Pathophysiology of infection with Ostertagia ostertagi in cattle

Novel epidemiological model of gastrointestinal nematode infection to assess grazing cattle resilience by integrating host growth, parasite, grass and environmental dynamics

Gastrointestinal nematode (GIN) infections are ubiquitous and often cause morbidity and reduced performance in livestock. Emerging anthelmintic resistance and increasing change in climate patterns require evaluation of alternatives to traditional treatment and management practices. Mathematical models of parasite transmission between hosts and the environment have contributed towards the design of appropriate control strategies in ruminants, but have yet to account for relationships between climate, infection pressure, immunity, resources, and growth. Here, we develop a new epidemiological model of GIN transmission in a herd of grazing cattle, including host tolerance (body weight and feed intake), parasite burden and acquisition of immunity, together with weather-dependent development of parasite free-living stages, and the influence of grass availability on parasite transmission. Dynamic host, parasite and environmental factors drive a variable rate of transmission. Using literature sources, the model was parametrised for Ostertagia ostertagi, the prevailing pathogenic GIN in grazing cattle populations in temperate climates. Model outputs were validated on published empirical studies from first season grazing cattle in northern Europe. These results show satisfactory qualitative and quantitative performance of the model; they also indicate the model may approximate the dynamics of grazing systems under co-infection by O. ostertagi and Cooperia oncophora, a second GIN species common in cattle. In addition, model behaviour was explored under illustrative anthelmintic treatment strategies, considering impacts on parasitological and performance variables. The model has potential for extension to explore altered infection dynamics as a result of management and climate change, and to optimise treatment strategies accordingly. As the first known mechanistic model to combine parasitic and free-living stages of GIN with host feed-intake and growth, it is well suited to predict complex system responses under non-stationary conditions. We discuss the implications, limitations and extensions of the model, and its potential to assist in the development of sustainable parasite control strategies.

Trichostrongyloid nematodes in ruminants of northern Iran: prevalence and molecular analysis

BACKGROUND

This study was carried out to investigate the prevalence and analyze the molecular characteristics based on the internal transcribed spacer (ITS) 2 region of the ribosomal RNA (RNA) gene of trichostrongylid nematodes in different ruminants from Guilan province, northern of Iran.

METHODS

The gastrointestinal tracts of 144 ruminants including 72 cattle, 59 sheep, and 13 goats were collected from an abattoir in Guilan province during July to September 2018. After isolation the helminths, male specimens were identified based on morphological parameters. PCR and partial sequencing of the ITS2 fragment were conducted. After phylogenetic analysis, the intraspecific and interspecific differences were calculated.

RESULTS

The prevalence of total infections with the nematodes was 38.9, 74.6 and 84.6% among cattle, sheep and goats, respectively. Eleven species of trichostrongylid nematodes including Haemonchus contortus, Marshallagia marshalli, Trichostrongylus axei, T. colubriformis, T. vitrinus, Ostertagia trifurcata, Teladorsagia circumcincta, Marshallagia occidentalis, O. lyrata, O. ostertagi, and Cooperia punctate were recovered from the ruminants. The most prevalent trichostrongyloid nematodes in cattle, sheep and goats were O. ostertagi (26.4%), M. marshalli (64.4%) and T. circumcincta (69.2%), respectively. Phylogenetic tree was discriminative for Trichostrongylidae family, while phylogenetic analysis of the ITS2 gene represented low variations and no species identification of Haemonchidae and Cooperiidae families.

CONCLUSIONS

This study suggests the high prevalence and species diversity of trichostrongyloid nematodes in different ruminants, indicating the importance of implement antiparasitic strategies in north regions of Iran. As well, this study showed that the ITS2 fragment is not a discriminative marker for Haemonchidae and Cooperiidae families, and investigation of other genetic markers such as mitochondrial genes would be more valuable for better understanding of their phylogenetic relationships.

Repeated, drug-truncated infections with Ostertagia ostertagi elicit strong humoral and cell-mediated immune responses and confer partial protection in cattle

