4 MOSQUITO ERADICATION 



mosquito bites a person, these forms enter its stomach, where 

 they combine to form zygotes. The zygotes divide into sporo- 

 zoites, which finally appear in the salivary glands of the Ano- 

 pheles. From here they enter the blood of the person bitten by 

 the mosquito and start again on the non-sexual cycle. 



CHARACTERISTICS OF MALARIA 



It is noteworthy that it requires about 12 days after entering 

 the body of the mosquito before the sporozoites appear in its 

 salivary glands. This means that the mosquito cannot transmit 

 malaria until 12 days after it has bitten a malaria patient. The 

 parasite does not seem to injure the mosquito, which may live 

 many weeks and infect several persons successively. A mean 

 temperature of less than 60°F. inhibits development of the 

 parasite in the mosquito. 



"A person who once has had malaria," says Rosenau, 1 "is more apt to 

 have subsequent attacks. Ordinarily there is an increased susceptibility 

 rather than an immunity. However, repeated infections, especially 

 during early life, leave a very pronounced resistance. In malarious 

 regions many children carry the parasites in their circulating blood 

 without any manifestations of the disease. These carriers are important 

 factors. in spreading the infection in endemic areas, and must be taken 

 into account in preventive measures. 



"There is no true racial immunity in this disease. Occasionally a 

 congenital immunity seems to be transmitted ; this must be rare. Practi- 

 cally all persons who receive the infection for the first time are sus- 

 ceptible. The freedom from malaria which some persons seem to 

 enjoy may be accounted for partly by the fact that mosquitoes seldom 

 bite such persons. It is well known that on account of the odors, or 

 what not, mosquitoes do not bother certain individuals. No doubt the 

 infection of a small number of parasites is often overcome largely through 

 a vigorous phagocytosis. 



"Individual resistance varies in different individuals and in the same 

 individual at different times. The parasite may remain latent in the 

 spleen and other organs for years. Exposure, over-eating, fasting, 

 overwork, or worry, or anything that lowers the vitality of such indi- 

 viduals predisposes to an attack of malaria. The disease often breaks 

 out in persons in good health leaving a malarial region for a health 

 resort, whether mountain or seashore." 



1 "Preventive Medicine and Hygiene," New York and London, 1918. 



