Bacterium manipulates the human defence system: The Borrelia bacterium is a master of disguise

Borrelia bacteria are capable of masking themselves in the human body and deceiving the immune defence system. In this way they can hide in the human organism even for periods of years. In their recent studies Professor Seppo Meri and his team have managed to trace the evasive movements of the Borrelia bacterium in the body. Their work is part of the Microbes and Man research programme, jointly funded by the Academy of Finland and the Swedish Foundation for Strategic Research.

When they first enter the human organism, Borrelia bacteria do not always cause very intense inflammation. However, they proliferate unnoticed and later on the symptoms get worse. The immune system is unable in this situation to respond because the bacterium actively prevents any defensive reactions.

Professor Meri and his team have found that Borrelia bacteria, which are carried by ticks and birds, are capable of absorbing the protein that controls human inflammation (complement factor H). Normally, antibodies and the complement would kill off the bacteria, but this ingenious kidnap operation allows the Borrelia bacteria to disguise themselves and avoid being killed or devoured by inflammation cells. Consequently, the bacteria can continue to proliferate in the body and even reach the brain. An advanced bacterium may lead to a serious condition known as neuroborreliosis, which among other things may cause chronic headache or facial nerve paralysis.

One of the difficulties in diagnosing the symptoms caused by the Borrelia bacterium is that only half of all people who get a tick bite develop the tell-tale rash. Therefore, the bacterium often gets to make its way into the body and eventually into the bloodstream through the skin. Some one in ten patients are unable to shake off their symptoms even if they receive proper antibiotic treatment.