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{{Taxobox
| color = lightgrey
| name = ''Rickettsia''
| regnum = [[Bacterium|Bacteria]]
| phylum = [[Proteobacteria]]
| classis = Alpha Proteobacteria
| ordo = [[Rickettsiales]]
| familia = [[Rickettsiaceae]]
| genus = '''''Rickettsia'''''
| genus_authority = da Rocha-Lima, 1916
| subdivision_ranks = Species
| subdivision =
''[[Rickettsia felis]]''<br/>
''[[Rickettsia prowazekii]]''<br/>
''[[Rickettsia rickettsii]]''<br/>
''[[Rickettsia typhi]]''<br/>
''[[Rickettsia conorii]]''<br/>
''[[Rickettsia africae]]''<br/>
etc.
}}
__NOTOC__
__NOTOC__


{{CMG}}  {{AE}} {{IMD}}; {{KS}}  
{{CMG}}  {{AE}} {{IMD}}; {{KS}}  
__NOTOC__
{{SI}}
{{CMG}}


==Overview==
==Overview==
Rickettsial spotted fevers are a group of typhus [[disease]]s or illnesses [[vector (biology)|transmitted by]] [[tick]]s worldwide. As the incidence of typhus fevers increase and the geographic areas in which they are found expand, it becomes increasingly important for health professionals to be able to distinguish the diverse, and often overlapping, clinical presentations of these diseases.


==Pathophysiology==
'''''Rickettsia''''' is a [[genus]] of [[Motility|non-motile]], [[Gram-negative]], [[Endospore|non-sporeforming]], highly [[pleomorphic]] [[Bacterium|bacteria]] that can present as [[cocci]] (0.1 μm in diameter), rods (1-4 μm long) or thread-like (10 μm long). Obligate intracellular parasites, the ''Rickettsia''  depend on entry, growth, and replication within the [[cytoplasm]] of [[eukaryote|eukaryotic]] host cells (typically endothelial cells).<ref name=Barron>{{cite book | author = Walker DH | title = Rickettsiae. ''In:'' Barron's Medical Microbiology ''(Barron S ''et al'', eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | id = [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2078 (via NCBI Bookshelf)] ISBN 0-9631172-1-1 }}</ref> Because of this, ''Rickettsia'' cannot live in artificial nutrient environments and are grown either in [[Biological tissue|tissue]] or [[embryo]] cultures (typically, chicken embryos are used).  In the past they were regarded as microorganisms positioned somewhere between viruses and true [[bacterium|bacteria]]. The majority of ''Rickettsia'' bacteria are susceptible to [[antibiotic]]s of the [[tetracycline]] group.
 
''Rickettsia'' species are carried as [[parasite]]s by many [[tick]]s, [[flea]]s, and [[lice]], and cause [[disease]]s such as [[typhus]], [[rickettsialpox]], [[Boutonneuse fever]], [[African Tick Bite Fever]], [[Rocky Mountain spotted fever]], [[Australian Tick Typhus]], [[Flinders Island Spotted Fever]] and [[Queensland Tick Typhus]] <ref>http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=AbstractPlus&list_uids=17553271&tool=MedlinePlus</ref> in human beings.  They have also been associated with a range of plant diseases. Like [[virus]]es, they grow only in living cells.  The name rickettsia is often used for any member of the [[Rickettsiales]]. They are thought to be the closest living relatives to bacteria that were the origin of the [[mitochondria]] organelle that exist in most [[eukaryotic]] cells.
 
The method of growing Rickettsia in chicken embryos was invented by [[Ernest William Goodpasture]] and colleagues at [[Vanderbilt University]] in the early 1930s.
 
 
==Naming==
*The genus ''Rickettsia'' is named after [[Howard T. Ricketts|Howard Taylor Ricketts]] ([[1871]]&ndash;[[1910]]), who worked on and eventually died of typhus. 
*Despite the similar name, ''Rickettsia'' bacteria do not cause [[rickets]]. The disease of rickets takes its name from the [[Greek language|Greek]] word for [[vertebral column|spine]], ''hrake'', and is a [[Avitaminosis|vitamin D deficiency disease]], not an infectious disease.
 
==Human pathogenesis==
The ''Rickettsia'' human pathogens are generally grouped as follows:
 
===Spotted fever group===
:*''R. rickettsii'' (Western hemisphere)
::[[Rocky Mountain spotted fever]]
 
:*''R. akari'' (USA, former Soviet Union)
::[[Rickettsialpox]]


Typhus fevers are caused by rickettsia bacterial infections.
:*''R. conorii'' (Mediterranean countries, Africa, Southwest Asia, India)
::[[Boutonneuse fever]]


===Life Cycle and Spread of Rickettsial Disease===
:*''R. sibirica'' (Siberia, Mongolia, northern China)
::Siberian tick typhus


