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Leishmania are single-cell parasites and a genus of the trypanosomatid protozoa. There are about 20 species involved in human pathology . Unlike visceral leishmaniasis, the cutaneous leishmaniases, i.e. localised cutaneous leishmaniasis, diffuse cutaneous leishmaniasis and mucocutaneous leishmaniasis, are non-life threatening parasitic infections. There are three key players in the pathogenesis of cutaneous leishmaniases:
1) the parasite, in this case certain "dermotropic" species of leishmania;
2) a reservoir, always a mammal, the species of which varies depends on the species of Leishmania hosted;
3) a vector of the Phlebotomus genus, for example, the stinging sand fly, which also varies depending on the Leishmania species causing the infection.
The distribution of the disease worldwide depends on the distribution of the above. In broad outline, the disease is most prevalent in tropical countries. However, its incidence varies greatly from region to region within an endemic country. It is conventional to distinguish between the Old World leishmaniases and New World leishmaniases . The Old World form of the infection (affecting Southern Europe, Africa and Near and Middle East) is caused mainly by four species: L. major, L. tropica and, to a lesser extent, L. infantum and L. aethiopica. As a general rule, only one species of leishmania is found per infected zone; this makes it possible to assume that a given species is responsible when more precise means of identification are not available. There is greater diversity in the New World, which includes L. braziliensis, L. guyanensis, L. panamensis, L. amazonensis, L. mexicana, L. venezuelensis, L. peruviana and a few other species. In the tropical forests of South America, more than one species is present. In French Guiana, for example, any one of the following 5 species, in descending order of frequency, may be responsible: L. guyanensis (90-95% of cases), L. braziliensis (5-8%), L. amazonensis (2%), L. lainsoni (1%) and L. naiffi (<1%).
Cutaneous leishmaniasis is not a serious illness but it can be dermatologically spectacular and difficult to bear: it is not a medical emergency and it is imperative for the healthcare provider to reassure the patient’s family and friends to this effect, as organ involvement only arises in the very rare cases in which L. donovani or L.infantum infection begins with cutaneous symptoms, and in immunocompromised patients.
However, although it is painless, slow-developing and above all, not contagious, it is an unsightly disease that can cause multiple lesions in highly visible locations (nose and ears).
Most local cutaneous leishmaniases seem to be self-limiting. This is particularly the case for the Old World forms caused by L. major. The 12-month self-limiting course is no doubt the source of its "one year spot" nickname. More rapid regression is possible (3 months), mainly around the Mediterranean basin. Conversely, some forms are long lasting and tend to get worse over the years: this seems to be the rule with the New World forms.
It is important to stress that this is a condition for which antibiotics are of no use; There is an unfortunate clinical confusion between purulent or crusty tissue necrosis and "bacterial infection". Moniliform lymphangitis is a sign of locoregional spread of the parasitic infection with activation of the immune response.
Commensal bacteria at skin’s surface and crusty necrosis are easily cleaned by washing thoroughly with soap and water. Dressings are not necessary: the lesions should be allowed to dry and scab over. It should be noted that no cases of wound myiasis on ulcerated leishmaniosis lesions have been reported in Guiana where Cochlyiomia hominivorax myiasis is common.
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