Leptospirosis (also known as Weil's syndrome, canicola fever, canefield fever, nanukayami fever, 7-day fever, Rat Catcher's Yellows, Fort Bragg fever, black jaundice, and Pretibial fever is caused by infection with bacteria of the genus Leptospira and affects humans as well as other animals.

Leptospirosis is among the world's most common diseases transmitted to people from animals. The infection is commonly transmitted to humans by allowing water that has been contaminated by animal urine to come in contact with unhealed breaks in the skin, the eyes, or the mucous membranes. Because urine has a natural disinfecting effect and leptospirosis is one of the very few bacteria that can survive in such an environment, it is one of very few urine transmitted diseases. It also only persists outside a host in a warm, wet environment. As such, outside of tropical areas, leptospirosis cases have a relatively distinct seasonality with most cases occurring in spring and autumn where conditions are most favorable.

Causes and transmission

Leptospirosis is caused by a spiral shaped bacterium called Leptospira spp. There are at least five strains (Icterohaemorrhagiae, Canicola, Pomona, Grippotyphosa, and Bratislava).of importance in the United States and Canada, all of which cause disease in dogs.

There are other less common infectious strains. Genetically different leptospira organisms may be identical serologically and vice versa. Hence, an argument exists on which basis strains should be identified - by their common genetics or their common serology. The traditional serologic system is seemingly more useful from a diagnostic and epidemiologic standpoint at the moment (which may change with further development and spread of technologies like polymerase chain reaction (PCR).

Leptospirosis is transmitted by the urine of an infected animal and is contagious as long as it is still moist. Although rats, mice, and moles are important primary hosts, a wide range of other mammals including dogs, deer, rabbits, hedgehogs, cows, sheep, raccoons, opossums, skunks, and certain marine mammals are able to carry and transmit the disease as secondary hosts. Dogs can contract the disease by licking the urine of an infected animal off the grass or soil or drinking from an infected puddle.

There have been reports of house bound dogs contracting leptospirosis apparently from licking the urine of infected mice that entered the house. The type of habitats most likely to carry infective bacteria are muddy riverbanks, ditches, gullies, and muddy livestock rearing areas where there is regular passage of either wild or farm mammals. There is a direct correlation between the amount of rainfall and the incidence of leptospirosis, making it seasonal in temperate climates and year-round in tropical climates. Leptospirosis is also transmitted by the semen of infected animals.

....