Comparable sensitivity and specificity in three commercially available ELISAs to differentiate between cattle infected with or vaccinated against foot-and-mouth disease virus

Three commercially available ELISAs for the detection of antibodies to the non-structural proteins of foot-and-mouth disease virus (FMDV) were evaluated, using sera from uninfected, vaccinated, infected, inoculated, first vaccinated and subsequently infected, and first vaccinated and subsequently inoculated cattle. We compared antibody kinetics to non-structural proteins, sensitivity, and specificity. One of the ELISAs had a higher sensitivity and much lower specificity than the other two, therefore we established standardised cutoff values for the compared assays using receiver operated characteristic (ROC) curves. Using the standardised cutoff values, all three ELISAs produced comparable results with respect to sensitivity and specificity. Antibody development to non-structural proteins after infection and after vaccination/infection was not significantly different. Development of antibodies, however, both neutralising and directed to non-structural proteins, was significantly delayed after intranasal inoculation as compared to intradermolingual infection. Based on results of sera obtained after vaccination and experimental infection all three assays can be used for testing sera collected between 4 weeks and 6 months after infection. More information is needed on the prevalence of positive reactors in a situation where emergency vaccination has been used and FMD transmission was still observed.     

No foot-and-mouth disease virus transmission between individually housed calves

The foot-and-mouth disease outbreak in The Netherlands in 2001 most likely started on a mixed veal-calf/dairy-goat farm. The outbreak among the 74 calves on this farm appeared to be limited to four animals, and no clinical signs of FMD were reported. Also on a second veal-calf farm minor clinical signs and limited virus transmission were observed. Since FMD is known to be a very contagious disease, and can cause severe lesions, these observations were disputed. Therefore, we carried out two experiments to determine whether the Dutch FMD virus isolate from 2001 does spread among individually housed calves with limited contacts, either indirect (experiment 1) or direct (experiment 2). In experiment 1, four pairs of calves were housed in an individual box at 1m distance from each other. In experiment 2, two groups of three calves were housed in individual boxes, directly bordering each other. We infected one animal per pair in experiment 1, and the calf in the middle in experiment 2. We recorded clinical signs, virus shedding in saliva and the development of antibodies. In addition, we determined whether the virus was transmitted from the inoculated calves to the neighbour(s). All inoculated calves showed mild signs of FMD--fever, and some vesicles on hooves and/or in the mouth--but only one calf showed signs that were visible without physical examination. All inoculated calves shed virus in the saliva and developed neutralising antibodies. None of the contact animals seroconverted, indicating that virus transmission did not occur. These experiments showed that no virus transmission among individual housed calves can occur. This finding supports the hypothesis of the route of virus introduction to The Netherlands in 2001 and show that the observations on the two veal-calf farms were not impossible.     

Target species identity is more important than neighbor species identity

This study investigates how the ability to overtop other saplings and the ability to capture most of the incident light together determine interspecific competition in young and dense self-thinning stands. To this end we measured crown positions and stratification, and quantified the effect of total foliage mass and foliage mass density of neighboring trees on the relative crown depth (RCD) of target trees. Field measurements were done on naturally established saplings in two large forest gaps of different age (5- and 15-year-old) in The Netherlands, and consisting of four species differing in shade tolerance.     

Conversion rates of aldicarb and its oxidation products in soils. II. Aldicarb sulphoxide

The loss of aldicarb sulphoxide was studied in incubation experiments with soil from four plough layers and two deeper layers. The loss during the 111 days of the experiment could be described by first-order kinetics. The half-lives at 15°C ranged from 20 days in a clay loam to 46 days in a peaty sand. The loss of sulphoxide in deeper layers was considerably slower than in the corresponding top layers of a soil profile. In soil from a silty layer at 70–90 cm depth the half-life was about 53 days. In soil from a sand layer at 90–110 cm depth a loss of only about 15% was measured after 111 days of incubation. First-order rate constants for sulphoxide conversion in a clay loam at 6, 15 and 25°C were found to be 0.009, 0.033, and 0.05 day^?1 respectively; in a greenhouse soil these rate constants were 0.0052, 0.019 and 0.04 day^?1 respectively. The fractions of aldicarb sulphoxide that were oxidised to sulphone at 15°C in soil from plough layers were computed to range from 0.52 to 0.76.     

The fungicide-resistance problem

Mutation to resistance is more likely to occur to systemic fungicides than to conventional fungicides. The possibilities to obtain systemic fungicides, to which fungi will not readily become resistant, are discussed. A high potential for development of fungicide resistance does, however, not always imply that problems will arise in practice. If fungicide resistance is accompanied with reduced pathogenicity and fitness, the build-up of a resistant population will be hampered or prevented. Of importance are also the type of disease and the selection pressure exerted by the fungicide. The latter may be influenced by the management of fungicide application.     

Sensitivity to inhibitors of sterol biosynthesis in isolates of Venturia inaequalis from Italian and Dutch orchards

Samenvatting Een geringe, maar significante reductie in gevoeligheid vanVenturia inaequalis voor fungiciden die tot de sterol-biosyntheseremmers behoren werd vastgesteld bij isolaten uit proefboomgaar den in Italië, die gedurende enkele jaren met deze middelen behandeld waren. Bij isolaten uit enkele commerciële boomgaarden in Nederland werd nog geen significante verschuiving in gevoeligheid waargenomen.