Modeling and comparative study of the spread of zoonotic visceral leishmaniasis from Northern to Central Tunisia

The Role of the Leishmania infantum Infected Dogs as a Potential Reservoir Host for Toscana Virus in a Zoonotic Visceral Leishmaniasis Focus of Northern Tunisia

The role of dogs as reservoir hosts for Toscana virus (TOSV) remains undetermined. This study investigated TOSV and Leishmania infantum infections in one healthy and three infected dogs with Leishmania (A, B, C) following natural exposition to sandfly bites in a focus of zoonotic visceral leishmaniasis (ZVL) located in Northern Tunisia from June to October 2020. At the end of the exposition period, infected and healthy dogs were examined for TOSV and L. infantum infections by xenodiagnosis using a colony of Phlebotomus perniciosus. Pools of freshly engorged P. perniciosus at days 0 and those at days 7 post-feeding were screened for TOSV and L. infantum by nested PCR in the polymerase gene and kinetoplast minicircle DNA, respectively. In the exposure site, P. pernicious is the most abundant sandfly species. The infection rates of sandflies with TOSV and L. infantum were 0.10 and 0.05%, respectively. Leishmania infantum DNA and TOSV RNA were detected in P. perniciosus females fed on dog B and C, respectively. The isolation of TOSV in Vero cells was achieved from two pools containing P. perniciosus fed on dog C. No pathogens were detected in P. perniciosus females fed on dog A and on control dog. We report for the first time the reservoir competence of dog with ZVL in the transmission of TOSV to sandfly vectors in natural settings, in addition to its role as a main reservoir host of L. infantum.

Insights into the drug screening approaches in leishmaniasis

Leishmaniasis, a tropically neglected disease, is responsible for the high mortality and morbidity ratio in poverty-stricken areas. Currently, no vaccine is available for the complete cure of the disease. Current chemotherapeutic regimens face the limitations of drug resistance and toxicity concerns indicating a great need to develop better chemotherapeutic leads that are orally administrable, potent, non-toxic, and cost-effective. The anti-leishmanial drug discovery process accelerated the desire for large-scale drug screening assays and high-throughput screening (HTS) technology to identify new chemo-types that can be used as potential drug molecules to control infection. Using the HTS approach, about one million compounds can be screened daily within the shortest possible time for biological activity using automation tools, miniaturized assay formats, and large-scale data analysis. Classical and modern in vitro screening assays have led to the progression of active compounds further to ex vivo and in vivo studies. In the present review, we emphasized on the HTS approaches employed in the leishmanial drug discovery program. Recent in vitro screening assays are widely explored to discover new chemical scaffolds. Developing appropriate experimental animal models and their related techniques is necessary to understand the pathophysiological processes and disease host responses, paving the way for unraveling novel therapies against leishmaniasis.

Enhanced attraction of sand fly vectors of Leishmania infantum to dogs infected with zoonotic visceral leishmaniasis

BACKGROUND

The sand fly Phlebotomus perniciosus is the main vector of Leishmania infantum, etiological agent of zoonotic visceral leishmaniasis in the Western Mediterranean basin. Dogs are the main reservoir host of this disease. The main objective of this study was to determine, under both laboratory and field conditions, if dogs infected with L. infantum, were more attractive to female P. perniciosus than uninfected dogs.

METHODOLOGY/PRINCIPAL FINDINGS

We carried out a series of host choice experiments and found that infected dogs were significantly more attractive to P. perniciosus than uninfected dogs in the laboratory as well as in the field. Significantly more P. perniciosus fed on infected dogs than on uninfected dogs. However, the fecundity of P. perniciosus fed on infected dogs was adversely impacted compared to uninfected dogs by lowering the number of laid eggs. Phlebotomus perfiliewi, the second most abundant sand fly species in the field site and a competent vector of L. infantum had similar trends of attractivity as P. perniciosus toward infected dogs under field conditions.

CONCLUSIONS

The results strongly suggest that L. infantum causes physiological changes in the reservoir host which lead to the host becoming more attractive to both male and female P. perniciosus. These changes are likely to improve the chance of successful transmission because of increased contact with infected hosts and therefore, infected dogs should be particularly targeted in the control of zoonotic visceral leishmaniasis in North Africa.

Childhood visceral leishmaniasis in Tunisia: A cross-sectional study in local spatial analysis

This paper describes spatial distribution of Visceral Leishmaniasis (VL) and determines its correlation with climatic factors in an endemic focus in northern and central Tunisia. Data on VL cases in children under five years of age were obtained by consulting medical reports from all Tunisian Pediatric Departments (TPD) during 2006-2016. Three key climatic factors, namely precipitation, continentality index and pluviometric coefficient of Emberger were used as predictor variables to model the VL geographical distribution. Data handling and statistical analysis were performed using R and Arcview GIS software systems. Bayesian local spatial model was employed to analyse the data. The results show a progressive increase in the VL incidence rates in regions with high levels of precipitation, but with low values of both continentality index and pluviometric coefficient of Emberger. A likely explanation of these findings arises from the opposite local effects of climatic factors which tend to cancel each other out in the calculation of the mean parameter estimate over the whole study area. We conclude that using non-local spatial analysis approach leads to misleading epidemiological interpretations, which in turn are of relevance for more efficient and cost-effective resource allocation for control and well manage the spread of VL in the study region and elsewhere in Tunisia.

Vaccination of a multi-group model of zoonotic diseases with direct and indirect transmission

Vaccination plays an important role in preventing or reducing the spread of zoonotic diseases. In this paper, we develop a susceptible-vaccinated-exposed-infectious-pathogen multi-group epidemic model of zoonotic diseases incorporating nonlinear direct and indirect incidence rates, nonlinear pathogen shedding rates, and common environmental contamination. Under certain assumptions, we first obtained the basic reproduction number of the model. Then, we utilized the comparison principle and global Lyapunov function method to prove global stability of dynamical equilibria. Finally, we analyzed optimal vaccination strategy. All the theoretical predictions were verified by numerical simulations.