'''General Tick Life Cycle''' <ref name="LCT CDC”">Life Cycle of Ticks that Bite Humans (2015).  http://www.cdc.gov/ticks/life_cycle_and_hosts.html Accessed on December 30, 2015</ref>
:*''R. australis'' (Australia)
[[Image:Lifecycle.jpg|left|thumb| This image displays an example of the tick lifecycle, based on stages and the months that they are most likely to occur during.]]
::[[Australian tick typhus]]
*A tick's life cycle is composed of four stages: ''hatching'' (egg), ''nymph'' (six legged), ''nymph'' (eight legged), and an ''adult''.
*Ticks require blood meal to survive through their life cycle.
*Hosts for tick blood meals include mammals, birds, reptiles, and amphibians. Ticks will most likely transfer between different hosts during the different stages of their life cycle.
*Humans are most often targeted during the nymph and adult stages of the life cycle.
*Life cycle is also dependent on seasonal variation.
*Ticks will go from eggs to larva during the summer months, infecting bird or rodent host during the larval stage.
*Larva will infect the host from the summer until the following spring, at which point they will progress into the nymph stage.
*During the nymph stage, a tick will most likely seek a mammal host (including humans).
*A nymph will remain with the selected host until the following fall at which point it will progress into an adult.
*As an adult, a tick will feed on a mammalian host. However unlike previous stages, ticks will prefer larger mammals over rodents. 
*The average tick life cycle requires three years for completion.
**Different species will undergo certain variations within their individual life cycles.
<br>
<br>
<br>
<br>
===Spread of Rickettsial Disease===
*Ticks require blood meals in order to progress through their life cycles.
*The average tick requires 10 minutes to 2 hours when preparing a blood meal.
*Once feeding, releases anesthetic properties into its host, via its saliva.
*A feeding tube enters the host followed by an adhesive-like substance, attaching the tick to the host during the blood meal.
*A tick will feed for several days, feeding on the host blood and ingesting the host's pathogens.
*Once feeding is completed, the tick will seek a new host and transfer any pathogens during the next feeding process. <ref name="LCT CDC”">Life Cycle of Ticks that Bite Humans (2015).  http://www.cdc.gov/ticks/life_cycle_and_hosts.html Accessed on December 30, 2015</ref>


==Epidemiology and Demographics==
:*''R. japonica'' (Japan)
::Oriental spotted fever


===Incidence===
:*''R. africae'' (South Africa)
:: African Tick Bite Fever


*Tick based infections are generally non-specific in regards to age, race, or gender. (However babesiosis is more frequently observed in older, male populations. An explanation for this has not yet been formulated.) <ref name="LCT CDC”">Life Cycle of Ticks that Bite Humans (2015).  http://www.cdc.gov/ticks/life_cycle_and_hosts.html Accessed on December 30, 2015</ref>
===Typhus group===
*Certain tick-borne illnesses will vary within patient populations when an auto-immune deficiency is present.
:*''[[Rickettsia prowazekii|R. prowazekii]]'' (Worldwide)
*Tick bites are more frequently reported during the spring and summer months which are noted to be in correlation with high tick activity.
::Epidemic, recrudescent and sporadic [[typhus]]
*Higher risks are associated with individuals traveling within endemic areas.
*Inoculation within endemic areas is usually the result of a tick bite however transmission has been identified as a result of transfusions or transplantation.


===Species and Regions===
:*''R. typhi'' (Worldwide)
====United States====
::Murine (endemic) typhus


American Dog Tick (''[[Dermacentor variabilis|Dermacentor Variabilis]]'') <ref name="Ticks CDC”">Geographic Distribution of Ticks that Bite Humans (2015). http://www.cdc.gov/ticks/geographic_distribution.html Accessed on December 30, 2015</ref>
===Scrub typhus group===
*Pacific Coast and east of the Rocky Mountains.
:*The causative agent of [[scrub typhus]] formerly known as ''R. tsutsugamushi'' has been reclassified into the genus ''[[Orientia]]''.
*Transmits tularemia and rocky mountain spotted fever.
*Primarily infects humans during the spring and summer months.  


Blacklegged tick (''[[Ixodes scapularis|Ixodes Scapularis]]'') <ref name="Ticks CDC”">Geographic Distribution of Ticks that Bite Humans (2015). http://www.cdc.gov/ticks/geographic_distribution.html Accessed on December 30, 2015</ref>
==Plant pathogenesis==
*Northeastern and upper Midwest.
*Transmits [[Lyme disease]], [[babesiosis]], [[anaplasmosis]], and [[Powassan disease]].
*Primarily infects humans during the spring, summer, and fall months.


Brown dog tick (''[[Rhipicephalus sanguineus|Rhipicephalus Sanguineus]]'') <ref name="Ticks CDC”">Geographic Distribution of Ticks that Bite Humans (2015). http://www.cdc.gov/ticks/geographic_distribution.html Accessed on December 30, 2015</ref>
The following plant diseases have been assocaited with Rickettsia-like organisms<ref name=Smith>{{cite book | author = Smith IM, Dunez J, Lelliot RA, Phillips DH, Archer SA| title = European Handbook of Plant Diseases. | publisher = Blackwell Scientific Publications| year = 1988 | id = ISBN 0-632-01222-6}}</ref>.
*Widespread throughout the United States.
*Transmits [[Rocky mountain spotted fever]].


