VL cases along the extension region of Loess Plateau in China belong to zoonotic mountain type, which patients were mostly children under 10 years of age [2, 3]. High Leishmania spp. infection rate was detected in local dogs, so the number of human VL cases can be reduced by the elimination and suppression of local dogs [11, 25, 26]. The dog was the principal reservoir host in this epidemic area. The primary vector of the zoonotic mountainous type VL was Ph. chinensis, a zoophilic species that also feeds on human. Recently, VL cases in extension region of the Loess Plateau, China were recurrence after the eradication of the disease for 20 years, which posed a challenge for exploration and control.
Sandflies have a broad range of hosts as blood sources [19, 20, 27–29]. They take blood mostly from mammals [20, 30–33] and cold-blooded animals . In Jiuzhaigou Sichuan, China, swine was the dominant blood source of sandflies, followed by chickens and dogs . However, there has been no report concerning the blood sources of sandflies in extension region of the Loess Plateau, China. In this study, chickens and humans were the most common blood sources of sandflies in Yangquan, Wuxiang Shanxi and Shanxian Henan from China, while dogs, goats, cattle and pigs were blood sources of sandflies as well. The proportion of blood sources was different with the locations of collection and the environment. As a good and sufficient blood source in the region, chickens may contribute to the sustainability of a large sandfly population, which was similar to what has been documented in other investigations [34, 35]. Although chickens attract sandflies in Brazil and in this study, the role of chickens in the epidemiology of the sandfly-borne diseases has not been defined yet .
There are also many reports on the detection of Leishmania spp. in animals by PCR assay, such as in bovines (5%), buffaloes (4%) and goats (16%) , even in desert lizards . In another case, goats were believed to constitute a reservoir host of L. donovani in Nepal . Therefore, other reservoir animal hosts of Leishmania should be further investigated. In Yangquan Shanxi, China, Leishmania was found in sandflies andthe specific antibody was also positive in local dogs. However, there was no dog blood in the sandfly samples, probably because the collection sites were far away from the dogs’ haunts in Yangquan. In Shanxian and Wuxiang, where the ecologic niches of sandflies were similar to that in Yangquan, dog was one of the blood sources animals. Consequently, we believed that dogs were still the blood source of sandflies in Yangquan, which frequently moving around sandflies’ habitats. Multiple blood sources were found in individual fed specimens, suggesting a complex feeding behavior, which was critical for sandflies to transmit zoonotic diseases to humans.
In China, vector sandflies with Leishmania infection have been reported in Sichuan and Shaanxi Province [16, 38]. The natural infection rate of a new haplotype of L. donovani was 1.98% in some villages in Sichuan Province , consistent with the results of sandfly infection rate in this study. To the best of our knowledge, this study was the first report of sandfliesinfected with Leishmania spp. in the extension region of the Loess Plateau, China. Monitoring natural Leishmania infection in sandflies would provide critical information to estimate the vector competence and assess the local epidemic risk of VL situation. Of the seven positive samples, the amplified sequences were all conserved with L. donovani complex (L. donovani/L. infantum).. Multiple lines of evidence suggested that there were heterogeneous Leishmania strains in China. These strains were distinct from but phylogenetically related to L. donovani/L. infantum complex [24, 26, 37, 39, 40]. Our results would be a complement for the heterogeneity information of Leishmania in China.
Dogs were confirmed as the reservoir host of Leishmania spp. in mountainous type of zoonotic VL in the extension region of Loess Plateau, China [2, 3]. It has been reported that the positive rate of Leishmania spp. in dogs was above 50% in Jiuzhaigou Sichuan, 41.9% in Heishui Sichuan, and 77.21% in Wenxian Gansu, China [11, 25, 41]. In Shanxi Province, there was only one investigation in 1959, in which the Leishmania positive rate in dogs was 0.01% . In this study, the positive rate of serum antibodies in dogs from Yangquan Shanxi was 5.97%, and there was no disease manifestation in these dogs. Among the seven positive sandfly samples tested, at least three contained human blood. Based on the preceding investigation, local asymptomatic patients and dogs should the important sources of VL infection, and the screening and treatment of the disease need to be strengthened.
Although we have systematically detected the blood sources, Leishmania infection and the antibody of Leishmania in dog sera in this study, there were still some limitations in this study. First, the primers for PCR detection of blood sources were designed based on the observation of the environment of the collection sites, but some blood sources animals may not be observed, so they may be missed. Moreover, the pooled samples were used for blood sources and Leishmania infection detection, making the positive rates not accurate. In addition, the investigation of potential reservoir hosts was insufficient in the study. In the future, we will collect more animal blood samples to detect Leishmania infection and antibodies, so as to provide more accurate guidance on the prevention and control of VL in the extension region of Loess Plateau in China.