Cutaneous Leishmaniasis in Mali

While not as common as in other parts of the world, cutaneous leishmaniasis is endemic to countries in Africa, particularly in the north, central, east, and south. Sporadic case reports of cutaneous leishmaniasis in countries spanning West Africa have allowed scientists to propose an endemic belt in sub-Saharan Africa ranging from Senegal to Cameroon. While the presence of cutaneous leishmaniasis in West Africa is well established, there is a paucity of data regarding the parasite species, vector, and reservoir responsible for the disease in this part of the continent. This article focuses on cutaneous leishmaniasis in Mali, West Africa.

Leishmaniasis is a disease caused by obligate intracellular protozoan parasites belonging to the genus Leishmania, and it is transmitted by the bite of female phlebotomine sand flies. More than 20 Leishmania parasite species cause human disease. Depending on the causative agent, disease manifests as visceral, cutaneous, or mucocutaneous forms. In the most severe form of the disease, visceral leishmaniasis, the parasite migrates to internal organs such as the liver and spleen and can be fatal if left untreated. Mucocutaneous leishmaniasis results in disfiguring lesions of the nose, mouth, and throat mucous membranes. Cutaneous leishmaniasis, the most common form of the disease, is characterized by painless skin ulcerations usually on exposed areas such as the face and extremities. The lesions of cutaneous leishmaniasis develop at site of inoculation after an incubation period of weeks to months. Initially, the lesions are painless erythematous papules that become darker and develop a crust in the center over the course of several weeks. Eventually, the center of the lesion ulcerates, and the edges become raised. In 3 to 6 months, the lesions heal, leaving behind depigmented retracted scars ( Fig. 1 ).

Cutaneous leishmaniasis can be found in at least 88 countries, and it affects as many as 12 million people worldwide, with 1.5 to 2 million new cases every year. The disease is found in tropical and subtropical countries, from the rainforests of Central and South America to the deserts of West Africa and the Middle East. Cutaneous leishmaniasis is divided into Old World (including southern Europe, the Middle East, parts of southwest Asia and Africa) and New World (from the southern United States through Latin America to South America) forms based on geographic setting of the infection. Both Old World leishmaniasis and New World cutaneous leishmaniasis are caused by distinct vectors and sets of parasites. For example, New World infection is transmitted by the sand flies belonging to the genus Lutzomyia , whereas Old World disease is transmitted by sand flies belonging to the genus Phlebotomus . Leishmania mexicana , L brazilensis , and L amazonensis parasite species cause New World cutaneous leishmaniasis, and L major , L tropica , L aethiopica , and L infantum parasite species cause Old World cutaneous leishmaniasis.

Cutaneous leishmaniasis in Mali

Mali

Mali is a land-locked country in West Africa, surrounded by seven countries including Algeria, Burkina Fasso, Guinea, Ivory Coast, Mauritania, Niger, and Senegal. Mali extends southwest from the arid southern Sahara through the semiarid Sahel to the Sudanian savannah. Mali has a diverse population of over 12 million people, composed of at least six different ethnic groups. Approximately three quarters of its population live in rural areas, and roughly 10% are nomadic. Historically, Mali was at the center of the trans-Saharan gold and salt trade connecting North Africa to sub-Saharan Africa. This historical connection almost certainly accounts for the fact that approximately 90% of Malians are Muslim today. Mali was colonized by the French between 1892 and 1960. Despite nearly a half century as an independent state, the official language is still French, but the vast majority of Malians communicate in local African dialects, the most common being Bambara. Mali remains among the lowest ranking country in the world with regard to education and health indicators. The adult literacy rate ranges between 30% to 40%. Roughly 40% of the population do not have access to safe drinking water. The life expectancy is approximately 49 years, and the infant mortality rate is greater than 106 deaths per 1000 live births. In general, access to professional health care is limited, and many Malians still treat ailments with traditional remedies. Limited health resources have made it difficult for scientists to obtain accurate data regarding the prevalence and incidence of diseases, especially those that are not life-threatening like cutaneous leishmaniasis.

