A framework for evaluation of on-farm mastitis diagnostics in Australia

Numerous culture-based diagnostics are available on the Australian and international markets for on-farm detection of bacterial pathogens in milk. Use of such diagnostics may provide an opportunity to improve the prudent use of antimicrobials in udder health management. Farms are low-resource settings in terms of diagnostic microbiology capacity. The World Health Organisation has identified criteria for the evaluation of diagnostic tests in low resource settings based on Accuracy, Sensitivity, Specificity, User-friendliness, being Rapid or Robust, Equipment-free and being Deliverable (ASSURED). Here, we review how those criteria can be interpreted in the context of microbiological diagnosis of mastitis pathogens, and how on-farm diagnostics that are currently available in Australia perform relative to ASSURED criteria. This evaluation identifies multiple trade-offs, both with regard to scientific criteria and with regards to convenience criteria. More importantly, the purpose of testing may differ between farms, and test performance should be evaluated relative to its intended use. The ability of on-farm mastitis diagnostics to inform mastitis treatment decision-making in a timely and cost-effective manner depends not just on test characteristics but also on farm-specific pathogen prevalence, and on the farm enterprise's priorities and the farm manager's potential courses of action. With most assay evaluations to date conducted in professional laboratories, there is a surprising dearth of information on how well any of the diagnostic tests perform on-farm and, indeed, of the on-farm decision-making processes that they aim to inform.     

Grassland songbird occurrence on remnant prairie patches is primarily determined by landscape characteristics

Context

North American grassland songbird populations have declined significantly due to habitat loss and fragmentation. Understanding the influence of the surrounding landscape on prairie fragment occupancy is vital for predicting the fate of grassland birds in these heavily altered landscapes.

Objectives

We examined the relative importance of local and landscape variables on grassland bird occupancy of prairie fragments using a focal-patch study. We also investigated the spatial scale at which landscape variables were most influential.

Methods

We surveyed birds on 29 unplowed prairie fragments in western Minnesota and eastern North and South Dakota. We quantified local habitat on the fragment using vegetation surveys and aerial photographs and the landscape surrounding the fragment out to 4 km using aerial photographs. We analyzed occupancy using multi-model approaches applied to multiple logistic regression.

Results

Of 38 species encountered, nine were neither too rare nor too abundant to be analyzed. Predictors of patch occupancy were unique for each bird species, yet general patterns emerged. For eight species, landscape variables were more important than local variables. Mostly, those landscape variables measured configuration (e.g., edge density) and not composition (e.g., percent cover of a particular matrix element). Landscape effects were mostly from variables measured at the greatest extents from the prairie fragment.

Conclusions

Using a focal-patch study design we demonstrated the importance of the surrounding landscape, often out to 4 km from the fragment edge, on prairie occupancy by grassland birds. Effective management of grassland songbirds will require attention to the landscape context of prairie fragments.

     

Testing a model to track fish migrations in polar regions using pop‐up satellite archival tags

The use of pop‐up archival satellite tags (PSATs) to geolocate marine fishes in polar regions is challenging due to the brevity of periods during which there is a defined sunrise and sunset. Models using other environmental parameters are thus required to supplement geolocation data in the estimation of marine migratory routes. The objective of this work was to create a simple method that would estimate the migratory pathways of Atlantic salmon (Salmo salar) in polar regions using temperature and depth recordings. Validated geolocations from PSATs were used to test and constrict the model. The model’s predicted migratory routes were within 100 km of the light‐based geolocations calculated by the tags. By constraining the trajectories through the geolocations, bias was reduced. Sensitivity analyses demonstrated that slight alterations of the location and timing of the start and end points did not affect the mean migratory route estimates. This method is a management tool that can determine the primary habitat areas for any surface‐ or bottom‐dwelling marine species – especially in polar regions, where other methods may be impossible.     

Epizootics in farm-raised channel catfish, Ictalurus punctatus (Rafinesque), caused by the enteric redmouth bacterium Yersinia ruckeri

In the winters of 1995 and 1996, unusual disease outbreaks occurred on two separate channel catfish farms in Arkansas, USA. Affected fish exhibited extraordinary haemorrhaged rings around the eyes and raised haemorrhaged areas overlying the frontal foramens. Other signs included abnormal swimming, lethargy, loss of equilibrium, and exophthalmia. Bacterial isolates from the moribund fish were identified as Yersinia ruckeri by biochemical tests, no lysis by the Hafnia-specific bacteriophage 1672, and Y. ruckeri-specific growth patterns on Shotts-Waltman media. Fingerling catfish injected intraperitoneally with the bacterial isolate at 7.8 × 10⁶ bacteria fish^?1 developed lesions characteristic of the epizootics at 13, 18, and 22 °C and a biochemically identical isolate was recovered. Fingerling rainbow trout injected with the channel catfish isolate at 1 × 10⁵ bacteria fish^?1 and held at 20 °C developed signs typical of enteric redmouth by 4 days post-inoculation and were moribund by 5 days post-inoculation. Some differences of clinical signs occurred between experimentally infected rainbow trout and channel catfish. Clinical and biochemical similarities between infections of Y. ruckeri and many warmwater pathogens in affected catfish may lead to incorrect diagnosis of ERM infections.     

