Lepra Bacilli (Study Notes) | Microbiology

Let us make an in-depth study of the lepra bacilli. The below given article will help you to learn about the following things:- 1. Myco. Leprae 2. Immunology of Myco. Leprae 3. Lepromin and BCG Vaccination 4. Chemotherapy and Chemoprophylaxis and 5. Application to Nursing.

Myco. Leprae:

The organism, Myco. leprae, responsible for lep­rosy (Hansen’s disease) was discovered in 1874 by the Norwegian doctor; Hansen. Hence, it is called as Hansen’s bacillus.

Morphology:

Myco. leprae have many proper­ties common with tubercle bacilli. They are straight or slightly curved bacilli and have club-shaped swellings. They measure 1 to 8µ in length and 0.3 to 0.5 µ a in breadth, occurring in groups resembling packets of ciggrsorclusters. They are decolorized more eas­ily than Myco. tuberculosis. They are non-motile, they produce neither spores nor capsules and are Gram positive.

Myco.leprae is similar to Myco. tuberculosis in chemical composition. Their lipid content ranges from 9.7 to 18.6 per cent. Besides mycolic acid, they con­tain laeprosinic oxyacid, free fatty acids, wax (leprozine), alcohols and polysaccharides.

Cultivation:

Many workers have made attempts to cultivate Myco. leprae, but ultimately they became unsuccessful. However, successful results have been claimed by inoculating the armadillos and the foot pad of mouse.

Pathogenesis:

Leprosy is a disease of great antiquity and is infective granuloma developing as:

1. Lepromatous or nodular type in which granuloma­tous nodules (lepromata) form in the skin, mucous membrane and various organs (e.g., lungs, liver, spleen, testes);

2. Tuberculoid type, when the granu­lation tissues infiltrate certain nerves and lead to motor and sensory nerves paralysis with characteristic trophic change (e.g., anaesthetic skin areas—macu­lae). Both types of the lesions may occur in the same patient.

Immunology of Myco. Leprae:

Many million people encounter Myco. leprae, yet only a small proportion may develop clinical dis­ease; the majority develop protection immunity.

1. Protection antibody develops in most indi­viduals after a sub-clinical infection with Myco. leprae.

It may be from self-healing or with indeterminate or tuberculoid disease:2. Inside the macrophages, Myco. leprae are broken down and processed, with mycobacterial an­tigens then being displayed on the cell surface to­gether with Human Leucocyte Antigen (HLA), class II antigen. This antigen complex is recognised by and interacts with T cells through T cell receptors and T cell proliferation results from this antigen stimulation.

The activated T cell also produces cytokines which are polypeptides that act as molecular regulators by stimulating other components of the immune system. The growth and activation of T cells is enhanced by the cytokines inter leukine (IL) 1 and 2 while other cytokine interferon gamma (IFNy) activate macro­phage so that Myco. leprae are killed. Ultimately the immunological memory is established to encounter Myco. leprae subsequently. Based on this, there is possibility to discover a vaccine against leprosy. Laboratory Diagnosis:

Films of lymph exudate from the ulcerated nodule on the skin or non-ulcerated nodule as well as from scrapings or secretions from nasal mucosa can be stained with Ziehl-Neelsen method with 5 per cent sulphuric acid. The character­istic acid-fast bacilli are present in the films. When lungs are affected, the bacilli may be seen in the spu­tum which can be differentiated from tubercle bacilli by Ziehl-Neelsen staining and by inoculation into guinea pig. Infection of the mouse foot pad can be initiated with even a few leprosy bacilli and is fol­lowed by the production of characteristic lesion.

The production of Myco. leprae-antigens lead to hopes that a serological test for leprosy could be de­veloped. Myco. leprae synthesizes a unique species spe­cific lipid, phenolic glycolipid (PGL) which is found in substantial amounts in tissues surrounding foci of in­fection. PGL is an important antigen and high titers of antibodies directed against PGL are only found in lep­rosy patients. Serological test, which is not specific and sensitive and cross reacts with Myco. tuberculo­sis antigen, is not useful to detect antibody, yet is under experimentation.

As PCR method develops, it will be undoubt­edly be useful in the diagnosis of paucibacillary lep­rosy and early disease, when few bacilli are present. PCR to amplify part of a Myco. leprae protein antigen (36 K Da) was able to detect Myco. leprae with a detection limit of one bacterium when using purified Myco. leprae DN A and a limit of 1,000 bacte­ria when using armadillo liver. This is more considera­bly sensitive than other methods for direct detection of Myco. leprae such as microscopy. It will be exciting to use PCR as a tool for epidemiological studies.

Transmission:

Leprosy is often acquired in child­hood or early adult life and is most common among the lower social classes. Males are more often af­fected than females. Infection is probably spread by direct contact through the skin abrasion or may be acquired by inhalation of infected dust via the nasal mucosa.

Blood sucking insects also may possibly act as carriers. Patients with lepromatous lesions are much more infectious than tuberculosis cases. The incuba­tion period is variable (weeks to years), but it is most commonly 2-4 years. Because of its chronicity, crippling disabilities and social barriers, leprosy presents very large public health and economic problem in many developing countries.

Lepromin and BCG Vaccination:

Lepromin, as ordinarily used, is a boiled unstandardized extract of leprous tissues, which when injected intracutaneously, produces an area of nodu­lar infiltration reaching its maximum in 3 to 5 weeks (Mistuda reaction) in cases of tuberculoid leprosy and in apparently healthy people. The reaction is usually negative in cases of lepromatous leprosy.

Recently an antigen containing 160 millions le­pra bacilli per ml has been recommended as “standard lepromin” of which 1:4 dilution containing 40 million bacilli would, on intradermal injection, be ad­equate to produce a nodule of 3 mm or more after 4 weeks as a criterion of positivity. The positive reaction indicates the resistance to leprosy and the negative reaction is related to cell mediated immunity defi­ciency.

Chemotherapy and Chemoprophylaxis:

Oral administration, in particular dapsone (4-4’diamino-diphenylsulphone or DDS) has become the most practical chemotherapy for mass campaign against leprosy. The recommended dose ranged from 6.0 to 10 mg per kg. body weight per week over a period of 3-5 years or more depending upon the na­ture and extent of the infection. Long term chemoprophylaxis of leprosy with dapsone among child contacts of infective cases has given encouraging result in India.

Application to Nursing:

Public health nurse has a very important role to play in the control of programme of leprosy, she should have a main objective of creating in the minds of the community, the patients and their families a reasoned attitude towards leprosy. She should also educate in clear explicit language that the leprosy is a curable disease, if diagnosed early and the treatment started early.

Children can get the infection by contact with infective cases, which can be prevented by chemo­therapy with dapsone. Successfully she should also advise the community so that their children should not be allowed to come in contact with the infective cases and she should also take all possible steps to rehabilitate the lepers in the society through mass community education.