Bioterrorism: Smallpox as a biological weapon
Health
with Dr Walter Chin
Stabroek News
November 24, 2002
Over the past few years, especially over the past year, attention has become focused on the threat of biological warfare. The appropriate dispersion of even a small volume of a biological warfare agent may cause high morbidity and mortality. The disruptive effects of the release of anthrax in civilian settings are now well known, and several other microorganisms capable of producing disease could also be used as biological weapons.
Biological warfare agents are living organisms that can be used for hostile purposes and are intended to cause disease or death in human beings. They depend for their effects on their ability to multiply in the person attacked. Biological warfare agents are well suited for use in bioterrorism as they are cheap and easy to disperse. Infectious diseases have always played a major part in limiting military campaigns, and invading armies may also be assisted by disease, deliberately or inadvertently.
Smallpox was probably first used as a biological weapon by British forces during wars (1754-1767) in North America. The British forces used blankets contaminated with smallpox virus to infect the North American Indians; epidemics occurred with deaths taking more than 50 per cent of the affected tribes.
There are several requisites for a successful biological warfare agent. The agent must produce a given effect - death or disease - consistently. It must be highly contagious and infective in low doses. It must have a short and predictable incubation time. The target population must have little or no natural immunity, and little or no access to immediate immunisation or treatment. The agent must also be able to cause public panic and social disruption.
Biological warfare agents are most likely to be delivered by aerosol. They will probably be small enough to reach the alveoli when they are inhaled. They can be delivered by aerosol generators mounted in fixed locations or on trucks, cars, or boats as well as from missiles and planes.
Many biological warfare agents start with a non-specific febrile illness that could be mistaken for common diseases such as influenza, especially if they occur when cyclical epidemics are taking place, such as respiratory illnesses during the cold months.
One of the agents rated as the most dangerous of all potential biological weapons is smallpox.
Smallpox deserves its fearsome reputation, having caused more deaths than the plague and all wars in history combined. As recently as the 1950s, there were some 50 million cases each year, six million of which proved fatal. A global campaign, begun in 1967 under the direction of the World Health Organization (WHO), succeeded in eradicating smallpox in 1977. After the disease was eliminated from the world, routine vaccination among the general public was stopped because it was no longer necessary for prevention.
Subsequently, a WHO expert committee recommended that stocks of the virus should be kept in only two WHO reference laboratories - the Institute of Virus Preparations in Moscow, Russia, or the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia. However, it is believed that stocks exist in laboratories other than the two designated for this purpose. This has heightened concern that smallpox might be used as a bioweapon. An aerosol release of variola virus would disseminate widely, and the dose required for infection would be very small.
Smallpox is caused by the variola virus. It occurs in two forms - variola major and a much milder form, variola minor (the latter known as alastrim).
Smallpox spreads from person to person, primarily through droplets expelled from the mouth of infected persons, and by direct contact. Contaminated clothing or bed linens can also spread the virus. It is because it can be transmitted through the air that smallpox has the potential to be a bioterrorism threat.
There is an incubation period of 12-14 days during which there might be a low-grade fever. This is followed by a high fever, headache and body aches. A rash then emerges as small red spots on the tongue and in the mouth. These spots develop into sores that break open and spread large amounts of the virus into the mouth and throat. Around the time sores in the mouth break down, a rash appears on the skin, starting on the face and spreading to the arms and legs, and then to the hands and feet. The greatest concentration of lesions thus occurs on the face and distal extremities. The rash then becomes raised bumps which eventually become pus-filled blisters, scab and finally, form scars. Death may occur during the second week.
The classic smallpox lesions are deep-seated, and firm/hard. They are usually all in the same stage of development on any one part of the body. This helps to differentiate it from chickenpox, the disease most commonly confused with smallpox. In chickenpox, the lesions will be in different stages of development on any one part of the body.
The illness associated with variola minor is generally less severe, with fewer constitutional symptoms and a sparser rash. A milder form of the disease is also seen among those who have some immunity from previous vaccination.
A person with smallpox becomes infectious or contagious after the rash appears and remains contagious until the last smallpox scab falls off.
At the present time, the most that can be offered to the patient infected with smallpox is supportive therapy plus antibiotics as indicated for the treatment of secondary bacterial infections. No antiviral therapy has yet proved effective for the treatment of smallpox. Depending on the population and the infecting strain, over 30 per cent of patients die.
A smallpox outbreak would pose difficult public health problems. A terrorist aerosol release of smallpox would rapidly spread in any population now, given that the majority of people throughout the world are highly susceptible. This is so as vaccination against the disease was stopped nearly two decades ago.
Should a smallpox epidemic take place, isolation of infected individuals and prompt vaccination of all contacts would be critical for preventing the spread and controlling the epidemic. Vaccination can be administered to persons of all ages, from birth onward. Immunity to smallpox fades after 10-20 years or earlier in some people. Vaccination after exposure is moderately effective if it is given within four days. There are, however, some adverse reactions associated with the vaccine. These occur most frequently in those getting the vaccine for the first time.
Some of the complications include progressive vaccinia, generalized vaccinia, eczema vaccinatum, and postvaccinial encephilitis. In progressive vaccinia the vaccinial rash fails to heal and progresses to involve adjacent skin, to bones and to organs. This complication can be fatal. With generalized vaccinia, other secondary eruptions emerge 6-9 days after vaccination. In eczema vaccinatum, the vaccinial skin lesions extend to cover all or most of the areas afflicted with eczema. Postvaccinial encephalitis (inflammation of the brain) occurs rarely, and only in those getting the vaccine for the first time.
Between 8 and 15 days after vaccination, fever, headache, vomiting, convulsions and coma can develop. Recovery can be either complete or associated with residual paralysis. For most people, the smallpox vaccine is safe and effective. Because of the risks of severe reactions, however, the World Health Organization has stated that vaccination of entire populations is not recommended.
At the moment, international stocks of vaccine are acknowledged to be inadequate. The WHO has pointed to the need both to stimulate vaccine production and increase stocks of vaccine for use in the event of an outbreak.
