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Leptospirosis
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Leptospirosis Joseph M. Vinetz, George Watt
KEY FEATURES • Leptospirosis is a neglected emerging bacterial zoonosis endemic in impoverished regions of the tropics that is sporadically transmitted in developed countries. • Leptospirosis is a cause of morbidity and mortality. • Severe leptospirosis is characterized by refractory shock, pulmonary hemorrhage, jaundice, acute kidney injury, and a high mortality rate. • The pathogenesis of leptospirosis remains largely unexplained but probably is due to endothelial cell dysfunction, with key pathologic features being a paucity of histopathologic changes in organs despite marked functional impairment. • Actionable diagnostic confirmation is rarely available in areas where most disease transmission occurs. • Severe leptospirosis should be treated with parenteral penicillin or third-generation cephalosporins, whereas milder cases may be treated with oral doxycycline; other agents may also be effective. • There is no commercially available vaccine for use in humans, although prophylactic weekly doxycycline can be used to prevent disease among select at-risk populations and during outbreaks.
INTRODUCTION Leptospirosis is a globally important bacterial zoonosis caused by pathogenic spirochetes of the genus Leptospira, with a conservatively estimated 1.05 million cases and 60,000 deaths annually.1 The pathogenesis remains largely unexplained today even though Weil published a clinical description of leptospirosis in 1886. In 1916 Inada isolated spirochetes in pure culture, subsequently delineated Leptospira, identified them as the etiologic agent of leptospirosis, and linked rats to disease transmission.2 The disease is of greatest public health importance in the tropics, where it is a disease both of agricultural workers3,4 and residents of urban slums.5,6 Outbreaks superimposed on endemic disease activity are regularly linked to severe hurricane and flooding events throughout the world; notable examples have occurred in Brazil,5 Sri Lanka,7 the Philippines,8 and Thailand.9
important reservoir. Carrier rates of over 50% have been measured in Norway rats, which shed massive numbers of organisms for life without showing clinical illness. Some serovars appear to be preferentially adapted to select mammalian hosts. For example, the serovar Icterohaemorrhagiae is primarily associated with the Norway rat, Canicola with dogs, and Pomona with swine and cattle. However, a particular host species may serve as a reservoir for one or more serovars, and a particular serovar may colonize different animal species. Transmission of infection from animal to human usually occurs through contact with contaminated water or moist soil. Organisms enter humans through abrasions of the skin or through the mucosal surface of the eye, mouth, nasopharynx, or esophagus. Crowded cities that are flood-prone and have large rat populations provide ideal conditions for disease transmission. Escalating migration of the rural poor to urban slums is likely to further exacerbate the risks of leptospirosis transmission. An outbreak in Nicaragua in 199512 and an urban epidemic in Salvador, Brazil, in 19995 were associated with particularly heavy rains and flooding. In 2009 two typhoons struck the Philippines and caused massive flooding.8 Leptospirosis was recognized as the most urgent threat to health in the aftermath of these typhoons. Special clinics to treat the disease were set up in evacuation centers, and an estimated 1.3 million flood survivors were given chemoprophylaxis, the efficacy of which was presumed but not demonstrated. Intense exposure to leptospires has been documented in rice, sugar cane, and rubber plantation workers. Less frequently, leptospirosis is acquired by direct contact with the blood, urine, or tissues of infected animals. Epidemiologic patterns in the United States and UK have changed. Recreational exposure to freshwater (e.g., white water rafting, triathlons, sailing, water skiing) and animal contact at home are more common than occupational exposure as the chief sources of disease in industrialized areas other than slums. Measuring incidence by active surveillance confirms that leptospirosis is surprisingly common. Antibody positivity rates of 37% have been recorded in rural Belize, 23% in Vietnam, and 18% in inner city Baltimore, Maryland.13 More than 2527 human cases and 13 deaths were reported for the first 9 months of 1999 by the Ministry of Public Health in Thailand. Human leptospirosis is an important disease in China, Southeast Asia, India, Africa, and South and Central America. It is also of significance in eastern and southern Europe, Australia, and New Zealand. In the United States, the disease is primarily of veterinary importance, with only 50 to 150 human cases reported annually.
EPIDEMIOLOGY
NATURAL HISTORY, PATHOGENESIS, AND PATHOLOGY
Leptospirosis is caused by spirochetes of the genus Leptospira. This genus contains more than 35 species classified on the basis of comparative genomic analysis10,11 and more than 300 serovars based on diverse agglutinating lipopolysaccharide antigens. Leptospires colonize proximal renal tubules of mammalian hosts and are shed in the urine. They can survive for several months in the environment under moist conditions, particularly in the presence of warmth (above 22°C) and neutral pH (pH 6.2–8.0). These conditions occur all year round in the tropics but only during the summer and autumn months in temperate climates. Roughly 160 animal species harbor organisms, but rodents are a particularly
Infection may be asymptomatic, but 5% to 15% of cases are severe or fatal.1 Pathogenesis, particularly that of severe disease, remains poorly understood. Overall, severe pulmonary hemorrhage syndrome (SPHS) accompanied by refractory shock appears to be the most common cause of death in leptospirosis; oliguric renal failure without access to dialysis is also associated with fatal leptospirosis. It is unclear why renal failure predominates as the principal cause of death in some places, whereas pulmonary hemorrhage is the major cause in others, even where the most common infecting serovars are the same. There are only minor histopathologic changes in the kidneys and livers of patients with
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marked functional impairment of these organs. Patients who survive severe leptospirosis have complete recovery of hepatic and renal function, consistent with the lack of structural damage to these organs.
CLINICAL FEATURES The most common clinical features of leptospirosis are summarized in Table 79.1. Subclinical infection is common, and less than 10% of symptomatic infections result in severe, icteric illness. Even relatively virulent serovars, such as Copenhageni/ Icterohaemorrhagiae, lead more often to anicteric than to icteric disease. Old terms such as peapicker’s disease, swineherd’s disease, and canicola fever, which are linked to specific serotypes with distinct disease manifestations, are misleading and should be abandoned. The median incubation period is 10 days, with a range of 2 to 26 days. The duration of the incubation period has no prognostic significance. Once symptoms develop, they may or may not follow a biphasic course; after an initial febrile illness there is defervescence and symptomatic improvement followed by a second period of disease refractory to antibiotics. However, a clear demarcation between the first and second stages may not be observed in icteric leptospirosis and, in mild cases, the distinction can be unclear or the second stage may never occur. The diagnostic usefulness of a history of a biphasic illness has been overemphasized. HIV co-infection does not seem to affect the clinical presentation of leptospirosis in the few co-infected patients described thus far.
