The successful transmission of the infective stage of the parasite (miracidia) depends on different factors. These free-living stages miracidia rely on their own stored energy and are directly exposed to environmental factors including disturbance resulting from pollution and human activities. There are different environmental factors that affect the cercarial infection of the snail. These include pH, temperature, salinity, dissolved oxygen, water hardness, habitat conditions, presence of predators and competitors, etc. Each of these factors may increase or decrease the freshwater snail’s infectivity. The more hydrogen ion concentration in the aquatic habitat could have an effect on the maturation and physiology of the parasitic stage (miracidia), leading to impaired survival and reduced infectivity. In contrast, high temperature increases snail infectivity. While low dissolved oxygen in the aquatic environment results in low snail infectivity. Regarding the presence of predators can result in low snail infectivity by consuming the schistosome egg and the snails themselves. Total hardness also had a negative impact on the prevalence of snail infection. The hardness of the water results in the shell hardening of snails subsequently leads to low infection of snail by miracidia.
Part of the book: Update on Malacology