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SMALLPOX
Updated 9/2001
Agent: Variola
major is a DNA virus, which is a member of the orthopoxvirus family.
As a result of a worldwide eradication campaign, the last endemic case of
smallpox was reported in 1977. Russia and the U.S. are the last two known
repositories of smallpox virus (with Russia having virus at several sites).
Plans to destroy the virus by 1999 were delayed and it is not known when or
if they will be destroyed. There is reason to believe that the Soviet Union,
and later Russia, produced large amounts of smallpox virus and attempted (successfully?)
to develop more virulent and contagious recombinant strains of the virus (Henderson,
Inglesby, Bartlett, Ascher, Eitzen, Jahrling, Hauer, Layton, McDade, Osterhoim,
O'Toole, Parker, Perl, Russell, & Tonat, 1999; Wang, 1998).
The smallpox virus is specific for humans and non-pathogenic in animals. Smallpox is one of the two most dangerous BW agents (the other being anthrax) because of its high case-fatality rate (>30%), ready person-to-person transmission, lack of population immunity (possibly including persons immunized 25+ years ago), and lack of treatment (Henderson et al, 1999; Kortepeter & Parker, 1999).
Routes of Infection: Weaponized smallpox can be spread by aerosol and can be delivered directly (e.g., sprayed or released in enclosed spaces) or by bombs or missiles. The virus is stable and the infectious dose is small (Johns Hopkins University, 2000). Once introduced into a population, smallpox would spread by from person to person via respiratory secretions inhaled and implanted in oropharyngeal or respiratory mucosa, with many second-generation cases infected by first-generation cases. Clothing and related items are also infectious. People with smallpox are most infectious from the time of the onset of the rash (i.e., pox), by which time the patient is very ill and often prostrated, to the time of scab formation (though the scabs contain viable virus) (Bardi, 1999; Henderson et al, 1999).
It is estimated that smallpox virus released in an attack would remain viable in the environment for up to 24 hours and perhaps longer under ideal conditions (cool temperatures and low humidity). In hot humid weather, the virus would likely persist in the environment for about six hours (Henderson et al, 1999).
Incubation: The average incubation period is 12-14 days with a range of 7-17 days (Henderson et al, 1999; Johns Hopkins University, 2000).
CLINICAL FINDINGS & TREATMENT
Signs & Symptoms: In most cases, smallpox is initially characterized by high fever, malaise, and prostration with severe headache and backache. Severe abdominal pain and delirium may also be present. This initial presentation is followed by centrifugal maculopapular rash on the oral mucosa, face, and forearms; and then spreading to the trunk and legs. It is at this point that the illness becomes most contagious. The rash becomes vesicular and then pustular. Pustules are round, firm, and imbedded in the dermis. The lesions are densest on the face and extremities and in the various regions (e.g., face, arms, trunk) are usually at the same stage of development. Lesions of the oral mucosa and pharynx are the first to ulcerate. After about a week, the pustules begin to scab and later separate from the skin, leaving pitted scars. Scabbing marks decreased infectiousness. Other organ involvement and secondary bacterial infections are uncommon. Death usually occurs in the second week after onset of illness and is likely due to toxemia from circulating immune complexes and variola antigens (Henderson et al, 1999; Johns Hopkins University, 2000).
There are two less common known forms of smallpox: hemorrhagic and malignant. Assuming Soviet/Russian success in developing more virulent forms of smallpox, close attention should be paid to these (and other) less common presentations.
Hemorrhagic smallpox is characterized by a slightly shorter incubation period and more profound prostration period as described above. The rash is dusky and erythematous and is followed by petechiae hemorrhage into skin and mucous membranes. Fatality approaches 100% and usually occurs in less than a week after the onset of the rash (Henderson et al, 1999).
Malignant smallpox is characterized by abrupt onset and constitutional symptoms similar to the above. The rash is confluent and lesions are soft and velvety, more macular than popular, and do not become pustular. The skin is fine-grained, reddish, and in some cases, there are hemorrhages under the skin. The malignant form is frequently fatal (Henderson et al, 1999).
Complications: Encephalitis occasionally develops.
Diagnosis: In the event of an outbreak, laboratory confirmation would occur at a high-containment BL-4 facility with assistance from the CDC. Collection of a specimen requires vaccination of the person doing the collecting and transportation of the specimen requires safeguards as designated by the government. After confirmation, subsequent cases that are clinically similar would not require confirmation (Henderson et al, 1999).
Differential Diagnosis: Varicella is distinguished by more superficial lesions at varying stages of development that, in contradistinction to smallpox are seldom found on the palms or soles. Hemorrhagic smallpox may resemble meningococcemia or acute leukemia. Malignant smallpox has sometimes been mistaken for hemorrhagic chickenpox or surgical abdomen. Monkeypox is a differential in endemic areas and the disease may also resemble bullous erythema multiforma.
Treatment: There are no known antiviral agents effective in the treatment of smallpox; hence treatment is primarily supportive, except for antibiotics to treat secondary bacterial infections.
Smallpox vaccine is active only if administered in the first four days post-exposure (note that the incubation period is 7-17 days). Vaccination after exposure has an effect ranging from preventing illness to decreasing fatality, with earlier vaccination producing the best results. There are 6,000,000 to 7,000,000 vaccination doses (manufactured in the 1970s, hence viability is unknown) available in the U.S. and no nation or health organization has any surplus. Vaccine is being produced in the U.S., and the first 40 million doses scheduled for delivery in 2004. Persons who are immunocompromised may not be able to tolerate the vaccine (Henderson et al, 1999; Henderson, D.A.; Johns Hopkins University, 2000; Kortepeter & Parker, 1999).
Protection: In the event of a contagion, health and other public safety personnel should be vaccinated; as should all hospital employees and patients in facilities where a patient has been diagnosed with smallpox. Laundry personnel are at very high risk.
All persons suspected of having smallpox should be isolated in their homes and not in a hospital. Persons living with the patient or who have had face-to-face contact after the onset of fever should be vaccinated and placed under surveillance (recall that the disease is not contagious until the rash begins). Exposed persons should have their temperature checked daily (evening is best) and a fever of >101 F/38 C anytime within 17 days post-exposure may indicate smallpox, hence isolation is immediate.
Hospitalized patients should be kept in rooms with negative pressure and particulate air filtration, and staff should use standard precautions (gloves, gown, mask). In the event of contagion, it is likely that one or more hospitals in a given area would be designated for smallpox patients only. Bedding, clothing, other personal items - as well as protection gear should be autoclaved, or washed in hot water with bleach added. Contaminated surfaces should be cleaned with disinfectants such as hypochlorite and quaternary ammonia.
Corpses should be cremated
and mortuary personnel should be vaccinated (Henderson et al, 1999; Johns
Hopkins University, 2000).
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