Goto content

Leishrisk, Bridging Research and Leishmanianis Control

Leishrisk, Bridging Research and Leishmanianis Control

An introduction to neglected diseases and leishmaniasis

The problem of neglected diseases

Malaria, tuberculoses and HIV are well known diseases that have hit the developing world hard. These “big 3”-diseases receive a lot of well merited attention from the media, the pharmaceutical industry and policy makers. Neglected diseases do not receive the same kind of interest, even though up to 1 billion people are affected by this group of diseases. 
 
The group of the neglected diseases is made up of 14 diseases. Amongst others, the list features cholera, African trypanosomiasis (sleeping sickness), leprosy, dengue, trachoma, and leishmaniasis. They are labelled ‘neglected’ because they hover in the margins of international health policy and research. Therefore interest for these diseases is very limited. 
 
There are several interrelated reasons that explain the existence of neglected diseases. First and foremost, neglected diseases persevere in tropical and subtropical regions where populations are poor, undereducated, and have little or no political significance and voice. This entails that these people do not just lack the money to pay for their treatment; they also find themselves in a situation where interest for their burdens is minimal. Furthermore, neglected diseases and their causes are endemic to certain areas and so do not form an acute threat to the Western world. All this leaves very little incentive for pharmaceutical companies to research and develop treatments for neglected diseases, as the wealthy Western consumer is their prime target.

What is Leishmaniasis?

Leishmaniasis is a serious disease that has an impact on millions of people worldwide. It has many faces. In certain forms it is a lethal killer, in others a cruel mutilator leaving its victims disfigured for life. 
 
Leishmaniasis has caused much sorrow and scarred many lives, and yet it has not caught the attention of the broad public. Adding to the poignancy of the problem is the fact that treatment options are limited and that those most in need of help are the least likely to receive it as leishmaniasis mainly wreaks havoc in poor and remote regions.


Parasites and sand flies

Leishmaniasis is a disease caused by a “protozoan parasite”. A parasite is a life form that attaches itself to a host organism and uses it to survive and multiply. This relationship is beneficial for the parasite, but harmful to the host. The term “protozoan” refers to the one-celled motile nature of the parasite. 
 Figure 1: A sand fly, the Leishmania vector, on the skin. Photo copyright WHO : manual on visceral leishmaniasis control. Photo credit Meddia
A parasite needs a so-called “vector” to fulfil its lifecycle. A vector is an organism that does not cause disease in itself, but does spread the parasite to other life forms. For example, mosquito’s (malaria), fleas (bubonic plague) and ticks (Lyme disease) are all well known vectors. In the case of leishmaniasis the vector is a type of sand fly.
 

The Leishmania parasite is spread by certain species of tiny blood feeding sand flies. In contrary to what one might expect from the name, a sand fly is not confined to beaches and other sandy places, but can also be common in forests and urban areas. A sand fly becomes a host for the Leishmania parasite when it takes a blood meal from an already infected organism (for example a human, dog, or Figure 2: Leishmania parasite in promastigote phase.  Photo copyright: ITM/Meriem Ouakadrodent). The parasite then nests itself in the intestines of the sand fly and starts replicating. Once infected, the sand fly can infect other organisms when it feeds off of them. Whilst feeding, the infected sand fly is forced by the parasite to regurgitate, transmitting the parasite along with it, and thus infecting a new organism.





Same name, different disease

 
Leishmaniasis exists in different forms. A main distinction is made between “visceral leishmaniasis” and “cutaneous leishmaniasis”. 
 
Visceral leishmaniasis (or Kala Azar as it is called in the Indian Subcontinent) is the most serious variant Figure 3: Patient with visceral leishmaniasis. The infected spleen and liver are marked. Both organs are unusually large due to parasite infection. ITM archive. Photo PIDand is fatal if left untreated. As the name suggests, visceral leishmaniasis affects the visceral organs, most notably the liver, spleen and bone marrow. Infection with visceral leishmaniasis results in fever, weight loss, and an enlarged spleen and liver. Visceral leishmaniasis damages the immune system, making the host susceptible to secondary infections. Left untreated, visceral leishmaniasis can result in death within a matter of months. The incubation period (the time-span between infection and the development of actual symptoms) can differ from several months in most cases, to over a year. 
 


