Leishmaniasis is the name of a group of tropical diseases caused by infection with the microscopic parasite Leishmania spp.. The parasite is spread by the bite of an infected sand fly.
Leishmania mexicana parasites in the amastigote stage, SEM. Credit: University of Oxford, Richard Wheeler. Wellcome Collection
Phlebotomus papatasi sand fly taking a bloodmeal. Public Health Image Library
There are four main forms of leishmaniasis, which are caused by infection with different species of Leishmania which are found in different parts of the world:
1. Cutaneous leishmaniasis (CL) is the most common form of leishmaniasis, accounting for over 75% of all cases. This disease is characterised by skin lesions or ulcers which may take a long time to heal.
Child with cutaneous leishmaniasis awaiting treatment in Kabul, Afghanistan. WHO
2. Muco-cutaneous leishmaniasis (MCL) is a complication of CL in which the parasites invade and severely damage mucous membranes, particularly around the mouth and nose.
3. Visceral leishmaniasis (VL) is also known as kala-azar. This is the most severe form of the disease, which causes damage to the liver and spleen and is usually fatal unless treated.
4. Post kala-azar dermal leishmaniasis (PKDL) is a complication seen in a minority of patients following treatment for VL. This form of the disease is characterised by a nodular rash that appears on the face, arms and upper trunk, due to parasite migration to the skin.
The Leishmania parasite cannot be spread via person-to-person contact, in the air or in water droplets. Infections are spread via the bite of sand flies which have previously fed on people or animals (e.g. dogs) carrying the disease. The Leishmania parasite has to undergo changes inside the insect which take approximately 2 weeks, before it can be passed on to another person or animal when the sand fly bites them.
The parasite has been found in some bat populations but it is not clear whether this has any effect on spreading the disease to people. Sand flies are known to be highly attracted to chickens but the parasites do not survive inside these birds.
Neglected Tropical Diseases (NTDs)
Leishmaniasis is part of a diverse group of health conditions known as the Neglected Tropical Diseases or NTDs. Many of the NTDs are chronic conditions which do not cause high numbers of death in comparison to, for instance, malaria, TB or HIV. However, the NTDs may be highly debilitating or stigmatising. In combination, the NTDs affect over a billion people worldwide and disproportionately affect the poorest communities, reinforcing the cycle of poverty. The NTDs have historically been low priority for public health interventions and for research funding bodies but over the last decade much progress has been made to highlight the huge burden of these conditions on global health and to improve the situation for people living with NTDs.
ECLIPSE focuses on cutaneous leishmaniasis (CL) which is considered to be one of the most neglected of the NTDs, both in terms of unmet patient needs and research investment in applied health service research.
Geographical spread of CL
CL represents a major public health burden for many of the poorest communities in low- and middle-income countries (LMICs). CL is found in 88 countries worldwide with over 250,000 new cases reported to the WHO in 2018.
World map showing state of endemicity of cutaneous leishmaniasis (2018) WHO
CL is most commonly found in areas of extreme poverty, conflict or poor sanitation where sand flies are found in greatest numbers. The true number of cases across the world is likely to be much higher as not all countries report CL and formal diagnosis is not available to all those with the disease, particularly in remote regions.
There are many local names for CL, including the following: tropical sore, oriental sore, Chiclero ulcer, Chiclero’s ulcer and many names referring to locality (Aleppo, Baghdad, Delhi or Jericho boil, Aden ulcer or Biskra button). In Tigray, the region where the ECLIPSE team works in Ethiopia, CL is known locally as gizwa.
Symptoms of CL
The characteristic signs of CL are skin lesions at the site of the sand fly bite. These may ulcerate and can take months or even years to heal and commonly leave permanent scarring. In some cases, the infection may also spread (disseminate) resulting in multiple lesions.
Old World cutaneous leishmaniasis (CL): multiple lesions. Wellcome Collection
Certain species of Leishmania parasite (e.g. L. braziliensis found in South America) can cause MCL, in which the parasite invades the mucous membranes. This disseminated form of CL disease can cause severe damage to the face and may even be life-threatening. Early treatment is paramount when there is a risk of MCL.
Stigma associated with CL
There is some evidence that the skin lesions and resulting scars cause people to be stigmatized by their community, partly due to fear of catching the disease. This can lead to depression and further poverty. Children with CL may be kept off school, with long term effects on their education.
Treatment and prevention of CL
There are currently no vaccines or preventative drugs available to prevent human leishmaniasis despite the geographical spread of CL. Current treatment for CL relies on the use of old drugs which are toxic, expensive and difficult to administer. The most commonly used treatments for CL are the pentavalent antimonials (e.g. sodium stibogluconate) which are administered as a course of daily injections for 2-3 weeks or more.
Control of CL is difficult and centres around the control of sand flies or reducing the risk of being bitten. Studies suggest that insecticide-treated bednets only give limited protection against sand flies.