Bovine ostertagiasis causes significant production losses to the cattle industry. Protective immunity induced by natural infection is slow to develop and anthelmintic resistance is rapidly developing. There is a need to advance alternatives for control of gastrointestinal nematode parasites. The present study investigated the effects of repeated, drug-truncated infections (rDTI) on development of protective immunity and attenuation of a challenge infection by O. ostertagi. Helminth-free calves were randomly assigned to either a rDTI or a control group (n = 5). The rDTI group received daily oral infections of 5000 Ostertagia L3 for 5 consecutive days, then were drug-treated on 14 and 15 days post infection (dpi), to attenuate O. ostertagi at the late fourth larval (L4) through young adult stages. DTI was repeated 3 weeks after the drug treatment. A total of 5 DTIs were administered to the DTI-treated animals. Non-DTI-treated, control animals received tap water as infection control. All animals were drug-treated at the same time. Animals were challenge-infected 4 weeks following the final round of rDTI. The results show that eggs per gram of feces (EPG) in the rDTI group were significantly reduced (P < 0.05) from 21 to 39 dpi, with an overall reduction in cumulative EPG. The control group exhibited reduced (P = 0.0564) average weight gains when compared to those of the rDTI group during weeks 4-5 post infection, a period coinciding with peak EPG output of control animals. Antigen-specific IgG, IgE and IgA responses were detected after the 2nd DTI, and stronger antibody recall responses were elicited by challenge infection. High levels of antigen-specific peripheral blood mononuclear cell (PBMC)/T cell proliferation to whole worm and excretory-secretory (ES) antigens were detected in rDTI-treated animals. These data indicate that partial protective immunity against ostertagiasis, involving cell-mediated and humoral responses, can be attained by rDTI which allowed for maximal antigen exposure from staggered parasitic developmental stages. The data suggest that rDTI can be used as a model to study host-parasite interactions and identify parasite antigens responsible for eliciting host protective immune responses.

Chemical Composition and In vitro Anthelmintic Activity of Extracts of Tagetes patula Against a Multidrug-Resistant Isolate of Haemonchus contortus

Sheep breeding has suffered economic losses due to parasitism by gastrointestinal nematodes, particularly Haemonchus contortus. The use of natural products, specifically Tagetes patula, has been suggested as an alternative method of combatting this issue. Chemical analyses of the extracts of this species described in the literature report the presence of important classes of secondary metabolites such as thiophenes, flavonoids, alkaloids, and benzofurans, some of which were identified and isolated in this study. The aim of this work was to test the effect of the essential oil (EO) and the ethanolic extract of the aerial parts (Tp_EtOH ) of T. patula on eggs and larvae of H. contortus, through an egg hatch test (EHT) and a larval development test (LDT). In the EHT, the EO showed 100% inhibition at 0.75 mg mL^-1 (LC₅₀ = 0.0780 mg mL^-1 ), and the Tp_EtOH showed 100% inhibition at 100 mg mL^-1 (LC₅₀ = 12.8 mg mL^-1 ). In the LDT, the EO showed 100% inhibition at 0.375 mg mL^-1 (LC₅₀ = 0.0400 mg mL^-1 ), and the Tp_EtOH showed 100% inhibition at 1.56 mg mL^-1 (LC₅₀ = 0.340 mg mL^-1 ). Compared to available literature data, the results presented here suggest that the crude extracts of T. patula have substantial potential for controlling this nematode by interrupting its life cycle and/or preventing it from reaching the infective stage.

Characterization of Ostertagia ostertagi annexin-like proteins at different developmental stages

Ostertagiosis remains an economically important parasitic disease in cattle in the temperate regions of the world. Repeated exposures to Ostertagia ostertagi in calves cause significant pathology in the abomasum but elicit little protective immunity. The larvae use the host's gastric glands as a niche for development, where the parasite completes its parasitic stages, while in the gastric glands, the larvae must down-regulate the host inflammatory immune responses. Annexin (ANX) A1, commonly found in most eukaryotes, is heavily involved in controlling anti-inflammatory responses by binding receptors on leukocytes. We hypothesized, therefore, that parasite proteins of the ANX family may be involved in host-parasite interactions during ostertagiosis. BLASTN search with the bovine ANXA1 identified two families of Oos-ANX like proteins (Oos-ANXL), each of which was highly conserved at the genetic level and identical at the amino acid sequence level. Oos-ANXL-1 is encoded by two transcripts and Oos-ANXL-2 by 20 transcripts. The present study characterized one Oos-ANXL, representing the most abundant Oos-ANXL, which was further defined as Oost-ANXL-2.1. Oos-ANXL-2.1 with a coding sequence of 519 bp was PCR-amplified, cloned, and expressed. Oos-ANXL-2.1 was immunolocalized to both L3 and adult, but not L4. The staining appeared to be associated with the gut and hypodermis in L3, but it was specifically localized to the hypodermis in adult worms. Western blots detected three protein bands in parasite lysates using anti-recombinant Oos-ANXL-2.1 antibody. Integrated optical density for each of the 3 Oos-ANXL-2s or the total Oos-ANXL-2s detected by Western blots (P < 0.05) was higher in adult worms than in L3 or L4. The results indicate that the production of Oos-ANXL-2s is developmentally regulated and most abundant in the adult worm. This rather large family of proteins could be a potential vaccine target against O. ostertagi infection and warrants further investigation.

Modelling the impacts of pasture contamination and stocking rate for the development of targeted selective treatment strategies for Ostertagia ostertagi infection in calves

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Stocking rate effect on design of targeted selective treatments (TST) was evaluated.

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Initial pasture contamination effect on the design of TST was evaluated.

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Different phenotypic traits and methods of selection for treatment were addressed.

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Benefit was assessed as weight gain/frequency of resistant alleles in helminths.

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Treatment according to threshold triggers of average daily gain was most beneficial.

