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Published on: October 7, 2011
Virulence of variola viruses for suckling mice
1St Mary's Hospital Medical School, London, UK.
Abstract:
We report work done in 1971 to determine the quantitative virulence for suckling mice of 26 variola virus isolates from different countries and from cases of differing severity. Strains of recognized variola major and variola minor viruses differed up to 100-fold (expressed as the harmonic mean dose of inoculum which killed mice 2-4 d old, inoculated intracranially, in 5 d). Isolates from Indonesia and from East and West Africa gave intermediate values. Unlike tests on chick embryos, this test distinguished between African and Indonesian isolates.
Insights
This 1971 study quantified variola virus virulence in mice, finding significant differences between major and minor strains. The mouse model effectively distinguished geographic isolates, unlike chick embryo tests.
Area of Science:
- Virology
- Infectious Diseases
- Animal Models
Background:
- Variola virus, the causative agent of smallpox, exhibits varying virulence.
- Understanding geographic and clinical variations in variola virus strains is crucial for epidemiology.
- Previous methods, like chick embryo tests, had limitations in differentiating certain isolates.
Purpose of the Study:
- To quantitatively assess the virulence of 26 variola virus isolates in suckling mice.
- To compare the virulence of recognized variola major and variola minor strains.
- To evaluate the utility of a mouse model in distinguishing between geographic and severity-based variola virus isolates.
Main Methods:
- Intracranial inoculation of 2-4 day old suckling mice with 26 variola virus isolates.
- Determination of the harmonic mean lethal dose (HMLD) within 5 days.
- Comparison of results with those from chick embryo inoculation tests.
Main Results:
- Significant differences in virulence (up to 100-fold) were observed between variola major and variola minor virus strains.
- Isolates from Indonesia, East Africa, and West Africa exhibited intermediate virulence values.
- The mouse model successfully differentiated between African and Indonesian variola virus isolates, a distinction not achieved with chick embryo tests.
Conclusions:
- Suckling mice provide a sensitive model for quantitative assessment of variola virus virulence.
- The mouse model is effective in distinguishing between geographic variants of variola virus.
- This study highlights the utility of animal models in virological research and epidemiology.