Gulf Coast Tick (''[[Amblyomma maculatum|Amblyomma Maculatum]]'') <ref name="Ticks CDC”">Geographic Distribution of Ticks that Bite Humans (2015). http://www.cdc.gov/ticks/geographic_distribution.html Accessed on December 30, 2015</ref>
:* Beet latent Rosette RLO
*Atlantic Coast and Gulf of Mexico (Along the coast of Northeastern Virginia until the Southern most portions of Florida. From Southeast Florida through the Gulf of Mexico into Texas).
:* Citrus Greening bacterium
*Transmits Rickettsia parkeri rickettsiosis (spotted fever).
:* Clover leaf RLO
:* Grapevine infectious necrosis RLO
:* Grapevine Pierce's RLO
:* Grapevine yellos RLO
:* Larch witche's broom disease
:* Peach phoney RLO


Lone Star Tick (''[[Amblyomma americanum|Amblyomma Americanum]]'') <ref name="Ticks CDC”">Geographic Distribution of Ticks that Bite Humans (2015). http://www.cdc.gov/ticks/geographic_distribution.html Accessed on December 30, 2015</ref>
==Genomics==
*Southeastern and Eastern United States.
*Certain segments of Rickettsial [[genome]]s resemble that of [[mitochondria]].<ref name=Emelyanov_2003>{{cite journal | author=Emelyanov VV | title=Mitochondrial connection to the origin of the eukaryotic cell | journal=Eur J Biochem | year=2003 | pages=1599-618 | volume=270 | issue=8 | id={{PMID|12694174}} }}</ref>
*Transmits [[Ehrlichiosis]], [[tularemia]], [[STARI]].
*The deciphered genome of ''R. prowazekii''  is 1,111,523 [[base pair|bp]] long and contains 834 protein-coding [[genes]].<ref name=Andersson_1998>{{cite journal | author=Andersson SG, ''et al'' | title=The genome sequence of Rickettsia prowazekii and the origin of mitochondria | journal=Nature | year=1998 | pages=133-40 | volume=396 | issue=6707 | id={{PMID|9823893}} }}</ref>  
*Unlike free-living bacteria, it contains no genes for [[anaerobic]] [[glycolysis]] or genes involved in the biosynthesis and regulation of [[amino acid]]s and [[nucleoside]]s.
*In this regard it is similar to mitochondrial genomes; in both cases, nuclear (host) resources are used. [[Adenosine triphosphate|ATP]] production in ''Rickettsia'' is the same as that in mitochondria.
*In fact, of all the microbes known, the ''Rickettsia'' is probably the closest "relative" (in [[phylogenetic]] sense) to the mitochondria.
*The genome of ''R. prowazekii'' contains a complete set of genes encoding for the [[tricarboxylic acid cycle]] and the [[respiratory-chain]] complex. 
*The genomes of the Rickettsia as well as the mitochondria are frequently said to be "small, highly derived products of several types of reductive evolution".


[[Rocky Mountain Wood Tick]] (''[[Dermacentor andersoni|Dermacentor Andersoni]]'') <ref name="Ticks CDC”">Geographic Distribution of Ticks that Bite Humans (2015). http://www.cdc.gov/ticks/geographic_distribution.html Accessed on December 30, 2015</ref>
*Colorado, Nevada, eastern California, eastern Oregon, eastern Washington, Idaho, Montana, Wyoming, and Utah.
*Transmits [[Rocky mountain spotted fever]], [[Colorado tick fever]], and [[tularemia]].


[[Western Blacklegged tick]] (''[[Ixodes pacificus|Ixodes Pacificus]]'') <ref name="Ticks CDC”">Geographic Distribution of Ticks that Bite Humans (2015). http://www.cdc.gov/ticks/geographic_distribution.html Accessed on December 30, 2015</ref>
==Epidemiology and Demographics==
*Pacific Coast
*Transmits [[Anaplasmosis]] and [[Lyme Disease]].


====International====
===Incidence===
''Hyalomma Marginatum'' <ref name="Ticks ECDC”">Ticks that Bite Humans (2015). http://ecdc.europa.eu/en/healthtopics/vectors/vector-maps/Pages/VBORNET-maps-tick-species.aspx Accessed on December 30, 2015</ref>
*Widespread: North Africa, Europe, and Asia.
*Transmits Crimean-Congo hemorrhagic fever.


''Ixodes Ricinus'' <ref name="Ticks ECDC”">Ticks that Bite Humans (2015). http://ecdc.europa.eu/en/healthtopics/vectors/vector-maps/Pages/VBORNET-maps-tick-species.aspx Accessed on December 30, 2015</ref>
*Widespread throughout Europe and parts of North Africa.
*Transmits encephalitis and Lyme Disease.


