Researchers recently discovered the bacterium Francisella tularensis that causes the disease tularemia or “rabbit fever”—which could be fatal whether occurring naturally or used as a bioweapon—can survive outside its small animal or insect hosts in cold water during winter months. This poses a threat to the Joint Force deployed in the Northern Hemisphere areas where the bacteria are prevalent.
The Defense Threat Reduction Agency’s (DTRA) Chemical and Biological Technologies Department in its role as the Joint Science and Technology Office (JSTO) for the Chemical and Biological Defense Program invested in research by Northern Arizona University (NAU) in collaboration with the Swedish Ministry of Defence to study the survivability and persistence of F. tularensis outside of its known hosts.
The disease can result from inhaling as few as 10 F. tularensis organisms and is life threatening if untreated. Although tularemia is not passed from human to human, it is highly infectious by drinking water, getting bitten by deer flies or ticks, or eating or handling small animals—such as rabbits, hares, squirrels, and other rodents—that are infected with the bacteria.
Tularemia cases in humans normally occur during late summer and fall months in rural areas exclusively in the Northern Hemisphere. The bacteria typically attack lungs, lymph nodes, skin, and eyes. The resulting disease can be successfully treated with antibiotics, but it can be fatal if untreated, depending on how it was contracted:
- Inhaling the bacteria causes the most severe symptoms in the lungs.
- Being bitten by an insect or tick causes an ulcer that can spread to the lymph glands, producing a fever, chills, headache, and exhaustion.
- Ingesting the bacteria from eating infected food or liquids causes a sore throat with possible mouth ulcers, vomiting, and diarrhea.
The NAU team and their Swedish collaborators researched how F. tularensis could survive in the time between usual tularemia outbreaks. One hypothesis was that F. tularensis forms biofilms in aquatic environments on sand, rocks, or leaves that supply energy and organic matter to the food chain. The researchers tested this hypothesis using two strains mainly associated with human disease, a Type A strain found only in North America and a Type B strain found throughout the Northern Hemisphere, along with three control strains. They performed the tests in water at 39.2°F and 68°F that represented Scandinavian winter and summer conditions.
The study produced three general observations on F. tularensis survivability in low-nutrient water:
1. F. tularensis strains do not form biofilms at either 68°F or 39.2°F.
2. Both Type A and Type B strains showed increased survival at 39.2°F compared to 68°F.
3. Type B but not Type A maintained virulence after 24 weeks at 39.2°F.
The test results show that neither of the Northern Hemisphere test strains formed biofilms, which indicates the two human disease strains do not appear to require biofilm formation to survive. Temperature seems to play a role in survival, with none of the five strains used in the test surviving after 12 to 14 weeks at 68°F. The results show that the virulence of the two human disease strains is aided by lower temperatures: the Northern Hemisphere Type B retained its virulence for 24 weeks, but the North America Type A was virulent for only 12 to 14 weeks.
Whether tularemia cases are the result of a natural outbreak or an intentional release, knowing that a pathogen like F. tularensis can survive in water in cold weather for several months can help ensure the Joint Force is properly protected, whether by administering a vaccine or preparing for situational awareness and mission planning in areas where tularemia outbreaks could occur year-round.
NAU recently published their findings that describe some conditions in which F. tularensis survives outside of a host system (Appl Environ Microbiol 87:e02713-20). https://doi.org/10.1128/AEM.02713-20
POC: Donald Cronce, Ph.D., Donald.T.Cronce.civ@mail.mil
| Date Taken: |
03.28.2022 |
| Date Posted: |
03.28.2022 23:14 |
| Story ID: |
417356 |
| Location: |
FT. BELVOIR, VA, US |
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