Epidemiology
Leishmaniasis is a globally common disease that affects more than 98 countries and territories. Even though its effects are mainly observed in underdeveloped or developing countries, this parasite has spread to Europe and the United States due to the traveling to these areas and immigration from these areas.
Old World leishmaniasis is endemic in Asia, Africa, the Mediterranean, and the Middle East. L. tropica, L. major, Leishmania aethiopica, and L. donovani are the four common species causing Old World leishmaniasis. New World leishmaniasis is caused by the Leishmania mexicana, Leishmania braziliensis, and Leishmaniaguyanensis. In total, six Old World countries (Afghanistan, Algeria, Arabian Peninsula, Syria, Sudan, and Iran) and two New World countries (Brazil and Peru) make up 90% of all leishmaniasis reports [18].Poor process of record taking in underdeveloped and developing countries makes it difficult to determine its incidence and prevalence in certain areas. Syria is reported to have highest amount of incidence in the Middle East with 52,983 cases being reported in 2012 [19]. In Iraq, leishmaniasis had a prevalence of 45.5 cases per 100,000 of population in 1992 due to the war and population migration which can give an estimate of current situation [19].
In Asia, Afghanistan, Iran, and Syria are the three Middle Eastern countries where CL is endemic and reported most. Syria having the most amount of CL cases also named the disease as Aleppo boil [20]. Moving toward Eastern Asia, Pakistan holds great number of CL cases, whereas India and Bangladesh can be considered as the sole reservoir for VL [7]. In China, there are three defined VL types: anthroponotic VL, which is caused by L. donovani; zoonotic mountain-type zoonotic VL; and zoonotic desert-type VL in which both are caused by L. infantum [21]. Depending on the habitat, there are four vectors when it comes to VL transmission in China [21]: Phlebotomus chinensis and Phlebotomus longiductus for anthroponotic VL in domiciliary habitats, P chinensis for mountain-type zoonotic VL in wild and peridomestic habitats, and Phlebotomus wui and Phlebotomus alexandri for zoonotic desert-type VL in wild habitats [21].
In Africa, three Leishmania species, L. infantum, L. major, and L. tropica, are responsible from the CL cases [8]. Egypt, Algeria, Morocco, Tunisia, and Libya are the Northern African countries with the highest amount of reported CL cases between 2003 and 2009 [7]. Among East Africa, countries such as Ethiopia, Sudan, and Somalia have highest number of reported VL cases between years 2004 and 2009, which contribute to a large portion of total amount of 8569 cases in the region [7]. In Cameroon, survey done in Mokolo region consisting of 32,466 people showed 146 active CL lesions and 261 people having scars probably as a result of prior CL infection [22]. Interestingly, it was also noted that 4.8% of the patients with CL observed to be positive for HIV infection [22].
Realizing the importance of leishmaniasis in most of the African countries is a challenge compared to other countries because of the low quality healthcare services, poor data management, and absent reports. East Africa and sub-Saharan Africa are the geographical regions where leishmaniasis was the least common until 2012 [7]. Considering leishmaniasis is endemic in these regions, it is safe to say that observed value will be much different than the real outcome once enough data are gathered.
When it comes to Europe, countries in the Mediterranean region such as Italy, Greece, Turkey, and Albania have highest prevalence of VL cases [7]. In addition, few number of VL cases were observed in France, Spain, Portugal, and Croatia [7]. In terms of CL cases, Turkey holds great percentage of reports compared to others. In the Netherlands, 185 CL, 8 VL, and 2 MCL cases were observed between 2005 and 2012 [23]. In general, traveling to endemic regions such as Afghanistan or Morocco is shown as a significant risk factor of Leishmania cases in developed countries. Due to the nature of leishmaniasis infection, developed European countries have low amount of reported cases, and in most of the cases, insufficient immune system is the other most important risk factor in addition to trips to endemic regions [24].
American region has low VL and high amount of CL cases reported in general with a 1-20 difference. Brazil has the highest amount of reported cases both in VL and CL. Colombia, Peru, Nicaragua, and Venezuela are other areas where CL cases happen frequently [7].
Mexico, the United States, and Canada have relatively low amount of reported cases in terms of global occurrence. A total of 811 CL and 7 VL cases were reported in Mexico between 2004 and 2008. The US Army Forces going to endemic regions such as Afghanistan for military duty resulted in few reported Leishmania cases in the United States.
Australia and Antarctica are the two continents where leishmaniasis is not considered to be endemic [2]. Between the years 2008 and 2014, 52 CL and 3 VL cases were reported in Australia [25]. Traveling to Leishmania parasite endemic regions is thought to be the reason for most of these cases as similar with the cases seen in Europe [25]. L. tropica was identified in 30 patients and was the highest compared to 4 other identified species [25].
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