Assessing changes in forest fragmentation following infestation using time series Landsat imagery

The current epidemic of mountain pine beetle (Dendroctonus ponderosae Hopkins) in British Columbia, Canada, has impacted an area of over 13 million hectares presenting a considerable challenge to provincial forest resource managers. Remote sensing technologies offer a highly effective tool to monitor this impact due to very large areas involved and its ability to detect dead and dying tree crowns. Conventionally, change detection procedures based upon spectral values have been applied; however, analysis of landscape pattern changes associated with long-time series change detection approaches present opportunities for the generation of unique and ecologically important information. This study is focussed on the detection and monitoring of the shape and area characteristics of lodgepole pine stands during mountain pine beetle infestation to quantify the progression of forest fragmentation and related loss of landscape connectivity. A set of landscape pattern indices were applied to a set of images consisting of six Landsat satellite images spanning the period from 1993 to 2006. Our results indicate that the impacts of the mountain pine beetle infestation on forest spatial pattern consist of an increase in the number of patches, an increase in forest patch shape complexity, a reduction in forest patch size, an increase in forest patch isolation, and a decrease in interspersion. These findings demonstrate the unique information available from long-time series satellite imagery combined with pattern analysis to better understand the combined effects of insect infestation and forest salvage and harvesting.     

Detection and distribution of toxigenic Pasteurella multocida in pig herds with different degrees of atrophic rhinitis

Four herds of pigs were selected which had different degrees of clinical atrophic rhinitis and used different specific counter-measures. In two of them, the clinical signs occurred spasmodically and were slight. The sows, suckling pigs and growing pigs in all the herds were sampled for toxigenic Pasteurella multocida. In one of the slightly affected herds (herd D), the weaners were moved to a second farm for finishing. No toxigenic P multocida were found at the breeding farm, but 50 per cent of the large growing pigs were positive. It seemed that the organism had entered only at the finishing farm and that the mild clinical signs were due to the infection starting in older pigs than usual. In the second mildly affected herd, 47 per cent of the sows and 42 per cent of the growers were infected. Three toxigenic isolates from this herd produced as severe turbinate damage experimentally in specific-pathogen-free pigs as a stock pathogenic strain. Except in herd D, toxigenic P multocida were found in all the age groups of pigs sampled. However, the pattern of distribution of the organism within the herds was not obviously correlated with the severity of the disease. In a fifth herd there were obvious cases of clinical atrophic rhinitis, with marked turbinate atrophy, from which toxi-genic P multocida were recovered in abundance. Subsequently, the clinical disease disappeared and, despite extensive and repeated sampling, the organism was not found again.     

Sectional notes

American Journal of Potato Research -     

Gastrointestinal transit times in normal and reovirus-inoculated turkeys

Brilliant pigment powder was used to measure minimum gastrointestinal transit times (GTT) in control and cloned-reovirus-inoculated turkey poults. Compared with controls, inoculated poults had longer GTT at 120 hr (P less than 0.05) but not at 24 and 72 hr after receiving a single oral dose of cloned reovirus. Reovirus inoculation was associated with failure to eat following a fasting period. Feces passed by reovirus-inoculated turkeys were more fluid and less well formed than normal.     

Apparent reinfection of enzootic-pneumonia-free pig herds: search for possible causes

In a control scheme for enzootic-pneumonia-free herds, run by the Pig Health Control Association, a detailed study was made of 55 herds that developed enzootic pneumonia without a simple explanation. These herds were compared with 57 herds that were still free from enzootic pneumonia in mid-1984. A high standard of precautions against the risk of infection being transferred by people and fomites seemed to confer no obvious benefit. This observation was in keeping with in vitro studies which showed that, although Mycoplasma hyopneumoniae could survive for a long time in favourable liquid medium, it could not be recovered from material such as cloth, once the culture had become dry. Under field conditions, the organism would probably cease to be infective within 48 hours. The organism survived particularly well in rain water at lower temperatures, however, and transmission via moist cold air seemed a possibility. There was a tendency for breakdowns to start in the autumn and winter, particularly in highly secure units, and several farmers associated colder misty conditions with the arrival of infection. One herd was probably infected by an imported boar and the very close proximity of foreign pigs, such as in slaughterhouse transport, seemed the most likely explanation in 15 other herds. One herd was replaced without this danger being attended to and it soon broke down again, whereas the three herds in this category that have survived after replacement all had this risk eliminated. Data was available on 37 of the 39 remaining herds to compare them with the 57 surviving herds, using a risk index based on the proximity of other pig units.(ABSTRACT TRUNCATED AT 250 WORDS)