The disease neoehrlichiosis is caused by the bacterium Candidatus Neoehrlichia mikurensis, which is transmitted by ticks in Europe. Neoehrlichiosis occurs mainly in persons with a weakened immune system, but occasionally also in patients without underlying diseases.

Candidatus Neoehrlichia mikurensis has been detected in ticks and rodents in several countries in Europe and Asia. Infections have been observed in Sweden, Germany, the Czech Republic, Austria and China.

Rodents are the natural host animals. Rodent infections show seasonal patterns with lower rates in the winter months.

Transmission of bacteria through the bite of an infected tick.

A characteristic symptom is high and temporarily subsiding fever, often accompanied by chills and night sweats. In many cases, there is severe muscle and joint pain. Skin rashes and less specific symptoms such as cough, diarrhea, and weight loss may also occur. Laboratory diagnostics reveal anemia (anemia of the blood). In neoehrlichiosis patients, complications such as venous thrombosis, pulmonary embolism, etc. occur with striking frequency.

The antibiotic doxycycline is active against intracellular bacteria and is used for the treatment of neoehrlichiosis. The treatment resulted in a rapid decrease of symptoms in case studies.

A vaccine is currently not available. The most important preventive measure is protection against tick bites or the rapid removal of ticks from the body.

Around four percent of ticks are infected with the bacterium Candidatus Neoehrlichia mikurensis. In Vienna and Tyrol, ticks are most frequently affected with just over eight percent. Illnesses in people infected in Austria have been documented repeatedly, but almost exclusively in patients with impaired immune systems, such as those with leukemia, rheumatism or after organ transplantation. A study from Austria showed that the pathogen was detectable in 2.5% of healthy individuals after a tick bite, without causing disease.

The first description of Candidatus Neoehrlichia mikurensis was published in 1999, and human cases of Neoehrlichiosis were first described in 2010. Ca. Neoehrlichia mikurensis is a species within the genus Neoehrlichia, which belongs to the family Anaplasmataceae, order Rickettsiales.

Neoehrlichiosis is thought to be an underdiagnosed infection because most infected patient:s already have underlying disease and infection with Ca. N. mikurensis is overlooked as the cause of symptoms. In addition, detection of the bacterium presents a difficulty because it does not grow on common culture media, serology is not yet available, and molecular detection methods are available in only a few laboratories. Both of these factors probably contribute to the fact that neoehrlichiosis is rarely diagnosed.

When treating patients with unexplained fever, rash, and thromboembolic events, neoehrlichiosis should be considered and previous tick bites should be inquired about, especially if there is underlying autoimmune disease, hemolytic disease, or immunosuppressive treatment.