Mahmoud I. Moussa

Rift Valley fever virus transmission by different Egyptian mosquito species.

4 Egyptian mosquito species were tested for their ability to transmit the Egyptian ZH-501 strain of Rift Valley fever virus (RVFV) to golden Syrian hamsters. Culex (Cx.) antennatus was the most efficient vector, showing a 37.5% transmission rate following a hamster blood meal containing 10 suckling mouse intracerebral 50% lethal doses (SMILD50) per ml. Fully engorged mosquitoes of this species showed an infection rate of 85% with the mean viral titres of transmitting mosquitoes 100-fold higher than non-transmitters. Autogenous and anautogenous populations of Aedes (Ae.) caspius were tested separately, and the transmission rates were 23.1% and 9.7% respectively, following feeding on hamsters with similar levels of viraemia. Two anopheline species, Anopheles (An.) multicolor and An. pharoensis, showed 12.5% and 3.5% transmission rates under similar conditions. In these 3 species infection rates exceeded 75% and mosquitoes transmitting had a higher average titre than those not transmitting.

Aride virus, a new ungrouped arbovirus infectingAmblyomma loculosum ticks from roseate terns in the Seychelles

SummaryA previously undescribed arbovirus, proposed name Aride virus, was recovered fromAmblyomma loculosum Neumann, collected from dead roseate ternsSterna dougallii arideensis Mathews in the Seychelles. Some important tick-virus-host associations are discussed.

Bahig virus (Tete group) in naturally- and transovarially-infected Hyalomma marginatum ticks from Egypt and Italy.

Arboviruses of the Tete group (Tete, Bahig, Matruh, Tsuruse) were previously recorded only from avian blood and organs from South Africa, Egypt, Italy, and Japan. We report Bahig virus, identified by complement-fixation and neutralization teats, from 2 subspecies ofHyalomma marginatum (family Ixodidae) ticks. One isolate was from larvae of the African subspecies,H. marginatum rufipes Koch, parasitizing a northward-migrating common wheatear,Oenanthe oenanthe subsp., in Egypt. Other isolates were from transovarially-infected F1 larvae and nymphs reared from an engorged female of the Eurasian subspecies,H. m. marginatum Koch, taken from a race horse near Naples, Italy. Transovarial transmission is relatively rarely documented among arboviruses. BothH. marginatum subspecies have already been implicated as vectors of pathogens causing serious human diseases in Eurasia and Africa. The present findings indicate the need for field and laboratory investigations of Tete group epidemiology and factors possibly involving human infections.

Reduced pathogenicity associated with a small plaque variant of the Egyptian strain of Rift Valley fever virus (ZH501)

Variants of Rift Valley fever virus producing plaques in CER cells of four different sizes are described. A plaque-forming unit (PFU) variant forming minute plaques was isolated and purified. Virus derived from this variant was not pathogenic to adult Swiss albino mice by the intraperitoneal (i.p.) route and was less pathogenic than the parent strain (ZH501) to adult Sprague Dawley rats by i.p. route, but produced typical severe liver necrosis in adult Syrian hamsters with intranuclear and intracytoplasmic eosinophilic inclusions. Antigen and antiserum to the minute variant prepared in mice reciprocally cross-reacted with antisera and antigens of the original strain (ZH501) in the complement fixation test. Plaque size of the minute variant remained constant after serial passages in cell culture and in suckling mouse brain. When the minute plaque variant was passaged i.p. in hamsters, virus which formed large plaques in CER cells was recovered from the hamster sera.