Quinine and chloroquine affect malarial parasites only at life stages when the parasites are forming hematin-pigment (hemozoin) as a byproduct of hemoglobin degradation.
Among protozoan endoparasites, such as the malarial parasites and trypanosomes, infective stages in the hosts blood are transported to new hosts by biting-insects, or vectors.
It was horrible, a writer said, the 400 miserable, helpless, emaciated specimens of humanity, subjected for months to the malarial atmosphere of the river bottom.