''Ixodes Persulcatus'' <ref name="Ticks ECDC”">Ticks that Bite Humans (2015). http://ecdc.europa.eu/en/healthtopics/vectors/vector-maps/Pages/VBORNET-maps-tick-species.aspx Accessed on December 30, 2015</ref>


''Dermacentor Reticulatus'' <ref name="Ticks ECDC”">Ticks that Bite Humans (2015). http://ecdc.europa.eu/en/healthtopics/vectors/vector-maps/Pages/VBORNET-maps-tick-species.aspx Accessed on December 30, 2015</ref>


==Tick-borne disease Classification==
==Rickettsial disease classification==


{|style="font-size: 14px; background: #7D7D7D; text-align:center;" colspan="5d" | '''{{fontcolor|#FFF|Typhus (Rickettsia)}}'''
{|style="font-size: 85%;"
! style="width: 80px; background: #4479BA; text-align: center;" |{{fontcolor|#FFF|Disease}}
! style="width: 720px; background: #4479BA; text-align: center;" | {{fontcolor|#FFF|Organism}}
! style="width: 720px; background: #4479BA; text-align: center;" | {{fontcolor|#FFF|Vector}}
! style="width: 720px; background: #4479BA; text-align: center;" | {{fontcolor|#FFF|Endemic Regions}}
|-
|style="font-size: 14px; background: #7D7D7D; text-align:center;" colspan="5d" | '''{{fontcolor|#FFF|Typhus (Rickettsia)}}'''
|-
|-
| style="background: #F5F5F5; padding: 5px; text-align: center;" | '''[[Rocky Mountain Spotted Fever]]''' <ref name="RMSF CDC”">Rocky Mountain Spotted Fever Information. Centers for Disease Control and Prevention (2015).  http://www.cdc.gov/rmsf/  Accessed on December 30, 2015</ref>
| style="background: #F5F5F5; padding: 5px; text-align: center;" | '''[[Rocky Mountain Spotted Fever]]''' <ref name="RMSF CDC”">Rocky Mountain Spotted Fever Information. Centers for Disease Control and Prevention (2015).  http://www.cdc.gov/rmsf/  Accessed on December 30, 2015</ref>
Line 262: Line 281:
! style="width: 80px; background: #4479BA; text-align: center;" |{{fontcolor|#FFF|Disease}}
! style="width: 80px; background: #4479BA; text-align: center;" |{{fontcolor|#FFF|Disease}}
! style="width: 720px; background: #4479BA; text-align: center;" | {{fontcolor|#FFF|Symptoms}}
! style="width: 720px; background: #4479BA; text-align: center;" | {{fontcolor|#FFF|Symptoms}}
|-
| style="font-size: 14px; background: #7d7d7d; text-align: center;" colspan="5d" | {{fontcolor|#FFF|'''Bacterial Infection'''}}
|-
| style="background: #F5F5F5; padding: 5px; text-align: center;" | ''Borreliosis (Lyme Disease)'' <ref name="Lyme CDC”">Lyme Disease Information for HealthCare Professionals. Centers for Disease Control and Prevention (2015).  http://www.cdc.gov/lyme/healthcare/index.html Accessed on December 30, 2015</ref>
| style="background: #DCDCDC; padding: 5px;" |Flu-like illness, fatigue, fever, arthritis, neuroborreliosis, cranial nerve palsy, carditis and erythema migrans.
|-
| style="background: #F5F5F5; padding: 5px; text-align: center;" | ''Relapsing Fever'' <ref name="TBRF CDC”">Relapsing Fever Information. Centers for Disease Control and Prevention (2015).  http://www.cdc.gov/relapsing-fever/ Accessed on December 30, 2015</ref>
| style="background: #DCDCDC; padding: 5px;" |Consistently documented high fevers, flu-like illness, headaches, muscular soreness or joint pain, altered mental state, painful urination, rash, and rigors.
|-
|-
| style="font-size: 14px; background: #7d7d7d; text-align: center;" colspan="5d" | {{fontcolor|#FFF|'''Typhus (Rickettsia)'''}}
| style="font-size: 14px; background: #7d7d7d; text-align: center;" colspan="5d" | {{fontcolor|#FFF|'''Typhus (Rickettsia)'''}}
Line 296: Line 307:


==Risk Factors==
==Risk Factors==
*The greatest risk factor associated with tick-borne diseases is actually being bitten by a tick.
 
*Traveling or residing within endemic regions will increase chances of infection.  
*Traveling or residing within endemic regions will increase chances of infection.  
*Tick activity is generally heightened during certain the spring and summer months.  
*Tick activity is generally heightened during certain the spring and summer months.  
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! style="width: 80px; background: #4479BA; text-align: center;" |{{fontcolor|#FFF|Disease}}
! style="width: 80px; background: #4479BA; text-align: center;" |{{fontcolor|#FFF|Disease}}
! style="width: 720px; background: #4479BA; text-align: center;" | {{fontcolor|#FFF|Treatment}}
! style="width: 720px; background: #4479BA; text-align: center;" | {{fontcolor|#FFF|Treatment}}
|-
| style="font-size: 14px; background: #7d7d7d; text-align: center;" colspan="5d" | {{fontcolor|#FFF|'''Bacterial Infection'''}}
|-
| style="background: #F5F5F5; padding: 5px; text-align: center;" | ''Borreliosis (Lyme Disease)'' <ref name="Lyme CDC”">Lyme Disease Information for HealthCare Professionals. Centers for Disease Control and Prevention (2015).  http://www.cdc.gov/lyme/healthcare/index.html Accessed on December 30, 2015</ref>
| style="background: #DCDCDC; padding: 5px;" | '''Antibiotics'''
*[[Doxycycline]]
*[[Amoxicillin]] (first-line in pregnancy)
|-
| style="background: #F5F5F5; padding: 5px; text-align: center;" | ''Relapsing Fever'' <ref name="TBRF CDC”">Relapsing Fever Information. Centers for Disease Control and Prevention (2015).  http://www.cdc.gov/relapsing-fever/ Accessed on December 30, 2015</ref>
| style="background: #DCDCDC; padding: 5px;" | '''Antibiotics'''
*[[Erythromycin]] (first-line)
*[[Doxycycline]]
*[[Tetracycline]]
|-
|-
| style="font-size: 14px; background: #7d7d7d; text-align: center;" colspan="5d" | {{fontcolor|#FFF|'''Typhus (Rickettsia)'''}}
| style="font-size: 14px; background: #7d7d7d; text-align: center;" colspan="5d" | {{fontcolor|#FFF|'''Typhus (Rickettsia)'''}}
Line 357: Line 355:
|}
|}


