Leprosy and Tuberculosis: Chronic Diseases Caused by Mycobacteria

Mycobacteria in Tuberculosis

The genus Mycobacterium contains many members, few of which are pathogens. But when pathogenic, chronic diseases such as tuberculosis and Hansen’s Disease may result.

All members of the genus Mycobacterium have special features that make these species resistant to control. Mycobacteria have a unique bacterial cell wall that contains large quantities of a lipid called mycolic acid. This lipid results in a waxy bacterial cell wall that is directly responsible for the control-resistant features of pathogens in this genus.

Staining Mycobacteria

The presence of mycolic acid also makes it difficult to reliably stain Mycobacteria with water-based stains, such as the Gram stain, used to help identify groups of bacteria. A special stain, called the acid-fast stain, must be used to identify Mycobacteria. This staining protocol employs heat to permanently drive a pink dye into the waxy cell wall.

The Chronic Nature of Mycobacterial Diseases

Mycobacterial diseases are chronic, developing slowly due to relatively long generation time of these bacteria. Generation time is how long it takes for a bacterial population to double, as individual bacteria divide by binary fission. Whereas it only takes Escherichia coli, a nonacid-fast bacterium, a matter of minutes to double its population, Mycobacterial generation time varies from hours to days.

Pathogenicity of Mycobacteria

The waxy cell wall also protects this type of bacteria from osmotic effects and many antibiotics. Mycobacteria are one of the few bacteria types that are capable of intracellular growth (multiplying within an animal cell); and when engulfed by phagocytic cells of the immune system, Mycobacteria are resistant to degradation by digestive enzymes of these phagocytes.

Tuberculosis Caused by Mycobacteria

Caused mainly by the bacterium Mycobacterium tuberculosis, TB (also known as Tubercle bacillus) is an infectious disease of the respiratory system that can ultimately disseminate from the lungs and result in a body-wide, systemic infection. The waxy cell wall of M. tuberculosis enables the bacteria to remain viable, in dried aerosol droplets, for up to 8 months. Only a small percentage of people infected with this bacterium will develop the disease, but it only takes one bacterium to infect, and left untreated, active TB results in a mortality rate of approximately 50%.

Those in the medical field, and others with a high risk of contracting TB, are routinely tested with the Mantoux test or the tuberculin skin test (TST). The TST involves injection of a very small amount of a purified protein derivative or tuberculin into the inner part of the lower arm. Testing positive does not, however, indicate a definite infection with TB. False positive TB test results are common and require follow up diagnostics.

Leprosy Caused by Mycobacteria

Also known as Hansen’s disease, this dreaded infection is caused by M. leprae. This unusual bacterium grows best in a climate lower than body temperature, a preference evidenced by the peripheral locations on the human body (fingers, toes, lips, earlobes) where the bacteria is most prone to thrive.

The disease manifests in one two forms. Those who only develop the nonprogessive form, called tuberculoid leprosy, have a strong immune response to the bacteria that is able to kill the body cells infected with M. leprae. Individuals with a weak cell-mediated immune response develop the more well-known form of the disease, lepromatous leprosy, which disfigures by slowly destroying infected tissues.

Those infected, who have access to medical care, typically aren’t diagnosed until they display desensitized lesions or disfigurement. At that point, a skin test, similar to that for tuberculosis, is done.

Treatment of Tuberculosis and Leprosy

Pathogenic Mycobacteria are inherently resistant to eradication, due to the protection derived from the mycolic acid. This genera also is quick to develop resistance to antimicrobial medication. Multi-drug therapy is required to eliminate, or sometimes only control, infection.

Tuberculosis Prevention and Control

Tuberculosis prevention and control

Tuberculosis is a worldwide public health problem and prevention and treatment are necessary to control it.

The three worst public health problems in the world today are malaria, tuberculosis, and human immunodeficiency virus infection. Human immunodeficiency virus infection is the strongest risk factor for the development of active tuberculosis. Should the two diseases occur together, they each worsen the clinical course of the other. More than one-third of the world’s population today has tuberculosis.

Tuberculosi prevention
One hundred years ago, tuberculosis and other infectious ailments were the leading causes of death in the world. In the mid-twentieth century, the development of drugs to treat tuberculosis significantly brought the disease under control. Institutionalized patients who had been contagious for years were no longer capable of spreading tuberculosis to others, and they were able to return to the community.

Over the last few decades, however, the HIV/AIDS epidemic changed the management of this disease.

In essence, there has been a resurgence of tuberculosis because of HIV/AIDS. Worldwide, nine million people acquire tuberculosis each year, and two million deaths from the disease occur yearly. Moreover, there are problems with resistance to anti-tuberculous medications. Specifically, there is multi-drug resistance in which more than one of the agents to treat tuberculosis are not effective.

In Russia, Latvia, South Africa, the United States, and other countries, there are cases of extensively drug resistant tuberculosis, which are quite deadly not only for the patients, but also for the health care staff who manage them.

Groups at risk

Aside from those who are HIV-positive, several other groups of people are at risk for the acquisition of tuberculosis. These include elderly people, infants and small children, injection drug users, and patients with chronic diseases, which impair the immune system such as diabetes and cancer. Patients who are underweight have a predisposition for tuberculosis, and individuals who take long-term steroid therapy are capable of activation of latent tuberculosis.

Anyone who has had tuberculosis during the last two years may experience a recurrence of the disease, and patients whose tuberculosis did not receive adequate treatment will be at risk for it again.

Signs and symptoms of tuberculosis include weakness, coughing blood, weight loss, night sweats, chest pain, and fever. If a person has these symptoms or has spent time around someone who has tuberculosis, he or she must visit a physician or local health department for evaluation. Tuberculosis transmits from one person to another via the air.

In other words, an individual with active tuberculosis can spread the disease to someone else when he or she coughs, speaks, laughs, sneezes, or sings. It does not transmit through hand shakes, kissing, contact with linens or toilet seats, or sharing food or drinks.

If one has exposure to the bacterium which causes tuberculosis, he or she will not necessarily develop active disease. Their tuberculin skin test may become positive, but they may spend the rest of their lives without ever becoming contagious. Active tuberculosis, however, is contagious and requires the use of several drugs over a period of nearly one year. The duration of therapy and the choice of drugs will depend on the individual patient’s condition.

Tuberculosis and pregnancy

Tuberculosis and Pregnancy

Anti-tuberculous agents are necessary for pregnant women who have the disease. Although some of the drugs, such as streptomycin and pyrazinamide, may not be safe for the fetus, other agents, such as isoniazid, ethambutol, and rifampin, are available which do not appear to pose a problem for the baby. The baby is at risk for low birth weight if the mother does not take medication for tuberculosis during pregnancy.

Mothers who are HIV-positive can take pyrazinamide during pregnancy because the benefits of the drug for these patients outweigh its risks.

There is no reason why a mother who takes anti-tuberculous medication cannot breastfeed her child. Small amounts of these medications are present in breast milk, but there is no evidence that this is unsafe for the infant. If the mother takes isoniazid while she breastfeeds, she should also take vitamin B6 supplementation.