Helsingin yliopisto

 

Helsingin yliopiston verkkojulkaisut

University of Helsinki, Helsinki 2006

Control and eradication of viral diseases of ruminants

Lasse Nuotio

Doctoral dissertation, June 2006.
University of Helsinki, Faculty of Veterinary Medicine, Department of Clinical Veterinary Sciences and Finnish Food Safety Authority Evira, Department of Virology.

The monitoring and control of infectious animal diseases, limiting or prevention of their spread and efforts towards their 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. Decisive control and eradication measures are necessarily based on the biological, veterinary and diagnostic characteristics of the afflictions, as well as on their epidemiology in terms of the intrinsic determinants of the hosts, host-agent relationships, transmission of the infection and occurrence of these infections or diseases. This information is compiled with special reference to available or possible control and eradication measures, and those employed in major cattle and sheep producing countries are outlined and assessed briefly.

The domestic and EU legislation that forms the official framework for disease control and eradication, as well as the official measures and the voluntary programmes are reviewed. The first 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 flocks, starting during the first half of the 1990s, enabled the estimation of actual prevalences of these infections and diseases. The successful eradication of IBR and EBL in 1994 and 1996, respectively, and the significant reduction in the occurrences of BVD and MV from 1990 to date, are reported in detail.

The efficacies of the official control and eradication measures and of the voluntary control programmes are analyzed further with a heuristic formulation for the infection reproduction number (R), i.e. the number of secondary cases produced by one infective animal. The influence of the measures is resolved into 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 official measures complemented by voluntary actions for control and eradication have for the most part been adequate. In the case of BVD the decisive measures for final 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 monitoring for both overseeing the situation with BVD and MV, and maintaining an IBR and EBL-free status is emphasized.

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Last updated 09.06.2006

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