January 29, 2005

LEISHMANIASIS, the skin disease being reported from Sindh since the last few months, is an infection caused by the parasite belonging to the genus Leishmania.

There are more than 20 species of Leishmania which infect humans. Some of these only involve the skin (cutaneous leishmaniasis), some involve skin and mucous membrane (muco-cutaneous leishmaniasis) and some involve the internal organs of the body (visceral leishmaniasis). Visceral leishmaniasis, if untreated carries high mortality, while cutaneous leishmaniasis (CL) is usually a self-limiting disease.

It was reported in Dawn (Jan 17) that about 4,200 cases of CL have occurred so far in the Dadu District and adjoining areas. These figures represent only the number of patients who presented their cases at the hospitals and clinics. The total number of infected individuals is certainly higher, hence the need to take urgent measures to control the disease.

Leishmania have a simple lifecycle. The infective stage of the parasite known as the promastigote enters a macrophage (large phagocytic cell) and multiplies in it. The infection spreads from one macrophage to another and the stage involved is known as the amastigote.

The amastigotes are picked up by the sandfly when it takes a blood meal. The amastigotes turn into promastigotes in the sandfly's gut and the infection is passed on to an individual during the bite of the fly. The infection is not directly transmitted from a person and CL is not a contagious disease.

In humans the lesion appears at the site of the bite, as a papule (small swelling). It then grows into a nodule, which ultimately ulcerates. The ulcer is mostly on the exposed parts of the body, which are approachable for the sandfly such as the face and extremities. Often there is a single ulcer, but sometimes multiple ulcers are present, if many sandflies have bitten the individual.

Sanflies are small insects (2 to 3mm) and are covered with minute hairs. The female lays eggs in cracks and holes in the ground, rodent burrows, on manure and leaf litter. The adults emerge in about two weeks. Only the female takes blood meal during the night.

The mainstay of treatment are the pentavalent antimony salts, sodium stibogluconate (Pentostam) and meglumine antimonite (Glucantime). Generic sodium stibogluconate is also available.

In case of a solitary lesion of CL, the World Health Organization (WHO) recommends 1 to 3mls of sodium stibogluconate, to be infiltrated into the base of the ulcer. This should be repeated once or twice at intervals of 1 to 2 days.

In case of multiple and large ulcers, intramuscular injection of 20mg per kilogramme of sodium stibogluconate is given daily for 20 days. Antifungal azoles (ketoconazole and fluconazole) are worth trying if the patient is not responding to antimony salts.

Recently a new drug, Miltefosine, has given very encouraging results. It is given orally and is well tolerated. This drug is not available in Pakistan and WHO should be contacted for its supply. There is no evidence that Flagyl (metronidazole) is of value in the treatment of CL, as has been reported in news items appearing in Dawn.

Local application of an antibiotic — paromomycin (Humatin) — is also efficacious. Unfortunately, this drug too is not available locally. A combination of paromomycin (15 per cent) and methylbenzethonium chloride (12 per cent) is marketed in some countries and has proven to be effective. Even if untreated, the ulcers must always be cleaned with a disinfectant (70 per cent alcohol) and bandaged to prevent access to sandfly.

This disease is best controlled by instituting anti-sandfly measures. Spraying of Insecticide (pyrethroids) in homes, near boundary walls, cowsheds and neighbouring areas is very effective, as the insect is very susceptible to insecticides.

In addition, cleaning up of the environment will also deter the sandflies from breeding. Aerial spraying, alone, is not likely to work and will cause considerable ecological damage.

Individual protection is best accomplished by sleeping under small mesh bed nets. The fly passes through the large mesh bed nets. Insect repellent applied to the exposed parts of the body also helps. Insecticide-impregnated bed nets are superior to the untreated ones. As yet, no vaccine for CL is available although a great deal of research is going on to produce one.

It is important to find out if the parasite has an animal reservoir. Most likely, this is a purely human infection (anthroponotic). However, if animals such as dogs are shown to be involved, control will become more difficult and will require elimination of the stray dog population.

The writer is a visiting professor at the Aga Khan University

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