2601:86:4380:8FC0:A52A:13F6:3A04:946F at 13:43, 7 May 2025

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{{Short description|Species of bacterium}}
{{Italic title}}
{{Speciesbox
| image = Anaplasma phagocytophilum cultured in human promyelocytic cell line HL-60.jpg
| image_caption = Human [[HL60]] cells containing ''Anaplasma phagocytophilum'' (indicated by arrows) which are basophilic intracytoplasmic inclusions when stained with [[Wright-Giemsa stain]]
| taxon = Anaplasma phagocytophilum
| authority = (Foggie 1949) Dumler et al. 2001<ref name=LSPN>[https://lpsn.dsmz.de/genus/anaplasma Page Anaplasma on lpsn.dsmz.de]</ref>
| synonyms = ''Rickettsia phagocytophila ovis''<br/>''Rickettsia phagocytophila''<br/>''Cytoecetes phagocytophila''<br/>''Cytoecetes phagocytophila''
}}

'''''Anaplasma phagocytophilum''''' (formerly '''''Ehrlichia phagocytophilum''''')<ref>{{cite journal |vauthors =Dumler JS, Barbet AF, Bekker CP |title=Reorganization of genera in the families Rickettsiaceae and Anaplasmataceae in the order Rickettsiales: unification of some species of Ehrlichia with Anaplasma, Cowdria with Ehrlichia and Ehrlichia with Neorickettsia, descriptions of six new species combinations and designation of Ehrlichia equi and 'HGE agent' as subjective synonyms of Ehrlichia phagocytophila |journal=Int. J. Syst. Evol. Microbiol. |volume=51 |issue=Pt 6 |pages=2145–65 |year=2001 |pmid=11760958 |doi=10.1099/00207713-51-6-2145|display-authors=etal|doi-access=free }}</ref> is a [[Gram-negative]] bacterium that is unusual in its [[tropism]] to [[neutrophils]]. It causes [[anaplasmosis]] in sheep and cattle, also known as '''tick-borne fever''' and '''pasture fever''', and also causes the [[zoonotic]] disease [[human granulocytic anaplasmosis]].<ref name="WikiVet">[http://en.wikivet.net/Tick-Borne_Fever Tick-Borne Fever] reviewed and published by [[WikiVet]], accessed 12 October 2011.</ref>

''A. phagocytophilum'' is a Gram-negative, [[obligate]] bacterium of neutrophils. It causes human [[Granulocyte|granulocytic]] anaplasmosis, which is a tick-borne rickettsial disease. Because this bacterium invades neutrophils, it has a unique adaptation and pathogenetic mechanism.<ref name=Dumler05>{{cite journal |vauthors =Dumler JS, Choi KS, Garcia-Garcia JC |title=Human granulocytic anaplasmosis and ''Anaplasma phagocytophilum'' |journal=Emerging Infect. Dis. |volume=11 |issue=12 |pages=1828–34 |date=December 2005 |pmid=16485466 |pmc=3367650 |doi=10.3201/eid1112.050898 |display-authors=etal}}</ref>

==Biology==
''A. phagocytophilum'' is a small, obligate, intracellular bacterium with a Gram-negative cell wall. It is 0.2–1.0 μm and lacks a lipopolysaccharide biosynthetic machinery. The bacterium first resides in an early [[endosome]], where it acquires nutrients for binary fission and grows into small groups called morulae. This bacterium prefers to grow within myeloid or granulocytic cells.<ref name=Dumler05 />

===Hosts===
Hosts include [[goat|goats]], [[cattle]], [[horse|horses]] and [[dog|dogs]]. Cattle infections had been suspected but were only first confirmed by Nieder et al. 2012.<ref name="Brown-Barbet-2016">{{cite journal | last1=Brown | first1=Wendy C. | last2=Barbet | first2=Anthony F. | title=Persistent Infections and Immunity in Ruminants to Arthropod-Borne Bacteria in the Family Anaplasmataceae | journal=[[Annual Review of Animal Biosciences]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=4 | issue=1 | date=2016-02-15 | issn=2165-8102 | doi=10.1146/annurev-animal-022513-114206 | pages=177–197| pmid=26734888 }}</ref>

==Role in human disease==
''A. phagocytophilum'' causes human granulocytic [[anaplasmosis]] (HGA). This disease was first identified in 1990, although this pathogen was known to cause veterinary disease since 1932. Since 1990, incidence of HGA has increased, and it is now recognized in Europe. This disease was first identified due to a Wisconsin patient who died with a severe febrile illness two weeks after a tick bite. During the last stage of the infection, a group of small bacteria was seen within the neutrophils in the blood. Other symptoms include fever, headache, absence of skin rash, [[leucopenia]], [[thrombocytopenia]], and mild injury to the liver.<ref name=Dumler05 />

