Leptospirosis

Leptospira magnified 200-fold with a dark-field microscope.

### Risk factors

Exposure to infected animals, especially their urine, or fresh water or damp soil contaminated with infectious urine

### Diagnostic method

Testing blood for antibodies against the bacterium or its DNA

### Differential diagnosis

Malaria, enteric fever, rickettsiosis, dengue

### Prevention

Personal protective equipment, hygiene measures, doxycycline

### Prognosis

Risk of death ~7.5%

**Leptospirosis** is a blood infection caused by the bacteria Leptospira that can infect humans, dogs, rodents and many other wild and domesticated animals. Signs and symptoms can range from none to mild (headaches, muscle pains, and fevers) to severe (bleeding in the lungs or meningitis). Weil's disease, the acute, severe form of leptospirosis, causes the infected individual to become jaundiced (skin and eyes become yellow), develop kidney failure, and bleed. Bleeding from the lungs associated with leptospirosis is known as **severe pulmonary haemorrhage syndrome**.

More than ten genetic types of *Leptospira* cause disease in humans. Both wild and domestic animals can spread the disease, most commonly rodents. The bacteria are spread to humans through animal urine, or water or soil contaminated with animal urine, coming into contact with the eyes, mouth, nose or breaks in the skin. In developing countries, the disease occurs most commonly in farmers and low-income people who live in areas with poor sanitation. In developed countries, it occurs during heavy downpours and is a risk to sewage workers and those involved in outdoor activities in warm and wet areas. Diagnosis is typically by testing for antibodies against the bacteria or finding bacterial DNA in the blood.

Efforts to prevent the disease include protective equipment to block contact when working with potentially infected animals, washing after contact, and reducing rodents in areas where people live and work. The antibiotic doxycycline is effective in preventing leptospirosis infection. Human vaccines are of limited usefulness; vaccines for other animals are more widely available. Treatment when infected is with antibiotics such as doxycycline, penicillin, or ceftriaxone. The overall risk of death is 5–10%. However, when the lungs are involved, the risk of death increases to the range of 50–70%.

It is estimated that one million severe cases of leptospirosis in humans occur every year, causing about 58,900 deaths. The disease is most common in tropical areas of the world but may occur anywhere. Outbreaks may arise after heavy rainfall. The disease was first described by physician Adolf Weil in 1886 in Germany. Infected animals may have no, mild or severe symptoms. These may vary by the type of animal. In some animals *Leptospira* live in the reproductive tract, leading to transmission during mating.

## Signs and Symptoms

Schematic depiction of the symptoms and signs of leptospirosis

The symptoms of leptospirosis usually appe e to two weeks after infection, but the incubation period can be as long as anth. The illness is biphasic in a majority of symptomatic cases. Symptoms of the first phase (acute or leptospiremic phase) last five to seven days. In the second phase (immune phase), the symptoms resolve as antibodies against the bacteria are produced. Additional symptoms develop in the second phase. The phases of illness may not be distinct, especially in patients with severe illness. 90% of those infected experience mild symptoms while 10% experience severe leptospirosis.

Leptospiral infection in humans causes a range of symptoms, though some infected persons may have none. The disease begins suddenly with fever accompanied by chills, intense headache, severe muscle aches and abdominal pain. A headache brought on by leptospirosis causes throbbing pain and is characteristically located at the head's bilateral temporal or frontal regions. The person could also have pain behind the eyes and a sensitivity to light. Muscle pain usually involves the calf muscle and the lower back. The most characteristic feature of leptospirosis is the conjunctival suffusion (conjunctivitis without exudate) which is rarely found in other febrile illnesses. Other characteristic findings on the eye include subconjunctival bleeding and jaundice. A rash is rarely found in leptospirosis. When one is found alternative diagnoses such as dengue fever and chikungunya fever should be considered. Dry cough is observed in 20–57% of people with leptospirosis. Thus, this clinical feature can mislead a doctor to diagnose the disease as a respiratory illness. Additionally, gastrointestinal symptoms such as nausea, vomiting, abdominal pain, and diarrhoea frequently occur. Vomiting and diarrhea may contribute to dehydration. The abdominal pain can be due to acalculous cholecystitis or inflammation of the pancreas. Rarely, the lymph nodes, liver, and spleen may be enlarged and palpable.

