As with all medical conditions, there may be many causal factors. Further relevant information on causes of Smallpox may be found in:
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The monkeypox virus, belonging to the orthopoxvirus group of viruses, causes monkeypox. It's related to variola and cowpox. People can contract monkeypox from an infected animal through a bite or direct contact with the animal's blood, body fluids, or lesions. It's spread person to person via respiratory droplets during direct and prolonged face-to face contact. It's less infectious than smallpox, but it can also be spread through direct contact with an infected person's body fluids or with virus-contaminated objects, such as bedding or clothing.
Source: Professional Guide to Diseases (Eighth Edition), 2005
Chickenpox can occur at any age, but it's most common in children ages 2 to 8. Congenital varicella may affect infants whose mothers had acute infections in their first or early second trimester. Neonatal infection is rare, probably because of transient maternal immunity. However, neonates born to mothers who develop varicella 5 days before delivery or up to 2 days after delivery are at risk for developing severe generalized varicella. Second attacks are also rare. This infection is transmitted by direct contact (primarily with respiratory secretions; less commonly, with skin lesions) and indirect contact (airborne). The incubation period usually lasts 14 to 17 days but can be as short as 10 days and as long as 20 days. (See Incubation and duration of common rash-producing infections, page 232.) Chickenpox is probably communicable from 1 day before lesions erupt to 6 days after vesicles form (it's most contagious in the early stages of eruption of skin lesions).
Chickenpox occurs worldwide and is endemic in large cities. Outbreaks occur sporadically, usually in areas with large groups of susceptible children. It affects all races and both sexes equally. Seasonal distribution varies; in temperate areas, incidence is higher during late autumn, winter, and spring.
Most children recover completely. Potentially fatal complications may affect children on corticosteroids, antimetabolites, or other immunosuppressants and those with leukemia, other neoplasms, or immunodeficiency disorders. Congenital and adult varicella may also have severe effects.
Source: Professional Guide to Diseases (Eighth Edition), 2005
Smallpox affected people of all ages. In temperate zones, incidence was highest during the winter; in the tropics, during the hot, dry months. Smallpox was transmitted directly by respiratory droplets or dried scales of virus-containing lesions or indirectly through contact with contaminated linens or other objects. Variola major was contagious from onset until after the last scab was shed.
Source: Professional Guide to Diseases (Eighth Edition), 2005
Congenital varicella may affect infants whose mothers had acute infections in their first or early second trimester. Neonatal infection is rare, probably due to transient maternal immunity. Second attacks are also rare.
Varicella is transmitted by direct contact (primarily with respiratory secretions; less often with skin lesions) and respiratory droplets. The incubation period lasts from 13 to 17 days. It’s probably communicable from 1 day before lesions erupt to 6 days after vesicles form (it’s most contagious in the early stages of eruption of skin lesions).
Most children recover completely, but potentially fatal complications may affect children receiving corticosteroids, antimetabolites, or other immunosuppressant agents, and those with leukemia, other neoplasms, or immunodeficiency disorders. Congenital and adult varicella may also have severe effects.
Varicella occurs worldwide and is endemic in large cities. Outbreaks occur sporadically, usually in areas with large groups of susceptible children. It affects all races and both sexes equally. Seasonal distribution varies; in temperate areas, incidence is higher during late autumn, winter, and spring.
Source: Handbook of Diseases, 2003
Variola can affect people of all ages. Before its eradication, incidence was highest during the winter in temperate zones; during the hot, dry months in the tropics. It’s transmitted directly by respiratory droplets or dried scales of virus-containing lesions or indirectly through contact with contaminated linens or other objects. In a terrorist attack, exposure would most likely occur through inhalation.
CLINICAL TIP: Variola major is contagious from onset until after the last scab is shed. Individuals infected with variola minor and varioloid are infectious at the appearance of the first rash and remain contagious until the last variola scab falls off.
Source: Handbook of Diseases, 2003
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