Relapsing fever pathophysiology: Difference between revisions
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keywords: VMP:Variable membrane proteins | keywords: VMP:Variable membrane proteins | ||
==Overview== | ==Overview== | ||
[[Borrelia]] is usually transmitted via the [[tick bite]] or [[body louse]] to the human host. After entering the [[bloodstream]], [[spirochetes]] replicate [[Extracellular|extracellularly]] and remain predominantly in the [[plasma]] space. Patients generally remain [[asymptomatic]] until high-level [[spirochetemia]] | [[Borrelia]] is usually transmitted via the [[tick bite]] or [[body louse]] to the human host. After entering the [[bloodstream]], [[spirochetes]] replicate [[Extracellular|extracellularly]] and remain predominantly in the [[plasma]] space. Patients generally remain [[asymptomatic]] until high-level [[spirochetemia]] develops, at which time [[symptoms]] begin abruptly. Organisms are cleared predominantly by opsonizing [[antibodies]] with the resolution of [[symptoms]] ( [[afebrile]] period), followed several days or weeks later by the reemergence of a new [[antigenic]] strain, high-level [[spirochetemia]], and recurrence of [[symptoms]]. There are multiple [[genes]] in the [[spirochete]] encoding [[variable]] [[membrane]] [[proteins]]( [[VMPs]]). These '''VMPs''' determine the [[antigenic]] [[serotype]] of the [[organism]]. At any given time, each [[spirochete]] has VMP [[genes]] that are [[expressed]] and others that are [[silent]]. An [[Antigenic variation|antigenic switch]] occurs when a given [[VMP]] gene transposes from silent to an expressed [[locus]]. This cyclical process of initially effective [[immune response]] followed by [[antigenic variation]] and [[immunologic]] escape is responsible for the relapsing nature of this illness. | ||
==Pathophysiology== | ==Pathophysiology== | ||
===Cyclical process=== | |||
*[[Borrelia]] is usually transmitted via the [[tick bite]] or [[body louse]] to the human host. | *[[Borrelia]] is usually transmitted via the [[tick bite]] or [[body louse]] to the human host. | ||
*[[Borrelia]] is able to induce cycles of disease by varying antigen expression and by displaying new [[Outer membrane|outer-surface proteins]](VMPs) during the disease course([[antigenic variation]]). The antigenic variation contributes to the recurring nature of [[relapsing fever]].There are multiple [[genes]] in the [[spirochete]] encoding [[variable]] [[membrane]] [[proteins]]( [[VMPs]]). These '''VMPs''' determine the antigenic serotype of the organism. At any given time, each [[spirochete]] has VMP genes that are [[expressed]] and others that are [[silent]]. An [[Antigenic variation|antigenic switch]] occurs when a given [[VMP]] gene transposes from silent to an expressed [[locus]]. This cyclical process of initially effective [[immune response]] followed by [[antigenic variation]] and [[immunologic]] escape is responsible for the relapsing nature of this illness. | |||
===Incubation period=== | ===Incubation period=== | ||
[[Incubation period]] = time from tick bite to illness | [[Incubation period]] = time from tick bite to illness | ||
*7 days, range 2 to 18 days | *7 days, range 2 to 18 days | ||
===Symptomatic period=== | ===Symptomatic period=== | ||
[[Symptomatic]] period= Length of illness = time from symptom onset to resolution of symptoms | [[Symptomatic]] period= Length of illness = time from symptom onset to resolution of symptoms | ||
* 3 days, range 2 to 7 days | * 3 days, range 2 to 7 days | ||
* | *During episodes of [[spirochetemia]] and replicate [[extracellularly]] and remain predominantly the [[plasma]] space. [[Borrelia]] invades the [[endothelium]]. After multiplying in the [[endothelial cells]], the [[bacteria]] are released into the [[bloodstream]] and patients develop symptoms that include [[fever]]. However,the [[organisms]] may invade the brain, eye, inner ear, heart, liver. Splenic [[abscesses]] and infarcts, and hemorrhages within the central nervous system, a perivascular histiocytic interstitial [[myocarditis]], conduction defects, [[arrhythmias]], and [[myocardial]] failure, [[splenic rupture]] with massive hemorrhage, [[cerebral hemorrhage]], and [[hepatic failure]] are seen in LBRF which can result in sudden death.Hepatitis with patchy [[hemorrhages]] and [[necrosis]], [[meningitis]], and [[perisplenitis]], thrombi in small [[vessels]] also are found. [[Thrombi]] are occasionally found occluding [[small vessel]]s.