The ecology of Haemonchus contortus in a winter rainfall region in Australia: the development of eggs to infective larvae

Ecology of the free-living stages of cattle nematodes in the dry season in the Lerma Valley, Salta province, Argentina

The objective of this work was to describe the dynamics of development and survival of the free-living stages of cattle gastrointestinal nematodes (GIN) in fecal matter (FM) and pasture during the dry season in the Lerma Valley, Salta province, northwestern Argentina (NWA) to contribute to GIN management. The climate in the region is characterized by a rainy summer followed by a dry season from middle autumn to early spring. Fecal matter from calves naturally infected with GIN was deposited on three experimental field plots in April, July and October 2019, corresponding to the beginning, middle and end of the dry season, respectively. Each experimental unit consisted of 7 stools of about 800 g and had four repetitions. To determine the development from egg to infective larvae (L3), the first sampling (5 g fecal matter) was performed from the 10th day post-contamination and continued every 3 days until L3 were found. Subsequently, a monthly sampling was made until two consecutive negative results were obtained. Sampling of pasture began three days after the L3 recovery from FM, and continued monthly until two negative results were obtained. The following parameters were evaluated: development time and development rate from egg to L3; permanence time of L3 in feces; time of appearance on pasture; migration rate; and permanence time of L3 on pasture. The main genera of parasites present were Cooperia and Haemonchus. Significant differences were observed in the development time among contamination months (p < 0.001); development time was highest in the July contamination (28 days), with October and April contamination averaging 9 and 10 days, respectively. Development time also showed significant differences (p < 0.01) among contamination months, being highest in October (31.48%). The highest permanence time in fecal matter values were recorded in the July contamination (183 days) and migration rate was highest in the October contamination (42.49%). The highest time of appearance on pasture value was recorded in the July contamination (117 days). Finally, the highest permanence time of L3 in feces values were detected in the October contamination (148 days). The results of this work show that fecal contamination in the NWA region in the dry season would play an epidemiological role in the GIN cycle as a source of infection for the next productive cycle in the rainy season.

Influence of environmental factors on the detection of blood in sheep faeces using visible-near-infrared spectroscopy as a measure of Haemonchus contortus infection

BACKGROUND

Existing diagnostic methods for the parasitic gastrointestinal nematode, Haemonchus contortus, are time consuming and require specialised expertise, limiting their utility in the field. A practical, on-farm diagnostic tool could facilitate timely treatment decisions, thereby preventing losses in production and flock welfare. We previously demonstrated the ability of visible-near-infrared (Vis-NIR) spectroscopy to detect and quantify blood in sheep faeces with high accuracy. Here we report our investigation of whether variation in sheep type and environment affect the prediction accuracy of Vis-NIR spectroscopy in quantifying blood in faeces.

METHODS

Visible-NIR spectra were obtained from worm-free sheep faeces collected from different environments and sheep types in South Australia (SA) and New South Wales, Australia and spiked with various sheep blood concentrations. Spectra were analysed using principal component analysis (PCA), and calibration models were built around the haemoglobin (Hb) wavelength region (387-609 nm) using partial least squares regression. Models were used to predict Hb concentrations in spiked faeces from SA and naturally infected sheep faeces from Queensland (QLD). Samples from QLD were quantified using Hemastix® test strip and FAMACHA© diagnostic test scores.

RESULTS

Principal component analysis showed that location, class of sheep and pooled versus individual samples were factors affecting the Hb predictions. The models successfully differentiated 'healthy' SA samples from those requiring anthelmintic treatment with moderate to good prediction accuracy (sensitivity 57-94%, specificity 44-79%). The models were not predictive for blood in the naturally infected QLD samples, which may be due in part to variability of faecal background and blood chemistry between samples, or the difference in validation methods used for blood quantification. PCA of the QLD samples, however, identified a difference between samples containing high and low quantities of blood.

CONCLUSION

This study demonstrates the potential of Vis-NIR spectroscopy for estimating blood concentration in faeces from various types of sheep and environmental backgrounds. However, the calibration models developed here did not capture sufficient environmental variation to accurately predict Hb in faeces collected from environments different to those used in the calibration model. Consequently, it will be necessary to establish models that incorporate samples that are more representative of areas where H. contortus is endemic.

