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Leptospirosis (also known as Weil’s disease, Weil’s syndrome, canicola fever, canefield fever, nanukayami fever, 7-day fever and many more[1]) 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 Adolf Weil in 1886 when he reported an “acute infectious disease with enlargement of spleen, jaundice and nephritis”. Leptospira was first observed in 1907 from a post mortem renal tissue slice.[2]
Though being recognised among the world’s most common zoonoses, leptospirosis is a relatively rare bacterial infection in humans. 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, eyes or with the mucous membranes. Outside of tropical areas, leptospirosis cases have a relatively distinct seasonality with most of them occurring August-September/February-March.
Leptospirosis is caused by a spirochaete bacterium called Leptospira spp. that has at least 5 serovars of importance in the United States and Canada causing disease in dogs (Icterohaemorrhagiae, Canicola, Pomona, Grippotyphosa, and Bratislava)[3] There are other (less common) infectious strains. It should however be 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 seemingly more useful from a 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. Although rats, mice and voles are important primary hosts, a wide range of other mammals including dogs, deer, rabbits, hedgehogs, cows, sheep, raccoons, possums, skunks, and even certain marine mammals are also able to carry and transmit the disease as secondary hosts. Dogs may lick the urine of an infected animal off the grass or soil, or drink from an infected puddle. There have been reports of “house 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, gulleys 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.[4] Abattoir workers can contract the disease through contact with infected blood or body fluids. (urine)
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 bacterial dissemination in convalescence are extremely rare in humans. Leptospirosis is common among watersport enthusiasts in specific areas as prolonged immersion in water is known to promote the entry of the bacteria. Surfers are especially at high risk in areas that have been shown to contain the bacteria and can contract the disease by swallowing contaminated water, contacting water with the eyes and nose, or entrance through open wounds.[5] Occupational risk factors include veterinarians, slaughter house workers, farmers, sewer workers, and architects and other building workers working on derelict buildings. An outbreak in an inner city environment has been linked to contact with rat urine.[3]
In animals, the incubation period (time of exposure to first symptoms) is anywhere from 2 to 20 days. In dogs, the liver and kidney are most commonly damaged by leptospirosis. Vasculitis can occur, causing edema and potentially disseminated intravascular coagulation (DIC). Myocarditis, pericarditis, meningitis, and uveitis are also possible sequelae. [3] One should strongly suspect leptospirosis and include it as part of a differential diagnosis if the sclerae of the dog’s eyes appear jaundiced (even slightly yellow), though the absence of jaundice does not eliminate the possibility of leptospirosis, and its presence could indicate hepatitis or other liver pathology rather than leptospirosis. Vomiting, fever, failure to eat, reduced urine output, unusually dark or brown urine, and lethargy are also indications of the disease.
In humans, leptospiral infection causes a wide range of symptoms, and some infected persons may have no symptoms at all. Leptospirosis is a biphasic disease that begins with flu-like symptoms (fever, chills, myalgias, intense headache). The first phase resolves, and the patient is briefly asymptomatic until the second phase begins. This is characterized by meningitis, liver damage (causing jaundice), and renal failure; because of the wide range of symptoms the infection is often wrongly diagnosed. This leads to a lower registered number of cases than there really are. Symptoms of leptospirosis include high fever, severe headache, chills, muscle aches, and vomiting, and may include jaundice, red eyes, abdominal pain, diarrhea, and/or a rash. The symptoms in humans appear after a 4-14 day incubation period.’
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