Leptospirosis: risks during recreational activities
Jarlath E. Nally, Veterinary Sciences Centre, UCD School of Agriculture Food Science & Veterinary Medicine, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland. E-mail: Jarlath.Nally@ucd.ie
Rats, dogs, cattle, bats and sea lions, exemplify the diversity of mammalian species that can facilitate transmission of the zoonotic disease leptospirosis. The causative agent, pathogenic species of Leptospira, is shed in urine of chronically infected hosts. Direct contact with infected urine, or indirectly with water sources contaminated with infected urine, poses a risk of infection for humans exposed during water-related recreational and occupational activities. New serovars of Leptospira and maintenance hosts continue to be identified. In the western world, incidences of recreational exposure are increasing, while incidences of occupational exposure are decreasing. Adventure travellers returning from tropical regions, are presenting at clinics with symptoms of leptospirosis following participation in high risk activities including white water rafting, triathlons, endurance races and caving. Risks of infection can be reduced with increased awareness of how the disease is contracted, by avoiding contact with high risk water sources and the use of prophylaxis during high risk activities. Molecular techniques can be used to provide risk assessments prior to competition, to supplement epidemiology, and to assess shedding of Leptospira in urine samples.
Leptospires, a dynamic group of bacteria belonging to the genus Leptospira, are capable of surviving in a wide range of moist environmental conditions including soil, mud, ground water, streams and rivers. Humans and animals become infected either through direct contact with urine from infected animals or by indirect contact with contaminated water. Disease manifestations are variable, ranging from an acute febrile illness from which the patient may recover without medical attention to the more severe form of the disease known as Weil’s disease characterized by jaundice, acute renal failure, aseptic meningitis and haemorrhagic diathesis (Vinetz et al. 1996; Faine et al. 1999; Bharti et al. 2003). The severe pulmonary haemorrhagic form of leptospirosis (SPFL) is especially rapid and severe with high mortality rates (Sehgal et al. 1995; Trevejo et al. 1998; Yersin et al. 2000; Seijo et al. 2002). More than 200 serovars of pathogenic leptospires have been typed to date; Leptospira species are sub-divided into serovar groups defined by agglutination after cross-absorption with homologous antigen (Levett 2001; Valverde Mde et al. 2008). The true incidence and global distribution of the disease is unknown. Diagnosis of the disease is problematic: other illnesses including dengue fever, yellow fever, malaria and rickettsioses present with similar symptoms making differential diagnosis difficult (Bharti et al. 2003), while serological tests are limited. The classical diagnostic test for serologic diagnosis is the microscopic agglutination test (MAT) where the patient’s serum is reacted with live antigen suspensions of leptospiral serovars to determine if specific agglutinating antibodies are present (Levett 2004). A fourfold or greater rise in titre between paired serum samples confirms infection (Faine et al. 1999). The MAT requires live cultures representing serovars from all serogroups and locally common serovars (Levett 2004). This may pose a problem when western travellers return to their native country following infection in a tropical endemic region, where the range of serovars differs from that of their home country where the MAT will be carried out. Increasing numbers of travellers exposed to Leptospira during recreational activities are being observed. A 2004 study in California revealed that 59% of patients contracted the disease through recreational exposure either at home or abroad in the 20-year period of 1982–2001, rising to 85% in the years between 1997 and 2001 (Meites et al. 2004). A recent retrospective study in France from 1995 to 2005 indicated that 42% of the patients became infected following a water sport activity and 19% from contact with still waters (Abgueguen et al. 2008).
Leptospira in the environment
Transmission of leptospirosis is facilitated by chronically infected domestic and wild animal species. Leptospira survive in the renal tubules of chronically infected maintenance hosts without any obvious clinical symptoms, and are shed in urine, into the environment. This host adaptation was first recognized by Babudieri (1958) who observed ‘biological equilibrium’ between rodent hosts and certain Leptospira serovars. Leptospiruria in maintenance hosts is of high intensity, constant and of long duration compared with the accidental hosts where it is of low intensity, intermittent and of short duration (Chernukcha et al. 1974). Direct contact with infected urine or contaminated water sources facilitates transmission as leptospires can penetrate breaches of the skin or mucosal surfaces such as conjunctival tissues of the eye (Faine et al. 1999; Levett 2001). Transmission is not thought to occur through ingestion of contaminated food (Faine et al. 1999); however, swallowing contaminated water is reportedly a risk factor of infection (Morgan et al. 2002). The probability of infection following immersion in contaminated water has been reported to increase following ingestion of that water (Hadad et al. 2006). In addition, prolonged immersion may make the skin more penetrable and allow for leptospiral invasion in the absence of skin abrasions (Faine et al. 1999).
