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Leptospirosis
H.AL-Zoubi , M.A.AL-Housani , A.Abu-Romman , S.Tablieh ,
O.Rahamneh .
Abstract
Leptospirosis is a widely spread disease of global concern. It caused by a unique
microorganism that share features of both Gram-positive and -negative bacteria, and
considered as an environmental pathogen transmitted from animals to humans,
through direct and indirect ways of transmission. After which, it goes through many
phases inside human body to cause the disease. Although leptospirosis could be mild
and self-limiting, In more severe cases it could be life threatening, with massive
pulmonary hemorrhages, including fatal sudden hemoptysis, may occur. this disease
could be treated by antimicrobial therapy given to Symptomatic patients presenting
for medical attention in order shorten the duration of illness and reduce shedding of
organisms in the urine. But antimicrobial therapy could suffer from resistance,
although no enough data to show the main criteria for resistance, there is some
assumptions related to the structure itself and mutations result in efflux.
There are a multitude of unresolved, practically relevant areas on this illness that need
to be addressed by further research. In this review, we focus on four important areas,
i.e., diagnostics, vaccine development, and identification mechanism of action for
pathogen and resistance.
Introduction
Leptospirosis, a contagious disease endemic in tropical and subtropical regions
affecting both animals and humans and spread by infection with a bacterial pathogen
called Leptospira [1,2], Complex disease with multiple modes of transmission such as
: inadequate sanitation and hygiene, lack of potable water, flooding, and close contact
with livestock (e.g., fishing, farming) increase the risk of transmission, it is
predominantly rodents who play a role in transmitting infection to humans[3].
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Furthermore, leptospirosis has emerged as a health threat in new settings due the
influence of globalization and climate; In particular, unusually high rainfall and
flooding in some regions often give rise to severe leptospirosis epidemics [4], with an
estimated 873,000 infections and 48,000 deaths annually [5]. however, inadequate
diagnosis has affected the awareness of the disease among the medical community
because Gold standard diagnostic methods (i.e., microscopic agglutination test [MAT]
and polymerase chain reaction [PCR]) are not widely available in resource-limited
settings with the highest burden of disease [6,7] ,and Human vaccinations are
available in only a few countries (e.g., China, Cuba), and are not widely available in
resource-limited settings with the highest burden [8].
Primarily manifesting as an acute febrile illness, severe forms of leptospirosis affect
multiple organ systems, resulting in acute kidney injury, pulmonary hemorrhage
hepatitis, myocarditis, disseminated intravascular coagulation, and meningoencephalitis [9].
Structure of leptospirosis
Leptospires are thin, helically coiled, motile spirochetes usually 6–20 μm in length.
[10] The hooked ends of this bacterium give its distinctive question-mark shape.[11]
The leptospires have surface structures that share features of both Gram-positive and negative bacteria.[12] The double-membrane and the presence of LPS are
characteristic of Gram-negative bacteria, while the close association of the
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cytoplasmic membrane with murrain cell wall is reminiscent of Gram-positive
envelope architecture.[13]
Motility in leptospires is a function of the two periplasmic flagella or endoflagella,
which arise from each end of the bacterium. [14] The disruption of the flagellum gene
flaB by a kanamycin marker in saprophytic L.biflexa through homologous
recombination resulted in the absence of the endoflagella with the corresponding loss
in bacterial movement. [15] On the other hand, the flagellar motor switch fliY mutant
of the pathogenic L. interrogans exhibited attenuated rotative motion in both liquid
and semi-solid media. [16]
Microbiology
The genus Leptospira contains 21 species; 9 are regarded as pathogenic (Leptospira
interrogans, L. kirschneri, L. noguchii, L. alexanderi, L. weilii, L. alstonii, L.
borgpetersenii, L. santarosai, and L. kmetyi), 5 are of intermediate or unclear
pathogenicity (L. inadai, L. fainei, L. broomii, L. licerasiae, and L wolffii), and the
remaining 7 are nonpathogenic free-living saprophytic species that do not infect
animal hosts (L. biflexa, L. meyeri, L. wolbachii, L. vanthielii, L. terpstrae, L.
yanagawae, and L. idonii) [17,18].
Transmission
Leptospira enters the body via cuts or abrasions in the skin or through mucous
membranes of the eyes, nose or throat. Infection by pathogenic strains of Leptospira
commonly occurs through direct contact with infected animal urine or indirectly
through contaminated water or soil with urine from infected animals. Almost every
mammal can serve as a carrier of leptospires, harboring the spirochete in the proximal
renal tubules of the kidneys, leading to urinary shedding. Rats (Rattusnorvegicus)
serves as the major carriers in most human leptospirosis, excreting high
concentrations of leptospires (107 organisms per ml) months after their initial
infections. Humans, on the other hand, are considered as incidental hosts, suffering
from acute but sometimes fatal infections [19,20].
