Class Note: Leishmaniasis: Introduction, Epidemiology and Transmission

Leishmaniasis is a parasitic disease caused by several species of genus Leishmania (protozoa) and transmitted by the bite of sand flies.Sand flies are primarily infected by animal reservoir, but humans are also a reservoir for some Leishmania species.

Leishmaniasis currently threatens 350 million men, women and children in 88 countries around the world. The leishmaniases are parasitic diseases with a wide range of clinical symptoms:

1. Cutaneous leishmaniasis: Involving the skin at the site of a sandfly bite. Cutaneous forms of the disease normally produce skin ulcers on the exposed parts of the body such as the face, arms and legs. The disease can produce a large number of lesions-sometimes upto 200 causing serious disability.  
2. Visceral Leishmaniasis: Involving liver, spleen and bone marrow. It is also known as Kala azar and is characterised by irregular bouts of fever, substantial weight loss, Hepatomegaly and Splenomegaly and anaemia. If left untreated, the fatality rate in developing countries can be as high as 100% within 2 years.
3. Mucocutaneous Leishmaniasis: Involving mucous membrane of the mouth and nose after spread from a nearby cutaneous lesion.Lesions can lead to partial or total destruction of the mucous membranes of the nose, mouth and throat cavities and surrounding tissues.
   

Marked enlargement of the spleen typical of visceral leishmaniasis
in a patient in lowland Nepal.
Photo: C. Bern, CDC.

Typical New World cutaneous leishmaniasis ulcer.
Photo: B. Arana, MERTU, Guatemala.

 
Different species of  leishmania cause different disease.

1. Leishmania donovani causes Viceral leishmaniasis also called Kala-azar. The infection is generalized and the parasite is distributed in the internal organs. The parasite may also cause a variety of skin lesions (dermal leishmaniasis) without any visceral manifestations.
2. L. tropica, causes oriental sore. The infection is limited to a local lesion of the skin and subcutaneous tissues.
3. Leishmania brasiliensis causes Espundia. The infection is limited to a local lesion of the skin but may metastasise to other areas of skin and oro-nasal mucosa

Epidemiology

Leishmaniasis is endemic in more than 60 countries worldwide, including southern Europe, North Africa, the Middle East, Central and South America, and the Indian subcontinent. It is not endemic in SouthEast Asia and Australia. There are estimated 500,000 new cases of VL and more than 50,000 deaths from the disease each year.
The burden of cutaneous leishmaniasis disease (90% of cases) is borne by Afghanistan, Pakistan, Syria, Saudi Arabia, Algeria, Iran, Brazil and Peru and for Visceral leishmaniasis by India, Bangladesh, Nepal, Sudan and Brazil. Only India, Nepal and Bangladesh harbours an estimated 67% of the global VL disease burden.

VL in Nepal is mainly confined to the southern plain of the eastern and central regions, bordering VL endemic districts of Bihar state in India. Siraha, Dhanusa and Mohattari district are considered endemic with the disease. Occasional sporadic cases occur elsewhere. Around 5.5 million people live in affected areas, so are classified “at risk”.

A total of 25704 cases with 530 deaths were reported between 1980 and 2004 (440 cases per 100,000 in 20 years), and the case fatality rate in reported cases varied between 0.23 (in 1988) to 13.6 (in 1982).