Kala-azar is an arthropod-borne disease that affects millions of humans in more than 101 countries worldwide [
1,
3]. Due to the importance of this disease in Iran, in recent years, various studies examining aspects of VL have been conducted in the Fars Province, Southwestern Iran. A total of 260 cases of VL have been recorded between 2001 to 2009 in the south of Iran, based on hospital records. Mean age of patients was 3.5 years, with the highest prevalence in 2 year old patients. The disease appeared to be more common in males [
5], and the results were identical to our findings. Nourabad, Kavar, Kazeroun, and Darab in Fars are known to be the main foci for the disease in south of Iran [
19]. Based on this study, it seems that Larestan and Ghiro-Karzin are also important regions for the disease in Fars province. The prevalence of VL in the south of the country may be considered as the second focal region of the disease in Iran. The primary focus of the disease is in the north (Meshkine-Shahr) [
20]. Between 1985 and 1990, 1,051 cases of VL were reported in Meshkin-Shahr [
22], which was the region with the highest incidence of the disease [
23]. A retrospective study on VL cases in Shiraz, Iran (from January 2010 to December 2013), showed that the highest rates of VL infection were in 2010, with 33 reported cases (62.3%), and the lowest rate in 2011, with 12 cases (37.5 %) [
21]. Dashti and Dashtestan counties (Bushehr province) are other endemic regions of VL infection in the south of Iran, and between 1991 to 1997, 92 cases of VL were detected in those 2 counties [
20,
24]. Bushehr is near the south of Fars province, where this study was conducted. In the present study, 95% of the cases were from children under 5 years old. This feature could be due to a different immunological response in children to the parasite. Similarly, in the northwest of the country, 90% of VL cases were from children under 5 years old [
22]. The main causative organism of VL in north and south Iran is
L. infantum [
4,
5]. A few case reports have also shown the presence of
L. major or
L. tropica in patients with VL in Iran [
25,
26].
Zoonotic VL (ZVL) and anthroponotic VL (AVL) have been described as 2 main forms of VL. ZVL affects mainly young children and has the domestic dog as its main reservoir. It is the most dominant form in the Mediterranean basin and Brazil. AVL affects people of all ages and is transmitted from human-to-human via infectious sandfly bites. This form is epidemic in the northern Indian subcontinent and in the northeastern countries of Africa [
27]. Therefore, it is important to pay attention to the control of vectors by indoor residual spraying (IRS) of households with insecticide and removal of infected dogs as the source of infection. Asymptomatic infected dogs play an important role in the epidemiology of VL in endemic areas and are the source of infection for both human and animals [
28]. Various risk factors are involved in the disease, including socioeconomic status, environmental changes, malnutrition, population movement, and climate change [
1].
The findings in this study indicate that there is a slightly higher incidence of VL in rural areas with the disease occurring more frequently in boys. This could be due to more exposure of boys to mosquitoes. Because the physical coverage is lower in boys than girls in Islamic countries. Despite a reduction in cases of the disease in recent years, continued attention in control methods should still be increased. Control measures including health education by public health professionals, improving the environment, and construction of new housing must be performed. In addition, further studies on the ecology, abundance and biology of vectors for disease control are required.
