Leishmaniasis (overview) B55.-

Granulomatous infectious disease caused by protozoa of the genus Leishmania.

Commonly isolated pathogens of leishmaniasis (see under Leishmania):

• Leishmaniadonovani (s.a.u. visceral leishmaniasis).
• Leishmaniabrasiliensis (see also South American leishmaniasis).
• Leishmaniamexicana, L.braziliensis, L.amazonensis, L. peruvia, L.panamensis, Chiclero ulcer (Solitary cutaneous leishmaniasis; see also South American leishmaniasis with the different clinical variants).
• Leishmania tropica (Oriental bump; see also below for cutaneous leishmaniasis).
• Leishmania major, L. infantum, L. aethiopicum (Oriental bump; see also solitary cutaneous leishmaniasis).

Vectors: Leishmania is transmitted by sandflies, in the Old World by Phlebotomus spp. and in the New World by Lutzomyia species. Sandflies live in dark and damp places and can travel only 20-50 m from their breeding site in the biotope. New World sandflies do not fly very high and therefore usually bite their victim near the ground (e.g., lower leg). Because of their biological adaptability, they are common in tropics, subtropics, deserts, rainforests, and plateaus.

When uninfected sandflies bite an infectious host, the amastigotes are ingested during bloodsucking and transformed into promastigotes in the mosquito. Depending on the Leishmania species and host factor, local or disseminated distribution of the parasites may occur. Spontaneous healing is achieved by imprinting parasite-specific T cells, which migrate into the skin and activate macrophages by means of interferon gamma and other cytokines.

Depending on the clinic and pathogen, a distinction is made between:

• Old World Leishmaniasis
  • Old World cutaneous leishmaniasis
    • Solitary Old World cutaneous leishmaniasis (classic Oriental bump).
    • Erysipelas-like cutaneous Old Worldleishmaniasis (rare variant)
    • other rarer variants such as: paronychial, chankriform, annular, palmoplantar, zosteriform or even eczematoid cutaneous leishmaniasis.

    • Old World Recurrent Cutaneous Leishmaniasis (Leishmaniasis recidivans - lupoid leishmaniasis).

    • Diffuse (anergic) cutaneous leishmaniasis of the Old World
  • Old World mucocutaneous leishmaniasis
• New World Leishmaniasis
  • New World cutaneous leishmaniasis (South) American leishmaniasis
    • Solitary cutaneous leishmaniasis of the New World (classical form, analogous to Oriental bump)
    • Recurrent cutaneous New World leishmaniasis
    • Diffuse (anergic) cutaneous New World leishmaniasis
  • New World mucocutaneous leishmaniasis
• Visceral le ishmaniasis

About 10% of the world's population live in endemic areas and are at increased risk of disease.

Incidence: Approximately 1.6 million new cases/year worldwide; of these, 1.2 million are of the cutaneous forms. Leishmaniasis is the third most common vector-borne infectious disease after malaria and dengue fever.

Prevalence: worldwide (excluding Australia and Southeast Asia), approximately 12 million people are affected.

Increasingly, leishmaniasis occurs in tourists and HIV patients.

About 90% of the new cases occur in the Old World (Afghanistan, Algeria, Saudi Arabia, Iran, Iraq, Ethiopia, Middle East, Spanish Mediterranean islands). Pathogens here are predominantly: L. major, L. tropica, L. aethiopica, L. infantum.

About 10% of the new cases occur in the New World (Brazil, Mexico, Bolivia, Peru). The pathogens here are predominantly: L. mexicana, L. brasiliensis.

The co-infection of humans with HI virus and Leishmania parasites is seen as problematic. Protracted parasitemia occurring in HIV-infected individuals increases the likelihood of humans serving as reservoir hosts.

Clinical findings (different clinic)

Detection of pathogens in smear, smear preparation (only for experienced examiners) or biopsy of a fresh lesion (biopsy from untreated lesion with pathogen detection is the option of 1st choice as primary examination).

Clearance preparation: In Giemsa and HE staining, amastigotes appear as light blue, oval-shaped corpuscles with a dark nucleolus and a small, punctate kinetoplast within the cytoplasm of the macrophages.

Antigen detection by PCR: highly sensitive method that can be performed on native material as well as from formalin-fixed material.

Culture: identification of the pathogen species (important for therapy and prognosis) from native preparations, e.g. non-fixed biopsies, in laboratories specialized for this purpose (e.g. Bernhard Nocht Institute for Tropical Medicine in Hamburg -www.bni-hamburg.de).

Serological detection methods: Leishmania-specific immunoglobulins can be detected (direct agglutination test (DAT), immunofluorescence antibody tests (IFAT), enzyme-linked immunosorbent assays (ELISA). They are of little use in uncomplicated Leishmaniasis infection (usually negative). In complicated cases, serological detection of antibodies may be diagnostically helpful.

A wait-and-see attitude may be justified for solitary lesions of old world forms; the lesions usually heal spontaneously and lead to a permanent immunity (against the pathogen, not also against other Leishmania spp.)

Multiple lesions and lesions in cosmetically significant areas should be treated as early as possible.

Systemic therapy is usually more effective than topical therapy, but is also associated with significant side effects.

If an infection with L. brasiliensis is present, a systemic therapy is always indicated as this can prevent a transition to a mucocutaneous form.

The best prevention against theinfection is to avoid the sandfly bites.

People traveling to areas where the infection is common, or people living in such areas, can take the following measures:

• Applying insect repellents containing DEET (diethyltoluamide) to exposed skin.
• Using fly screens, mosquito nets and clothing impregnated with insecticides such as permethrin
• Wearing long-sleeved shirts, long pants and socks
• Avoiding outdoor activities between sunset and sunrise, when sandflies are most active

Geographical distribution of leishmania and leishmaniasis (modified after Lainson)

Leishmaniasis is classified by the WGO as a neglected tropical disease (NTD). These are poverty-associated infectious diseases that occur mainly in the tropics (subtropics), are associated with high morbidity and mortality, and for which there are as yet no safe and long-lasting therapies.

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