THE PROBLEMS AND PRINCIPLES OF MALARIA 



PREVENTION. 



By A. J. Oke.x STEIN, M.D. 



It might be well to summarise briefly the mechani-ir. of 

 malaria transmission from one ])erson to another, so that those 

 of my readers who have not partictilarly studied the subject may 

 be better able to follow the rationale of the ])reventive niea-ures 

 which T shall endeavour to otitline. 



In 18S0. Laveran discovered in the blood of malaria jjatients 

 certain organisms, and came to the conclusion tliat the disease 

 is caused by these organisms. Acting u])on the suggestion of 

 Sir Patrick Manson — the Nestor of tropical medicine — Mai'or 

 (now Sir) Ronald Ross traced the development of a bird parasite, 

 similar to the parasite of malaria, in the Ciile.r mosquito, and 

 also partially in the Anopheles. Grassi stibsequently showed that 

 only Anopheles are concerned in the transmission of malaria. 

 Since the days of Laveran's. Ross's, and (irassi's discoveries, a 

 great deal of work has been done in this field, and the prc-ent 

 stattts of our knowledge can be briefly stimmarised thus :— 



Malaria is caused by a pi"otozoan organism, and the three 

 varieties of malaria — quartan, tertian, and sub-tertian (or. as 

 it is otherwise known, .Tstivo-atitumnal or tropical) — are caused 

 by dift'erent sjjecies of this organism, namely, (|uartan — the com- 

 mon form of malaria in Italy and other European countrie- — l)y 

 the Plasiiuuiiitiii inalarice, discovered by Laveran in 1881 ; tertian, 

 by the Plosiiiodiiini z'k'ax \ and sub-tertian — which is the com- 

 monest form in tropical cotmtries — by the Laverania maiarice. 

 The last two were first described by Grassi and Filetti in 1889. 



It is also not uncommon to see cases infected v/ith more than 

 one of these organisms. 



All the parasites causing malaria have one thing in common 

 — they require for their complete development two hosts, namely, 

 the Anopheles mosquito and man. When the female Anopheles 

 mosquito of certain species (only the females can stick blood) 

 sucks some blood from a man in whose circulation the parasite 

 exists in the sexual form, the parasite, under favourable circum- 

 stances, enters upon a cycle of development known as sporogony, 

 which is a sexual process, and when that process of development 

 is completed — -which takes about 10 to 12 days — that female 

 Anopheles is capable of transmitting the parasite to man. 



In the human host a further, asextial, type of development 

 takes place. This is characterised by the following important 

 stages : — 



The young parasites injected through the proboscis of the 

 mosquito enter a red blood cell. In this cell they grow until 

 the blood corpuscles containing them are broken up, and the 

 l)arasites, which have now become subdivided into a number 

 ol small young parasites, are thrown into the circulation. Lhider 



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