Does the infectious disease, human ehrlichiosis, exist in Sweden? Ticks get a hold of new zoonoses

Human ehrlichiosis diseases, decently recognised as emerging human infections in the USA, are caused by vector-borne, strictly intracellular bacteria of the family Rickettsiaceae. Human monocytic ehrlichiosis is caused by Ehrlichia schaffeensis, whereas the agent causing human granulocytic ehrlichiosis (HGE) has yet to be identified [1]. The putative increase in the occurrence of these primary zoonoses is dependent on the complex relationship between the infectious agents, the vectors, and the hosts (rodents, deer) which constitute the wild-life reservoir. In Scandinavia, granulocytic ehrlichiosis is well known in veterinary medicine. Pasture fever in cattle and sheep is caused by Ehrlichia phagocytophila, whereas granulocytic ehrlichiosis in horses and dogs is caused by a new, recently characterised Ehrlichia species [2]. All species of Ehrlichia causing granulocytic ehrlichiosis are closely related both genetically and antigenically, and are all transmitted by ticks of the genus Ixodes. In Sweden, veterinary cases of granulocytic ehrlichiosis are characterised by a geographical distribution corresponding well with that of Ixodes ricinus, and a seasonal distribution similar to that of Lyme borreliosis. In Europe, clinical cases of HGE have so far been reported only from Slovenia [5], though seroprevalence figures of 8-17 per cent have been reported for tick-exposed populations [6, 7]. As most cases are probably subclinical, and as clinical symptoms, when present, are non-specific, clinical diagnosis is dependent on the clinician's awareness of the existence of the disease. Laboratory diagnostic tests are now available at Kalmar.