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Revision as of 23:31, 9 August 2020

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Relapsing fever is a bacterial infection caused by several species of spirochete bacteria in the Borrelia family. TBRF is caused by more the 15 Borrelia species: Borrelia hermsii, Borrelia turicatae, Borrelia parkeri, Borrelia duttonii, Borrelia johnsonii, B miyamotoi. The bacteria species associated with LBRF is Borrelia recurrentis which has a genome so similar to B. duttonii and B. crocidurae (causes of East and West African tick-borne relapsing fever). Louse-borne relapsing fever is more severe than the tick-borne variety. Humans are the sole reservoirs of B recurrentis, while small mammals (eg, pets, ground and tree squirrels, chipmunks) and reptiles (lizards, snakes, gopher tortoises) may serve as a reservoir for tickborne Borrelia species.

Causes

Causative agent

Relapsing fever is an infection with certain spirochete in the genus Borrelia which transmitted by ticks and lice. Borrelia recurrentis causes louse-borne (epidemic) relapsing fever; and more than 15 additional Borrelia species can cause tick-borne (endemic) relapsing fever.

Borrelia are gram-negative, helical, 8-30 11m long, 0.2-0.5 11m wide, and have 3-10 loosely coiled spirals. They are visible with light microscopy.they are flagellated and highly motile, and they divide by binary fission, with doubling times. They have a unique process of DNA rearrangement in their linear DNA. Each time the DNA is read a different antigenic marker, also known as a variable major protein, is created, which allows the organism to evade the immune system and therefore cause recurrent patterns of fever and other symptoms.

They are difficult to cultivate on artificial media and, because of frequent antigenic variation, difficult to serotype, and also identifying of Borrelia species by standard bacteriologic methods is problematic, so the nomenclature has relied on the vector specificity of these organisms.

Louse-borne relapsing fever

Borrelia recurrentis is the only agent of louse-borne disease. Pediculus humanus, is the specific vector. Louse-borne relapsing fever is more severe than the tick-borne variety.

Borrelia recurrentis causes louse-borne (epidemic)relapsing fever.
Transmission of LBRF is confined to the human body louse Pediculus humanus corporis, 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.
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
A single louse can only infect one person, but Nosocomial infections are possible from contamination by infected blood.
Louse-borne relapsing fever occurs in epidemics amid poor living conditions, famine and war in the developing world;^[1] it is currently prevalent in Ethiopia and Sudan.

Tick-borne Relapsing Fever

More than 15 additional Borrelia species can cause tick-borne (endemic) relapsing fever which is transmitted to humans through the bite of infected “soft ticks” of the genus Ornithodoros. Soft ticks (family Argasidae) differ in many ways from the so-called hard. also, Borrelia species are usually associated with specific species of ticks. For example, B. hermsii is transmitted by O. hermsi ticks, B. parkerii by O. parkeri ticks, and B. turicatae by O. turicata ticks. Each tick species has a preferred habitat and preferred set of hosts. They live in the nests of squirrels, chipmunks, and other small animals like chicken & pigs. They feed very quickly(less than a half-hour) and painlessly.

In the United States, TBRF is caused by one of three Borrelia species: B. hermsii, B. parkerii, and B. turicatae.

Other relapsing infections are acquired from other Borrelia species, such as Borrelia hermsii or Borrelia parkeri, which can be spread from rodents, and serve as a reservoir for the infection, via a tick vector. Borrelia hermsii and Borrelia recurrentis cause very similar diseases although the disease associated with Borrelia hermsii has more relapses and is responsible for more fatalities, while the disease caused by B. recurrentis has longer febrile and afebrile intervals and a longer incubation period.

Mortality rate is 1% with treatment; 30-70% without treatment.

Tick-borne relapsing fever is found primarily in Africa, Spain, Saudi Arabia, Asia, and certain areas in the Western U.S. and Canada. Most cases occur in the summer months and are associated in particular with sleeping in rustic cabins in mountainous areas of the Western United States. There are approximately 25 cases of TBRF in the United States each year.

References

↑ Cutler S (2006). "Possibilities for relapsing fever reemergence". Emerg Infect Dis. 12 (3): 369–74. PMID 16704771.

[Cutler_2006-1] Cutler S (2006). "Possibilities for relapsing fever reemergence". Emerg Infect Dis. 12 (3): 369–74. PMID 16704771.

