Within-farm spread of classical swine fever virus--a blueprint for a stochastic simulation model

A stochastic simulation model to investigate the transmission of classical swine fever (CSF) virus within an infected farm is described. The model is structured according to the processes that occur within and between management groups (pig units or houses). It uses the individual pig as the unit of interest and estimates the number of animals in the states 'susceptible', 'infected', 'infectious', and 'removed' for each day of the disease incident. Probabilities are assigned to the transitions between states. The probability of a pig becoming infected is made dependent on the probability of contact between a susceptible and an infectious pig as well as the probability of transmission. The more pigs become infected in one unit, the more likely is subsequent spread to another management group on the farm. Ultimately, the probability that a shipment of pigs from the farm will include at least one infected pig can be estimated in order to identify high-risk movements during a CSF epidemic. The model results were compared with experimental data on CSF transmission within one pig unit (management group). It could be shown that the model was capable of reproducing the experimentally observed infection and mortality rates. To improve the input parameters and for further model validation, more experimental data and field data from CSF outbreaks are needed.     

Identification of pathogenic Leptospira strains in tissues of a premature foal by use of polymerase chain reaction analysis.

Studies were carried out to determine the cause of death in a prematurely born Thoroughbred foal that died 24 hours after birth. Necropsy revealed gross lesions suggestive of septicemia. A commercial Leptospira polymerase chain reaction (PCR) assay designed to specifically amplify the hemolysis-associated protein 1 (hap1) gene present only in pathogenic Leptospira strains detected the presence of Leptospira DNA in various tissues of the foal. Histologic examination of lung, liver, kidney, and myocardium revealed numerous spirochetes in Warthin-Starry-stained tissue sections. Results of PCR analysis and histologic examination suggested a leptospiral infection in the newborn foal. At the moment of death, the infection coexisted with a streptococcal-associated aspiration bronchopneumonia and postpartum septicemia. These findings indicate that the PCR assay based on the amplification of the hap1 gene represents a useful tool for specific detection of pathogenic leptospira in field samples taken from horses.     

Die chemischen Pflanzenschutzmittel

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Handbuch der Pflanzenkrankheiten

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