Lemurs, Tuberculosis and Spillover, Oh My!

In October 2022, several lemurs at a zoo in Madagascar were discovered to have tuberculosis. The zoo isolated the lemurs from other animals, but kept the zoo open to the public, assuring that human visitors would be safe from the disease. No humans, guests or zookeepers, came down with tuberculosis from these lemurs.

What is TB?

Tuberculosis (TB) is an airborne bacterial infection caused by the organism Mycobacterium tuberculosis that primarily affects the lungs, although other organs and tissues may be involved.

Tuberculosis is spread when infected individuals cough or sneeze respiratory droplets containing the bacteria and it’s breathed in by others. Unlike respiratory viruses, which are easily passed between sick individuals, it takes prolonged exposure to become infected with TB. After the bacteria is inhaled, it lodges itself in the lung tissue.

In healthy individuals, TB can be latent and not become active until the immune system is in a weaker state. At that time, the TB may activate in the lungs and also move from the lungs through the blood or lymphatic system to different places in the body.

You are at a higher risk for contracting TB if:

• You are in close contact with someone who has the illness,
• You live in parts of the world with high rates of TB, such as India and parts of Asia and Africa
• You are living with HIV, experiencing homelessness or inject drugs
• You work in facilities with higher risk people, such as hospitals, shelters, prisons and nursing homes

Is TB treatable?

Symptoms of TB include fever, chills, a nagging cough that lasts more than three weeks, weight loss and night sweats. The weight loss and the so-called “wasting away” associated with TB led to the popular 19^th century name of consumption. Coughing up bloody mucus is a telltale sign of TB in the lungs. Although TB is no longer common in the United States, about 1.8 billion people in the world have inactive TB, while 10 million people have active TB. All TB is treatable with medication, but some more drug-resistant TB strains will require multiple medications for a longer period.

Despite being treatable, TB can make people very sick, so it is not a surprise that the Madagascar zoo took the illness of its lemurs seriously. Thanks to the actions of the zoo, no humans contracted tuberculosis from these lemurs, however, this does not mean humans are not capable of contracting respiratory illness from animals.

Spillover and Zoonotic Diseases

Many respiratory illnesses that we are familiar with were originally passed on to humans from animals. In fact, 60-75% of human infectious diseases started from pathogens that were originally passed around in non-human animal species. Such illnesses include three coronaviruses - Middle Eastern respiratory syndrome (MERS), severe acute respiratory syndrome (SARS), and COVID-19. While MERS originated in camels in the Middle East (as the name suggests), SARS is thought to have started in wild animals such as civets and raccoon dogs while COVID-19 is thought to have originated in bats. These are just some of the diseases that have jumped the species barrier, which is also known as “spillover” in the world of epidemiology.

Influenza viruses have spread from animals to humans such as the swine flu (H1N1) that began in pigs and in rare cases, avian flu which is typically in wild water birds and domestic poultry like chickens. There are many pathogens that jump between species and never make humans ill or cause an outbreak of disease. This is because human bodies are not the same as animals and many viruses cannot survive or replicate in a human host the same as they do in the animal.

But just how do illnesses in wild animals jump to humans? There are many ways in which a person can come into contact with illness from animals. The most common is through direct contact, such as during the handling, butchering and consumption of meat from animals that contain these pathogens. In addition to meat consumption, in many countries live animals are sold as pets, for livestock or for medicinal or cultural purposes, which brings humans into direct contact with these viruses. The viruses may then be passed on to humans through blood or other fluids and/or respiratory droplets.

Humanity’s impact on the environment also contributes to the increase in emerging viruses derived from animals. Deforestation and our continued encroachment into animals’ natural habitats will only continue to expose us to new viruses from animals, as they will have nowhere else to go.

How big of a risk did the infected lemurs pose?

Knowing these risks associated with handling sick animals, it was important that the Madagascar zoo took great care to ensure the safety of the zookeepers and guests. However, TB is less likely to be passed casually without prolonged exposure, so there was very little risk with guests being infected by viewing the lemurs in their enclosures. The zoo took the proper precautions by separating the infected animals while allowing guests to visit their zoo.

To learn more about tuberculosis, visit Lung.org/tuberculosis.