Foot and mouth disease virus transmission during the incubation period of the disease in piglets, lambs, calves, and dairy cows

Transmission of foot and mouth disease (FMD) virus by infected animals may already occur before clinical signs are evident. Quantitative data for FMD transmission rates during this so-called high-risk period are currently lacking and would provide useful information to develop surveillance systems in which the number of new outbreaks is an outcome variable. In order to address this, we used experimental data to quantify transmission in cattle, swine and sheep during the non-clinical phase of the disease. Groups consisted of vaccinated or non-vaccinated animals of one species; half of each group was inoculated with FMDV, the other half was contact-exposed. We estimated the reproduction ratio R(nonclin) using a mathematical SIR model. R(nonclin) was defined as the average number of secondary infections caused by one infectious individual in its non-clinical phase. Animals not showing clinical signs shed lower amounts of virus than clinically affected ones. Therefore, we estimated transmission proportionally to the virus excretion. Low estimates for R(nonclin) in groups with non-vaccinated and vaccinated calves; 0.30 [0.03; 3.43] and 1.03x10(-8) [0; infinity] respectively and 0.21 [0.02; 2.48] for the non-vaccinated and 0.16 [0.009; 2.96] for the vaccinated lambs, were observed. These results indicate that only few secondary infections are to be expected from infected calves and lambs when they are not clinically affected. In groups of non-vaccinated piglets estimates were R(nonclin)=13.20 [4.08; 42.68], and in vaccinated piglets R(nonclin)=1.26 [0.18; 8.96]. The estimate for R(nonclin) for non-vaccinated dairy cows was R(nonclin)=176.65 [80.38; 388.24], whereas R(nonclin) in the vaccinated groups could not be estimated. Our findings suggest that a large number of individuals might have been infected before clinical signs are noticed, especially in non-vaccinated swine and dairy herds. These findings suggest that after clinical recognition of FMD, priority should be given to trace back contacts with swine and dairy farms, as they may already have been infectious in the herd's incubation period.     

Total loss and distribution of nitrogen and phosphorus in the outdoor run of organic laying hens

1. The objective of this study was to determine the level and variation of the total mass, and load of nitrogen (N) and phosphorus (P) excreted into the outdoor run of organic egg production systems.

2. Three egg production farms with an aviary system and an outdoor run were selected for this study. Four measurements, one per season, were executed on each farm.

3. Mean content of N and P of a manure dropping was 14·0?g N?kg^?1 and 3·12?g P?kg^?1, mean mass of a dropping was 6·36?g and mean dry matter content of a dropping was 238?g?kg^?1. Mean rate of excretion in the outdoor run was 2·99 droppings per hen per h. Mean percentage of hens outside during the time the outdoor run could be accessed was lowest on Farm 1 (1·7%), highest on Farm 2 (16·0%), and intermediate on Farm 3 (7·1%).

4. On all farms an exponential decrease of the number of hens and of the load of N and P with increasing distance from the hen house was found. Load of N exceeded the fertilisation standard (of 170?kg?ha^?1?y^?1) in the region at a 0 to 19?m distance from the hen house on Farm 1, 0 to 146?m on Farm 2 and 0 to 52?m on Farm 3.

5. It is concluded that the husbandry system should be redesigned to solve the problem of overloading, unwanted loss of N and P to the environment and loss of N and P from the organic production cycle.     

A decision-tree to optimise control measures during the early stage of a foot-and-mouth disease epidemic

A decision-tree was developed to support decision making on control measures during the first days after the declaration of an outbreak of foot-and-mouth disease (FMD). The objective of the tree was to minimise direct costs and export losses of FMD epidemics under several scenarios based on livestock and herd density in the outbreak region, the possibility of airborne spread, and the time between first infection and first detection. The starting point of the tree was an epidemiological model based on a deterministic susceptible–infectious–recovered approach. The effect of four control strategies on FMD dynamics was modelled. In addition to the standard control strategy of stamping out and culling of high-risk contact herds, strategies involving ring culling within 1 km of an infected herd, ring-vaccination within 1 km of an infected herd, and ring-vaccination within 3 km of an infected herd were assessed. An economic model converted outbreak and control effects of farming and processing operations into estimates of direct costs and export losses. Ring-vaccination is the economically optimal control strategy for densely populated livestock areas whereas ring culling is the economically optimal control strategy for sparsely populated livestock areas.     

