Babesia microti

{{short description|Species of parasitic protist in the Apicomplexa phylum}} {{Speciesbox | image = Blood smear of Babesia microti, annotated.png | genus = Babesia | species = microti | authority = (França, 1912) }} thumb|360px|Life cycle of ''B. microti'', including human infection thumb|Typically, ''B. microti'' is transmitted by the nymphal stage of ''Ixodes scapularis'' ticks (about the size of a poppy seed).

'''''Babesia microti''''' is a parasitic blood-borne piroplasm transmitted by deer ticks. ''B. microti'' is responsible for the disease babesiosis, a malaria-like zoonosis which causes fever, hemolytic anemia caused by hemolysis, and enlarged spleen.<ref name=":0">{{Cite journal |last1=Si |first1=Wenwen |last2=Fang |first2=Chuantao |last3=Liu |first3=Chuang |last4=Yin |first4=Meng |last5=Xu |first5=Wenyue |last6=Li |first6=Yanna |last7=Yan |first7=Xiaoli |last8=Shen |first8=Yujuan |last9=Cao |first9=Jianping |last10=Sun |first10=Jun |date=2023-06-08 |title=Why is Babesia not killed by artemisinin like Plasmodium? |journal=Parasites & Vectors |language=en |volume=16 |issue=1 |page=193 |doi=10.1186/s13071-023-05783-4 |doi-access=free |issn=1756-3305 |pmc=10249562 |pmid=37291657}}</ref>

==Lifecycle== The lifecycle of ''B. microti'' includes two hosts: a vertebrate and an arthropod, the deer tick. When the tick bites a vertebrate, ''B. microti'' can be transmitted as sporozoites into the vertebrate host.<ref name=":0" /> The parasite starts infecting red blood cells, where it digests hemoglobin for amino acids. After this, ''B. microti'' undergoes asexual reproduction and differentiation to male and female gametocytes. These are then ingested by the arthropod host and ''B. microti'' gametes undergo a sporogonic cycle (sexual reproduction), where new sporozoites are made. The cycle begins again when the tick bites a new vertebrate host.<ref name=":1">{{Cite journal |last1=Sojka |first1=Daniel |last2=Jalovecká |first2=Marie |last3=Perner |first3=Jan |date=August 2022 |title=Babesia, Theileria, Plasmodium and Hemoglobin |journal=Microorganisms |language=en |volume=10 |issue=8 |page=1651 |doi=10.3390/microorganisms10081651 |doi-access=free |issn=2076-2607 |pmc=9414693 |pmid=36014069}}</ref>

''B. microti's'' usual vertebrate hosts include domesticated animals, such as cattle, dogs, and rats, and wild animals.<ref name=":0" /><ref name=":1" /> Humans are accidental hosts of ''Babesia'' in general, but ''B. microti'' is an important transfusion-transmitted infectious organism in humans. Between 2010 and 2014, it caused four out of 15 (27%) fatalities associated with transfusion-transmitted microbial infections reported to the US FDA (the highest of any single organism).<ref>{{Cite report|url=https://www.fda.gov/downloads/BiologicsBloodVaccines/SafetyAvailability/ReportaProblem/TransfusionDonationFatalities/UCM459461.pdf|title=Fatalities Reported to FDA Following Blood Collection and Transfusion: Annual Summary for Fiscal Year 2014 | work = U.S. Food and Drug Administration |last=|date=|archive-url=https://web.archive.org/web/20150906020905/https://www.fda.gov/downloads/BiologicsBloodVaccines/SafetyAvailability/ReportaProblem/TransfusionDonationFatalities/UCM459461.pdf|archive-date=6 September 2015}}</ref> In 2018, the FDA approved an antibody-based screening test for blood and organ donors.<ref>{{Cite report |url= https://www.fda.gov/downloads/BiologicsBloodVaccines/BloodBloodProducts/ApprovedProducts/LicensedProductsBLAs/BloodDonorScreening/InfectiousDisease/UCM601840.pdf|archive-url= https://web.archive.org/web/20180320230732/https://www.fda.gov/downloads/BiologicsBloodVaccines/BloodBloodProducts/ApprovedProducts/LicensedProductsBLAs/BloodDonorScreening/InfectiousDisease/UCM601840.pdf|archive-date= March 20, 2018|title=Approval Letter -Babesia microti AFIA/Babesia microti AFIA for Blood Donor Screening|date=6 March 2018|publisher=U.S. Food and Drug Administration |id=BLA/ STN#125589|access-date=20 March 2018| vauthors = Verdun N, Malarkey MA }}</ref>

