Ecology of the free-living stages of 'Haemonchus contortus' in a cool temperate environment

Current understanding of the ecology of 'Haemonchus contortus' is incomplete and seen as an impediment to effective control of the worm in summer rainfall regions, where outbreaks are common and can result in significant stock mortality. Although there has been a wealth of published research on the effects of temperature on free-living development of 'H. contortus', our level of understanding of how moisture in the micro- and macro-environments influences development to infective larvae on herbage is considerably lower. The current state of knowledge of the free-living ecology of 'H. contortus' is reviewed in Chapter 2, with a particular focus on research findings since the 1970s. Knowledge gaps are highlighted, and a proposal made for a framework on which future investigations of 'H. contortus' can be based in order to improve prediction of free-living development. The key hypotheses under investigation in the experimental studies concerned the quantitative effects of moisture on free-living development of 'H. contortus', and are summarised in Chapter 1 and in further detail in each of the experimental chapters (Chapter 4-6). Plot experiments were conducted in the Northern Tablelands of NSW, where 'H. contortus' is the most important parasite of sheep. Subsequent laboratory experiments, designed in order to extend and explain the findings of the plot experiments, were conducted in programmable incubators in which temperature was regulated to mimic conditions typical to the Northern Tablelands summer. All experiments focused on testing the effects of a range of rainfall and moisture-related variables on 'H. contortus' development from egg through to infective larvae

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Interaction between the effects of evaporation rate and amount of simulated rainfall on development of the free-living stages of 'Haemonchus contortus'

A factorial experiment (3 x 4 x 2 x 3) was conducted in programmable incubators to investigate interaction between the effects of rainfall amount, rainfall distribution and evaporation rate on development of 'Haemonchus contortus' to L3. Sheep faeces containing H. 'contortus' eggs were incubated on sterilised soil under variable temperatures typical of summer in the Northern Tablelands of NSW, Australia. Simulated rainfall was applied in 1 of 3 amounts (12, 24 or 32 mm) and 4 distributions (a single event on the day after deposition, or the same total amount split in 2, 3 or 4 equal events over 2, 3 or 4 days, respectively). Samples were incubated at either a Low or High rate of evaporation (Low: 2.1–3.4 mm/day and High: 3.8–6.1 mm/day), and faeces and soil were destructively sampled at 4, 7 and 14 days post-deposition. Recovery of L3 from the soil (extra-pellet L3) increased over time (up to 0.52% at day 14) and with each increment of rainfall (12 mm

Ecology of the free-living stages of major trichostrongylid parasites of sheep

Significant developments over recent decades make it timely to review the ecology of the major gastrointestinal nematode (GIN) species of sheep. These include the relentless development and spread of anthelmintic resistance in all of the major sheep production regions of the world, and the consequent drive towards integrated parasite management (IPM) systems incorporating non-chemotherapeutic strategies such as grazing management. The success of such programs is dependent on a detailed understanding of the environmental influences on the free-living stages of the nematode life cycle. Major reviews of the subject were conducted prior to 1980, however considerable work has been completed since, including the development of mathematical models describing the epidemiology of GIN infection. Knowledge of the temperature thresholds for free-living development has also improved, while investigations of moisture influences and interactions with temperature have allowed more effective exploitation of environmental effects for IPM. This review re-evaluates our understanding of the factors that determine the success or failure of the free-living phases of the life cycle in light of these developments. Temperature and moisture are the dominant influences on the free-living stages of 'Haemonchus contortus', 'Teladorsagia circumcincta' and 'Trichostrongylus colubriformis', with the effects of pasture conditions playing a significant modulating role. Early in the free-living phase, the developmental success of the three GIN species is limited by susceptibility to cold temperatures. In general, 'H. contortus' is most susceptible, followed by 'T. colubriformis' and then 'T. circumcincta'. The length of the development cycle is dependent largely on temperature, with development rate increasing at warmer temperatures. However, in order for development to proceed to the infective larval stage, addition of moisture is generally required. There has been considerably less work quantifying the effects of moisture on free-living development, although it is clear that H. contortus is most susceptible to desiccation during the pre-infective stages. Once the infective stage is reached, the influences of temperature and moisture on survival are less important, resulting in considerable survival times under conditions lethal to pre-infective stages. However, hot, dry conditions can be lethal for infective larvae of all three species, while extreme cold is also lethal with significant species variation. While the existing body of knowledge is substantial, the interpretation of many studies and comparison between them is complicated by inadequate description of, or variation in, the environmental measurements used. Confounding the effects of environmental variables on development to infective stage is the migration of larvae from the faeces and subsequent survival on pasture. There is a need to build on recent efforts to explore interaction between the effects of temperature and moisture, and also the trend to more closely simulate field conditions in laboratory studies. We propose a logical framework for future ecological investigations to overcome some of these problems, facilitate the development of a more integrated dataset on the subject and improve prediction of free-living development

