Retrospective Study of Visceral Leishmaniasis in the Health District of Léré in Chad, Central Africa

Visceral leishmaniasis is a neglected tropical disease that is inevitably fatal without treatment, but early diagnosis and treatment can cure patients. It largely affects people living in underdeveloped countries and is the second leading cause of mortality from parasitic infection after malaria with 20,000 to 40,000 deaths per year. To assess the epidemiology of visceral leishmaniasis in Chad, we performed retrospective study in the health district of Léré in the southwest of the country area by extracting data from the laboratory records diagnosed visceral leishmaniasis cases between January 2015 to December 2019. Between 2015 and 2019, a total of 1,141 patients were tested for Visceral leishmaniasis in the laboratory of Léré district hospital, with a prevalence of 30% (n=345) among suspected cases. The majority of the positive patients were male (61%) and the peak reporting period of cases was between March and October. The lack of awareness of Visceral leishmaniasis, the underreporting of cases and the increasing incidence recorded at a health facility in Chad, highlight the need for strengthening Visceral leishmaniasis surveillance and case detection capacity in region. To develop appropriate prevention and control strategy of visceral leishmaniasis, further study is needed to characterize the distribution of visceral leishmaniasis and its transmission in the country.


Abstract
Visceral leishmaniasis is a neglected tropical disease that is inevitably fatal without treatment, but early diagnosis and treatment can cure patients. It largely affects people living in underdeveloped countries and is the second leading cause of mortality from parasitic infection after malaria with 20,000 to 40,000 deaths per year. To assess the epidemiology of visceral leishmaniasis in Chad, we performed retrospective study in the health district of Léré in the southwest of the country area by extracting data from the laboratory records diagnosed visceral leishmaniasis cases between January 2015 to December 2019. Between 2015 and 2019, a total of 1,141 patients were tested for Visceral leishmaniasis in the laboratory of Léré district hospital, with a prevalence of 30% (n=345) among suspected cases. The majority of the positive patients were male (61%) and the peak reporting period of cases was between March and October. The lack of awareness of Visceral leishmaniasis, the underreporting of cases and the increasing incidence recorded at a health facility in Chad, highlight the need for strengthening Visceral leishmaniasis surveillance and case detection capacity in region. To develop appropriate prevention and control strategy of visceral leishmaniasis, further study is needed to characterize the distribution of visceral leishmaniasis and its transmission in the country.

Background
Visceral leishmaniasis (VL) is a neglected tropical disease that is potentially fatal. It largely affects people living in underdeveloped countries and is often associated with malnutrition, population displacement, poor housing and weak immune systems (Okwor and Uzonna 2016;Okindo et al. 2016). Also known as Kala-azar, VL is the second leading cause of death from parasite infection after malaria with 20,000 to 40,000 deaths per year (Alvar 2012). It is characterized by a long oscillating fever, poor general condition, weight loss, immunosuppression, and enlarged spleen and liver, hence the name VL.
Without treatment, it is inevitably fatal, though with early diagnosis and treatment, virtually all patients can be cured. In Chad, there is little published data on the clinical and epidemiological pro le of VL. Its actual incidence is probably underestimated, as the cumulative number of cases from its rst noti cation in 1966 to 2003 was 64. During the same period, no deaths due to the disease were reported (Sirol 1976;Desjeux 1991;OMS 2009). In 2004, a patient from Chad was diagnosed with LV in Marseille/France (Aubry 2004). In recent years, VL has reappeared and spread to some areas where it was previously non-endemic. In the health district of Léré in southwestern Chad, the number of patients diagnosed as LV-positive is increasing, however, the lack of research for in-depth knowledge of the epidemiological characteristics often delays diagnosis and treatment.
In this article, we report up to date information on VL in Chad Republic by analyzing health facility laboratory data on VL collected over the last ve years in the district of Léré in Chad. The signi cance of the ndings in strengthening VL case detection, surveillance and response are discussed in detail.

Source of data and study site
The anecdotal discussions with Moundang, Foulbés and Fulani. The town of Léré is situated on the shores of Lake Léré, which is the only lake in Chad to be home to a large manatee colony, making this locality an important tourist destination.

Diagnostic of VL in Léré health district laboratory
The diagnosis of VL carried out in the Léré health district was based solely on serological tests without biological con rmation in accordance with the WHO manual protocol (1996). For each patient suspected with VL, 5 ml of blood was drawn by venipuncture to perform a formalin-gel test and/or rapid diagnostic test. For the formalin-gel test, two drops of formalin are added to 1 ml of plasma. When the test is positive, the serum bleaches and solidi es to form a gel. If the test is negative, the serum does not change and both bleaching and gelling only occurs after 30 minutes. The rapid diagnostic tests were  (Fig. 2). The number of VL cases was higher among males (61%) than females in all study years and also August to October cases are more frequent (Fig. 3).

Discussion
In Chad, as in most West African countries (Kone et al. 2019), the VL is very little studied and few countries regularly communicate the documents to the WHO.
We describe here the rst update of VL cases in 46 years based on laboratory diagnosis at the district Hospital of Léré in southwestern Chad. Over ve-year period (2015-2019), we observed an increase in the number of cases, indicating an active transmission of the disease. The increase in the number of cases could be due to the lack of control strategy to limit the spread of the disease.
In the present study, the proportion of VL positive test among clinically suspected case is 30% (345/1,141). This proportion could be even higher if other more sensitive diagnostic methods such as PCR were used, implying that the prevalence of the disease may be even higher (Sundar et  Analyzing the distribution of the total number of cases, we found that the VL was predominantly male (61%). Similar results have been reported in several studies (Zijlstra et al. 1994;Malaria Consortium 2010;Hailu et al. 2016) and may be explained by socio-cultural habits of the patients. In this community, agricultural eld activities and outdoor sleeping behavior increase the exposure of men to sand y bites than women. In our study area, males wear short trousers or sleep bare-chested, while women dress in clothing that covers the maximum body surface area.
Farming is the main activity in the study area with livestock and poultry being kept in pens near the houses creating favorable conditions for sand ies breeding site and exposing the population sleeping outdoor without bednet to high risk of VL transmission. Moreover, the high reporting period of cases is between August and November, suggesting that infection may have occurred in May-July (two to three months earlier). This period (March-May) correspond to the peak of the hot season with temperature reaching 45 0 C prompting people to sleep outdoor overnight, thus exposed to sand y bites.

Conclusion
In Chad, VL is little known and poorly documented, however, the incidence of the disease is increasing in areas that were not formerly endemic. To control VL, it is necessary to strengthen diagnostic capacity (laboratory tests and training of local health workers), data reporting, and increase awareness of the disease at all levels of health facilities and communities.
The presence of healthy carriers in a population represents an important but largely neglected reservoir that perpetuates the transmission of VL. Therefore, the detection and treatment of all cases of leishmaniasis is an essential measure for any attempt to eliminate this disease.
In order to develop and implement an appropriate control strategy, further research is needed to characterize the epidemiology of VL, the transmission pattern, the identi cation of the vector, the parasite and the reservoir. Figure 1 Source of data and study site. Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.