Exploring Fasciola infection dynamics in Coastal Caspian Sea region: implications of growing degree days (GDD) and Malone index across varied climatic zones in Iran

Fasciolosis, a neglected tropical disease caused by Fasciola spp., is a global parasitic infection whose prevalence is on the rise, particularly in warmer regions with favorable temperature and humidity conditions. This study examines the temporal presence of Fasciola spp. in various climatic zones across Iran, focusing on Gilan province as an endemic area. We calculated the Malone index for 5-year intervals spanning significant epidemics in 1988 and 1999 in Gilan, as well as 2005, 2010, 2015, and 2020. The results revealed a significant increase in Malone indices during August, September, and October in 1988, indicating a higher risk for Fasciola presence than in other months. These months were categorized as moderate risk. In 1999, September exhibited moderate risk, while October was classified as low risk. The risk levels remained relatively low in 2005, with the highest value in September and October. Similarly, October and September showed the highest risks in 2010, while October was identified as highly risky in 2015. In 2020, August displayed a higher risk, while September, October, and November indicated low risk. The analysis highlights the variability of risk levels across different years, with September and October consistently appearing as months with a higher probability of Fasciola presence. Conversely, the risk diminishes from January to July, which is considered a low-risk period in the region. Interestingly, a comparison with three different geographical regions in central, southern, and western Iran revealed that the Malone index was zero in all months of the year, except for two cases, suggesting unfavorable conditions for Fasciola presence in these areas. This research sheds light on the complex interplay between climatic variables and the presence of Fasciola spp., with the potential to inform the development of targeted strategies for preventing and controlling this parasite in Gilan province, a known hotspot for fasciolosis, as well as in other regions with similar climatic conditions.