New tick-borne disease threatens immunosuppressed patients

World Health Matters: Sweden by Gary Finnegan – A newly discovered tick-borne bacterium known as Candidatus Neoehrlichia mikurensis has been implicated in six cases of disease in Sweden. A study led by the Sahlgrenska Academy suggests that this bacterium is primarily a risk for people who are already sick and who are receiving immunosuppressive drugs.

The Candidatus Neoehrlichia mikurensis bacterium, known in the medical world by its short name Neoehrlichia, was discovered and described for the first time in a scientific article in 2010.

The bacterium, which is spread by rodents and ticks mainly in Asia and Europe, has been found in 19 cases worldwide, six of them in Sweden.

“Those who run the greatest risk are generally over the age of 50 years, suffer either from a haematological disease or a rheumatic disease, and are currently undergoing immunosuppressive treatment with, for example, chemotherapy or cortisone,” says Dr Christine Wennerås, of the Sahlgrenska Academy.

No figures are available for how common the tick-borne infection, neoehrlichiosis is in humans. This is mainly due to the infection being difficult to detect. The bacterium cannot be grown in culture, and this means that it is not picked up in routine diagnostic procedures.

Furthermore, the symptoms are deceptive. Several patients, for example, have been affected by blood clots in the leg or the blood vessels in the head, and this has not been linked to an infectious cause.

“Other typical symptoms such as fever, muscle pain and joint pain can be caused also by the patient’s underlying disease,” says Dr Wennerås.

She said very little is known about how the infection affects otherwise healthy people who are not taking immunosuppressive drugs. “Once neoehrlichiosis has been diagnosed, the patients recover completely after treatment with antibiotics.”