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Reduced pathogenicity associated with a small plaque variant of the Egyptian strain of Rift Valley fever virus
Abstract:
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.
Insights
A Rift Valley fever virus variant forming minute plaques showed reduced pathogenicity in mice and rats but caused liver necrosis in hamsters. This minute plaque variant reverted to large plaque formation after hamster passage.
Area of Science:
- Virology
- Pathogen Characterization
Background:
- Rift Valley fever virus (RVFV) causes significant disease in humans and animals.
- Understanding viral variants is crucial for disease control and vaccine development.
Purpose of the Study:
- To characterize a plaque-forming unit (PFU) variant of RVFV with minute plaque morphology.
- To assess the pathogenicity and genetic stability of this minute plaque variant.
Main Methods:
- Isolation and purification of a minute plaque RVFV variant from CER cells.
- Pathogenicity studies in Swiss albino mice, Sprague Dawley rats, and Syrian hamsters via intraperitoneal (i.p.) inoculation.
- Antigenic cross-reactivity testing using complement fixation tests.
- Serial passage in cell culture, suckling mouse brain, and hamsters to assess plaque size stability.
Main Results:
- The minute plaque variant was non-pathogenic to adult mice and less pathogenic to rats compared to the parent strain (ZH501).
- The variant induced severe liver necrosis in hamsters, with characteristic eosinophilic inclusions.
- Antigenic analysis confirmed cross-reactivity between the minute variant and the parent strain.
- Plaque size remained stable during serial passages in cell culture and mouse brain, but reverted to large plaques after hamster passage.
Conclusions:
- The minute plaque RVFV variant exhibits altered pathogenicity and plaque morphology.
- The variant demonstrates genetic instability, reverting to large plaque formation after passage in hamsters.
- These findings highlight the complex behavior of RVFV variants and their potential for reversion.