The Genus Borrelia
The genus Borrelia comprises spirochetes, which are spiral-shaped, long, thin bacteria that travel by spinning or twisting. Two main groupings comprise the genus. The first one is linked to Lyme disease, and Borrelia burgdorferi is the most prevalent species. The most prevalent species in the second category, which is linked to relapsing fever, are Borrelia hermsii, Borrelia turicatae, Borrelia parkeri, and Borrelia recurrentis. Of the second group, Borrelia recurrentis causes louse-borne relapsing fever, whereas the first three species cause relapsing fever spread by ticks.
Borrelia Membranes
Every species of Borrelia has three membranes: an inner membrane, an outer membrane that includes a substance resembling lipopolysaccharides, and a layer of peptidoglycan in the periplasmic space, which is the area between the inner and outer membranes. Gram-negative bacteria are defined as having a thin peptidoglycan coating that fails to hold onto the purple dye used in Gram staining. However, Gram staining makes it difficult to see them. Rather, the Wright or Giemsa stain, which gives the bacteria a purple appearance, and dark-field microscopy, which shows the bacteria as white against a dark backdrop, are the best ways to observe them.
Movement of Borrelia
Currently, endoflagella, long, thin filaments seen in the periplasmic space of Borrelia species, are what allow them to move about. The peptidoglycan layer and the outer membrane are separated by the rotating filaments, which give the bacteria a corkscrew-like motion as it moves ahead.
Growth of Borrelia
Lastly, the bacteria can be grown on Barbour-Stoenner-Kelly media or by injecting young lab mice intraperitoneally, however these procedures are not commonly accessible.
Transmission of Borrelia
Now, depending on the type of relapsing fever, there are two possible entry points for Borrelia into the body. Therefore, the bacterium that causes tick-borne relapsing fever, or TBRF, enters the circulation when an infected tick bites a human. The bacterium that causes louse-borne relapsing fever, or LBRF, is spread by lice. Lice that feed on sick persons pick up Borrelia, which grows in their hemolymph, or blood-like substance, and in their stomach. Subsequently, uninfected humans may become the food source for infected lice, and when a person scratches or crushes the louse's feeding region, the bacterium gets into their circulation.
Evasion of the Immune System
Through antigenic diversity, Borrelia species can evade the immune system once they are within the circulation. Variable small proteins, or Vsp, and variable large proteins, or Vlp, are surface proteins found on the outer membrane of Borrelia. Because these surface proteins are ever-changing, Borrelia may repeatedly elude the immune system. Therefore, they have already transformed by the time the immune system produces antibodies against Vsp or Vlp, allowing Borrelia to evade immune identification.
Reproduction of Borrelia
Borrelia uses binary fission to multiply in the blood after it is protected from immunological destruction. This indicates that the bacteria divides into two identical copies, and yes, it is just like mitosis! But the term binary fission is used to describe division of prokaryotic cells, which don’t have a nucleus, and therefore some steps in replication are different from mitosis. Once they multiplied sufficiently, they moved from the bloodstream to the central nervous system, liver, heart, lungs, and bone marrow. Therefore, if the illness is not treated, it may worsen and cause major side effects such myocarditis, hepatitis, acute respiratory distress syndrome, thrombocytopenia, meningitis, or cranial nerve palsy.
Types of Relapsing Fever
TBRF is spread by ticks like Ornithodoros parkeri and Ornithodoros turicata, which are normally found endemically in the mountainous sections of North America, plateau regions of Mexico, Central and South America, Mediterranean, central Asia and Africa. However, body lice are the means by which LBRF is spread. LBRF is most common in low-resource nations, war-affected areas, refugee camps, and among those with poor hygiene and lice exposure.
Symptoms of Relapsing Fever
The common symptoms of both types of relapsing fever include repeated fever episodes along with chills, sweats, headaches, muscle and joint pain, altered sensorium, nausea, and diarrhea. A crisis is a set of symptoms that follow a feverish episode. Every crisis has two stages: a chill phase, which typically lasts 10 to 30 minutes and is marked by sweats, a sharp drop in body temperature, and hypotension. During this phase, patients may have delirium, agitation, tachycardia, and tachypnea in addition to a very high fever. The febrile episode in TBRF typically lasts one to three days, and the time interval between the first incident and the first relapse is seven days on average. With LBRF, the initial febrile episode typically lasts three to six days, and the time interval between the onset and the first recurrence averages nine days. People experience no symptoms in between the episodes, and as afebrile periods increase, relapses usually grow shorter and milder with time.
Complications of Relapsing Fever
Complication symptoms vary depending on which organ is impacted. Hepatomegaly, exhaustion, nausea, vomiting, and stomach discomfort are all possible side effects of hepatitis. Palpitations, reducing of heart sounds, and chest discomfort are signs of myocarditis. Breathing too quickly or experiencing dyspnea are symptoms of acute respiratory distress syndrome. Thrombocytopenia can lead to nosebleeds and easily bruised areas. Meningitis symptoms include fever, stiff neck, headache, and impaired mental state. Last but not least, facial palsy, or a lack of movement in the face muscles, can result from cranial nerve palsy.
Diagnosis and Treatment
Giemsa or Wright stain, dark-field microscopy, or identification of Borrelia on a peripheral blood smear are the methods used for diagnosis. Additional diagnostics include PCR, which finds the bacterial DNA, and culture, although they are not often accessible. Serological tests that detect antibodies against Borrelia, such as enzyme immunoassay and Western immunoblot, can also produce false-positive results due to cross-reactions with other spirochetes, such as Leptospira, which causes leptospirosis, and Treponema pallidum, which causes syphilis. These tests can also produce false-negative results due to antigenic variation. Antibiotics like doxycycline and penicillin G are used in treatment. People who are receiving antibiotics need to be closely monitored since they may get a Jarisch-Herxheimer response. This is when the antibiotic therapy causes many spirochetes to burst open and release a large amount of antigens all at once, which might cause fever, perspiration, and muscular aches.
Conclusion
Spirochetes known as Borrelia species are the cause of relapsing fever, a disease spread by vectors. They are movable and visible under dark-field microscopy and with Wright or Giemsa stain. Their big and small proteins can change through a process known as antigenic variation, allowing them to evade the immune system. Both tick-and louse-borne relapsing fever are distinguished by recurring episodes of fever and constitutional symptoms, as well as sporadic intervals of overall health in between the feverish episodes. Antibiotics like penicillin G or doxycycline are used in therapy once Borrelia in peripheral blood smears is identified for the diagnosis.
