Weil's disease is an infection that humans can catch from animals, including domestic animals like dogs. Perhaps most commonly however, the disease is spread by rats. Rats carry and excrete an organism called Leptospira ictero-haemorrhagiae in their urine. Between 50 and 60% of all rats carry this organism. If humans are infected with this organism, it can make them very ill and even result in death. As many as 10% of all cases of human infection have resulted in death.

Previously, Weil's disease only infected people such as sewage or abattoir workers, although there have also been incidents of farm workers and miners contracting the disease. New research shows that people who perform water activities, such as cavers and potholers, are also at risk. Rats commonly live near water and other areas where they can find food, such as farms, stables and riverbanks. The organism that causes Weil's disease in humans cannot live for very long in dry conditions, but it can survive for some length in wet or damp areas. Salt water will kill off the organism.

The organism that causes Weil's disease enters the body through cuts, blisters or abrasions in the skin. It can also enter via the lining of the nose or through the throat or alimentary tract. Weil's disease begins with a fever, followed by muscular aches and pains. Loss of appetite and vomiting follow. The incubation period for Weil's disease is 7 to 13 days.

The sufferer may experience bruising of the skin, nose bleeds, sore eyes and jaundice. The fever lasts about a week and is usually followed by significant deterioration. The symptoms of Weil's disease can easily be mistaken for flu. If the sufferer has a clean occupation, the possibility of Weil's disease may be overlooked in the early stages, but a blood test will confirm the diagnosis of Weil’s disease. Treatment for Weil's disease is usually a penicillin antibiotic.

Weil's disease is curable if detected in time. Many doctors in urban areas may not be familiar with the disease. If you have any reason to suspect that you have been infected, you should alert your doctor as soon as possible.