Rats were first recognized as carriers of Leptospira in 1917 (Ido et al. 1917) and are an important transmission source for human infection in urban areas (Thiermann and Frank 1980; Vinetz et al. 1996). Like other maintenance hosts, the rat suffers few, if any, clinical symptoms of disease. Epidemiological studies confirm rat populations can have infection rates as high as 90% (Thiermann 1977; Vinetz et al. 1996). A high proportion of wild rats in different regions of the world have shown to be carriers of Leptospira (Al Saadi and Podt 1976; Vinetz et al. 1996; Sunbul et al. 2001; Priya et al. 2007). In experimentally infected Wistar rats, an initial leptospiraemic phase is described, facilitating rapid dissemination and colonization of renal tubules within 1 week, and subsequent clearance of leptospires from all other tissues 9 days postinfection (Athanazio et al. 2008). Quantification of leptospires in rat urine in experimentally infected rats have revealed numbers as high as 107 ml−1 of urine (Nally et al. 2005; Monahan et al. 2008).
Leptospirosis has been clearly documented in domestic animal species including dogs, pigs, cattle and horses (Faine et al. 1999). Potentially all mammalian species can be considered to be susceptible to acute and chronic infection, and thus excrete pathogenic Leptospira into the environment (Faine et al. 1999; Levett 2001). This includes sea mammals such as free-living Californian sea lions (Zalophus californianus; Colagross-Schouten et al. 2002; Acevedo-Whitehouse et al. 2003; Lloyd-Smith et al. 2007; Cameron et al. 2008), which have been recognized as susceptible hosts since 1970 (McIlhattan et al. 1971). The mode of transmission and source of infection of these marine sea lions is largely unknown as salt water is not ideal for survival of Leptospira (Trueba et al. 2004). Contact of sea lion pups with urine from other infected animals in the rookery during the first days of birth may facilitate disease transmission. A recent study has found that leptospirosis is endemic in Californian sea lion populations but also causes periodic epidemics of acute diseases (Lloyd-Smith et al. 2007). It is unknown whether recurring epidemics in sea lion populations are because of external sources of infection and contact with other animal species or from internal epidemic cycles. Epidemic cycles may relate to waning ‘herd immunity’ and the concept that an epidemic cannot occur if a percentage of the population is protected by vaccine or previous infection. As new pups are born and individuals migrate between groups, the percentage of susceptible individuals increases resulting in outbreaks (Lloyd-Smith et al. 2007). Northern elephant seals stranded along the coast of California (Mirounga angustirostris) were also found to be susceptible to leptospirosis (Colegrove et al. 2005). New animal sources of carriage, including bats, continue to be identified (Matthias et al. 2005).
Leptospires can survive for long periods of time in a range of environmental conditions including soil and water, thus increasing the probability of infecting a susceptible host. This facilitates indirect transmission of disease from animals to humans. Viscosity and salt concentration are reported to be critical for the survival of leptospires in fresh water with survival for 110 days observed in distilled water, increasing to 347 days in a more viscous solution (Trueba et al. 2004). When observed under the microscope, the leptospires in the viscous solution were arranged in aggregates, a possible mechanism utilized for surviving harsh environments (Trueba et al. 2004). More recent work has demonstrated biofilm formation that may be important for both survival in the environment and host colonization (Ristow et al. 2008). Alkaline conditions favour survival and growth of Leptospira (Faine et al. 1999).