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Individuals with occupations at risk for direct contact with potentially infected
animals include veterinarians, abattoir workers, farm workers (particularly in dairy
milking situations), hunters and trappers, animal shelter workers, scientists, and
technologists handling animals in laboratories or during fieldwork. ''The magnitude
of the risk depends on the local prevalence of leptospiral carriage and the degree and
frequency of exposure. Most of these infections are preventable by the use of
appropriate personal protective equipment such as rubber boots, gloves, and
protective eyewear. Since many of these infections are covered by occupational health
and safety regulations, local risk assessments and training are essential "[ 21[.
Indirect contact with water or soil contaminated with leptospires is much more
common, and can be associated with occupational, recreational, or a vocational
activities. In addition to that, sewer work, military exercises, and farming in high
rainfall tropical regions are recognized; the latter is by far the most important
numerically.
Recreational exposures include all freshwater water sports including caving (22),
canoeing ]23[, kayaking ]24;25[, rafting ]26[, and triathlons ]27;28[ .The importance
of this type of exposure has increased over the past 20 years as the popularity of
adventure sports and races has increased, and also because the relative cost of travel
to exotic destinations has decreased. ]29[
A vocational exposures are by far the most important exposures, affecting millions of
people living in tropical regions, because the lack of adequate sanitation and poor
housing combine to exacerbate the risk of exposure to leptospires in both rural and
urban slum communities. ]30;31;32;33[
Mechanism of action
Leptospires enter the body through small cuts or abrasions, via mucous membranes
such as the conjunctiva or thorough wet skin. They circulate in the blood stream, with
the bacteremic phase lasting for up to 8 days [34]. The second stage of acute
leptospirosis is also referred to as the immune phase, in which the leptospira
disappear from the blood and CSF, remaining intermittently in the urine and aqueous
humor coincides with the appearance of antibodies. [35]
4

The first step in the pathogenesis of leptospirosis is penetration of tissue
barriers to gain entrance to the body. "The importance of the oral mucosa as a
portal of entry is indicated by a number of studies that found that swallowing
while swimming in contaminated water is a risk factor for infection".
]36;37;38[. And The adhesion of leptospires to host tissue components is
thought of as an initial and necessary step for infection and pathogenesis.
Attachment to host cells and ECM components is likely to be necessary for the
ability of leptospires to penetrate, disseminate and persist in mammalian host
tissues.

The second step in pathogenesis is hematogenous dissemination. Unlike other
pathogenic spirochetes such as B. burgdorferi and T. pallidum, which cause
skin lesions indicating establishment of infection in the skin, pathogenic
leptospires make their way into the bloodstream and persist there during the
leptospiremic (bacteremic) phase of the illness. Results from inoculation of
blood into leptospiral medium and detection of leptospiremia by quantitative
PCR are more likely to be positive during the first 8 days of fever ]39[ prior to
antibody formation and clearance of organisms from the bloodstream.
But the mechanism by which leptospira cause the disease is still not well understood!
A number of putative virulence factors have been suggested, but with few exceptions
their role in pathogenesis remains unclear.
The known leptospiral virulence factors have been extensively reviewed [40–41], and
include LPS (a general virulence factor of Gram-negative bacteria), flagella, hemeoxygenase, the Omp A-like Loa22, and adhesion molecules. In addition, hemolysins
and sphingomyelinases may play a role during infection, although there are
conflicting reports regarding their true contributions to overall virulence [42]
"The onset of the disease in humans is variable, ranging from 1 day to 4 weeks after
exposure, and in survivors, infection can last for months" [43]
Resistance
As long as liptospira is a microorganism that live in the environment and mammalians
host before transmitted to humans , it’s survival outside the host is a key aspect of
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leptospiral ecology and hence for pathogenesis. [44] since these organisms are
capable of colonizing and multiplying inside the renal tubules of chronically infected
reservoir species, disseminating in the urine, and contaminating soil and water.
