Leptospirosis: An emerging disease in travellers
Introduction
Leptospirosis is the most common bacterial zoonosis worldwide, caused by spirochetes of the genus Leptospira that are transmitted from animals to humans. There are over 200 of known serovars, divided between 25 serogroups based on antigenic similarities. Many of the serovars circulating in animal reservoirs have been shown to cause disease in humans as well as in other animal species. Infection can be acquired either through direct contact with animals, or through environmental contamination by animal urine. This might occur through ingestion of contaminated food or water, through mucosal surfaces, or through skin contact, particularly if there are breaks in the skin. There is a wide range of animal hosts including rats, other rodents, livestock, and dogs. Infected animals are mostly asymptomatic, act as reservoir hosts to a particular serovar of leptospires, and shed the bacteria through their urine for prolonged periods of time. However, animals can develop illness after infection with a different serovar.1, 2, 3, 4, 5
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Geographic distribution
Leptospirosis is found throughout the world, particularly in tropical and subtropical regions where environmental conditions favour the survival and transmission of leptospires. Reliable epidemiological data are lacking from many countries, making it very difficult to accurately assess disease burden, but known high-risk areas include India, Sri Lanka, Thailand, Vietnam, Malaysia, China, Seychelles, the Caribbean, Brazil, and the Pacific Islands. Table 1 shows the incidence of leptospirosis in
Clinical presentation
After an incubation period of 2–30 days, the most common symptoms are fever, chills, headache, myalgia, conjunctival suffusion, and jaundice. Although it often presents as a mild influenza-like illness and resolves spontaneously, leptospirosis can be responsible for more serious illness (Weil's disease) including acute hepatic failure, acute renal failure, pulmonary haemorrhage, myocarditis, and meningoencephalitis.
Leptospirosis is often poorly recognised and overlooked as a cause of fever or
Risk factors
Risk factors for infection vary significantly between countries, and depend on many cultural, environmental, and ecological variables. In developing countries, infection is mostly related to farming activities, contact with animals (rats, other rodents, and livestock), poor sanitation, urban overcrowding, poor waste disposal, heavy rainfall, and floods.30, 31, 32, 33, 34, 35, 36 Globally, there have been many reports of epidemics after severe flooding.30, 37, 38, 39, 40 With climate change,
Changing epidemiology
The global burden of disease is unknown because of the paucity of data, but incidence estimates range from 0.1 to 1/100,000/year in temperate areas, to over 100/100,000/year during epidemics in the tropics. An estimated 300,000–500,000 severe cases occur each year, with case-fatality reports of up to 30%.1, 43
In developed countries such as Australia, leptospirosis has traditionally been an occupationally acquired disease, predominantly affecting males working in farming and livestock
Travel medicine perspective
In 2008, there were an estimated 922 million international tourist arrivals around the world, and this number is expected to increase to 1.6 billion by 2020.54 Most post-travel cases of leptospirosis were acquired in Southeast Asia, the Caribbean Islands, and Central and South America. These areas represent some of the most significant foci of leptospirosis worldwide (Table 1), and include many popular travel destinations where tourism numbers are forecast to rise significantly.11, 41, 54
With
Illness in returned travellers
Fever is one of the most common presentations of illness in returned travellers. The most likely diagnoses include malaria, respiratory illness, diarrhoeal illness, and dengue fever. However, significant numbers of post-travel febrile illnesses are undiagnosed. A recent international multi-centre survey of the causes of fever in returned travellers showed that 22% of 6957 cases did not have a specific diagnosis, with 10% of these requiring hospital admission.66
The etiology of fever in local
Diagnostic and laboratory challenges
There are a wide variety of diagnostic tests for leptospirosis, and their availability can vary significantly between laboratories. These include1, 83:
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Blood culture. A positive culture provides definitive proof of diagnosis, but leptospires can take many weeks to grow. This test is only useful in the first 10 days of illness, after which leptospires begin to disappear from the blood, and serodiagnosis should be used.
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Nucleid acid testing (PCR). This test is only useful in the first 7 days of the
Conclusion
Recreation and international travel are emerging as significant risk factors for leptospirosis in developed countries. With the growth of adventure tourism and travel, these trends are likely to strengthen and continue. Travellers should be advised about preventative measures to reduce their risk of infection such as avoiding flood waters, wearing protective clothing and boots, and covering up cuts and abrasions on their skin when engaging in outdoor activities. They should also be aware of the
Acknowledgements
We would like to thank Mary-Anne Burns at WHO/FAO/OIE Collaborating Centre for Reference and Research on Leptospirosis in Brisbane for providing data from the enhanced surveillance system for leptospirosis cases in Australia.
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