What causes leptospirosis?
Leptospirosis is caused by corkscrew-shaped bacteria belonging to the genus Leptospira. Leptospirosis is a zoonosis (an infectious disease which can be transmitted from animals to humans). Wild and domestic animals such as rodents, dogs, cattle, pigs, and horses are the reservoirs of the disease. Rats are the most common source of the disease worldwide. Leptospires may live for months to years within the kidneys of animals and are excreted in the urine where they can live, outside the body, for several weeks.
Infection is usually transmitted by direct contact with the urine of an infected animal or by contact with a urine-contaminated environment (such as swimming or immersion in contaminated freshwater, or contact with contaminated food or soil). Human-to-human transmission is rare.
The organism gains entry to humans through skin abrasions or the mucous membranes of the nose, mouth, and eyes. The organism then enters the bloodstream, multiplies, and spreads to all organs, particularly the liver and kidneys. In humans, leptospires rarely persist in the kidneys for longer than 60 days. However they can persist in the eyes for much longer.
Where is leptospirosis found?
Leptospirosis is found worldwide, but is more common in tropical countries. The true international incidence of leptospirosis is not known because it is generally under-diagnosed and under-reported. An estimated 100-200 cases are identified annually in the United States.
Risk factors for leptospirosis include:
- Occupations involving working outdoors or with animals, such as rice and sugar-cane field workers, farmers, sewer workers, veterinarians, dairy workers, and military personnel.
- Recreational pursuits such as travel to tropical areas, hiking, and swimming, fishing, or rafting in contaminated waters.
- In endemic areas cases may peak during the rainy season, and may dramatically increase after flooding.
- In developing countries, urban areas with inadequate sewage disposal and water treatment are an increasingly common source of infection.
Clinical features of leptospirosis
The clinical presentation varies from a mild ‘flu-like illness to a severe illness with multi-organ failure. Some infected persons may have no symptoms at all. Leptospirosis may occur in two phases separated by a period of apparent recovery. If a second phase occurs, it is more severe and may result in kidney or liver failure, or meningitis. This phase is also called Weil disease. Approximately 5-10% of patients develop this severe form.
- After an incubation period of around 5-14 days the patient abruptly develops a high fever, severe headache, and muscle pain (particularly the calf muscles and lower back).
- Other symptoms include chills, abdominal pain, bleeding into the skin and mucous membranes (including the lungs), vomiting, and diarrhoea.
- Liver and kidney involvement is characterised by jaundice and reduced urine output respectively.
- In severe cases, the heart may be involved, aseptic meningitis may occur, and damage to the vascular system as a whole can result in capillary leakage (shifting of body fluids) and shock. Patients may develop complications such as disseminated intravascular coagulation, thrombotic thrombocytopaenic purpura, and vasculitis.
Skin manifestations include:
- The classic finding is redness in the conjunctivae of the eyes. This occurs early in the course of the illness.
- Occasionally patients develop a transient petechial rash (small red, purple, or brown spots) that can involve the palate. If present, the rash often lasts less than 24 hours.
- Later in severe disease, jaundice and extensive purpura can develop.
Case-fatality rates in different parts of the world have been reported to range from less than 5% to 30%. However, these figures are not very reliable as the overall occurrence of the disease is unknown. Elderly people and people with impaired immunity are at the highest risk of death.
Because leptospirosis mimics many other diseases, a plausible history of exposure to infected animals or a contaminated environment is important. Various laboratory tests can be used to confirm infection:
- Detection of antibodies against leptospires – antibodies appear in the blood about 5–10 days after the onset of disease, but sometimes later, especially if antibiotics have been started.
- Culture of leptospires from blood, urine, or tissues – leptospires usually circulate in the blood for about 10 days after the onset of the disease. They also appear in other body fluids, such as urine and cerebrospinal fluid, a few days after the onset of disease and penetrate internal organs during this time.
- Demonstrating the presence of leptospires in tissues using antibodies labelled with fluorescent markers.
- Other methods may be available in some centres, eg polymerase chain reaction (PCR) and (immuno)staining.
Severe cases are usually treated with intravenous benzylpenicillin. Supportive therapy such as renal dialysis and mechanical ventilation may also be required. Less severe cases are treated with oral antibiotics such as doxycycline or amoxicillin. Third-generation cephalosporins and quinolone antibiotics may also be effective.
A Jarisch-Herxheimer reaction may occur after the start of antibiotic therapy. This is a clinical deterioration due to the release of toxins when large numbers of organisms are killed by antibiotics.
- Avoid swimming and other recreational pursuits in water potentially contaminated with animal urine
- People at occupational risk should wear protective clothing and footwear
- Antibiotics are sometimes given to prevent infection; they may be effective if short-term exposure is likely