Tularaemia

Abstract

Tularaemia is a zoonotic bacterial disease of the Northern hemisphere. The causative agent, Francisella tularensis, is spread to humans by direct contact with infected rodents or lagomorphs, aerogenic exposure, ingestion of contaminated food or water, or by arthropod bites. The prevalence of tularaemia shows a wide geographic variation. In some endemic regions, outbreaks occur frequently, whereas nearby rural parts of a country may be completely free. F. tularensis is a facultative intracellular pathogen and its primary mammalian target cell is the mononuclear phagocyte. When tularaemia is acquired via the skin, a primary ulcer is often detected and in general, regional lymph nodes become prominently enlarged. When contracted by inhalation, the disease may present with pneumonia. Nearly as frequent, however, is the development of fever and general illness with no respiratory symptoms and no pulmonary radiological changes. When present, the changes vary widely and may sometimes include hilar enlargement indistinguishable from that of lymphoma. Within an outbreak, the first case of tularaemia is not always readily diagnosed. A decade may have lapsed since the disease was encountered and its existence may be more or less forgotten. The difficulty refers especially to the respiratory form, in which symptoms are less specific. In cases of atypical pneumonia or acute febrile disease with no local symptoms, a history of exposure to hares or rodents or merely living in an endemic region should be sufficient to include tularaemia among differential diagnoses. The microbiological diagnosis of tularaemia relies mainly on serology, and the treatment on broad-spectrum antibiotics. For decades, a live vaccine has been successfully used in risk groups but is presently not available due to difficulties in standardisation.