Assessing the environmental risk for leptospirosis has in the past relied on attempts to culture pathogenic Leptospira from surface waters. Contamination by saprophytic Leptospira that are morphologically similar but grow faster confound this technique (Henry and Johnson 1978). A more accurate method combining quantitative polymerase chain reaction (PCR) and DNA sequencing techniques has been developed to determine risk for severe leptospirosis by analysis of environmental surface waters for pathogenic Leptospira in urban and rural areas of Iquitos in the Peruvian Amazon (Ganoza et al. 2006). Results confirm that surface water from urban slums had significantly higher concentrations of pathogenic Leptospira interrogans (c. 103 leptospires ml−1) than the rural areas (0·5 × 102 leptospires ml−1), correlating with increased risk of severe human leptospirosis in urban areas. This technique could be applied to assess the risk of infection prior to planning water-based recreational events including endurance races, triathlons or white water rafting. It would also be beneficial to know if risk of infection increases or decreases at particular times of the year, or during certain weather conditions.
Flooding facilitates outbreaks of leptospirosis worldwide, from Rio de Janeiro (Barcellos and Sabroza 2001), Mumbai (Karande et al. 2002; Maskey et al. 2006), Hawaii (Gaynor et al. 2007), Guyana (Liverpool et al. 2008), Thailand (Thammakumpee et al. 2005) and European countries such as Italy (Pellizzer et al. 2006). Flooding serves to wash contaminated mud and soils into larger water sources and increase the likelihood of host interactions. Flooding was thought to be a contributing factor to Leptospira infection of 46 males aged 8–19 who were admitted to hospital in Beaufort, Sabah after swimming in the creek (Koay et al. 2004). A 15-year-old boy subsequently died as a result of pulmonary haemorrhage. Increased exposure to Leptospira-contaminated animal urine owing to flooding was also thought to be the most likely explanation to a large epidemic of leptospirosis in Nicaragua in October and November 1995 (Trevejo et al. 1998). During times of flooding, education of the general population and awareness of the risks of leptospirosis may help reduce infection rates, particularly in areas where flooding occurs frequently or seasonally. Local inhabitants should be advised to use appropriate protective measures, such as covering skin abrasions, wearing suitable footwear, avoid water splashes, ingestion and direct contact with potentially contaminated water.
Recreational activities in both tropical (Wilkins et al. 1988; Gelman et al. 2002; Sejvar et al. 2003) and nontropical areas (Abb 2002; Morgan et al. 2002) have been identified as risk factors for exposure to leptospirosis. As the incubation period of the disease can be as long as 21 days (Katz et al. 2001), the association between symptoms and water exposure may not always be obvious, and lead to a delayed diagnosis.
Following the Eco-Challenge-Sabah 2000 multisport endurance race that took place in Malaysian Borneo from 21st August to 1st September 2000, the Idaho department of Health, the Los Angeles County Department of Health services and the GeoSentinel Network notified the Centres for Disease Control and Prevention (CDC) of approximately 20 cases of acute febrile illness (Sejvar et al. 2003). All patients were participants in the endurance race and reported acute symptoms including high fever, chills, headache and myalgias. Initial screening for leptospirosis was performed using the Dip-S-Ticks enzyme-linked immunodot assay (Integrated Diagnostics, Baltimore, MD, USA) or microplate immunoglobulin M (IgM)-enzyme-linked immunosorbent assay (ELISA; PanBio Ltd., Brisbane, Australia), which detect IgM antibodies. Race activities associated with water contact included jungle trekking, swimming and kayaking, caving, sailing, climbing and mountain-biking. A retrospective epidemiological survey of the area where the race took place, pointed at a number of risk factors for infection; contact with water in the Segema river, a jungle trek where participants suffered wounds to the skin and increased monthly rainfall in the region prior to the race (Sejvar et al. 2003). Further investigations of such outbreaks would help in identifying the infecting serovar, sources of infection and potential isolation of the serovar for future studies.
