Bacteria, Epidemiology, Infectious Diseases, Microbiology

Leptospirosis Bacteria: Rising Waters, Growing Threat

Author Chandana Balasubramanian , 22-Mar-2024

Leptospirosis is one of the most common zoonotic diseases worldwide. It is a bacterial infection that can infect animals and humans and can lead to severe disease. 


It is easily treatable but often misdiagnosed because its symptoms are similar to many other diseases. According to the World Health Organization (WHO), the infection is an emerging public health issue worldwide.


Let’s learn more about the history, epidemiology, biology, symptoms, diagnosis, and treatment of leptospirosis. In this article, we will also look at ways to prevent or lower the risk of leptospirosis infections.


  • Adolf Weil, a German bacteriologist, first described leptospirosis in 1886. He reported a disease characterized by spleen enlargement and jaundice. The severe form of leptospirosis came to be known as Weil’s disease in his honor.
  • However, the bacteria had been isolated about a hundred years ago when researchers in Japan and Europe identified and isolated Leptospira bacteria as the pathogen causing Weil’s disease (aka leptospirosis).
  • Leptospira was initially observed in 1907 within kidney tissue samples taken from a patient who had succumbed to leptospirosis. The term “Leptospira” comes from the Ancient Greek “leptós,” signifying fine or narrow, and the Latin “spira,” indicating coil, describing the bacteria’s long, spiral, rope-like appearance.
  • The clinical cause (etiology) of leptospirosis was demonstrated independently in 1915 in Japan and Germany, where specific antibodies and spirochetes were detected in patients with infectious jaundice.
  • In 1984, a randomized, double-blind, placebo-controlled trial demonstrated that treatment with the oral antibiotic doxycycline, 100 mg twice daily, decreased both the duration of illness and the severity of leptospirosis symptoms.

Leptospirosis is a historically important bacterial infection because its discovery helped us better understand the spread of infectious diseases, leading to progress in epidemiology. The disease is still common in many places and rears its head during hurricanes, floods, heavy rainfall, and other natural disasters, wreaking havoc on communities.



Endemic Regions

  • Leptospirosis is endemic to warm and humid environments that promote the survival of Leptospira bacteria, making wet tropical and subtropical regions endemic to the disease.
  • Outbreaks are often linked to floods and hurricanes following heavy rainfall, with humans being infected through indirect contact with contaminated environments like freshwater ponds and rivers.



  • In highly endemic regions, leptospirosis incidence is about 10 to 100 per 100,000.
  • In 2020, 21 countries reported 565 confirmed cases of leptospirosis, marking the lowest number between 2016 and 2020, as per the European Centre for Disease Prevention and Control, ECDC.
  • The notification rate in the EU/EEA was 0.14 confirmed cases per 100,000 population, with higher rates in males compared to females, according to the ECDC.


Risk Factors

  • People who work in jobs or do activities where they might encounter rodents, farm animals, or dirty water have a greater chance of getting leptospirosis. 
  • Jobs like farming, military service, mining, sewer work, and hobbies like water sports or gardening put individuals at risk
  • Leptospirosis is more common in men because they tend to do these high-risk activities more often.


How does it spread?

Leptospirosis primarily spreads through contact with the urine of infected animals, contaminating water or soil, where the bacteria can survive for weeks to months.

Here are the different ways in which the leptospirosis bacteria get transmitted:

  • Animal carriers: Various wild and domestic animals, including cattle, pigs, horses, rodents, wildlife, and even dogs, can carry Leptospira bacteria without displaying symptoms, according to the US Centers for Disease Control and Prevention (US CDC).
    The American Veterinary Medical Association (AVMA) also cautions that all dogs face leptospirosis risk, irrespective of age or breed. As a result, the AVMA advises yearly vaccinations for dogs rather than every three years. Recent studies have also found that bats can be a reservoir for Leptospira.
  • Environmental contamination: Infected animals excrete the bacteria into the environment via urine, and Leptospira can survive in freshwater for up to 16 days and in soil for nearly 24 days.
  • Human exposure: Infection can occur through contact with infected animal fluids, contaminated water, soil, or food or through cuts or mucous membranes. Ingesting contaminated water also poses a risk.
  • Activities and occupations: People who work in farming, sewer work, and mining or engage in recreational activities like water sports and gardening face higher exposure risks.