A mathematical model to predict the risk arising from the pasture infectivity of four nematode species in Australia

Gastrointestinal parasites cost the Australian sheep industry AU$436 million annually. Early warning of impending worm risk may reduce this cost by providing producers with sufficient time to implement control strategies. A biophysical model was developed to simulate the on-pasture lifecycle stages of the four predominant nematode species in Australia (Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus colubriformis and Trichostrongylus vitrinus). The influence of climatic variables (temperature and water availability) on the survival, development and migration of each lifecycle stage was incorporated and parameterised to available point estimates (H. contortus: R2 = 0.88, n = 1409; T. circumcincta: R2 = 0.56, n = 243; T. colubriformis: R2 = 0.61, n = 355; T. vitrinus: R2 = 0.66, n = 147). Constant fecundities (eggs/worm.day) provided the daily quantity of eggs deposited per sheep (H. contortus = 3275; T. circumcincta = 140; T. colubriformis = 300; T. vitrinus = 300). Farm management practices were considered via the specification of stocking rates (sheep/ha), and the administration of anthelmintic treatments (reducing egg deposition by a defined efficacy and duration for each nematode species). Pasture infectivity per nematode species was calculated as the quotient of larvae on herbage and herbage availability (t/ha). Risk was calculated as the product of pasture infectivity and the potential productive impact of each nematode species (H. contortus = 3.9%; T. circumcincta = 9.22%; T. colubriformis = 9.31%; T. vitrinus = 9.31%), and then summed across nematode species. This predictive model has been incorporated into the Sheep CRC’s ‘ASKBILL’ application (www.askbill.com.au, verified 13 April 2018), which uses 90-day weather forecast data (5-km grid resolution) provided by the Australian Bureau of Meteorology.

Population structure of Haemonchus contortus from seven geographical regions in China, determined on the basis of microsatellite markers

Background

Studying genetic variation within and among Haemonchus contortus populations can inform some aspects of this parasite’s population genetics and epidemiology. However, almost nothing is known about such variation in China.

Methods

Adult males of H. contortus (n = 184) representing seven distinct populations in China were collected, and genetic variation within and among these populations was explored using eight distinct microsatellite markers.

Results

Genetic parameters, such as heterozygosity and inbreeding coefficient (F_IS) indicated that all eight microsatellites were highly polymorphic. Various analyses (AMOVA, F_ST, phylogenetic, structure, mantel test and population dynamics) revealed high within-population variation, low population genetic differentiation and high gene flow for H. contortus in China.

Conclusions

This study provides a first snapshot of the genetic substructuring of H. contortus populations in China using polymorphic markers, and might provide a starting point for assessing genetic changes over space and time during or following the implementation of particular treatment or control strategies, or changes as a consequence of environmental, management and climatic factors.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1864-z) contains supplementary material, which is available to authorized users.

Intestinal parasite communities of six sympatric lemur species at Kirindy Forest, Madagascar

Abstract. Intestinal parasites impact host health, survival and reproductive success and therefore exert selective pressures on hosts' ecology and behavior. Thus, characterizing and comparing the parasitic fauna of different wildlife hosts sharing the same habitat can provide insights into the mechanisms underlying variation in parasitism, as well as the role of parasites as possible conservation threats. Several host traits have been proposed to generate differences in parasite diversity among different host species, including phylogeny, host body mass, host longevity, diet, and differences in ranging and social behavior. Here, we provide an overview of intestinal helminths and protozoa detected by fecal microscopy in six sympatric lemur species in Kirindy Forest, western Madagascar. The described patterns indicate that host phylogeny and diet may play an important role in shaping intestinal parasite assemblages in this system, as the closely related, omnivorous cheirogaleids showed the strongest overlap in parasite communities. No indication was found for an effect of body mass or longevity on parasite species richness. Regarding the effect of sociality, the two group-living lemur species, Propithecus verreauxi and Eulemur rufifrons, harbored directly transmitted parasites at higher prevalence than solitary foragers, but not at higher diversity. Effects of season and sex on parasite prevalence confirm the results of previous studies, with higher prevalence in the energetically demanding dry season and a male bias in parasitism. We highlight the opportunities of exploring the parasitic fauna of wildlife from a community ecology and evolutionary perspective, and identify prospects for future research on lemur parasitism.