An outbreak was reported following a triathlon in Springfield, Illinois, in 1998 when the Wisconsin Department of Health were notified of three athletes who were hospitalized with acute febrile illness in July of that year (Morgan et al. 2002). Following confirmation of leptospirosis by IgM-ELISA (PanBio) in at least one triathlete, a media advisory was issued to alert all 876 triathlon participants. Of 834 contacted for a telephone survey, 12% reported illness. Of 474 tested participants, 11% were positive for leptospirosis using the IgM-ELISA. In addition, 6% of the Springfield community residents who reported symptoms were also seropositive (Morgan et al. 2002). Of 27 lake water samples, only one, adjacent to the race starting point, was positive by PCR. Problems with retrospective environmental analysis include a delay from when the infection took place and the day the water is sampled, as environmental conditions change. An initial environmental investigation using quantitative PCR may have been beneficial in assessing the risk of infection prior to the event, and appropriate recommendations made, e.g. prophylaxis. Local fauna including raccoons, muskrats, opossums and deer were tested to determine a reservoir of infection but only 2 of 46 tissues, including a kidney from a raccoon and deer, were positive by immunohistochemistry analysis (Morgan et al. 2002).
A severe case of leptospirosis was documented in a male 12 days after returning home to Germany from an iron man contest in the Philippines (Teichmann et al. 2001). Leptospirosis was suspected owing to clinical presentation and impaired renal function. Participants in the same contest who had returned to Hong Kong also presented to two different hospitals with symptoms of infection and further serological examination revealed 8 of 16 patients were seropositive for L. interrogans serovar Autumnalis (Teichmann et al. 2001). A case report from Germany describes a 38-year-old male who was hospitalized on 5 September 2000 with acute febrile illness (Abb 2002). Laboratory tests confirmed leptospirosis and the most probable cause of infection was swimming in a local river in preparation for a triathlon (Abb 2002). These case studies show that outbreaks associated with endurance races in tropical and nontropical climates can result in large outbreaks of leptospirosis and water sport event organizers should have protocols to contact participants in the event of an outbreak, as well as participant education to highlight risks prior to competition. Information sessions on prevention of disease including the option to wear additional protective clothing such as foot and hand protection, as well as the use of chemoprophylaxis, would be advised.
In 1992, the risk of contracting leptospirosis through recreational use of water in the United Kingdom was calculated as 2·5 cases of Weil’s disease among an estimated 5 million recreational water users annually, resulting in one death in every 4 years with c. 1 : 200 000 canoeists becoming infected (Philipp et al. 1992). It is a legal requirement to notify the authorities of leptospirosis cases in the United Kingdom (McCormick 1993). Many case reports suggest patients present after returning from rafting or canoeing trips where leptospirosis is considered to be endemic. Two travellers in search of adventure departed from the United Kingdom independently and met on a wooden raft on the Tha Thon River in northern Thailand (Wilkins et al. 1988). Following heavy monsoon rains, the raft capsized and both swallowed a considerable volume of river water during a near drowning experience. A week later, both were admitted to Bangkok hospital and treated with oral penicillin for the headache, myalgia and fever. No diagnosis was made until they returned to the United Kingdom where both were admitted with aseptic meningitis. Diagnostic results were interpreted to indicate that each patient was infected with different serovars (Wilkins et al. 1988). Twelve days after returning to the United States, a 36-year-old female who suffered a near drowning incident while rafting in Costa Rica, presented with symptoms that resolved after treatment with doxycycline (Gelman et al. 2002). Similarly, following return from a white water rafting trip in Costa Rica on flooded rivers, a physician in Illinois reported five patients presenting with undiagnosed febrile illness (Anon 1997). Findings of the multistate investigation conducted by the Illinois Department of Public Health and by CDC in collaboration with the Ministry of Health of Costa Rica indicated that of 26 rafters, 34·6% reported case definition symptoms of leptospirosis with a median incubation period of 12 days (Anon 1997). Risk of infection included submergence in water after falling from the raft and ingestion of river water (Anon 1997). Risk of exposure owing to white water rafting is not unique to tropical climates as proven by an outbreak following a white water canoeing event on the river Liffey in Ireland during October 2001 (Boland et al. 2004). Of the 62 participants, there were six laboratory confirmed cases (IgM, ELISA or MAT) of leptospirosis. The river Liffey has previously been implicated in a case of leptospirosis following a triathlon (Tunbridge et al. 2002). Prior to the event, water was released from a hydroelectric water station, raising the river level and potentially increasing the flow of contaminated stagnant water from the river’s edge (Boland et al. 2004). The British Canoe Union (BCU) issues all of its members with a warning card on the dangers of Weil’s disease including symptoms and advises canoeists to avoid capsize drills and Eskimo rolls on slow stagnant water, to avoid cutting feet by using footwear and to shower following canoeing. Despite these warnings, a study of canoeists in the BCU revealed that there were gaps in understanding and adherence to preventative advice with the report concluding that health education for canoeists should be improved (Philipp et al. 1992). It is more difficult to warn canoeists who are not members of organizations or travellers who decide to participate in rafting abroad of the dangers of leptospirosis.
