Leptospirosis is a zoonotic contagious bacterial disease of animals affecting both humans and animals (Slack, 2010). Leptospirosis goes by many names like 7-day fever, harvest fever, field fever, canefield fever, mild fever, rat catcher's yellows, Fort Bragg fever, pretibial fever, rice field worker disease (Mosby's Medical Dictionary, 2015) etc. It has historically been known as black jaundice and in Japan it is called Nanukayami fever. It is caused by corkscrew-shaped spirochaete bacteria of the genus Leptospira (Slack, 2010). It causes various symptoms ranging from none to mild sickness such as headaches, muscle pains, and fevers and even severe with bleeding from the lungs or even meningitis (Bride et al., 2005). In case of Weil’s disease, the person becomes icteric having kidney failure and bleeding (Bride et al., 2005). Sometimes it causes a lot of bleeding into the lungs then it is known as severe pulmonary hemorrhage syndrome (Klopfleisch et al., 2011).
The disease was first described by physician Adolf Weil in 1886 in Germany when he reported an “acute infectious disease with enlargement of spleen, jaundice, and nephritis” (Stimson, 1907). Inada and Ito first identified Leptospira as the causative organism in 1908 (Inada and Ito, 1908; Inada et al., 1916). It is estimated that seven to ten million people are infected by leptospirosis annually. Almost one million cases of severe leptospirosis are observed every year claiming around 58,900 lives. Annual rates of infection vary from 0.02 per 100,000 in temperate climates to 10 to 100 per 100,000 in tropical climates. The disease is most common in tropical areas of the world but may occur anywhere. Outbreaks may occur in slums of the developing world. Weil’s disease and severe pulmonary haemorrhage syndrome result in death rates greater than 10% and 50%, respectively, even with treatment. As symptoms aren’t clear it’s may go unnoticed and thus cause serious problems. Leptospirosis is one of the most important diseases of public health importance.
Leptospirosis is caused by the spirochaete bacteria belonging to genus Leptospira of family Leptospiraceae under the class Spirochaetes. The genus Leptospira is divided into two species based mainly on their pathogenicity; L. interrogans consisting of pathogenic strains and L. biflexa consisting of non-pathogenic saprophyte strains. These species again consist of many serovars of Leptospira. The varied numbers of serovars are due to difference in agglutination reaction because of the surface lipopolysaccharide (LPS) of the bacteria. There are approximately more than 225 serovars for L. interrogans and more than 60 serovars for L. biflexa (Mohammed et al., 2011).
Leptospires are motile and aerobic, can’t survive dry environment, heat, acids and basics disinfectants but can sustain alkali pH up to pH 7.8 (Johnson and Faine, 1984). The bacteria can only be visualized using a dark field or phase contrast microscope. Though they are gram negative in nature, gram’s staining isn’t done for visualization of the bacteria. Silver impregnation staining, immunoperoxidase staining or immunofluorescence should be done to observe these bacteria (Terpstra, 2003). Being aerobic in nature, the bacteria can be cultured media enriched with vitamins like B1 and B12, long-chain fatty acids, and ammonium salts at 28-30°C. The fatty acids are the sole source of carbon and are utilized by β-oxidation (Evangelista and Coburn, 2010). The widely used media for culture of Leptospira is Ellinghausen–McCullough/ Johnson–Harris (EMJH) medium, which contains oleic acid, bovine serum albumin and polysorbate (Tween). Addition of 5-fluorouracil and antibiotics such as nulidixic acid or rifampicin makes the medium inhibitory for common laboratory contaminants (Evangelista and Coburn, 2010). The growth is often slow and thus the culture should be discarded only after 13 weeks. Very low amount of agar can be used to create a semi solid medium in which the bacteria grows and creates a highly turbid zone below the surface of the media. This is due to the optimum oxygen tension in that area and this is called as Dinger’s ring or Dinger’s disk (Mohammed et al., 2011).
The pathogenic strains can’t be differentiated from non-pathogenic ones on basis of their morphology. So to differentiate pathogenic and saprophytic strains some tests like pathogenicity to test animals, conversion to spherical forms in 1M NaCl, growth in presence of 8-azaguanine (225mg/l) and growth at 13°C are conducted. Saprophytes are able to grow at 13°C and in presence of 8-azaguanine and also are converted to spherical forms in presence of 1M NaCl which the pathogenic bacteria fails to do though L. interrogans Icterohaemorrhagiae can grow at 10°C. An ELISA test, in which the antigens of only pathogenic leptospires can react with the monoclonal F9-4 antibodies, can also be used (Terpstra, 2003).
Leptospirosis is mostly transmitted by the urine of an infected animal and is contagious as long as the urine is still moist as the bacteria can’t survive dryness for a longer period (Bharti et al., 2003). Although Leptospira have been detected in reptiles and birds, only mammals are reported to transmit the bacteria to humans and other animals. No report exist which shows the pathogen moving from reptiles or birds to humans. The disease infects a wide range of natural rodent and non-rodent as reservoir hosts which include foxes, rabbits etc. Rats, mice, and moles are important primary hosts but animals like dogs, cows, sheep etc are also responsible for disease transmission (James and Berger, 2006).