The Pathophysiology, Ecology and Epidemiology of Haemonchus contortus Infection in Small Ruminants

The parasitic nematode Haemonchus contortus occurs commonly in small ruminants, and it is an especially significant threat to the health and production of sheep and goats in tropical and warm temperate zones. The main signs of disease (haemonchosis) relate to its blood-feeding activity, leading to anaemia, weakness and frequently to deaths, unless treatment is provided. Due to the high biotic potential, large burdens of H. contortus may develop rapidly when environmental conditions favour the free-living stages, and deaths may occur with little prior warning. More chronic forms of haemonchosis, resulting in reduced animal production and eventually deaths, occur with smaller persistent infections, especially in situations of prolonged, poor nutrition. The global distribution of the main haemonchosis-endemic zones is consistent with the critical requirements of the egg and larval stages of H. contortus for moisture and moderate to relatively warm temperatures, but the seasonal propensity for hypobiosis (inhibition of the fourth-stage larvae within the host) largely explains the common, though sporadic, outbreaks of haemonchosis in arid and colder environments. The wide climatic distribution may also reflect the adaptation of local isolates to less favourable ecological conditions, while an apparent increase in the prevalence of outbreaks in environments not previously considered endemic for haemonchosis - especially cold, temperate zones - may be attributable to climatic changes. Although the risk of haemonchosis varies considerably on a local level, even where H. contortus is endemic, the extensive range of ecological investigations provides a sound basis for predictions of the relative geographical and seasonal risk in relation to climatic conditions.

Prevalence of gastrointestinal nematodes and Fasciola hepatica in sheep in the northwest of Spain: relation to climatic conditions and/or man-made environmental modifications

BACKGROUND

In the present study we studied and updated the prevalence of the infections caused by gastrointestinal nematodes (GIN) and Fasciola hepatica in grazing sheep in the northwest (NW) of Spain for the last six years (2006-2011), and its relationship with the current climatic conditions.

METHODS

We analyzed faecal samples from 110 flocks located in four different provinces of the Autonomous Community of Castilla y León: 76.4% of them were situated in León, 12.7% in Zamora, 9.1% in Palencia and 1.8% in Valladolid.

RESULTS

The prevalence of GIN was 100% and the mean of eggs per gram (epg) in faeces was 237.2 (± 375.9) per flock. Regarding climatic conditions, we found a direct relationship between the GIN infection level and the maximum humidity (p<0.05) but inverse with the degree of solar radiation (p<0.05). The prevalence of fasciolosis was 59.3%, with a mean epg of 17.5 (± 33.9) per flock; these values were correlated with the minimum humidity and precipitations (p<0.05). Comparing our results in León with previous studies during the early 1990s, the mean epg of GIN was increased slightly (134.3 epg); regarding fasciolosis, the prevalence rose significantly, from 26.7% to 60.5%. Since the 1990s we observed that the maximum temperature is nowadays 0.45°C higher (17.0°C) and the minimum 0.5°C lower (5.2°C); the rainfall values were very similar in both decades but at the present time the humidity is higher (75.9%).

CONCLUSIONS

We found that the prevalence of GIN and F. hepatica infections was directly influenced by the humidity and also by precipitations in the case of F. hepatica. Comparing the current prevalence with studies carried out in the same area for the early 1990s, we observed that nowadays the mean epg of GIN is higher with a possible cause being the differences in climatic conditions depending on the sampling year. Regarding F. hepatica infection, its prevalence rose significantly probably favoured by an increase in irrigated areas in the area of study.

Translation of H. contortus and T. colubriformis from egg to establishment in grazing sheep is unaffected by rainfall timing, rainfall amount and herbage height under conditions of high soil moisture in the Northern Tablelands of NSW

A field experiment was conducted at Armidale in the Northern Tablelands of NSW, Australia to determine the effects of simulated rainfall amount (0, 12 and 24 mm), rainfall timing (days -1, 0 and 3 relative to plot contamination) and herbage height (4 and 12 cm), on translation of Haemonchus contortus and Trichostrongylus colubriformis from egg to established stages in grazing sheep under conditions of high soil moisture (22-23%). The experiment was conducted in summer when temperature was not anticipated to be a limiting factor for development success. Development success was assessed using tracer sheep and expressed as percentage recovery of parasitic stages relative to egg output on pasture (translation%). For both species, translation (0.11% H. contortus; 0.55% T. colubriformis) was observed in the absence of simulated rainfall and was unaffected by treatment effects of rainfall amount and timing, and herbage height. We suggest that soil moisture (>20%) alone was sufficient to support development and translation (from eggs to parasitic stages in the gut of tracer animals) of these species which contrasts with expectations for development success on dry soils. These findings identify the importance of taking soil moisture into account when predicting the likely effects of rainfall and herbage height on development to L3 and ultimately in predictive epidemiological models of ovine gastrointestinal nematodiasis.

