Description, Causes and Risk Factors:

Alastrim is the milder strain of the variola virus that causes smallpox. Variola minor is of the genus orthopoxvirus, which are DNA viruses that replicate in the cytoplasm of the affected cell, rather than in its nucleus. Like variola major, alastrim is spread through inhalation of the virus in the air, which can occur through face-to-face contact or through fomites. Contagion with variola minor confers immunity against its more dangerous form, variola major. Variola minor is a less common form of the virus, and much less deadly. Although alastrim has the same incubation period and pathogenetic stages as smallpox, alastrim is believed to have a mortality rate of less than 1%, as compared to smallpox's 30%.

Because alastrim is a less debilitating disease than smallpox, patients are more frequently ambulant and thus able to infect others more rapidly. As such, variola minor swept through the USA, Great Britain, and South Africa in the early 20th century, becoming the dominant form of the disease in those areas and thus rapidly decreasing mortality rates.

RESEARCH: Alastrim variola minor virus, which causes mild smallpox, was first recognized in Florida and South America in the late 19th century. Genome linear double-stranded DNA sequences (186,986 bp) of the alastrim virus Garcia-1966, a laboratory reference strain from an outbreak associated with 0.8% case fatalities in Brazil in 1966 were determined except for a 530-bp fragment of hairpin-loop sequences at each terminus. The DNA sequences (EMBL Accession No. Y16780) showed 206 potential open reading frames for proteins containing >/=60 amino acids. The amino acid sequences of the putative proteins were compared with those reported for vaccinia virus strain Copenhagen and the Asian variola major strains India-1967. About one-third of the alastrim viral proteins were 100% identical to correlates in the variola major strains and the remainder were >/=95% identical. Compared with variola major virus DNA, alastrim virus DNA has additional segments of 898 and 627 bp, respectively, within the left and right terminal regions. The former segment aligns well with sequences in other orthopoxviruses, particularly cowpox and vaccinia viruses, and the latter is apparently alastrim-specific.


The onset of disease is sudden, with a fever of 40 C, severe headache and backache and sometimes vomiting. Researchers recorded the occurrence of pre-eruptive rashes in 48 of the cases they saw during this stage; there were typical erythematous prodromal rashes in 37 cases. The constitutional symptoms of the established disease were usually much less severe than those in cases of variola major with a comparable rash. The toxemia so evident in variola major rarely occurred, and patients with extensive skin rashes were often ambulant.

The characteristic rash would appear first on the face, forearms and hands on the 3rd or 4th day after the onset of symptoms and within a day after that, it would have spread to the trunk and lower limbs. The lesions began as macules that became firm papules that were pustular. After about 8-9 days after the rashes initial appearance, the papules would dry up and crust over by 14 to 16 days. The rash was more prevalent on the face, forearms, and lower legs than the thighs, abdominal region, and upper arms. This clinical presentation describes what is known as ordinary-type smallpox, which was the most common manifestation of a variola minor infection.


The diagnosis depended on the assessment of the clinical severity of the outbreak; if there were no deaths or only one among 50 or so patients the disease was usually variola minor.

Widespread use of electron microscopy as a diagnostic method was not feasible until the negative staining technique was introduced. Others have shown the value of this method for recognizing poxvirus or herpes virus particles in vesicle fluid and scabs taken directly from patients. Electron microscopy had the advantage of being much the most rapid method of making a presumptive diagnosis, which was a very important requirement, especially in nonendemic countries. In scabs or material that had been some time in transit, it was also the most sensitive, although fields might have to be searched for as long as 30 minutes before a specimen was declared negative. The appearance of characteristic virions on electron microscopy or Guarnieri bodies under light microscopy is useful but does not discriminate variola from vaccinia, monkeypox, or cowpox.


Treatment remains largely experimental. The antiviral medication may be used in emergency situations. In addition to other supportive care, antibiotics are given to reduce potential secondary bacterial infections. Vaccination after exposure to alastrim is protective if given sufficiently early.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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