Leptospirosis

• 1. Introduction

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  Leptospirosis, a blood infection that can kill, traces the first name of its bacterium to a punctuation mark. In 1907, Arthur Stimson examined a slice of kidney tissue taken at a post mortem. Under his microscope he saw a thin organism curled like a question mark, so he called it Spirocheta interrogans. The genus is now called Leptospira, and its members cause a blood infection that reaches humans, dogs, rodents and many other animals.

  Most people who catch it feel little more than headaches, muscle pains and fever. A few turn yellow, suffer kidney failure and begin to bleed. This documentary asks how a bacterium that lives quietly in animal kidneys becomes dangerous to people who only meet it by accident. It asks why rain and floods bring outbreaks, why doctors so often miss the disease, and who first learned to recognise it.

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• 2. A Slim Spiral

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  Measuring between 6 and 20 micrometers, Leptospira is a right-handed helix that lives on oxygen. Its architecture resembles that of Gram-negative bacteria, with lipopolysaccharide studding the outer surface and a peptidoglycan layer in the wall. The twist is placement. In Leptospira the peptidoglycan sits closer to the inner membrane, so the outer membrane hangs loosely around the cell and stays fluid.

  Movement is corkscrew-style. A flagellum runs inside the periplasm, and chemoreceptors at the two poles sense chemicals and steer the direction of travel. Because the bacteria stain so poorly, they are traditionally viewed unstained under dark-field microscopy.

  Genome sequencing sorts the 66 identified species into two clades and four subclades, named P1, P2, S1 and S2. The 19 members of P1 include eight species that can cause severe disease in people. Those are L. alexanderi, L. borgpetersenii, L. interrogans, L. kirschneri, L. mayottensis, L. noguchii, L. santarosai and L. weilii. The 21 species of P2 may cause mild disease. The remaining 26, in S1 and S2, are saprophytes that feed on decaying matter.

  About 300 pathogenic serovars are recognised. The mix of sugars on the lipopolysaccharide makes one serovar different from another. Oddly, serovars that are antigenically related can belong to different species, because the genes for building that sugar coat have moved sideways between species. The current sorting methods, cross-agglutination absorption and DNA-DNA hybridisation, are slow. Total genome sequencing could become the new gold standard.

  Outside a host, the pathogenic species do not multiply. They need high humidity to stay alive, though stagnant water and contaminated soil can keep them going. A temperature of 50 degrees Celsius kills them, and 70% ethanol, 1% sodium hypochlorite, formaldehyde, detergents and acids inactivate them. The saprophytes can live on decay, but the pathogens depend on kidneys, and the commonest kidneys belong to rodents.

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• 3. Accidental Hosts

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  Rats, mice and moles are the main carriers of Leptospira. Once an animal swallows the bacteria, they travel in the blood and slip out through the capillaries of the kidneys. There they colonise the lining of the proximal convoluted tubule and spill into the urine without pause. The animal barely notices. Biologists call this a commensal relationship, and they call the animal a reservoir host. The bacteria can be present in that urine consistently and may persist for years.

  The list of other carriers is long. It includes dogs, deer, rabbits, hedgehogs, cattle, sheep, swine, raccoons, opossums and skunks. Even the cold-blooded frogs, snakes, turtles and toads have tested positive. In Africa, researchers have identified the banded mongoose, the Egyptian fox, the Rusa deer and shrews as carriers.

  Dogs pick the bacteria up by licking urine off grass or soil, or by drinking from an infected puddle. House-bound dogs have also caught it, apparently from licking the urine of infected mice indoors. In some species the bacteria live in the reproductive tract, so mating spreads them, and semen from infected animals can carry them.

  Farmers, fishermen, garbage collectors and sewage workers face occupational risk. Humans are accidental hosts, infected through water or moist soil fouled by animal urine and feces. The bacteria enter through cuts and abrasions, through contaminated food, or across the mucous membranes of the mouth, nose and eyes. Intact skin is unlikely to let them through, which is why long immersion matters. The disease also follows recreation, from triathlons and rafting to canoeing and swimming in affected areas.