Soil moisture modulates the effects of the timing and amount of rainfall on faecal moisture and development of Haemonchus contortus and Trichostrongylus colubriformis to infective third stage larvae

Recent experiments on the effects of rainfall and/or soil moisture (SM) on development of sheep gastro-intestinal nematodes to infective L3 stage have used soil of relatively low moisture content in small experimental samples that dry out faster than field soil. To determine whether higher and more sustained SM content modulates the effects of rainfall amount and timing on faecal moisture (FM) and development of H. contortus and T. colubriformis to infective third stage larvae (L3), a climate-controlled chamber experiment was conducted. It was designed to test the effects of rainfall amount (0, 12 and 24 mm), rainfall timing (days -1, 0 and 3 relative to faecal deposition) and soil moisture maintained at 10, 20 and 30% on these variables. Total recovery of L3 14 days after faecal deposition was significantly affected by SM, rainfall timing and their interaction (P<0.01), but not by rainfall amount or species or other two-way interactions. Recovery of L3 was maximal (28%) with a SM treatment of 30% and simulated rainfall on day 3. Faecal moisture was significantly affected by collection day, SM treatment, rainfall amount and rainfall timing with significant interaction between many of these effects (P<0.05). A positive linear association between FM and total L3 recovery was strongest on day 4 after faecal deposition (R(2)=0.64, P<0.001) for H. contortus and day 6 (R(2)=0.78, P<0.001) for T. colubriformis. Overall the results show that SM is able to modulate the effects of rainfall timing and amount with increased SM acting to broaden the window of opportunity for the free-living stages to respond to post deposition rainfall to complete development to L3. If SM is maintained in the range 10-30%, the reported benefits of early rainfall (days -1 and 0) of up to 24 mm appear to be negated with later rainfall (day 3) proving more beneficial. These results require field confirmation.

Soil moisture influences the development of Haemonchus contortus and Trichostrongylus colubriformis to third stage larvae

Two climate chamber experiments were conducted to determine the effect of varying initial soil moisture (0, 10 and 15%), simulated rainfall amount (0, 12 and 24 mm) and simulated rainfall timing (days -1, 0 and 3 relative to faecal deposition) on development (day 14) of Haemonchus contortus and Trichostrongylus colubriformis to the third stage larvae (L3) and faecal moisture (FM). Increasing initial soil moisture content from 0 to 10 or 15% led to higher recovery of total L3 (P<0.001). Total L3 recovery increased with each level of simulated rainfall (P<0.001) in the ascending order of 0, 12 and 24 mm. There was an interaction between the effects of initial soil moisture and simulated rainfall amount on the recovery of total L3, showing that the benefit of increased simulated rainfall lessened with increasing soil moisture. Simulated rainfall on the day of deposition resulted in higher recovery of L3 (P<0.001) than simulated rainfall on other days. FM on day 3 relative to faecal deposition was best associated with recovery of total H. contortus and T. colubriformis L3 (R(2)=0.32-0.46), reinforcing the importance of sufficient moisture soon after faecal deposition. The effects of initial soil moisture, and the amount and timing of simulated rainfall on development to L3 were largely explained by changes to FM and soil moisture values within 4 days relative to faecal deposition. These results highlight the influence of soil moisture and its interaction with rainfall on development of H. contortus and T. colubriformis to L3. Consequently we recommend that soil moisture be given greater importance and definition in the conduct of ecological studies of parasitic nematodes, in order to improve predictions of development to L3.

Effect of simulated rainfall timing on faecal moisture and development of Haemonchus contortus and Trichostrongylus colubriformis eggs to infective larvae

Three climate-controlled chamber experiments were conducted to determine the effect of 32 mm simulated rainfall applied prior to (days -4 to -1) or after (days 0-7) faecal deposition and as a single (32 mm) or split (2 × 16 mm) application on faecal moisture (FM) and development of H. contortus and T. colubriformis to third stage infective larvae (L3). The timing of simulated rainfall regulated extra-pellet L3 recovery for H. contortus (P<0.05) but not T. colubriformis. Recovery of L3 was highest (P<0.05) when simulated rainfall was applied on the day of deposition followed by days -1, 1 and 2, which resulted in similar but lower development success rates. Recovery of intra-pellet T. colubriformis L3 was two-fold greater (P=0.008) than for H. contortus and was higher (P=0.007) following simulated rainfall on days 0 and 1 than on other days. There was a positive association between FM and total L3 recovery indicating the importance of FM in the period 48-72 h (H. contortus) and 72-96 h (T. colubriformis) after deposition. Simulated rainfall on the day prior to deposition was as effective in supporting total L3 recovery as application on days 1 or 2 and this effect could be predicted through FM. This highlights the importance of soil in transferring moisture to the faecal pellet. The importance of precedent rainfall and soil moisture in determining the development success of H. contortus and T. colubriformis, in addition to the general effects of the timing of simulated rainfall, need to be accommodated in grazing management programs to combat these species.

