Vera Cruz, and probably other points on
the Gulf coast of Mexico, are, however, at the present time, endemic
foci of the disease. In South America it has prevailed as an epidemic at
all of the seaports on the Gulf and Atlantic coasts, as far south as
Montevideo and Buenos Aires, and on the Pacific along the coast of Peru.
The region in which the disease has had the greatest and most frequent
prevalence is bounded by the shores of the Gulf of Mexico, and includes
the West India islands. Within the past few years yellow fever has been
carried to the west coast of North America, and has prevailed as an
epidemic as far north as the Mexican port of Guaymas, on the Gulf of
California.
It must be supposed that _Culex fasciatus_ is only found where yellow
fever prevails. The propagation of the disease depends upon the
introduction of an infected individual to a locality where this mosquito
is found, at a season of the year when it is active. Owing to the short
period of incubation (five days or less), the brief duration of the
disease and especially of the period during which the infectious agent
(germ) is found in the blood, it is evident that ships sailing from
infected ports, upon which cases of yellow fever develop, are not likely
to introduce the disease to distant seaports.
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