title: Vector independent transmission of the vector-borne bluetongue virus.
abstract: Bluetongue is an economically important disease of ruminants. The causative agent, Bluetongue virus (BTV), is mainly transmitted by insect vectors. This review focuses on vector-free BTV transmission, and its epizootic and economic consequences. Vector-free transmission can either be vertical, from dam to fetus, or horizontal via direct contract. For several BTV-serotypes, vertical (transplacental) transmission has been described, resulting in severe congenital malformations. Transplacental transmission had been mainly associated with live vaccine strains. Yet, the European BTV-8 strain demonstrated a high incidence of transplacental transmission in natural circumstances. The relevance of transplacental transmission for the epizootiology is considered limited, especially in enzootic areas. However, transplacental transmission can have a substantial economic impact due to the loss of progeny. Inactivated vaccines have demonstrated to prevent transplacental transmission. Vector-free horizontal transmission has also been demonstrated. Since direct horizontal transmission requires close contact of animals, it is considered only relevant for within-farm spreading of BTV. The genetic determinants which enable vector-free transmission are present in virus strains circulating in the field. More research into the genetic changes which enable vector-free transmission is essential to better evaluate the risks associated with outbreaks of new BTV serotypes and to design more appropriate control measures.
authors.affiliation: a MSD Animal Health, Research and Development , Wim de Korverstraat , Boxmeer , The Netherlands .
authors.forename: Mirjam Tineke Willemijn
authors.initials: MT
authors.lastname: van der Sluijs
authors.affiliation: b Merial, Research and Development , Lyon , France .
authors.forename: Abraham J
authors.initials: AJ
authors.lastname: de Smit
authors.affiliation: c Central Veterinary Institute , Lelystad , The Netherlands , and.|d Department of Infectious Diseases and Immunology, Virology Division , Utrecht University , Yalelaan , The Netherlands.
authors.forename: Rob J M
authors.initials: RJ
authors.lastname: Moormann
mesh_terms: D000818:Animals; D001819:Bluetongue / Q000453:epidemiology / Q000517:prevention & control / Q000635:transmission* / Q000821:virology*; D001820:Bluetongue virus / Q000145:classification / Q000302:isolation & purification / Q000502:physiology*; D002417:Cattle; D004199:Disease Vectors; D005060:Europe; D018445:Infectious Disease Transmission, Vertical; D012756:Sheep; D014611:Vaccination; D014613:Vaccines, Attenuated; D014765:Viral Vaccines / Q000276:immunology
chemical_list: D014613:Vaccines, Attenuated; D014765:Viral Vaccines
keywords: Bluetongue; cattle; sheep; transmission; vaccination