Epidemiology

The first report of cutaneous leishmaniasis in Mali dates back to 1948 when Lefrou described two cases from Nioro, a town near the Mauritania border. Ten years later, two foci of cutaneous leishmaniasis were identified in the western and central part of the country. In the 1960s, nearly 600 cases of cutaneous leishmaniasis were reported in six different regions, expanding the total area containing the disease to most of the country. More recently, Keita and colleagues reported on 251 cases of cutaneous leishmaniasis from throughout Mali. While the first reports of cutaneous leishmaniasis in Mali came from archives of medical records, the first objective data regarding the epidemiology of the disease were established between 1969 and 1970, when Imperato and colleagues used the leishmanin skin test to show that the disease was present in most parts of the country, particularly in the Sahel. One study reported that the condition was slightly more common in males compared with females, 21.1% and 15.1% respectively, and that 18.1% of the subjects had contracted the disease at some point during their lives. Moreover, of the subjects studied (mostly school-aged children), a higher percentage of older individuals were positive. A more recent study on the epidemiology of cutaneous leishmaniasis in two neighboring villages in central Mali confirmed Imperato’s prevalence findings in one village (19.9% in Sougoula) but showed a twofold higher prevalence in the other village (45.4% in Kemena). The same study also showed a difference in the incidence of Leishmania infection between Kemena and Sougula, approximately 18% and 6%, respectively. The prevalence and incidence findings of this study also illustrated an interesting phenomenon long known about cutaneous leishmaniasis; two foci as close as a few kilometers apart can have disparate prevalence and incidence statistics. Among other factors, the difference can likely be accounted for by the availability of infected reservoirs at each locus.

Leishmania Parasite

More than 20 Leishmania species cause human infection. L major , L tropica , L aethiopica , and L infantum parasite species cause Old World cutaneous leishmaniasis. Of all the Old World Leishmania parasite species, only L major has been found in Mali. Before 2009, L major had been isolated from only two patients in Mali, one a tourist and the other a native of the country. A more recent study identified four different L major strains in Mali. While these reports established the presence of L major in Mali, they did not address whether L major is the only parasite species in the country, nor did they provide information on the geographic distribution of the parasite. Indeed, reports from countries adjacent to Mali have shown that parasite species other than L major can transmit cutaneous leishmaniasis. To address these questions, scientists in Mali are amplifying Leishmania DNA from skin scrapings of approximately one hundred cutaneous leishmaniasis patients from different regions of the country. Their study is designed to distinguish between parasite species on the basis of the size of the resultant PCR product and by DNA sequencing. Based on published reports, L major may be the predominant, if not exclusive species responsible for cutaneous leishmaniasis in Mali. However, given the diversity of geographic and eco-climatic zones, it is possible that other parasite species will be detected.

Vector

For the most part, cutaneous leishmaniasis is a disease of animals but affects people when sand flies, the animal reservoir, and humans coexist. Female phlebotomine sand flies transmit cutaneous leishmaniasis to people. In West Africa, two main genera of sand flies exist, Phlebotomus and Sergentomyia . Whereas Phlebotomus sand flies are known vectors of cutaneous leishmaniasis, Sergentomyia sand flies do not generally transmit the disease. In a focus of infection in neighboring Senegal, Phlebotomus duboscqi was identified as the vector for cutaneous leishmaniasis. Consistent with what is known about sand fly genera in West Africa, members of the Phlebotomus genera, including P duboscqi , have been found in Mali. A study of possible vectors in Mali found P duboscqi throughout every region of the country, while a more recent study recorded P duboscqi in Kemena, a village with active cases of cutaneous leishmaniasis. While the presence of P duboscqi sand flies in Mali is well established, to date there have been no reports of Leishmania- infected sand flies collected in the country. Malian scientists are now actively involved in an effort to characterize the diversity of sand fly species in villages with active cases of the disease. Moreover, they have started to utilize molecular biology techniques, including PCR to detect infected sand flies. If the prevalence and incidence studies are correct, it should not be long before they definitely identify the vector in Mali.

Reservoir

Throughout the world, nonhuman mammals, especially dogs and rodents, are reservoirs of cutaneous leishmaniasis. People, it turns out, are not good reservoirs. In the early 1980s, rodent species Mastomys erythroleucus, Tatera gambiana, and Arvicanthis niloticus and a dog were identified as the bearers of Leishmania parasites in Senegal and Gambia. While dogs are certainly commonplace in Mali, they are not as common as rodents. Indeed, a multitude of rodent species can be found in Mali, including those known to be vectors of cutaneous leishmaniasis in the neighboring country of Senegal. The reservoir of cutaneous leishmaniasis in Mali has (have) not been identified. Given the promiscuity of Leishmania parasites toward mammalian hosts, any number of the mammalian species in Mali could theoretically serve as the reservoir. Malian scientists have made limited, but unsuccessful, attempts at identifying Leishmania-infected rodents in villages with active cases of cutaneous leishmaniasis. Until an infected non-human mammal is identified, the reservoir in Mali will remain unknown.

Only gold members can continue reading. Log In or Register to continue