Leishmaniasis: Epidemiology, Transmission, Prevention

Last updated on May 30th, 2021

Leishmaniasis is a parasitic disease caused by several species of genus Leishmania (protozoa) and transmitted by the bite of sandflies. Sandflies are primarily infected by animal reservoirs, 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:

Types of Leishmaniasis

  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, 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 the partial or total destruction of the mucous membranes of the nose, mouth and throat cavities and surrounding tissues.

Different species of Leishmania cause different disease;

  1. Leishmania donovani causes visceral 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. Leishmania 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 metastasize 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 an 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 (VL) by India, Bangladesh, Nepal, Sudan, and Brazil. Only India, Nepal, and Bangladesh harbors an estimated 67% of the global VL disease burden. 

Transmission of Kala- azar

Kala-azar (visceral leishmaniasis) is transmitted from person to person by the bite of the infected female phlebotamine sandfly, Phlebotomus argentipes which is a highly anthropophilic species. Transmission may also take place by contamination of the bite wound or by contact when the insect is crushed during the act of feeding. Transmission of kala-azar has also been recorded by blood transfusion, veneral and transplacental but are very rare.  

Different factors involved in the transmission of kala-azar

Agent Factor

  1. Agents: Leishmania donovani, are intracellular parasites that infect and divide within macrophages is the causative agent of kala-azar.
  2. Reservoir of infection: There is a variety of animal reservoirs e.g. dogs, jackals, foxes, rodents, and other mammals. Indian kala-azar is considered to be a non-zoonotic infection with a man as the sole reservoir.

Host Factor

  1. Age: Kala-azar can occur in all age groups including infants below the age of one year.
  2. Sex: Males are affected twice as often as females.
  3. Population movement: Movement of population between endemic and non-endemic areas can result in the spread of infection.
  4. Socio-economic movement: Kala-azar usually affects the poorest of the poor.
  5. Occupation: The disease strongly associated with the occupation. People who work in various farming practices, forestry, mining, and fishing have a great risk of being bitten by sandflies.

Environmental Factors

  1. Altitudes: Kala-azar is mostly confined to the plains, it does not occur in altitudes over 2000 feet.
  2. Season: High Prevalence during and after rains.
  3. Rural areas: The disease is generally confined to rural areas, where conditions for the breeding of sandflies readily exist compared to urban areas.
  4. Vector: Only the female sandfly transmits the protozoa, infecting itself with the Leishmania parasites contained in the blood it sucks from its human or mammalian host. Sandflies breed in cracks and crevices in the soil and buildings, tree holes, caves, etc.

Prevention and Control of Visceral Leishmaniasis

The current control strategies for visceral leishmaniasis rely on the reservoir and vector control, the use of insecticide-impregnated materials and active case detection and treatment. Anti-leishmanial vaccines are still being developed. 

Reservoir Control

Since man is the only reservoir of kala-azar in Nepal, active and passive case detection and treatment of those found to be infected (including PKDL) may be sufficient to abolish the human reservoir and control the disease. 

Vector Control

The application of residual insecticides has proved effective in the control of sandflies. DDT is the first choice since the vector of kala-azar P. argentipes is susceptible to DDT. Insecticide spraying should be undertaken in human dwellings, animal shelters and all other resting places up to a height of 6 feet from floor level. Spraying should be preceded and followed by an assessment of susceptibility. Any sign of resistance in vector should lead to an immediate change in insecticide. BHC should be kept as a second line of defence. 

Insecticide-impregnated materials 

The use of insecticide-treated bednets (ITNs) could concomitantly prevent visceral leishmaniasis and other vector-borne diseases, such as malaria and Japanese encephalitis. Depending on the sleeping traditions of the population and the biting habits of the local vector, other insecticide-impregnated materials such as curtains and blankets should be evaluated for use in visceral leishmaniasis prevention. 

Early diagnosis and treatment

Early diagnosis and treatment are essential for both individual patients and for the community. Untreated VL patients act as a reservoir for parasites and therefore contribute to disease transmission in anthroponotic VL areas. 

Personal Prophylaxis

The risk of infection can be reduced through health education and by the use of individual protective measures such as avoiding sleeping on floor, using fine-mesh nets around the bed. Insect repellents for temporary protection and keeping the environment clean.

About Acharya Tankeshwar 473 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.

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