By David H. Paul

Summary: This is the second of two articles discussing potential waterborne bioterrorism agents. In the first article, the bacterial diseases of anthrax, botulism and plague were discussed. In this article, the bacterial disease Tularensis is discussed, plus some potential viral bioterrorism agents.

Tularemia is caused by the bacterium, Francisella tularensis. The disease is sometimes known as “rabbit fever” or “deerfly fever.” Tularensis is known to have been weaponized in the past. The term “weaponized” means that the bacteria and hardware were created to disperse deadly quantities of F. tularensis during a military engagement.

There are several variations of the disease depending upon where the bacteria are introduced into the body. They are:

  • Pneumonic—enters through lungs,
  • Glandular—enters through skin,
  • Oculoglandular—enters through eyes,
  • Oropharyngeal—enters through mouth, and
  • Typhoidal—enters throughout the body with no known entry point.

An infection by any route with as few as 10-50 bacterial cells may initiate disease. In each case, the lymph system is attacked. The disease is spread to humans from animals that harbor the bacterium. In the United States, rabbits and squirrels are most commonly the bacterial reservoirs.

Transmission to humans is frequently from tick bites, but handling infected animal parts, ingestion of contaminated food or water, and inhalation of infected particles (hay dust, lawn mowing particles, and vegetation cutting particles) can also cause disease. During the 1990s, there was an average of 124 cases reported each year in the United States. In the latest outbreak in 2000, 15 people acquired the disease (mainly pneumonic) and one died.

During World War II, Japan researched using F. tularensis as a biological weapon. The United States developed F. tularensis weapons that could be delivered in aerosol form. These were destroyed in 1973 after the signing of the 1972 Biological and Toxin Weapons Convention. The former Soviet Union also developed such weapons and reportedly developed antibiotic and vaccine resistant strains.

In 1969, the World Health Organization estimated that 100 pounds (50 kg) of F. tularensis spread over a city with five million people would cause 250,000 illnesses along with 19,000 deaths. The Tularensis bacteria don’t form spores. While cells can survive in natural water for an extended period of time, they’re easily killed by the chlorine residual (0.2-1.0 milligrams per liter) in typical water treatment.

Vaccines have been available in the past. These aren’t currently approved for use in the United States. Naturally occurring Tularensis bacterial infections are typically controlled with antibiotics including ampicillin, gentamicin and ciprofloxacin. Weaponized F. tularensis strains, however, may be antibiotic and vaccine resistant. Since ingestion isn’t the primary mode of transmission of this disease, dispersion in a bioterrorism event would likely be by aerosol. Secondary contamination of drinking water source streams would also be possible.

Potentially viral agents
Viruses are smaller than full-grown bacteria. They’re in the size range of around 0.02-0.08 micrometers (microns, µm). Almost everyone has had a cold or flu sometime in his/her lifetime. These are common diseases caused by viruses.

Everyone is probably equally aware there aren’t “antibiotics” for viruses like there are for other microorganisms. When a person gets a cold or flu, he/she likely won’t receive antibiotics unless there’s a secondary microbial infection. The term “antibiotics” essentially refers to chemicals that kill microorganisms like bacteria, fungi and algae. The reason for this is viruses are essentially genetic material, either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) housed in a protein capsid. The genetic material is inserted into the body’s cells. Once inside the cells, the DNA or RNA genes “tell” the cell to produce more viruses. They replicate within the cell, then exit (usually destroying the cell) and enter other cells to start the process over again. If enough cells are damaged and/or enough viruses produced, the viral infection can overwhelm the body and cause death.

While anti-viral drugs have been produced that may help in certain viral infections, they don’t really “stop” an infection like an antibiotic does, for example, for a bacterial infection. Vaccines have historically been the most reliable way to prevent viral infections. Vaccines are usually inactivated and/or “close-relative” viruses that can be injected into a human to cause the body to create antibodies against the agent. If the “real” agent gets into the body at a subsequent date, the body has an immediate defense and can disable the viral particles. Rapidly mutating viruses or those that are genetically altered in the laboratory, however, are often unrecognizable to the immune system, which is one reason why flu shots don’t always work.

The really deadly viral agents aren’t common in developed countries so vaccines aren’t routinely administered. This may change in the future due to potential and/or realized bioterrorism threats.

Smallpox is caused by the variola virus in the Poxviridae family and Orthopoxvirus genus. Smallpox is a DNA virus. The virus usually enters a human through inhalation of airborne contaminated particles originating from an infected person. The infectious dosage is estimated to be between 10-100 variola (or pox-like) virus organisms.

The viral particles quickly enter the lymph nodes and travel to the spleen, bone marrow, liver and kidneys. The virus then attacks the blood vessels of the skin. Skin lesions occur, which subsequently scab over. When skin lesions are present, the patient is highly infectious.

In about two weeks, the disease is full blown. Between 15-45 percent of people with full-blown smallpox disease die. The good news is there’s no longer any naturally occurring smallpox disease on the planet. A massive vaccination and containment effort between 1967-1979 eradicated the disease. The bad news is smallpox has been used in the past as a biological weapon and the former Soviet Union reportedly weapon-ized the variola virus. The potential of weaponized smallpox was a recent concern (which did not materialize) in the Iraq war.

