Precautions against infection

To minimise the chances of infection, the only truly effective way is to avoid contact with contaminated water and animals, thus avoiding exposure to the bacterium. If you are in a high risk area, you should always attempt to minimise contact, as there are many hundreds of other organisms that can lurk in the water apart from Leptospira. Unless you are required to enter the water, you should stay away from it. Animals themselves present a risk while infected, as their body fluids can contain the bacteria.


The vast majority of human cases are from contaminated water, and of those the majority are occupational cases from areas of the world where agriculture and rodents mix – rice-farming, cane-growing and so forth. Recreational exposure is next, with cases amongst swimmers being the obvious top grouping. Lowest of the risk groups is occupational exposure in the developed world – water and sewer engineers, construction, pest control and so on.

Clearly there are problems in preventing exposure in the highest risk activities (rice-farming and such) and in those areas the only option is to be aware of symptoms and seek early treatment. At this time there is no universally-agreed human vaccine, and the preventative use of antibiotics can only be considered for short periods.

Swimming is the greatest risk, and several cases are reported each year from swimming in contaminated water (both in the developed world and in activities such as adventure racing). There is no practical way to prevent exposure as some water will always enter the mouth. For one-off activities such as expeditions there is an argument for using a preventative antibiotic (doxycycline) which can offer increased resistance to illness for a few weeks. It should never be used long-term.

Anglers and bankside/sewer workers should wear splashproof clothing and expecially gloves. Anglers are at higher risk as it is reasonably common to cause minor cuts with hooks, knives and the like, and this greatly increases the ease by which the bacteria can enter the body. Fish caught from suspect areas should of course never be eaten. Whilst cooking does in theory kill any bacteria within a fish, very often the level of cooking is insufficient to guarantee safety.

Recreational exposure (swimming, skiing, sailing, caving, etc) is clearly done at the person’s own risk and they must weigh up their own balance of risk vs. desire. The same preventative measures apply – minimise the risk of water entering the body by any and all means, consider antibiotics if the risks are very high, and be aware of the symptoms and seek treatment immediately. There are no ‘quick fixes’ to prevent infection. Some swimmers wash their mouths with antibacterial rinse, though this has not been proved to offer any significant benefit other than keeping their teeth clean.

Scuba divers, who are particularly at risk, should opt for drysuits and try as much as possible to avoid swallowing any water when purging or changing regs. Commercial divers are required by their employment regulations and insurance to comply with strict rules when working in contaminated water, these include the use of hard-hat systems, wash-down stations and regular medical testing.

Remember that this advice applies to FRESH water – the risks in saltwater are virtually zero.

Animal exposure

One of the major concerns of people contacting us over the years is transmission from animals. In the developed world the direct exposure to water can often be minimised, but domestic pets can either bring in rodents or become infected themselves, and occupational exposure to rodents (as part of garbage collection, pest control, construction or agriculture) is often hard to avoid.

Distinction must be made between infection and carrier-state. An infected animal has an illness, and will either recover from it or die. A carrier has a colony of bacteria living in their body but shows no illness. They can remain like this for their entire lives and suffer no adverse effects. Both are potential sources of infection, but clearly an animal that is not a carrier will eventually be safe.

The obvious carriers are rats, but other rodents can do this (but less frequently). It is usually safe to assume that across the developed world, 1 in 5 wild rats are carriers of pathogenic leptospires. The reason rats are such efficient hosts is that they live in close proximity to water and they are incontinent. Carrier-state rats emit bacteria in their urine, and this is distributed everywhere they go. Normally this is inactivated once it dries out, but if it enters water the bacteria can remain viable for longer periods. Anyone handling wild rats should be aware that their urine, damp soil, bedding and nearby water are all potential sources of infection – and rat bites themselves can cause infection both by leptospira and other unrelated organisms.

A dead rat (wherever it may be) remains a risk but only in terms of direct contact. Simple disinfection of the surface after disposal is all that is required. Similarly, domestic pets that are contaminated but not infected (such as for example after swimming) can be rinsed and dried as usual, and will be no significant risk thereafter. Dogs and farm livestock are usually vaccinated, cats rarely contract infection.

A domestic or farm animal that is infected and ill will be a potential source of infection during the first few weeks of the disease, but only in terms of bites or contact with body fluids. Airborne and skin-to-skin transfer is almost impossible and has never been recorded. During treatment the animal should be handled with care, and any body fluids cleaned away using disinfectant, but beyond that there are few risks. Animals should be kept apart to minimise the risk of direct infection, though again this is statistically rare.

Endemic exposure

Visitors and residents of countries where the bacterium is widespread (such as the Indian subcontinent) are likely to be exposed to contaminated water as a matter of course. In these cases it is almost impossible to prevent exposure, and the best option is to be aware of the early symptoms and react to them. Leptospiral contamination is akin to malaria in that it will probably always be there, and cannot realistically be avoided in certain countries.

VISITORS to these countries are at a higher risk than residents, as in the resident population there is a statistically higher immunity, due to childhood infection or placental antibody transfer. Having said this, there are many pathogenic serovars of leptospira, and immunity to one does not prevent infection from the others. Nobody is immune to the disease as a whole, and the serovars found at a selected location can change over time as host populations change. The highest concentrations of cases will always be in developing countries where wet farming and rodent populations combine. Tourists visiting these areas should be aware of the risks and limit their activities accordingly. Of course, the majority of ‘tourist’ activities are prefectly safe even in areas of high risk, but the growth of ‘adventure vacations’ with swimming, survival and back-country hiking all increase the dangers. As more of the world is opened up to tourism, we must accept that the dangers of those areas are opened up to us.