  The disease is not known to spread from person to person. Even so, bacterial shedding from the kidneys usually continues for up to 60 days after a person is infected. Rare routes exist. An organ transplant can carry the infection, and so can the placenta during pregnancy, which can cause miscarriage or infection in infants. Eating the raw meat of wild animals has also been reported as a route, in psychiatric patients with allotriophagy, a craving for unusual things to eat.

  In horses, the harm arrives as an eye disease. Equine recurrent uveitis is the most common Leptospira-linked illness of horses in North America and may lead to blindness. It is an autoimmune disease in which antibodies against the Leptospira proteins LruA and LruB cross-react with proteins of the eye. People can suffer eye trouble too, often months after they have recovered.

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• 4. Rain and Floods

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  In Brazil, India and the Philippines, outbreaks often follow heavy rainfall and flooding. The pattern is general. Case numbers rise and fall with the amount of rain, so the disease is seasonal in temperate climates and year-round in the tropics. Warmth and humidity suit the bacteria, which turn up in ponds, rivers, puddles, sewers, farm fields and moist soil. Pathogenic strains have even been found living as aquatic biofilms, which may help them last.

  Standing water is only part of the story. Growing evidence suggests Leptospira can persist in soil and freshwater for long stretches, with temperature, pH and nutrient supply governing how well it survives. That widens the window of exposure. A person can be infected with no recent contact with an animal at all.

  Urban slums in the tropics carry much of the burden. Urbanisation and weak waste management let rodent populations grow, and rodents are the primary reservoirs. Poor housing and inadequate sanitation raise the risk, while in rural areas farming and animal husbandry are the major drivers. Dense cities with limited sanitation leave the urban poor in direct contact with contaminated floodwater. Climate change is linked to higher incidence, because extreme weather creates the conditions for outbreaks.

  An estimated one million severe cases occur each year, with about 58,900 deaths. The heaviest burden falls on tropical and subtropical regions, especially South and Southeast Asia, Latin America and parts of Africa. Measured in disability-adjusted life years, the disease costs 42 per 100,000 people per year, more than rabies or filariasis. It is classed as a neglected tropical disease.

  Antarctica is the only place untouched by leptospirosis. Everywhere else the true toll is probably higher than the records show, because many affected countries lack notification or do not make it mandatory. Doctors struggle to tell the disease apart from other illnesses, and laboratories able to confirm it are scarce. Low awareness among health workers deepens the undercount.

  In the United States, cases ran at 100 to 150 a year. In 1994 the disease stopped being nationally notifiable, except in 36 states and territories where it is prevalent, such as Hawaii, Texas, California and Puerto Rico. About half of the reported cases came from Puerto Rico. In January 2013, leptospirosis was reinstated as a nationally notifiable disease.

  Many of the world's poorest people are malnourished, and missing micronutrients may raise the risk of infection and death from leptospirosis. Iron, calcium and magnesium are the nutrients researchers want to study next.

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• 5. Inside the Body

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  Through a cut, a scrape, or the soft lining of the eyes, nose or mouth, Leptospira reaches the bloodstream. Researchers still understand little about what happens next. The bacteria latch onto the endothelial cells lining blood vessels and onto the extracellular matrix, using their flagella to slide between cell layers. They also bind fibroblasts, macrophages and kidney epithelial cells. Surface proteins called Lig proteins, including LigB and LipL32, let them grab human proteins such as thrombin, fibrinogen and plasminogen. Every pathogenic species carries the genes for these proteins.

  Toll-like receptor 2 is the only sensor in human monocytes that responds to Leptospira lipopolysaccharide. The lipid A molecule goes unrecognised by TLR4, and that blind spot probably contributes to the disease.

  Interleukin 6, tumour necrosis factor alpha and interleukin 10 surge in severe cases. The resulting sepsis-like symptoms threaten life instead of helping to fight the infection. People with the HLA-DQ6 genotype face a greater risk of sepsis, possibly because of superantigen activation that damages organs. Macrophages can swallow Leptospira, yet the bacteria can survive and multiply inside them.