Moisture requirements for the free-living development of 'Haemonchus contortus': Quantitative and temporal effects under conditions of low evaporation

The key influence of moisture availability on development of the free-living stages of 'Haemonchus contortus' is well-documented, although quantitative relationships between moisture variables and development are poorly defined. A factorial experiment (3 x 2 x 2) was conducted in programmable incubators to determine the effects of amount and distribution of simulated rainfall on 'H. contortus' development at low evaporation rates (approximately 2mm/day) under temperatures typical of summers on the Northern Tablelands of NSW, Australia. Sheep faeces containing 'H. contortus' eggs were placed in experimental units containing sterile soil and had one of the three amounts (12, 24 and 32 mm) of simulated rainfall applied, in either a single event on the day after deposition (d 1) or three split events over 6 days (d 1, 3 and 6). Treatments were applied either in week 1 only, or in weeks 1 and 2. Recovery of infective larvae (L3) at 4, 7 and 14 days post-contamination increased with each incremental amount of simulated rainfall over the range of 12-32 mm and was significantly higher under the single 'rain' event (2.8%), compared with the three smaller, split events (1.9%). The second application of simulated rainfall in week 2 had only a very small influence on L3 recovery, suggesting that the majority of development to L3 occurred in response to simulated rainfall events in the first 7 days. Both faecal moisture content and the cumulative ratio of precipitation and evaporation (P/E) were strongly and positively correlated with recovery of L3. Recovery of L3 from treatments, which received simulated rainfall in week 1 only was best described by P/E at d 5. Whether the relationships observed in this study hold under field conditions, where macroclimactic conditions such as evaporation rate are substantially more limiting to free-living development, is yet to be determined

The effects of amount, timing and distribution of simulated rainfall on the development of 'Haemonchus contortus' to the infective larval stage

Three studies were undertaken to determine the effects of amount, timing and distribution of simulated rainfall on the developmental success of ‘Haemonchus contortus’. Faeces containing ‘H. contortus’ eggs were deposited onto pasture plots under a rainfall-activated retractable roof which eliminated incident rainfall. In October (spring) 2004 and January (summer) 2005, the effects of amount (6, 12, 18 or 24 mm) and timing (1, 4, 8 or 15 days post-faecal deposition) of a single simulated rainfall event was investigated via manual application of water to plots. More ‘H. contortus’ pre-infective larvae (L1 and L2) developed under the d 1 simulated rainfall treatment than later treatments. There was no effect of rainfall amount on development in either experiment, and negligible development to infective larvae (L3). In February (summer) 2006, the effects of amount (12, 24 or 32 mm) and distribution (single event or three smaller but equal split events over 32 h) of simulated rainfall events was investigated with water applied via sprinkler. In this experiment L3 were recovered from the herbage in one-third of the plots harvested, however recovery was low (0.08% of eggs deposited) and there were no treatment effects. Recovery of L1 and L2 from faeces increased with simulated rainfall amount at d 4, and more L1 and L2 were recovered from the split distribution treatment at d 4. The results indicate that moisture conditions soon after faecal deposition are key determinants of ‘H. contortus’ development success, with significant penalties on development when simulated rainfall was applied 7 days or more post-deposition, and when the duration of simulated rainfall was short. High rates of evaporation during both summer experiments resulted in rapid drying of the micro-environment and this appears to have limited development to L3

Trapping efficacy of 'Duddingtonia flagrans' against 'Haemonchus contortus' at temperatures existing at lambing in Australia

The aim of this study was to determine the trapping efficacy of 'Duddingtonia flagrans' against 'Haemonchus contortus' at the temperature ranges experienced around lambing in the major sheep producing regions of Australia. Faeces were collected from Merino wethers, maintained in an animal house and which had received either D. 'flagrans chlamydospores' for a 6-day period (DF) or not (NIL). Faeces were incubated at one of four daily temperature regimens which were composed of hourly steps to provide 6–19 °C, 9–25 °C, 14–34 °C and 14–39 °C to mimic normal diurnal air temperature variation. Enumeration of the number of preinfective and infective larvae that had migrated from or remained in faecal pellets was used to calculate percentage recovery and trapping efficacy of 'D. flagrans'. Recovery of 'H. contortus' larvae of both stages was significantly lower in DF faeces but the magnitude of the effect was considerably greater for infective larvae. Mean recovery of infective larvae from NIL and DF faeces was 10.6 and 0.4%, respectively, indicating a mean trapping efficacy of 96.4%. The lowest trapping efficacy (80.7%) was observed at 6–19 °C but total recovery of infective larvae, from DF faeces, was greatest at the two highest temperature regimens, although still less than 0.9%. The results of this study indicate that typical Australian lambing temperatures should not be a barrier to the use of 'D. flagrans' as an effective biocontrol of 'H. contortus' in Australia