Looking Far Afield . . .
Interesting and amusing notes from the borderlands of dermatology
Alastrim (Variola minor) Remembered
Medical journal editors relish reports of new diseases, but who is looking out for diseases that have vanished? The government protects species on the verge of extinction; even disappearing languages have their advocates. The saga of alastrim shows that an extinct disease may still have important implications.
With the eradication of smallpox (Variola major) in 1977, and an official WHO proclamation to that effect in 1980, it is not surprising that, except for interests related to bioterrorism, studies of the Variola virus waned. Articles about the mild form of smallpox — alastrim (Portuguese for “to scatter over”) aka Variola minor — have almost vanished from the literature. Molecular biology to the rescue: A recent study of Variola genetics and evolution makes alastrim relevant once more. Studies are aided by the viruss very low mutation rate and by the reserves of virus banked from epidemics in many geographic regions. Variola aficionados have always been puzzled by its absence from the Bible and Greek historical medical literature, but we know from Chinese historical records that it is at least 3000 years old. This hypothesis is consistent with the time estimated to have been necessary for the molecular evolution of virus variants. The close genetic relation between human Variola virus and the Central Asian camelpox virus is especially intriguing, spurring speculation that the disease was disseminated along the Silk Road from Asia to Europe and Africa.
Li and colleagues propose that mild forms of Variola infection may have existed in the Western hemisphere before the Spanish conquest. Although history shows profound effects on indigenous populations in the Americas, documented instances of populations that did not decrease after the Spanish conquest also exist.
Alastrim was well described during the late nineteenth and early twentieth centuries, especially in the Caribbean: A sparse, fine red papular eruption that healed with minimum crusting was accompanied by systemic complaints, including fever, malaise, and backache. The case fatality rate of less than 1% contrasts dramatically with a V. major rate as high as 30% in unvaccinated populations. Genetic trees show a close relation between West African and South American clades (organisms derived from a common ancestor), which probably reflects results of the slave trade. Molecular studies show that even relatively “recent” Variola strains have an older origin, and the differences in infectivity between V. major and V. minor is of more ancient origin than previously considered.
Comment: Studies of genetic variability over time in alastrim may elucidate environmental and genetic influences not yet understood in other infectious diseases.
Published in Journal Watch Dermatology October 12, 2007
Li Y et al. On the origin of smallpox: Correlating variola phylogenics with historical smallpox records. Proc Natl Acad Sci U S A 2007 Oct 2; 104:15787.
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