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.

[Determination of limits of ashworthiosis foci in eastern and southern Poland]

The task was to establish the foci of ashworthiosis. The locations were: Białowieza Forest and Bieszczady Mountains. The wild cervides including: 52 red deer and 15 roe deer as well as domestic ruminants: 17 cattle and 18 sheep were examined parasitologically. Also, the examination was extended to neighbouring and additional areas. Contents of abomasa after multiple decantation were conserved with 2% formaldehyde. All nematodes were isolated from the contest, cleared in 70% ethanol with 5% glycerol and determinated to the species on the basis of structure of bursa copulatrix. Intensity of invasions of red deer oscillated from 3 to 296 specimens of A. sidemi and of roe deer from 42 to 545 nematodes. There were found none of domestic ruminants infected with this nematode in areas neighbouring with woods in both foci. Examinations showed that relatively new (found in 2000 year) focus of ashworthiosis in Polish part of Białowieza Forest has not dispersed yet beyond the limits of this forest complex. However, focus of ashworthiosis found in Bieszczady Mountains in 1997 year initially in Lutowiska Forest District expanded on the area of neighbouring Bieszczady forest districts: Komańcza, Cisna and Baligród and also on the area of Forest District Krasiczyn lying in Pogórze Przemyskie. So it is necessary further monitoring of status of A. sidemi infection of wild and domestic ruminants in neighbouring of both till now found foci.

Immune response to Haemonchus contortus infection in susceptible (INRA 401) and resistant (Barbados Black Belly) breeds of lambs

The immune responses to Haemonchus contortus were compared in studies in resistant Barbados Black Belly (BBB) and susceptible INRA 401 (INRA) breeds of lambs. The cytokine patterns indicated a Th2-biased response in both breeds. A more persistent and elevated Th2 cytokine mRNA transcription and blood eosinophilia were noted in the BBB lambs. However, at days 4 and 30 post-infection, abomasal recruitment of eosinophils and mast cells were similar between the two breeds. Following primary infections, the BBB demonstrated a substantially lower faecal egg count compared to the INRA lambs. Furthermore, worm counts at 4 and 30 days post-infection, and adult female worm size and in utero egg counts 30 days after the first infection were significantly lower in the BBB than in the INRA breed. In the INRA breed, re-infection caused a significant reduction in most parasitological parameters compared with those observed after the primary infection. A similar response was not observed in the BBB sheep. In conclusion, while the major driving force in the response to H. contortus infection is a Th2-biased immunity in which the BBB showed its maximal performance during the primary infection, the INRA breed performed better after re-infection compared to its response to first exposure.

In vitro detection of benzimidazole resistance in Haemonchus contortus: egg hatch test versus larval development test

The present study was designed to compare the egg hatch test (EHT) and the larval development test (LDT) as in vitro tools for detection of benzimidazole (BZ) resistance in Haemonchus contortus, a nematode parasite of small ruminants. Comparisons were made during a course of infection and changes in both EHT and LDT were monitored to measure the correlation between resistance and susceptibility in different parasite stages (eggs and larvae). In addition, mixed doses of known numbers of susceptible and BZ-resistant H. contortus eggs were used to assess the sensitivity of LDT for the detection of low levels of resistance. The degree of resistance for each test was expressed as resistance factor (RF). The LDT showed a greater ability to distinguish between four susceptible and four resistant isolates of H. contortus with higher resistance factors compared to the EHT. For the EHT the RF by using ED(50) criterion ranged from 3.2 to 13.3 and from 7.4 to 25.2 by using LC(99). For LDT the resistant isolates were 4.3-63.1 times more tolerant than the susceptible isolates using the ED(50) criterion and 91.1-1411.0 times more tolerant using the LC(99) criterion. The LDT was also able to clearly indicate the presence of low level (4%) of resistant larvae amongst a susceptible background population.

