Smallpox

Infectious agent:

Variola virus, a species of Orthopoxvirus

Incubation:

From 7-19 days, commonly 10-14 days to onset of illness, and 2-4 days more to onset of rash.

Mode of transmission:

Indirect spread (ie. not requiring face-to-face contact with an infectious person) through fine-particle aerosols. Spread through articles containing the virus is less common. In biowarfare, most likely disseminated in an aerosol cloud.

Period of communicability:

From the time of development of the earliest lesions to disappearance of all scabs; about 3 weeks. Most contagious during the preruptive period by aerosol droplets from oropharyngeal lesions.

Clinical Symptoms:

Sudden onset with fever, malaise, headache, severe backache and occasional abdominal pain and vomiting. After 2-4 days, fever falls, and a deep-seated rash develops with individual lesions containing infectious virus progressing through successive stages of macules, papules, vesicles and crusted scabs which fall off after 3-4 weeks. Lesions are first evident on face and extremities, and subsequently on trunk (centrifugal rash distribution). The lesions of smallpox can initially be confused with chickenpox, except that unlike chickenpox, they are usually at the same stage of development on any given part of the body.

Prophylaxis if exposed:

With the current eradication of smallpox, vaccine would only be indicated in laboratory settings or where biological warfare was a distinct possibility. A licensed, live Vaccinia Virus vaccine has been maintained frozen at the CDC Drug Service. Vaccinia Immune Globulin (VIG) may prove a useful adjunct to vaccination, although precise role is unclear.

Diagnosis:

Virus easily scene with electron microscope. Laboratory culture from scrapings of lesions, vesicular or pustular fluid and from blood during febrile preruptive stage.

Precautions:

All suspect cases should be placed in strict isolation with immediate telephone consultation with the local Medical Officer of Health. All material used in patient care or in contact with smallpox patients should be autoclaved, boiled or burned.

Outbreak Control:

With the potential for person to person spread, all contacts of infectious cases should be quarantined for 16-17 days following exposure and given prophylaxis as indicated. Animals are not susceptible to smallpox.

Source:

>Control of Communicable Diseases Manual, Chin 17^th edition, 2000, and Biological Agent Information Papers, United States Army Institute of Infectious Diseases.