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Author: Vanessa Ngan, Staff Writer, 2003.
Leprosy is a chronic bacterial infection with Mycobacterium leprae. It primarily affects the skin, mucous membranes (eg, nose), peripheral nervous system (nerve function), eyes and testes. The form the disease takes depends on the person's immune response to the infection.
Leprosy is also known as Hansen disease and is one of the oldest known diseases of mankind. It is curable but if untreated can lead to severe deformities.
In 2008, a new species, M. lepromatosis, was described causing a diffuse form of lepromatous leprosy in Mexico.
There are several forms of leprosy that range from the mildest indeterminate form to the most severe lepromatous type. More severe forms arise because of a less effective immune response to the infection. Most of those infected mount an appropriate immune response and never develop signs of leprosy.
Depending on clinical features, leprosy is classified as:
Patients with indeterminate leprosy, a very early form of leprosy, may either be cured or progress to one of the other forms of leprosy depending on their immune status. Within each type of leprosy, a patient may remain in that stage, improve to a less debilitating form or worsen to a more debilitating form depending on their immune state. Lepromatous leprosy is the only form that never reverts to a less severe form.
Leprosy can affect people of all races all around the world. However, it is most common in warm, wet areas in the tropics and subtropics. Worldwide prevalence is reported to be around 5.5 million, with 80% of these cases found in 5 countries: India, Indonesia, Myanmar, Brazil and Nigeria. In New Zealand, we most often come across cases from Samoa, Tahiti and the Cook Islands.
Leprosy presents most often during two different periods of life, between the ages of 10 and 14 and in those aged 35–44 years old. It is rarely seen in infants. In nearly all cases, leprosy is due to prolonged contact with another person with the disease. It has rarely been associated with handling infected armadillos in Southern states of the USA.
Leprosy bacteria have been found in armadillos in Brazil, and to a lesser extent, in the southern United States of America. People who hunt, kill, process or eat armadillo meat are at a higher risk for infection with M. leprae .
Once infected with the mycobacteria, the average incubation period is two to three years, but it can range from 6 months to 40 years or longer. In 90% of patients, the first sign of the disease is a feeling of numbness, which may precede skin lesions by a number of years. Temperature is the first sensation lost, followed by light touch, pain and then deep pressure. Sensory loss usually begins in the extremities (toes and fingertips).
The first skin lesion is usually the indeterminate type, which causes one or a few hypopigmented (pale) spots before evolving into the borderline, tuberculoid or lepromatous types.
Left untreated, the following problems may occur in lepromatous leprosy.
Leprosy has very characteristic clinical features but the diagnosis must be confirmed because of the need for prolonged treatment with antibiotics. A skin biopsy may show characteristic histopathology, with granulomas (mixed inflammatory cell infiltrate in the deeper layers of the skin, the dermis) and involvement of the nerves. Special staining of the tissue may show acid-fast bacilli, the number visible depending on the type of leprosy. Immunohistochemistry stains can be helpful when the bacilli are few in number.
The bacteria may also be found in lepromatous leprosy on smears taken from skin slits made in the ear lobes, but the smears will be negative in the tuberculoid or borderline forms of the disease.
Management of leprosy is aimed at stopping the infection and minimising potential physical deformities. Antibiotics used first-line to eliminate organisms include dapsone, rifampicin and clofazimine. Varying regimens with multidrug therapy (MDT) are used depending on the type of leprosy and the severity of the infection. This may be a combination of two or three antibiotics given over varying lengths of time (up to years). Other antibiotics include minocycline, ofloxacin and clarithromycin.
The World Health Organization has produced treatment guidelines for leprosy (2018), which advocate three drugs including clofazamine for 6 months in paucibacillary leprosy and 12 months in multibacillary leprosy.
Surgery may sometimes be used to drain abscesses to restore nerve function, reconstruct a collapsed nose, or to improve function or appearance of affected areas.
Patient education is paramount. Leprosy can be cured but it is essential to take the full course of medication. It is no longer infectious once treatment has begun. Patients should be instructed how to deal with existing nerve damage, for example, protecting numb feet from injury. Physical, social and psychological rehabilitation is necessary for those in whom the neglected disease has caused havoc.
Lepra reactions occur in 30–50% of patients with leprosy. They may occur before, or more often, after the start of treatment and are induced by medicines, stress and surgical procedures. There are 3 main types of reaction.
Lepra type I (reversal) reaction often affects those with borderline shifting toward tuberculoid type, as the cell-mediated immune system improves in the first few months of drug treatment or for some other reason such as pregnancy.
Type 1 reactions result in fever, red swollen skin, and tender peripheral nerves. Treatment requires oral corticosteroids and nonsteroidal anti-inflammatories.
Lepra type II reaction is also called erythema nodosum leprosum (ENL). It affects those with borderline lepromatous or lepromatous leprosy and is a humoral (antibody-antigen) reaction to immune complexes. Repeated episodes tend to occur later in treatment than the type I reaction, usually after several years.
ENL presents as painful red nodules (lumps), which can blister or ulcerate, accompanied by fever, malaise, joint pain, nerve pain, eye disease and involvement of other organs. Treatment may include clofazimine, thalidomide, corticosteroids, colchicine, ciclosporin or tumour necrosis factor antagonists.
Lucio phenomenon is a cutaneous vasculitis in patients with lepromatous leprosy. It is difficult to treat and regimens must include MDT.
Lucio phenomenon presents as odd-shaped red patches and ulcers on hands, wrists, ankles and feet. It is associated with fever, arthritis, liver and kidney disease.
People in contact with someone with leprosy may be treated with single-dose rifampicin for short-term (2 years) postexposure prophylaxis; this reduces the risk of developing paucibacillary leprosy by 50%.
Research is being undertaken to determine whether immunisation can be achieved using a non-pathogenic, environmental mycobacterium, M. indicus pranii, which may reduce the risk of developing leprosy in at-risk populations as well as reducing the severity of leprosy in those that are infected.
Guidelines for the diagnosis, treatment and prevention of leprosy. World Health Organization. 2018. PDF download.
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