Comparison of genome segments 2, 7 and 10 of bluetongue viruses serotype 2 for differentiation between field isolates and the vaccine strain

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.     

Monitoring of atrazine treatment on soil bacterial,fungal and atrazine-degrading communities by quantitative competitive PCR

We report the development of quantitative competitive (QC) PCR assays for quantifying the 16S, 18S ribosomal and atzC genes in nucleic acids directly extracted from soil. QC-PCR assays were standardised, calibrated and evaluated with an experimental study aiming to evaluate the impact of atrazine application on soil microflora. Comparison of QC-PCR 16S and 18S results with those of soil microbial biomass showed that, following atrazine application, the microbial biomass was not affected and that the amount of 16S rDNA gene representing 'bacteria' increased transitorily, while the amount of 18S rDNA gene representing fungi decreased in soil. In addition, comparison of atzC QC-PCR results with those of atrazine mineralisation revealed that, in response to atrazine treatment, the amount of atzC gene increased transitorily in soil pre-treated with atrazine, suggesting that accelerated atrazine biodegradation in soil could be due to a transient increase in the size of the atrazine mineralising community.     

Epidemiology and control of an outbreak of classical swine fever in wild boar in Switzerland

An outbreak of classical swine fever in wild boar in the southern part of Switzerland (Canton of Ticino) was investigated after the implementation of control measures in a defined infected area (the risk zone), and in a surrounding surveillance zone (the non-risk zone). After the disease had been detected, hunting was not allowed in the risk zone for over six months, during which the disease was left to run its course, but hunting was continued in the non-risk zone for one month. After seven months, a hunting strategy targeted at young animals was implemented in both zones. Between May 1998 and January 2000,1294 wild boar were shot or found dead, and diagnostic and biological data were collected and analysed. Only one animal from the non-risk zone was found to be seropositive for antibodies to the virus, whereas 179 of 528 wild boar from the risk zone were virus positive and 162 were seropositive. The proportion of virus-positive animals decreased from 62.7 per cent to zero over one year. During the first hunting season, seropositive animals were found in all age groups, but 12 months later only animals more than one year old had antibodies against the virus.     

Incidence of reinfections with Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae in pig farms located in respiratory-disease-free regions of Switzerland--identification and quantification of risk factors

The objective of the study was to identify risk factors for reintroduction of Actinobacillus pleuopneumoniae and Mycoplasma hyopneumoniae (enzootic pneumonia) onto pig farms in areas in Switzerland that were involved in an eradication programme from 1996 to 1999 and to assess the role of dealers in relation to these reinfections. The study was based on the comparison of pig farms that were reinfected in the year 2000 (cases) and pig farms that remained uninfected in the same area (controls). Additionally, data were collected from Swiss pig dealers and transport companies. Out of a total of 3983 farms, 107 farms were reinfected in the year 2000. The incidences were 0.1% for Actinobacillus pleuopneumoniae and 2.6% for Mycoplasma hyopneumoniae (enzootic pneumonia). Compared to reinfection rates prior to the eradication programme, this is a considerable reduction. Statistically significant risk factors for the reinfection were 'finishing farm', 'large mixed breeding-finishing farm', 'reinfected neighbour' and 'parking site for pig transport vehicles close to the farm'. Pig farmers that purchased pigs from only one supplier per batch had a lower risk of reintroducing infection (protective factor). As long as infected and uninfected regions co-exist in Switzerland, direct and indirect contact between farms, pig herds and slaughter sites via transport vehicles are a major pathway of disease spread. Risk management measures linked to these contacts are therefore of key importance. The survey of dealers indicated various areas for improvement such as strategic planning of pick-up routes or cleaning and disinfecting of trucks.     

Tick salivary gland extract-activated transmission of Borrelia afzelii spirochaetes

Saliva-activated transmission of Borrelia afzelii Canica, Nato, du Merle, Mazie, Baranton et Postic, 1993 was demonstrated using salivary gland extract (SGE) from Ixodes ricinus (L., 1758) ticks and C3H mice. Injection of Borrelia spirochaetes together with SGE increased the level of bacteraemia and accelerated the appearance of bacteria in the urinary bladder, compared with the injection of spirochaetes alone. More I. ricinus nymphs became infected when feeding on mice inoculated with B. afzelii plus SGE. Analysis of cytokines produced by cells of draining lymph nodes from SGE-treated mice showed a suppression of proinflammatory cytokines IFN-gamma, IL-6 and GM-CSF following a transient upregulation in comparison with the control mice infected without SGE.     

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.