A multi-species model to assess the effect of refugia on worm control and anthelmintic resistance in sheep grazing systems

OBJECTIVE

Develop a computer simulation model that uses daily meteorological data and farm management practices to predict populations of Trichostrongylus colubriformis, Haemonchus contortus and Teladorsagia (Ostertagia) circumcincta and the evolution of anthelmintic resistance within a sheep flock. Use the model to explore if increased refugia, provided by leaving some adult sheep untreated, would delay development of anthelmintic resistance without compromising nematode control.

PROCEDURES

Compare model predictions with field observations from a breeding flock in Armidale, NSW. Simulate the impact of leaving 1-10% of adult sheep untreated in diverse sheep-grazing systems.

RESULTS

Predicted populations of Tr. colubriformis and T. circumcincta were less than those observed in the field, attributed to nutritional stress experienced by the sheep during drought and not accounted for by the model. Observed variation in faecal egg counts explained by the model (R(2) ) for these species was 40-50%. The H. contortus populations and R(2) were both low. Leaving some sheep untreated worked best in situations where animals were already grazing or were moved onto pastures with low populations of infective larvae. In those cases, anthelmintic resistance was delayed and nematode control was maintained when 1-4% of adult stock remained untreated.

CONCLUSIONS

In general, the model predicted that leaving more than 4% of adults untreated did not sufficiently delay the development of anthelmintic resistance to justify the increased production risk from such a strategy. The choice of a drug rotation strategy had an equal or larger effect on nematode control, and selection for resistance, than leaving 1-10% of adults untreated.

Blueprint for an automated specific decision support system for countering anthelmintic resistance in Haemonchus spp. at farm level

This article is the first of a series aimed at developing specific decision support software for on-farm optimisation of sustainable integrated management of haemonchosis. It contains a concept framework for such a system for use by farmers and/or their advisors but, as reported in the series, only the first steps have been taken on the road to achieve this goal. Anthelmintic resistance has reached such levels of prevalence and intensity that recently it evoked the comment that for small ruminants the final phase of resistance was being entered, without effective chemotherapeutic agents on some farms with which to control worms at a level commensurate with profitable animal production. In addition, in the case of cattle, a recent survey in New Zealand showed 92% of worm populations to be resistant to at least one anthelmintic group. Ironically, new technology, such as the FAMACHA(©) system which was devised for sustainable management of haemonchosis, is at present being adopted relatively slowly by the majority of farmers and it is suggested that an important reason for this is the complexity of integration of new methods with epidemiological factors. The alternatives to the simple drenching programmes of the past are not only more difficult to manage, but are also more labour-intensive. The problem is further complicated by a progressive global shortage of persons with the necessary experience to train farmers in the new methods. The opinion is advanced that only computerised, automated decision support software can optimise the integration of the range of factors (such as rainfall, temperature, host age and reproductive status, pasture type, history of host and pasture infection, and anthelmintic formulation) for more sustainable worm management than is obtainable with present methods. Other than the conventional method (in which prospective analysis of laboratory and other data is mainly used to suggest when strategic prophylactic drenching of all animals for preventing excessive helminthosis should be conducted during the relevant worm season), the computer model being proposed is to be based on targeted selective treatment, supported by progressive periodic retrospective analysis of clinical data of a given worm season. It is emphasised that, in order not to repeat the mistakes of the past, such an automated support system should ideally be developed urgently in a attempt to engineer greater sustainability of any unrelated new anthelmintics which may reach the market.

Vertical migration of Haemonchus contortus third stage larvae on Brachiaria decumbens grass

The present study aimed at evaluating the vertical migration of Haemonchus contortus third stage larvae (L3) on Brachiaria decumbens grass, as well as at verifying whether larval numbers on pasture varies over the day due to climatic conditions. Feces containing H. contortus L3 were deposited on the soil in the middle of herbage which was initially 30 cm high. Seven days later, samples of different herbage strata (0-10, 10-20 and >20 cm), remaining feces and a layer of approximately 1cm soil were collected. Tests were carried out in four periods: September 2006, December 2006, March 2007, and June 2007. Samples were collected at sunrise, mid-day, sunset, and mid-night. The humidity and temperature conditions observed in different months influenced larval migration from the feces to the grass. In September, December and March, it rained after fecal deposition on pasture, which favored migration of larvae from the feces to the herbage. Conversely, in June 2007, when there was no rainfall after fecal deposition and temperatures were lower, L3 were mainly recovered from feces. As regards the vertical migration of larvae, the numbers of H. contortus L3 in the forage strata remained relatively constant over the day. This indicates there is not a determined period in which sheep on pasture are at higher risk of infection. Finally, in all collection periods a considerable amount of third stage larvae was observed on the herbage top, which is the first plant part consumed by sheep.

