Relapsing fever
Encyclopedia
Relapsing fever is an infection caused by certain bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 in the genus Borrelia
Borrelia
Borrelia is a genus of bacteria of the spirochete phylum. It causes borreliosis, a zoonotic, vector-borne disease transmitted primarily by ticks and some by lice, depending on the species...

. It is a vector-borne disease that is transmitted through the bites
Arthropod bites and stings
Many species of arthropods regularly or occasionally bite or sting human beings. Insect saliva contains anticoagulants and enzymes that cause local irritation and allergic reactions. Insect venoms can be delivered by their stingers, which often are modified ovipositors, or by their mouthparts....

 of lice
Louse
Lice is the common name for over 3,000 species of wingless insects of the order Phthiraptera; three of which are classified as human disease agents...

 or soft-bodied ticks
Argasidae
Argasidae is a family of ticks containing the soft ticks. They lack the hard scutum that is present in the hard ticks . The capitulum is located on the underside of the animal's body and is not readily visible...

.

Louse-borne relapsing fever

Borrelia recurrentis
Borrelia recurrentis
Borrelia recurrentis is a species of Borrelia.It can be associated with relapsing fever. B. recurrentis is usually transmitted from person to person via the human body louse....

is one of three pathogens (along with Rickettsia prowazekii
Rickettsia prowazekii
Rickettsia prowazekii is a species of gram negative, Alpha Proteobacteria, obligate intracellular parasitic, aerobic bacteria that is the etiologic agent of epidemic typhus, transmitted in the feces of lice. In North America, the main reservoir for R. prowazekii is the flying squirrel. R...

and Bartonella quintana
Bartonella quintana
Bartonella quintana, originally known as Rochalimaea quintana, and "Rickettsia quintana", is a microorganism that is transmitted by the human body louse. This microorganism is the caustative agent of trench fever...

) of which the body louse
Body louse
The body louse is a louse which infests humans. The condition of being infested with head lice, body lice, or pubic lice is known as pediculosis.-Origins:...

, or Pediculus humanus humanus is a vector. Louse-borne relapsing fever is more severe than the tick-borne variety.

Louse-borne relapsing fever occurs in epidemics amid poor living conditions, famine and war in the developing world
Developing country
A developing country, also known as a less-developed country, is a nation with a low level of material well-being. Since no single definition of the term developing country is recognized internationally, the levels of development may vary widely within so-called developing countries...

; it is currently prevalent in Ethiopia
Ethiopia
Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...

 and Sudan
Sudan
Sudan , officially the Republic of the Sudan , is a country in North Africa, sometimes considered part of the Middle East politically. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the...

.

Mortality rate is 1% with treatment; 30-70% without treatment. Poor prognostic signs include severe jaundice
Jaundice
Jaundice is a yellowish pigmentation of the skin, the conjunctival membranes over the sclerae , and other mucous membranes caused by hyperbilirubinemia . This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluid...

, severe change in mental status, severe bleeding, and prolonged QT interval
QT interval
In cardiology, the QT interval is a measure of the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle. In general, the QT interval represents electrical depolarization and repolarization of the left and right ventricles...

 on ECG.

Lice that feed on infected humans acquire the Borrelia organisms that then multiply in the gut of the louse. When an infected louse feeds on an uninfected human, the organism gains access when the victim crushes the louse or scratches the area where the louse is feeding. B. recurrentis infects the person via mucous membranes and then invades the bloodstream. No animal reservoir exists.

Tick-borne relapsing fever

Tick-borne relapsing fever is found primarily in Africa, Spain, Saudi Arabia, Asia, and certain areas in the Western U.S. and Canada.

Other relapsing infections are acquired from other Borrelia species, which can be spread from rodents, and serve as a reservoir for the infection, via a tick
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...

 vector.
  • Borrelia hermsii
    Borrelia hermsii
    Borrelia hermsii is a species of Borrelia.It can be associated with relapsing fever.It can infect Ornithodoros hermsi....

  • Borrelia parkeri
    Borrelia parkeri
    Borrelia parkeri is a species of Borrelia.It can be associated with relapsing fever....

  • Borrelia duttoni
    Borrelia duttoni
    Borrelia duttoni is a species of Borrelia.It can be associated with relapsing fever....

    , transmitted by the soft-bodied African tick Ornithodoros moubata
    Ornithodoros moubata
    Ornithodoros moubata is a species of tick. It may be a vector of relapsing fever....

    , is responsible for the relapsing fever found in Central, East and southern Africa.
  • Borrelia miyamotoi
    Borrelia miyamotoi
    Borrelia miyamotoi is a spirochete bacteria and part of the Borrelia genus. A zoonotic bacteria, B. miyamotoi can be transferred to humans through the deer tick , the same tick species that spreads B. burgdorferi, the causative agent of Lyme Disease...

    ,


Borrelia hermsii and Borrelia recurrentis cause very similar diseases. However, one or two relapses are common with the disease associated with Borrelia hermsii which is also the most common cause of relapsing disease in the U.S. (Three or four relapses are common with the disease caused by B. recurrentis. B. recurrentis has longer febrile and afebrile intervals and a longer incubation period than Borrelia hermsii.)

Diagnosis

Most people who are infected get sick around 5–15 days after they are bitten by the tick. The symptoms may include a sudden fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...

, chills, headaches, and muscle or joint aches, and nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

; a rash may also occur. These symptoms continue for 2–9 days, then disappear. This cycle may continue for several weeks if the person is not treated. Relapsing Fever is easily treated with 1–2 weeks of antibiotics. Most people improve within 24 hours of starting antibiotics. Complications and death due to relapsing fever are rare.

Relapsing fever is a candidate etiology for a mysterious series of plagues in late medieval and early renaissance-era England referred to at the time as sweating sickness
Sweating sickness
Sweating sickness, also known as "English sweating sickness" or "English sweate" , was a mysterious and highly virulent disease that struck England, and later continental Europe, in a series of epidemics beginning in 1485. The last outbreak occurred in 1551, after which the disease apparently...

 but which have not recurred in epidemic form since the 16th Century.

Treatment

Antibiotics of the tetracycline class are most effective, but may induce a Jarisch-Herxheimer reaction
Herxheimer reaction
The Herxheimer reaction resembles bacterial sepsis and can occur after initiation of antibiotic therapy or treatment of tick-borne relapsing fever. An association has been found between the release of heat-stable proteins from spirochetes and the reaction. The same can be true for candida die-off...

, which occurs in over 50% of patients. This reaction produces apprehension, diaphoresis
Diaphoresis
Diaphoresis is excessive sweating commonly associated with shock and other medical emergency conditions.Diaphoretic is the state of perspiring profusely, or something that has the power to cause increased perspiration....

, fever, tachycardia
Tachycardia
Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...

, and tachypnea
Tachypnea
Tachypnea means rapid breathing. Any rate between 12-20 breaths per minute is normal. Tachypnea is a respiration rate greater than 20 breaths per minute. - Distinction from other breathing terms :...

 with an initial pressor response followed rapidly by hypotension
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...

. Recent studies have shown that tumor necrosis factor-alpha (TNF-alpha) may be partly responsible for the reaction.

External links

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