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.     

A meta-analysis quantifying transmission parameters of FMDV strain O Taiwan among non-vaccinated and vaccinated pigs

Our aim was to provide additional estimates of main parameters for the transmission of foot-and-mouth disease virus (FMDV) strain O Taiwan (3/97). We used the data of previous experiments in non-vaccinated and vaccinated pigs and combined the data of experiments with the same treatment(s). First, we quantified the reproduction ratio R for the various groups using a final-size method. Our final-size results predicted that vaccination with a four-fold vaccine dose (but not with a single dose) at 1 week before inoculation (-7 dpi) would reduce R compared to the non-vaccinated group. Secondly, we used the daily results of virus excretion to quantify the transmission rate beta (by using generalized linear modelling), and the infectious period T (by using survival analysis). We used the estimates of beta and T to estimate R more precisely as compared to the final-size method and also for the groups for which a finite estimate could not be obtained using a final-size method. Our modelling results predicted that beta for non-vaccinated, for single-dose and four-fold-dose groups would be 6.1 (3.7, 10)day(-1), 2.0 (1.0, 4.0)day(-1) and 0.4 (0.1, 1.4)day(-1), T at 6.5 (5.7, 7.3), 5.3 (4.7, 6.0) and 2.3 (0.9, 5.7) days and R at 40 (21, 74), 11 (4.9, 24) and 1.0 (0.1, 7.8), respectively. These results predicted that both vaccination with a four-fold vaccine dose and with a single dose at -7 dpi would reduce beta, T and R significantly as compared to the non-vaccinated pigs, thereby showing that vaccination will reduce transmission of FMDV significantly already 1 week post vaccination.     

Prevalence of the causes of fleece derangement among sheep flocks in New South Wales

SUMMARY An investigation of sheep flocks with unknown histories of fleece derangement, selected at random from the main sheep raising areas of New South Wales, showed that Psorergates ovis was present in 53 of the 177 flocks surveyed and In 162 of the 3495 sheep examined. Of the single causes of fleece derangement, the most prevalent was grass seed contamination (15.7%) followed by Infestation with sheep body lice, Bovicola ovis, (14.7%) and Infestation with Itch mite (7.8%). The prevalence of fleece derangement was significantly higher on sheep In which lice were the only ectoparasites found than on those In which Itch mites were the only ectoparasites present. The greatest prevalence of P ovis was In flocks In the Young, Yass, Mudgee and Tenterfield districts. In most affected flocks, more than one potential cause of fleece derangement was present. Itch mite Infestation was more prevalent in flocks that received no treatment for ectoparasites than in those that had been treated in the year preceding the survey. Our results did not support a commonly held belief among farmers that arsenical compounds control Infestations of Itch mites more effectively than other types of pesticides. There was no significant difference in prevalence of fleece derangement between flocks treated with different pesticide groups and those that received no treatment, but mean fleece derangement score was significantly lower in sheep treated with organophosphates than in untreated sheep. Infestations of lice were significantly more prevalent in sheep from flocks treated with synthetic pyrethroids than from those treated with organophosphates or those that received no treatment.     

In vitro Effect of Zearalenone and α-Zearalenol on Boar Sperm Characteristics and Acrosome Reaction

This study was conducted to determine the in vitro effects of three different concentrations (125, 187.5 and 250 microM in diluted semen) of zearalenone (zen) and alpha-zearalenol (alpha-zen) on boar sperm. Semen parameters such as motility, viability and spontaneous acrosome reaction were evaluated. From the results it was shown that both zen and alpha-zen affected the sperm characteristics significantly (p < 0.05), except for alpha-zen at the low concentration which did not decrease the percentage of live reacted spermatozoa significantly. In conclusion, zen and alpha-zen are directly toxic when they affect boar semen in vitro and consequently decrease the fertilization ability of the sperm. The higher the concentration of mycotoxin tested, the greater the decline of sperm parameters noticed. The influence of mycotoxins was found to be time- and dose-dependent.