Development and survival of Haemonchus contortus infective larvae derived from sheep faeces under sub-tropical conditions in the Potohar region of Pakistan

Assessment on the development and survival of Haemonchus contortus larvae was made to evaluate the influence of microclimatic variables viz., relative humidity (%), temperature (degreesC), rainfall (mm) and intensity of sunlight (hrs). Pasture plots in a subtropical area, Pakistan were contaminated with H. contortus eggs at the start of every month. The plots were sampled on fortnightly basis after contamination for three consecutive months. The overall pattern indicated the most favorable conditions for survival, development and translation to herbage was during the wet season from July to October and the least favorable was during the dry season from April to June. Peak infective larvae (L3) recovery was during the 15-45 day interval for each plot and the lowest number was during the 75-90 day interval. Herbage was collected in the morning, afternoon and evening and greatest recovery of L3 was in the morning time and least in the afternoon. The number of L3 on pasture was directly related to the pattern of rainfall and relative humidity with a significant (P<0.05) positive correlation and temperature and intensity of sunshine were negatively correlated (P<0.05). The results suggest that pastures can remain infective for up to 2 months and become relatively clean by 90 days after contamination. Thus, long pasture rest periods, especially during the high risk wet season, may be a helpful strategy to reduce the infection levels.

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: <0.01%; 24 mm: 0.10%; 32 mm: 0.45%) but was reduced under the High evaporation rate (0.01%) compared with the Low evaporation rate (0.31%). All rainfall amounts yielded significantly different recoveries of L3 under Low evaporation rates but there was no difference between the 12 and 24 mm treatments under the High evaporation rate. The distribution of simulated rainfall did not significantly affect recovery of infective larvae. Faecal moisture content was positively associated with L3 recovery, as was the ratio of cumulative precipitation and cumulative evaporation (P/E), particularly when measured in the first 4 days post-deposition. The results show that evaporation rate plays a significant role in regulating the influence of rainfall amount on the success of L3 transmission.

The influence of temperature on the development, hatching and survival of Nematodirus battus larvae

Although Nematodirus battus (Nematoda: Trichostrongyloidea) is an economically important and highly pathogenic parasite of sheep in the temperate regions, very little is known about the population dynamics of its free-living stages and their relationship with ambient temperature. Here we describe the temperature-related vital rates and thresholds of egg development, hatching and larval survival for the first time. N. battus eggs were able to develop between 11.5 and 27 degrees C, but development at the lower end of this range was more successful. Embryonated eggs did not hatch below 11 degrees C or above 17 degrees C. This is the first description of an upper threshold for hatching in trichostrongyloids. In contrast with most previous studies, although some eggs hatched only after being chilled, substantial proportions of eggs were also found to hatch without the need for chilling. These proportions were lower with increasing, within-hatching range, temperatures. Larval death rates significantly increased at temperatures towards and above the upper hatching threshold. The peculiar hatching behaviour of N. battus may therefore be explained in terms of optimization of larval survival. We argue that our findings confirm the likelihood of an arctic origin of the parasite. Probable changes and adaptations of parasite behaviour in the temperate regions, and the driving forces behind them, are discussed, as well as factors affecting persistence and geographical spread against a background of climate change.

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 (3x2x2) 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 2 mm/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 macroclimatic 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.

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 lifecycle. 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 lifecycle 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.

Defecation behavior and ecology of insects

Whereas foraging has been a major focus of ecological and entomological research, its obligate partner, defecation, has been comparatively neglected. Insects exhibit a range of intriguing behavioral and morphological adaptations related to waste disposal in a range of contexts, including predator-prey interactions, hygiene, habitat location, reproduction, feeding, and shelter construction. Some insects, for example, make use of their own excrement as a physical or chemical defense against natural enemies, while others actively distance themselves from their waste material. Internally feeding insects, fluid-feeders, and social insects face particular challenges because their feeding behavior and/or site fidelity makes them especially vulnerable to problems associated with waste accumulation. As is true for foraging, ecological interactions involving defecation may have far-reaching evolutionary consequences and merit further study.

