Smallpox - Cause

Cause

Variola virus (Smallpox)
This transmission electron micrograph depicts a number of smallpox virions. The "dumbbell-shaped" structure inside the virion is the viral core, which contains the viral DNA; Mag. = ~370,000x
Virus classification
Group: Group I
Order: Unassigned
Family: Poxviridae
Subfamily: Chordopoxvirinae
Genus: Orthopoxvirus
Type species
Vaccinia virus
Species

Variola virus

Smallpox is caused by infection with variola virus, which belongs to the genus Orthopoxvirus, the family Poxviridae and subfamily chordopoxvirinae. Variola is a large brick-shaped virus measuring approximately 302 to 350 nanometers by 244 to 270 nm, with a single linear double stranded DNA genome 186 kilobase pairs (kbp) in size and containing a hairpin loop at each end. The two classic varieties of smallpox are variola major and variola minor.

Four orthopoxviruses cause infection in humans: variola, vaccinia, cowpox, and monkeypox. Variola virus infects only humans in nature, although primates and other animals have been infected in a laboratory setting. Vaccinia, cowpox, and monkeypox viruses can infect both humans and other animals in nature.

The lifecycle of poxviruses is complicated by having multiple infectious forms, with differing mechanisms of cell entry. Poxviruses are unique among DNA viruses in that they replicate in the cytoplasm of the cell rather than in the nucleus. In order 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.

Read more about this topic:  Smallpox

Other articles related to "cause":

Periodic Fever, Aphthous Stomatitis, Pharyngitis And Adenitis - Cause
... fever syndromes, but it is unknown whether the cause is primarily genetic or due to an initial infection ...
Smallpox Survivors - Cause - Transmission
... Smallpox is highly contagious, but generally spreads more slowly and less widely than some other viral diseases, perhaps because transmission requires close contact and occurs after the onset of the rash ... The overall rate of infection is also affected by the short duration of the infectious stage ...