  Plasmin is a weapon the bacteria borrow. They convert the host's plasminogen into plasmin, which breaks down the extracellular matrix and fibrin clots and also degrades the complement proteins C3b and C5. Leptospira recruits Factor H, C4b-binding protein, factor H-like binding protein and vitronectin to block the membrane attack complex on its surface. Secreted proteases dismantle C3. Binding thrombin reduces fibrin formation, which raises the risk of bleeding. Sphingomyelinase and haemolysin attack red blood cells.

  Hepatocytes, the liver's working cells, take the brunt. Bacteria invade the spaces between them and trigger apoptosis, and damaged junctions let bile leak into the blood. Rising bilirubin then yellows the skin and eyes. In the lungs, petechiae or frank bleeding appear in the alveolar septum and between the alveoli. Toxins injure the kidneys, causing mild to severe failure or interstitial nephritis. The kidneys can heal fully or end with atrophy and fibrosis.

  Roughly 90% of infected people have mild symptoms, and 10% develop severe leptospirosis. Symptoms usually appear one to two weeks after infection, though incubation can last as long as a month. Onset is sudden, with fever and chills, intense headache, severe muscle aches and abdominal pain. The headache throbs at both temples or across the forehead. Some patients feel pain behind the eyes and sensitivity to light, and muscle pain centres on the calves and lower back.

  Conjunctival suffusion, redness of the eye without discharge, is the most characteristic sign and rarely appears in other fevers. A rash is unusual, and when one appears doctors should consider dengue or chikungunya. A dry cough affects 20-57% of patients and can mislead a doctor toward a respiratory diagnosis. Nausea, vomiting, diarrhoea and abdominal pain are frequent, and fluid loss can cause dehydration.

  In most symptomatic people the illness runs in two phases. The first, the leptospiremic phase, lasts five to seven days. Symptoms then ease for one to three days before the immune phase begins, which can last from four to 30 days as antibodies appear. The phases blur in severe illness. The hallmark of the second phase is inflammation of the membranes around the brain, bringing severe headache and neck stiffness. Kidney involvement shows up as reduced or absent urine.

  Weil's disease is the classic severe form, marked by liver damage with jaundice, kidney failure and bleeding. Lung and brain damage may follow. Neurological complications include paralysis of one side of the body, inflammation across a whole section of the spinal cord, and Guillain-Barré syndrome. Bleeding shows as petechiae, ecchymoses, nosebleeds, black stools from stomach bleeding, vomiting of blood and bleeding from the lungs. Pulmonary haemorrhage means bleeding into the alveoli, with massive coughing up of blood and acute respiratory distress syndrome.

  The risk of death across all cases is 5-10%, and it climbs to as much as 15% in people with jaundice. Confusion and neurological signs point to high danger, as do reduced urine output, age above 36 and respiratory failure. When the lungs are badly involved, the risk reaches 50-70%. With proper care most patients recover completely. Some who had acute kidney failure keep a mild, persistent impairment, and 30% of acute cases report lasting weakness, muscle pain and headaches.

  Eye trouble strikes 10% of survivors, anywhere from two weeks to a few years later and most often around six months. The eye's immune privilege shields it from damage during the first phase, which delays the harm. Uveitis ranges from mild anterior uveitis to severe panuveitis, which involves all three vascular layers of the eye. It is most common in young to middle-aged men and in agricultural workers. Leptospira DNA turns up in the aqueous humour of up to 80% of infected people. Anterior uveitis needs only topical steroids and mydriatics, while panuveitis calls for periocular corticosteroids.

  A prolonged prothrombin time on a coagulation test tracks with severe bleeding, yet a low platelet count does not.

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• 6. Proving the Diagnosis

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  The World Health Organization proposed Faine's criteria in 1982, with three parts: clinical findings, epidemiological factors, and laboratory and bacteriological data. The original laboratory part relied on culture and the microscopic agglutination test, both difficult. The modified criteria of 2004 added ELISA and slide agglutination tests, which are easier to perform. An amendment in 2012 added shortness of breath and coughing up blood, and in 2013 India recommended its own modification.

