Borrelia burgdorferi is the name for a screw bacterium. It causes Lyme disease in humans.
What is Borrelia burgdorferi?
Borrelia burgdorferi is a gram-negative screw bacterium that belongs to the genus Borrelia. It has an irregularly coiled structure. Borrelia burgdorferi is the causative agent of Lyme disease. The disease is caused by the three subspecies Borrelia burgdorferi sensu stricto, Burgdorferi afzelli and Burgdorferi garinii. The bacterial species was named after the Swiss bacteriologist Willy Burgdorfer (1925-2014), who discovered it in 1981. Various infectious diseases such as Lyme disease and relapsing fever are caused by Borrelia burgdorferi. However, in Europe, the term Lyme disease is often equated with Lyme borreliosis.
Occurrence, distribution, and characteristics
North America is considered the most important distribution area of Borrelia burgdorferi. However, the bacterium is also found on the European continent. In this context, the pathogens always reside where their host lives. Thus, both humans and various mammals are infected by the Borrelia bacteria. In order to trigger an infection, however, the bacteria need lice or ticks as carriers. This means that the Borrelia bacteria can only enter the body of another living being through a parasite bite. Impossible, on the other hand, is transmission from person to person. While Borrelia burgdorferi sensu stricto is most common in the USA, Burgdorferi garinii and Burgdorferi afzelli are most common in Europe. However, there is greater variation in the distribution of species as well as in the infestation of ticks. All known European Borrelia burgdorferi species are also found in Germany. In Europe, the common wood tick (Ixodes ricinus) is primarily responsible for Borrelia infections, while in the USA these are caused by the shield ticks Ixodes scapularis and Ixodes pacificus. In Asia, the taiga tick (Ixodes persulcatus) causes infections with Borrelia burgdorferi. Smaller rodents such as mice and rats as well as deer serve as reservoir hosts of the borrelia. These animals usually do not develop symptoms of disease. Bacteria can be transmitted to other hosts by turtles. Borrelia are able to survive in mammals that complement other habitats because they can adapt their gene expression to the new environment. Borrelia burgdorferi is ingested by tick larvae during a blood meal on an infested rodent and later transmitted to other hosts. The bacteria infect the midgut of the tick nymphs, where they attach to the outer membrane through the lipoprotein OspA. After the Borrelia have multiplied, they replace the OspA with the lipoprotein OspC. From the intestine, they migrate toward the salivary glands, from which they can enter the next host body. The ticks, which have now reached their adult stage, now infest larger mammals. However, these do not represent suitable reservoir hosts for Borrelia burgdorferi, resulting in a dead end. When humans are infected, Lyme disease results from a reaction of the immune system, which defends itself against the substances of the bacteria. Borrelia burgdorferi is one of the few pathogens that are able to survive without iron. Thus, the bacterium’s metabolism replaces the iron–sulfur enzyme complexes with enzymes based on manganese. This allows the germ to bypass the complex process of iron recruitment in the host body. Borrelia burgdorferi is actively motile and represents a helical gram-negative bacterium. It has only a few coils and reaches a diameter of 0.3 micrometers. Its length varies between 10 and 20 micrometers. It uses coated flagella bundles as a means of locomotion. Depending on the phase of the particular infection cycle, changes occur in the composition of the cell wall and outer membrane.
Diseases and symptoms
In Europe and North America, Borrelia burgdorferi mainly causes Lyme disease. Another disease is tick-borne or lice-borne fever, which occurs primarily in tropical and subtropical regions. The infection reaches Germany only in rare cases through travelers. The most common disease caused by Borrelia burgdorferi on the European continent is thus Lyme borreliosis.However, there are no typical Lyme disease areas as with early summer meningoencephalitis (TBE). Plant-rich and forested areas where ticks settle are considered to be at risk. Rodents live in these forests, which are infested by the ticks, resulting in the ingestion of the Borrelia bacteria onto the tick. The bacteria are able to overwinter in the tick. This leads to a resurgence of Lyme disease every year. Transmissions to humans occur primarily during the summer months. However, infestation with Borrelia occurs in only 1 to 6 percent of all tick bites. The risk of infection increases with the duration of the sucking process. But even in the case of an infestation, not everyone automatically becomes ill. Lyme disease becomes noticeable after an incubation period of between 5 and 30 days. Borrelia bacteria have the ability to hide from the immune system in the human body. Thus, they settle in areas such as the joints or the brain, which are difficult to control by the defense system. The first symptoms of Lyme disease include the painless spread of redness of the skin at the site of the infection, as well as general symptoms such as headache, muscle pain, fever, conjunctivitis, joint pain and swollen lymph nodes. Without prompt treatment, there is a risk of serious complications that make a full recovery much more difficult. Antibiotics are suitable for eliminating the Borrelia bacteria.
