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University of Iowa News Release

Release: April 16, 2003

(Photo: Charles Grose, M.D., UI professor of pediatrics and director of the UI Division of Pediatric Infectious Diseases)

UI Patents Mutant Chicken Pox Virus

The University of Iowa Research Foundation has been issued a patent for the first-known mutant chicken pox virus. The initial discovery was made in 1998 by Charles Grose, M.D., UI professor of pediatrics and director of the UI Division of Pediatric Infectious Diseases, and Richard Santos, M.D., Ph.D., a graduate of the UI Medical Scientist Training Program and now a resident in internal medicine at Washington University in St. Louis. The U.S. Patent 6,528,066 was issued on March 4.

The patent is useful for the potential development of a new diagnostic test for chicken pox, Grose said. The current chicken pox diagnostic test has been available since 1984 and cannot screen for the mutant form. Until Grose and Santos' finding, chicken pox was thought to be the same strain worldwide.

"The patent will help allow us to make an improved test which will detect all currently known forms of chicken pox -- the mutant form and the most commonly known form," Grose said. "It is generally difficult to patent a living organism such as a virus or a bacteria. The criteria include that there be no precedence for the finding and that it was not anticipated."

Chicken pox diagnostic tests are not routinely used in healthy people. The disease is noted and allowed to run its course. However, in children with existing serious illnesses such as cancer, any signs of infection are analyzed. If these children are found to have a verified case of chicken pox, they receive intravenous drugs to stop chicken pox from further developing.

Grose and Santos became involved in the mutant chicken pox investigation when a laboratory in Minnesota reported a child with cancer whose chicken pox resembled typical chicken pox but which did not test positive through the diagnostic test. The sample was sent to Grose's laboratory, where he and Santos analyzed it and found that one of the 70 genes in the virus had mutated. They later published their findings in the September 1998 issue of the journal Virology.

The patent also has implications for the possible development of a vaccine against the new strain of chicken pox. The current chicken pox vaccine came into use in 1995, before the discovery of the mutant form and thus may offer protection only against the previously known, common form. In developing the vaccine, approximately 6,000 children in Europe, Japan and the United States with chicken pox were analyzed between 1985 and 1995, and no mutant virus was seen at that time.

"One reason chicken pox was believed to be a perfect disease against which to make a vaccine was that it was thought to be the same virus all around the world," Grose said. "However, no one can be sure if the current chicken pox vaccine will be entirely protective against the mutant virus should it become more widely distributed in the population."

The current chicken pox vaccine is recommended for children between ages 1 and 2 but required only in some states.

In 2000, the National Virology Laboratory in Canada contacted Grose when the mutant chicken pox strain that he and Santos had identified was found in another patient. That finding suggested that the mutant form was contagious, rather than being a second, isolated case of the chicken pox having mutated on its own.

"The fact that the mutation was found a second time in the same site in the same gene but in a different person made us think that it is scientifically unlikely that in a virus containing 70 genes that the exact same mutation just happened to occur in two different people," Grose said. "We think that there are small populations of people in Canada and the United Sates who are carrying and passing on the mutant form of the virus."

Grose is collaborating with the Canadian laboratory to study groups of people who have active chicken pox to see if the mutant virus is more common than previously known.

"The broader implication of the mutant chicken pox strain relates to immunization goals to eliminate other diseases, such as measles," Grose said. "If chicken pox has this ability to mutate, which was not previously anticipated, then it means that it may be more difficult to eliminate as a disease. Mutated forms of chicken pox and other infectious diseases in the community may be more resistant to immunization."

Chicken pox, which also is known by its Latin name of varicella, is a misnomer. The disease has nothing to do with chickens, Grose said. Chicken pox comes from the Middle French term "chiche pois" -- which means "chickpea."

"In the Middle Ages, people in Europe made the distinction between chicken pox and smallpox. The French called chicken pox 'varicella' but the English decided on a new word that referred to the size of a chickpea. The lesions on the skin were thought to be the size of chickpeas. 'Chichepois' eventually became 'chicken pox,' " Grose said.

The chicken pox virus itself is the second-largest known virus in the world and is about half the size of the smallpox virus. Of the 70 genes contained in chicken pox, only a few of the genes are important for the ability of the virus to infect people.

University of Iowa Health Care describes the partnership between the UI Roy J. and Lucille A. Carver College of Medicine and UI Hospitals and Clinics and the patient care, medical education and research programs and services they provide. Visit UI Health Care online at

STORY SOURCE: University of Iowa Health Science Relations, 5137 Westlawn, Iowa City, Iowa 5224-1178

CONTACTS: (media) Becky Soglin, 319 335-6660

PHOTOS/GRAPHICS: A photo of Charles Grose, M.D., is available for downloading at