Causes of leptospirosis 

Leptospirosis is caused by a strain of bacteria called leptospira, which is found in certain animals and can spread to humans.

These animals include:

  • rats and mice
  • most farm animals, such as pigs, cattle, horses and sheep
  • dogs

It is rare to catch leptospirosis from domestic pets, although there have been cases where the infection was caught from pet rats.

An animal carrying the leptospira bacteria may show no outward signs of illness. The bacteria live inside the animal's kidneys and can be passed out in their urine. Bacteria passed into soil or water can survive for several weeks or even months.

It is possible to become infected with the leptospira bacteria if contaminated water or soil comes into contact with your eyes, mouth, nose or any open cuts in the skin. The bacteria can also be spread through rodent bites or by drinking contaminated water. Less commonly, the infection can be passed to humans who come into close physical contact with the blood or tissues of an infected animal.

Outbreaks of leptospirosis can also occur, particularly at events that involve close contact with infected fresh water sources, such as some water sports. It is also possible for people to become infected after a natural disaster, such as a flood.

Human to human transmission of infection is extremely rare, but it is thought that it may be possible during sex or by an infected mother passing it on to her baby while breastfeeding.

Where is leptospirosis found?

Leptospirosis is found throughout the world, including western Europe, but is most common in tropical and subtropical areas. This is because the leptospira bacteria are able to survive longest in hot and humid conditions. 

The countries and regions where leptospirosis is most common include:

  • India
  • China
  • South East Asia
  • Africa
  • Australia
  • Central and South America  
  • the Caribbean

If you are travelling to these parts of the world, certain outdoor activities could bring you into contact with contaminated water or soil and may place you at a slightly higher risk of contracting leptospirosis. For example:

  • camping in rural areas
  • sailing
  • swimming, particularly if you submerge your head under the water for long periods of time
  • rafting
  • caving or potholing
  • canoeing

Areas of the developing world where there has been sudden flooding tend to have an associated outbreak of leptospirosis. This is because previously clean sources of drinking water can become contaminated by flood water.

Occupational risk

There are several occupations that increase your risk of contracting leptospirosis. However, this risk is most significant if you are working in the parts of the world listed above, rather than in the UK. These occupations include:

  • farmers, particularly pig, cattle and rice farmers
  • sewage workers
  • people who regularly work with animals, such as vets
  • freshwater fishermen
  • people who work with dead animals, such as butchers or abattoir workers

Read about preventing leptospirosis for information and advice about how to reduce your risk of contracting the disease.

Page last reviewed: 07/11/2012

Next review due: 07/11/2014