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Virus or Bacteria? Vaccine or Antibiotics?

The best vaccine against hysteria is good information.
— Susan Allan, "BioAttack"

What should you do during a biological attack?

Bioterrorism exploits the devastating power of disease to inflict physical and psychological damage on a population. Bioweapons researchers can manipulate pathogens to amplify their destructive potential, making them more lethal, more contagious, more easily dispersed, or more resistant to drugs. Potential agents of bioterror include some of the most infamous diseases known, such as anthrax, plague, and smallpox.

Biological weapons can be divided into three principal categories: toxins, viruses, and bacteria. Toxins are chemicals that disrupt essential cellular processes required for life. In 1995, terrorists attacked the Tokyo subway system by dispersing sarin, a deadly nerve agent. Sarin works by inhibiting cholinesterase, a crucial enzyme found in the blood and neural systems. Chemical agents are most deadly in close quarters since their molecules quickly disperse when diluted in the open air.

By contrast, when microorganisms such as bacteria and viruses are deployed as biological weapons, the devastation can actually increase over time as the contagion sweeps through a population. Infected individuals can unwittingly carry the disease far beyond the original site of exposure. The stealth with which biological agents travel makes bioterrorism especially horrific.

Anthrax Bacteria

A photomicrograph of Bacillus anthracis
bacteria, the cause of anthrax.
From CDC Public Health Image Gallery

Until the nineteenth century, quarantine and isolation were the principal defenses against infectious disease. In the twentieth century, medical advances such as antibiotics and vaccinations radically decreased the risk of infectious disease. Today, however, bioterrorism revives the specter of diseases long believed to have been conquered or controlled.

Bacteria and viruses often cause similar symptoms, but they are two distinct classes of infectious agents that respond to different treatments. This confusion can cause serious harm if the wrong treatment is given.

Up close, the distinctions between viruses and bacteria are striking. A bacterium is a single-cell microorganism. Like any living cell, a bacterium contains DNA, enzymes, and proteins that allow it to function, grow, and reproduce. A virus is an infectious agent that consists of genetic material, either RNA or DNA, surrounded by a protein coat called a capsid.

Straddling the line between living and nonliving, viruses are parasites that cannot grow or reproduce on their own. They remain dormant until they locate a host in which to replicate. After burrowing into the host cell, the virus hijacks the cell's reproductive machinery to replicate itself. Once enough copies of the virus are made, the new viruses burst out of the host cell, killing it and sending the new viruses out to seek new hosts.

Ebola Virus

Transmission electron micrograph of Ebola virus.
From CDC Public Health Image Gallery

Most bacteria are harmless or even beneficial to living systems. Humans have billions of such bacteria living in the digestive tract that perform essential tasks in eliminating waste and even producing some vitamins. Other bacteria can cause illnesses; lethal bacteria, such as anthrax, plague, or cholera, all have the potential to devastate a population.


Treatments

Although bioterrorists aim to make pathogens as resistant to treatment as possible, traditional drugs still offer the first line of defense. The variety of drugs available to combat biowarfare reflects the diversity of infectious agents that can be manipulated for an attack.

The two major classes of drugs are antibiotics and antivirals. Antibiotics treat bacterial infections, and antivirals treat viral infections. Each class of drug targets a particular mechanism in the bacteria or virus, killing it or rendering it unable to reproduce.

The antibiotic penicillin works by destroying the cell walls of the bacteria. The transpeptidase enzyme, critical to the construction of cell walls, incorporates the penicillin molecule, which then deactivates the enzyme. Without the protection of cell walls, the bacterium dies. AZT, an antiviral that targets HIV, blocks the production of the enzyme reverse transcriptase, preventing the virus from splicing itself into the host cell's DNA and replicating itself.

Some antibiotics can be effectively administered prophylactically, prior to exposure. Such preventive use of antibiotics was widespread during the anthrax attacks of 2001.

Vaccination, a prophylactic or preventive measure, builds immunity against a future exposure to a pathogen, either bacterial or viral. Most vaccines contain weakened or killed particles of the pathogen, which do not cause disease but which trigger an immune response. The body responds to the vaccine by building antibodies that will fight future infection.

While most vaccination is dispensed prior to exposure, in some cases postexposure vaccination may cut the risk of disease. This may have particular application in the event of a bioterror attack.

Smallpox vaccination poster

Pre-1979 poster created as part of a campaign to promote vaccinations against measles and smallpox. In 1979, the CDC declared the eradication of smallpox.
From CDC Public Health Image Gallery

Smallpox, one of the most deadly viral diseases, has been eradicated in nature through mass vaccination, but it is known to have been cultivated by biological weapons programs in the former Soviet Union as well as other countries. An attack of smallpox could have particularly devastating consequences today since vaccination of smallpox is no longer routine. In such a case, the CDC advises that the risk of contracting smallpox illness may be reduced if individuals are vaccinated shortly after exposure.

If there is a confirmed outbreak of a viral agent, do not take antibiotics. Viruses are not living cells; antibiotics have no effect on them. In fact, indiscriminate use of antibiotics is considered one of the most serious threats to public health today. Treating a viral infection such as the common cold with antibiotics is not only ineffective, it is gravely dangerous. Over time, misuse and overuse of antibiotics increases bacteria's resistance to drugs, making infections harder and harder to fight. Drug-resistant bacteria are one of the principal weapons in the bioterrorists' arsenal. Individuals can defend the public health by ensuring that they take all antibiotics exactly as prescribed.

Bacterial Biological Agent: Spotlight on Plague

In "BioAttack," terrorists unleash an outbreak of pneumonic plague on the fictional town of Springfield. While the scenario is hypothetical, the risk of a bioattack of plague is real.

Plague infected blood

Blood smear containing Yersinia pestis plague bacteria.
From CDC Public Health Image Gallery

What is plague?
Plague is a bacterial illness caused by the bacteria Yersinia pestis. Bubonic plague and pneumonic plague differ only in how they are transmitted. Under natural conditions, bubonic plague is only transmitted through the bites of infected rodents or insects. Since it cannot be transmitted from person to person, bubonic plague is a less effective agent of bioterror than pneumonic plague, which spreads through inhaled droplets. (There are, however, historical instances of bubonic plague being used as a weapon. For instance, the Japanese in World War II dropped plague-ridden fleas on China.)

How is it transmitted?
Pneumonic plague does spread from person to person through the inhalation of respiratory droplets infected with the bacteria. This mode of transmission makes it a more likely agent of bioterror. Aerosolized forms of plague could have a devastating impact if released in an act of bioterrorism. Indeed, scientists in the former Soviet Union developed techniques to aerosolize and mass-produce plague.

What are the symptoms?
Bubonic plague derives its name from the enlarged lymph nodes called buboes that appear shortly after transmission. Patients with pneumonic plague usually have fever, weakness, and rapidly developing pneumonia with shortness of breath, chest pain, cough, and sometimes bloody or watery sputum. Nausea, vomiting, and abdominal pain may also occur. Without early treatment, pneumonic plague usually leads to respiratory failure, shock, and rapid death.

What is the treatment?
Individuals exposed to plague need to receive treatment as quickly as possible. After exposure, a person may develop symptoms in one to six days. Since pneumonic plague is caused by bacterial infection, the most effective treatment would be a course of antibiotics. Once a person displays symptoms, antibiotics must be administered within 24 hours to reduce the high risk of death. Several types of antibiotics are effective in combating plague. Currently there is no vaccine available to prevent plague.

 

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