Of the six internationally quarantinable diseases, four are arthropod-borne. Only one of these is an arbovirus disease - yellow fever. But in many respects yellow fever is of the greatest potential and actual importance, one reason being that it is transmitted by Aedes aegypti; the mosquito which has biologically adapted most successfully to association with the urban proclivities of man. During the past year yellow fever has erupted in a greater number of cases in more widely distributed situations than has been recognized for many years.

In reviewing this, the fourteenth issue of the Arbovirus Information Exchange, which contains a greater number of reports on a greater variety of arbovirus subjects than ever before, it is apparent that the magnitude of what has happened with yellow fever this past year has not come through. It is therefore considered to be of sufficient importance to bring this to the attention of the participants. Not only is this pertinent to what expert advisors to many governmental health authorities need to know, but it illuminates needs for better epidemiological reporting, development of surveillance commensurate with augmented arbovirus facilities and modern techniques, and actually, for further field and laboratory investigations to supply solutions to previously unsolved or newly emerging problems .

Several times in the past half century, it has been assumed that enough was known about yellow fever to make its elimination as a human disease amenable to application of simple public health measures of Aedes aegypti control or vaccination Several times some new feature of the virus, the vector or change in behavior of the human host has brought the problem of yellow fever back again as a subject which requires further special attention of specially qualified medical scientists.

In this issue is a map of the occurrence of yellow fever in Africa and South American in 1965, prepared by the World Health Organization, on the basis of official reports. It should be emphasized that this is a minimum documentation because it is based on official information. Scientific information and information from scientists expands this considerably, and brings what knowledge is available to the point where it is the subject of this note.

From mid-October to mid-December, 1965, Senegal in West Africa was the site of a major epidemic of yellow fever. Following the extensive vaccination campaigns begun in the late 1930’s, Senegal had recorded only sporadic cases of yellow fever until 1965. In 1960 the periodic vaccination campaigns were discontinued and by 1965 there was a growing population of non-immune young children. The epidemic centered around the city of Diourbel, 125 kilometers east of Dakar. Although the official number of reported cases is 238, the actual number was much higher. Serological surveys carried out in Senegal suggest that at least 5,000 human infections occurred during the epidemic. Aedes aegypti mosquitoes were prevalent in the Diourbel region breeding in domestic water containers. The method of introduction of virus into the epidemic region is unknown, although it is suspected that it accompanied migratory workers from Portuguese Guinea where epidemic yellow fever had been reported earlier. To prevent spread of epidemic yellow fever from the Senegalese hinterland into Dakar, prophylactic vaccination of children with mouse brain vaccine (because sufficient 17D was not available) was followed by The shift in public health practice following change in the status of former colonial territories has resulted in decrease or cessation of routine vaccination against yellow fever. This has led to accumulation of non-immunes over vast areas in Africa, susceptible to exposure to potential or actual intrusion of yellow fever virus from a sylvan or human transported infection.

Rescheduling of priorities, wrought by political changes, and the population explosion has separated more rural residents from the routine vaccination practices of public health programs. This is what led to the spill of jungle yellow fever into residents of Paraguay, Brazil, Argentina and Bolivia, even though

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