Mycobacterium leprae

Tiny germs cause a sickness called leprosy.

These germs live in skin and nerves. They like cool parts of the body.

Some armadillos can have these germs too. A doctor found these germs a long time ago.

Now, doctors use special medicine to help. This medicine can make people well again. It is good to know that people can get better.

A tiny germ called Mycobacterium leprae causes Hansen's disease. People often call this disease leprosy.

This germ is a rod-shaped bacterium. It is very small. It is hard to grow in a lab. This is because it is an obligate intracellular parasite. This means it must live inside the cells of a host to survive. It takes many nutrients from the host to grow.

The germ likes cool parts of the body. It targets the skin, nose, and nerves. Humans are the main hosts. But nine-banded armadillos and red squirrels can carry it too.

A doctor named Gerhard Armauer Hansen found this germ in 1873. It was the first germ found to cause disease in people. In the past, one medicine called dapsone helped. Now, the germ can resist that medicine. Doctors use a set of three drugs to treat it. This helps people get well. The number of new cases has dropped a lot since the 1980s.

A tiny germ called Mycobacterium leprae causes Hansen's disease. Many people call this disease leprosy.

This germ is a rod-shaped bacterium. It is very small, measuring only 0.3 micrometers wide. It can be straight or slightly curved. The germ has a waxy coating called mycolic acid. This coating makes the bacterium hard to destroy. It also makes the germ grow very slowly. It can take 12 to 14 days just to double in number. This is much slower than other bacteria like E. coli. Because it grows so slowly, it is a very patient germ.

This bacterium is an obligate intracellular parasite. This means it must live inside the cells of a living host. It cannot grow in a lab using normal food. Instead, it relies on the host for nutrients and energy. It mostly infects specific cells like macrophages and Schwann cells. The germ likes cool temperatures between 27 and 30 degrees Celsius. This is why it targets the skin, nose, and nerves. These parts of the body are often cooler than the core.

The germ has lost many genes over time. This is called reductive evolution. It happens because the host provides what the germ needs.

A doctor named Gerhard Armauer Hansen discovered the germ in 1873.

This was a huge discovery in science. It was the first time anyone identified a bacterium as a cause of disease in humans. For a long time, a medicine called dapsone was used to treat it. However, the germ started to resist this drug in the 1960s. Now, doctors use a multidrug treatment called MDT. This includes dapsone, rifampicin, and clofazimine.

Using three drugs together helps keep the germ from resisting the medicine.

Humans are the main hosts for this germ. However, other animals can carry it too. Nine-banded armadillos and red squirrels are the only other natural hosts. In the United States, people have been infected after contact with armadillos. This is known as zoonotic transmission. Scientists have even found the germ's DNA in soil. They found it in houses in Bangladesh and in armadillo holes in Suriname. The germ is found all over the world. It is most common in parts of Africa, Asia, and South America. It is found in places like Brazil, India, and Nepal.

Even though the disease is serious, it is curable. Since the 1980s, the number of cases has dropped by 95 percent. This is thanks to the new multidrug treatments. The World Health Organization says leprosy is now eliminated as a public health problem. This means there is less than one case for every 10,000 people. Scientists are still studying the germ's genome to learn more. They completed the first genome sequence in 2001. They also finished a sequence from a strain in India in 2013. Learning about these tiny germs helps us protect people everywhere.

Mycobacterium leprae is a specialized bacterium that causes Hansen's disease, commonly known as leprosy. This chronic infectious disease targets the skin, eyes, nose, and muscles, and it can damage peripheral nerves.

The bacterium is a Gram-positive, rod-shaped organism. It is also described as an acid-fast bacterium. This means it possesses a waxy coating of mycolic acid. This unique cell wall makes the organism difficult to destroy. It also contributes to an extremely slow replication rate. Scientists classify it as an obligate intracellular parasite. This means it must live inside the cells of a host to survive.

Because it is an obligate intracellular parasite, Mycobacterium leprae cannot be grown in standard laboratory media. It lacks the ability to survive in a cell-free environment. Instead, it relies heavily on its host for nutrients and metabolic intermediates. The bacterium primarily infects macrophages and Schwann cells. Within these host cells, the bacteria are often found in clumps called "globi." They may also appear organized in structures known as a palisade. The bacteria prefer cool temperatures between 27 and 30 degrees Celsius. This temperature preference explains why they target the skin, nasal mucosa, and peripheral nerves.

This reliance on a host is the result of a process called reductive evolution. Over time, the bacterium's genome has experienced significant gene deletion and decay. This evolution has impaired many of its metabolic abilities. For example, it has lost the ability to use common carbon sources like acetate and galactose. Its ability to degrade lipids is also impaired due to missing enzymes. However, its anabolic pathways remain largely unaffected. It can still synthesize most amino acids, though it cannot make methionine or lysine. It also retains the ability to produce essential genetic material like nucleotides. This reduction in genome size is an extreme case of evolutionary downsizing.

The genome of Mycobacterium leprae is notably small. The first genome sequence was completed in 2001. A second sequence from a strain in Tamil Nadu, India, was finished in 2013. This Indian strain contains 3,263,203 base pairs. It has an average G+C content of 57.8 percent. This is much lower than its relative, Mycobacterium tuberculosis. In Mycobacterium leprae, less than half of the genome contains functional genes. More than 1,000 genes are actually pseudogenes. These are non-functional segments of DNA that resulted from mutations. This high number of pseudogenes is the highest among published bacterial genomes.

History shows that Mycobacterium leprae was a landmark discovery in medicine. In 1873, the Norwegian physician Gerhard Armauer Hansen identified the bacterium.

This was the first time a bacterium was identified as the cause of a human disease. For many years, the antibiotic dapsone was used as a treatment. However, the bacterium developed resistance to dapsone alone during the 1960s. To combat this, the World Health Organization now recommends multidrug therapy (MDT). This treatment combines dapsone with rifampicin and clofazimine.

Using multiple drugs prevents the bacteria from developing resistance.

While humans are the primary hosts, the bacterium has a narrow host range. The only other natural hosts are nine-banded armadillos and red squirrels.

Contact with armadillos can lead to zoonotic transmission in humans. In the United States, studies have linked leprosy cases to armadillo contact. Scientists have also detected the bacterium's DNA in environmental sources. This includes soil in Bangladesh and armadillo holes in Suriname. The disease has a global distribution, but it is most prevalent in sub-Saharan Africa, Asia, and South America. High infection rates have been noted in armadillos in the Brazilian state of Pará.

Since the introduction of multidrug therapy in the 1980s, the impact has been massive. The prevalence of leprosy cases has declined by 95 percent globally. Because of this success, the World Health Organization declared leprosy eliminated as a public health problem. This status is defined as having fewer than one case per 10,000 people. Research into the bacterium's evolution continues to provide new insights. Studies of medieval skeletons have even allowed scientists to sequence ancient DNA. These studies help us understand how the disease spread from East Africa to Europe and the Americas.