There will be a resolution of symptoms for one to three days. The immune phase starts after this and can last from four to 30 days and can be anything from brain to kidney complications. The hallmark of the second phase is inflammation of the membranes covering the brain. Signs and symptoms of meningitis include severe headache and neck stiffness. Kidney involvement is associated with reduced or absent urine output.

The classic form of severe leptospirosis, known as Weil's disease, is characterised by liver damage (causing jaundice), kidney failure, and bleeding, which happens in 5–10% of those infected. Lung and brain damage can also occur. For those with signs of inflammation of membranes covering the brain and the brain itself, altered level of consciousness can happen. A variety of neurological problems such as paralysis of half of the body, complete inflammation of a whole horizontal section of spinal cord, and muscle weakness due to immune damage of the nerves supplying the muscles are the complications. Signs of bleeding such as non-traumatic bruises at 1 mm (0.039 in), non-traumatic bruises more than 1 cm (0.39 in), nose bleeding, blackish stools due to bleeding in the stomach, vomiting blood and bleeding from the lungs can also be found. Prolongation of prothrombin time in coagulation testing is associated with severe bleeding manifestation. However, low platelet count is not associated with severe bleeding. Pulmonary haemorrhage is alveolar haemorrhage (bleeding into the alveoli of the lungs) leading to massive coughing up of blood, and causing acute respiratory distress syndrome, where the risk of death is more than 50%. Rarely, inflammation of the heart muscles, inflammation of membranes covering the heart, abnormalities in the heart's natural pacemaker and abnormal heart rhythms may occur.

## Cause

### Bacteria

Scanning electron micrograph of a number of Leptospira sp. bacteria atop a 0.1 µm polycarbonate filter

Leptospirosis is caused by spirochaete bacteria that belong to the genus *Leptospira*, which are aerobic, right-handed helical, and 6–20 micrometers long. Like Gram-negative bacteria,

*Leptospira* have an outer membrane studded with lipopolysaccharide (LPS) on the surface, an inner membrane and a layer of peptidoglycan cell wall. However, unlike Gram-negative bacteria, the peptidoglycan layer in *Leptospira* lies closer to the inner than the outer membrane. This results in a fluid outer membrane loosely associated with the cell wall. In addition, *Leptospira* have a flagellum located in the periplasm, associated with corkscrew style movement. Chemoreceptors at the poles of the bacteria sense various substrates and change the direction of its movement. The bacteria are traditionally visualised using dark-field microscopy without staining.

A total of 66 species of *Leptospira* has been identified. Based on their genomic sequence, they are divided into two clades and four subclades: P1, P2, S1, and S2. The 19 members of the P1 subclade include the 8 species that can cause severe disease in humans: *L. alexanderi*, *L. borgpetersenii*, *L. interrogans*, *L. kirschneri*, *L. mayottensis*, *L. noguchii*, *L. santarosai*, and *L. weilii.* The P2 clade comprises 21 species that may cause mild disease in humans. The remaining 26 species comprise the S1 and S2 subclades, which include "saprophytes" known to consume decaying matter (saprotrophic nutrition). Pathogenic *Leptospira* do not multiply in the environment. *Leptospira* require high humidity for survival but can remain alive in environments such as stagnant water or contaminated soil. The bacterium can be killed by temperatures of 50 °C (122 °F) and can be inactivated by 70% ethanol, 1% sodium hypochlorite, formaldehyde, detergents and acids.

