Editing Leptospirosis (section)

==Cause==
===Bacteria===
[[File:Leptospira scanning micrograph.jpg|thumb|left|upright=1.3|alt=A scanning electron micrograph of several lepitospira bacteria on a filter | [[Scanning electron micrograph]] of a number of ''Leptospira'' sp. bacteria atop a 0.1 µm [[polycarbonate]] filter]]
Leptospirosis is caused by [[spirochaete]] bacteria that belong to the [[genus]] ''[[Leptospira]]'', which are [[Cellular respiration#Aerobic respiration|aerobic]],<ref name="Lane 2016"/> [[Screw thread#Handedness|right-handed]] [[Helix|helical]],<ref name=Picardeau2017/> and 6&nbsp;–20&nbsp;[[Micrometre|micrometer]]s long.<ref name="Karpagm2020"/> Like [[Gram-negative]] bacteria, ''Leptospira'' have an [[Bacterial outer membrane|outer membrane]] studded with [[lipopolysaccharide]] (LPS) on the surface, an [[Cell membrane|inner membrane]] and a layer of [[peptidoglycan]] cell wall. However, unlike Gram-negative bacteria, the peptidoglycan layer in ''Leptospira'' lies closer to the inner than the outer membrane. This results in a fluid outer membrane loosely associated with the cell wall.<ref name=Cameron2015>{{cite journal | vauthors = Cameron CE | title = Leptospiral structure, physiology, and metabolism | journal = Current Topics in Microbiology and Immunology | volume = 387 | pages = 21–41 | date = 2015 | pmid = 25388131 | doi = 10.1007/978-3-662-45059-8_3 | isbn = 978-3-662-45058-1 }}</ref> In addition, ''Leptospira'' have a [[flagellum]] located in the [[periplasm]], associated with corkscrew style movement.<ref name="Karpagm2020"/> [[Chemoreceptor]]s at the poles of the bacteria sense various substrates and change the direction of its movement.<ref name=Picardeau2017/> The bacteria are traditionally visualised using [[dark-field microscopy]] without staining.<ref name="Karpagm2020"/>

A total of 66&nbsp;species of ''Leptospira'' has been identified. Based on their genomic sequence, they are divided into two [[clade]]s and four subclades: P1, P2, S1, and S2.<ref name=Caimi2020>{{cite journal | vauthors = Caimi K, Ruybal P | title = Leptospira spp., a genus in the stage of diversity and genomic data expansion | journal = Infection, Genetics and Evolution | volume = 81 | pages = 104241 | date = February 2020 | pmid = 32061688 | doi = 10.1016/j.meegid.2020.104241 }}</ref> The 19 members of the P1 subclade include the 8 species that can cause severe disease in humans: ''[[Leptospira alexanderi|L. alexanderi]]'', ''[[Leptospira borgpetersenii|L. borgpetersenii]]'', ''[[Leptospira interrogans|L. interrogans]]'', ''[[Leptospira kirschneri|L. kirschneri]]'', ''L. mayottensis'', ''[[Leptospira noguchii|L. noguchii]]'', ''L. santarosai'', and ''[[Leptospira weilii|L. weilii]].''<ref name=Picardeau2017/><ref name=Caimi2020/> The P2 clade comprises 21 species that may cause mild disease in humans. The remaining 26 species comprise the S1 and S2 subclades, which include "saprophytes" known to consume decaying matter ([[saprotrophic nutrition]]).<ref name=Caimi2020/> Pathogenic ''Leptospira'' do not multiply in the environment. ''Leptospira'' require high humidity for survival but can remain alive in environments such as stagnant water or contaminated soil. The bacterium can be killed by temperatures of {{cvt|50|°C}} and can be inactivated by 70%&nbsp;[[ethanol]], 1%&nbsp;[[sodium hypochlorite]], [[formaldehyde]], detergents and acids.<ref name="Spickler 2013"/>

