Control and eradication of viral diseases of ruminants

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Title: Control and eradication of viral diseases of ruminants
Author: Nuotio, Lasse
Date: 2006-06
Language: en
Belongs to series: 1/2006
ISBN: 952-10-3214-6 (pdf)
ISSN: 1796-4660
952-5662-00-4 (print)
Abstract: The monitoring and control of infectious animal diseases, limiting or prevention of their spread and efforts towards their eventual eradication are central tasks of the veterinary civil service. In addition to the cost-effectiveness of prophylaxis over disease and treatment, the animal welfare aspect is also involved. The purpose of this work is to review, describe and assess the available control measures against selected viral infections or diseases of domestic ruminants. The selected infections or diseases are bovine viral diarrhoea / mucosal disease (BVD), infectious bovine rhinotracheitis / infectious pustular vulvovaginitis (IBR), enzootic bovine leukosis (EBL) and maedi–visna (MV) of sheep. Each is recognized as a signifi cant disease of domestic animals. Decisive control and eradication measures are necessarily based on the biological, veterinary and diagnostic characteristics of the affl ictions, as well as on their epidemiology in terms of the intrinsic determinants of the hosts, host–agent relationships and sources and transmission of the infection, and occurrence of these infections or diseases. This information is compiled and presented in the fi rst part of the thesis with special reference to available or possible control and eradication measures. These measures and programmes against the four affl ictions employed in major cattle and sheep producing countries in individuals and herds and on national and international levels are outlined and assessed briefl y. In the descriptive part of the thesis the domestic and EU legislation that forms the offi cial framework for disease control and eradication are outlined. The development in the situation concerning these four infections or diseases is described from the early records to date. The fi rst recorded entries of the occurrence of BVD and EBL in Finland date back to the 1960s, those of IBR to the beginning of the 1970s and of MV to the beginning of the 1980s. Large-scale surveillance and health monitoring among dairy, suckler-cow and beef herds and sheep fl ocks, starting during the fi rst half of the 1990s, enabled the estimation of actual prevalences of these infections and diseases. A common feature of the occurrence of these infections or diseases is that none has had a prevalence of more than an estimated few percent before 1990, and a maximum of 1% since then. This has formed a very favourable starting point for the nation-wide control and eradication measures. The voluntary control programmes or schemes, as well as the offi cial control and eradication measures are described. The successful eradication of IBR and EBL in 1994 and 1996, respectively, and the signifi cant reduction in the occurrences of BVD and MV from 1990 to date, are reported in detail. The effi cacies of the offi cial control and eradication measures and of the actions of the voluntary control programmes or schemes are analyzed further, making use of a heuristic formulation for the infection reproduction number (R), i.e. the number of secondary cases produced by one infective animal. The infl uence of the measures is resolved into the three components of R: the probability of transmission, frequency of infectious contacts and length of the infectious period, and the impact of the measures on each component is graded on a three-step scale. The conclusion is drawn that the offi cial measures complemented by voluntary actions for control and eradication have for the most part been adequate. The signifi cance of fi nancial compensation from the state for the costs incurred in the control of notifi able diseases is noted. In the case of BVD the decisive measures for fi nal eradication have only been available since 2004 and their impact will be seen in the next few years. The role of continued surveillance and health moni toring for both overseeing the situation with BVD and MV, and maintaining an IBR and EBLfree status is emphasized.

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