Obviously, an effective vaccine is available since the disease has been eradicated. The United States stores enough vaccine to vaccinate virtually every one of its citizens. There are risks associated with vaccination, however. It’s estimated that vaccinating everyone in the United States between the ages 1-65 could result in around 5,000 adverse reactions and 300 deaths. This doesn’t include high-risk individuals such as those with deficient immune systems.

Since smallpox is not a naturally occurring disease, it’s a difficult decision to vaccinate populations who will likely never contract the disease other than in a bioterrorism or warfare situation. Additionally, it’s possible to genetically engineer differences in the variola virus to make existing vaccines less effective.

The mode of transmission for a bioterrorist dispersion of smallpox would likely be aerosol (airborne). The variola virus doesn’t survive long in the environment. It survives longer, however, in low-humidity, low-temperature environments.

Variola virus organisms that secondarily enter drinking water sources would likely pose an insignificant threat compared to their presence in the air. Using household disinfectants such as chlorinated compounds inactivates the virus.

Hemorrhagic fever viruses
There are several viruses that can cause deadly diseases with symptoms that include bleeding (hemorrhaging) throughout the infected body. The ones listed as having the greatest potential as bioterrorism agents include:

  1. Ebola virus,
  2. Marburg virus,
  3. Lassa virus,
  4. New World arenaviruses such as Machupo (Bolivian hemorrhagic fever), Junin (Argentine hemorrhagic fever), Guanarito (Venezuelan hemorrhagic fever) and Sabia (Brazilian hemorrhagic fever),
  5. Rift Valley fever virus,
  6. Yellow fever virus,
  7. Kyasanur Forest disease virus, and
  8. Omsk hemorrhagic fever virus.

Other potentially hemorrhagic viruses such as Dengue virus, Crimean-Congo virus, and Hantaviruses aren’t considered likely bioterrorism agents due to current barriers to mass production. Inhalation is the most common method of contracting these diseases, although other methods sometimes occur (i.e., mosquito or tick bites). The number of virus particles required to initiate disease is very low, estimated to be 1-10 organisms.

The viruses attack the lining of blood vessels, causing loss of blood. Multiple organ failures are common. Many of these viruses have been rare, localized to a particular area of Africa or South America. For example, Sabia virus was discovered in Brazil in 1990 when a single fatal case was identified. Two deaths in laboratory personnel have since occurred.

The more common hemorrhagic viruses include Ebola, Marburg, Lassa and Yellow Fever. The rest are relatively uncommon. Ebola virus has received a lot of press coverage in the past decade. It was identified in 1976. There have been increasing outbreaks since the mid-1990s. The death rate has been documented to be between 50-90 percent of those contracting the disease. Marburg virus was first identified in 1967. There were few outbreaks until a large one in 1998. The death rate has been documented to be 23-70 percent. Lassa virus was first identified in 1969. It’s relatively common in West Africa. The death rate has been documented to be 15-25 percent.

Yellow fever was first recognized in the 1600s. It’s very common in certain areas of Africa. It’s transmitted through the bites of certain mosquitoes. The death rate has been documented to be 5-7 percent. Vaccines aren’t available for any of the viral hemorrhagic fevers except yellow fever. Anti-viral agents may or may not help with any particular disease.

Similar to what was described above for smallpox, any of the hemorrhagic virus organisms that secondarily enter drinking water sources would likely pose an insignificant threat compared to their presence in the air. Using household disinfectants such as chlorinated compounds have been shown to inactivate the viruses.

In this series of two articles, potential bacterial diseases discussed as candidates for bioterrorism weapons were anthrax, botulism, plague, and Tularensis . Potential viral diseases that were discussed as candidates for bioterrorism weapons were smallpox and hemorrhagic viruses. All of the disease organisms discussed are classified as Class A agents. Class A agents are the most deadly and most likely to be used for bioterrorism. The most likely route of dispersion, for any of the agents in a bioterrorism event, is by aerosol. Waterborne threats, however, are likely to be secondary considerations to a primary airborne bioterrorism attack.

Primary attack on source water for drinking water supplies would be less effective due to the dilution effect of the source water and normal water treatment. Both of these reduce the concentration of the disease-causing agent. Typical chlorination of drinking water eliminates some of the disease organisms (botulism, Tularensis , viruses). There are water treatment technologies (membranes, activated carbon, ultraviolet irradiation, etc.) that can also be used to greatly reduce waterborne threats. Contamination post-treatment is a concern for bioterrorism agents that can withstand the typical chlorine residual of drinking water.

About the author
David Paul is president of David H. Paul Inc, an advanced water treatment training and technical services firm in Farmington, NM. He has over 25 years of experience in advanced water treatment. Paul has published over 100 technical articles and papers. He has created and administers a 4,000-page, college-accredited correspondence training program plus three on-campus college degree programs in advanced water treatment. He holds a bachelor’s degree in biology and a master’s degree in microbiology from New Mexico State University. Paul can be reached at (877) 711-4347, (505) 327-2934 (fax), email: or website:


Comments are closed.