Pathogen and transmission
Tularaemia, which is also known as rabbit fever, is an infectious disease that is caused by a bacterium named Francisella tularensis (which also has various subtypes). Tularaemia is an animal disease that is occasionally transmitted to humans. (Such diseases are known as zoonoses.) The tularaemia bacterium infects various smaller mammals (especially wild rabbits and hares and rodents such as mice, rats and squirrels); but it is also found in the natural environment, in water and in soil.
The disease is generally transmitted to other animals or to humans via tick or insect bites, through direct human contact with a contaminated environment or an infected animal (e.g. while hunting, skinning or slaughtering), through the consumption of undercooked meat from such animals or through ingesting or inhaling contaminated water or dust (e.g. from hay or earth). A few pathogens are all it takes for the disease to develop. No cases of human-to-human transmission have been recorded to date.
Pathology
The period between infection and the development of the disease is generally between three and five days, but can in rarer cases be between one and 21 days. Depending on the mode of transmission, the organs affected and the pathogen subtype, the disease can progress in any of a number of ways. Tularaemia presents with symptoms such as fever, progressive inflammation of the point of bacterial entry and swelling of the lymph nodes. It can be fatal if left untreated, although the subtype of the pathogen seen in Switzerland has a mortality rate of under one per cent. Tularaemia is also well treatable, thanks to effective antibiotics.
Distribution and frequency of occurrence
Tularaemia is found throughout the Northern Hemisphere. In Switzerland the disease has been subject to mandatory reporting since 2004. The numbers of reported cases of tularaemia in Switzerland have been rising since 2015.
Prevention
There is no anti-tularaemia vaccine available in Switzerland. But the disease can be treated with antibiotics. Persons who may have been exposed to tularaemia infection can – with a doctor’s approval – be given a prophylactic treatment of antibiotics to prevent the disease developing.
In view of the pathogen’s widespread occurrence, its low infective dose, its stability in the natural environment and the severity of the disease’s pathology if it affects the lungs, there is a risk that Francisella tularensis could be deployed as a biological weapon.