From: Risk profiling of schistosomiasis using remote sensing: approaches, challenges and outlook
Parasite-related factors | Effect on schistosomiasis transmission | Reference(s) |
---|---|---|
Temperature | Length of prepatent period; activity, survival and infection rate of free-living stages of the parasite | |
Water flow velocity | Passive transport of parasites in flowing water determines cercarial density | [20] |
Predators | Fish and carnivorous invertebrates reduce parasite population as natural predators | |
Sunlight | Stimulation of cercarial shedding | [19] |
Pathogenicity | Different strains of S. mansoni and S. haematobium result in geographical variations of disease severity | [22] |
Species | Different efficiency in identifying and infecting snails | [19] |
Snail-related factors | Effect on schistosomiasis transmission | Reference(s) |
Water temperature | Fecundity, mortality and rate of reproduction | |
Water flow velocity | Flow velocity >0.3Â m/s may dislodge and swep away snails | |
Vegetation | Food supply, surface to crawl and deposit egg masses; increase of dissolved oxygen | [23] |
Substratum | Nature of substratum is related to snail abundance | |
Water depth | Snails generally found in shallow water near the margins of their habitats; below 1.5-2Â m, snails have little importance for the transmission of schistosomiasis | [29] |
Fluctuations of water level | Permanence of available habitats determines the distribution patterns of snails | |
Rainfall | Creation of temporary snail habitats; increase of water flow velocity; supports contamination of water and passively transports snails when rains are heavy | |
Turbidity | Turbidity can impact the reproduction cycle | |
Water chemistry/quality | Low pH, refuse from factories directly harm snails; high abundance where water is polluted with human excrements | |
Sunlight | Completely shaded pools provide unsuitable habitat and activity of snails is high in direct sunlight | [23] |
Predators/pathogens | Natural predators, parasites and pathogens may limit the abundance of snails | [23] |
Species | Variation of susceptibility to parasite and efficiency to produce cercariae | |
Human-related factors | Effect on schistosomiasis transmission | Reference(s) |
Water contact behaviour | Exposure of the skin to parasite infested water is the prerequisite for human infection | [33] |
Hygiene | Contamination of water due to excrements of infected humans in or aside water | |
Gender | Relationship between gender and risk of infection is culturally variable and a determinant of water contact activities | |
Age | Highest risk for children as consequence of degree of exposure and low level of immunity | |
Immunity | Resistance to reinfection can be developed by the human body as a consequence of previous infections | [38] |
Ethnic origin | Variation in the susceptibility to infection | [20] |
Religion | Religious rules related to water contact related to disease exposure | |
Socioeconomic status | Relation to hygiene, the availability of protected water supplies and ability to cope with the disease | [39] |
Migration | Population movements can modify spatial patterns of disease transmission through both introduction of the parasite or the acquisition of infection | |
Occupation | Work related to water increases the exposure and risk of infection (fishermen, farmers, etc.) | |
Location of house | Location of house in relation to suitability of closest water source can influence infection status | |
Prevention/control measures | Spatial pattern of disease transmission can be highly modified by mass treatment campaigns and successful preventive measures |