==The best way to remove a tick==
==Prevention==
===The best way to remove a tick===


#Use fine-tipped tweezers or notched tick extractor, and protect your fingers with a tissue, paper towel, or latex gloves. Persons should avoid removing ticks with bare hands.
#Use fine-tipped tweezers or notched tick extractor, and protect your fingers with a tissue, paper towel, or latex gloves. Persons should avoid removing ticks with bare hands.
Line 367: Line 366:
*Save the tick for identification in case you become ill. This may help your doctor to make an accurate diagnosis. Place the tick in a sealable plastic bag and put it in your freezer. Write the date of the bite on a piece of paper with a pencil and place it in the bag. <ref name="Tick Removal CDC”">Tick Removal. Centers for Disease Control and Prevention (2015).  http://www.cdc.gov/ticks/removing_a_tick.html Accessed on December 30, 2015</ref>
*Save the tick for identification in case you become ill. This may help your doctor to make an accurate diagnosis. Place the tick in a sealable plastic bag and put it in your freezer. Write the date of the bite on a piece of paper with a pencil and place it in the bag. <ref name="Tick Removal CDC”">Tick Removal. Centers for Disease Control and Prevention (2015).  http://www.cdc.gov/ticks/removing_a_tick.html Accessed on December 30, 2015</ref>


==Gallery==
==Developments and future therapies==
<gallery>
*The recent discovery of another parallel between ''Rickettsia'' and viruses may become a basis for fighting [[HIV]] infection.<ref>{{cite journal | author=Kannangara S, DeSimone JA, Pomerantz RJ | title=Attenuation of HIV-1 infection by other microbial agents | journal=J Infect Dis | year=2005 | pages=1003-9 | volume=192 | issue=6 | id={{PMID|16107952}} }}</ref>  
Image:Tick bite01.jpg|Tick bite. <SMALL><SMALL>''[http://www.atlasdermatologico.com.br/  Adapted from Dermatology Atlas.]''<ref name="Dermatology Atlas">{{Cite web | title = Dermatology Atlas | url = http://www.atlasdermatologico.com.br/}}</ref></SMALL></SMALL>
*Human immune response to the [[scrub typhus]] pathogen, ''[[Orientia tsutsugamushi]]'' rickettsia,  appears to provide a beneficial effect against HIV infection progress, negatively influencing the virus replication process.
Image:Tick bite02.jpg|Tick bite. <SMALL><SMALL>''[http://www.atlasdermatologico.com.br/  Adapted from Dermatology Atlas.]''<ref name="Dermatology Atlas">{{Cite web | title = Dermatology Atlas | url = http://www.atlasdermatologico.com.br/}}</ref></SMALL></SMALL>
*A probable reason for this actively studied phenomenon is a certain degree of [[homology (biology)|homology]] between the rickettsia and the virus - namely, common [[epitope]](s) due to common genome fragment(s) in both pathogens.  
Image:Tick bite03.jpg|Tick bite. <SMALL><SMALL>''[http://www.atlasdermatologico.com.br/  Adapted from Dermatology Atlas.]''<ref name="Dermatology Atlas">{{Cite web | title = Dermatology Atlas | url = http://www.atlasdermatologico.com.br/}}</ref></SMALL></SMALL>
*Another infection reported to be likely to provide the same effect (decrease in viral load) is the virus-caused illness [[dengue fever]].
</gallery>


==References==
==References==
{{reflist|2}}
{{Reflist|2}}
 
==External links==
* [http://patric.vbi.vt.edu/organism/overview.php?organismId=3 Rickettsia] (from [http://patric.vbi.vt.edu/ PATRIC] the PathoSystems Resource Integration Center, a [http://www3.niaid.nih.gov/ NIAID] Bioinformatics Resource Center)
 
* African Tick Bite Fever [http://www.cdc.gov/ncidod/EID/vol12no09/05-1540.htm] from Centre for Disease Control and Prevention [http://www.cdc.gov/ncidod/eid/]


==Related Chapters==
==Related Chapters==

Revision as of 15:47, 28 January 2016

Rickettsia
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Alpha Proteobacteria
Order: Rickettsiales
Family: Rickettsiaceae
Genus: Rickettsia
da Rocha-Lima, 1916
Species

Rickettsia felis
Rickettsia prowazekii
Rickettsia rickettsii
Rickettsia typhi
Rickettsia conorii
Rickettsia africae
etc.


Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ilan Dock, B.S.; Kiran Singh, M.D. [2]


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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [3]

Overview

Rickettsia is a genus of non-motile, Gram-negative, non-sporeforming, highly pleomorphic bacteria that can present as cocci (0.1 μm in diameter), rods (1-4 μm long) or thread-like (10 μm long). Obligate intracellular parasites, the Rickettsia depend on entry, growth, and replication within the cytoplasm of eukaryotic host cells (typically endothelial cells).[1] Because of this, Rickettsia cannot live in artificial nutrient environments and are grown either in tissue or embryo cultures (typically, chicken embryos are used). In the past they were regarded as microorganisms positioned somewhere between viruses and true bacteria. The majority of Rickettsia bacteria are susceptible to antibiotics of the tetracycline group.

Rickettsia species are carried as parasites by many ticks, fleas, and lice, and cause diseases such as typhus, rickettsialpox, Boutonneuse fever, African Tick Bite Fever, Rocky Mountain spotted fever, Australian Tick Typhus, Flinders Island Spotted Fever and Queensland Tick Typhus [2] in human beings. They have also been associated with a range of plant diseases. Like viruses, they grow only in living cells. The name rickettsia is often used for any member of the Rickettsiales. They are thought to be the closest living relatives to bacteria that were the origin of the mitochondria organelle that exist in most eukaryotic cells.

The method of growing Rickettsia in chicken embryos was invented by Ernest William Goodpasture and colleagues at Vanderbilt University in the early 1930s.


Naming

Human pathogenesis

The Rickettsia human pathogens are generally grouped as follows:

Spotted fever group

  • R. rickettsii (Western hemisphere)
Rocky Mountain spotted fever
  • R. akari (USA, former Soviet Union)
Rickettsialpox
  • R. conorii (Mediterranean countries, Africa, Southwest Asia, India)
Boutonneuse fever
  • R. sibirica (Siberia, Mongolia, northern China)
Siberian tick typhus
  • R. australis (Australia)
Australian tick typhus
  • R. japonica (Japan)
Oriental spotted fever
  • R. africae (South Africa)
African Tick Bite Fever

Typhus group

Epidemic, recrudescent and sporadic typhus
  • R. typhi (Worldwide)
Murine (endemic) typhus

Scrub typhus group

  • The causative agent of scrub typhus formerly known as R. tsutsugamushi has been reclassified into the genus Orientia.

Plant pathogenesis

The following plant diseases have been assocaited with Rickettsia-like organisms[3].

  • Beet latent Rosette RLO
  • Citrus Greening bacterium
  • Clover leaf RLO
  • Grapevine infectious necrosis RLO
  • Grapevine Pierce's RLO
  • Grapevine yellos RLO
  • Larch witche's broom disease
  • Peach phoney RLO

Genomics

  • Certain segments of Rickettsial genomes resemble that of mitochondria.[4]
  • The deciphered genome of R. prowazekii is 1,111,523 bp long and contains 834 protein-coding genes.[5]
  • Unlike free-living bacteria, it contains no genes for anaerobic glycolysis or genes involved in the biosynthesis and regulation of amino acids and nucleosides.
  • In this regard it is similar to mitochondrial genomes; in both cases, nuclear (host) resources are used. ATP production in Rickettsia is the same as that in mitochondria.
  • In fact, of all the microbes known, the Rickettsia is probably the closest "relative" (in phylogenetic sense) to the mitochondria.
  • The genome of R. prowazekii contains a complete set of genes encoding for the tricarboxylic acid cycle and the respiratory-chain complex.
  • The genomes of the Rickettsia as well as the mitochondria are frequently said to be "small, highly derived products of several types of reductive evolution".


Epidemiology and Demographics

Incidence

Rickettsial disease classification

Disease Organism Vector Endemic Regions
Typhus (Rickettsia)
Rocky Mountain Spotted Fever [6] Rickettsia Rickettsii Wood Tick (Dermacentor Variabilis), D. andersoni United States:
  • Eastern Region
  • Southwest Region
Helvetica Spotted Fever[7] Rickettsia Helvetica Ixodes Ricinus (European) Europe:
  • Sweden
  • Switzerland
  • France
  • Laos
Ehrlichiosis Anaplasmosis [8] Ehrlichia Chaffeensis, E. Equi Lone Star Tick (Amblyomma Americanum), Ixodes Scapularis United States:
  • South Atlantic Regions
  • South-central Regions
Tularemia [9] Francisella Tularensis D. Andersoni, D. Variabilis United States:
  • Widespread throughout the region, including higher populations in the Southeast, South-central, and the West.
Human neoehrlichiosis [8] [7] Neoehrlichia mikurensis Lone Star Tick (Amblyomma Americanum)' Widespread:
  • Europe
  • Asia
Rickettsiosis [7] Rickettsia No specific species identified Widespread:
  • South Africa
  • Morocco
  • Mediterranean
African tick-bite fever [7] Rickettsia africae Amblyomma, Dermacentor, and Rhipicephalus species Africa:
  • Sub-Saharan
  • West Indies
Queensland tick typhus [10] [7] Rickettsia austalis Ixodes species Widespread:
  • Australia
  • Tasmania
Q-fever (Typhus-like infection) [10] Coxiella burnetii (mimics the mechanisms of Rickettsia) Ixodes holocyclus and Amblyomma triguttatum Australia
  • Widespread throughout Australia
Mediterranean spotted fever (Boutonneuse fever) [11] [7] Rickettsia conorii Brown Dog Tick (Rhipicephalus sanguineus) Widespread:
  • Southern Europe
  • Southern and Western Asia
  • Africa
  • India
Far Eastern spotted fever [7] Rickettsia heilong-jiangensis Tick Widespread:
  • Far portions of Eastern Russia
  • Northern portions of China
  • Eastern Asia
Aneruptive fever [7] [12] Rickettsia helvetica Ixodes species Widespread:
  • Northern and Central portions of Europe
  • Non-specific portions of Asia
Flinders Island spotted fever (Thai tick typhus) [7] [10] Rickettsia honei Tick Widespread in Independent Regions
  • Australia
  • Thailand
Japanese spotted fever [7] Rickettsia japonica Tick Japan
  • Widespread yet isolated to portions of Japan
Mediterranean spotted fever-like disease [7] Rickettsia massiliae and R. monacensis Tick Widespread:

R.massiliae induced:

  • France
  • Greece
  • Spain
  • Portugal
  • Switzerland
  • Sicily
  • Central Africa
  • Mali

R.monacensis induced:

  • Europe
  • North Africa
Maculatum infection Rickettsia parkeri Tick Americas:
  • United States
  • Portions of Canada
  • South America
Tick-borne necrosis and lymphadenopathy [13] Rickettsia raoultii Dermacentor marginatus Widespread:
  • Europe
  • Asia
North Asian Tick Typhus [7] Rickettsia sibirica Tick Widespread:
  • Russia
  • China
  • Mongolia
Lymphangitis [7] Rickettsia sibirica mogolotimonae 'No specific species identified Widespread:
  • Southern France
  • Portugal
  • China
  • Africa
TIBOLA [7] [13] Rickettsia slovaca Dermacentor species Widespread:
  • Southern and Eastern Europe
  • Asia

Differentiating Tick-Borne Diseases

Disease Symptoms
Typhus (Rickettsia)
Rocky Mountain Spotted Fever Fever, alterations in mental state, myalgia, rash, and headaches.
Helvetica Spotted Fever [6] Rash: spotted, red dots. Respiratory symptoms (dyspnea, cough), muscle pain, and headaches.
Ehrlichiosis Anaplasmosis [8] Fever, headache, chills, malaise, muscle pain, nausea, confusion, conjunctivitis, or rash (60% in children and 30% in adults).
Tularemia [9] Ulceroglandular, Glandular, Oculoglandular, Oroglandular, Pneumonic, Typhoidal.

Diagnosis

Physical Examination

A round red rash with a 2-5 mm central black area (eschar, an area of dead tissue) as shown in the photo is suggestive of a tick bite.

Laboratory Findings

In general, specific laboratory tests are not available to rapidly diagnose tick-borne diseases. Serological tests are frequently performed, but may be unreliable in differentiating acute from chronic conditions.

Risk Factors

  • Traveling or residing within endemic regions will increase chances of infection.
  • Tick activity is generally heightened during certain the spring and summer months.
  • Within endemic regions, tick may choose an animal host, including a domesticated animal such as a dog or cat.
  • Although rare, cases of blood transfusion and organ transplantation have been recorded as methods of transmission.
  • All together, individuals who spend time outdoors and/or have pets that go outdoors in endemic regions are at risk for tick-borne disease. [14]

Treatment

Medical Therapy

  • Antibiotic treatment is often justified based on clinical presentation alone. However all clinical treatments must be tailored according to a patients personal profile; considering age, immunocompetance, pregnancy, allergen profile, splenic function, and current medical status. [15]
  • If there is a collection of pus, the area will need to be incised and drained.
Disease Treatment
Typhus (Rickettsia)
Rocky Mountain Spotted Fever [6] Antibiotics
Helvetica Spotted Fever Antibiotics
Ehrlichiosis Anaplasmosis [8] Antibiotics
  • Doxycycline, dosages should begin prior to lab results if ehrlichiosis is suspected.
  • Adults: 100 mg PO q12h for 7-14 days
  • Children (under 100lbs/45kg): 2.2 mg/kg PO q12h for 7-14 days
Tularemia [9] Antibiotics
Other Spotted Fevers (Rickettsia bacterial infections) [7] Antibiotics
  • Adults: 100 mg PO q12h for 7-14 days
  • Children (under 100lbs/45kg): 2.2 mg/kg PO q12h for 7-14 days