Haemonchosis and teladorsagiosis in a Scottish sheep flock putatively associated with the overwintering of hypobiotic fourth stage larvae

The cause of ill thrift and deaths was investigated in a group of 40 Scottish lowground ewes, which had been treated with levamisole and then turned onto clean grazing after lambing, 6-8 weeks previously. Concurrent haemonchosis and teladorsagiosis were diagnosed, putatively associated with the spring maturation of large numbers of hypobiotic larvae. Ill thrift due to parasitic gastroenteritis consequently occurred in the lambs which had been turned onto the 'clean' grazing with their dams, despite metaphylactic anthelmintic treatments. The contributory role of haemonchosis resulting in serious production-limiting disease is unusual in Scottish sheep flocks. It is suggested that the problem may have arisen as a consequence of the adaptation of Haemonchus contortus to survive overwinter in a cold climate as arrested early fourth stage larvae, which were not eliminated when the ewes were treated with levamisole at turnout.

Immunological aspects of nematode parasite control in sheep

Gastrointestinal nematode parasitism is arguably the most serious constraint affecting sheep production worldwide. Economic losses are caused by decreased production, the costs of prophylaxis and treatment, and the death of the infected animals. The nematode of particular concern is Haemonchus contortus, which can cause severe blood loss resulting in anemia, anorexia, depression, loss of condition, and eventual death. The control of nematode parasites traditionally relies on anthelmintic treatment. The evolution of anthelmintic resistance in nematode populations threatens the success of drug treatment programs. Alternative strategies for control of nematode infections are being developed, and one approach is to take advantage of the host's natural or acquired immune responses, which can be used in selection programs to increase the level of resistance in the population. Vaccination can also be used to stimulate or boost the host's acquired immunity. The induction of protective resistance is dependent on the pattern of cytokine gene expression induced during infection by two defined CD4+ T-helper cell subsets, which have been designated as Th1 or Th2. Intracellular parasites most often invoke a Th1-type response, and helminth parasites a Th2-type response. Breeds of sheep resistant to infection have developed resistance over a much longer term of host-parasite relationship than genetically selected resistant lines. The immune components involved in these different responses and types of host-parasite relationships will be reviewed. The potential for using vaccines has been investigated, with variable results, for several decades. The few successes and potential new antigen candidates will also be reviewed.

In vitro pre-exposure ofHaemonchus contortusL3 to blood eosinophils reduces their establishment potential in sheep

Different authors have reported that eosinophils are capable of immobilising infective larvae of different species of nematodes in vitro. However, classifying larvae as mobile or immobile is so subjective that it does not always mean all apparently immobile larvae are dead or those that are mobile are capable of surviving further immune responses if administered to their natural hosts. The objective of this experimental study was therefore to substantiate the role of eosinophils in the killing of Haemonchus contortus infective larvae by comparing the infectivity in sheep of larvae that had been incubated with eosinophil-enriched cell suspensions with control larvae. Since it was not possible to isolate pure eosinophils from sheep blood, we were compelled to evaluate the effects of other blood cells contaminating our eosinophil-enriched suspensions. Although eosinophils and neutrophils were the only cells found adherent to H. contortus infective larvae in vitro, induced eosinophils in the presence of immune serum were primarily responsible for the drastic reduction in larval motility compared to the minor effects of neutrophils and mononuclear cells. Corresponding reductions in faecal egg count and worm numbers were observed when the incubated larvae were transferred intra-abomasally to sheep. Interestingly, the proportion of larvae that failed to establish was much higher following incubation with induced eosinophils compared with other cells or with immune serum alone. Although this study did not address the in vivo role of eosinophils in sheep, the results strongly indicate that sheep blood eosinophils have a larval killing potential in vitro, and a larval mobility test alone may not fully explain the level of damage inflicted on the larvae.

Morphological characterization of Haemonchus contortus in goats (Capra hircus) and sheep (Ovis aries) in Penang, Malaysia

The large stomach worm, Haemonchus contortus is an important pathogen of goats (Capra hircus) and sheep (Ovis aries). This paper describes characteristics of surface cuticular ridges (synlophe) of H. contortus adults from the two hosts. There were more ridges in H. contortus from goats compared to that from sheep. Total body length, vulvar morphology, spicule length and cervical papillae had been considered as markers of physical adaptation and were studied and described.