Anicteric Leptospirosis Symptoms and Signs Typically, the disease begins with the abrupt onset of intense headache, fever, chills, and myalgia. Fever often exceeds 40°C (103°F) and is preceded by rigors. Muscle pain can be excruciating and occurs most commonly in the thighs, calves, lumbosacral region, and abdomen. Abdominal wall pain accompanied by palpation tenderness can mimic an acute surgical abdomen. Nausea, vomiting, diarrhea, and sore throat are other frequent symptoms. Cough and chest pain figure prominently in reports of patients from Korea and China. TABLE 79.1 The Most Common Clinical Manifestations of 208 Leptospirosis Patients in Puerto Rico Symptoms (% of Cases)
Anicteric (106 Cases)
Icteric (102 Cases)
Fever Myalgia Headache Chills Sore throat Nausea Vomiting Eye pain Diarrhea Oliguria Cough Hemoptysis
100 97 82 84 72 71 65 54 23 20 15 5
99 97 95 90 87 81 75 38 30 30 32 14
Signs (% of Cases) Conjunctival infection Muscle tenderness Hepatomegaly Pulmonary findings Lymphadenopathy Petechiae, ecchymoses
100 70 60 11 35 4
98 79 60 36 12 29
Adapted from Alexander AD, Benenson AS, Byrne RJ, et al. Leptospirosis in Puerto Rico. Zoonoses Res 1963;2:152–227.
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Conjunctival suffusion is a helpful diagnostic clue that usually appears 2 or 3 days after the onset of fever and involves the bulbar conjunctiva. Pus and serous secretions are absent, and there is no matting of the eyelashes and eyelids. Mild suffusion can easily be overlooked. Less common and less distinctive signs include pharyngeal injection, splenomegaly, hepatomegaly, lymphadenopathy, and skin lesions. Within a week, most patients become asymptomatic. After several days of apparent recovery, the illness resumes in some individuals. Manifestations of the second stage are more variable and mild than those of the initial illness and usually last 2 to 4 days. Leptospires disappear from the blood, cerebrospinal fluid (CSF), and tissues but appear in the urine. Serum antibody titers rise—hence the term immune phase. Aseptic meningitis is the hallmark of this stage of leptospirosis but is not associated with mortality. Pleocytosis of the CSF can be demonstrated in 80% to 90% of all patients during the second week of illness, although only about 50% will have clinical signs and symptoms of meningitis. Meningeal signs can last several weeks but usually resolve within a day or two. Uveitis is a late manifestation of leptospirosis, generally seen 4 to 8 months after the illness has begun. The anterior uveal tract is most frequently affected, and pain, photophobia, and blurring of vision are the usual symptoms.
Laboratory Findings White blood cell count varies, but neutrophilia is usually present. Urinalysis may show proteinuria, pyuria, and microscopic hematuria. Enzyme markers of skeletal muscle damage, such as creatinine kinase and aldolase, are elevated in the sera of 50% of patients during the first week of illness. Chest radiographs from patients with pulmonary manifestations show a variety of abnormalities, but none is pathognomonic of leptospirosis. The most common finding is patchy, non-lobal, diffuse infiltrates.
Icteric Leptospirosis (Weil’s Disease) Weil’s disease refers to severe, life-threatening leptospirosis and is characterized by jaundice, renal dysfunction, hemorrhagic manifestations, refractory shock, and a high mortality rate. Although jaundice is the hallmark of severe leptospirosis, true liver failure does not occur. The degree of jaundice has no prognostic significance, but its presence or absence does—virtually all leptospirosis deaths occur in icteric patients but are usually related to other associated mechanisms (hemorrhage or oliguric renal failure). Icterus first appears between the fifth and ninth days of illness, reaches maximum intensity 4 or 5 days later, and continues for an average of 1 month. Hepatomegaly is found in the majority of patients; hepatic percussion tenderness is a reliable clinical marker of continuing disease activity. There is no residual liver dysfunction in survivors of Weil’s disease, consistent with the absence of structural damage. Bleeding is occasionally seen in anicteric cases but is most prevalent in severe disease. Purpura, petechiae, epistaxis, bleeding of the gums, and minor hemoptysis are the most common hemorrhagic manifestations; however, deaths occur from subarachnoid hemorrhage and exsanguination from gastrointestinal bleeding. Conjunctival hemorrhage is an extremely useful diagnostic finding and, when combined with scleral icterus and conjunctival suffusion, produces eye findings strongly suggestive of leptospirosis (Fig. 79.1). The frequency with which severe pulmonary hemorrhage complicates leptospirosis is variable but is a cardinal feature of some outbreaks. Life-threatening oliguric renal failure is a complication of icteric disease, although all forms of leptospirosis may be associated with non-oliguric kidney dysfunction. Oliguria or anuria usually develop during the second week of illness but may appear earlier. Complete anuria is a grave prognostic sign often seen in patients who present late in the course of illness with frank uremia and irreversible
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suffusion and severe myalgia with tenderness. In the context of a known outbreak of leptospirosis, individuals must be carefully assessed for signs of severe disease. The most important signs of severity are jaundice, severe thrombocytopenia, bleeding, pulmonary involvement, oliguria, hypomagnesemia and hypokalemia, and elevated serum creatinine.
Diagnosis
Fig. 79.1 Jaundice, hemorrhage, and conjunctival suffusion in acute leptospirosis.
disease. Because renal failure develops very quickly in leptospirosis, symptoms and signs of uremia are frequently encountered. Anorexia, vomiting, drowsiness, disorientation, and confusion are seen early and rapidly progress to convulsions, stupor, and coma in severe cases. Disturbances of consciousness in a patient with severe leptospirosis are usually caused by uremic encephalopathy, whereas in anicteric cases aseptic encephalitis is the usual cause. Renal function eventually returns to normal in survivors of Weil’s disease, although detectable abnormalities may persist for several months. Leptospirosis-associated SPHS is now recognized as a widespread public health problem with a case fatality rate of about 50%. This lethal complication of leptospirosis can occur either with or without jaundice and renal failure. Hemoptysis is the cardinal sign but may not be apparent until patients are intubated. Real-time polymerase chain reaction (PCR) has shown that leptospiremia is 10,000 or more bacteria per milliliter of blood in SPHS—the apparent critical threshold for severe outcomes such as SPHS and death.6
Laboratory Features of Weil’s Disease Hyperbilirubinemia results from increases in both conjugated (direct) and unconjugated (indirect) bilirubin, but elevations of the direct fraction predominate. Prolongations of the prothrombin time commonly occur but are easily corrected by the administration of vitamin K; modest elevations of serum alkaline phosphatase are typical. There is mild hepatocellular necrosis; greater than fivefold increases of transaminase (aminotransferase) levels are unusual. Jaundiced patients usually have leukocytosis in the range of 15,000 to 30,000 per mm3, and neutrophilia is constant. Anemia is common and multifactorial; blood loss and renal dysfunction contribute frequently, intravascular hemolysis less often. Mild thrombocytopenia often occurs, but decreases in platelet count sufficient to be associated with bleeding are exceptional. The specific gravity of the urine is high. Hypokalemia due to renal potassium wasting can occur, and hypomagnesemia has been reported.