''Leptospira'' are also classified based on their [[Serotype|serovar]]. The diverse sugar composition of the lipopolysaccharide on the surface of the bacteria is responsible for the antigenic difference between serovars.<ref name=Picardeau2017/> Over 250&nbsp;pathogenic serovars of ''Leptospira'' are recognised, with closely related serovars gathered into over 26 pathogenic serogroups.<ref name="Lane 2016"/> Strains of different species of ''Leptospira'' may be members of the same serogroup because of [[horizontal gene transfer]] of LPS biosynthetic genes between different species.<ref name=Picardeau2017/>

===Transmission===
The bacteria can be found in ponds, rivers, puddles, sewers, agricultural fields and moist soil.<ref name="Karpagm2020"/> Pathogenic ''Leptospira'' have been found in the form of aquatic [[biofilms]], which may aid survival in the environment.<ref name=Barragan2017>{{cite journal | vauthors = Barragan V, Olivas S, Keim P, Pearson T | title = Critical Knowledge Gaps in Our Understanding of Environmental Cycling and Transmission of Leptospira spp | journal = Applied and Environmental Microbiology | volume = 83 | issue = 19 | date = October 2017 | pmid = 28754706 | pmc = 5601346 | doi = 10.1128/AEM.01190-17 }}</ref>

''Leptospira'' live in the kidneys of various wild and domestic animals. When animals ingest the bacteria, they circulate in the bloodstream, then lodge themselves into the kidneys through the [[Glomerulus|glomerulular]] or [[peritubular capillaries]]. The bacteria then pass into the [[Lumen (anatomy)|lumens]] of the [[renal tubules]] and colonise the [[brush border]] of the [[proximal convoluted tubule]]. This causes the continuous shedding of bacteria in the urine without the animal experiencing significant ill effects. This relationship between the animal and the bacteria is known as a [[commensal relationship]], and the animal is known as a [[Natural reservoir|reservoir host]].<ref name="Haake 2015">{{cite journal | vauthors = Haake DA, Levett PN | title = Leptospirosis in humans | journal = Current Topics in Microbiology and Immunology | volume = 387 | issue = 387 | pages = 65–97 | date = 25 May 2015 | pmid = 25388133 | pmc = 4442676 | doi = 10.1007/978-3-662-45059-8_5 | isbn = 978-3-662-45058-1 }}</ref>

''Leptospira'' are found mostly in mammals.<ref name="Zoey2020"/> However, reptiles and [[Poikilotherm|cold-blooded animals]] such as frogs, snakes, turtles, and toads have been shown to have the infection.<ref name="Ellis2015"/> Whether there are reservoirs of human infection  is unknown.<ref name="Haake 2015"/><ref name="Ellis2015"/> Rats, mice, and moles are important [[Host (biology)#Definitive and secondary hosts|primary hosts]], but other mammals including dogs, deer, rabbits, hedgehogs, cows, sheep, swine, raccoons, opossums, and skunks can also carry the disease.<ref name="Ellis2015"/> In Africa, a number of wildlife hosts have been identified as carriers, including the [[banded mongoose]], [[Fennec fox|Egyptian fox]], [[Rusa deer]], and [[shrews]].<ref name=Allan2015>{{cite journal | vauthors = Allan KJ, Biggs HM, Halliday JE, Kazwala RR, Maro VP, Cleaveland S, Crump JA | title = Epidemiology of Leptospirosis in Africa: A Systematic Review of a Neglected Zoonosis and a Paradigm for 'One Health' in Africa | journal = PLOS Neglected Tropical Diseases | volume = 9 | issue = 9 | pages = e0003899 | date = 2015 | pmid = 26368568 | pmc = 4569256 | doi = 10.1371/journal.pntd.0003899 }}</ref> There are various mechanisms whereby animals can infect each other. Dogs may lick the urine of an infected animal off the grass or [[soil]], or drink from an infected puddle.{{Citation needed|date=August 2020}} House-bound domestic dogs have contracted leptospirosis, apparently from licking the urine of infected mice in the house.{{Citation needed|date=August 2020}} Leptospirosis can also be transmitted via the semen of infected animals.<ref name="Ellis2015"/> The duration of bacteria being consistently present in animal urine may persist for years.<ref name="Ellis2015"/>

