Key Features of Leptospirosis in Humans

Leptospirosis is an important zoonotic bacterial disease of worldwide public health importance. It affects humans, domestic animals, and wildlife and is caused by different Leptospira serovars.

Humans become infected through direct contact with the urine of infected animals, or through contact with water or soil that is contaminated with this infected urine. The risk of disease transmission is increased by various environmental factors, including heavy rainfall or flooding, poor sanitation, and population growth. Infection risk is also influenced by other factors, such as an individual’s behavior (eg, swimming in fresh water; working outdoors) and their contact with animals. The bacteria typically enter the body through the mucous membranes or through cuts on the skin, and then disseminate through the bloodstream.

Leptospirosis can cause a wide range of symptoms, but usually presents initially as a nonspecific, sudden onset febrile illness with fever, myalgia, and headache. Some patients may experience vomiting, diarrhea, and nausea. Signs of bleeding are also common, and occur in most patients with severe leptospirosis. Jaundice and cough may also occur.

The illness lasts from a few days for several weeks and can range from mild to fatal. Severe leptospirosis involves dysfunction of multiple organs, in particular the liver, kidneys, lungs, and brain. Weil’s disease represents one of the most clinically recognizable forms of leptospirosis. This is the most severe form of the disease and involves liver failure (with jaundice) and kidney failure. While many mild cases of leptospirosis are self-limiting, more severe disease can be life-threatening. Studies have identified several predictors of mortality in patients with leptospirosis, including altered mental status, lung involvement, acute kidney failure, oliguria, hypotension, and arrhythmias.

Diagnosis of leptospirosis can be challenging. Bacterial culture of the organism is time consuming and not recommended. As a consequence, the use of serologic and molecular techniques is typically used to diagnose leptospirosis. Serologic tests include the microscopic agglutination test (MAT) for identification and characterization of Leptospira serogroups, as well as enzyme-linked immunosorbent assay (ELISA) for Leptospira immunoglobulin (typically IgM). Molecular tests include real-time DNA polymerase chain reaction for analysis samples of blood, urine, and cerebrospinal fluid.

Although mild cases of leptospirosis may resolve without treatment, antibiotic therapy (such as oral doxycycline or penicillin) can shorten the course of illness, and, when given early in the disease, can help prevent progression to severe disease. Patients with more severe symptoms may require intravenous antibiotics, as well as supportive therapy to manage other complications such as liver and kidney failure. Pre-exposure antibiotic prophylaxis may also help to prevent disease in people, such as military personnel, who travel to regions in which there is a high risk of contracting leptospirosis.

People should be aware of preventive measures that can help to reduce the risk of contracting leptospirosis. These include avoiding contact with potentially infected animals or water sources. Individuals who work in environments that may increase their risk of exposure to leptospirosis, such as veterinarians or farmers, should wear personal protective equipment. Although leptospirosis vaccines for humans are not available commercially in the United States, they are available in some countries, and have been used, in particular, to protect individuals such as sewer workers who are at high risk of contracting leptospirosis.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.