leprosy and mycobacterium

Leprosy, also known as Hansen's disease, is a chronic infectious disease caused by the bacterium Mycobacterium leprae. It primarily affects the skin, peripheral nerves, mucosa of the upper respiratory tract, and the eyes. Leprosy is one of the oldest known diseases and remains a public health concern in some parts of the world.

Transmission:

Leprosy is thought to be transmitted through respiratory droplets when untreated individuals with the disease cough or sneeze. However, it is relatively difficult to contract, and not everyone who comes into contact with the bacteria will develop the disease. The exact mode of transmission is not fully understood, and the incubation period can be quite long, ranging from months to years.

Clinical Presentation:

Leprosy can present in various forms, depending on the individual's immune response to the bacterium. There are two main types of leprosy based on the clinical and immunological features:

1. Tuberculoid Leprosy: This form is characterized by a strong cellular immune response, causing well-demarcated skin lesions with raised edges and a loss of sensation in the affected areas. Nerve damage can lead to muscle weakness or paralysis.

2. Lepromatous Leprosy: This form is associated with a weaker immune response, resulting in widespread skin lesions, nodules, and thickening of the skin. The nasal mucosa can also be affected, leading to a characteristic "lion-like" facial appearance.

Diagnosis:

Diagnosing leprosy involves a combination of clinical examination and laboratory tests. Skin biopsies, slit-skin smears, and specific antibody tests are used to confirm the presence of M. leprae in affected tissues.

Treatment:

Leprosy is treatable with a combination of antibiotics, usually a multidrug therapy (MDT) regimen. The World Health Organization (WHO) recommends the use of rifampicin, dapsone, and clofazimine for various durations depending on the type and severity of the disease. Early diagnosis and treatment are crucial to prevent disability and complications associated with nerve damage.

Prevention and Control:

Leprosy is preventable and can be controlled through the following measures:

- Early detection and treatment of cases

- Contact tracing and screening of close contacts

- Implementing multidrug therapy for affected individuals

- Health education and raising awareness about the disease

- Improved living conditions and social support for affected communities

Today, leprosy is considered a controlled disease in most countries due to improved diagnostic tools and access to effective treatment. However, efforts are still ongoing to eliminate the disease and ensure access to treatment and care for those affected. Stigma and discrimination associated with leprosy are also addressed through awareness campaigns and advocacy.

The lepromin test, also known as the lepromin skin test or lepromin sensitivity test, is a diagnostic test used in the evaluation of leprosy, a chronic infectious disease caused by Mycobacterium leprae. The test helps to determine the individual's immune response to the leprosy bacillus and is useful in classifying the disease into two main types: tuberculoid leprosy and lepromatous leprosy.

Procedure:

The lepromin test involves injecting a small amount of lepromin antigen, which is a protein derivative of M. leprae, into the skin of the forearm or back. The test site is then observed for any skin reaction over the next 48 to 72 hours. The two main types of lepromin tests used are the Mitsuda test and the Fernandez test.

1. Mitsuda Test: This is the classic lepromin test and is more commonly used. The injected lepromin antigen contains both killed (inactivated) Mycobacterium leprae and some other constituents. The skin reaction is measured at the test site after 48 to 72 hours.

2. Fernandez Test: This variation of the lepromin test uses a purified protein derivative (PPD) of M. leprae, containing only specific components of the bacterium. The skin reaction is also observed after 48 to 72 hours.

Interpretation:

The interpretation of the lepromin test results helps to distinguish between tuberculoid leprosy and lepromatous leprosy:

1. Tuberculoid Leprosy: In individuals with tuberculoid leprosy, the lepromin test usually elicits a positive delayed-type hypersensitivity reaction. This means that the test site shows induration (raised and hardened skin) with or without erythema (redness). A positive reaction indicates that the individual's immune system is reacting to the lepromin antigen, suggesting a strong cellular immune response. This is typical of patients with a more limited and localized form of leprosy.

2. Lepromatous Leprosy: Individuals with lepromatous leprosy may show a negative or weak response to the lepromin test. This suggests a weaker cellular immune response to the lepromin antigen, and it is characteristic of patients with a more widespread and disseminated form of leprosy.

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It is important to note that the lepromin test is not used to diagnose leprosy itself but to aid in classifying the disease type and assessing the individual's immune response to M. leprae. The diagnosis of leprosy is usually made based on clinical symptoms, skin biopsy, and other laboratory tests. The lepromin test provides additional information to support the overall diagnostic process and treatment planning.

Click for a  online MCQ test on microbiology

 Here are ten multiple-choice questions (MCQs) on Mycobacterium:

1. Which genus of bacteria includes the species Mycobacterium tuberculosis, the causative agent of tuberculosis?

   a) Streptococcus

   b) Escherichia

   c) Mycobacterium

   d) Staphylococcus

   Answer: c) Mycobacterium

2. Mycobacteria are classified as Gram-negative bacteria due to the presence of:

   a) A thick layer of peptidoglycan in the cell wall

   b) A thin layer of peptidoglycan in the cell wall

   c) A thick layer of lipopolysaccharides in the cell membrane

   d) A thin layer of lipopolysaccharides in the cell membrane

   Answer: b) A thin layer of peptidoglycan in the cell wall

3. Mycobacterium leprae is the causative agent of:

   a) Tuberculosis

   b) Leprosy (Hansen's disease)

   c) Diphtheria

   d) Whooping cough (pertussis)

   Answer: b) Leprosy (Hansen's disease)

4. Which staining method is commonly used to visualize Mycobacterium species?

   a) Gram staining

   b) Acid-fast staining (Ziehl-Neelsen staining)

   c) Crystal violet staining

   d) Giemsa staining

   Answer: b) Acid-fast staining (Ziehl-Neelsen staining)

5. Mycobacterium tuberculosis primarily infects which organ in the human body?

   a) Liver

   b) Lungs

   c) Kidneys

   d) Brain

   Answer: b) Lungs

6. The unique waxy outer layer of Mycobacterium species is composed of:

   a) Cholesterol

   b) Peptidoglycan

   c) Mycolic acids

   d) Lipopolysaccharides

   Answer: c) Mycolic acids

7. Mycobacterium avium complex (MAC) infections most commonly affect individuals with:

   a) Tuberculosis

   b) HIV/AIDS

   c) Diabetes

   d) Asthma

   Answer: b) HIV/AIDS

8. Mycobacterium bovis is responsible for which zoonotic disease in humans?

   a) Brucellosis

   b) Anthrax

   c) Bovine tuberculosis

   d) Plague

   Answer: c) Bovine tuberculosis

9. The BCG vaccine is used to protect against which disease caused by Mycobacterium species?

   a) Tuberculosis

   b) Leprosy

   c) Anthrax

   d) Meningitis

   Answer: a) Tuberculosis

10. Mycobacterium species are characterized by their slow growth, often requiring special media and extended incubation periods. This property is due to:

    a) Lack of cell wall

    b) High oxygen requirements

    c) Formation of endospores

    d) Thick, waxy cell wall

    Answer: d) Thick, waxy cell wall