Explained | Leptospirosis, a disease that surges in the monsoon months

The disease is an occupational hazard for people working in agricultural settings. Its severity ranges from a mild flu-like illness to being life-threatening.

June 13, 2023 10:30 am | Updated June 30, 2023 06:48 pm IST

A scanning electron micrograph of many Leptospira bacteria on a polycarbonate filter.

A scanning electron micrograph of many Leptospira bacteria on a polycarbonate filter. | Photo Credit: Public domain

Leptospirosis has emerged as an important infectious disease in the world today. It is a potentially fatal zoonotic bacterial disease that tends to have large outbreaks after heavy rainfall or flooding.

The disease is more prevalent in warm, humid countries and in both urban and rural areas. It affects an estimated 1.03 million people every year, killing around 60,000. The burden of leptospirosis is expected to increase in the future as the urban poor population in tropical countries increases even as sanitary infrastructure falls shorter. In India, thousands of people are affected by leptospirosis every year.

However, the numbers at the global and regional levels aren’t exact because of misdiagnosis (its symptoms mimic those of dengue, malaria, and hepatitis), limited access to reliable diagnostics, lack of awareness among treating physicians, and lack of environmental surveillance.

Within India, studies have found that leptospirosis is more common in the south, although this could be due to the region’s better healthcare and thus better disease detection.

What causes the disease?

The disease is caused by a bacterium called Leptospira interrogans, or leptospira. It is a contagious disease in animals but is occasionally transmitted to humans in certain environmental conditions.

The carriers of the disease can be either wild or domestic animals, including rodents, cattle, pigs, and dogs.

The cycle of disease transmission begins with the shedding of leptospira, usually in the urine of infected animals.

According to the U.S. Centres for Disease Control and Prevention, infected animals can continue to excrete the bacteria into their surroundings for a few months, but sometimes up to several years.

Which people are at risk?

Humans become part of the cycle when they come in direct contact with this urine or indirectly, through soil and water that contain leptospira bacteria. A person is more likely to contract leptospirosis if they have cuts or abrasions on their skin.

The disease is also considered an occupational hazard for people working in agricultural settings, with animals, or in sanitary services that bring them into contact with contaminated water.

Recreational activities in contaminated lakes and rivers are also reported to increase the risk of leptospirosis.

What are the symptoms of leptospirosis?

The severity of a leptospirosis infection ranges from a mild flu-like illness to being life-threatening.

The infection can affect many organs, reflecting the systemic nature of the disease. This is also why the signs and symptoms of leptospirosis are often mistaken for other diseases.

In milder cases, patients could experience a sudden onset of fever, chills, and headache – or no symptoms at all. But in severe cases, the disease can be characterised by the dysfunction of multiple organs, including the liver, kidneys, lungs, and the brain.

Animals exhibit a variety of clinical symptoms and indications. In cattle and pigs, the disease can potentially cause reproductive failure, stillbirths, and weak calves or piglets. Dogs experience a range of symptoms, including fever, jaundice, vomiting, diarrhoea, renal failure, and even death.

What are the misconceptions about leptospirosis?

Preventing leptospirosis requires appropriate and adequate health education, community health empowerment, and preventive habits.

The disease has been called “ili jwara” in Kannada and “eli pani” in Malayalam, both meaning “rat fever”. This usage has fed the common belief that rats are the sole cause of the disease, which is not true.

Leptospirosis has a spectrum of reservoir hosts, including pigs, cattle, water buffaloes, goats, dogs, horses, and sheep. Further, seasonal patterns such as the onset of the monsoon can also potentially facilitate the disease’s incidence and transmission.

Ambient air that is more humid can help the pathogenic leptospira survive longer in the environment, thus increasing the risk of disease exposure in the community.

Working barefoot in a flooded paddy field increases the risk of contracting leptospirosis. Representative photo.

Working barefoot in a flooded paddy field increases the risk of contracting leptospirosis. Representative photo. | Photo Credit: Foto Murthy/Unsplash

The incidence of the disease is also linked to extreme weather events like floods and hurricanes, when people are exposed to contaminated water.

Similarly, poor waste management, a high density of stray animals, faulty drainage systems, and unhygienic sanitation facilities are major drivers of the disease in urban areas. In rural parts, these are contaminated paddy fields, dirty livestock shelters, and poor water-quality and sanitation.

Despite this complexity, the use of “rat fever” as a colloquial term for leptospirosis undermines a more holistic understanding of the disease’s causes.

If we are to protect people, we must use the correct terms, study the ecology of the disease and use the findings to inform healthcare policy, improve health literacy, and engage with people’s concerns.

How can we prevent leptospirosis?

Leptospirosis control can benefit from a ‘One Health’ approach. ‘One Health’ is an interdisciplinary approach that recognises the interconnections between the health of humans, animals, plants, and their shared environment.

People who frequently interact with animals or their urine should exercise particular caution, such as by wearing personal protective equipment like gloves and boots. The same goes for workers in flooded fields where there’s a chance of being exposed to contaminated water. They should take extra care if they have cuts or abrasions on their lower extremities.

Preventing animals from getting infected is also important to reduce the risk of leptospirosis spreading and to limit farmers’ economic losses (when the disease causes reproductive failures in pigs and cattle). This in turn requires sanitary animal-keeping conditions, which is also desirable to improve the animals’ health and to prevent the spread of many diseases.

Given the spike in leptospirosis during the monsoons, it is best to take precautions, including washing one’s arms and legs with an antiseptic liquid after handling animal waste and after working in water.

In sum, with ‘One Health’ in mind, public health professionals must work closely with the animal husbandry department to familiarise people about the dangers of leptospirosis, and create countermeasures that work for the health of both people and animals.

Irfan shakeer is a Senior Research Associate and Iswarya Lakshmi is a Research Associate at Ashoka Trust for Research in Ecology and the Environment, Bengaluru where they are associated with the IndiaZooRisk+ project (India-U.K. joint initiative).

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