PATIENT EVALUATION, DIAGNOSIS, AND DIFFERENTIAL DIAGNOSIS Patient Evaluation Patients who present with an undifferentiated febrile illness must be carefully evaluated for possible leptospirosis. A history of submersive water exposure or direct animal contact is essential to suspecting diagnosis. Key symptoms and signs are conjunctival
Most cases go undiagnosed because symptoms and signs are often non-specific and diagnostic confirmation is rarely available where most disease transmission occurs. Failure to diagnose leptospirosis is particularly unfortunate: severely ill patients often recover completely with prompt treatment, but delayed therapy is likely to result in a poor clinical outcome. Late disease can often be recognized by its typical clinical manifestations, but the presentation of early leptospirosis is usually non-specific and is therefore difficult to identify clinically. Leptospirosis has long been acknowledged to be a frequent cause of undifferentiated febrile illness in developing countries. Co-infection with diseases such as dengue, malaria, and scrub typhus has been reported and adds to the diagnostic confusion of tropical fevers. Laboratory diagnosis of leptospirosis remains problematic. The microscopic agglutination test is considered the serodiagnostic method of choice for leptospirosis, but its complexity limits its use to reference laboratories and requires paired acute and convalescent serum samples. Dilutions of patient sera are applied to a panel of live, pathogenic leptospires. The results are viewed under dark-field microscopy and expressed qualitatively as the proportion of organisms cleared from the field by agglutination. Inadequate quality controls of the live reference strain panels can lead to frequent false-negative results.7 A new generation of commercially available, rapid serodiagnostic kits that rely on whole Leptospira antigen preparations have been developed. Unfortunately, these assays seem to have unacceptably low sensitivities during acute-phase illness, and persistent antibody produces low specificity in regions of high endemic transmission. The need for practical, affordable diagnostic kits to be available in areas where leptospirosis is common cannot be overemphasized. PCR and urine antigen detection are research tools that would be of the greatest potential diagnostic value in patients who present early, before antibodies have reached detectable levels; these tests are not available for most affected populations. Isolation of leptospires from blood or CSF is possible during the first 10 days of clinical illness, but specialized media are necessary. Serially diluted urine provides the highest yield. Unfortunately, culture results are only known many weeks later—too late to benefit severely ill, hospitalized patients. Several attempts have been made to formulate diagnostic algorithms by assigning points to various clinical, epidemiologic, and laboratory parameters. The points are totaled and the score is then used to represent the likelihood that the patient in question has leptospirosis. An example is shown in Table 79.2. The usefulness of these scoring systems is limited by their complexity, by marked regional variability in the quality of available diagnostic tests, and by regional differences in the prevalent differential diagnoses that must be considered. However, these scoring systems are useful teaching tools and emphasize the important epidemiologic and clinical characteristics of leptospirosis.
Differential Diagnosis The typical leptospirosis patient has a history of water or animal contact, conjunctival suffusion, and severe myalgia. It is important to solicit these findings in both mild and severe cases of leptospirosis. Atypical or mild cases are often confused with other entities, but because of a low index of suspicion and the disease’s protean manifestations, the diagnosis is often missed, even in typical cases.
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TABLE 79.2 Modified World Health Organization (WHO) Criteria for Diagnosis of Leptospirosis
BOX 79.2 Clinical Pearl
Part A Clinical signs and symptoms (score) • Fever >39.0°C • Conjunctival suffusion • Myalgias • Meningeal signs • Jaundice • Proteinuria
(2 (4 (4 (4 (1 (1
Kawasaki’s disease (mucocutaneous lymph node syndrome) must be differentiated from leptospirosis in children <5 years old with desquamation and involvement of the gallbladder and myocardium.
Part B Risk factors for exposure (score) • Heavy rainfall • Flooding • Animal contact
(5 points) (5 points) (1 point)
Part C Laboratory test results (score) • Positive IgM ELISA • MAT – single high titer • MAT fourfold rise in titer
(15 points) (15 points) (25 points)
points) points) points) points) point) point)
Interpretation: Presumptive leptospirosis if score ≥25 points. Possible leptospirosis if score between 20 and 25 points. ELISA, Enzyme-linked immunosorbent assay; IgM, immunoglobulin M; MAT, microscopic agglutination test.
BOX 79.1 Clinical Pearl Muscles of patients with leptospirosis can be exquisitely tender and painful to the touch, but palpation of painful muscles in patients with scrub typhus sometimes provides pain relief.
The most important differential diagnoses differ in mild and severe disease.
Anicteric Leptospirosis Acute undifferentiated febrile illness, fever of unknown origin, and aseptic meningitis are the most common clinical impressions in mild leptospirosis. Severe myalgia involving several different muscle groups, particularly the calves—not just the abdominal wall—suggests leptospirosis rather than appendicitis. Fever and vomiting are frequently misdiagnosed as gastroenteritis.
Weil’s Disease Viral hepatitis is a common misdiagnosis in patients with Weil’s disease. Leukocytosis, elevated serum bilirubin levels without marked transaminase elevations, and renal dysfunction are typical of leptospirosis but unusual in hepatitis. Marked leukocytosis and a negative blood film argue against malaria. Jaundice, severe renal dysfunction, and leukocytosis are atypical of typhoid fever. Differentiating leptospirosis from scrub typhus and Korean hemorrhagic fever (caused by Hantaan virus) in areas where these diseases co-exist is more difficult. Both are associated with animals, and both can cause conjunctival suffusion. Korean hemorrhagic fever is transmitted by infected rodent urine, and mixed infection with Leptospira interrogans and Hantaan virus has been reported. Liver disease is not usually a prominent manifestation of Korean hemorrhagic fever. Splenomegaly and generalized lymphadenopathy are characteristic of scrub typhus but not leptospirosis. Serum creatinine levels are usually normal, even in jaundiced patients with Orientia tsutsugamushi infection. The myalgia of leptospirosis is usually more severe than that of scrub typhus (Box 79.1).