Effectiveness of grazing management in controlling gastrointestinal nematodes in weaner lambs on pasture in Denmark

A dose and move to clean pasture strategy for nematode control in weaner sheep was compared to a move only strategy. Sixteen ewes with twin lambs (2-3 weeks old) were turned out on infected pasture on 4 May 1999. On 1 July, the lambs were allocated to four groups of eight and weaned on to clean pasture. Two groups (DM1+2) were treated with anthelmintics, while the other two (M1+2) were not treated. Each group was allocated to a separate paddock and set stocked until 27 September when all the animals were slaughtered to perform worm counts. Moving the weaned lambs to clean pasture reduced the faecal egg counts to less than one third within 4 weeks while the treatment reduced it to zero for 4 weeks. Faecal egg counts of the dose and move groups remained significantly lower for 6 weeks (P<0.0001) after moving to the clean pasture. After this period the differences were not significant as the dose and move groups started shedding eggs in faeces. The pasture infectivity was lower in the paddocks grazed by groups (DM1+2). The weight gains and the serum albumin levels were comparable in all four groups. O. circumcinta and Trichostrongylus vitrinus were the major species recovered. The total worm counts were significantly lower in (DM1+2) compared to M1+2, particularly the mean counts in the small intestines (T. vitrinus) (P<0.01). It was concluded that weaning lambs at the beginning of July and moving them before the expected mid-summer rise in herbage infection to a clean pasture will prevent parasitic gastroenteritis and achieve good production whether the move is accompanied by anthelmintic treatment or not. The effects will be subject to prevailing nematode species, local climatic conditions and length of the grazing season.

Dynamics of pasture contamination by gastrointestinal nematodes of cattle under extensive management systems: proposal for strategic control

An epidemiological study of gastrointestinal nematode parasitism in beef cattle in mountainous areas of Spain was performed. The dynamics of contamination with gastrointestinal nematode larvae of Pyrenean pastures was studied over four years at five areas at different altitudes (900 m to 2100 m), grazed by animals according to traditional systems of beef cattle in mountainous areas. Grass samples were taken every two weeks and larval differentiation was performed. Worm egg counts of grazing animals were assessed in cows, heifers and calves. A consistent seasonal pattern of infective larvae on pasture through the study was observed. In hay meadows, located below 1000 m, infective larvae were found from the end of October until June of the following year. At higher altitudes (1200-2100 m), a bimodal pattern of pasture larvae contamination was observed with increases in late spring (March-June) and in late autumn (September-November). Ostertagia spp., Cooperia spp., Trichostrongylus spp., Oesophagostomum spp., and Nematodirus spp. were found, with Ostertagia spp. being the most frequently found, followed by Cooperia spp. The highest increase of larval contamination in autumn coincided with the grazing of animals in hay meadows. This elevated autumn larval population had a very important epidemiological role because these larvae remained as overwintered larvae until the following grazing season, starting the cycle of contamination of the animals.

Development and survival of infective larvae of gastrointestinal nematodes of cattle on pasture in central Kenya

On a series of pasture plots, 2 kg pats of bovine faeces containing known numbers of strongylid (Haemonchus, Cooperia, Oesophagostomum and Trichostrongylus) eggs were deposited at intervals of 4 weeks from July 1995 to June 1996. The plots were sampled every 2 weeks after contamination and infective larvae were identified and counted. Larvae of all the genera developed throughout the year, but the pats exposed during the rainy season yielded more abundant larvae on the herbage. Irrespective of the season of deposition of the pats, larvae were found in larger numbers from 2 to 6 weeks after deposition and generally declined to below detectable levels within 12 to 16 weeks of contamination. The comparatively short survival times noted in this experiment may present opportunities for manipulation of the population dynamics of the gastrointestinal nematodes in the tropical environment of Kenya.

Effect of plant species on the larvae of gastrointestinal nematodes which parasitise sheep

Faeces containing Trichostrongylus colubriformis and/or Ostertagia circumcincta eggs were used to provide four contaminations in each of 2 years on plots of browntop, Yorkshire fog, ryegrass, tall fescue, lucerne, chicory, cocksfoot, white clover, and prairie grass and in the second year a mixed sward of ryegrass/white clover. Third stage larvae were recovered from faeces and from four strata of herbage, 0-2.5, 2.5-5, 5-7.5 and > 7.5 cm above the soil surface at 2, 4, 6, 8, 11, and 14 weeks after faeces were deposited on the swards. Herbage species had a significant (P < 0.0001) effect on the number of larvae recovered. Greatest numbers of larvae, as indicated by ranking analysis, were recovered from Yorkshire fog, ryegrass, and cocksfoot and lowest numbers from white clover and lucerne. The difference between herbages in numbers of larvae recovered was due to the "development success", the ability of larvae to develop to the infective stage and migrate on to herbage, rather than "survival", the rate of population decline once on the herbage. Faecal degradation was most rapid from white clover and browntop, intermediate from tall fescue, lucerne, prairie grass, cocksfoot, and ryegrass, and slowest from Yorkshire fog swards. The numbers of larvae recovered from herbages were related (r2 = 0.59, P < 0.05) with the faecal mass remaining. A greater proportion of the total larvae recovered from the herbage was recovered from the bottom stratum of Yorkshire fog and prairie grass than from white clover, with the other herbages intermediate, indicating that larvae had greater difficulty migrating up Yorkshire fog and prairie grass than the other herbage species. In most herbage species, despite more larvae being recovered from the lowest stratum, larval density (L3/kg herbage DM) was highest in the top stratum. This study has demonstrated that herbage species can have a significant impact on the population dynamics and vertical migration of T. colubriformis and O. circumcincta larvae.

