Leptospires are shed into the environment, come into contact with the mucous membranes of a potential host or are ingested by small animals, then disease develops. For example, dogs can acquire leptospirosis by coming in direct contact with soil or water contaminated with animal urine, or by consuming waste products from other animals. Although cattle and horses can contract, carry and pass the disease, the most likely transmissions come from wildlife such as opossums, raccoons, pigs, and skunks. It is extremely rare for cats to contract the disease. The carrying animal usually recovers from the disease, but it can continue to carry and excrete the leptospires for weeks or even up to years. Leptospires can survive in moist conditions outside the host for many days or even weeks. They are killed by drying, exposure to detergents, disinfectants, or heating to 50°C for 5 minutes and they only survive for a few hours in salt water.
Humans can be infected by other animals. The spirochetes invade mucous membranes and/or damaged skin and migrate to various organs in the body via direct or indirect contact with infected animal urine, or, less frequently, from animal bites, handling infected animal tissues or swallowing contaminated food or water. Direct or person to person spread is exceptionally rare. The bacteria enter through skin abrasions or through the eyes, nose and mouth. Human infection can range from a mild influenza-like illness to meningitis or kidney failure, severe pains in calf and back muscles, red eyes and prostration, fever, headache, chills, conjunctival suffusion, and less frequently by rash, jaundice, or renal insufficiency. Some cases develop abdominal pains with diarrhoea and vomiting. 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. In those cases where jaundice occurs the illness is know as Weil's 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 or three weeks.
Diagnosis is determined by detection of antibodies to leptospires in the patient's blood, or more rarely by growing the bacteria from blood and other body fluids. Diagnosis is difficult because the bacteria is only found in the blood for 4-5 days. The serologic test for antibodies in the blood must be done at that time. There 170 serovars and different animals can carry different serovars.
Although many human cases recover without specific treatment, treatment
with antibiotics during the first few days of the illness may limit the
course of this infection. There is no vaccine for human use
available in this country. Currently, vaccines are available from
veterinarians to protect animals against some serologic varieties of leptospirosis.
Vaccines for some serovars, such as L grippotyphosa and L pomona, have
not been developed. Vaccine makers are now attempting to include
protection for these emerging forms.
Simple precautions can significantly reduce the risk. Immunisation of cattle will reduce the excretion of leptospires in their urine. The rat population should always 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, swimming or performing other water activites. It is sensible for those in risk groups to carry 'warning cards' to show their doctor if they become ill.
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