Prevention

The best way to remove a tick

  1. Use fine-tipped tweezers or notched tick extractor, and protect your fingers with a tissue, paper towel, or latex gloves. Persons should avoid removing ticks with bare hands.
  2. Grasp the tick as close to the skin surface as possible and pull upward with steady, even pressure. Do not twist or jerk the tick; this may cause the mouthparts to break off and remain in the skin. (If this happens, remove mouthparts with tweezers. Consult your health care provider if illness occurs.)
  3. After removing the tick, thoroughly disinfect the bite site and wash your hands with soap and water.
Tick removal process
  • Do not squeeze, crush, or puncture the body of the tick because its fluids may contain infectious organisms. Skin accidentally exposed to tick fluids can be disinfected with iodine scrub, rubbing alcohol, or water containing detergents.
Removal of an embedded tick using fine-tipped tweezers
  • Save the tick for identification in case you become ill. This may help your doctor to make an accurate diagnosis. Place the tick in a sealable plastic bag and put it in your freezer. Write the date of the bite on a piece of paper with a pencil and place it in the bag. [16]

Developments and future therapies

  • The recent discovery of another parallel between Rickettsia and viruses may become a basis for fighting HIV infection.[17]
  • Human immune response to the scrub typhus pathogen, Orientia tsutsugamushi rickettsia, appears to provide a beneficial effect against HIV infection progress, negatively influencing the virus replication process.
  • A probable reason for this actively studied phenomenon is a certain degree of homology between the rickettsia and the virus - namely, common epitope(s) due to common genome fragment(s) in both pathogens.
  • Another infection reported to be likely to provide the same effect (decrease in viral load) is the virus-caused illness dengue fever.

References

  1. ↑ Walker DH (1996). Rickettsiae. In: Barron's Medical Microbiology (Barron S et al, eds.) (4th ed. ed.). Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1.
  2. ↑ http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=AbstractPlus&list_uids=17553271&tool=MedlinePlus
  3. ↑ Smith IM, Dunez J, Lelliot RA, Phillips DH, Archer SA (1988). European Handbook of Plant Diseases. Blackwell Scientific Publications. ISBN 0-632-01222-6.
  4. ↑ Emelyanov VV (2003). "Mitochondrial connection to the origin of the eukaryotic cell". Eur J Biochem. 270 (8): 1599–618. PMID 12694174.
  5. ↑ Andersson SG; et al. (1998). "The genome sequence of Rickettsia prowazekii and the origin of mitochondria". Nature. 396 (6707): 133–40. PMID 9823893.
  6. ↑ 6.0 6.1 6.2 Rocky Mountain Spotted Fever Information. Centers for Disease Control and Prevention (2015). http://www.cdc.gov/rmsf/ Accessed on December 30, 2015
  7. ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 7.13 7.14 Disease Index General Information, Rickettsia (2015). http://www.cdc.gov/otherspottedfever / Accessed on December 30, 2015
  8. ↑ 8.0 8.1 8.2 8.3 Disease index General Information (2015). http://www.cdc.gov/parasites/babesiosis/health_professionals/index.html Accessed on December 30, 2015
  9. ↑ 9.0 9.1 9.2 Rocky Mountain Spotted Fever Information. Centers for Disease Control and Prevention (2015). \http://www.cdc.gov/tularemia/index.html Accessed on December 30, 2015
  10. ↑ 10.0 10.1 10.2 Australian Tick Index http://www.karlmcmanusfoundation.org.au/ticks-in-oz Accessed on December 30, 2015
  11. ↑ Oztoprak N, Celebi G, Aydemir H, et al. [Mediterranean spotted fever due to contact with dog-tick]. Mikrobiyol Bul. 2008;42(4):7016.http:// http://www.ncbi.nlm.nih.gov/pubmed/19149095 Accessed on December 30, 2015
  12. ↑ Fournier PE, Allombert C, Supputamongkol Y, Caruso G, Brouqui P, Raoult D. Aneruptive fever associated with antibodies to Rickettsia helvetica in Europe and Thailand. J Clin Microbiol. 2004;42(2):816-8. http://http://www.ncbi.nlm.nih.gov/pmc/articles/PMC344501/ Accessed on December 30, 2015
  13. ↑ 13.0 13.1 Dermacentor-borne necrosis erythema and lymphadenopathy: clinical and epidemiological features of a new tick-borne disease. Oteo JA, Ibarra V, Blanco JR, et al. Dermacentor-borne necrosis erythema and lymphadenopathy: clinical and epidemiological features of a new tick-borne disease. Clin Microbiol Infect. 2004;10(4):327-31 http://www.ncbi.nlm.nih.gov/pubmed/15059122 Accessed on December 30, 2015
  14. ↑ General Information (2015). http://www.cdc.gov/ticks/index.html Accessed on December 30, 2015
  15. ↑ Tick-borne diseases of the United States. Treatment Information Center for Disease Control and Prevention (2015). http://www.cdc.gov/ticks/index.html Accessed on December 30, 2015
  16. ↑ Tick Removal. Centers for Disease Control and Prevention (2015). http://www.cdc.gov/ticks/removing_a_tick.html Accessed on December 30, 2015
  17. ↑ Kannangara S, DeSimone JA, Pomerantz RJ (2005). "Attenuation of HIV-1 infection by other microbial agents". J Infect Dis. 192 (6): 1003–9. PMID 16107952.

External links

  • Rickettsia (from PATRIC the PathoSystems Resource Integration Center, a NIAID Bioinformatics Resource Center)
  • African Tick Bite Fever [4] from Centre for Disease Control and Prevention [5]

Related Chapters


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