THE PREVENTION OF MALARIA

THE prevention of malaria has been a vexed problem through the centuries. Ross's epochmaking discoveryof the insectvector of the disease, followed by Gorgas'snotableachievementin making habitablethe PanamaCanalzone, drew attentionto the value of drainageand other measuresaimed at the exterminationof the anophelinemosquitoitself. But.thereare many placesin which anti-anopheline measures,to be effective, would need to be carried out on sucha large scalethat they are impracticable for reasonsof finance. There are many wild and semi-civilized placeswhere the anophelinemosquito flourishes unchecked, where there is a constant sourceof infection in the untreatednative peoples, and where, in consequence,malaria is rampant. Almost every white man proceeding to one such place,doesso in the foreknowledgethat, whetherhe wins a fortune or not, he will certainly acquire a malarial infection. It is perhapsunfortunatethat peopleshould accepttheir fate with such utter lack of emotion, and should regard a disabling illness merely as an incidental concomitantto existencein a malarious country; if the prospect of infection gave them greater perturbation, they would he more eager to undertake measures of personal prophylaxis, and thus provide a greater quantity ? f more suitable material for the study of a wry Important aspectof the malaria problem. Natives are not usually suitable subjectson whom to test the prophylactic value of drugs; for in the vast majority of instancesthey arealreadyinfectedwhen the experiment is commenced,and, perhaps,have become partially immune. It was not until the introduction of malarial therapy for generalparalysis of the insane that the prophylactic value of quinine was satisfactorilyinvestigated. As a result, it is now known that quinine is not a true prophylactic, in that its administrationdoes not prevent infection; that is, it has no effect on the sporozoite. The value of quinine in prophylaxis is its effect of preventingthe developmentof malarial paroxysms. The introduction a few yearsago of "Plasmoquine" (N-diethylamino-isopentyl-S-amino-6-methoxy-quinoline, derived synthetically) gave new hope to investigators. Its valueasan agentcapableof destroying the sexual forms of the malaria parasitewas soon demonstrated,and it now deservedly holds an assured place in the therapeutics of malaria. Numerous extravagantand some well considered statementshave been made concerning its efficacy as a true prophylactic against malaria; that is, its specific action on the sporozoite. But British observers.with their customarycaution, generally laudable,have not hastenedto enter the field; the development of British opinion has consequently beenslow. It is only quite recently that the results of carefully controlled experimentsby S. P. James, W. D. Nicol and P. G. Shutehave been published. ' The object of their investigationswas to ascertain whether any known preparationwas of value as a prophylactic against malaria transmitted by the hite of the mosquito. In a series of eight experimentsthey found that "Plasmoquine"was effective; under similar conditions six other preparations proved valueless. They repeatedtheir experiments with "Plasmoquine"at the Horton Mental Hospital, Epsom, in a further series of cases,with similar satisfactoryresults. At the same time Nicol submitted to a test of the efficiency of the drug as a prophylactic against benign tertian infection, and Shuteagainstmalignanttertian; neithercontracted malaria.Jamesand nine medicalstudentssubmitted to a confirmatory test. Each took one dose of 0·02l grammeof "Plasmoquine"on the first day; on the secondday three dosesof 0·02 grammewere taken, and eachsubjectwas bitten by infected mosquitoes. The administration of 0'02 gramme three times a (lay was continued for the next five days. The volunteerswere kept underobservationfor 27 days. Tn no instance was there any clinical or protozoological evidenceof infection. At the sametime all the patients used as controls suffered definite malarial paroxysmsdespite that one of them had heen given quinine in prophylactic doses before heing bitten and for eight days thereafter. There can be no doubt that sporozoiteswere introduced into the blood of eachvolunteer; for it was shown that eachhad been bitten by at least one mosquito harbouringlive sporozoitesin its salivary glands. -Iames, Nicol and Shute are convinced that "Plasrnoqulne"in much smaller doseswould be of equalvalue. They remark that the next stepshould he to ascertainwhether the preparationis effective