TOPOGRAPHICAL AND RELATED FACTORS IN THE 
EPIDEMIOLOGY OF MALARIA IN NORTH 
AMERICA, CENTRAL AMERICA, AND 
THE WEST INDIES 
By ROBERT BRIGGS WATSON and REDGINAL HEWITT 
HEALTH AND SAFETY DEPARTMENT, TENNESSEE VALLEY AUTHORITY, WILSON DAM, ALABAMA 
In common, with other diseases which re¬ 
quire an insect vector, perhaps to the great¬ 
est extent, malaria is characteristically a 
disease of place. The constant close asso¬ 
ciation of its regional prevalence with still 
water has been recorded by numerous writ¬ 
ers during the period of 2000 years which 
preceded Ross’ discovery of the definitive 
host of Plasmodium. The subsequent defi¬ 
nition of the bionomics of the many species 
of Anopheles now permits rationalization 
of the occurrence of malaria, as regards 
both time and place, largely in terms of the 
natural history of the regional vector. 
The density of the vector, probably more 
than any other factor, determines the rate 
of malaria transmission. Therefore, physio- 
graphical factors which tend to produce an 
environment favorable to the propagation 
of a regional vector are of considerable in¬ 
terest from an epidemiological standpoint. 
The following discussion seeks to correlate 
the occurrence of malaria in several regions 
with certain physical factors. Considera¬ 
tion is given chiefly to the influence of geo¬ 
logical and topographical factors on the 
disposal of water, with special reference to 
this influence on the propagation of the 
regional vector; and to the influence of alti¬ 
tude and of temperature on the prevalence 
of anophelism and malaria. 
Anopheles quadrimaculatus and A. mac- 
ulipennis are certainly the principal vec¬ 
tors of malaria in the United States. The 
six other representatives of this genus which 
occur in this country are of relatively little 
consequence from an epidemiological stand¬ 
point. 
East of the Rocky Mountains, A. quadri¬ 
maculatus is chiefly, if not wholly, re¬ 
sponsible for malaria transmission. This 
mosquito propagates in permanent or semi¬ 
permanent collections of water under a 
wide variety of conditions. Its optimum 
requirements are clear, still water, partially 
shaded, with a pH of about 7.0 and con¬ 
taining emergent vegetation and floating 
debris. Perceptible current, gross pollution 
with sewage or industrial wastes, and salin¬ 
ity inhibit or prevent larval development. 
The diminished propagation of A. quadri¬ 
maculatus in polluted streams is probably 
due, either directly or indirectly, to the lack 
of dissolved oxygen in them. Very little 
malaria is found associated with the brack¬ 
ish water marshes along the coasts of the 
United States. This probably indicates 
that A. atropos, which propagates in such 
places, does not transmit malaria to a sig¬ 
nificant extent. While aquatic environ¬ 
ments which approach the optimum for A. 
quadrimaculatus propagation occur prin¬ 
cipally in the Atlantic and Gulf coastal 
plains at an altitude less than 500 feet, 
neither this mosquito nor malaria due to its 
presence are confined to this area. A. 
quadrimaculatus probably occurs through¬ 
out the entire Southeastern United States, 
whether or not it can be detected by usual 
means (Watson and Spain 1937). That 
this statement may apply also to the Cen¬ 
tral and Northeastern states is attested by 
the recent occurrence of malaria in Ohio 
(Hoyt and Worden 1935) and New Jersey 
(Butts 1937). 
Altitude does not of itself inhibit propa¬ 
gation of A. quadrimaculatus and malaria 
transmitted by it; it is the climatic and 
topographic circumstances which are usu¬ 
ally associated with high places. In most 
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