Geographical distribution of Parasite

The presence or absence of a number of biological and physiological factors in the environment affects directly or indirectly the densities and distribution of parasites.

1.      Climate: The development and survival of free living stages of parasites are greatly influence by temperature and humidity.  Intense dry heat or direct sunlight may destroy the larval forms. Low temperature arrests the development of ova and larva. Sufficient moisture is required for the survival and development of eggs and larvae.

2.      Intermediate host: Distribution of parasites is greatly influenced by the presence or absence of I/H where it required. The availability of an I/H is dependent on its ecological condition such as suitable temperature, humidity, food, vegetation and natural enemies. Eg. Fasciola hepatica is absent from Bangladesh because the I/H Lymnaea trunculata (snail) is absent in Bangladesh.

3.      Ecology: Habit of the host may allow them to come in contact with the parasites. The habit of eating raw or insufficiently cooked food exposes the people in the temperate region to tapeworm. Eating caltrop gives rise to Fasciolopsis in man in Indo-China.

4.      Availability of the susceptible definitive host or host range: The parasite cannot survive in an area where the susceptible hosts are not available. The distribution of parasites are more wide when it has a wide host range such as Trichostrongylus axei has world wide in distribution because of the wide host range.