirus strains of mousepox alarmed many people because of the possibility that a disease as deadly and as infectious as smallpox could be revived. An altered form of smallpox or some other virus could conceivably be used as a biological weapon, either by terrorists or by countries as a weapon of mass destruction. As a result, mousepox experiments have generated strong disagreement among scientists, public health experts, politicians, and others. Many believe that it is essential to conduct such research vigorously and openly, in order to anticipate and counter the threat of terrorists who might attempt to unleash an epidemic using an altered form of smallpox or some other virus. Others argue that if such experiments are openly published in scientific literature, terrorists could actually make practical use of the research for their purposes. See also Chemical and Biological Warfare; Terrorism; Counterterrorism.