*Leptospira* are also classified based on their serovar. The diverse sugar composition of the lipopolysaccharide on the surface of the bacteria is responsible for the antigenic difference between serovars. About 300 pathogenic serovars of *Leptospira* are recognised. Antigenically related serovars (belonging to the same serogroup) may belong to different species because of horizontal gene transfer of LPS biosynthetic genes between different species. Currently, the cross agglutination absorption test and DNA-DNA hybridisation are used to classify *Leptospira* species, but are time consuming. Therefore, total genomic sequencing could potentially replace these two methods as the new gold standard of classifying *Leptospira* species.

### Transmission

The bacteria can be found in ponds, rivers, puddles, sewers, agricultural fields and moist soil. Pathogenic *Leptospira* have been found in the form of aquatic biofilms, which may aid survival in the environment.

The number of cases of leptospirosis is directly related to the amount of rainfall, making the disease seasonal in temperate climates and year-round in tropical climates. The risk of contracting leptospirosis depends upon the risk of disease carriage in the community and the frequency of exposure. In rural areas, farming and animal husbandry are the major risk factors for contracting leptospirosis. Poor housing and inadequate sanitation also increase the risk of infection. In tropical and semi-tropical areas, the disease often becomes widespread after heavy rains or after flooding.

*Leptospira* are found mostly in mammals. However, reptiles and cold-blooded animals such as frogs, snakes, turtles, and toads have been shown to have the infection. Whether there are reservoirs of human infection is unknown. Rats, mice, and moles are important primary hosts, but other mammals including dogs, deer, rabbits, hedgehogs, cows, sheep, swine, raccoons, opossums, and skunks can also carry the disease. In Africa, a number of wildlife hosts have been identified as carriers, including the banded mongoose, Egyptian fox, Rusa deer, and shrews. There are various mechanisms whereby animals can infect each other. Dogs may lick the urine of an infected animal off the grass or soil, or drink from an infected puddle. House-bound domestic dogs have contracted leptospirosis, apparently from licking the urine of infected mice in the house. Leptospirosis can also be transmitted via the semen of infected animals. The duration of bacteria being consistently present in animal urine may persist for years.

Humans are the accidental host of *Leptospira*. Humans become infected through contact with water or moist soil that contains urine from infected animals. The bacteria enter through cuts, abrasions, ingestion of contaminated food, or contact with mucous membrane of the body (e.g. mouth, nose, and eyes). Occupations at risk of contracting leptospirosis include farmers, fishermen, garbage collectors and sewage workers. The disease is also related to adventure tourism and recreational activities. It is common among water-sports enthusiasts in specific areas, including triathlons, water rafting, canoeing and swimming, as prolonged immersion in water promotes the entry of the bacteria. However, *Leptospira* are unlikely to penetrate intact skin. The disease is not known to spread between humans, and bacterial dissemination in recovery period is extremely rare in humans. Once humans are infected, bacterial shedding from the kidneys usually persists for up to 60 days.

Rarely, leptospirosis can be transmitted through an organ transplant. Infection through the placenta during pregnancy is also possible. It can cause miscarriage and infection in infants. Leptospirosis transmission through eating raw meat of wildlife animals have also been reported (e.g. psychiatric patients with allotriophagy).

## Prevention

Rates of leptospirosis can be reduced by improving housing, infrastructure, and sanitation standards. Rodent abatement efforts and flood mitigation projects can also help to prevent it. Proper use of personal protective equipment (PPE) by people who have a high risk of occupational exposure can prevent leptospirosis infections in most cases.

There is no human vaccine suitable for worldwide use. Only a few countries such as Cuba, Japan, France, and China have approved the use of inactivated vaccines with limited protective effects. Side effects such as nausea, injection site redness and swelling have been reported after the vaccine was injected. Since the immunity induced by one *Leptospira*serovar is only protective against that specific one, trivalent vaccines have been developed. However, they do not confer long-lasting immunity to humans or animals. Vaccines for other animals are more widely available.