  The microscopic agglutination test, or MAT, is the reference test. Serial dilutions of the patient's serum are mixed with different serovars of Leptospira and examined under a dark-field microscope for clumping. The highest dilution at which 50% agglutination occurs is the result. Titres from 1:100 to 1:800 are diagnostic, and a fourfold or greater rise between two samples confirms the diagnosis. In the acute phase the test cannot pinpoint the serovar because of cross-reactivity, but in convalescence it is more specific. It needs a panel of live antigens and laborious work.

  Quicker screening looks for IgM antibodies by ELISA, typically with L. biflexa antigen. Its specificity depends on the antigen used and on antibodies left by earlier infections. Epstein-Barr virus infection, viral hepatitis and cytomegalovirus infection can all cause false positives. Dipsticks, latex tests and slide agglutination tests have been developed as other rapid screens.

  Polymerase chain reaction can amplify Leptospira DNA from serum, urine, aqueous humour, cerebrospinal fluid and autopsy specimens. It detects the bacteria faster than MAT in the first days, without waiting for antibodies to appear. It also still works after antibiotics have killed the bacteria.

  Routine blood work offers more clues. A complete blood count may show a high white cell count and low platelets. Blood urea and creatinine rise, while potassium and sodium fall because the disease increases potassium loss in urine. Urine cultures turn positive from the second week of illness until about 30 days after infection. In liver involvement, transaminases and direct bilirubin climb, and the Icterohaemorrhagiae serogroup is linked to jaundice. People with glucose-6-phosphate dehydrogenase deficiency are especially prone to acute haemolytic anaemia. Abnormal amylase and lipase point to pancreatitis. When meningitis is suspected, spinal fluid shows mostly lymphocytes at about 500 per cubic millimetre with normal glucose, consistent with aseptic meningitis. Chest X-rays can show diffuse opacities in the alveoli.

  In animals, silver staining and immunogold silver staining detect the bacteria in tissue sections, and the organisms stain poorly with Gram stain. A positive culture is definitive, but results can take 13-26 weeks to arrive.

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• 7. Treatment and Prevention

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  In 2001, the World Health Organization recommended oral doxycycline, 2 mg/kg up to 100 mg every 12 hours for five to seven days, for mild leptospirosis. Most cases resolve on their own, but early antibiotics may stop progression to severe disease. In places with few resources, treatment can begin once leptospirosis is suspected from history and examination. Tetracycline, ampicillin and amoxicillin are alternatives. Where rickettsia and leptospirosis both occur, azithromycin and doxycycline are the drugs of choice. Doxycycline is avoided in liver damage because it has been linked to hepatotoxicity. The recommendations for mild disease rest on in vitro testing alone.

  A 1988 study underpins the recommendation of intravenous benzylpenicillin, also called penicillin G, for severe cases. The dose is 30 mg/kg up to 1.2 g every six hours for five to seven days. Ceftriaxone at 1 g intravenously every 24 hours for seven days also works. Cefotaxime and intravenous doxycycline are equally effective as benzylpenicillin, and amoxicillin, ampicillin and erythromycin may also be used. No evidence shows a difference in deaths between benzylpenicillin and ceftriaxone or cefotaxime.

  A 2007 study compared oral doxycycline with azithromycin for suspected leptospirosis. Doxycycline was 200 mg followed by 100 mg every 12 hours for seven days. Azithromycin was 2 g on day one and 1 g daily for two more days. Fever resolved equally well, and azithromycin was better tolerated.

  Outpatients receive doxycycline or azithromycin. Doxycycline can shorten the illness by two days, improve symptoms and stop bacteria from shedding in urine. Pregnant women and children receive azithromycin or amoxicillin. A Jarisch-Herxheimer reaction can rarely develop in the first hours after antibiotics. Meta-analyses in 2012 and 2013 found the benefit of antibiotics unclear, though they may shorten illness by two to four days.

  Severe cases need more than antibiotics. Intravenous fluids and potassium supplements counter dehydration and low potassium in patients who waste potassium. When the kidneys fail, early haemodialysis or peritoneal dialysis improves survival. For respiratory failure, intubation with low tidal volume helps. Corticosteroids have been proposed because infection releases chemical signals that inflame blood vessels in the lungs, but evidence is too thin to say whether they help.