Vaccination of goats with recombinant galectin antigen induces partial protection against Haemonchus contortus infection

The efficacy of vaccination against Haemonchus contortus infection with two recombinant proteins, rHco-gal-m and rHco-gal-f, was studied in 9-10-month-old goats. Vaccination with 100 microg protein reduced faecal egg output and worm burdens by 37.25% and 41.1%, respectively. Corresponding reductions with 200 microg protein were 48.03% and 46.19%. Vaccinated groups had significantly higher IgG levels than the negative and positive controls. Significant negative correlations were detected between IgG level, mucosal homogenate IgA concentration, haemoglobin and abomasal worm burden at necropsy. By contrast a positive correlation was found between the percentage of B cells, monocytes and abomasal worm burden. These findings suggested that vaccination with a combination of recombinant rHco-gal-m/f proteins had a role in protecting goats against H. contortus infection.

Performance and nematode infection of ewe lambs on intensive rotational grazing with two different cultivars of Panicum maximum

The daily live weight gain (DLWG), faecal nematode egg counts (FEC), and packed cell volume (PCV) of Suffolk, Ile de France and Santa Inês ewe lambs were evaluated fortnightly for 56 days in the dry season (winter) and 64 days in the rainy season (summer) of 2001-2002. The animals were distributed in two similar groups, one located on Aruana and the other on Tanzania grass (Panicum maximum), in rotational grazing system at the Instituto de Zootecnia, in Nova Odessa city (SP), Brazil. In the dry season, 24 one-year-old ewe lambs were used, eight of each breed, and there was no difference (p > 0.05) between grasses for DLWG (100 g/day), although the Suffolk had higher values (p < 0.05) than the other breeds. In the rainy season, with 33 six-month-old ewe lambs, nine Suffolk, eight Ile de France and 16 Santa Inês, the DLWG was not affected by breed, but it was twice as great (71 g/day, p < 0.05) on Aruana as on Tanzânia grass (30 g/day). The Santa Inês ewe lambs had the lowest FEC (p < 0.05) and the highest PCV (p < 0.05), confirming their higher resistance to Haemonchus contortus, the prevalent nematode in the rainy season. It was concluded that the best performance of ewe lambs on Aruana pastures in the rainy season is probably explained by their lower nematode infection owing to the better protein content of this grass (mean contents 11.2% crude protein in Aruana grass and 8.7% in Tanzania grass, p < 0.05) which may have improved the immunological system with the consequence that the highest PCV (p < 0.05) observed in those animals.

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.

Duration of anthelmintic effect of three formulations of ivermectin (oral, injectable and pour-on) against multiple anthelmintic-resistant haemonchus contortus in sheep

We report the results of investigations that were conducted in a sheep flock in Uttaranchal, India where repeated failure of anthelmintic medication was noted. The study revealed that Haemonchus contortus in sheep had developed resistance to benzimidazoles (fenbendazole, mebendazole and albendazole), imidazothiazole (levamisole) and salicylanide (rafoxanide), while it was fully susceptible to avermectins (ivermectin). Further, the suppression of nematode egg output in faeces of sheep naturally infected with multiple anthelmintic-resistant H. contortus following treatment with ivermectin tablet (0.4 mg/kg body weight (bw), orally), ivermectin injection (1% w/v, 0.2 mg/kg bw, subcutaneously) and ivermectin pour-on (0.5 w/v, 0.5 mg/kg bw) was also studied over a period of 10 weeks post treatment. It was noted that ivermectin tablet after initial clearance of infection (faecal egg count reduction 100%), could not prevent establishment of new patent natural infection for even a single day, while ivermectin pour-on and injection prevented the establishment of new infection for 7 and 14 days post treatment, respectively. Maximum protection period (duration for which mean faecal egg count of sheep reaches 500 eggs per gram of faeces or more) of 68 days was recorded in sheep treated with injectable ivermectin, followed by pour-on (60 days) and oral (53 days) preparations.

