Eight confirmed cases of a new tick-borne disease in the world

The bacterium Candidatus Neoehrlichia mikurensis was for the first time detected in the Netherlands in 1999. The name was first given in 2004 since it is found in ticks and brown rats in Japan and was verified as new bacteria by phylogenetic DNA-analysis. The bacteria can only grow inside cells and seem to infect cells in the vessel walls. It belongs to Anaplasmataceae family as well as two other tick bacteria: Anaplasma and Ehrlichia. The bacterium could not so far been сultured, so that its characterization is mainly based on molecular biological methods.

Totally in the world there are 8 cases of infection with Neoehrlichia mikurensis known in humans, three of them were diagnosed in Sweden. The very first case was reported in Sweden in the Sahlgrenska hospital in an elderly man who fell ill in summer 2009. Since then cases were described in Germany, Switzerland and the Czech Republic. Two more cases, Swedish patients, were later diagnosed in Gothenburg (unpublished data). Only one of the reported patients has been described previously healthy without underlying diseases. Other seven cases had an impaired immune system due to underlying serious diseases or immunosuppressive treatment, most of the cases had not spleen. The symptoms are often described as influenza like symptoms. Patients had fever and some had muscle pain. Four of the patients described had deep vein thrombosis. The diagnosis of candidates Neoehrlichia mikurensis infection was based on PCR analysis of blood and subsequent sequencing of the amplified DNA fragments.

The risk of the bacteria to cause the disease in healthy individuals is probably very low. The natural reservoir of Candidatus Neoehrlichia mikurensis is different rodent species and it is transmitted via tick bites. A study conducted in five locations in Sweden in 2008 has shown that a bacterium was present in bank vole, field vole and small and large field mouse with an average prevalence of 9 %. Although these results suggest that the bacteria are relatively common in Swedish nature, there are no clinical reports which would suggest that this transmission is normal after a tick bite.

The patients were symptoms free after the treatment with tetracyklin and Candidatus Neohrlichia mikurensis DNA was not detected in patients after treatment was finished.

It is worth noting that the diagnosis at the moment is only possible in symptomatic patients. Antibody detection is not possible because Candidatus Neoehrlichia mikurensis cannot be grown and thus suitable antigens for antibody diagnostics cannot be found. Cross reaction of antibodies against Candidatus Neoehrlichia mikurensis with their relatives, Anaplasma and Ehrlichia, does not occur.