The facts about...

Leptospirosis

What is leptospirosis?

Leptospirosis is an acute bacterial infection which affects humans and a wide range of animals. The disease occurs more commonly in tropical countries, and man is invariably infected from animal sources. Human leptospirosis was recognised in Europe in the 1880s but the causative organisms called leptospires were first grown in Japan in 1914. Human infection can range from a mild influenza-like illness to meningitis or kidney failure. In those cases where jaundice occurs, the illness is known as Weil's disease.

How are leptospires spread?

The natural reservoirs for leptospires are wild animals, which recover from the infection but continue to excrete organisms in their urine. There are many different types of leptospires, each tends to be associated with a particular animal species. The most common ones in this country are Leptospira hardjo, which is found in cattle and Leptospira icterohaemorrhagiae which is associated with rats. Leptospires can survive in moist conditions outside the host for many days or even weeks. However, they are readily killed by drying, exposure to detergents, disinfectants, heating to 50oC for five minutes and they only survive for a few hours in salt water.

Man becomes infected through direct or indirect contact with infected animal urine, or, less frequently, from animal bites, handling infected animal tissues or swallowing contaminated food or water. Person to person spread is exceptionally rare. The bacteria enter through skin abrasions or through the eyes, nose and mouth.

The Disease

Human infection is more common in men than women. An incubation period of 7 to 12 days is usual. Most cases present with an influenza-like illness which resolves in two to three weeks. Common features are sudden onset of fever, intense headache, severe pains in calf and back muscles, red eyes and prostration. Some cases develop abdominal pains with diarrhoea and vomiting or meningitis. Only a few cases develop severe leptospirosis with jaundice and kidney failure, but of these 10-15% may die. A fatal outcome is virtually unknown in patients in whom jaundice is not a feature.

Laboratory Diagnosis

This depends on detecting antibodies to leptospires in the patient's blood, or, more rarely, growing the bacteria from blood and other body fluids.

Treatment

Treatment with antibiotics during the first few days of the illness may be helpful in limiting the course of this infection. However, many human cases recover without specific treatment.

Who is at risk?

Traditionally leptospirosis was associated with miners, fish workers and sewermen, but as preventative measures were introduced into the working procedures, so the incidence in these groups declined. Over the last decade, an average of 54 cases of leptospirosis per year have been diagnosed in England and Wales. This represents about one case per million of population per year. About one third of cases were confirmed to be due to Leptospira icterohaemorrhagiae and the remaining two thirds are almost entirely caused by Leptospira hardjo. Today, farmers form the main occupational risk group due to their inevitable exposure to rats and their urine and to cattle urine. Workers in contact with canal and river water or those who use inland water for recreational activities are potentially at risk, although the risk is judged to be very small.

Preventative measures

No vaccine for human use is available in this country although an effective vaccine is licensed for veterinary use. Simple precautions can significantly reduce the risk. Immunisation of cattle will reduce the excretion of leptospires in their urine. The rat population needs to be reduced, with destruction of their habitats and rat proofing buildings. Those at risk should cover all cuts with waterproof plasters and wear protective clothing or other materials. Immersion in natural waters such as rivers, lakes and canals should be avoided, and individuals should wear footwear and wash or shower after canoeing, windsurfing or swimming. It is sensible for those in risk groups to carry 'warning cards' to show their doctor if they become ill.