A novel approach for combining the use of in vitro and in vivo data to measure and detect emerging moxidectin resistance in gastrointestinal nematodes of goats

Ivermectin and moxidectin are closely related avermectin/milbemycin anthelmintics and available data suggest that side resistance occurs with these two drugs. However, moxidectin remains effective against many species of ivermectin-resistant worms due to its higher potency. The larval development assay (LDA) is routinely used to diagnose ivermectin resistance in Haemonchus contortus but laboratory diagnosis of moxidectin resistance is hampered by the lack of any validated in vitro tests. The objective of this study was to measure the relative susceptibility/resistance of H. contortus to moxidectin on goat farms in Georgia, and to validate the DrenchRite LDA for detecting resistance to moxidectin. Fecal egg count reduction tests (FECRT) were performed at five different moxidectin dose levels and DrenchRite LDAs were performed in duplicate on nine meat goat farms in Georgia, USA. To improve our ability to make inferences on the relative levels of resistance between farms, FECRT data were first analysed using a linear mixed model, and then Tukey's sequential trend test was used to evaluate the trend in response across dose levels. LDA data were analysed using log-dose logit-response and probit models. Using these statistical results, we were able to rank the nine farms from the least to the most resistant, and to develop a set of criteria for interpreting DrenchRite LDA results so that this assay can be used to diagnose both clinically apparent moxidectin resistance, as well as sub-clinical emerging resistance. These results suggest that our novel approach for examining these types of data provides a method for obtaining an increased amount of information, thus permitting a more sensitive detection of resistance. Based on results of the LDA, moxidectin-resistant farms had resistance ratios, compared with an ivermectin-sensitive farm, ranging from 32 to 128, and had resistance ratios of 6-24 compared with an ivermectin-resistant/moxidectin naive farm. Moxidectin resistance was diagnosed both in Haemonchus and Trichostrongylus on almost half of the farms tested, despite this drug only being used on these farms for 2-3 years.

Effect of sainfoin (Onobrychis viciifolia) silage and hay on established populations of Haemonchus contortus and Cooperia curticei in lambs

The objective of the study was to examine the effect of dried and ensiled sainfoin (Onobrychis viciifolia) on established populations of Haemonchus contortus (abomasum) and Cooperia curticei (small intestine) in lambs under controlled conditions. Twenty-four parasite naïve lambs were inoculated with a single dose of infective larvae of these parasites 28 days prior to the start of the feeding experiment. Twenty-four days post-infection, 4 days prior to the start of the feeding experiment, animals were allocated to four groups according to egg excretion, live weight and sex. Groups A and B received sainfoin hay and control hay, respectively, for 16 days. Groups C and D were fed on sainfoin silage or control silage for the same period. Feeds were offered ad libitum and on the basis of daily refusals were supplemented with concentrate in order to make them isoproteic and isoenergetic. Individual faecal egg counts on a dry matter basis (FECDM) were performed every 3-4 days and faecal cultures and packed cell volume (PCV) measurements were done weekly. After 16 days of experimental feeding, all animals were slaughtered and adult worm populations were determined. The consumption of conserved sainfoin was associated with a reduction of adult H. contortus (47% in the case of hay, P<0.05; 49% in the case of silage, P=0.075) but had little effect on adult C. curticei. Compared to the controls, H. contortus specific FECDM was reduced by 58% (P<0.01) in the sainfoin hay group and by 48% (P=0.075) in the sainfoin silage group. For both sainfoin feeds FECDM specific to C. curticei were significantly decreased when compared to the control feeds (hay 81% and silage 74%, both tests P<0.001). Our data suggest that different mechanisms were responsible for the reduction in FECDM in response to feeding tanniferous fodder. For H. contortus, the decrease seemed to be due to a nematocidal effect towards adult H. contortus. In contrast for C. curticei, the reduction in FECDM appeared to be a result of a reduced per capita fecundity. For both, hay and silage, an antiparasitic effect could be shown, offering promising perspectives for the use of conserved tanniferous fodder as a complementary control approach against GIN.

Heterosis analysis of Haemonchus contortus resistance and production traits in Rhoen sheep, Merino Land sheep and crossbred lambs

A crossbreeding program was conducted to evaluate the resistance status to Haemonchus contortus in reciprocal crossbred (F(1)) lambs and their Merino Land sheep (Ml) and Rhoen sheep (Rh) purebred counterparts. A total of 406 lambs were included in the study. Faecal egg counts (FEC) and haematocrit values (Hc) of all the lambs were collected 4 and 8 weeks after an artificial infection with H. contortus. FAMACHA scores were given at the same time. Worm counts of all lambs were obtained after slaughtering at 21 weeks of age. The Ml group consistently showed the highest body weights, daily weight gains and best carcass performances, whereas the Rh group showed the lowest results. Most of the body weight parameters in the F(1) group fell intermediately between the Ml and Rh groups, though the heterosis analysis of body weight and carcass parameters showed a tendency to favour the crossbreeding group Rh x Ml. The Rh group showed, on average, the highest FEC and the lowest Hc values compared to the Ml. However, the nematode counts were not significantly different between the pure breeds. In comparison, the worm counts of the Rh x Ml crosses were significantly different from those in the Ml x Rh crosses. A heterosis analysis showed that FEC, Hc and the worm count in the F(1) group favoured the crossbreeding group Rh x Ml. These results suggested that crossbreeding Rh to Ml sheep may be a suitable way of producing lambs with improved resistance to H. contortus infection without any negative effects on production traits.