Severe Pulmonary Hemorrhage Syndrome Leptospirosis with prominent hemorrhagic manifestations is easily misdiagnosed as dengue virus infection. A severe outbreak of leptospirosis with SPHS in Nicaragua was initially thought to be dengue.12
Childhood Leptospirosis This shares many features with adult disease; pulmonary hemorrhage occurs, and severe renal dysfunction is common. Distinct clinical features include hypotension, acalculous cholecystitis, pancreatitis, and abdominal causalgia (burning pain). Skin lesions may desquamate and become gangrenous (Box 79.2).
TREATMENT Placebo-controlled, double-blind trials have demonstrated that doxycycline benefits patients with early, mild leptospirosis and that intravenous penicillin helps adults with severe, late disease.14 The outcome of severe, pediatric leptospirosis is also improved by penicillin therapy.15 Antibiotics should therefore be given to all patients with leptospirosis, regardless of age or when in their disease course they are seen. Doxycycline is given at doses of 100 mg orally twice a day for 1 week. Patients who are vomiting or are seriously ill require parenteral therapy. Intravenous penicillin G is administered to adults as 1.5 million units every 6 hours for 1 week. Recent trials from Thailand indicate that treatment with ceftriaxone, cefotaxime, and doxycycline had equivalent efficacy to penicillin in patients with mild to moderately severe disease. However, it is not known whether these antibiotics are as effective as high-dose penicillin for treatment of the most severely ill individuals. Doxycycline and azithromycin had comparable efficacy as presumptive treatment of mildly ill patients found later to have leptospirosis, scrub typhus, or dual infections. There is controversy regarding the occurrence of a Jarisch– Herxheimer reaction in leptospirosis. If present, it is much less prominent in leptospirosis than in other spirochetal illnesses. The important practical consideration is that antibiotics should not be withheld because of the fear of a possible Jarisch–Herxheimer reaction. The management of pulmonary hemorrhage often requires prompt intubation and mechanical ventilation. SPHS patients have physiologic and pathologic evidence of acute respiratory distress syndrome, so ventilation using low tidal volumes and high postexpiratory end pressures should be provided; hemodialysis even in the absence of renal failure may be useful for the pulmonary hemorrhage syndrome.14 Respiratory support to maintain adequate tissue oxygenation is essential because in non-fatal cases complete recovery of pulmonary function can be achieved. Ensuring adequate renal perfusion prevents renal failure in the vast majority of oliguric individuals. Continuous hemofiltration has been shown to be more effective than peritoneal dialysis in treating infection-associated hypercatabolic renal failure. Peritoneal dialysis, however, may be the only option in resource-limited settings. Whichever method of dialysis is chosen, it must be started promptly—delays increase mortality.
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PREVENTION Doxycycline 200 mg taken once a week prevents infection by pathogenic leptospires.16 Widespread use of doxycycline prophylaxis is not indicated, but it can benefit those who are at high risk for a short time, such as military personnel and certain agricultural workers. Infection by leptospires confers only serovar-specific immunity; second attacks caused by different serovars can occur. The efficacy and safety of human leptospiral vaccines have yet to be conclusively demonstrated. Prevention of leptospirosis in the tropics is particularly difficult. The large animal reservoir of infection is impossible to eliminate, the occurrence of numerous serovars limits the usefulness of serovar-specific vaccine, and the wearing of protective clothing (e.g., rubber boots in rice fields) is both prohibitively expensive and impractical. Providing proper sanitation in urban slum communities would be the most effective control measure in this setting. REFERENCES
1. Costa F, Hagan JE, Calcagno J, et al. Global morbidity and mortality of leptospirosis: a systematic review. PLoS Negl Trop Dis. 2015;9(9):e0003898. 2. Inada R, Ido Y, Hoki R, et al. The Etiology, Mode of Infection, and Specific Therapy of Weil’s disease (Spirochaetosis Icterohaemorrhagica). J Exp Med 1916;23(3):377–402. 3. Agampodi S, Peacock SJ, Thevanesam V. The potential emergence of leptospirosis in Sri Lanka. Lancet Infect Dis 2009;9(9):524–6. 4. Bharti AR, Nally JE, Ricaldi JN, et al. Leptospirosis: a zoonotic disease of global importance. Lancet Infect Dis 2003;3(12):757–71. 5. Ko AI, Galvao Reis M, Dourado CMR, et al. Urban epidemic of severe leptospirosis in Brazil. Lancet 1999;354:820–5.
6. Vinetz JM, Glass GE, Flexner CE, et al. Sporadic urban leptospirosis. Ann Intern Med 1996;125:794–8. 7. Agampodi SB, Peacock SJ, Thevanesam V, et al. Leptospirosis outbreak in Sri Lanka in 2008: lessons for assessing the global burden of disease. Am J Trop Med Hyg 2008;85(3):471–8. 8. Matsushita N, Ng CFS, Kim Y, et al. The non-linear and lagged short-term relationship between rainfall and leptospirosis and the intermediate role of floods in the Philippines. PLoS Negl Trop Dis. 2018;12(4):e0006331. 9. Thaipadungpanit J, Wuthiekanun V, Chierakul W, et al. A dominant clone of Leptospira interrogans associated with an outbreak of human leptospirosis in Thailand. PLoS Negl Trop Dis. 2007;1(1):e56. 10. Thibeaux R, Iraola G, Ferres I, et al. Deciphering the unexplored Leptospira diversity from soils uncovers genomic evolution to virulence. Microb Genom 2018;4(1). 11. Fouts DE, Matthias MA, Adhikarla H, et al. What makes a bacterial species pathogenic?:comparative genomic analysis of the genus Leptospira. PLoS Negl Trop Dis. 2016;10(2):e0004403. 12. Zaki SR, Shieh W-J. Leptospirosis associated with outbreak of acute febrile illnesses and pulmonary haemorrhage, Nicaragua, 1995. Lancet 1996;347:535–6. 13. Childs JE, Schwartz BS, Ksiazek TG, et al. Risk factors associated with antibodies to leptospires in inner-city residents of Baltimore: a protective role for cats. Am J Public Health 1992;82(4):597–9. 14. Watt G, Padre LP, Tuazon ML, et al. Placebo-controlled trial of intravenous penicillin for severe and late leptospirosis. Lancet 1988;1(8583):433–5. 15. Takafuji ET, Kirkpatrick JW, Miller RN, et al. An efficacy trial of doxycycline chemoprophylaxis against leptospirosis. N Engl J Med 1984;310(8):497–500. 16. Andrade L, Cleto S, Seguro AC. Door-to-dialysis time and daily hemodialysis in patients with leptospirosis: impact on mortality. Clin J Am Soc Nephrol 2007;2(4):739–44.
