because of successful re-isolation from many samples and because samples 
were processed on different days in most cases, 2) that there was bird to 
bird transmission in Egypt either before capture or during transport to 
the laboratory - unlikely (but not disproven) because of the very short 
time elapsed between arrival in Egypt and bleeding, and 3) that birds 
captured in any given day represented arrivals from a given flock or 
flocks which originated or passed through a given enzootic focus. Implicit 
in this reasoning is that related but antigenically differing viruses occur 
in enzootic foci which are geographically or biologically separate. 
Laboratory experiments, designed to determine if Bahig virus would 
multiply in and be transmitted by mosquitoes, demonstrated multiplication 
but not transmission. The actual mode of transmission in nature is not yet 
known. A possibility still to be considered is that of latency in the bird, 
with viremia provoked by the stress of migration. Latency would adequately 
explain the very high percentage of viremia in birds arriving in Egypt. 
Hoogstraal (1961, 1963, 1964) have documented the abundance and 
variety of ticks on migrating palearctic birds. Infected ticks on migrating 
birds could readily transport viruses over long distances. Viruses were not 
isolated from ticks in the present study; however, the small number of ticks 
examined (221 pools from 424 birds) do not represent a sufficient sample to 
rule out ticks as a significant mechanism of virus transport. 
To summarize, this and previous studies have demonstrated that migrating 
viremic birds carry arboviruses both north and south, and that these viruses 
represent a large variety of tick-bome and mosquito-borne agents. The evi¬ 
dence with at least one virus (West Nile) favors transport over a long distance 
from Africa to Cyprus. Evidence with other viruses (Tete group, Thimiri) 
favors transport by enormous numbers of warblers from Europe to Africa. The 
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