It is clear from what has been said regarding the life cycle of the malarial parasite that the mosquito is harmless if not itself diseased. Hence malarial-bearing species may abound in the neighborhood where there is no malaria, the disease being absent simply because the mosquitoes are uninfected. Such a locality is potentially malarious and needs only the introduction of a malarial patient who is exposed to the mosquitoes. It is found that such patients may harbor the parasites in their blood long after they are apparently well and thus may serve as a menace, just as do the so-called typhoid carriers. In some malarious regions as high as 80-90 per cent of the natives are such malaria-carriers and must be reckoned with in antimalaria measures.
Based upon our present day knowledge of the life cycle of the malarial parasite the fight against the disease becomes primarily a problem in economic entomology,—it is a question of insect control, in its broadest interpretation.
The lines of defence and offence against the disease as outlined by Boyce (1909) are:
1. Measures to avoid the reservoir (man):
Segregation.
Screening of patients.
2. Measures to avoid Anopheles:
Choice of suitable locality, when possible.