The chief source of most parasitic diseases of man is

Definitive host: The host, in which the adult parasite lives and undergoes sexual reproduction is called the definitive host, e.g. mosquito acts as definitive host in malaria.In the majority of human parasitic infections, man is the definitive host (e.g. filaria, roundworm, hookworm).So human is the chief source of most parasitic infections.Panicker 7e pg:2