Four orthopoxviruses cause infection in humans: variola, vaccinia, cowpox, and monkeypox. Variola infects only humans in nature, although primates and other animals have been infected in an experimental setting. Vaccinia, cowpox, and monkeypox viruses can infect both humans and other animals in nature.The life cycle of poxviruses is complicated by having multiple infectious forms, with differing mechanisms of cell entry. Poxviruses are unique among human DNA viruses in that they replicate in the cytoplasm of the cell rather than in the nucleus. To replicate, poxviruses produce a variety of specialized proteins not produced by other DNA viruses, the most important of which is a viral-associated DNA-dependent RNA polymerase. Both enveloped and unenveloped virions are infectious. The viral envelope is made of modified Golgi membranes containing viral-specific polypeptides, including hemagglutinin. Infection with either variola major or variola minor confers immunity against the other. Variola Major
The more common, infectious form of the virus comes from the Variola major strain. Variola minor
Variola minor, also called alastrim, was a less common form of the virus, and much less deadly. Although Variola minor had the same incubation period and pathogenetic stages as smallpox, it is believed to have had a mortality rate of less than 1%, as compared to smallpoxs 30%. Like Variola major, Variola minor was spread through inhalation of the virus in the air, which could occur through face-to-face contact or through fomites. Infection with Variola minor conferred immunity against the more dangerous variola major.
I called Andropov, who at that time was Chief of KGB, and informed him of the exclusive recipe of smallpox obtained on Vozrazhdenie Island. Others contend that the first patient may have contracted the disease while visiting Uyaly or Komsomolsk-on-Ustyurt, two cities where the boat docked.Responding to international pressures, in 1991 the Soviet government allowed a joint U.S.–British inspection team to tour four of its main weapons facilities at Biopreparat. The inspectors were met with evasion and denials from the Soviet scientists and were eventually ordered out of the facility. In 1992, Soviet defector Ken Alibek alleged that the Soviet bioweapons program at Zagorsk had produced a large stockpile – as much as twenty tons – of weaponized smallpox (possibly engineered to resist vaccines, Alibek further alleged), along with refrigerated warheads to deliver it. Alibeks stories about the former Soviet programs smallpox activities have never been independently verified. In 1997, the Russian government announced that all of its remaining smallpox samples would be moved to the Vector Institute in Koltsovo. With the breakup of the Soviet Union and unemployment of many of the weapons programs scientists, U.S. government officials have expressed concern that smallpox and the expertise to weaponize it may have become available to other governments or terrorist groups who might wish to use virus as means of biological warfare.