Leptospirosis

Leptospirosis (also known as Weil's disease, canicola fever, canefield fever, nanukayami fever or 7-day fever) is a bacterial zoonotic disease caused by spirochaetes of the genus Leptospira that affects humans and a wide range of animals, including mammals, birds, amphibians, and reptiles. It was first described by Adolph Weil in 1886 when he reported an "acute infectious disease with enlargement of spleen, jaundice and nephritis". The pathogen, Leptospira-genus bacteria was isolated in 1907 from post mortem renal tissue slice. more...

Though being recognised among the world's most common zoonosis, leptospirosis is a relatively rare bacterial infection in humans. The infection is commonly transmitted to humans by allowing fresh water that has been contaminated by animal urine to come in contact with unhealed breaks in the skin, eyes or with the mucous membranes.

Except for tropic areas, leptospirosis cases have a relatively distinct seasonality with most of them occurring August through September (in the Northern Hemisphere).

Causes

Leptospirosis is caused by a spirochaete bacterium called leptospira interrogans that has at least 4 different serovars of importance in the United States causing disease (icterohaemorrhagiae, canicola, pomona, grippotyphosa). There are other (less common) infectious strains. It should be however noted that genetically different leptospira organisms may be identical serologically and vice versa. Hence, an argument exists on the basis of strain identification. The traditional serologic system is seemingfully more useful from diagnostic and epidemiologic standpoint at the moment (which may change with further development and spread of technologies like PCR).

Leptospirosis is transmitted by the urine of an infected animal, and is contagious as long as it is still moist. Rats, raccoons, possums, voles, skunks, mice and even infected dogs may serve as hosts. Dogs may lick the urine of an infected animal off the grass, or drink from an infected puddle. There have even been reports of "house dogs" getting leptospirosis apparently from licking the urine of infected mice that entered the house. There is a direct correlation between the amount of rainfall and the incidence of leptospirosis.

Humans become infected through contact with water, food, or soil containing urine from these infected animals. This may happen by swallowing contaminated food or water or through skin contact. The disease is not known to be spread from person to person and cases of bacteria dissemination in convalescence are extremely rare in humans. Leptospirosis is common among watersport enthusiasts in certain areas as prolonged immersion in water is known to promote the entry of the bacteria.

Symptoms

In animals, the incubation period (time of exposure to first symptoms) is anywhere from 2 to 20 days. One should strongly suspect leptospirosis and include it as part of a differential diagnosis if the whites of the dog's eyes appear jaundiced (even slightly yellow), but the absence of jaundice does not rule out leptospirosis, and its presence could indicate hepatitis or liver pathology other rather than leptospirosis. Vomiting, failure to eat or drink, reduced urine output, unusually dark or brown urine, lethargy, and other such symptoms are also indications of the disease.

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