The aim of this analysis was to characterise the temporal pattern of infection during the 1997/98 classical swine fever (CSF) epidemic in The Netherlands and hence identify and quantify risk factors for infection in different enterprise types and areas. Survival analysis and Cox proportional hazards regression were used to describe the epidemic. Substantial differences in temporal survival patterns (herd breakdown rate) were found between areas where different control policies operated. Factors with a significant influence on the infection hazard of individual herds included: sow numbers as a percentage of total sows and fatteners (HR = 3.38 for mixed herds (0.1–60% sows) vs. fattening herds (0% sows) and HR = 2.74 for breeding herds (60–100% sows) vs. fattening herds), the number of ‘transport contacts per month’ (>0.3 vs. <0.3; HR = 4.11), pig density (pigs/km2) in the area (HR1000 pigs 1.48) and herd size (HR100 pigs = 1.01).
Pre-emptive slaughter in an area appeared to be associated with lower subsequent disease levels. Higher frequency of transport contacts for welfare slaughter during the epidemic, however, well regulated and controlled, was associated with a substantially higher risk of becoming infected. The positive association of a higher pig density with CSF indicates the potential importance of local spread as a factor in disease transmission and emphasizes that dilution of the pig population can contribute to reduction in CSF occurrence. This analysis suggests however, that if pre-emptive slaughter can promptly be applied effectively in an area after initial diagnosis, pig density is then not a significant factor. Mixed and breeding herds had a higher probability of becoming infected than fattening herds, possibly due to different types and frequencies of inter-herd contacts. These contacts continue to some extent during the epidemic, despite the standstill of animal movements. 相似文献
Summary Increasing numbers of human and animal diseases have been shown to be disseminated by micro-organisms in aerial suspension.
The viability of such airborne organisms declines progressively as the result of physical and other factors which are summarized
in the text. Relative humidity strongly influenced viability in experimental studies, but strain differences also appear to
play an important role in certain diseases.
Laboratory results were confirmed by observations made in the field on poliomyelitis, smallpox, foot and mouth disease, rinderpest
and Newcastle disease; it is probable that Marek's disease, avian infectious bronchitis and numerous other maladies spread
in the same manner.
Long range dissemination by airstreams may be influenced, to some extent, by the virulence of the causal agent and by the
fall-out rate for particles of a size which is optimal for deposition at the predilection site of the specific organism. Furthermore,
local geographical and climatic factors may greatly modify distributional patterns of airborne disease during major epidemics
or epizootics: specific outbreaks are cited as examples.
Sumario Se ha demostrado que un número criente de enfermedades tanto en el hombre como en los animales son diseminadas por micro-organismos
que se encuentran en suspension en el aire. La viabilidad de tales micro-organismos en el aire declina en forma progresiva
como resultado de factores fisicos y otros factores sumarizados en el texto. La humedad relativa influencia de manera especial
la viabilidad en estudios experimentales, pero las diferencias entre las cepas tambien parece jugar un importante rol en algunas
enfermedades.
Resultados de laboratorio fueron confirmados por observaciones hechas en el campo sobre poliomielitis, viruela, fiebre aftosa,
peste bovina y enfermedad de Newcastle; Es probable que la enfermedad de Marek. la bronquitis infecciosa aviar y otras numerosas
enfermedades seandiseminadas de la misma manera.
La diseminación a grandes distancias por corrientes de aire puede ser influenciada, hasta cierto punto, por la virulencia
del agente causal y por la tasa de acentamiento para particulas de un tama?o, las cuales son óptimas para su acentamiento
en el lugar de predilección del organismo específico. Mas aun, factores locales geográficos y climáticos pueden modificar
grandemente los patrones de distribución de enfermedades diseminadas por el aire durante grandes epidemias ó epizootias: Se
citan como ejemplos brotes específicos.
Résumé Il a été démontré qu'un nombre croissant de maladies humaine et animale sont dísséminées par des microorganismes en suspension
dans l'atmosphère. La viabilité de tels agents pathogènes décroit progressivement en fonction de l'influence des facteurs
physiques et autres qui sont énumérés dans ce texte. L'humidité relative influence fortement cette possibilité de survie comme
l'ont montré des études expérimentales, mais des différences de souches semblent aussi jouer un r?le important pour certaines
maladies.
Les résultats expérimentaux ont été confirmés par des observations faites sur le terrain à propos de la poliomyélite, la variole,
la fièvre aphteuse, la peste bovine et la maladie de Newcastle; il est probable que la maladie de Marek, la bronchite infectieuse
aviaire et de nombreuses autres infections se répandent de la même manière.
La dissémination à longue distance par les courants aériens peut être influencée, dans une certaine mesure, par la virulence
de l'agent causal et par le pourcentage de particules dont la taille est optimale pour leur arrivée au site d'élection du
microorganisme spécifique. En outre, des facteurs géographique et climatique locaux peuvent grandement modifier le schéma
épidémiologique des maladies disséminées par voie aérienne; des foyers spécifiques sont cités en example.
Based on a paper presented at a Meeting of the Central Canada Veterinary Association on 9th December 1970. 相似文献
Bluetongue (BT) virus serotype 2 (BTV 2) was first confirmed in Tunisia in February 2000 and has since spread northward and westward, infecting several other countries and islands, including Corsica, where clinical disease was reported in October 2000. BT was again reported on the Island in July 2001, some six months after a vaccination campaign against BTV 2. The molecular relationship between isolates of the BTV 2 Corsican wild-type viruses from 2000 and 2001, and the attenuated BTV 2 vaccine were determined by comparing corresponding sequences of genome segments 2, 7 and 10 with each other and with already published sequences available in the genome database. Complete genetic stability was observed between the isolates of the Corsican BTV 2. There was some divergence between the nucleotide sequences of segment 10 obtained from the wild-type and vaccine virus strains. Based on these differences, primers were selected that could be used in RT-PCR to differentiate between the wild-type and the vaccine viruses. 相似文献