==Clinical signs in animals==
The disease is multisystemic, but the most severe changes are [[anaemia]] and [[leukopenia]]. This organism causes [[lameness]], which can be confused with symptoms of [[Lyme disease]], another tick-borne illness. It is a vector-borne [[zoonotic disease]] whose morula can be visualized within [[neutrophil]]s (a type of white blood cell) from the peripheral blood and synovial fluid. It can cause [[lethargy]], [[ataxia]], [[loss of appetite]], and weak or painful limbs.<ref name="WikiVet"/>

==Bacterial mechanism==
''A. phagocytophilum'' binds to fucosylated and sialylated scaffold proteins on neutrophil and granulocyte surfaces. A [[type IV secretion apparatus]] is known to help in the transfer of molecules between the bacterium and the host. The most studied ligand is PSGL-1 ([[P-selectin glycoprotein ligand-1|CD162]]). The bacterium adheres to PSGL-1 (CD162) through the 44-kDa major surface protein-2 (Msp2). After the bacterium enters the cell, the endosome stops maturation and does not accumulate markers of late endosomes or [[phagolysosome]]s. Because of this, the vacuole does not become acidified or fused to [[lysosome]]s. ''A. phagocytophilum'' then divides until [[cell lysis]] or when the bacteria leave to infect other cells.<ref name=Dumler05 />

This bacterium has the ability to affect neutrophils by altering their function. It can survive the first encounter with the host cell by detoxifying [[superoxide]] produced by [[NADPH oxidase#Neutrophilic type|neutrophil phagocyte oxidase]] assembly. It also disrupts normal neutrophil function, such as endothelial cell adhesion, transmigration, motility, degranulation, respiratory burst, and phagocytosis.<ref name=Dumler05 /> It causes an increase in the secretion of [[Interleukin 8|IL-8]], a chemoattractant that increases the phagocytosis of neutrophils. The purpose of this is to increase bacterial dissemination into the neutrophil.<ref>{{cite journal |vauthors =Thomas V, Fikrig E |title=''Anaplasma phagocytophilum'' specifically induces tyrosine phosphorylation of ROCK1 during infection |journal=Cell. Microbiol. |volume=9 |issue=7 |pages=1730–7 |date=July 2007 |pmid=17346310 |doi=10.1111/j.1462-5822.2007.00908.x |s2cid=20043230 }}</ref>

==Laboratory diagnosis==
These tests can be performed to determine an ''A. phagocytophilum'' infection:
#Indirect immunofluorescence assay is the principal test used to detect infection. The acute and convalescent phase serum samples can be evaluated to look for a four-fold change in antibody titer to ''A. phagocytophilum''.
#Intracellular Inclusions (morulae) are visualized in granulocytes on Wright- or [[Giemsa stain|Giemsa-]] stained blood smears.
#Polymerase chain reaction assays are used to detect ''A. phagocytophilum'' DNA.<ref name="health.state">{{cite web |title=Human Anaplasmosis Information for Health Professionals: Diagnostic tests |work=Diseases |publisher=Minnesota Department of Health |url=http://www.health.state.mn.us/divs/idepc/diseases/anaplasmosis/hcp.html#tests |access-date=2011-04-27 |archive-url=https://web.archive.org/web/20190213103116/http://www.health.state.mn.us/divs/idepc/diseases/anaplasmosis/hcp.html#tests |archive-date=2019-02-13 |url-status=dead }}</ref>

[[File:Doxycycline 100mg capsules.jpg|thumb|Doxycycline]]

==Antibiotic therapy==
Patients with HGA undergo [[doxycycline]] therapy, 100 mg twice daily until the patient's fever subsides for at least 3 days. This drug has been the most beneficial to those patients infected with the bacteria. Some other [[tetracycline]] drugs are also effective. In general, patients with symptoms of HGA and unexplained fever after a tick exposure should receive empiric doxycycline therapy while their diagnostic tests are pending, especially if they experience [[leukopenia]] and/or [[thrombocytopenia]].<ref name="health.state" />

In animals, antibiotics such as [[oxytetracycline]], sulphamethazine, [[sulphadimidine]], [[doxycycline]], and [[trimethoprim]]-[[Sulfonamide (medicine)|sulphonamides]] have been used.<ref name="WikiVet"/>

== References ==
{{Reflist}}

== External links ==
* [https://web.archive.org/web/20080623201116/http://cmr.jcvi.org/tigr-scripts/CMR/GenomePage.cgi?org=gaph ''Anaplasma'' phagocytophilum HZ Genome Page]
* {{MeshName|Anaplasma+phagocytophilum}}
*{{cite journal |vauthors =Zhang L, Liu Y, Ni D |title=Nosocomial transmission of human granulocytic anaplasmosis in China |journal=JAMA |volume=300 |issue=19 |pages=2263–70 |date=November 2008 |pmid=19017912 |doi=10.1001/jama.2008.626 |display-authors=etal|doi-access=free }}

{{Gram-negative bacterial diseases}}
{{Taxonbar|from=Q292189}}

[[Category:Rickettsiales]]
[[Category:Bacteria described in 1949]]
[[Category:Pathogenic bacteria]]

Anaplasma phagocytophilum - Revision history

2601:86:4380:8FC0:A52A:13F6:3A04:946F at 13:43, 7 May 2025