<ref name="pmid30869050">{{cite journal |vauthors=Warrell DA |title=Louse-borne relapsing fever (Borrelia recurrentis infection) |journal=Epidemiol. Infect. |volume=147 |issue= |pages=e106 |date=January 2019 |pmid=30869050 |pmc=6518520 |doi=10.1017/S0950268819000116 |url=}}</ref>[[CNS]] involvement is more common in [[Tick-borne relapsing fever|TBRF]] than [[Louse-borne relapsing fever|LBRF]], however [[eschar|eschars]], [[ARDS]], [[cranial nerve palsies]], focal neurologic deficits, [[uveitis]], [[iritis]] or [[iridocyclitis]], [[splenic rupture]] and [[myocarditis]] may be seen in both [[Tick-borne relapsing fever|TBRF]] and [[Louse-borne relapsing fever|LBRF]].<ref name="pmid18646588">{{cite journal |vauthors=Blevins SM, Greenfield RA, Bronze MS |title=Blood smear analysis in babesiosis, ehrlichiosis, relapsing fever, malaria, and Chagas disease |journal=Cleve Clin J Med |volume=75 |issue=7 |pages=521–30 |date=July 2008 |pmid=18646588 |doi=10.3949/ccjm.75.7.521 |url=}}</ref><ref name="pmid18755384">{{cite journal |vauthors=Dworkin MS, Schwan TG, Anderson DE, Borchardt SM |title=Tick-borne relapsing fever |journal=Infect. Dis. Clin. North Am. |volume=22 |issue=3 |pages=449–68, viii |date=September 2008 |pmid=18755384 |pmc=3725823 |doi=10.1016/j.idc.2008.03.006 |url=}}</ref>Most information on the pathophysiologic aspects of fatal cases comes from autopsy data of louse-borne disease in humans or experimental animals.<ref name="pmid18755384">{{cite journal |vauthors=Dworkin MS, Schwan TG, Anderson DE, Borchardt SM |title=Tick-borne relapsing fever |journal=Infect. Dis. Clin. North Am. |volume=22 |issue=3 |pages=449–68, viii |date=September 2008 |pmid=18755384 |pmc=3725823 |doi=10.1016/j.idc.2008.03.006 |url=}}</ref> | ||
[[File:Pathophysiology LBRF.jpg|CNS, Eye involvement in LBRF]] | [[File:Pathophysiology LBRF.jpg|CNS, Eye involvement in LBRF]] | ||
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[[Afebrile]] period= Length of time before reoccurrence = time from the resolution of symptoms to reoccurrence of symptoms | [[Afebrile]] period= Length of time before reoccurrence = time from the resolution of symptoms to reoccurrence of symptoms | ||
* 7 days, range 4 to 14 days | * 7 days, range 4 to 14 days | ||
* Organisms are cleared predominantly by opsonizing [[antibodies]] with the resolution of symptoms ( [[afebrile]] period), followed several days or weeks later by the reemergence of a new [[antigenic]] strain, high-level spirochetemia, when high-level [[spirochetemia]] (104-108 organisms m!) develops, at which time symptoms begin abruptly. | * Organisms are cleared predominantly by opsonizing [[antibodies]] with the resolution of symptoms ( [[afebrile]] period), followed several days or weeks later by the reemergence of a new [[antigenic]] strain, high-level spirochetemia, when high-level [[spirochetemia]] (104-108 organisms m!) develops, at which time symptoms begin abruptly. | ||
===Crisis=== | ===Crisis=== | ||
* | *Most cases eventually resolve spontaneously. Occasionally, the crisis occurs after the resolution. During the crisis, patients may develop cerebral edema with seizures, cardiac failure, or death. This stage may result in death in up to 10% of patients. | ||
===Immunity=== | ===Immunity=== | ||
Latest revision as of 21:49, 26 September 2020
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Roghayeh Marandi keywords: VMP:Variable membrane proteins
Overview
Borrelia is usually transmitted via the tick bite or body louse to the human host. After entering the bloodstream, spirochetes replicate extracellularly and remain predominantly in the plasma space. Patients generally remain asymptomatic until high-level spirochetemia develops, at which time symptoms begin abruptly. Organisms are cleared predominantly by opsonizing antibodies with the resolution of symptoms ( afebrile period), followed several days or weeks later by the reemergence of a new antigenic strain, high-level spirochetemia, and recurrence of symptoms. There are multiple genes in the spirochete encoding variable membrane proteins( VMPs). These VMPs determine the antigenic serotype of the organism. At any given time, each spirochete has VMP genes that are expressed and others that are silent. An antigenic switch occurs when a given VMP gene transposes from silent to an expressed locus. This cyclical process of initially effective immune response followed by antigenic variation and immunologic escape is responsible for the relapsing nature of this illness.