Leptospirosis Joseph M. Vinetz, George Watt
KEY FEATURES • Leptospirosis is a neglected emerging bacterial zoonosis endemic in impoverished regions of the tropics that is sporadically transmitted in developed countries. • Leptospirosis is a cause of morbidity and mortality. • Severe leptospirosis is characterized by refractory shock, pulmonary hemorrhage, jaundice, acute kidney injury, and a high mortality rate. • The pathogenesis of leptospirosis remains largely unexplained but probably is due to endothelial cell dysfunction, with key pathologic features being a paucity of histopathologic changes in organs despite marked functional impairment. • Actionable diagnostic confirmation is rarely available in areas where most disease transmission occurs. • Severe leptospirosis should be treated with parenteral penicillin or third-generation cephalosporins, whereas milder cases may be treated with oral doxycycline; other agents may also be effective. • There is no commercially available vaccine for use in humans, although prophylactic weekly doxycycline can be used to prevent disease among select at-risk populations and during outbreaks.
INTRODUCTION Leptospirosis is a globally important bacterial zoonosis caused by pathogenic spirochetes of the genus Leptospira, with a conservatively estimated 1.05 million cases and 60,000 deaths annually.1 The pathogenesis remains largely unexplained today even though Weil published a clinical description of leptospirosis in 1886. In 1916 Inada isolated spirochetes in pure culture, subsequently delineated Leptospira, identified them as the etiologic agent of leptospirosis, and linked rats to disease transmission.2 The disease is of greatest public health importance in the tropics, where it is a disease both of agricultural workers3,4 and residents of urban slums.5,6 Outbreaks superimposed on endemic disease activity are regularly linked to severe hurricane and flooding events throughout the world; notable examples have occurred in Brazil,5 Sri Lanka,7 the Philippines,8 and Thailand.9
important reservoir. Carrier rates of over 50% have been measured in Norway rats, which shed massive numbers of organisms for life without showing clinical illness. Some serovars appear to be preferentially adapted to select mammalian hosts. For example, the serovar Icterohaemorrhagiae is primarily associated with the Norway rat, Canicola with dogs, and Pomona with swine and cattle. However, a particular host species may serve as a reservoir for one or more serovars, and a particular serovar may colonize different animal species. Transmission of infection from animal to human usually occurs through contact with contaminated water or moist soil. Organisms enter humans through abrasions of the skin or through the mucosal surface of the eye, mouth, nasopharynx, or esophagus. Crowded cities that are flood-prone and have large rat populations provide ideal conditions for disease transmission. Escalating migration of the rural poor to urban slums is likely to further exacerbate the risks of leptospirosis transmission. An outbreak in Nicaragua in 199512 and an urban epidemic in Salvador, Brazil, in 19995 were associated with particularly heavy rains and flooding. In 2009 two typhoons struck the Philippines and caused massive flooding.8 Leptospirosis was recognized as the most urgent threat to health in the aftermath of these typhoons. Special clinics to treat the disease were set up in evacuation centers, and an estimated 1.3 million flood survivors were given chemoprophylaxis, the efficacy of which was presumed but not demonstrated. Intense exposure to leptospires has been documented in rice, sugar cane, and rubber plantation workers. Less frequently, leptospirosis is acquired by direct contact with the blood, urine, or tissues of infected animals. Epidemiologic patterns in the United States and UK have changed. Recreational exposure to freshwater (e.g., white water rafting, triathlons, sailing, water skiing) and animal contact at home are more common than occupational exposure as the chief sources of disease in industrialized areas other than slums. Measuring incidence by active surveillance confirms that leptospirosis is surprisingly common. Antibody positivity rates of 37% have been recorded in rural Belize, 23% in Vietnam, and 18% in inner city Baltimore, Maryland.13 More than 2527 human cases and 13 deaths were reported for the first 9 months of 1999 by the Ministry of Public Health in Thailand. Human leptospirosis is an important disease in China, Southeast Asia, India, Africa, and South and Central America. It is also of significance in eastern and southern Europe, Australia, and New Zealand. In the United States, the disease is primarily of veterinary importance, with only 50 to 150 human cases reported annually.
EPIDEMIOLOGY
NATURAL HISTORY, PATHOGENESIS, AND PATHOLOGY
Leptospirosis is caused by spirochetes of the genus Leptospira. This genus contains more than 35 species classified on the basis of comparative genomic analysis10,11 and more than 300 serovars based on diverse agglutinating lipopolysaccharide antigens. Leptospires colonize proximal renal tubules of mammalian hosts and are shed in the urine. They can survive for several months in the environment under moist conditions, particularly in the presence of warmth (above 22°C) and neutral pH (pH 6.2–8.0). These conditions occur all year round in the tropics but only during the summer and autumn months in temperate climates. Roughly 160 animal species harbor organisms, but rodents are a particularly
Infection may be asymptomatic, but 5% to 15% of cases are severe or fatal.1 Pathogenesis, particularly that of severe disease, remains poorly understood. Overall, severe pulmonary hemorrhage syndrome (SPHS) accompanied by refractory shock appears to be the most common cause of death in leptospirosis; oliguric renal failure without access to dialysis is also associated with fatal leptospirosis. It is unclear why renal failure predominates as the principal cause of death in some places, whereas pulmonary hemorrhage is the major cause in others, even where the most common infecting serovars are the same. There are only minor histopathologic changes in the kidneys and livers of patients with
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marked functional impairment of these organs. Patients who survive severe leptospirosis have complete recovery of hepatic and renal function, consistent with the lack of structural damage to these organs.
CLINICAL FEATURES The most common clinical features of leptospirosis are summarized in Table 79.1. Subclinical infection is common, and less than 10% of symptomatic infections result in severe, icteric illness. Even relatively virulent serovars, such as Copenhageni/ Icterohaemorrhagiae, lead more often to anicteric than to icteric disease. Old terms such as peapicker’s disease, swineherd’s disease, and canicola fever, which are linked to specific serotypes with distinct disease manifestations, are misleading and should be abandoned. The median incubation period is 10 days, with a range of 2 to 26 days. The duration of the incubation period has no prognostic significance. Once symptoms develop, they may or may not follow a biphasic course; after an initial febrile illness there is defervescence and symptomatic improvement followed by a second period of disease refractory to antibiotics. However, a clear demarcation between the first and second stages may not be observed in icteric leptospirosis and, in mild cases, the distinction can be unclear or the second stage may never occur. The diagnostic usefulness of a history of a biphasic illness has been overemphasized. HIV co-infection does not seem to affect the clinical presentation of leptospirosis in the few co-infected patients described thus far.
