Abstract
Rift Valley fever (RVF) is an arthropod-borne viral disease of importance in livestock and humans. Epidemics occur periodically in domestic ruminants. People in contact with infected livestock may develop disease that varies from mild flu-like symptoms to fatal viraemia. Livestock vaccination may assist in disease control. Rift Valley fever virus (RVFV) Clone 13 is a relatively new vaccine against RVF, derived from an avirulent natural mutant strain of RVFV, and has been shown to confer protective immunity against experimental infection with RVFV. The hypothesis tested in the current trial was that rams vaccinated with RVFV Clone 13 vaccine would not experience a reduction in semen quality (measured by evaluating the percentage progressively motile and percentage morphologically normal spermatozoa in successive ejaculates) relative to unvaccinated control animals. Ram lambs were screened for antibodies to RVFV using a serum neutralisation test. Animals without detectable antibodies (n = 23) were randomly allocated to either a test group (n = 12) or a control group (n = 11). Animals in the test group were vaccinated with RVFV Clone 13 vaccine. Daily rectal temperature measurements and weekly semen and blood samples were taken from all animals. Seven animals were eliminated from the statistical analysis because of potential confounding factors. Logistic regression analysis was performed on data gathered from the remaining animals to determine whether an association existed between animal group, rectal temperature and semen quality parameters. No correlation existed between the treatment group and values obtained for the semen quality parameters measured. There was no statistically significant post-vaccination decline in the percentage of live morphologically normal spermatozoa, or the percentage of progressively motile spermatozoa, either when assessed amongst all animals or when assessed within individual groups. A repeat study with a larger sample size and a more comprehensive pre-screening process may be indicated to avoid the inclusion of unsuitable animals.
Highlights
Rift Valley fever (RVF) (Phlebovirus, Bunyaviridae) is a mosquito-borne viral disease of ruminants with significant economic and public health implications
In South Africa, three vaccines are available: a modified-live vaccine (MLV), a killed vaccine, and a vaccine derived from an avirulent natural mutant strain of Rift Valley fever virus (RVFV Clone 13)
Animals used in the study were young, peripubertal ram lambs
Summary
Rift Valley fever (RVF) (Phlebovirus, Bunyaviridae) is a mosquito-borne viral disease of ruminants with significant economic and public health implications. The virus may cause fatal disease in juvenile and adult animals and may induce abortion in pregnant animals (Flick & Bouloy 2005). People who live and work with livestock are at greatest risk of contracting the disease (Swanepoel & Coetzer 2004). Vaccination of livestock helps prevent the spread of disease by reducing the population of viraemic animals that may infect vectors. Vaccination of dams confers colostral immunity to offspring, which reduces juvenile mortality (Gerdes 2004). In South Africa, three vaccines are available: a modified-live vaccine (MLV), a killed vaccine, and a vaccine derived from an avirulent natural mutant strain of Rift Valley fever virus (RVFV Clone 13)
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