Factsheet about leptospirosis
Name and nature of infecting organism
Leptospirosis is a zoonosis occurring worldwide, caused by pathogenic spirochaetes of the genus Leptospira. Pathogenic leptospires live in the kidneys of a large variety of mammalian species and are excreted into the environment with the urine. Indirect infection through contact with leptospires secreted into the environment is probably the main route of acquiring leptospirosis. Pathogenic leptospires survive longer in a warm and humid environment. Therefore, the disease is particularly prevalent in wet tropical and subtropical regions. The bacterium is sensitive to dry conditions, extreme temperatures and detergents. Currently nearly 300 serovars have been identified, divided into 25 serogroups. Seven main pathogenic species are known.
Clinical features
The incubation period varies from 2 to 30 days, with an average of 7–10 days. Leptospirosis varies from mild to severe clinical presentation, and may cause potentially fatal conditions such as Weil’s syndrome and the emerging Severe Pulmonary Haemorrhagic Syndrome (SPHS). Generally, leptospirosis is an acute biphasic illness: the first phase (4–9 days) presents with an abrupt onset of a flu-like illness, with a severe headache, chills, muscle aches, and vomiting, while in the second phase the patient develops fever, jaundice, abdominal pain and diarrhoea. In severe cases there may be organ failure. If untreated, recovery may take several months.
Transmission
Reservoir
About 160 mammalian species have been identified as natural carriers of pathogenic leptospires. These include feral, semi-domestic and farm and pet animals as important infection sources. The infectious period of natural hosts can be lifelong. Accidental hosts can act as intermediate infection source, and may shed leptospires for days or months.
Transmission mode
The route of transmission is via broken skin and through mucous membranes of eyes, mouth and nose (consumption, inhalation). Transmission through water-weakened skin is controversial. Transmission may also occur via sexual contact and mother’s milk. In-uterus transmission can lead to reproductive failures such as abortion.
Risk groups
The risk of acquiring leptospirosis is associated with contact with animals and thus with occupations such as farmers, veterinarians and sewer workers. Case severity is associated with physical condition and increasing age. Leptospirosis as a recreational disease in travellers is increasing in Western countries.
Prevention measures
Prevention and control mainly focus on the identification and reduction of the infection source and the prevention of penetration of leptospires into the accidental host. Prevention of transmission can be achieved by wearing protective clothing. Prophylactic treatment with doxycycline is protective to some extent. Vaccination is available in a limited number of countries, but currently not considered as a generally applicable option.
Improving water and food storage conditions, increasing public awareness about the disease and infection risks, as well as the control of rodents, may reduce the risk of transmission. Infection risk from domestic animals can be reduced by vaccination or treatment of carriers. Both approaches should be combined with herd management. Vaccines are available for cattle, dogs and pigs, and provide a short-term serovar-specific protection.
Diagnosis
The confirmation of a clinically suspected leptospirosis case is usually done through culturing and the Microscopic Agglutination Test (MAT); both are quite laborious and require well-equipped laboratories with experienced staff. Several rapid tests for humans are currently available, mainly for screening purposes, and results must be confirmed by standard tests.
Management and treatment
Early diagnosis is critical in the treatment of patients with leptospirosis. In severe cases, high doses of intravenous penicillin are recommended, but Jarish-Herxheimer reactions may occur. In less severe cases, oral antibiotics such as amoxycillin, ampicillin, doxycycline or erythromycin are administered. Third generation cephalosporins and quinolone antibiotics also seem to be effective.
Key areas of uncertainty
The lack of effective cross-reactive vaccines limits the potential effect of immunisation strategies in animals and humans. The true spread and increase of leptospirosis remains unknown, as the quality and availability of diagnostic tests, testing facilities and surveillance systems are very variable and frequently not available. Novel or adapted simplified diagnostic tests, both for diagnosis in humans and animals, are badly needed.
References
Bharti AR, Nally JE, Ricardi JN et al. Leptospirosis: a zoonotic disease of global importance. Lancet Infect Dis 2003;3:757–771.
Laurichesse H, Gourdon F, Smits HL et al. Safety and immunogenicity of subcutaneous or intramuscular administration of a monovalent inactivated vaccine against Leptospira interrogans serogroup Icterohaemorrhagiae in healthy volunteers. Clin Microbiol Infect 2007;13:395–403.
Levett PN. Leptospirosis. Clin Microbiol Rev 2001;14:196–326.
McBride AJA, Athanazio DA, Reis MG et al. Leptospirosis. Cur Opin Infect Dis 2005;18:376–386.
Sanders EJ, Rigau-Perez JG, Smits HL et al. Increase of leptospirosis in dengue-negative patients after a hurricane in Puerto Rica in 1996. Am J Trop Med Hyg 1999;61:935–941.
Watt G, Padre LP, Tuazon ML at al. Placebo-controlled trial of intravenous penicillin for severe and late leptospirosis. Lancet 1988;1:433–435.
World Health Organization. Leptospirosis worldwide, 1999. Wkly Epidemiol Rec 1999;74,29:237–244.
World Health Organization. Human leptospirosis: guidance for diagnosis, surveillance and control. Geneva: World Health Organization; 2003.
Zaki RS, Shieh W-J, and the Epidemic Working Group. Leptospirosis associated with outbreak of acute febrile illness and pulmonary haemorrhage, Nicaragua, 1995. Lancet 1996;347:535.