Pathophysiology
Cyclical process
- Borrelia is usually transmitted via the tick bite or body louse to the human host.
- Borrelia is able to induce cycles of disease by varying antigen expression and by displaying new outer-surface proteins(VMPs) during the disease course(antigenic variation). The antigenic variation contributes to the recurring nature of relapsing fever.There are multiple genes in the spirochete encoding variable membrane proteins( VMPs). These VMPs determine the antigenic serotype of the organism. At any given time, each spirochete has VMP genes that are expressed and others that are silent. An antigenic switch occurs when a given VMP gene transposes from silent to an expressed locus. This cyclical process of initially effective immune response followed by antigenic variation and immunologic escape is responsible for the relapsing nature of this illness.
Incubation period
Incubation period = time from tick bite to illness
- 7 days, range 2 to 18 days
Symptomatic period
Symptomatic period= Length of illness = time from symptom onset to resolution of symptoms
- 3 days, range 2 to 7 days
- During episodes of spirochetemia and replicate extracellularly and remain predominantly the plasma space. Borrelia invades the endothelium. After multiplying in the endothelial cells, the bacteria are released into the bloodstream and patients develop symptoms that include fever. However,the organisms may invade the brain, eye, inner ear, heart, liver. Splenic abscesses and infarcts, and hemorrhages within the central nervous system, a perivascular histiocytic interstitial myocarditis, conduction defects, arrhythmias, and myocardial failure, splenic rupture with massive hemorrhage, cerebral hemorrhage, and hepatic failure are seen in LBRF which can result in sudden death.Hepatitis with patchy hemorrhages and necrosis, meningitis, and perisplenitis, thrombi in small vessels also are found. Thrombi are occasionally found occluding small vessels.[1]CNS involvement is more common in TBRF than LBRF, however eschars, ARDS, cranial nerve palsies, focal neurologic deficits, uveitis, iritis or iridocyclitis, splenic rupture and myocarditis may be seen in both TBRF and LBRF.[2][3]Most information on the pathophysiologic aspects of fatal cases comes from autopsy data of louse-borne disease in humans or experimental animals.[3]
Afebrile period
Afebrile period= Length of time before reoccurrence = time from the resolution of symptoms to reoccurrence of symptoms
- 7 days, range 4 to 14 days
- Organisms are cleared predominantly by opsonizing antibodies with the resolution of symptoms ( afebrile period), followed several days or weeks later by the reemergence of a new antigenic strain, high-level spirochetemia, when high-level spirochetemia (104-108 organisms m!) develops, at which time symptoms begin abruptly.
Crisis
- Most cases eventually resolve spontaneously. Occasionally, the crisis occurs after the resolution. During the crisis, patients may develop cerebral edema with seizures, cardiac failure, or death. This stage may result in death in up to 10% of patients.
Immunity
- Specific serotypes can recur within an individual. Infection with a given strain of Borrelia may cause partial protection against subsequent infection by the same strain. In some highly endemic areas, relapsing fever is more severe in newcomers than natives.
Genetics
The development of the cyclical process is the result of antigenic variation and subsequent immunologic escape:
- There are multiple genes in the spirochete encoding variable membrane proteins( VMPs) which are the outer membrane of spirochetes contains surface proteins. Attacks of relapsing fever end abruptly when specific bactericidal immunoglobulin M antibodies generated by the B1b cell subset lyse spirochaetes in the blood, independently of complement and T cells. These VMPs determine the antigenic serotype of the organism and at any given time, each spirochete has VMP genes that are expressed and others that are silent. An antigenic switch occurs when a given VMP gene transposes from silent to an expressed locus. This mechanism of antigenic variation presumably leads to immunologic escape and relapse. Because of the organism’s ability to undergo antigenic variation, several serotypes may be present in the bloodstream at one time.
References
- ↑ Warrell DA (January 2019). "Louse-borne relapsing fever (Borrelia recurrentis infection)". Epidemiol. Infect. 147: e106. doi:10.1017/S0950268819000116. PMC 6518520 Check
|pmc=value (help). PMID 30869050. - ↑ Blevins SM, Greenfield RA, Bronze MS (July 2008). "Blood smear analysis in babesiosis, ehrlichiosis, relapsing fever, malaria, and Chagas disease". Cleve Clin J Med. 75 (7): 521–30. doi:10.3949/ccjm.75.7.521. PMID 18646588.
- ↑ 3.0 3.1 Dworkin MS, Schwan TG, Anderson DE, Borchardt SM (September 2008). "Tick-borne relapsing fever". Infect. Dis. Clin. North Am. 22 (3): 449–68, viii. doi:10.1016/j.idc.2008.03.006. PMC 3725823. PMID 18755384.