Argas (Persicargus) arboreus ticks were collected monthly between March 1963 and February 1964 from a nesting site of Bubulcus i. ibis L. (cattle egret) in the Nile Barrage Park near Cairo, Egypt. A total of 2,500 ticks, tested in 500 pools of 5 each, yielded 42 strains of Quaranfil virus and 76 strains of Nyamanini virus. No virus strains were recovered from 2,400 specimens of A. (P.) persicus from domestic chickens in the same general area.
Natural infection indexes of both viruses showed an early spring rise and a less marked fall rise in the tick population. The spring rise of Nyamanini was maintained through most of the summer months; that of Quaranfil dropped in midspring and remained at a low level until fall. Cattle egrets are absent from the nesting sites during winter; they return and are easily available hosts for these ticks early in spring when the weather becomes warmer. Adult and young birds are present in the same trees till the end of summer or early fall.
While no Nyamanini viremia resulted from experimental inoculation of newly hatched domestic chicks, Quaranfil viremia occurred regularly and death ensued on the fourth and fifth days. Nyamanini virus is postulated to be transovarially transmitted by A. (P.) arboreus.
The possibility of concurrent natural infection of single ticks with both viruses appears to be slight. The presence of residual blood in field-collected A. (P.) arboreus appeared to have little or no diminishing effect on virus detection in the laboratory. Quaranfil and Nyamanini viruses were found to be antigenically unrelated to each other or to Chenuda virus and to differ in pathogenicity to experimental animals and in tissue culture.
It is concluded that Quaranfil and Nyamanini viruses are primarily bird viruses. Argas (P.) arboreus, the tick vector, sustained by and restricted to the avian host population, provides for the maintenance and dissemination of these viruses.