Variola (Smallpox) Virus

Variola major or Variola minor are the two virus strains that cause the contagious sickness known as smallpox. The variola virus (VARV) agent is a member of the genus Orthopoxvirus. The World Health Organization (WHO) verified the disease's universal eradication in 1980 after the final naturally occurring case was discovered in October 1977, making it the only human disease to have achieved this feat.

Background of Variola (Smallpox) Virus

Variola virus is a sizable, brick-shaped virus that is between 302 and 350 nm and 244 and 270 nm in size. It has a single, linear, double-stranded DNA genome that is 186 kbp in size and has a hairpin loop at each end. Variola major and variola minor are the two traditional subtypes of smallpox. Although monkeys and other animals have contracted the virus in an experimental environment, variola only infects humans in nature.

Symptoms of Smallpox

The only known hosts or reservoirs of smallpox are humans. As its fatality rate ranges from 1% for instances of Variola mild to >97% for haemorrhagic smallpox in unvaccinated patients, smallpox is one of the most feared illnesses in the world. After 8–14 days incubation period, there is a virus-like invasion phase (high fever, shaking, and arthralgia) before a maculopapular rash develops, producing blisters on the third day and infected pustules on the seventh. If the subject lives, there is a drying period between days 10 and 12, when the scabs come off and leave scars that won't heal. In the case of the hemorrhagic type, bleeding from the skin and/or mucous membranes causes the patient to pass away within the first 24 hours of the invasion phase. The virus is typically spread through direct touch, first through patient breath and subsequently through coming into contact with skin lesions. The virus is quite stable and can persist in the scabs for many years.

Epidemiology of Smallpox

Smallpox was first and most conclusively described in the fourth century in China. Later, in the seventh century, it was also described in India, Southwest Asia, and the Mediterranean (tenth century). It was widespread in southern Europe in the 13th century, at which point it began to spread across the continent and over the years caused millions of deaths. It wiped out Amerindian communities during the conquest of the New World starting in the early 16th century, and what little the Inca civilisation had survived was devastated by a series of deadly diseases brought over from the Old World, including smallpox epidemics.