Anicteric Leptospirosis Symptoms and Signs Typically, the disease begins with the abrupt onset of intense headache, fever, chills, and myalgia. Fever often exceeds 40°C (103°F) and is preceded by rigors. Muscle pain can be excruciating and occurs most commonly in the thighs, calves, lumbosacral region, and abdomen. Abdominal wall pain accompanied by palpation tenderness can mimic an acute surgical abdomen. Nausea, vomiting, diarrhea, and sore throat are other frequent symptoms. Cough and chest pain figure prominently in reports of patients from Korea and China. TABLE 79.1 The Most Common Clinical Manifestations of 208 Leptospirosis Patients in Puerto Rico Symptoms (% of Cases)
Anicteric (106 Cases)
Icteric (102 Cases)
Fever Myalgia Headache Chills Sore throat Nausea Vomiting Eye pain Diarrhea Oliguria Cough Hemoptysis
100 97 82 84 72 71 65 54 23 20 15 5
99 97 95 90 87 81 75 38 30 30 32 14
Signs (% of Cases) Conjunctival infection Muscle tenderness Hepatomegaly Pulmonary findings Lymphadenopathy Petechiae, ecchymoses
100 70 60 11 35 4
98 79 60 36 12 29
Adapted from Alexander AD, Benenson AS, Byrne RJ, et al. Leptospirosis in Puerto Rico. Zoonoses Res 1963;2:152–227.
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Conjunctival suffusion is a helpful diagnostic clue that usually appears 2 or 3 days after the onset of fever and involves the bulbar conjunctiva. Pus and serous secretions are absent, and there is no matting of the eyelashes and eyelids. Mild suffusion can easily be overlooked. Less common and less distinctive signs include pharyngeal injection, splenomegaly, hepatomegaly, lymphadenopathy, and skin lesions. Within a week, most patients become asymptomatic. After several days of apparent recovery, the illness resumes in some individuals. Manifestations of the second stage are more variable and mild than those of the initial illness and usually last 2 to 4 days. Leptospires disappear from the blood, cerebrospinal fluid (CSF), and tissues but appear in the urine. Serum antibody titers rise—hence the term immune phase. Aseptic meningitis is the hallmark of this stage of leptospirosis but is not associated with mortality. Pleocytosis of the CSF can be demonstrated in 80% to 90% of all patients during the second week of illness, although only about 50% will have clinical signs and symptoms of meningitis. Meningeal signs can last several weeks but usually resolve within a day or two. Uveitis is a late manifestation of leptospirosis, generally seen 4 to 8 months after the illness has begun. The anterior uveal tract is most frequently affected, and pain, photophobia, and blurring of vision are the usual symptoms.
Laboratory Findings White blood cell count varies, but neutrophilia is usually present. Urinalysis may show proteinuria, pyuria, and microscopic hematuria. Enzyme markers of skeletal muscle damage, such as creatinine kinase and aldolase, are elevated in the sera of 50% of patients during the first week of illness. Chest radiographs from patients with pulmonary manifestations show a variety of abnormalities, but none is pathognomonic of leptospirosis. The most common finding is patchy, non-lobal, diffuse infiltrates.
Icteric Leptospirosis (Weil’s Disease) Weil’s disease refers to severe, life-threatening leptospirosis and is characterized by jaundice, renal dysfunction, hemorrhagic manifestations, refractory shock, and a high mortality rate. Although jaundice is the hallmark of severe leptospirosis, true liver failure does not occur. The degree of jaundice has no prognostic significance, but its presence or absence does—virtually all leptospirosis deaths occur in icteric patients but are usually related to other associated mechanisms (hemorrhage or oliguric renal failure). Icterus first appears between the fifth and ninth days of illness, reaches maximum intensity 4 or 5 days later, and continues for an average of 1 month. Hepatomegaly is found in the majority of patients; hepatic percussion tenderness is a reliable clinical marker of continuing disease activity. There is no residual liver dysfunction in survivors of Weil’s disease, consistent with the absence of structural damage. Bleeding is occasionally seen in anicteric cases but is most prevalent in severe disease. Purpura, petechiae, epistaxis, bleeding of the gums, and minor hemoptysis are the most common hemorrhagic manifestations; however, deaths occur from subarachnoid hemorrhage and exsanguination from gastrointestinal bleeding. Conjunctival hemorrhage is an extremely useful diagnostic finding and, when combined with scleral icterus and conjunctival suffusion, produces eye findings strongly suggestive of leptospirosis (Fig. 79.1). The frequency with which severe pulmonary hemorrhage complicates leptospirosis is variable but is a cardinal feature of some outbreaks. Life-threatening oliguric renal failure is a complication of icteric disease, although all forms of leptospirosis may be associated with non-oliguric kidney dysfunction. Oliguria or anuria usually develop during the second week of illness but may appear earlier. Complete anuria is a grave prognostic sign often seen in patients who present late in the course of illness with frank uremia and irreversible
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suffusion and severe myalgia with tenderness. In the context of a known outbreak of leptospirosis, individuals must be carefully assessed for signs of severe disease. The most important signs of severity are jaundice, severe thrombocytopenia, bleeding, pulmonary involvement, oliguria, hypomagnesemia and hypokalemia, and elevated serum creatinine.
Diagnosis
Fig. 79.1 Jaundice, hemorrhage, and conjunctival suffusion in acute leptospirosis.
disease. Because renal failure develops very quickly in leptospirosis, symptoms and signs of uremia are frequently encountered. Anorexia, vomiting, drowsiness, disorientation, and confusion are seen early and rapidly progress to convulsions, stupor, and coma in severe cases. Disturbances of consciousness in a patient with severe leptospirosis are usually caused by uremic encephalopathy, whereas in anicteric cases aseptic encephalitis is the usual cause. Renal function eventually returns to normal in survivors of Weil’s disease, although detectable abnormalities may persist for several months. Leptospirosis-associated SPHS is now recognized as a widespread public health problem with a case fatality rate of about 50%. This lethal complication of leptospirosis can occur either with or without jaundice and renal failure. Hemoptysis is the cardinal sign but may not be apparent until patients are intubated. Real-time polymerase chain reaction (PCR) has shown that leptospiremia is 10,000 or more bacteria per milliliter of blood in SPHS—the apparent critical threshold for severe outcomes such as SPHS and death.6
Laboratory Features of Weil’s Disease Hyperbilirubinemia results from increases in both conjugated (direct) and unconjugated (indirect) bilirubin, but elevations of the direct fraction predominate. Prolongations of the prothrombin time commonly occur but are easily corrected by the administration of vitamin K; modest elevations of serum alkaline phosphatase are typical. There is mild hepatocellular necrosis; greater than fivefold increases of transaminase (aminotransferase) levels are unusual. Jaundiced patients usually have leukocytosis in the range of 15,000 to 30,000 per mm3, and neutrophilia is constant. Anemia is common and multifactorial; blood loss and renal dysfunction contribute frequently, intravascular hemolysis less often. Mild thrombocytopenia often occurs, but decreases in platelet count sufficient to be associated with bleeding are exceptional. The specific gravity of the urine is high. Hypokalemia due to renal potassium wasting can occur, and hypomagnesemia has been reported.
