16 
MAIjARIA 
assistance of the Gorgas Memorial Labora¬ 
tory and the agencies of the Canal Zone. 
Based on the diagnosis of malaria plas- 
modia in blood films or on enlarged spleens 
in representative groups of the population, 
these surveys show a latent malaria inci¬ 
dence many fold higher than the reported 
malaria morbidity, approaching at times 
75-95 per cent of the entire population of 
certain areas. Such surveys provide a much 
more reliable basis for estimating the ma¬ 
laria incidence than do hospital records or 
mortality statistics. 
The relative proportion of the three com¬ 
mon species of human malaria plasmodia 
varies considerably. In the interior of Mex¬ 
ico, in Guatemala, Nicaragua, Costa Rica 
and Panama, Plasmodium vivax preponder¬ 
ates; in Nicaragua it is reported to consti¬ 
tute 79.5% of the total infections. In Cuba, 
extensive surveys indicate that P. vivax and 
P. falciparum are about equal. In the 
littoral areas of Mexico and in Yucatan, in 
El Salvador, Honduras, Haiti, Republica 
Dominicana and the Lesser Antilles, P. 
falciparum is much the more common spe¬ 
cies, or at least is the species most com¬ 
monly found in blood film examinations. 
Although P. malariae ranks third in all of 
the countries, its proportion of the total 
infections varies from 12.7% in Guatemala 
to 0% in Nicaragua and Cuba. (In Cuba, 
cases of diagnosed quartan malaria are re¬ 
ported to have been imported.) In Costa 
Rica surveys show that it is relatively com¬ 
mon on the Pacific Coast. However varied 
its incidence may be in the populations of 
the several countries, P. falciparum is pri¬ 
marily the parasite responsible for malaria 
mortality. 
General Considerations and Conclusions 
From the days when malaria was first 
recognized as a serious, disabling, and fre¬ 
quently fatal disease in the Western Hemi¬ 
sphere, attempts have been made to combat 
it. Control measures became more effective 
with the known relationship of anopheline 
mosquitoes to the life cycle. Yet, with few 
exceptions, the epidemiology of malaria in 
the Americas has been scientifically under¬ 
taken on an extensive scale only within the 
past two decades and in some countries is 
only now being initiated. Moreover, there 
is evidence in at least two countries of Cen¬ 
tral America that extensive antimalarial 
treatment is in progress without any ante¬ 
cedent fundamental epidemiological investi¬ 
gations based on surveys of the prevalence 
of the malaria parasites in the population. 
While there is some indication that the most 
heavily malarious areas in the United States 
are gradually coming under control, the 
much more intensely infected areas in tropi¬ 
cal America are probably as malarious to¬ 
day as they were fifty years ago. In many 
localities the urban communities are under 
relative control as a result of anti-mosquito 
and therapeutic measures, while the rural 
population, with higher parasite rates and 
better opportunity for mosquito transmis¬ 
sion, constitutes the essential seedbed of the 
infection. 
The data which have been assembled vary 
from scant statements admittedly inaccu¬ 
rate to voluminously documented evidence 
covering practically all phases of the epi¬ 
demiology of malaria in every subdivision 
of the country. Such data cannot be placed 
in the same category. They indicate public 
health attitudes as widely separated as apa¬ 
thetic tolerance and progressive realism. 
In spite of the difficulties encountered in 
evaluating such varied evidence, the follow¬ 
ing conclusions may be tentatively drawn: 
1. Malaria is widespread throughout the 
Southern United States, where all three 
common species of human malaria plas¬ 
modia are established. It also has an ex¬ 
tensive distribution in the Eastern, Central 
and Western States, where P. vivax is the 
only proven autochthonous species. Ma¬ 
laria is probably not now endemic in 
Canada. 
2. Except for the Bahama Islands and 
Barbados, malaria is a serious menace 
throughout practically all of Mexico, the 
countries of Central America and the West 
Indies, in which countries practically every 
political subdivision has an unsolved ma¬ 
laria problem. 
3. In the United States outside of the 