Cutaneous leishmaniasis causes skin sores that, depending on the type of the parasite, can be localized on a specific place on the body (mostly on the limbs or the face) or spread. The skin sores usually develop within a few weeks after being infected. In specific varieties of cutaneous leishmaniasis these lesions can cause massive tissue damage, leaving the patient disfigured and the subject of social prejudice and stigma. Cutaneous leishmaniasis can be self healing, although treatment is always highly recommended as the sores can spread, take months and even years to heal, or even cause death following secondary infections.
Figure 4: Cutaneous leishmaniasis lesion. ITM archive. Copyright unknown Figure 5: Cutaneous leishmaniasis lesion. ITM archive. Copyright unknown


Impact of Leishmaniasis

Leishmaniasis is endemic in numerous tropical and sub-tropical areas, and is gaining ground in the European Mediterranean area. In total, leishmaniasis affects 88 countries with an estimated 12 million people currently infected worldwide. 90% of the visceral leishmaniasis variant occur in no more than 5 countries:

Bangladesh, India, Nepal, Sudan and Brazil. Also, 90% of cutaneous leishmaniasis cases occur in just seven countries: Afghanistan, Algeria, Brazil, Iran, Peru, Saudi Arabia and Syria. 
 
Every year 500.000 people contract visceral leishmaniasis, and 1.500.000 people develop cutaneous leishmaniasis. It is thought that these numbers are just the top of the iceberg and represent only 30% of the cases. The other 70% goes unreported. The population at risk worldwide is estimated at 350 million. It is also estimated that leishmaniasis is responsible for over 80.000 deaths annually worldwide. This makes leishmaniasis one of the world’s deadliest parasites, coming second only to malaria.
 
It has been established that the spread of leishmaniasis is increasing dramatically in several regions. This is due to several factors including environmental changes, migration from rural to urban areas and the development of new settlements in or near primary forests. The overall health of the population at risk also plays an important factor in the spread of infection. Healthy bodies are more able to withstand the Leishmania parasite and its effects. Unfortunately, many people in developing countries suffer from malnutrition and have a weak constitution, thus increasing the risk of Leishmania infection. In this respect people with HIV are very much at risk of so-called co-infection. Because of their dwindling immune systems, HIV patients who come into contact with leishmaniasis have no chance of resisting the parasite.


Treatment and prevention

Although there are different treatments at hand for leishmaniasis, there is no ideal cure available at the moment. There are several reasons for this. 
  • Drugs that used to work well have lost their effectiveness due to the parasite growing increasingly resistant to existing treatments.
  • Chemotherapy treatment can be effective against leishmaniasis, but is poisonous when used in long term treatments. Existing treatments can also cause serious side-effects, including cardiovascular problems.
  • The costs of treatment are too high to carry for the large majority of the infected population. Many of them live in ‘underdeveloped’ regions and do not have the money to pay for the medication. 
  • Because the major proportion of the population who are infected or at risk is poor, there is a lack of interest for leishmaniasis treatment from the pharmaceutical industry.
 
Because of the difficulties concerning the treatment of leishmaniasis, prevention of infection is of the utmost importance. Preventive measures are aimed at avoiding contact with sand flies and include:
  • The use of bed nets with ultra fine meshing that have been impregnated with insecticide.
  • Vector control. This entails the elimination of sand flies by environmental measures and chemical means.
  • Wearing protective clothing and use of insect repellent on uncovered areas of the skin.
  • “Reservoir control” is aimed at the population management of animals that have been, or have a high risk of being, infected with leishmaniasis.

Supporting projects

Search

news

LeishRisk supports the initiative to develop a VL Diagnostics Quality Assurance Network.  

Download a report of the first consultation meeting <here>