Report by : Gan Yung Chyan
/ KUCINTA SETIA
Image : Scientists study the virus strains used to make smallpox vaccines during the American Civil War. (Alamy Stock Photo)
A study published in Genome Biology on 20 July 2020 showed that the virus strain used in the smallpox vaccine during the American Civil War had been identified and its genome was reconstructed.
"The fact that smallpox was successfully eradicated by vaccination shows that this practice is of vital importance in human history." said Ana Duggan, one of the corresponding authors of the paper and a research team led by McMaster University in Canada for smallpox vaccine research.
According to "New Scientist", smallpox is caused by the variola virus, with a fatality rate of about 30%. In 1980, after consistent global vaccination efforts, smallpox was officially eradicated.
Early measures to prevent smallpox include infecting people with a related virus, a relatively mild disease, so that they can be vaccinated against the smallpox virus. This is usually done by applying infected pus or scab to the skin wound. This process is called smallpox vaccination.
Duggan and his colleagues collected genetic material from vaccination kits during the American Civil War to determine the strain used for smallpox vaccination at that time. They analyzed five vaccination tools in the museum's collection, which were used by doctors in the Philadelphia area from the mid-19th century to the end of the 19th century.
These kits contain scalpels, tin boxes for scabs, and small glass plates for mixing fluids collected from infected people’s blisters. By analyzing the scabs and blisters in the four kits, the research team reconstructed the genomes of all viruses. In a kit with no direct evidence of biological material, the researchers soaked a tin box in a solution containing an enzyme that could collect virus fragments without destroying the box.
All five viruses identified are strains of vaccinia virus. They are distantly related to smallpox and are the cause of vaccinia. No virus has complete genetic material, which means it is not infectious. With the help of computer algorithms and using the complete vaccinia virus gene sequence as a reference, the research team put the virus fragments together like a jigsaw puzzle.
"The previously discovered smallpox strains from the 1940s to the 1970s are very similar, even though they are distributed globally," Duggan said. "It is almost certain that the decrease in strain diversity in the 20th century was caused by widespread vaccination."
Duggan believes that this study demonstrates the efforts people have made to vaccinate for nearly 200 years before smallpox was eradicated.
Ref : https://doi.org/10.1186/s13059-020-02079-z
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