An important difference from malaria is that ''B. microti'' does not infect liver cells or require haem iron for their metabolical processes.<ref name=":0" /> Additionally, the piroplasm is spread by tick bites (''Ixodes scapularis'', the same tick that spreads Lyme disease), while the malaria protozoans are spread by mosquitoes. Finally, under the microscope, the merozoite form of the ''B. microti'' lifecycle in red blood cells forms a cross-shaped structure, often referred to as a "Maltese cross" or tetrad, in addition to intracellular "ring forms", which are also seen in the malaria parasite (''Plasmodium'' spp.).<ref>{{cite book| vauthors = Goldberg S |title=Clinical Microbiology made Ridiculously Simple|edition=4th |year=2007 |publisher=Medmaster|isbn=978-0-940780-21-7}}</ref>

==Taxonomy== {{Piroplasmida|align=left}} Until 2006, ''B. microti'' was thought to belong to the genus ''Babesia'', as ''Babesia microti'', until ribosomal RNA comparisons placed it in the sister genus ''Theileria''.<ref>{{cite journal | vauthors = Uilenberg G, Goff WL | title = Polyphasic taxonomy | journal = Annals of the New York Academy of Sciences | volume = 1081 | issue = 1 | pages = 492–497 | date = October 2006 | pmid = 17135557 | doi = 10.1196/annals.1373.073 | s2cid = 38312613 | bibcode = 2006NYASA1081..492U }}</ref><ref>{{cite journal | vauthors = Uilenberg G | title = Babesia--a historical overview | journal = Veterinary Parasitology | volume = 138 | issue = 1–2 | pages = 3–10 | date = May 2006 | pmid = 16513280 | doi = 10.1016/j.vetpar.2006.01.035 }}</ref> {{as of| 2012}}, the medical community still classified the parasite as ''B. microti''<ref name="NEJM Babesiosis Review">{{cite journal | vauthors = Vannier E, Krause PJ | title = Human babesiosis | journal = The New England Journal of Medicine | volume = 366 | issue = 25 | pages = 2397–2407 | date = June 2012 | pmid = 22716978 | doi = 10.1056/NEJMra1202018 }}</ref> though its genome showed it does not belong to either ''Babesia'' or ''Theileria''.<ref name="Cornillot_2012"/>

==Genomics== The genome of ''Babesia microti'' has been sequenced and published.<ref name=Cornillot_2012>{{cite journal | vauthors = Cornillot E, Hadj-Kaddour K, Dassouli A, Noel B, Ranwez V, Vacherie B, Augagneur Y, Brès V, Duclos A, Randazzo S, Carcy B, Debierre-Grockiego F, Delbecq S, Moubri-Ménage K, Shams-Eldin H, Usmani-Brown S, Bringaud F, Wincker P, Vivarès CP, Schwarz RT, Schetters TP, Krause PJ, Gorenflot A, Berry V, Barbe V, Ben Mamoun C | display-authors = 6 | title = Sequencing of the smallest Apicomplexan genome from the human pathogen ''Babesia microti'' | journal = Nucleic Acids Research | volume = 40 | issue = 18 | pages = 9102–9114 | date = October 2012 | pmid = 22833609 | pmc = 3467087 | doi = 10.1093/nar/gks700 }}</ref>

The mitochondrial genome is circular.<ref name="Cornillot_2012"/>

== Vaccine == In May 2010, a vaccine to protect cattle against East Coast fever reportedly had been approved and registered by the governments of Kenya, Malawi, and Tanzania.<ref>{{cite journal | vauthors = Florin-Christensen M, Suarez CE, Rodriguez AE, Flores DA, Schnittger L | title = Vaccines against bovine babesiosis: where we are now and possible roads ahead | journal = Parasitology | volume = 141 | issue = 12 | pages = 1563–1592 | date = July 2014 | pmid = 25068315 | doi = 10.1017/S0031182014000961 | s2cid = 34025694 | hdl = 11336/35696 | hdl-access = free }}</ref>

A vaccine to protect humans has yet to be approved.<ref>{{cite journal | vauthors = Puri A, Bajpai S, Meredith S, Aravind L, Krause PJ, Kumar S | title = ''Babesia microti'': Pathogen Genomics, Genetic Variability, Immunodominant Antigens, and Pathogenesis | journal = Frontiers in Microbiology | volume = 12 | article-number = 697669 | year = 2021 | pmid = 34539601 | pmc = 8446681 | doi = 10.3389/fmicb.2021.697669 | doi-access = free }}</ref> {{clear}}

== References == {{Reflist|30em}}

== External links == * [https://web.archive.org/web/20170603003632/http://www.health.state.mn.us/divs/idepc/diseases/babesiosis/index.html Babesia microti] Minnesota Department of Health

microti Category:Apicomplexa species