The history of the connection between yellow fever and the mosquito is discussed under etiology.
Fig. 40.—Geographical distribution of yellow fever.
Geographical Distribution.—As will be seen from the chart the chief epidemic centers are the islands and coasts of the Gulf of Mexico and the West Coast of Africa. The disease has at times extended down the West Coast of South America and is now rather prevalent in Ecuador. The last epidemic in the United States was that in New Orleans.
The disease has never invaded Asia or Australia and there is fear that the opening of the Panama canal may bring this about.
Guiteras, who has recently returned from an investigation of the problem of yellow fever on the West Coast of Africa, was unable to find evidence of its existence there at the present time. He notes an absence of the extreme heat and abundance of mosquitoes which are features of yellow fever ports of South America.
Etiology and Epidemiology
Etiology.—It is now generally accepted that the cause of yellow fever is a spirochaete, Leptospira icteroides, which is very similar to but slightly smaller than L. icterohaemorrhagiae of infectious jaundice. Noguchi injected 74 guinea pigs with about 5 cc. of blood from 27 cases of yellow fever. The blood from 6 of these cases proved infectious, producing in 8 guinea pigs fever, conjunctival injection, albuminuria, a leucocytosis followed by leucopenia and, after a few days, a subsidence of the fever to normal or subnormal. At this time jaundice and haemorrhages occurred.
Fig. 41.—Dark-field view of Leptospira icteroides in a culture 16 days old. × 1000. (After Noguchi.)