Researchers at the Swedish Defense Research Agency FOI NBC Defense and Umeå University are part of an international consortium that is now publishing its results in the prestigious journal Nature Genetics. The article is a report from the charting of the complete DNA sequence of the bacterium, so-called sequencing, and the study of the genome of a fully pathogenic strain of Francisella tularensis. The genome consists of nearly 1.9 billion base pairs, among which the scientists have managed to find 1,804 genes.

The functional description of the genome presents the pathogenic properties of the bacterium, including the formation of so-called pili, a type of projection that is used in infecting human cells. Another property described is the ability of the bacterium to absorb iron, a feature that is necessary for the bacterium to be able to bring about disease.

The mapping of the complete genome of Francisella tularensis is an important step forward in our understanding of how this bacterium causes disease in humans, and it will provide a great impetus for future work to create the possibility of protective measures to combat this potential biological weapon, which might be used by states or by terrorists. Japan developed weapons based on the bacterium in the 1930s and 1940s. The U.S. and the Soviet Union did the same thing later. There is some concern that biological weapons containing this bacterium still exist elsewhere in the world.

Rabbit fever is an acute disease that has been known in Sweden since the 1930s. The disease flares up among rodents at intervals of a few years, and the disease can then also infect humans, an example of zoonosis. The infection is normally transmitted by the bite of an anthropod that has previously eaten from an infected animal. An average of one hundred cases of rabbit fever are registered each year in Sweden, and more than 700 cases occurred in 2003.

The bacteria can be transmitted via insects, dust, and, in rare cases, water. The symptoms vary depending on how it was transmitted. Sores, swollen lymph nodes, and pneumonia, accompanied by a high and persistent fever, are characteristic. Ordinary penicillin has no effect on the bacterium, so special antibiotics are required for successful treatment. Without treatment, there is a great risk of complications, although these are not fatal in the Swedish variant of rabbit fever. In North America there is a more aggressive variant of the bacterium, which the sequenced strain belongs to, and there a certain proportion of rabbit fever cases lead to death.

The article is published at www.nature.com/naturegenetics. The lead author is Pär Larsson, who works at the Swedish Defense Research Agency FOI NBC Defense, and is a doctoral student at the Section for Clinical Bacteriology, Department of Clinical Microbiology, Umeå University.