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Leprosy has been found in wild chimpanzees

A new study led by the University of Exeter and the Robert Koch Institute reveals that leprosy has been found in wild chimpanzees for the first time. The origins of the infections discovered in Guinea-Bisau and Tai National Park are unclear, but scientists believe that it is probably circulating in more wild animals than previously suspected, either as a result of exposure to infected humans or other unknown environmental sources.

Humans are the main hosts of Mycobacterium leprae, the bacterium causing leprosy. However, spillovers to other mammals such as red squirrels, armadillos, or even captive primates have been known to occur occasionally. This study is the first to document the presence of leprosy in two distinct populations of wild chimpanzees.

“This is the first confirmation of leprosy in nonhuman animals in Africa,” said study lead author Dr Kimberley Hockings, a senior lecturer in Conservation Science at University of Exeter’s Centre for Ecology and Conservation. “It’s amazing that it also happens to be in our closest living relative, the chimpanzee, especially considering how well studied chimpanzees are in the wild.”

The scientists first noticed possible symptoms of leprosy, such as lesions and “claw” hands, in a population of wild chimpanzees in Guinea-Bissau. Since then, further cases have been identified in Tai National Park in western Ivory Coast.

“The strains identified in each chimpanzee population are different, and both are rare in humans and other animal reservoirs worldwide,” reported Dr. Charlotte Avanzi, a postdoctoral fellow at Colorado State University.

“This study unlocks a new step toward the understanding of the disease transmission in endemic countries and more investigations will eventually shed light on the dynamic of transmission between human, animal, and environmental sources.”

According to the scientists, it is possible that in Guinea-Bissau chimpanzees acquired leprosy from humans. However, in Ivory Coast, chimpanzees are more distant from human settlements, so they might have acquired the infection from another animal species, or from environmental sources such as water bacteria or ticks.

Since western chimpanzees are already critically endangered, even the loss of a few individuals could be significant. Further research and long-term health monitoring are needed in order to establish the scale and effects of leprosy among wild chimpanzees.

The study is published in the journal Nature

More about leprosy

Leprosy, also known as Hansen’s disease, is an infectious disease caused by two types of bacteria: Mycobacterium leprae and Mycobacterium lepromatosis. Named after the scientist Gerhard Armauer Hansen who discovered it, the bacteria was the first disease-causing bacterium identified in humans. This slow-growing, chronic bacterial infection primarily affects the skin and nerves, but can also impact the eyes, the inside of the nose, and peripheral nerves in the limbs.

Here’s a summary of what we know about leprosy:


Leprosy is not highly contagious, but it can be passed from person to person. It is believed to be transmitted via droplets from the nose and mouth during close and frequent contact with untreated cases. It is also worth mentioning that a significant portion of people are naturally immune to leprosy.


The disease causes skin lesions that are lighter than the normal skin color and may become numb due to nerve damage. Other symptoms might include weakness and poor eyesight. Because the bacteria reproduce very slowly, the disease has a long incubation period, often taking 5 to 20 years for symptoms to appear after infection.

Types of Leprosy:

Leprosy can manifest in different forms, depending on the individual’s immune response:

  1. Tuberculoid: A mild, less severe form of leprosy. People with this type have only one or a few patches of flat, pale-colored skin (often with decreased sensation). The nerves may be enlarged and inflamed. Tuberculoid leprosy is less contagious than other forms.
  2. Lepromatous: A more severe form of the disease. It causes widespread skin bumps and rashes, numbness, muscle weakness, and other complications. Lepromatous leprosy is more contagious.
  3. Borderline: People with this type of leprosy have symptoms of both tuberculoid and lepromatous leprosy. The disease may get better or worse, or may switch between types.


Doctors often diagnose leprosy through a clinical examination of the characteristic skin lesions and testing sensation in the skin. Additionally, they may take a skin biopsy or a nasal swab for laboratory examination.


Leprosy is curable with a treatment known as multidrug therapy (MDT), as recommended by the World Health Organization (WHO). The treatment uses a combination of antibiotics, usually dapsone, rifampicin, and clofazimine, to kill the bacteria. The duration of treatment can range from 6 months to 2 years or more, depending on the severity of the disease.


Although treatment can cure the disease and prevent it from getting worse, it doesn’t reverse nerve damage or physical disfigurement that occurred before treatment. Therefore, early diagnosis and treatment are key to preventing disability due to leprosy.


The disease occurs worldwide, but it is most common in warm, wet areas in the tropics and subtropics. WHO is striving to eliminate the disease, and over the past decades, there has been significant progress towards this goal, with a major decrease in the number of cases.

However, leprosy remains a significant health problem in some areas, including parts of India, Brazil, and Indonesia.

In the animal kingdom, armadillos are the only known non-human carriers of leprosy. The bacterium causing leprosy has been found in wild armadillos in the southern United States, and there have been reported cases of transmission to humans.

It’s important to note that information about leprosy continues to evolve, and research is

ongoing to further understand the transmission, symptoms, treatment, and prevention of leprosy.

Vaccination and Immunity:

The BCG (Bacillus Calmette–Guérin) vaccine, initially developed for tuberculosis, offers some protection against leprosy and is often given in countries where leprosy is more common. However, the immunity it offers varies and is not fully protective.

In addition, it seems that a significant number of people are naturally immune to leprosy, likely due to genetic factors. It’s worth mentioning that the majority of people who are exposed to the bacteria that cause leprosy never develop the disease.

Leprosy and Stigma:

Historically, leprosy has been a highly stigmatized disease due to its potential to cause physical disfigurement and disability. In some cultures, people with leprosy have been ostracized or segregated from the rest of society.

While effective treatments now exist, this stigma can still persist, contributing to delays in seeking treatment and psychological distress for those affected. Efforts are being made worldwide to combat this stigma and to ensure that people with leprosy can lead normal lives and are not discriminated against.

By Andrei Ionescu, Staff Writer

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