SUMMARYRift Valley fever virus isolates from the 1977 outbreak in Egypt were studied at an ultrastructural level. The particles measured 90 to 11o nm in diam. using negative staining and sectioning techniques, with a core component of 8o to 85 nm. The surface of the virions was calculated to be covered by approx. 16o sub-units. The particles were found in smooth endoplasmic reticular systems, which were made up of either multi-tubular complexes, or of a single large vacuole. The majority of these membrane systems were found to be unassociated with Golgi apparatus. Inclusion bodies were found within the host cell nuclei (made up of rods and fine granules) and in the cytoplasm (aggregates of fine or coarse granules). The possible relationship of these structures to virus replication is discussed.
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.
Studies were conducted into the development of anti-tick vaccines against two tick species, namely Boophilus annulatus Say, 1821 and Argas persicus (Oken) 1818, which, respectively, are responsible for high economic losses in the cattle and chicken industries in Egypt. Repeated infestation of spring chicken with Argas persicus females stimulated 35.9 % resistance to tick feeding compared to 20.4 % in controls. This resistance was associated with the presence of antibody activity to tick salivary gland antigens. There was increase of both the chicken serum total protein and the number of protein bands separated by SDS-PAGE, which suggested an increase in immunoglobulins. Chicken resistance to tick feeding was also induced by repeated injection (vaccination) with crude Argas persicus salivary gland antigens, with intramascular injection being more efficient at inducing immunity than subcutaneous injection.Prolonged infestation with Boophilus annulatus ticks induced immunity in cattle. Salivary gland and gut crude extracts of cattle exposed to the ticks contained antigenic proteins, with dominant 66 and 150 KDa glycoproteins. Antibodies against the two extracts or PAGE-separated antigens were detected in cattle that resisted tick feeding. Cell-mediated immunity (CMI) was also detected. The immune response was strong in non-infested Bos indicus and Bos indicus x Bos taunts Linneaeus, 1766 crossbreeds with low infestation, and weak in heavily infested Bos taurus.Resume-Des etudes ont ete menees pour la mise au point de vaccins anti-tiques contre deux especes de tiques, Boophilus annulatus Say, 1821 et Argas persicus (Oken) 1818, qui sont responsables respectivement de pertes economiques importantes dans la production de bovins et de poulets en Egypte. Des infestations repetees de poussins avec des femelles d'Argas persicus stimulent la resistance aux repas des tiques (35,9%) compart aux temoins (20,4%). Cette resistance est associee a la presence d'anticorps contre les antigenes des glandes salivaires de tiques. On observe a la fois une augmentation des proteines totales du serum des poussins et du nombre de bandes proteiniques separees par SDS-PAGE, ce qui suggerent une augmentation des immunoglobulines. La resistance des poussins aux repas des tiques est egalement induite par des injections repetees (vaccination) d'extraits bruts d'antigenes de glandes salivaires d'Argas persicus. Les injections intramusculaires induisent plus efficacement l'immunite que les injections souscutanees.Des infestations prolonge'es avec des tiques de l'espece Boophilus annulatus induisent une immunity du betail. Les extraits bruts de glande salivaire et d'estomac de bovins exposes aux tiques contiennent
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