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

Many different kinds of animals can carry the bacteria, but it is most commonly associated with:

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

It's 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 can survive for several weeks, and even months, when it's passed into soil or water.

You can 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, it 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 water, such as some water sports, or after a flood.

It's extremely rare for it to be passed from human to human, but 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 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.

Leptospirosis is most common in:

• India
• China
• southeast 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, placing you at a higher risk of contracting leptospirosis. For example:

• camping in rural areas
• sailing, rafting or canoeing 
• swimming
• caving or potholing

Flooding also tends to be linked with outbreaks of leptospirosis, when drinking water becomes infected with contaminated flood water.

Occupational risk

There are several occupations that increase your risk of contracting leptospirosis. This risk is most significant if you are working in higher risk countries, 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 advice about how to reduce your risk of contracting the disease.