Characterization of HC58cDNA, a putative cysteine protease from the parasite Haemonchus contortus

Because of the complexity of the cathepsin B-like (CBL) family, an information on the biological and biochemical characteristics of individual CBL genes is lacking. In this study, we investigated the degradative effects of the recombinant HC58 protein isolated from Haemonchus contortus parasites on protein substrates over a broad pH range in vitro. This protein, which hydrolyzed the synthetic peptide substrates Z-FR-AMC and Z-RR-AMC, had characteristics of the cysteine protease class of proteins. In the acidic pH range, the isolated protein actively degraded hemoglobin (Hb), the heavy chain of goat immunoglobulin G, and azocasein. By contrast, it degraded fibrinogen in the alkaline pH range. These activities were strongly inhibited in the presence of the cysteine protease inhibitor E-64. While the protein digested Hb, it did not induce the agglutination of erythrocytes from its natural host. These results suggest that the HC58 protein may play a role in the nutrition of this parasite.

Ivermectin selection on beta-tubulin: evidence in Onchocerca volvulus and Haemonchus contortus

Ivermectin resistance is common in trichostrongylid nematodes of livestock, such as Haemonchus contortus. This anthelmintic is the only drug approved for mass administration to control onchocerciasis caused by the nematode parasite, Onchocerca volvulus. In parts of West Africa up to 18 rounds of ivermectin treatment have been administered to communities and there are reports of poor parasitological responses to treatment. Understanding ivermectin resistance and ivermectin selection is an important step to reduce selection pressure for resistance, and to develop molecular markers which can be used to monitor the development of resistance and its spread. Here we report evidence that ivermectin selection changes the frequency of beta-tubulin alleles in both the sheep parasite, H. contortus, and the human parasite, O. volvulus. In O. volvulus we have been able to look at the frequency of beta-tubulin alleles in O. volvulus obtained before any ivermectin was used in humans in Africa, and following its widespread use. In H. contortus, we have been able to look at the frequency of beta-tubulin alleles in a strain which has not seen any anthelmintic selection and in an ivermectin selected strain derived from the unselected strain. We have found ivermectin selects on beta-tubulin in both of these nematode species. In the case of O. volvulus, we had previously reported that ivermectin selects for specific single nucleotide polymorphisms in the O. volvulus beta-tubulin gene. This polymorphism results in three amino acid changes in the H3 helix of beta-tubulin, as well as deletions in an associated intron. We report a simple PCR assay to detect the amplicon length polymorphism, resulting from these intronic deletions, which can be used to monitor the frequency of the beta-tubulin allele selected for by ivermectin in O. volvulus.

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.

[Experiences with the FAMACHA-Eye-Colour-Chart for identifying sheep and goats for targeted anthelmintic treatment]

The bloodsuckling abomasal parasite Haemonchus contortus is the most pathogenic worm in sheep and goats. High prevalences of anthelmintic-resistant isolates make H. contortus difficult to control. Detecting the most anaemic animals could support a targeted selective treatment approach. Leaving the rest of the flock untreated would generate a refuge for anthelmintic-sensitive parasites. South-African researchers tried the FAMACHA-Eye-Colour-Chart for anaemic sheep and goats with good success. Field studies, carried out in Northern Germany on naturally infected sheep and goats showed, that at a comparatively low prevalence of H. contortus the FAMACHA-test proved not being sufficient in detecting all animals with high fecal egg counts. Under these conditions there was no satisfying reliability to identify small ruminants for selective deworming only based on the FAMACHAEye-Colour-Test. But if not working hours are the limiting factor, the repeated score could support the selection of pale animals in need to be treated.

