Borrelia is a genus of bacteria of the spirochete phylum.

It causes Lyme disease.

Lyme disease is a zoonotic, vector-borne disease transmitted primarily by ticks and by lice, depending on the species of bacteria.

Of 52 known species of Borrelia, 21 are members of the Lyme disease group, and 29 belong to the relapsing fever group.

Borelliella, uses hard and soft ticks and lice as vectors.

Testing for the presence of the bacteria in a human includes two-tiered serological testing, including immunoassays and immunoblotting.

Borrelia burgdorferi is the causative agent of Lyme disease.

Borrelia has a characteristic spiral shape.

Most species are obligate anaerobes.

Borrelia species have an outer membrane with a substance similar to lipopolysaccharides, an inner membrane, and a layer of peptidoglycan in a periplasmic space, which classifies them as Gram-negative.

It is not easily visualized using Gram staining.

Infections have been reported in all 50 states.
Infections are prevalent in the north east and north central regions of the country.
Borrelia are typically 20-30 μm long and 0.2-0.3 μm wide.

Spirochetes are mobilized using axial filaments, endoflagella, in their periplasmic space.

The axial filaments rotate between the outer membrane and the peptidoglycan layer, propelling the bacterium forward in a corkscrew-like motion.

Its outer membrane contains outer surface proteins play a role in their virulence.

Hard ticks of the family Ixodidae are the only type of ticks shown to transmit Lyme disease bacteria to humans.

Hard ticks of the family Ixodidae are common vectors of Borellia bacteria.

Global hard tick species cause Lyme disease

Other species are carried by soft ticks.

Ornithodoros a soft tick carries the species of Borellia that cause relapsing fever.

The bacteria grow in the midgut of the ticks and then travel to the salivary glands to be transmitted to a new host.

Ticks can spread the bacteria to each other when co-feeding.

Most commonly the bacteria are transmitted to humans through ticks in the nymph stage of development.

Ticks in the nymph phase are smaller and less likely to be noticed and removed.

The ticks must have around 36 to 48 hours of contact with its host to successfully transmit the bacteria.

The three major Borrelia species causing Lyme disease are Borrelia burgdorferi, Borrelia afzelii, and Borrelia garinii.

Twenty-five species of Borrelia are known to cause relapsing fever.

Relapsing fever can be spread lice or ticks.

B. recurrentis, a common species in relapsing fever, is transmitted by the human body louse.

B. recurrentis infects the person via mucous membranes and then invades the bloodstream.

Diagnostic tests include culture of Borrelia from skin, blood, or cerebrospinal fluid (CSF), and detection of genetic material by polymerase chain reaction in skin, blood, or synovial fluid.

Serological testing is performed for differential diagnosis of Borrelia infection.

The first-tier tests detect specific antibodies IgM, IgG and include enzyme-linked immunoassays and immunofluorescent assays.

If the first-tier testing is positive, confirmation by second-tier testing consists of standardized immunoblotting, either by using Western blots or blots striped with diagnostically important purified antigens.

Spirochetes can also be seen using Wright-stained blood smears.

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