Doxycycline is given once a week as a prophylaxis and is effective in reducing the rate of leptospirosis infections amongst high-risk individuals in flood-prone areas. In one study, it reduced the number of leptospirosis cases in military personnel undergoing exercises in the jungles. In another study, it reduced the number of symptomatic cases after exposure to leptospirosis under heavy rainfall in endemic areas.

## Treatments

Most leptospiral cases resolve spontaneously. Early initiation of antibiotics may prevent the progression to severe disease. Therefore, in resource-limited settings, antibiotics can be started once leptospirosis is suspected after history taking and examination.

For mild leptospirosis, antibiotic recommendations such as doxycycline, azithromycin, ampicillin and amoxicillin were based solely on *in vitro* testing. In 2001, the WHO recommended oral doxycycline (2 mg/kg up to 100 mg every 12 hours) for five to seven days for those with mild leptospirosis. Tetracycline, ampicillin, and amoxicillin can also be used in such cases. However, in areas where rickettsia and leptospirosis are both endemic, azithromycin and doxycycline are the drugs of choice.

Based on a 1988 study, intravenous (IV) benzylpenicillin (also known as penicillin G) is recommended for the treatment of severe leptospirosis. Intravenous benzylpenicillin (30 mg/kg up to 1.2 g every six hours) is used for five to seven days. Amoxicillin, ampicillin, and erythromycin may also be used for severe cases. Ceftriaxone (1 g IV every 24 hours for seven days) is also effective for severe leptospirosis. Cefotaxime (1 g IV every six hours for seven days) and doxycycline (200 mg initially followed by 100 mg IV every 12 hours for seven days) are equally effective as benzylpenicillin (1.5 million units IV every six hours for seven days). Therefore, there is no evidence on differences in death reduction when benzylpenicillin is compared with ceftriaxone or cefotaxime. Another study conducted in 2007 also showed no difference in efficacy between doxycycline (200 mg initially followed by 100 mg orally every 12 hours for seven days) or azithromycin (2 g on day one followed by 1 g daily for two more days) for suspected leptospirosis. There was no difference in the resolution of fever and azithromycin is better tolerated than doxycycline.

Outpatients are given doxycycline or azithromycin. Doxycycline can shorten the duration of leptospirosis by two days, improve symptoms, and prevent the shedding of organisms in their urine. Azithromycin and amoxicillin are given to pregnant women and children. Rarely, a Jarisch–Herxheimer reaction can develop in the first few hours after antibiotic administration. However, according to a meta-analysis done in 2012, the benefit of antibiotics in the treatment of leptospirosis was unclear although the use of antibiotics may reduce the duration of illness by two to four days. Another meta-analysis done in 2013 reached a similar conclusion.

For those with severe leptospirosis, including potassium wasting with high kidney output dysfunction, intravenous hydration and potassium supplements can prevent dehydration and hypokalemia. When acute kidney failure occurs, early initiation of haemodialysis or peritoneal dialysis can help to improve survival. For those with respiratory failure, tracheal intubation with low tidal volume improves survival rates.

Corticosteroids have been proposed to suppress inflammation in leptospirosis because *Leptospira* infection can induce the release of chemical signals which promote inflammation of blood vessels in the lungs. However, there is insufficient evidence to determine whether the use of corticosteroids is beneficial.

## Prognosis

The overall risk of death for leptospirosis is 5–10%. For those with jaundice, the case fatality can increase up to 15%. For those infected who present with confusion and neurological signs, there is a high risk of death. Other factors that increase the risk of death include reduced urine output, age more than 36 years, and respiratory failure. With proper care, most of those infected will recover completely. Those with acute kidney failure may develop persistent mild kidney impairment after they recover. In those with severe lung involvement, the risk of death is 50–70%. Thirty percent of people with acute leptospirosis complained of long-lasting symptoms characterised by weakness, muscle pain, and headaches.