A caver who returned to the United States following an expedition in Sarawak, Malaysia became ill with leptospirosis 10 days after his last cave trip, despite taking prophylaxis of 100 mg per day of doxycycline (Mortimer 2005). Caving in tropical regions is a high risk sport for a number of reasons: minimal protective clothing is worn owing to high humidity and the incidence of skin abrasions is high as a result of contact with rock (Mortimer 2005). Underground streams can drain areas inhabited by rats and bats that are known to be carriers of Leptospira (Matthias et al. 2005). Limestone in the Gunung Buda caves is likely to carbonate water percolating through it, giving rise to a high water pH, which is favourable to Leptospira survival (Mortimer 2005).
The mean annual incidence rate of 1·29 cases of leptospirosis per 100 000 for Hawaii during the period 1974–1998 is c. 30 times higher than that reported in the United States (Katz et al. 2002). A recent case was associated with Hawaii, when a 63-year-old male presented with symptoms following swimming and kayaking in canals and rivers after returning from vacation there (Coursin et al. 2000). Recreational swimming in fresh water presents obvious risks for contracting leptospirosis and a common source outbreak was identified on the Waimea River on southwestern Kauai in July 1987 when three youths were hospitalized with suspected leptospirosis after swimming regularly in the river (Katz et al. 1991). In California, three of eight men holidaying on a houseboat went hiking, swam in a remote cove and were exposed to muddy waters following a thunder storm. They developed a range of symptoms with each of them suffering renal failure (Meites et al. 2004). Leptospirosis associated with recreational activities and swimming in rivers has also been documented in Japan where 16 of the 22 suspected patients were confirmed by MAT of which all but two had swum or played in rivers within 1 month before the date of onset during summer months (Nakamura et al. 2006).
A 48-year-old woman became infected chasing glider planes with her son in wet fields in upstate New York (Sanders 2005). Contact with contaminated water while duck hunting likely caused infection of a 38-year-old male in Butte County, California (Meites et al. 2004). In the endemic tropical Northern Territory near Darwin in Australia, a 31-year-old male presented with symptoms following a pig hunting activity on a quad bike 2 weeks prior to infection (Thomas and Stephens 2006). MAT was positive for L. interrogans serovar Australis but blood, sputum and urine cultures were negative.
Household pets including dogs (Brown and Prescott 2008) and mice can carry Leptospira. One case report describes a 37-year-old male admitted to hospital in California and leptospirosis was confirmed by MAT. The patient kept two pet white mice in a cage at home and shared cage changing duties with his wife and three daughters. The patient, when asked why he rather than the other family members became ill, speculated that after an argument, one of his daughters used his toothbrush to clean the mouse-cage (Friedmann et al. 1973). Dogs are a maintenance host for L. interrogans serovar Canicola but may also be incidental hosts of other serovars. Vaccinated dogs can shed Leptospira in their urine despite being asymptomatic (Feigin et al. 1973). Recently a dog was presented to University Veterinary Hospital (UVH) at University College Dublin with suspected leptospirosis (data not shown). The dog had a 5-day history of hyperthermia, jaundice, inappetence and vomiting. Spirochetes were observed in urine directly by dark-field microscopy and leptospires subsequently quantified by quantitative PCR. At the time of hospital admission, 2·5 × 107 leptospires ml−1 of urine were quantified. Following antibiotic treatment and symptom resolution by day 7, 2·4 × 104 leptospires ml−1 urine was detected. This highlights the need for continued therapy until cessation of shedding, and not just symptom resolution. Dogs are usually discharged once symptoms resolve but can still pose a risk of infection to members of the household to which they are returning to, if shedding persists.