Segregation of natural and experimental gastrointestinal nematode infection in F2 progeny of susceptible Suffolk and resistant Gulf Coast Native sheep and its usefulness in assessment of genetic variation

Gastrointestinal nematode parasitism is a concern to small ruminants worldwide. Productivity has been compromised because such nematodes, particularly Haemonchus contortus, have developed resistance to available anthelmintics. Some sheep breeds and lines within breeds are relatively resistant to infection, a trait that may be useful for developing control strategies. Suffolk sheep, which are susceptible to infection, were crossed with Gulf Coast Native sheep, which are more resistant to infection, to produce F1 progeny. F1 rams were bred to F1 ewes which produced 227 F2 offspring. These F2 offspring were evaluated for variability in infection levels, based on fecal egg count (FEC) and blood packed cell volume (PCV), under two natural infection conditions (one at weaning and another after a summer grazing period) and one experimental infection. The range of both FEC and PCV was large for all three infection periods with annual variation. Overall, the range for the three infection periods, respectively, were 167-149,933, 0-31,400 and 17-114,667 eggs per gram (EPG) of feces and 8.7-37.0%, 7.3-33.0% and 8.3-36.0%. This segregation of infection is what would be expected of F(2) progeny from susceptible and resistant parent breeds. Heritabilities of FEC and PCV for the three infection periods, respectively, were 0.15, 0.29 and 0.12, and 0.11, 0.22 and 0.12. Based on segregation of infection, larger heritabilities and maternal environment effects that declined after weaning, the summer natural infection was probably the best model for assessing genetic variation.

Ovicidal and larvicidal activity of Melia azedarach extracts on Haemonchus contortus

Haemonchus contortus is responsible for severe economic losses in sheep and goat breeding in the Northeast of Brazil. However, the effectiveness of control is compromised due to anthelmintic resistance and misuse. In the search for natural anthelmintics, Melia azedarach L., a plant indigenous to India but now distributed throughout Brazil, was selected due to the reported anthelmintic properties of its seeds. The aim of this study was to evaluate the anthelmintic activity of the seed and leaf extracts of the Brazilian adapted plant and investigate the type of organic chemical compounds present in the most active extracts. The ovicidal and larvicidal activity of M. azedarach extracts on H. contortus was evaluated through egg hatching and larval development tests. Hexane and ethanol extracts of seeds and chloroform and ethanol extracts of leaves of M. azedarach were used in the tests. To perform the larval development test, feces of an animal free from parasites were mixed with third instar H. contortus larvae and extracts in several concentrations. The coprocultures were incubated for 7 days at 30 degrees C, then the larvae were recovered and counted. LC50 was calculated by probits using the SPSS 8.0 program. The seed ethanol extract was the most active on eggs (LC50=0.36mgmL(-1)) and the leaf ethanol extract showed the best inhibition of larval development (LC50=9.18mgmL(-1)). Phytochemical analysis of the most active extracts revealed the presence of condensed tannins, triterpenes and alkaloids.

Prospects for exploring molecular developmental processes in Haemonchus contortus

Haemonchus contortus of small ruminants is a parasitic nematode of major socio-economic importance world-wide. While there is considerable knowledge of the morphological changes which take place during the life cycle of H. contortus, very little is understood about the molecular and biochemical processes which govern developmental changes in the parasite. Recent technological advances and the imminent genomic sequence for H. contortus provide unique opportunities to investigate the molecular basis of such processes in parasitic nematodes. This article reviews molecular and biochemical aspects of development in H. contortus, reports on some recent progress on signal transduction molecules in this parasite and emphasises the opportunities that new technologies and the free-living nematode, Caenorhabditis elegans, offer for investigating developmental aspects in H. contortus and related strongylid nematodes, also in relation to developing novel approaches for control.

