RF Annual Report - 1935 - The Rockefeller Foundation

INTERNATIONAL HEALTH DIVISION 3!
plained without invalidating the general rule.
The region thus delimited may be considered as
endemic in the sense that the infection is always
present and widely distributed. This is the endemic
region of the Eastern Hemisphere. It is
one of the two great endemic regions of the
world, the other being the one in South America
discussed above.
The African yellow fever region may
be divided
into two parts. There is a western area
which extends to the eastern border of Nigeria
and includes also the coastal regions from Nigeria
to Angola. This western area has had numerous
epidemics of yellow fever, both on the coast and
in the interior, and is still having them. All the
historic outbreaks of yellow fever in Africa south
of the Sahara have occurred within this area. In
the eastern area, which includes the remainder
of the endemic region, the situation is radicallydifferent.
Yellow fever, outside of perhaps a
single sporadic case, has never been recognized
there. It is possible that we may
here be dealing
with strains of yellow fever virus which differ
from those in classic epidemics by having a
lowered virulence or a lack of selective localization
in vital organs. There may be environmental
conditions similar to those responsible for the
perpetuation and limitation of the jungle yellow
fever now being studied in South America. This
© 2003 The Rockefeller Foundation