Some of the high risk occupation groups for contracting leptospirosis include sewer workers, abbatoir workers, farmers, miners, fish farmers and water workers (Waitkins 1986; Katz et al. 2002). With increased hygiene, sanitation, protective equipment and mass closure of mines in the west, the trend of occupationally acquired leptospiral infections in Italy has decreased; this contrasts with the increased incidence of disease associated with recreational exposure (Ciceroni et al. 2000). Occupational exposure remains high in those workers who maintain long exposure with water (Natarajaseenivasan et al. 2002). In a serological survey of workers who spend significant amounts of time in tanks of water soaking rice grains, 68·3% (225/329) were seropositive by MAT for L. interrogans serovar Icterohaemorrhagiae and Autumnalis (Natarajaseenivasan et al. 2002). Standing in stagnant water in an area infested with rats is the most likely cause of a high seroprevalence of Leptospira antibodies in gold panning workers and the unemployed in an area in the Gabon (Bertherat et al. 1999). Exactly 47% of the 59 sugar factory workers in a sugar cane plantation in the Wonji area of Ethiopia reported an ‘unexplained fever’ and were seropositive for Leptospira (Yimer et al. 2004); workers often stood around in mud and water during irrigation of plantations. In the developing world, education about the disease and prevention, improvements in sanitary conditions would reduce the incidence of infection and exposure (Yimer et al. 2004).
Humans are purely incidental hosts of infection and rarely implicated in spreading the disease to others (Bolin and Koellner 1988). However, the possibility of undiagnosed chronic disease and leptospiruria in humans following symptom resolution has not been fully explored. A patient who was treated with penicillin during the febrile stage of illness, did not fully recover and leptospires were detected in the urine after 28 days (Kobayashi 2001). Leptospiruria continued for at least 60 days after infection with L. interrogans serovar Hardjo (Songer and Thiermann 1988). Alterations in kidney pathology have been noted in chronically infected hosts, including pigs (Faine et al. 1999), cattle (Yener and Keles 2001), raccoons (Hamir et al. 2001) and rats (Tucunduva de Faria et al. 2007; Monahan et al. 2008). It is clear from previous animal studies that resolution of acute disease can be followed by a carrier condition in which leptospires grow and remain in renal tubules (Faine 1962; Faine et al. 1999). Patient treatments should therefore consider clearance of Leptospira and not just symptom resolution.
Treatment regimes for leptospirosis vary depending on the severity of the disease and often only symptomatic treatment is required for mild, flu-like symptoms (Levett 2001). Early appropriate treatment of leptospirosis is vital in preventing severe disease progression (Kobayashi 2001). The use of antimicrobial therapy in the treatment of leptospirosis is one of some debate. An ideal treatment regimen is confounded by a range of virulent serovars and also variations in the size of inoculum. Several papers question the use of antibiotics in late/severe cases of leptospirosis (Suputtamongkol et al. 2004; Pappas and Cascio 2006). Interpretation of studies is difficult owing to lack of consensus on the definition of severe leptospirosis (Pappas and Cascio 2006). Further, in vitro models do not often correlate well with in vivo models (Kim et al. 2006).
Doxycycline is regarded as the drug of choice for prophylaxis as few other drugs have been tried or even considered (McClain et al. 1984; Takafuji et al. 1984). Penicillin is the primary antibiotic for treating later stages of leptospirosis, although recent reports support the use of third-generation cephalosporins (Pappas and Cascio 2006). Unfortunately the terms ‘severe’ and ‘late’ have been used synonymously throughout the literature. It has been suggested that this late stage of leptospirosis is an ‘immune-mediated event’, where antimicrobial therapy is ineffective but immunomodulation would be considered to be an ideal if not optimal approach (Pappas and Cascio 2006).
During an Eco-Challenge endurance race, 20 (11%) athletes surveyed were taking doxycycline prophylaxis, 17 of which took 100 mg orally daily and 3 who took 100 mg sporadically throughout the race (Sejvar et al. 2003). The preventative efficacy attributable to any doxycycline usage during the race was 55%. Efficacy of 200 mg doses of doxycycline, taken once weekly during an epidemic in India were studied (Sehgal et al. 2000). Doxycycline did not prevent leptospiral infection, but had a significant protective effect in reducing the morbidity and mortality during the outbreak (Sehgal et al. 2000). Doxycycline has a relatively short half-life, hence dosage at 1 week intervals may not be ideal (Haake et al. 2002). Using doxycycline for long periods of time can have adverse effects such as photosensitivity and gastric upset; nor is it suitable for use in children aged under 8 or pregnant women (Haake et al. 2002). However, more careful studies are needed to fully evaluate the usefulness of doxycycline as a prophylactic drug and to determine the most effective dose that is required for successful prophylaxis. Clinical trials to explore the possibility of using other, more suitable prophylactic drugs with longer half-lives would be helpful.
