Weaker strain may explain nonfatal monkeypox in US
When a monkeypox outbreak in 2003 affected 72 individuals in the US but not one of them died, scientists were puzzled because the virus’ fatality rate is commonly reported to be 10 percent. A new study, reported in the July issue of Virology, provides a possible answer for this mystery: the monkeypox virus introduced in the US was a different, less virulent strain than the typical strain.
The 2003 US outbreak was blamed on the importation of monkeypox-carrying pets from Africa. As it turns out, not all monkeypox viruses in Africa are the same. The strains from the Congo basin can be deadly, whereas those from West Africa cause a less severe infection.
In the present study, Dr. R. Mark L. Buller, from St. Louis University Health Sciences Center, and colleagues show that isolates from the Congo are more virulent in monkeys than are isolates from West Africa. This may explain why the 2003 outbreak caused no fatalities because a West African strain of the virus was involved.
“We were the first research group to show in a head-to-head comparison using a monkey model that the West African isolate wasn’t as virulent as the Congo isolate,” Buller told Reuters Health.
The investigators also identified several genes in the Congo strain that could explain the greater virulence. In particular, a gene for a complement-binding protein, D14L, is a leading candidate as a potential virulence factor.
Buller said that his team is “now comparing West African strains with Congo stains in a dormouse model of monkeypox infection,” which could lead to mapping of the virulence genes and a better understanding of what determines virulence in humans.
SOURCE: Virology, July 2005.
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