Humans and other mammals are then infected by direct contact with animal fluids or
contaminated water. [45] Importantly, this scenario is worsened by the capability of
forming biofilms [46] making it more resistant to environmental conditions, with the
result that, more chances to survive and infect humans. the suggestions that biofilm
growth requires the extensive reprogramming of transcription patterns along the three
replicons of L. biflexa and involves many regulatory networks like c-di-GMP
signaling, anti-anti-sigma factors, and canonical two-component systems that control
basal functions, like DNA metabolism and replication, as well as more specific
functions like cell motility or lipid and sugar metabolisms. [47] in addition to forming
biofilm , L. biflexa shows to possess a mechanical barrier, the outer membrane (OM),
as a basic defense against toxic compounds. Due to the presence of
lipopolysaccharide (LPS) in the OM of Leptospira, hydrophilic agents, including EtBr
and some antibiotics, cannot diffuse into the periplasm. [48]
As an indication to suggested way for antibiotics resistance, the studies show that,
even though EtBr may enter via porins, then enter the cytoplasm from the periplasm
via simple diffusion and bind to the DNA , leptospira can prevent diffusion , by
multidrug efflux pumps spanning both the outer and the inner membranes . In addition
to efflux pumps, inner-membrane single-drug transporters can contribute to the efflux
of EtBr back to the periplasm. [48] In general , overexpression of proteins involved in
the process of drug efflux or mutational gain of function in the genes encoding these
proteins contribute to antibiotic resistance in a number of bacterial species . [49]
Disease
The disease is caused by spirochete bacteria from the genus of leptospira. ]50[ And is
transmitted by an infected animal's urine, especially if the urine is still moist to
contaminate the soil and water. ]51[ The transmition could be directly or indirectly,
and after the entry of microorganism to the body it will start to cause hematogenous
dissemination. ]52[ Early diagnosis for the bacteria is very important because the
treatment is very effective in early stages, so we can detect the bacteria by PCR, there
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are another methods but they cannot detect it in early phase like culture and
microscopic agglutination test. ]53[, the tests are applied on blood and CSF for the
first 7-10 days after that the microorganism can be found in fresh urine, and we have
to know that negative results don't mean ruling out early infection.
Severity of the disease could be mild and self-limiting to life threatening condition.
Serious effects of the disease come from both invasions of microorganism and host
defense mechanism and due to these effects the mortality is high, and what makes the
condition worse that the early manifestations are undiffrential such as fever, chills and
headache.
Laboratory tests and chest radiographs should be done when there are fever with
pneumonitis and respiratory failure. ]54[ Some common signs and symptoms are
muscle pain, tenderness, icterus, nonproductive cough, nausea, vomiting, diarrhea and
abdominal pain. In sever stages, multiple organs dysfunctions will happen like weal's
disease (a combination of jaundice and renal failure), in addition to bleeding. ]52[
The incubation phase is 7 to 12 as an average, but it could be as short as only 3 days
or as long as 1 month, and most patients recover completely from the disease, the
complications such as acute renal failure could be reversible but still permanent
damage happen too, there are patients who complain from post leptospirosis
symptoms chronically, such as fatigue, myalgia, malaise, headache, and weakness. As
we mention before that the disease itself limiting with supportive care, but early
initiation of antibiotic prevent the complications and progression of the disease.
Treatment
Most cases of leptospirosis are self-limited in the absence of antimicrobial therapy,
although a proportion of patients do develop severe complications with significant
morbidity and mortality. In general, if the illness is severe enough to come to clinical
attention and the diagnosis is recognized, antibiotic therapy should be administered.
Symptomatic patients presenting for medical attention should receive antimicrobial
therapy to shorten the duration of illness and reduce shedding of organisms in the
urine.
For outpatients with mild disease , patients should receive either doxycycline (adults:
100 mg orally twice daily; children ≥8 years of age: 2 mg/kg per day in two equally
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divided doses, not to exceed 200 mg daily), or azithromycin (adults: 500 mg orally
once daily for three days; children: 10 mg/kg orally on day one [maximum dose
500 mg/day] followed by 5 mg/kg/day orally once daily on subsequent days
[maximum dose 250 mg/day]). ]55;56[, ]57;58[
For hospitalized with severe disease, patients should receive penicillin (1.5 million
units intravenously [IV] every six hours), ampicillin (0.5–1 g IV every 6
h), ceftriaxone (1 to 2 g IV once daily), or cefotaxime (1 g IV every six hours).
''Ceftriaxone has been shown to be noninferior to penicillin for serious leptospirosis ''
]59[ .The duration of treatment in severe disease is usually seven days.
Pregnant women with severe leptospirosis may be treated with penicillin, ceftriaxone,
cefotaxime, or azithromycin; doxycycline should not be used.
To prevent complications we hydrate the patient adequately and prevent oliguric renal
failure, potassium supplementation for those with hypokalemia due to potassium
wasting high-output renal dysfunction.
People who are at high risk should receive killed, whole-cell vaccines
which will lead to significant decrease in the incidence of leptospirosis, the
recommended vaccination protocol involves two booster doses after the initial
immunization followed by re-immunization every 2 years. There is a vaccine on
animals to decrease spread to humans.
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