RICHARD J. GREEN / SCIENCE PHOTO LIBRARY RICHARD J. GREEN / SCIENCE PHOTO LIBRARY
Smallpox virus. Coloured transmission electron micrograph (TEM) of a variola virus, the cause of smallpox. Variola is the most virulent member of the orthopoxvirus group of viruses. It is specific to humans and has no other animal hosts. The symptoms of smallpox include a high temperature and skin spots that develop into scarring pustules. It is transmitted by coughed droplets or by the pus from pustules. Smallpox was eradicated in the 1970s by a global vaccination programme but isolated cultures of variola viruses are still kept in laboratories for research purposes.
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