Controlling internal parasites in grazing ruminants without recourse to anthelmintics: approaches, experiences and prospects

Interest in ways of raising stock without using anthelmintics has been stimulated by the desire for intensive grazing systems to adopt more sustainable methods of internal parasite control and by potential premiums for "organic" produce. This requires grazing management systems which are practicable and achieve levels of parasite control sufficient to meet realistic production objectives. This paper will summarise 3 years experience of lamb and cattle production without a recourse to anthelmintics on 2 production systems: a mixed cropping, lamb finishing, and cattle rearing unit and an all grass, mixed-stock, hill country unit in which all non-replacement lambs are sold at weaning. On both units parasite control was almost entirely dependent on integrated grazing management of sheep and cattle and strict systems of grazing management had to be rigidly applied. Acceptable productivity could be more readily achieved in sheep than cattle. Rams selected for resistance to nematodes were also used in both sheep flocks. Their influence on lamb production was equivocal. There is a need for more information on factors influencing parasite epidemiology and for consideration of strategies other than alternate grazing. The impact of pasture species on parasite epidemiology needs to be clarified. Current research indicates substantial differences between grasses in terms of parasite burdens acquired and production losses suffered by lambs grazing them. Grazing management may need to vary with pasture species. Also, specialty forage crops, particularly those containing condensed tannins (i.e. Hedysarum coronarium, Lotus pedunculatus and Lotus corniculatus) hold special promise as a means of countering parasite-induced production losses and dagginess. Using biological control of free-living larval stages and vaccination, may in the long term, also prove useful. Developing effective and acceptable systems for raising stock without using anthelmintics presents a considerable challenge, to parasitologists, as well as to plant breeders, agronomists, and farming systems researchers.

Relative effect of temperature and moisture on the development of strongyle eggs to infective larvae in bovine pats in Argentina

To determine the most efficient microclimatic factors in bovine faeces that could explain the rate of development of parasitic nematode species, experimental pats were deposited in three locations (sun, shade and laboratory) in central-west Argentina during summer, autumn and winter seasons. Faecal water content (FWC) and temperature inside the pats were recorded during the duration of the experimental periods. The mean temperature and minimal values of FWC explained 54% of the variability of the rate of development of Haemonchus (third-stage larvae per 100 eggs) and mean maximal temperature and minimal FWC values were the two main factors regulating Cooperia development (R2 = 0.42). Rainfall was the third factor. No microclimatic component explained the development of Ostertagia in our experiments.

The ecology of Haemonchus contortus in a winter rainfall climate in Australia: the survival of infective larvae on pasture

At sites near Albany, on the south coast of Western Australia, sheep faecal pellets containing either eggs or infective larvae (L3) of Haemonchus contortus were deposited onto natural pasture plots at intervals over 3 years. Faecal and pasture samples were collected periodically and processed to detect L3. On annual pasture plots, L3 were recovered for from 10 to over 20 weeks from depositions made between autumn and early spring, at which time temperatures were mild or low, rainfall was frequent and the pasture was visibly green. During the hot and dry summer, when the pasture was completely dry, L3 often failed to develop or were recovered on only a single occasion, and the mean larval survival period on positive plots was less than 5 weeks. In contrast, L3 deposited on green perennial pasture plots in summer were recovered for up to 4 months in faecal pellets and on pasture. The longest periods of larval survival were associated with the lowest temperature and highest rainfall recordings, and with the greatest quantity of green plant material in the pasture. It is suggested that the poor survival of L3 during the dry summer period could be used in a strategic treatment programme to interrupt the transmission cycle of H. contortus in winter rainfall climates. However, areas of green pasture which persist in summer may provide a sufficiently moist microclimate to permit the survival of H. contortus L3 despite otherwise unfavourable environmental conditions.