infectious diseases
Smallpox
Pathophysiology of Smallpox
There are at least 2 strains of smallpox virus: Variola major (classic smallpox), the more virulent strain Variola minor (alastrim), the less virulent strain Smallpox is transmitted from person to person by inhalation of respiratory droplets or, less efficiently, by direct contact. Contaminated clothing or bed linens can also transmit infection. The infection is most communicable for the first 7 to 10 days after the rash appears. Once crusts form on the skin lesions, infectivity declines. The attack rate is as high as 85% in unvaccinated people, and infection may lead to as many as 4 to 10 secondary cases from each primary case. However, infection tends to spread slowly and mainly among close contacts. The virus invades the oropharyngeal or respiratory mucosa and multiplies in regional lymph nodes, causing subsequent viremia. It eventually localizes in small blood vessels of the dermis and the oropharyngeal mucosa. Other organs are seldom clinically involved, except for occasionally the central nervous system, with encephalitis. Secondary bacterial infection of the skin, lungs, and bones may develop. 