Tularemia transmission mystery solved
Francisella tularensis type bacteria are among the most infectious pathogenic bacteria known to science. The bacteria cause the reportable zoonosis tularemia, which mainly affects rodents such as rabbits, which is why the disease is also known as rabbit plague. If it spreads to humans, tularemia can be life-threatening. A research team has now resolved a long-standing mystery in how the disease is transmitted.
Researchers at Northern Arizona University solved a mystery surrounding the transmission of tularemia. The discovery provides a plausible explanation for how Francisella tularensis manages to survive for long periods in the environment outside of a host. The results were published in the specialist journal “Applied and Environmental Microbiology” presents.
Francisella tularensis: a potential bio-weapon?
Due to the extreme infectivity of the bacterium and the high death rate in the American subtype, Francisella tularensis is viewed as a serious potential bio-terrorist threat. The research team estimates that ten organisms are enough to infect one person. A better understanding of the life cycle and behavior of the bacterium is therefore a high priority.
Mysterious life cycle of Francisella tularensis
However, there were some gaps in knowledge regarding the transmission of the bacterium. For example, Francisella tularensis cannot be spread through human contact. However, it can spread to humans through direct or indirect contact with infected animals. In addition, the bacteria can survive in a dormant state for long periods of time outside the host. The researchers have now been able to find out more about the life cycle of the dangerous bacterium.
Bacteria in hibernation
As the working group shows, the rabbit plague pathogens can survive outside of hosts by falling into a kind of hibernation. In this state they remain viable, but cannot reproduce. This phenomenon has remained largely a mystery to this day, although research has been concerned with the bacterium for more than 100 years.
Tularemia pathogens survive for six months without a host
As part of a three-year project, the researchers analyzed the life cycle and behavior of the pathogen. “The most important finding is that Francisella tularensis can survive in cold water without nutrients for more than six months in a dormant state,” emphasizes research director Professor David Wagner. This means that the bacterium has the ability to survive directly in the environment outside of a mammalian host. This is unexpected because many other bacteria that can survive in the environment for so long form spores. An example of spore-forming bacteria is the anthrax caused by Bacillus anthracis.
No resemblance to the plague
Although the disease is known as rabbit plague, the bacterium bears no resemblance to the plague-causing pathogen Yersinia pestis. This only survives in a host or in flea vectors. Francisella tularensis, on the other hand, has the ability to survive long-term outside a host in the environment and remain infectious without forming spores or having to resort to a vector.
Francisella tularensis survival strategy
“These study results have completely changed our view of the ecology of this bacterium,” emphasizes Wagner. Mammals are only a small but important aspect of the bacterium’s survival strategy. The pathogen survives in the environment and thus provides for periodically occurring diseases. The mammals as hosts are primarily important for the reproduction of the bacterium.
How is tularemia transmitted?
According to the research team, tularemia cannot be transmitted from person to person. Infection can occur through
- Insect bites,
- drinking contaminated water,
- contact with infected animals,
- breathing in particles in the air that contain bacteria.
How is tularemia treated?
The disease is treated with antibiotics. Existing resistances are currently being investigated. There is currently no vaccine against tularemia.
How common is tularemia in humans?
The researchers report that Francisella tularensis occurs naturally throughout the northern hemisphere. In Europe, however, only the less dangerous subtype holarctica is widespread. The number of reported human cases is low overall. For example, in 2016, 230 cases of tularemia were reported in the United States. According to the Robert Koch Institute, there are 500 to 1,000 cases in Europe every year. People who spend a lot of time in the great outdoors are often affected. (vb)
Author and source information
This text complies with the requirements of specialist medical literature, medical guidelines and current studies and has been checked by medical professionals.
Diploma-Editor (FH) Volker Blasek
- Igor Golovliov, Stina Bäckman, Malin Granberg, et al.: Long-Term Survival of Virulent Tularemia Pathogens outside a Host in Conditions That Mimic Natural Aquatic Environments; in: Applied and Environmental Microbiology, 2021, aem.asm.org
- Northern Arizona University: Bacterium causing rabbit fever remains virulent for months in cold water (veröffentlicht: 27.05.2021), eurekalert.org
- Robert Koch Institute: RKI guide tularemia (as of: 02/23/2016), rki.de
This article is for general guidance only and is not intended to be used for self-diagnosis or self-treatment. He can not substitute a visit at the doctor.