### Eye complications

Eye problems can occur in 10% of those who recovered from leptospirosis in the range from two weeks to a few years post-infection. Most commonly, eye complications can occur at six months after the infection. This is due to the immune privilege of the eye which protects it from immunological damage during the initial phase of leptospiral infection. These complications can range from mild anterior uveitis to severe panuveitis (which involves all three vascular layers of the eye). The uveitis is more commonly happen in young to middle-aged males and those working in agricultural farming. In up to 80% of those infected, *Leptospira* DNA can be found in the aqueous humour of the eye. Eye problems usually have a good prognosis following treatment or they are self-limiting. In anterior uveitis, only topical steroids and mydriatics (an agent that causes dilation of the pupil) are needed while in panuveitis, it requires periocular corticosteroids. Leptospiral uveitis is characterised by hypopyon, rapidly maturing cataract, free floating vitreous membranes, disc hyperemia and retinal vasculitis.

## History

The disease was first described by Adolf Weil in 1886 when he reported an "acute infectious disease with enlargement of spleen, jaundice, and nephritis." Before Weil's description, the disease was known as "rice field jaundice" in ancient Chinese text, "autumn fever", "seven-day fever", and "*nanukayami* fever" in Japan; in Europe and Australia, the disease was associated with certain occupations and given names such as "cane-cutter's disease", "swine-herd's disease", and "*Schlammfieber*" (mud fever). It has been known historically as "black jaundice", or "dairy farm fever" in New Zealand. Leptospirosis was postulated as the cause of an epidemic among Native Americans along the coast of what is now New England during 1616–19. The disease was most likely brought to the New World by Europeans.

*Leptospira* was first observed in 1907 in a post mortem kidney tissue slice by Arthur Stimson using silver deposition staining technique. He called the organism *Spirocheta interrogans* because the bacteria resembled a question mark. In 1908, a Japanese research group led by Ryukichi Inada and Yutaka Ito first identified this bacterium as the causative agent of leptospirosis and noted its presence in rats in 1916. Japanese coal mine workers frequently contracted leptospirosis. In Japan, the organism was named *Spirocheta icterohaemorrhagiae*. The Japanese group also experimented with the first leptospiral immunisation studies in guinea pigs. They demonstrated that by injecting the infected guinea pigs with sera from convalescent humans or goats, passive immunity could be provided to the guinea pigs. In 1917, the Japanese group discovered rats as the carriers of leptospirosis. Unaware of the Japanese group's work, two German groups independently and almost simultaneously published their first demonstration of transmitting leptospiral infection in guinea pigs in October 1915. They named the organism *Spirochaeta nodosa* and *Spirochaeta Icterogenes* respectively.

Leptospirosis was subsequently recognised as a disease of all mammalian species. In 1933, Dutch workers reported the isolation of *Leptospira canicola* which specifically infects dogs. In 1940, the strain that specifically infects cattle was first reported in Russia. In 1942, soldiers at Fort Bragg, North Carolina, were recorded to have an infectious disease which caused a rash over their shinbones. This disease was later known to be caused by leptospirosis. By the 1950s, the number of serovars that infected various mammals had expanded significantly. In the 1980s, leptospirosis was recognised as a veterinary disease of major economic importance.

In 1982, there were about 200 serovars of *Leptospira* available for classification. The International Committee on Systematic Bacteriology's subcommittee on taxonomy of *Leptospira* proposed classifying these serovars into two big groups: *L. interrogans* containing pathogenic serovars and *L. biflexa* containing saprophytic serovars. In 1979, the leptospiral family of *Leptospiraceae* was proposed. In the same year, *Leptospira illini* was reclassified as the new genus *Leptonema*. In 2002, "Lepthangamushi syndrome" was coined to describe a series of overlapping symptoms of leptospirosis with Hantavirus hemorrhagic fever with renal syndrome, and scrub typhus caused by *Orientia tsutsugamushi*. In 2005, *Leptospira parva* was classified as *Turneriella*. With DNA-DNA hybridisation technology, *L. interrogans* was divided into seven species. More *Leptospira* species have been discovered since then. The WHO established the Leptospirosis Burden Epidemiology Reference Group (LERG) to review the latest disease epidemiological data of leptospirosis, formulate a disease transmission model, and identify gaps in knowledge and research. The first meeting was convened in 2009. In 2011, LERG estimated that the global yearly rate of leptospirosis is five to 14 cases per 100,000 population.

