Leptospirosis (Human)

Unique identifier / Notation

BI0046

Synonyms

Not applicable.

Leptospirosis is an infectious disease caused by pathogenic Spirochaetes of the genus Leptospira. These bacteria called leptospires affect both humans and animals. Humans become infected through direct contact with the urine of infected animals or with a urinecontaminated environment. It is a zoonosis. Human-to-human transmission occurs only very rarely (adapted from WHO and ILS, 2003 and WHO, 2020).

Primary reference(s)

WHO, 2020. Leptospirosis. World Health Organization (WHO). Accessed 6 October 2020.

WHO and ILS, 2003. Guidance for Diagnosis, Surveillance and Control. World Health Organization (WHO) and International Leptospirosis Society (ILS). Accessed 6 October 2020.

Additional scientific description

Leptospires are bacteria which can be either pathogenic (i.e., having the potential to cause disease in animals and humans) or saprophytic (i.e., free living and generally considered not to cause disease) (WHO, no date).

Pathogenic leptospires are maintained in nature in the renal tubules of certain animals. Saprophytic leptospires are found in many types of wet or humid environments ranging from surface waters and moist soil to tap water. Saprophytic halophilic (salt-loving) leptospires are found in seawater (WHO and ILS, 2003).

The bacteria enter the body through cuts or abrasions on the skin, or through the mucous membranes of the mouth, nose and eyes. Person-to-person transmission is rare (WHO, 2020a).

In the early stages of the disease, symptoms include high fever, severe headache, muscle pain, chills, redness of the eyes, abdominal pain, jaundice, haemorrhages in the skin and mucous membranes, vomiting, diarrhoea, and rash (WHO, 2020a).

The clinical manifestations are highly variable. Typically, the disease presents in four broad clinical categories: a mild, influenza-like illness; Weil’s syndrome characterised by jaundice, renal failure, haemorrhage and myocarditis with arrhythmias; meningitis/meningoencephalitis; and pulmonary haemorrhage with respiratory failure (YANG, 2007).

Clinical diagnosis is difficult because of the varied and non-specific presentation. Confusion with other diseases, such as dengue and other haemorrhagic fevers, is particularly common in the tropics. It may present with a wide variety of clinical manifestations ranging from a mild ‘flu’-like illness to a serious and sometimes fatal disease. Icterus (jaundice) is a relatively common symptom in leptospirosis but is also found in many other diseases involving the liver such as the various forms of hepatitis (WHO, 2020a).

Metrics and numeric limits

Not applicable.

Key relevant UN convention / multilateral treaty

International Health Regulations (2005), 3rd ed. (WHO, 2016).

Examples of drivers, outcomes and risk management

Case-fatality rates in different parts of the world have been reported to range from <5% to 30%. These figures are not reliable because in many areas the occurrence of the disease is not well documented. In addition, mild cases may not be diagnosed as leptospirosis (WHO and ILS, 2003).

Little is currently known regarding the true incidence of leptospirosis. It is estimated that 0.1 to 1 per 100,000 people living in temperate climates are affected each year, with the number increasing to 10 or more per 100,000 people living in tropical climates. If there is an epidemic, the incidence can soar to 100 or more per 100,000 people. Major improvements in the prognosis of severe leptospirosis have been made in recent decades, owing to the use of haemodialysis as a means of supporting the reversible renal failure that may occur in some cases and to aggressive supportive care (WHO, 2020a).

Leptospirosis occurs worldwide but is most common in tropical and subtropical areas with high rainfall (WHO, 2020a).

Leptospirosis is overlooked and under-reported for many reasons including difficulty in distinguishing clinical signs from those of other endemic diseases and lack of appropriate diagnostic laboratory services (WHO, 2003).

The World Health Organization (WHO) has set a number of goals concerning leptospirosis: to provide estimates of the global burden of leptospirosis according to age, sex and region, to increase awareness of and commitment to the disease in developing countries; and to encourage developing countries to undertake active disease surveillance and strengthen control measures (WHO, 2020a).

These efforts will ultimately enable policy makers and other stakeholders to translate knowledge into policy by setting appropriate evidence-based priorities in the area of leptospirosis disease control and prevention.

To coordinate and direct global research and action against human leptospirosis, the WHO has established the Leptospirosis Burden Epidemiology Reference Group (LERG). It has been assigned the following tasks: to review and appraise epidemiological evidence based on commissioned reviews and studies; to develop epidemiological tools to estimate disease burden; to estimate and express disease burden through summary measures of population health (including disability-adjusted life years); and to identify technical gaps for research (WHO, 2020a).

The WHO Secretariat for the LERG is based at the Department of Food Safety and Zoonoses with functions of facilitating, coordinating, guiding and monitoring the work of the LERG. The LERG also partners other international actors including the Global Burden of Disease (GBD 2005) initiative coordinated by the Institute for Health Metrics and Evaluation (WHO, 2020b).