Abstract
Lumpy skin disease (LSD) is an economically important disease of cattle due to its ability to cause hide damage, reduced production and infertility. It has recently spread from Africa to parts of Europe and Asia, where the costs of control efforts have amounted to millions of euros. In Africa,
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its effects on livelihoods is tremendous while the ability of the virus to cross borders also impacts international trade from Africa, and elsewhere. The disease is mainly transmitted by biting insects, but the virus can also be found in semen. The thesis described 5 studies designed to investigate the reproductive effects of LSDV in cattle. In the first study, experimental challenge of post-pubertal, seronegative bulls produced clinical LSD in all bulls, but with varying severity. LSDV viral DNA was demonstrated in all fractions of semen, and shown not to be associated with red blood cells. We furthermore showed that the virus stayed in the testes of diseased bulls for a long time since it was associated with dead tissue. The second study involved the use of LSDV-infected semen for artificial insemination of a group of superovulated cows and a group of non-superovulated cows. Results from this study allowed the first report of sexual transmission of the disease. All experimentally infected cows showed varying clinical LSD, and LSDV viral DNA could be demonstrated in embryos flushed from the superovulated cows. The third study attempted to shed light on the effects of LSDV within an in vitro embryo production (IVEP) setting. Within the lab setting, a dose-dependent effect of LSDV was shown, with LSDV viral DNA being identified in fertilization media, unfertilized oocytes and degenerate embryos, and in blastocysts and expanded blastocysts when the viral dose was high. In the fourth and fifth study, we showed that the current disinfection methods were not able to completely remove the virus from semen, but vaccinating animals twice, with a month interval between vaccination, prevented virus shedding in semen and would be useful in protecting cattle herds from Lumpy skin disease. We furthermore demonstrated the ultrastructural association of the virus with the sperm membrane. Some disinfection methods did reduce viral loads, but did so at the expense of semen quality parameters. Future research efforts should focus on investigating the relative importance of the different transmission methods in the field, and on developing effective disinfection methods so that trade can occur without disease risk.
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