## Other Animals

Infected animals can have no, mild, or severe symptoms; the presenting symptoms may vary by the type of animal. In some animals the bacteria live in the reproductive tract, leading to transmission during mating.

Animals also present with similar clinical features when compared to humans. Clinical signs can appear in 5–15 days in dogs. The incubation period can be prolonged in cats. Leptospirosis can cause abortions after 2–12 weeks in cattle, and 1–4 weeks of infection in pigs. The illness tends to be milder in reservoir hosts. The most commonly affected organs are the kidneys, liver, and reproductive system, but other organs can be affected. In dogs, the acute clinical signs include fever, loss of appetite, shivering, muscle pain, weakness, and urinary symptoms. Vomiting, diarrhea, and abdominal pain may also present. Petechiae and ecchymoses may be seen on mucous membranes. Bleeding from the lungs may also be seen in dogs. In chronic presentations, the affected dog may have no symptoms. In animals that have died of leptospirosis, their kidneys may be swollen with grey and white spots, mottling, or scarring. Their liver may be enlarged with areas of cell death. Petechiae and ecchymoses may be found in various organs. Inflammation of the blood vessels, inflammation of the heart, meningeal layers covering the brain and spinal cord, and uveitis are also possible. Equine recurrent uveitis (ERU) is the most common disease associated with *Leptospira* infection in horses in North America and may lead to blindness. ERU is an autoimmune disease involving antibodies against *Leptospira* proteins LruA and LruB cross-reacting with eye proteins. Live *Leptospira* can be recovered from the aqueous or vitreous fluid of many horses with *Leptospira*-associated ERU. Risk of death or disability in infected animals varies depending upon the species and age of the animals. In adult pigs and cattle, reproductive signs are the most common signs of leptospirosis. Up to 40% of cows may have a spontaneous abortion. Younger animals usually develop more severe disease. About 80% of dogs can survive with treatment, but the survival rate is reduced if the lungs are involved.

ELISA and microscopic agglutination tests are most commonly used to diagnose leptospirosis in animals. The bacteria can be detected in blood, urine, and milk or liver, kidney, or other tissue samples by using immunofluorescence or immunohistochemical or polymerase chain reaction techniques. Silver staining or immunogold silver staining is used to detect *Leptospira* in tissue sections. The organisms stain poorly with Gram stain. Dark-field microscopy can be used to detect *Leptospira* in body fluids, but it is neither sensitive nor specific in detecting the organism. A positive culture for leptospirosis is definitive, but the availability is limited, and culture results can take 13–26 weeks for a result, limiting its utility. Paired acute and convalescent samples are preferred for serological diagnosis of leptospirosis in animals. A positive serological sample from an aborted fetus is also diagnostic of leptospirosis.

Various antibiotics such as doxycycline, penicillins, dihydrostreptomycin, and streptomycin have been used to treat leptospirosis in animals. Fluid therapy, blood transfusion, and respiratory support may be required in severe disease. For horses with ERU, the primary treatment is with anti-inflammatory drugs.

Leptospirosis vaccines are available for animals such as pigs, dogs, cattle, sheep, and goats. Vaccines for cattle usually contain *Leptospira* serovar Hardjo and Pomona, for dogs, the vaccines usually contain serovar Icterohaemorrhagiae and Canicola. Vaccines containing multiple serovars do not work for cattle as well as vaccines containing a single serovar, yet the multivalent vaccines continue to be sold. Isolation of infected animals and prophylactic antibiotics are also effective in preventing leptospirosis transmission between animals. Environmental control and sanitation also reduce transmission rates.