TOPOGRAPHICAL FACTORS IN EPIDEMIOLOGY OF MALARIA 
147 
meridians arid or semi-arid. Thus the des¬ 
ert regions of Utah, Arizona, Nevada and 
New Mexico do not provide favorable sites 
for the propagation of mosquitoes, unless, 
of course, man-made irrigation systems in¬ 
terfere with the natural land conditions. 
In the South, easterly winds from the At¬ 
lantic Ocean and Gulf of Mexico bring most 
of the southern states into the semi-marine 
or semi-tropical belts. Rainfall in this area 
generally exceeds 40 inches per year (Fig. 
10 ). 
Boyd and Ponton (1933) have shown that 
periods of excessive summer rainfall coin¬ 
cide with periods of increased malaria mor¬ 
bidity. In so far as generalization is per¬ 
missible it may be said that when the season 
of highest temperature coincides with the 
season of greatest rainfall general condi¬ 
tions for the transmission of malaria are 
most favorable. Recent observations in 
the Tennessee Valley indicate that prolific 
propagation of A. quadrimaculatus occurs 
only during periods when minimum water 
temperatures of 70° F are maintained. 
This coincides roughly with the period when 
the mean daily temperature is 70° F or 
higher. High atmospheric humidity is con¬ 
ducive to longevity of Anopheles and prob¬ 
ably influences favorably the development 
of the exogenous development bf Plas¬ 
modium. 
Summary 
Malaria in the United States is confined 
largely to the Atlantic and Gulf Coastal 
Plains. In this region it is transmitted by 
A. quadrimaculatus which propagates in 
collections of water associated principally 
with two types of topography, namely: 
(1) Solution topography produced by 
erosion of limestone strata by percolating 
ground water. Subterranean caverns are 
formed and these tend to collapse, produc¬ 
ing surface “sinkholes” which often con¬ 
tain water and constitute suitable breeding 
places for mosquitoes. 
(2) Collections of water associated with 
meandering old-age streams of the region. 
Relatively minor endemic foci of malaria 
transmitted by A. maculipennis occur in 
the Southwest and along the Pacific Coast, 
particularly in the San Joaquin and Sacra¬ 
mento River valleys of California. For the 
most part, this malaria is due to A. macu¬ 
lipennis propagation in irrigation waters; 
to a minor extent it is correlated with nat¬ 
ural breeding places of this mosquito. 
Malaria in the lowlands of Mexico, Cen¬ 
tral America and the West Indies is asso¬ 
ciated with the propagation of A. albimanus 
and A. tarsimaculatus. These mosquitoes 
find breeding places in collections of water 
at altitudes less than 500 feet above sea 
level in the coastal plains of these places. 
In the high lands of Mexico A. pseudopunc- 
tipennis and perhaps A. maculipennis are 
the vectors. Their breeding places are not 
associated with a particular topography but 
rather with collections of water for irriga¬ 
tion. 