PATIENT EVALUATION, DIAGNOSIS, AND DIFFERENTIAL DIAGNOSIS Patient Evaluation Patients who present with an undifferentiated febrile illness must be carefully evaluated for possible leptospirosis. A history of submersive water exposure or direct animal contact is essential to suspecting diagnosis. Key symptoms and signs are conjunctival
Most cases go undiagnosed because symptoms and signs are often non-specific and diagnostic confirmation is rarely available where most disease transmission occurs. Failure to diagnose leptospirosis is particularly unfortunate: severely ill patients often recover completely with prompt treatment, but delayed therapy is likely to result in a poor clinical outcome. Late disease can often be recognized by its typical clinical manifestations, but the presentation of early leptospirosis is usually non-specific and is therefore difficult to identify clinically. Leptospirosis has long been acknowledged to be a frequent cause of undifferentiated febrile illness in developing countries. Co-infection with diseases such as dengue, malaria, and scrub typhus has been reported and adds to the diagnostic confusion of tropical fevers. Laboratory diagnosis of leptospirosis remains problematic. The microscopic agglutination test is considered the serodiagnostic method of choice for leptospirosis, but its complexity limits its use to reference laboratories and requires paired acute and convalescent serum samples. Dilutions of patient sera are applied to a panel of live, pathogenic leptospires. The results are viewed under dark-field microscopy and expressed qualitatively as the proportion of organisms cleared from the field by agglutination. Inadequate quality controls of the live reference strain panels can lead to frequent false-negative results.7 A new generation of commercially available, rapid serodiagnostic kits that rely on whole Leptospira antigen preparations have been developed. Unfortunately, these assays seem to have unacceptably low sensitivities during acute-phase illness, and persistent antibody produces low specificity in regions of high endemic transmission. The need for practical, affordable diagnostic kits to be available in areas where leptospirosis is common cannot be overemphasized. PCR and urine antigen detection are research tools that would be of the greatest potential diagnostic value in patients who present early, before antibodies have reached detectable levels; these tests are not available for most affected populations. Isolation of leptospires from blood or CSF is possible during the first 10 days of clinical illness, but specialized media are necessary. Serially diluted urine provides the highest yield. Unfortunately, culture results are only known many weeks later—too late to benefit severely ill, hospitalized patients. Several attempts have been made to formulate diagnostic algorithms by assigning points to various clinical, epidemiologic, and laboratory parameters. The points are totaled and the score is then used to represent the likelihood that the patient in question has leptospirosis. An example is shown in Table 79.2. The usefulness of these scoring systems is limited by their complexity, by marked regional variability in the quality of available diagnostic tests, and by regional differences in the prevalent differential diagnoses that must be considered. However, these scoring systems are useful teaching tools and emphasize the important epidemiologic and clinical characteristics of leptospirosis.
Differential Diagnosis The typical leptospirosis patient has a history of water or animal contact, conjunctival suffusion, and severe myalgia. It is important to solicit these findings in both mild and severe cases of leptospirosis. Atypical or mild cases are often confused with other entities, but because of a low index of suspicion and the disease’s protean manifestations, the diagnosis is often missed, even in typical cases.
CHAPTER 79 Leptospirosis
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TABLE 79.2 Modified World Health Organization (WHO) Criteria for Diagnosis of Leptospirosis
BOX 79.2 Clinical Pearl
Part A Clinical signs and symptoms (score) • Fever >39.0°C • Conjunctival suffusion • Myalgias • Meningeal signs • Jaundice • Proteinuria
(2 (4 (4 (4 (1 (1
Kawasaki’s disease (mucocutaneous lymph node syndrome) must be differentiated from leptospirosis in children <5 years old with desquamation and involvement of the gallbladder and myocardium.
Part B Risk factors for exposure (score) • Heavy rainfall • Flooding • Animal contact
(5 points) (5 points) (1 point)
Part C Laboratory test results (score) • Positive IgM ELISA • MAT – single high titer • MAT fourfold rise in titer
(15 points) (15 points) (25 points)
points) points) points) points) point) point)
Interpretation: Presumptive leptospirosis if score ≥25 points. Possible leptospirosis if score between 20 and 25 points. ELISA, Enzyme-linked immunosorbent assay; IgM, immunoglobulin M; MAT, microscopic agglutination test.
BOX 79.1 Clinical Pearl Muscles of patients with leptospirosis can be exquisitely tender and painful to the touch, but palpation of painful muscles in patients with scrub typhus sometimes provides pain relief.
The most important differential diagnoses differ in mild and severe disease.
Anicteric Leptospirosis Acute undifferentiated febrile illness, fever of unknown origin, and aseptic meningitis are the most common clinical impressions in mild leptospirosis. Severe myalgia involving several different muscle groups, particularly the calves—not just the abdominal wall—suggests leptospirosis rather than appendicitis. Fever and vomiting are frequently misdiagnosed as gastroenteritis.
Weil’s Disease Viral hepatitis is a common misdiagnosis in patients with Weil’s disease. Leukocytosis, elevated serum bilirubin levels without marked transaminase elevations, and renal dysfunction are typical of leptospirosis but unusual in hepatitis. Marked leukocytosis and a negative blood film argue against malaria. Jaundice, severe renal dysfunction, and leukocytosis are atypical of typhoid fever. Differentiating leptospirosis from scrub typhus and Korean hemorrhagic fever (caused by Hantaan virus) in areas where these diseases co-exist is more difficult. Both are associated with animals, and both can cause conjunctival suffusion. Korean hemorrhagic fever is transmitted by infected rodent urine, and mixed infection with Leptospira interrogans and Hantaan virus has been reported. Liver disease is not usually a prominent manifestation of Korean hemorrhagic fever. Splenomegaly and generalized lymphadenopathy are characteristic of scrub typhus but not leptospirosis. Serum creatinine levels are usually normal, even in jaundiced patients with Orientia tsutsugamushi infection. The myalgia of leptospirosis is usually more severe than that of scrub typhus (Box 79.1).
