Smallpox Information
Smallpox, also called
VARIOLA, one of the world's most dreaded plagues until 1977, when it was
declared eradicated. The disease was described as early as 1122 BC in
China and is referred to in ancient Sanskrit texts of India. The mummified
head of the Egyptian pharaoh Ramses V (died c. 1156 BC) bears
evidence of the disease.
Smallpox is an acute infectious
disease caused by a virus, characterized by fever and, beginning about two
days later, an eruption that, after passing through the stages of papule,
vesicle, and pustule, dries up, leaving more or less distinct scars. The
characteristic eruption may be so profuse as to be confluent, especially
on the face, or so scanty that the lesions are missed altogether.
Modifications, both toward fewer
lesions and toward their being more superficial, may occur either
naturally or because of vaccination that was not recent enough to give
complete protection against the disease. With nearly complete vaccinal
protection, few lesions will appear; but even if vaccination has been
effected many years before, smaller and more superficial lesions are the
rule in cases in which an unvaccinated person would have a severe attack.
Such superficial lesions are also characteristic of the naturally
occurring mild strains of the disease (variola minor).
Besides the characteristic focal
eruptions (papule to vesicle to pustule to scab to scar), there is
sometimes a toxic eruption during the initial fever, before the appearance
of the true smallpox
rash. These toxic
rashes may be diffuse blushes on trunk or limbs, somewhat suggestive of
scarlet fever or measles; they may, on the other hand, be deeper red, with
small hemorrhages like fleabites or larger blotches in the skin. The first
type of rash is clinically unimportant, but the deep red, hemorrhagic rash
occurs in the most severe, usually fatal cases of the disease. Frequently
such patients die before the true smallpox rash has time to develop, and
the disease is not diagnosed. These cases are not usually sources of
infection, however, because smallpox is not infectious until the
characteristic focal eruption comes out in the throat and on the skin.
Each case of smallpox arises from
contact, direct or indirect, with another case of the disease, and there are
no natural animal carriers or natural propagation of the virus outside the
human body. The virus is very stable and can survive for long periods
outside the body. It has survived in bales of cotton for 18 months, so
that laundry contaminated by a smallpox patient is a source of infection,
and in outbreaks in Europe laundry has often been shown to have spread the
disease. The virus can also survive dried in dust, probably for several
months, so that terminal disinfection of wards or sickrooms after the
removal or death of a patient is important. Most victims are, however,
infected by contact with an infected person by inhalation of the virus
expelled in the breath or mouth spray.
Despite the hardiness of the
virus, smallpox is not a highly infectious disease; a patient does not
usually infect more than one or two of his closest contacts. The great
danger from the disease is that it can cause very mild attacks in
vaccinated persons, and these persons can spread the fatal form of the
disease to their contacts without knowing that they themselves have been
infected. It is therefore essential in dealing with an outbreak to make
thorough enquiry into all possible contacts of patients and to follow
these contacts until it is certain they have escaped infection or to
isolate them at once if they show any sign of infection.
The smallpox virus exists in one
main strain, varida major, and a vaccine prepared from varida major will
also protect man against the one or two other closely related strains,
such as variola minor, which causes a much milder form of the disease. The
availability of one single-type vaccine against all forms of clinical
smallpox, combined with the absence of any reservoir of smallpox virus in
nature, made possible the attempt by the World Health Organization
to eradicate smallpox from the world. This immense project involved
following all contacts of every case of smallpox and vaccinating them in
time, in order to prevent the spread of infection. The project is believed
to have been successful. Smallpox is estimated to have caused 2,000,000
deaths in 1967. No cases were reported from 1977 to 1980, with the
exception of two cases in England in 1978 whose source was virus in a
laboratory. Routine smallpox vaccination has been discontinued in most
countries, and the virus is to be kept in not more than four laboratories
throughout the world, ready to make vaccine
should it ever again be necessary.
Copyright 1994-1999 Encyclopedia Britannica
Anthrax | Bioterrorism | Smallpox Danger |
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