Humans are the [[Host (biology)#Dead-end hosts|accidental host]] of ''Leptospira''.<ref name="Zoey2020"/> Humans become infected through contact with water or moist soil that contains urine from infected animals.<ref name="Karpagm2020"/> The bacteria enter through cuts, abrasions,<ref name="Karpagm2020"/> ingestion of contaminated food, or contact with [[mucous membrane]] of the body (e.g. mouth, nose, and eyes).<ref name="Kin Chin 2019"/> Occupations at risk of contracting leptospirosis include farmers, fishermen, garbage collectors and sewage workers.<ref name="Zoey2020"/> The disease is also related to [[adventure tourism]] and recreational activities.<ref name="Zoey2020"/> It is common among water-sports enthusiasts in specific areas, including [[triathlon]]s, water [[rafting]], [[canoeing]] and swimming, as prolonged immersion in water promotes the entry of the bacteria.<ref name="Zoey2020"/> However, ''Leptospira'' are unlikely to penetrate intact skin.<ref name="Lane 2016"/> The disease is not known to spread between humans, and bacterial dissemination in [[Convalescence|recovery period]] is extremely rare in humans.<ref name="Lane 2016">{{cite journal|last1=Lane|first1=Alison B|last2=Dore|first2=Michael M|title=Leptospirosis: A clinical review of evidence based diagnosis, treatment and prevention|journal=World Journal of Clinical Infectious Diseases|volume=6|issue=4|year=2016|pages=61|issn=2220-3176|doi=10.5495/wjcid.v6.i4.61|doi-access=free}}</ref> Once humans are infected, bacterial shedding from the kidneys usually persists for up to 60 days.<ref name="Spickler 2013"/>

Rarely, leptospirosis can be transmitted through an organ transplant.<ref>{{cite journal | vauthors = Song AT, Abas L, Andrade LC, Andraus W, D'Albuquerque LA, Abdala E | title = A first report of leptospirosis after liver transplantation | journal = Transplant Infectious Disease | volume = 18 | issue = 1 | pages = 137–40 | date = February 2016 | pmid = 26671230 | doi = 10.1111/tid.12490 }}</ref> Infection through the [[placenta]] during pregnancy is also possible.<ref>{{cite journal | vauthors = Puliyath G, Singh S | title = Leptospirosis in pregnancy | journal = European Journal of Clinical Microbiology & Infectious Diseases | volume = 31 | issue = 10 | pages = 2491–6 | date = October 2012 | pmid = 22549729 | doi = 10.1007/s10096-012-1625-7 | s2cid = 14033595 }}</ref><ref>{{cite journal | vauthors = Carles G, Montoya E, Joly F, Peneau C | title = [Leptospirosis and pregnancy. Eleven cases in French Guyana] | journal = Journal de Gynécologie, Obstétrique et Biologie de la Reproduction | volume = 24 | issue = 4 | pages = 418–21 | date = 1995 | pmid = 7650320 }}</ref><ref>{{cite journal | vauthors = Koe SL, Tan KT, Tan TC | title = Leptospirosis in pregnancy with pathological fetal cardiotocography changes | journal = Singapore Medical Journal | volume = 55 | issue = 2 | pages = e20-4 | date = February 2014 | pmid = 24712035 | pmc = 4291937 | doi = 10.11622/smedj.2013194 }}</ref> It can cause [[miscarriage]] and infection in [[infant]]s.<ref>{{cite journal | vauthors = Shaked Y, Shpilberg O, Samra D, Samra Y | title = Leptospirosis in pregnancy and its effect on the fetus: case report and review | journal = Clinical Infectious Diseases | volume = 17 | issue = 2 | pages = 241–3 | date = August 1993 | pmid = 8399874 | doi = 10.1093/clinids/17.2.241 }}</ref>