Severe Pulmonary Hemorrhage Syndrome Leptospirosis with prominent hemorrhagic manifestations is easily misdiagnosed as dengue virus infection. A severe outbreak of leptospirosis with SPHS in Nicaragua was initially thought to be dengue.12
Childhood Leptospirosis This shares many features with adult disease; pulmonary hemorrhage occurs, and severe renal dysfunction is common. Distinct clinical features include hypotension, acalculous cholecystitis, pancreatitis, and abdominal causalgia (burning pain). Skin lesions may desquamate and become gangrenous (Box 79.2).
TREATMENT Placebo-controlled, double-blind trials have demonstrated that doxycycline benefits patients with early, mild leptospirosis and that intravenous penicillin helps adults with severe, late disease.14 The outcome of severe, pediatric leptospirosis is also improved by penicillin therapy.15 Antibiotics should therefore be given to all patients with leptospirosis, regardless of age or when in their disease course they are seen. Doxycycline is given at doses of 100 mg orally twice a day for 1 week. Patients who are vomiting or are seriously ill require parenteral therapy. Intravenous penicillin G is administered to adults as 1.5 million units every 6 hours for 1 week. Recent trials from Thailand indicate that treatment with ceftriaxone, cefotaxime, and doxycycline had equivalent efficacy to penicillin in patients with mild to moderately severe disease. However, it is not known whether these antibiotics are as effective as high-dose penicillin for treatment of the most severely ill individuals. Doxycycline and azithromycin had comparable efficacy as presumptive treatment of mildly ill patients found later to have leptospirosis, scrub typhus, or dual infections. There is controversy regarding the occurrence of a Jarisch– Herxheimer reaction in leptospirosis. If present, it is much less prominent in leptospirosis than in other spirochetal illnesses. The important practical consideration is that antibiotics should not be withheld because of the fear of a possible Jarisch–Herxheimer reaction. The management of pulmonary hemorrhage often requires prompt intubation and mechanical ventilation. SPHS patients have physiologic and pathologic evidence of acute respiratory distress syndrome, so ventilation using low tidal volumes and high postexpiratory end pressures should be provided; hemodialysis even in the absence of renal failure may be useful for the pulmonary hemorrhage syndrome.14 Respiratory support to maintain adequate tissue oxygenation is essential because in non-fatal cases complete recovery of pulmonary function can be achieved. Ensuring adequate renal perfusion prevents renal failure in the vast majority of oliguric individuals. Continuous hemofiltration has been shown to be more effective than peritoneal dialysis in treating infection-associated hypercatabolic renal failure. Peritoneal dialysis, however, may be the only option in resource-limited settings. Whichever method of dialysis is chosen, it must be started promptly—delays increase mortality.
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PREVENTION Doxycycline 200 mg taken once a week prevents infection by pathogenic leptospires.16 Widespread use of doxycycline prophylaxis is not indicated, but it can benefit those who are at high risk for a short time, such as military personnel and certain agricultural workers. Infection by leptospires confers only serovar-specific immunity; second attacks caused by different serovars can occur. The efficacy and safety of human leptospiral vaccines have yet to be conclusively demonstrated. Prevention of leptospirosis in the tropics is particularly difficult. The large animal reservoir of infection is impossible to eliminate, the occurrence of numerous serovars limits the usefulness of serovar-specific vaccine, and the wearing of protective clothing (e.g., rubber boots in rice fields) is both prohibitively expensive and impractical. Providing proper sanitation in urban slum communities would be the most effective control measure in this setting. REFERENCES
1. Costa F, Hagan JE, Calcagno J, et al. Global morbidity and mortality of leptospirosis: a systematic review. PLoS Negl Trop Dis. 2015;9(9):e0003898. 2. Inada R, Ido Y, Hoki R, et al. The Etiology, Mode of Infection, and Specific Therapy of Weil’s disease (Spirochaetosis Icterohaemorrhagica). J Exp Med 1916;23(3):377–402. 3. Agampodi S, Peacock SJ, Thevanesam V. The potential emergence of leptospirosis in Sri Lanka. Lancet Infect Dis 2009;9(9):524–6. 4. Bharti AR, Nally JE, Ricaldi JN, et al. Leptospirosis: a zoonotic disease of global importance. Lancet Infect Dis 2003;3(12):757–71. 5. Ko AI, Galvao Reis M, Dourado CMR, et al. Urban epidemic of severe leptospirosis in Brazil. Lancet 1999;354:820–5.
6. Vinetz JM, Glass GE, Flexner CE, et al. Sporadic urban leptospirosis. Ann Intern Med 1996;125:794–8. 7. Agampodi SB, Peacock SJ, Thevanesam V, et al. Leptospirosis outbreak in Sri Lanka in 2008: lessons for assessing the global burden of disease. Am J Trop Med Hyg 2008;85(3):471–8. 8. Matsushita N, Ng CFS, Kim Y, et al. The non-linear and lagged short-term relationship between rainfall and leptospirosis and the intermediate role of floods in the Philippines. PLoS Negl Trop Dis. 2018;12(4):e0006331. 9. Thaipadungpanit J, Wuthiekanun V, Chierakul W, et al. A dominant clone of Leptospira interrogans associated with an outbreak of human leptospirosis in Thailand. PLoS Negl Trop Dis. 2007;1(1):e56. 10. Thibeaux R, Iraola G, Ferres I, et al. Deciphering the unexplored Leptospira diversity from soils uncovers genomic evolution to virulence. Microb Genom 2018;4(1). 11. Fouts DE, Matthias MA, Adhikarla H, et al. What makes a bacterial species pathogenic?:comparative genomic analysis of the genus Leptospira. PLoS Negl Trop Dis. 2016;10(2):e0004403. 12. Zaki SR, Shieh W-J. Leptospirosis associated with outbreak of acute febrile illnesses and pulmonary haemorrhage, Nicaragua, 1995. Lancet 1996;347:535–6. 13. Childs JE, Schwartz BS, Ksiazek TG, et al. Risk factors associated with antibodies to leptospires in inner-city residents of Baltimore: a protective role for cats. Am J Public Health 1992;82(4):597–9. 14. Watt G, Padre LP, Tuazon ML, et al. Placebo-controlled trial of intravenous penicillin for severe and late leptospirosis. Lancet 1988;1(8583):433–5. 15. Takafuji ET, Kirkpatrick JW, Miller RN, et al. An efficacy trial of doxycycline chemoprophylaxis against leptospirosis. N Engl J Med 1984;310(8):497–500. 16. Andrade L, Cleto S, Seguro AC. Door-to-dialysis time and daily hemodialysis in patients with leptospirosis: impact on mortality. Clin J Am Soc Nephrol 2007;2(4):739–44.