The authors of Smallpox and its Eradication recognise this by discussing types of
Variola major such as 'haemorrhagic' and 'flat' adding: that with a virus that was initially extremely virulent, several different strains which differed substantially in virulence arose within a few years and persisted in nature ...
Smallpox in people is not zoonotic and presents in two clinical forms,
variola major (25% to 30% fatality rate with signs of shock, toxemia, and intravascular coagulation) and a similar but milder disease known as variola minor (less than 1% fatality rate).
The mortality rate of smallpox
variola major infection is approximately 30 percent.
Of the four clinical forms of smallpox, the two most commonly observed were
variola major and variola minor.
A Smallpox (
variola major) kills about a third of those infected.
Smallpox infection can occur in a more severe form,
variola major, where mucous membranes become hemorrhagic, and lesions are large and confluent on the body.
The agents most likely to be used as weapons in the commission of an act of bioterrorism include
variola major (smallpox), Bacillus anthracis (anthrax), Yersinia pestis (plague), Francisella tularensis (tularemia), Brucella species (brucellosis), and Clostridium botulinum intoxication (botulism).
The gravest fears involve smallpox, and they are not without warrant: If terrorists were to use the
variola major strain of the virus, which once racked the Indian subcontinent, 40 percent of the people who are infected would die.
In part this is because smallpox strains--even
variola major, the form responsible for most infections throughout human history--vary quite a lot in their virulence.
Agents of highest concern are Bacillus anthracis (anthrax), Yersinia pestis (plague),
variola major (smallpox), Clostridium botulinum toxin (botulism), Francisella tularensis (tularemia), filoviruses (Ebola hemorrhagic fever, Marburg hemorrhagic fever); and arenaviruses (Lassa [Lassa fever], Junin [Argentine hemorrhagic fever], and related viruses).
The more potent form of the disease, called
variola major, killed about 30 per cent of its victims, and the survivors were disfigured with ugly scars.
This very same strategy was successful with smallpox, and, for all intents and purposes, smallpox (
Variola Major) only exists in the laboratory.
