600 Malaria 



Ohio River and by its general restriction to the so-called "malarial belt." 

 This area extends eastward from the plains of Texas and Oklahoma and 

 includes the lower Mississippi valley and the Gulf Coast. Even within 

 this area, where malaria is mainly a rural disease, reduction in incidence 

 has been marked and continued reduction is to be expected with the 

 extension and improvement of control measures now in operation (1). 

 At present, however, endemic malaria in the southeastern states remains 

 a local problem of some importance as well as a potential threat to other 

 North American regions. 



THE MALARIAL PARASITES OF MAN 



Malarial parasites apparently were first seen by Meckel in 1847. 

 Their significance was not recognized until Laveran reported, in 1880, 

 that he was able to find them only in corpuscles of malaria patients. Five 

 years later, Marchiafava and Celli produced apparently the first cases 

 of experimental malaria by inoculating human volunteers with blood 

 containing the parasites. 



Four species of Plasmodium are now generally recognized as parasites 

 of man: P. vivax, causing tertian (benign tertian) malaria; P. falciparum, 

 causing malignant tertian (subtertian, aestivo-autumnal) malaria; P. ma- 

 lariae, causing quartan malaria; and P. ovale, causing a comparatively 

 mild tertian type. 



The relative incidence of these malarias varies in different parts of the 

 world. Benign tertian is primarily a disease of temperate and subtropical 

 areas and, while widely distributed throughout the tropics, it is ap- 

 parently uncommon in some tropical countries. Malignant tertian is pre- 

 dominantly tropical, although extending into temperate regions where 

 it is generally much less common than vivax malaria. Quartan malaria is 

 widely distributed but is usually a second-rate problem in comparison 

 with the dominant type (vivax or falciparum, malaria) in any given 

 region. However, there are exceptions, such as the Belgian Conge, in 

 which quartan malaria is especially prevalent. P. ovale produces a malaria 

 resembling but appreciably milder than benign tertian. Latent infections 

 tend to develop early and are less liable to relapse than in the other 

 malarias (103). P. ovale was observed by Craig (32) in American troops 

 returning from the Philippines, and was described later (33) as a variety 

 of P. vivax with a strong resemblance to P. malariae. The specific name, 

 P. ovale, was proposed by Stephens in 1922 after careful study of the 

 parasites (105). This species has since been investigated in additional 

 material (55, 77, 103, 108, 122). Strains have retained their characteristics 

 in passage through paretics (103, 122) and through mosquitoes (55, 103). 

 Examination of stained preparations convinced Craig (34) that P. ovale is 

 the same species which he had observed earlier. Infections have been re- 

 ported from certain parts of Africa (Belgian Congo, East Africa, Gold 