[1]

@@ Line 7: / Line 7: @@
 ==Causes==
-===Infection===
+===Causative agent===
-*Borrelia recurrentis causes louse-borne (epidemic)relapsing fever
+*Relapsing fever is an infection with certain spirochete in the genus Borrelia which transmitted by ticks and lice. Borrelia recurrentis causes louse-borne (epidemic) relapsing fever; and more than 15 additional Borrelia species can cause tick-borne (endemic) relapsing fever.
-*ore than 15 additional Borrelia species can cause tick-borne (endemic) relapsing fever
-In the United States, TBRF is caused by one of three Borrelia species: ''B. hermsii'', ''B. parkerii'', and ''B. turicatae''.  Most human illness is caused by ''B. hermsii''.
+*Borrelia are gram-negative, helical, 8-30 11m long, 0.2-0.5 11m wide, and have 3-10 loosely coiled spirals. They are visible with light microscopy.they are flagellated and highly motile, and they divide by binary fission, with doubling times. They have a unique process of DNA rearrangement in their linear DNA.  Each time the DNA is read a different antigenic marker, also known as a variable major protein, is created, which allows the organism to evade the immune system and therefore cause recurrent patterns of fever and other symptoms.
-The relapsing fever Borrelia spp are gram-negative helical bacteria normally 0.2 to 0.5 microns in width and 5 to 20 microns in length.  They are visible with light microscopy and have the cork-screw shape typical of all spirochetes (see picture).  They have a unique process of DNA rearrangement in their linear DNA.  Each time the DNA is read a different antigenic marker, also known as a variable major protein, is created, which allows the organism to evade the immune system and therefore cause recurrent patterns of fever and other symptoms.
+*They are difficult to cultivate on artificial media and, because of frequent antigenic variation, difficult to serotype, and also identifying of  Borrelia species by standard bacteriologic methods is problematic, so the nomenclature has relied on the vector specificity of these organisms.
-Borrelia is transmitted to humans through the bite of infected soft ticks of the genus Ornithodoros.  Soft ticks (family Argasidae) differ in many ways from the so-called hard [[tick]]s (family [[Ixodidae]]), including the more familiar dog tick and deer tick.
+====Louse-borne relapsing fever====
+''Borrelia recurrentis'' is the only agent of louse-borne disease. ''[[Pediculus humanus]]'', is the specific vector. Louse-borne relapsing fever is more severe than the tick-borne variety.
+*Borrelia recurrentis causes louse-borne (epidemic)relapsing fever.
+*Transmission of LBRF is confined to the human body louse Pediculus humanus corporis, 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.
+*''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
+*A single louse can only infect one person, but Nosocomial infections are possible from contamination by infected blood.
+*Louse-borne relapsing fever occurs in [[epidemics]] amid poor living conditions, famine and war in the developing world;<ref name=Cutler_2006>{{cite journal |author=Cutler S |title=Possibilities for relapsing fever reemergence |journal=Emerg Infect Dis |volume=12 |issue=3 |pages=369-74 |year=2006 |pmid=16704771}}</ref> it is currently prevalent in Ethiopia and Sudan.
+====Tick-borne Relapsing Fever====
+*More than 15 additional Borrelia species can cause tick-borne (endemic) relapsing fever which is transmitted to humans through the bite of infected “soft ticks” of the genus Ornithodoros. Soft ticks (family Argasidae) differ in many ways from the so-called hard. also, Borrelia species are usually associated with specific species of ticks. For example, B. hermsii is transmitted by O. hermsi ticks, B. parkerii by O. parkeri ticks, and B. turicatae by O. turicata ticks. Each tick species has a preferred habitat and preferred set of hosts. They live in the nests of squirrels, chipmunks, and other small animals like chicken & pigs. They feed very quickly(less than a half-hour) and painlessly.
+*In the United States, TBRF is caused by one of three Borrelia species: ''B. hermsii'', ''B. parkerii'', and ''B. turicatae''.
+*Other relapsing infections are acquired from other ''Borrelia'' species, such as ''Borrelia hermsii'' or ''Borrelia parkeri'', which can be spread from rodents, and serve as a reservoir for the infection, via a [[tick]] vector. ''Borrelia hermsii'' and ''Borrelia recurrentis'' cause very similar diseases although the disease associated with ''Borrelia hermsii'' has more relapses and is responsible for more fatalities, while the disease caused by ''B. recurrentis'' has longer febrile and afebrile intervals and a longer incubation period.
