Of course the most important advice is to go and see your doctor if you start to feel unwell. Early symptoms resemble a cold or flu, with a fever. Remember also that water contaminated with leptospires is likely to be contaminated with other harmful bacteria and chemicals. You may not have been infected with leptospires, but there are a whole host of other things you could have caught.

When you visit your doctor, explain what you were doing and what you think you have been exposed to. If you say 'Doctor, I went swimming and now I've got a fever and a headache' you will most likely be given penicillin and sent home with a suspected case of the flu, or sinusitis. If you say 'Doctor, i went swimming and there were rats about, or a funny smell. I've heard of people getting a nasty illness from rats and I'm worried I've got it' then you'll prompt your doctor into ordering the right blood tests without putting their nose out of joint. Many doctors have never seen a case of leptospirosis and may not associate it with your symptoms. However, they also may not like you arriving and quoting medical terms at them like you're a consultant bacteriologist. If you're not getting anywhere, then you can resort to helping them towards a diagnosis a bit more forcibly.

If you know someone else who may have been exposed, and they won't visit a doctor, then watch them for the classic symptoms of the infection - fever, a short-lived rash, headaches, nausea. Most important is to watch for anyone getting a mild illness, recovering and then about a week later feeling very ill again.

Firstly, the bacteria is water-borne. You cannot catch it from shaking hands, talking to someone, petting an animal, sharing clothes, etc. If you suspect something or somone to be infected, you should avoid contact with water and fluids, including damp soil, toothbrushes, facecloths, etc. For pets and animals, avoid any contact with excreta and wash your hands after grooming them. It is extremely unlikely that saliva from a pet could transfer infection, though letting your dog lick your face or share food is a bad idea, for many reasons. Unlike a cold or flu infection, the bacteria is not asily aerosolized, so living next door to a human or animal patient will present no risk in itself.

Humans will only fall ill if infected with a small sub-group of the 200 or so leptospira strains. Animals are similarly specific to the strains that can infect them and become resident as a host. For example, humans can be infected directly from rats, and directly from domestic dogs, however it is rare for infection to pass from dogs to rats or vice versa. There is no guaranteed method of predicting what species of animal could be infectious to humans, and ANY mammal, from rats to dolphins, can carry the bacteria and transmit it. One point to note is that the infection in domestic dogs is far more common than in domestic cats, despite the notorious connections between cats and rodents.

Human to human infection can take two routes - direct and indirect:

• Direct transmission occurs when body fluids of an infected person are transferred to a target individual. This can occur via exchange of blood, semen, milk, urine, faeces or through the placenta to an unborn infant. There is of course a risk from handling body tissues, which is relvent to medical staff.
  The bacteria must enter the target body, via ingestion, sexual contact or direct blood contact. It is not currently considered that saliva exchange (via kissing) carries a significant risk. Sexual intercourse does however pose a risk and infection has been reported via this route.
• Indirect transmission occurs when body fluids (usually blood or urine) are transferred via the environment to a target. This could occur in the handling or washing of urine- or blood- soaked clothes or bedding, but is rare. Some isolated cases of urine contamination of drinking water have been reported from isolated locations.

What are the chances of catching this infection from my local river/pond/cess pit?

Obviously this depends on two things - if the water is infected with the bacteria, and if you and said bacteria get in close enough contact to be friendly.
On average in the devleoped world (Europe, mainland USA, etc) about 20% of all rats carry strains of leptospira that could cause illness in humans. This of course varies locally - in your area you may have 100% rat carriers, or 0%. It just depends on the social lives of the rats in question. It's therefore sensible to assume that on average 20% of all open water sites are infectious, with more probability for sites which stand good chances of hosting rats nearby (urban ponds, slow-moving rivers and canals, lakes near farm buildings, etc) and less of a risk for non-rodent-friendly sites such as rapid flowing highland streams.

The chances that being exposed to this water would lead to infection depends on what you do in the water. As we describe in our Risks Page you must actually allow water to enter your body to risk infection - though that could be as simple as through an open cut, or by licking a damp finger.

In general in the developed world people are wary of open water sites from general cleanliness viewpoints, and would not drink from a lake without a very good reason. The chances of infection are therefore quite low, but these statistics hide the fact that in many cases the infection is mild, and goes unreported. Despite only a few hundred cases being reported in each European country each year, there may well be several times more cases which are simply written off as a cold or stomach bug.

In developing countries the risks are greater, as rat populations are more widespread and water use is different. The quantity of untreated water used for washing, bathing and drinking is far higher, and the association between hygiene risks and open water is rarely made. It is for these reasons that leptospirosis is the second most widespread bacterial illness in the world, surpassed only by malaria. Education in developing countries is the only solution to this issue, as the bacteria and the rats are there to stay.

Leptospirosis (Weil's disease) is caused by a bacterium which is carried in rat's urine and can contaminate freshwater and wet waterside areas. The germ does not survive long in dry conditions.

The problem can occur in any water including swift streams and rivers. However, the likelihood of becoming infected is greater when water is stagnant or in a slow moving waterway.

The illness most commonly starts a week or two after exposure to infected water. It may begin with a 'flu-like' illness with temperature, headache and joint & muscle pains (particularly the calves and thighs).

If you have these symptoms and suspect you may have been exposed to leptospirosis, seek early medical advice and remember to mention all the relevant details to the doctor.

The disease may be mild but it can become serious, sometimes leading to hospital admission and even possibly to liver and kidney failure.
The disease can be successfully treated with antibiotic medicines.

There is no effective immunisation for humans against Weil's disease - prevention is the best way to avoid problems. Take these simple precautions:

• Cover all cuts, scratches, sores, abrasions and areas of skin affected by eczema with water proof plasters and/or gloves.
• If you are likely to become submerged in the water while wind surfing or canoeing etc - it is best to use a face mask or nose clip. Always wash or shower afterwards.
• Don't put wet fishing line, ropes or other objects in your mouth.
• If you can, wash your hands before eating/drinking in the waterside environment. If this is not possible, hold your food with a clean wrapper while you eat it.
• Don't use open-toed footwear or go barefoot while in or near the water or waterside areas.
• Don't touch dead animals, especially rats, unless you are wearing gloves.
• Don't leave food, bait or ground bait etc. in waterside areas - it only encourages rats!
• Always wash or shower after activities involving freshwater rivers, canals, ponds, lakes, marshes etc.