Further protection studies using recombinant forms of Haemonchus contortus cysteine proteinases

Significant levels of protection against Haemonchus contortus have been achieved in sheep by vaccination with a cysteine proteinase-enriched fraction (TSBP) isolated from the gut of adult parasites. Protection is associated with three cathepsin B-like cysteine proteinases (hmcp 1, 4 & 6). Lambs vaccinated with these proteinases, expressed in bacteria as glutathione S-transferase fusion proteins, had significantly reduced (38%) worm burdens compared to challenge controls although, intriguingly, egg output was unaffected. Here, a repeat trial with similar results is reported and protection obtained compared to that induced by vaccination with the predicted mature forms of hmcp1, 4 and 6 expressed in bacteria as non-fusion proteins. Sheep immunized with a cocktail of these non-fusion proteins had reduced faecal egg counts of 27% (P = 0.17) and worm burdens of 29% (P = 0.01) compared to controls. High levels of host serum IgG were detected in GST-hmcp and non-fusion hmcp-immunized animals, although no correlation with protection could be determined. Sera from these groups bound to the microvillar surface of the gut of H. contortus.

Effect of nutritional status and fat reserves on the periparturient immune response to Haemonchus contortus infection in sheep

A study was made of the effect of body fat stored by ewes in early pregnancy on the subsequent immune response to gastrointestinal parasites around parturition. Pregnant ewes were given access to a lucerne pelleted diet either ad libitum (H) or at approximately 0.70 of their maintenance requirements (L) from the 42nd day of pregnancy in order to achieve a clearly differentiated level of body reserves by the 90th day of pregnancy. Then, all animals were put on the same plane of nutrition till 3 weeks after parturition. All ewes in both groups received 7,000 infective larvae of Haemonchus contortus per week for 7 weeks prior to lambing. The dietary treatments led to large differences between both groups of ewes in back-fat thickness that had a high correlation with mean plasma concentrations of leptin. In spite of the fact that animals were on the same plane of nutrition at infection time, host resistance, as measured by faecal egg counts, was significantly affected by the nutritional treatment established during early pregnancy. This effect produced noticeable differences in worm size and in worm burden at lambing. The response was accompanied by a marked increase in circulating eosinophils in better-fed ewes than in those maintained on a restricted diet in early pregnancy. Serum pepsinogen concentration, however, was inversely affected by the nutritional treatment till lambing, showing a maximum difference as early as 2 weeks after infection. The results support the view that higher levels of nutrition during early pregnancy enhance the expression of immunity against gastrointestinal parasites around parturition. Furthermore, the differences in the immune response appeared associated with serum leptin levels suggesting that leptin may be a key link between nutritional status and the protective immune reactivity against GI nematode infection.

Effects of legume forages on ovine gastrointestinal parasite development, migration and survival

Lambs grazing certain legumes have reduced parasite intensities compared to lambs grazing ryegrass swards. Eighteen replicates of white clover (cv. AberHerald), lucerne (cv. Luzelle), red clover (cv. Merviot) and perennial ryegrass (cv. Abersilo) were sown at equivalent field rates in 25 cm diameter PVC pots and maintained outside for 6 months. On day 0, forage in each pot was cut to 50 mm from soil level and the pots were placed in a glasshouse (at 19-25 degrees C and 70% humidity) in a randomised block design. Ten grams sheep faeces containing 2,133 Haemonchus contortus eggs per gram were placed on the soil in each pot. Six replicates of each forage were destructively sampled on days 14, 21 and 29. Forage samples were cut at 50 mm from the soil surface and at the soil surface to give two samples per pot. The number of nematodes was determined by a modification of the Whitehead tray method. The ratio of free-living to infective-stage larvae was determined from at least 10% of the larvae. The number of H. contortus larvae kgdrymatter(-1) (DM) forage was calculated and the data rank transformed prior to analysis by ANOVA. There were fewer larvae on legumes compared with ryegrass on samples from forage above 50 mm (P<0.001) but there was no forage effect on larvae below this height. The sum of larvae present on all forage per kilogram DM showed fewer larvae on red clover compared with ryegrass on day 21 (P<0.05). There was an effect of day on the total number of larvae on forage (P<0.001) but there were no foragexday interactions. Analysis of the data according to the leaf area above 50 mm from the soil surface confirmed these results, that there were fewer larvae on legume forages than ryegrass above this height (P<0.01). Overall, red clover affected the development of H. contortus and all legumes affected larval migration above 50 mm compared with ryegrass but survival of larvae was similar on all forages. Further work is needed to determine if these effects of legume forages would reduce the number of parasitic larvae ingested by livestock under field conditions.