 [[Image:Ornithodoros hermsi.jpg|left|frame|Ornithodoros hermsi]]
-In contrast to hard ticks, soft ticks take brief blood meals lasting less than a half hour, usually at night.  Between meals the ticks live in the nesting materials in their host burrows.  Individual ticks will take many such blood meal during each stage of their life cycles, including the development of eggs by adult females. The bites of soft ticks are usually painless and the persons who are bitten while asleep are usually unaware that they were bitten.
-The individual Borrelia species that cause TBRF are usually associated with specific tick vectors.  For instance, ''B. hermsii'' is transmitted to humans by ''O. hermsi'' ticks, while ''B. parkerii'' is transmitted by ''O. parkeri'' and ''B. turicatae'' is transmitted by ''O. turicata''.  Each tick has a preferred environment and preferred set of hosts.
-* ''O. hermsi'' tends to be found at higher altitudes (1500 – 8000 feet) where it is associated primarily with ground or tree squirrels and chipmunks.
-* ''O. parkeri'' occurs at lower altitudes, where they inhabit caves and the burrows of ground squirrels and prairie dogs, as well as those of burrowing owls.
-*  ''O. turicata'' occurs in caves and ground squirrel or prairie dog burrows in the plains regions of the Southwest, feeding off these animals and occasionally burrowing owls or other burrow- or cave-dwelling animals.
-In the tick, Borrelia can be found in all the tissues including salivary glands and ovaries of certain subspecies of ticks (Schwan and Piesman 2002).  Infected Ornithodoros ticks can transmit relapsing fever spirochetes to humans through their saliva while feeding.
-* ''O. turicatae'' and ''O. parkeri'' ticks also can transmit spirochetes through secretion of infectious fluids from their coxal glands, which are excretory organs located at the base of the ticks' legs.
-* ''O. hermsi'' also secretes infectious coxal fluid but in such small amounts that it dries very quickly after being secreted and, therefore, poses little or no threat to its hosts.  Since the infection is also in the ovaries of certain ticks, such as O. hermsi, they can transmit their infections over many generations from female ticks to their offspring.
-* Soft ticks can live up to 10 years.
-*In certain parts of the Russia the same tick has been found to live almost 20 years.
-====Louse-borne relapsing fever====
-''Borrelia recurrentis'' is the only agent of louse-borne disease. ''[[Pediculus humanus]]'', is the specific 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;<ref name=Cutler_2006>{{cite journal |author=Cutler S |title=Possibilities for relapsing fever reemergence |journal=Emerg Infect Dis |volume=12 |issue=3 |pages=369-74 |year=2006 |pmid=16704771}}</ref> it is currently prevalent in Ethiopia and Sudan.
-Mortality rate is 1% with treatment; 30-70% without treatment. Poor prognostic signs include severe [[jaundice]], severe change in mental status, severe [[bleeding]], and prolonged [[QT interval]] on [[ECG]].
+*Mortality rate is 1% with treatment; 30-70% without treatment.
-''Borrelia'' species causing relapsing fever include ''Borrelia recurrentis'', caused by human body louse. No animal reservoir exists. 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.
-====Tick-borne Relapsing Fever====
-Other relapsing infections are acquired from other ''Borrelia'' species, such as ''Borrelia hermsii'' or ''Borrelia parkeri'', which can be spread from rodents, and serve as a reservoir for the infection, via a [[tick]] vector. ''Borelia hermsii'' and ''Borrelia recurrentis'' cause very similar diseases although the disease associated with ''Borrelia hermsii'' has more relapses and is responsible for more fatalities, while the disease caused by ''B. recurrentis'' has longer febrile and afebrile intervals and a longer incubation period.
 Tick-borne relapsing fever is found primarily in Africa, Spain, Saudi Arabia, Asia, and certain areas in the Western U.S. and Canada. Most cases occur in the summer months and are associated in particular with sleeping in rustic cabins in mountainous areas of the Western United States.  There are approximately 25 cases of TBRF in the United States each year.