  Taken once a week, doxycycline lowers infection rates among high-risk people in flood-prone areas. In one study it reduced cases among military personnel exercising in jungles. In another it reduced symptomatic cases after exposure during heavy rain in endemic areas.

  Only a few countries, including Cuba, Japan, France and China, have approved human vaccines, and these inactivated vaccines protect only a little. Side effects include nausea, and redness and swelling where the shot was given. Immunity from one serovar protects against that serovar alone, so trivalent vaccines were developed. They do not give lasting immunity in humans or animals.

  Cattle vaccines usually contain the serovars Hardjo and Pomona, while dog vaccines usually contain Icterohaemorrhagiae and Canicola. Vaccinating livestock and domestic animals, especially dogs and cattle, protects the animals and stops spread to people. Multi-serovar vaccines work less well in cattle than single-serovar ones, yet they continue to be sold. Isolating infected animals and giving prophylactic antibiotics also limit spread between animals.

  Proper personal protective equipment prevents most infections among people with high occupational exposure. Rates also fall with better housing, infrastructure and sanitation, along with rodent abatement and flood mitigation. The One Health framework joins healthcare providers, veterinarians, environmental scientists and policymakers around surveillance, early diagnosis, rodent control, livestock vaccination and drainage that reduces standing water. For contaminated waterways and sewers, one disinfection method mixes effective microorganisms into bokashi mudballs.

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• 8. Names Before Science

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  In 1886 in Germany, the physician Adolf Weil reported an acute infectious disease with an enlarged spleen, jaundice and nephritis. Older names had tied the illness to places and trades. An ancient Chinese text calls it rice field jaundice. Japan knew autumn fever, seven-day fever and nanukayami fever. In Europe and Australia it was cane-cutter's disease, swine-herd's disease and Schlammfieber, meaning mud fever. Other names included black jaundice, and dairy farm fever in New Zealand.

  An epidemic among Native Americans along the coast of what is now New England in 1616-1619 has been postulated as leptospirosis. The disease was most likely brought to the New World by Europeans.

  Ryukichi Inada and Yutaka Ito led the Japanese research group that identified the bacterium as the cause in 1908. Japanese coal mine workers frequently contracted the disease. The group called the organism Spirocheta icterohaemorrhagiae, noted it in rats in 1916 and named rats as carriers in 1917. They also ran the first immunisation experiments in guinea pigs. Serum from convalescent humans or goats gave infected guinea pigs passive immunity.

  Two German groups, unaware of the Japanese work, almost simultaneously published their first demonstration of transmitting the infection to guinea pigs in October 1915. They named the organism Spirochaeta nodosa and Spirochaeta Icterogenes.

  In 1917, Hideyo Noguchi investigated whether American rats carried the jaundice-causing bacteria of Weil's disease, as European and Japanese rats did. He later suggested the genus name Leptospira, meaning slim spiral.

  Leptospirosis was then recognised as a disease of all mammalian species. In 1933, Dutch workers reported isolating Leptospira canicola, which infects dogs. In 1940, a strain specific to cattle was first reported in Russia. In 1942, soldiers at Fort Bragg, North Carolina, developed a rash over their shinbones that was later traced to leptospirosis. By the 1950s the serovars infecting mammals had multiplied, and in the 1980s the disease was recognised as a veterinary problem of major economic importance.

  By 1982 about 200 serovars were available for classification. A subcommittee of the International Committee on Systematic Bacteriology proposed two groups, L. interrogans for pathogenic serovars and L. biflexa for saprophytic ones. The family Leptospiraceae had been proposed in 1979, the year Leptospira illini was moved to the new genus Leptonema. In 2002, the term Lepthangamushi syndrome was coined for overlapping symptoms of leptospirosis, Hantavirus hemorrhagic fever with renal syndrome, and scrub typhus caused by Orientia tsutsugamushi. In 2005, Leptospira parva was reclassified as Turneriella. DNA-DNA hybridisation divided L. interrogans into seven species, and more have been found since.

  The World Health Organization created the Leptospirosis Burden Epidemiology Reference Group, known as LERG, to review the latest data, build a transmission model and identify gaps in research. Its first meeting convened in 2009. In 2011 it estimated the global yearly rate at five to 14 cases per 100,000 people.

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