Pet dogs mainly contract leptospirosis, mostly from licking the urine of infected mice in the house or outside and thus act as source of infection to others (McKay, 2001). The type of habitats most likely to carry infective bacteria are moist and damp areas like riverbanks, muddy livestock rearing areas where there is a regular passage of wild or farm mammals (Kohn et al., 2010). The disease is, seasonal in temperate climates and year-round in tropical climates and directly with the amount of rainfall. Leptospirosis is also reported to be transmitted via the semen of the infected animals (Wasiński and Dutkiewicz, 2013). Humans can only become infected through contact with food, water, or soil that is contaminated with urine from these infected animals. This may happen by swallowing contaminated food or water or through skin contact. No human to human transmission is reported (Wasiński and Dutkiewicz, 2013).
It is an occupational hazard for many people who work outdoors or with animals, such as: farmers, mine workers, sewer workers, slaughterhouse workers, veterinarians and animal caretakers, fish workers, dairy farmers etc. where there is presence of water lodging conditions (James and Berger, 2006). The disease has also been associated with swimming, wading and rafting in contaminated lakes and rivers. As such, it is a recreational hazard for campers or those who participate in outdoor sports. Persons who actively participate in such activities in tropical or temperate climates are in a very high risk zone. In addition, incidence of leptospirosis infection among urban children appears to be increasing (Langston and Heuter, 2003).
Leptospirosis is an infectious disease caused by Leptospira interrogans complex, which has over 20 serogroups and more than 200 serovars. Rodents, domestic & wild animals form the reservoir of infection where domestic animals such as cattle, dogs, and pigs may act as carriers for several months (temporary carrier) while rodents usually remain carrier throughout their life (permanent carrier). Rodents are therefore considered as the major reservoir of infection. Leptospires are excreted in the urine of the animals and they affect man when he comes into contact with urine of infected animals, directly or indirectly (Shivakumar, 2008).
Leptospirosis can occur in both urban and rural areas. In urban areas of developing countries, a contaminated environment due to various factors such as overcrowding, inadequate drainage and sanitation facilities for man and animals, presence of stray animals, domestic rats, bandicoots, unhygienic slaughter houses and people walking bare foot contribute to the spread of the illness (Shivakumar, 2008). Persons of all ages and races are susceptible. In India, urban leptospirosis has been reported from Chennai and Mumbai while rural leptospirosis has been reported from Gujarat, Kerala and Andamans. Non-reporting of leptospirosis from other states of India does not mean that it is absent in those parts (Shivakumar, 2008).
Leptospirosis is reported to be of endemic importance from many States of India.
Andaman and Nicobar Islands
Andaman and Nicobar Islands are endemic for leptospirosis since early part of the 20th century. Outbreaks of Andaman Hemorrhagic fever (AHF) were reported since 1988. This was proved to be leptospirosis in 1994. 524 cases of AHF (leptospirosis) were reported from 1988-97 (Sehgal, 1998; Singh et al., 1999; Shivakumar, 2008).
The disease is endemic in south Gujarat since 1994. The endemic districts are Valsad, Navsari and Surat (Patel et al., 2006; Shivakumar, 2008).
Leptospirosis has been reported regularly since 1998. 2355 cases and 167 deaths were reported in 2005, mainly due to large outbreak during the post monsoon floods. The number of districts in Maharashtra reporting leptospirosis has expanded from two in 1998 to ten districts in 2005 (Karande et al., 2002, 2003; Shivakumar, 2008).
Leptospirosis is endemic in many areas of Kerala. Kolenchery is in the midlands of Kerala. In this area leptospirosis was rarely diagnosed before 1987. Since then an annual increase in incidence was observed (Kuriakose et al., 1997; Shivakumar, 2008).
Leptospirosis has been reported from Chennai since 1980’s. The leptospirosis laboratory at Institute of Microbiology, Madras Medical College was established in 1994 (Ratnam et al., 1983a, b; Chinari Pradeep et al., 1999; Shivakumar, 2008).
In a study of 33 icteric patients from Puducherry, 22 had altered sensorium and 20 had multi-organ failure and thrombocytopenia and 13 patients died (39.3%) (Dutta and Christopher, 2005; Shivakumar, 2008).
Leptospirosis outbreaks have been reported from 15 districts of Karnataka. The highest incidence of cases have occurred in Bangalore city, Uttara kannada, Shimoga, Bidar, Gulbarga, Udupi and dakshina kannada districts. During the year 2004, 152 cases and 11 deaths were reported and during 2005, 224 cases and 19 deaths were reported.
After the cyclone during the October-November 1999, 142 patients with febrile illness and hemorrhagic manifestations were evaluated. 28 (19.2%) had evidence of leptospirosis which was confirmed by MAT. 6 were positive by culture / PCR (Joint Publication by Office of WHO, Representative to India, New Delhi and Regional Medical Research Centre (ICMR), WHO Collaborating Centre for Diagnosis, Research, Reference and Training in Leptospirosis, 2006; Shivakumar, 2008).
