Monitoring vectors is a crucial aspect of planning, executing, and assessing vector control measures. Gaining a comprehensive understanding of the distribution of malaria vector populations across a country is an invaluable asset in combating malaria transmission [35]. As global temperatures rise, it is crucial to comprehend and alleviate the impact of climate change on disease vectors to ensure effective public health interventions and the preservation of natural ecosystems.
Anopheles mosquitoes have demonstrated remarkable adaptability to their evolving natural habitats, creating favorable conditions for the proliferation of their species. However, this adaptability comes with consequences for mosquitoes and hosts, as they act as vectors for a range of human pathogens such as malaria parasites, filarial worms, and arboviruses [36, 37]. Particularly noteworthy are the An. stephensi species, which have evolved and adjusted to ecological changes, emerging as invasive and highly effective vector for malaria transmission in Africa and Asia [8, 9].
This study delved into the distribution patterns of the An. stephensi species in Hormozgan Province over the past three decades. The findings revealed a concentration of these species in the central and eastern regions of this province. This clustering may be attributed to the proximity to Sistan-Baluchistan Province, where malaria is highly prevalent, and the movement of malaria cases in the eastern part of the province. These factors likely contribute to the higher incidence of malaria in these areas, possibly due to more conducive climate conditions for An. stephensi establishment, especially when compared to the western regions.
Research in biological ecology, eco-biology, and bio-geosciences is crucial as it allows us to predict optimal growth conditions, and distribution in both present and future scenarios, as well as the potential expansion or contraction of biological distribution in the future [38, 39]. The Ecological Niche Model (ENM) is a widely used predictive tool for assessing suitable habitats for various organisms, with the MaxEnt model standing out as one of its popular variants. In the context of Hormozgan province, the MaxEnt model was utilized to evaluate potential ecological niches for An. stephensi, considers current and future years under three greenhouse gas emission scenarios (RCP2.6, RCP4.5, and RCP8.5). The analysis suggests that the geographic range of An. stephensi is likely to change in the coming years across different GCM scenarios.
Moreover, the MaxEnt model has been instrumental in identifying suitable ecological niches for several crucial malaria vector species in the southern regions of the country, including An. stephensi, An. fluviatilis and An. culicifacies [40, 41]. This model has also been applied in diverse geographic regions and for various species. For instance, Fuller and colleagues used the MaxEnt model in 2012 to project the distribution of the An. albimanus complex in the Caribbean and Central America region until 2080. Sinka and colleagues employed the model in 2010 to predict the distribution of Anopheles mosquitoes in African, European, and Middle Eastern regions [36, 42]. Additionally, Foley and colleagues utilized the model in 2008 to forecast the distribution of the An. minimus complex, a primary vector in Southeast Asia, alongside the GARP model [43]. Furthermore, Zhoupeng and colleagues conducted a prediction of the distribution status of four species, An. dirus, An. minimus, An. sinensis, and An. lesteri, in China using GCM models and three RCP scenarios (RCP2.6, RCP4.5, and RCP8.5) for the present, 2030s, and 2050s [33].
Among the 19 bioclimatic variables used for the ecological niche prediction of An. stephensi by the maximum entropy model, according to Jackknife analysis, Isothermality is the most influential variable in the model. Isothermality is defined as the quantification of day-to-night temperature oscillations in relation to the seasonal temperature oscillations. This metric is particularly relevant for tropical, insular, and maritime environments. Understanding Isothermality helps in assessing how temperature fluctuations within a month compared to the year can impact species distribution [44]. In MaxEnt modelling by using projected climatic variables, Isothermality (Bio3) became the most influential predictor in Mansonia africana mosquito (Vector of Rift Valley fever in Kenya) [45]. Isothermality (Bio3) was identified as the most influential among the 19 bioclimatic variables in the distribution of An. gambiae [35, 46].
Other variables such as Mean Temperature of Wettest Quarter (°C), Mean Temperature of Driest Quarter (°C), Annual Precipitation (mm), and Precipitation Seasonality were also found to have considerable impacts. This discovery suggests that the optimal temperature and Precipitation played critical role in determining the spatial distribution of An. stephensi. Anopheles and Plasmodium are both influenced by temperature sensitivity. Given that mosquitoes are ectothermic organisms, temperature plays a crucial role in the developmental and mortality rates of each life stage [47, 48]. Moreover, the gonotrophic cycle in adult female mosquitoes, which involves the blood meal-egg laying process, is also influenced by temperature fluctuations [38]. A notable correlation was observed between the monthly density of An. stephensi larvae and adults and the levels of precipitation and mean temperature [49].
Based on the MaxEnt modeling findings in this research, around 19–27% of the land in Hormozgan province is identified as highly suitable for the proliferation and dispersal of An. stephensi, with suitability levels exceeding 60%. These areas include the counties of Bandar Abbas, Minab, Jask, Bashagard, the islands of Qeshm, Kish, Hormoz, and a small area of Bandar Lengeh. In terms of elevation, these areas are more suitable for flat areas in the province compared to the topographic map of the province. This prediction perfectly matches with the results of the flat nature of the majority of An. stephensi species. The centers of gravity of areas suitable for the presence of An. stephensi were concentrated with very little difference for different years and scenarios in the western part of Minab County. This county is Located in Iran's tropical region [13] and experienced an average temperature of 27.4 ± 0.9 ºC over the past 25 years. The lowest recorded temperature, 19.7 ± 1.2 ºC, was noted in February, while the highest, 34.9 ± 0.7 ºC, was observed in July. Despite an annual average precipitation of around 196.8 mm/year, the district is crisscrossed by various rivers that originate from the northern mountains [50]. It appears that this city offers the most favorable conditions for the proliferation of the invasive Anopheles species under all circumstances within Hormozgan province, necessitating the implementation of a structured and all-encompassing strategy for managing the larval habitats in these regions.
The research outlines the geographic spread of primary malaria vectors in Hormozgan province and constructs an ecological niche model to fill knowledge gaps. The model offers data-driven forecasts to assist public health policymakers in shaping upcoming national surveillance and control initiatives. These findings highlight the pressing necessity for proactive actions to tackle the influence of climate change on vector-borne diseases like malaria.