The MAT that is the standard diagnostic test for leptospirosis diagnosis is technically difficult, requires maintenance of live cultures, results in cross-reaction between serogroups and a fourfold rise in titre between paired acute and convalescent serum samples is required that adds to the time required for a positive diagnosis (Levett 2004). Some patients with fulminant leptospirosis may die before seroconversion occurs (Levett 2001). This time-consuming technique can delay rapid diagnosis and administration of the correct drug regime. Recently, there has been a push to apply molecular PCR techniques for confirming infection from clinical samples such as urine and cerebrospinal fluid (CSF; Romero et al. 1998; Levett et al. 2005). These techniques detect Leptospira directly with a sensitivity of 10 cells in urine and 2 cells in serum (Smythe et al. 2002), allowing for diagnosis in the early acute stages of infection.
The MAT has frequently been misused to infer the identification of the infecting serovar (Levett 2003). The MAT cannot be used to exclude the possibility of co-infection with more than one serovar; additionally, only a limited panel of antigens are used (Levett 2003). Misinterpretation of MAT results can give false epidemiological serovar presence in a population or geographical area. Analysis of variable-number-tandem repeats (VNTR) has shown to be a powerful tool for rapid typing and identification of L. interrogans serovars (Majed et al. 2005; Salaun et al. 2006). Current methods for typing Leptospira require culture of these fastidious bacteria, which is often difficult and sometimes impossible. Application of the VNTR method for typing Leptospira from biological samples would allow for identification of serovars directly from human, animal and environmental samples without the need for culture. In addition, typing of Leptospira from biological samples may reveal new serovars, which had not previously been typed as they are not amenable to culture.
New Leptospira serovars and susceptible hosts continue to be discovered (Rossetti et al. 2005; Mgode et al. 2006; Matthias et al. 2008; Valverde Mde et al. 2008). The discovery of a new species, Leptospira licerasiae serovar Varillal, as an important cause of leptospirosis in the Peruvian Amazon region is significant as it also belongs to a new serogroup and did not agglutinate other serogroup reference strains (Matthias et al. 2008). There are potentially many other undiscovered Leptospira species, serovars and serogroups. If an MAT is carried out on a patient infected with an undiscovered serovar, it is possible that a diagnosis of leptospirosis will not be made unless it is cross-reactive with other serovars in the panel. Similarly, the discovery of new serovars may have been missed if the unidentified serovar is cross-reactive with the serovars used in the MAT. This highlights the need for widespread use of molecular techniques such as PCR and VNTR analysis for accurate diagnosis and typing of Leptospira, particularly from biological samples.
Prevention is better than cure, but can be difficult. The first step in prevention is to analyse the risk and potential sources of infection. This is especially important during the organization of large-scale activities where participants will be in contact with water, which may be harbouring Leptospira. Awareness, education and simple preventative measures can reduce risks of exposure to pathogenic species of Leptospira. Use of protective clothing during water activities that prevent skin abrasion would help reduce the risk of infection. Knowledge of the symptoms of disease will allow for early diagnosis and successful treatment. Leptospirosis is a global disease; new maintenance hosts, as well as new serovars continue to be identified. Moist environmental conditions are essential for disease transmission and potential exposures should be considered in a patient’s clinical history. Diagnostics are limited to seroconversion and should not be used to infer the infecting serovar. Molecular methods can supplement culturing of Leptospira from areas associated with outbreaks for epidemiological purposes. Molecular methods can also be used to assess suspect water bodies prior to planned recreational events and appropriate prophylactic recommendations made.
Our research group is supported by grant number 05/YI2/B696, President of Ireland Young Researcher Award from Science Foundation Ireland and grant number RSF06 363 from the Research Stimulus Fund from the Department of Agriculture, Fisheries and Food.