Data from Andhra Pradesh, Uttar Pradesh, West Bengal and Delhi were analysed. Evaluation of acute febrile patients in Uttar Pradesh revealed that 7% had leptospirosis (25/ 346). 17 of the 25 patients had jaundice. In a study of 55 cases of leptospirosis in Hyderabad, 52 % had renal failure and jaundice occurred in 42%. Out of 42 persons with jaundice who were evaluated in Calcutta, 10 (23.8 %) were found positive for leptospirosis. 75 patients from Delhi with symptoms of leptospirosis were evaluated, 32 were found positive for leptospirosis and 5 died. 180 febrile patients from urban slums of Delhi were evaluated and 27 (15 %) were positive for leptospirosis (Shivakumar, 2008).
The bacteria enter the body through small abrasions, mucosa, conjunctiva and genital tracts. It involves some chemotactic interactions and then transmembrane passage. The bacteria settle down in the convoluted tubules of the kidney and thus keep on shedding the pathogen in urine. The period of shedding varies from a few weeks to many months. After the bacteria reach a higher concentration in blood and tissue, there is tissue damage due to endotoxins secreted by the pathogen. Hemolysin is also secreted by the bacteria and leads to damage of blood cells. Endothelium gets damaged which leads to ischemia and other complications. The exact molecular basis of virulence is yet unknown however the humoral response has been observed to be active in first week of infection leading to phagocytosis by macrophages and neutrophils (Mohammed et al., 2011).
Signs and Symptoms
In humans, the disease is characterized by variety of symptoms, including high fever, vomiting, jaundice (yellow skin and eyes), red eyes, headache, chills, muscle aches, , abdominal pain, diarrhoea, rash etc. Many of these symptoms can be mistaken for other diseases. In addition, some infected persons may have no symptoms at all. Illness usually begins abruptly with fever and other symptoms. The symptoms appear after an incubation period of 7–12 days (NHS, 2012).
Leptospirosis may occur in two phases-
Majority of the cases of the leptospirosis are mild form. However, there has been reports of severe disease, which develops during the second stage or occurs as a single progressive illness. The classic form of severe leptospirosis is known as Weil’s disease, which is characterized by liver damage (causing jaundice), kidney failure, and bleeding. The disease affects brain also causing meningitis, encephalitis of brain tissue with same signs and symptoms; and lung affected as the most serious and life-threatening of all leptospirosis complications. The infection is often incorrectly diagnosed due to the nonspecific symptoms. The patients of leptospirosis are likely to be misdiagnosed as malaria, dengue hemorrhagic fever, and viral hepatitis etc. (Mosby’s Medical Dictionary, 2013).
On infection the bacteria can be found in blood and cerebrospinal fluid (CSF) for the first 7 to 10 days (invoking serologically identifiable reactions) and then moving to the kidneys. After 7 to 10 days the microorganism can be found in fresh urine. Hence, early diagnostic efforts include isolation from blood or other clinical materials through culture of pathogenic leptospires. Diagnosis of leptospirosis is confirmed with tests such as enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR).
The Microscopic Agglutination Test (MAT) is still considered the gold standard test in diagnosing leptospirosis according to CDC. Live Leptospira are to be cultured regularly and agglutination reaction is carried out to check the species and serovar of the pathogen. It is a very laborious and expensive method and needs live bacterial antigen to test. That’s why this test is only conducted in specially designed labs (Picardeau et al., 2014).
Differential diagnosis is difficult as the signs and symptoms match a lot of diseases. Focus should be made towards the medical history like low-lying areas, seasonality, contact with stagnant contaminated water or rodents in vicinity support the leptospirosis hypothesis and serve as indications for specific tests. Leptospira can be cultured in Ellinghausen-McCullough-Johnson-Harris medium (EMJH), which is incubated at 28° to 30°C. Due to its slow growth in laboratory media, culture techniques are useless for diagnostic purposes but are commonly used in research.
Antibiotics like amoxicillin, doxycycline, ceftriaxone etc. are used. Fluid therapy can be advised as per the requirement. Persons with symptoms suggestive of leptospirosis should contact a health care provider as soon as possible.
Leptospirosis has been an underreported disease and there are a few reliable global incidence data as the disease is not detected in common laboratory tests. As the symptoms are very much similar to many other diseases and the bacteria being destroyed by common antibiotics, the disease is very hard to detect in a population. The risk of leptospirosis can be greatly avoiding water contaminated with animal urine or contact with potentially infected animals. Occupational workers should wear protective clothing or footwear. Any skin cuts should be covered with waterproof dressing while swimming in freshwater to protect against a range of infections. In pet dogs, vaccination against the bacteria protects the animal and the house hold. Human immunization also helps to provide a certain degree of protection against infection but only available in countries like China and Cuba (McBride et al., 2005). Immunization of local reservoirs of the pathogen like dogs and livestock should be implemented in the areas prone to leptospirosis like low-lying areas, damp and muddy environment, locality with high rice cultivation etc. Destruction of mice and rodents is a necessary step towards prevention of leptospirosis and many other rodent borne infections.