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Borrelia

life science Maturity 11-13 Next article →

Borrelia is a genus of bacteria belonging to the spirochete phylum. These organisms are famous because many of their species cause significant illnesses in humans. Some species are responsible for Lyme disease, which is a zoonotic, vector-borne disease. This means the disease moves from animals to humans via a carrier, or vector. Other species cause relapsing fever. The genus is named after the French biologist Amédée Borrel. He lived from 1867 to 1936 and was a pioneer in microbiology. Borrel was the first to distinguish between Borrelia anserina and another spirochete called Treponema pallidum.

Structurally, Borrelia bacteria possess a unique spiral shape. They are classified as Gram-negative bacteria. This means they have an outer membrane, an inner membrane, and a peptidoglycan layer in a periplasmic space. Because of this structure, they do not show up easily with standard Gram staining. Most species are obligate anaerobes, meaning they live in environments without much oxygen. Some species are aerotolerant, so they can survive in the presence of oxygen. They are very small, typically measuring 20–30 μm in length. They are also incredibly thin, ranging from 0.2 to 0.3 μm in width.

One of the most fascinating aspects of Borrelia is how it moves. The bacteria use axial filaments called endoflagella to travel. These filaments are located within the periplasmic space. This space sits between the outer membrane and the peptidoglycan layer. The endoflagella rotate within this internal space. This rotation creates a corkscrew-like motion that propels the bacterium forward. This specialized movement allows the spirochetes to navigate through various environments.

Scientists have identified 52 known species of Borrelia. These species are organized into three distinct groups. Twenty species belong to the Lyme disease group. There are also three additional species proposed for this group. Twenty-nine species belong to the relapsing fever group. Two species form a genetically distinct third group that is usually found in reptiles. Some researchers have suggested moving the Lyme disease group into a new genus called Borelliella. However, this taxonomic change is not widely accepted by the scientific community.

Transmission occurs through various vectors like ticks and lice. Hard ticks of the family Ixodidae are common vectors for Lyme disease. In the United States, Ixodes scapularis is known as the black-legged or deer tick. On the Pacific Coast, Ixodes pacificus is the western black-legged tick. In Europe, the sheep tick is called Ixodes ricinus. In Asia, the Taiga tick is Ixodes persulcatus. Inside the tick, the bacteria grow in the midgut. They then travel to the salivary glands to be transmitted to a new host. Ticks must have about 36 to 48 hours of contact to transmit the bacteria.

Relapsing fever is another major concern caused by Borrelia. Twenty-five species are known to cause this condition. Most of these use soft ticks from the family Argasidae as their vector. However, some species use lice. For example, Borrelia recurrentis is transmitted by the human body louse. This species infects humans through mucous membranes and then enters the bloodstream. Other species like Borrelia hermsii and Borrelia parkeri are spread from rodents via ticks. Borrelia hermsii can cause more fatalities than Borrelia recurrentis.

Diagnosing a Borrelia infection requires specific medical tests. Doctors often use two-tiered serological testing. The first tier uses immunoassays, such as ELISAs, to detect antibodies like IgM and IgG. If these tests are positive, a second tier of testing is required. This second tier uses standardized immunoblotting, such as Western blots. Other methods include culturing the bacteria from skin, blood, or cerebrospinal fluid. Scientists can also use polymerase chain reaction to find genetic material. To see the cells, researchers use dark-field microscopy. This makes the cells appear white against a dark background.

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