Biology of the disease

Leptospira enters the human body through mucus and broken skin. Once inside, the bacteria spread through the lymphatic system and bloodstream, multiplying primarily in the liver, kidney, and central nervous system. The exact modes of infection are not known yet, and research is still underway.

Symptoms typically appear within 1 to 2 weeks but can take up to a month to manifest.



According to the CDC, leptospirosis symptoms include:

  • Fever
  • Chills 
  • Headache
  • Muscle pain
  • Abdominal pain
  • Vomiting
  • Diarrhea
  • Red eyes
  • Rash
  • Jaundice (yellow skin and eyes).


The disease typically progresses in two phases:

  • Phase I: Initially, symptoms like fever, chills, headache, muscle aches, vomiting, and diarrhea may manifest abruptly. Following this phase, there may be a temporary recovery period before a more severe second phase occurs. 
  • Phase II: Individuals may experience kidney or liver failure, meningitis, or other severe complications.


Some infected individuals may not exhibit any symptoms at all. The time between exposure to the bacteria and the onset of symptoms (incubation period) ranges from 2 days to 4 weeks.

Leptospirosis can present with a wide range of symptoms, often resembling other diseases, and may vary in severity. Signs of leptospirosis resemble infections like influenza, dengue, and viral hemorrhagic fevers. 

Weil syndrome: severe leptospirosis

Symptoms of Weil syndrome, an acute, severe form of leptospirosis, can include:

  • Disturbances in consciousness
  • Muscle and abdominal pain
  • Nausea
  • Vomiting
  • Fever
  • Yellowing of the skin and eyes (jaundice)
  • Internal bleeding
  • Respiratory distress syndrome
  • Kidney abnormalities like protein or blood in the urine.



Since the symptoms of leptospirosis are similar to those of other conditions, including aseptic meningitis and influenza, the infection is often misdiagnosed.

Lab tests are essential to confirm leptospirosis, especially in regions where the disease is common but often goes undiagnosed without proper testing.

  • Culture isolation: Leptospira culture can be performed to isolate the bacteria from clinical samples, aiding in a definitive diagnosis. Culture isolation can help provide a definitive diagnosis by isolating the bacteria from clinical samples. However, culture methods may have limitations in sensitivity and specificity.
  • Serological techniques: Serological tests detect antibodies against Leptospira bacteria. These tests include ELISA and agglutination testing, which can be used to confirm infection in acute and convalescent samples.
  • Molecular tests: Tests like PCR (polymerase chain reaction) are used to detect nucleic acids in Leptospira bacteria. Whole blood qPCR is the standard test to diagnose leptospirosis until day 10 of illness, while MAT (microscopic agglutination test) may be considered in specific cases. It’s important to do PCR on whole blood in the first week of illness, urine in the second week, and CSF for patients with meningitis symptoms to help diagnose the infection.



Antibiotics play a crucial role in treating leptospirosis. Penicillin, doxycycline, and third-generation cephalosporins can be used. Leptospirosis infections should be treated promptly after diagnosis, and in severe cases, intravenous antibiotics may be necessary.



The disease surges during monsoon months and is more prevalent in warm, humid countries across urban and rural areas. For example, leptospirosis is a high risk during hurricane season. 

In high-risk areas, prevention can be through:

  • Personal management: Avoid water that might contain animal urine and limit your contact with possibly infected animals. If you have to be near them for work or fun, wear protective gear like clothes or shoes to avoid contact with dirty water or soil. The CDC also recommends wading, swimming, bathing, or ingesting floodwater during hurricane season. Again, in an emergency, if you have to be in floodwater, the CDC recommends wearing waterproof gear and covering any open cuts with bandages.
  • Environment management: Prevent leptospirosis by controlling rodents, maintaining clean animal living spaces, and disinfecting contaminated areas. These practices reduce Leptospira bacteria in the environment, lowering the risk of infection.


Currently, there is no human vaccine for leptospirosis; vaccine research is in progress in an attempt to reduce the disease burden.



In conclusion, leptospirosis is a serious bacterial infection that’s more common than many people realize but often goes unreported. It becomes a bigger problem during stormy weather and natural disasters, spreading easily and infecting a large number of people.

Even though antibiotics can help, it’s hard to diagnose leptospirosis because its symptoms look like other illnesses.

To stop leptospirosis from spreading, we need to focus on prevention. This means taking steps to protect ourselves and making sure there are robust public health measures in place to stop the spread of this bacterial infection. Global collaboration is required to lower the incidence of leptospirosis in endemic regions and prevent transmission to other parts of the world.


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Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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