A simulation study was carried out to assess whether variation in pasture contamination or stocking rate impact upon the optimal design of targeted selective treatment (TST) strategies. Two methods of TST implementation were considered: 1) treatment of a fixed percentage of a herd according to a given phenotypic trait, or 2) treatment of individuals that exceeded a threshold value for a given phenotypic trait. Four phenotypic traits, on which to base treatment were considered: 1) average daily bodyweight gain, 2) faecal egg count, 3) plasma pepsinogen, or 4) random selection. Each implementation method (fixed percentage or threshold treatment) and determinant criteria (phenotypic trait) was assessed in terms of benefit per R (BPR), the ratio of average benefit in weight gain to change in frequency of resistance alleles R (relative to an untreated population). The impact of pasture contamination on optimal TST strategy design was investigated by setting the initial pasture contamination to 100, 200 or 500 O. ostertagi L3/kg DM herbage; stocking rate was investigated at a low (3calves/ha), conventional (5 calves/ha) or high (7 calves/ha) stocking rates. When treating a fixed percentage of the herd, treatments according to plasma pepsinogen or random selection were identified as the most beneficial (i.e. resulted in the greatest BPR) for all levels of initial pasture contamination and all stocking rates. Conversely when treatments were administered according to threshold values ADG was most beneficial, and was identified as the best TST strategy (i.e. resulted in the greatest overall BPR) for all levels of initial pasture contamination and all stocking rates.

Modelling the consequences of targeted selective treatment strategies on performance and emergence of anthelmintic resistance amongst grazing calves

The development of anthelmintic resistance by helminths can be slowed by maintaining refugia on pasture or in untreated hosts. Targeted selective treatments (TST) may achieve this through the treatment only of individuals that would benefit most from anthelmintic, according to certain criteria. However TST consequences on cattle are uncertain, mainly due to difficulties of comparison between alternative strategies. We developed a mathematical model to compare: 1) the most 'beneficial' indicator for treatment selection and 2) the method of selection of calves exposed to Ostertagia ostertagi, i.e. treating a fixed percentage of the population with the lowest (or highest) indicator values versus treating individuals who exceed (or are below) a given indicator threshold. The indicators evaluated were average daily gain (ADG), faecal egg counts (FEC), plasma pepsinogen, combined FEC and plasma pepsinogen, versus random selection of individuals. Treatment success was assessed in terms of benefit per R (BPR), the ratio of average benefit in weight gain to change in frequency of resistance alleles R (relative to an untreated population). The optimal indicator in terms of BPR for fixed percentages of calves treated was plasma pepsinogen and the worst ADG; in the latter case treatment was applied to some individuals who were not in need of treatment. The reverse was found when calves were treated according to threshold criteria, with ADG being the best target indicator for treatment. This was also the most beneficial strategy overall, with a significantly higher BPR value than any other strategy, but its degree of success depended on the chosen threshold of the indicator. The study shows strong support for TST, with all strategies showing improvements on calves treated selectively, compared with whole-herd treatment at 3, 8, 13 weeks post-turnout. The developed model appeared capable of assessing the consequences of other TST strategies on calf populations.

A stochastic model to investigate the effects of control strategies on calves exposed to Ostertagia ostertagi

Predicting the effectiveness of parasite control strategies requires accounting for the responses of individual hosts and the epidemiology of parasite supra- and infra-populations. The first objective was to develop a stochastic model that predicted the parasitological interactions within a group of first season grazing calves challenged by Ostertagia ostertagi, by considering phenotypic variation amongst the calves and variation in parasite infra-population. Model behaviour was assessed using variations in parasite supra-population and calf stocking rate. The model showed the initial pasture infection level to have little impact on parasitological output traits, such as worm burdens and FEC, or overall performance of calves, whereas increasing stocking rate had a disproportionately large effect on both parasitological and performance traits. Model predictions were compared with published data taken from experiments on common control strategies, such as reducing stocking rates, the ‘dose and move’ strategy and strategic treatment with anthelmintic at specific times. Model predictions showed in most cases reasonable agreement with observations, supporting model robustness. The stochastic model developed is flexible, with the potential to predict the consequences of other nematode control strategies, such as targeted selective treatments on groups of grazing calves.

The Effect of Marshallagia marshalli on Serum Gastrin Concentrations in Experimentally Infected Lambs

:  Because there appeared to be no data available on serum gastrin concentrations in animals infected with Marshallagia marshalli, and considering the high prevalence of this parasite in livestock throughout many countries, we decided to perform research in the field using experimental infection. After surgical implantation of abomasal cannula into 10 male Baluchi sheep, each animal was orally infected with 5,000 M. marshalli larvae. Serum gastrin concentrations and abomasal pH were measured with a human ELISA kit and a PHM LE438 standard pH electrode, respectively. According to the results obtained from the study, serum gastrin increased after 14 and 21 days post-infection (dpi), while abomasal pH increased after 7 dpi and reached a maximal value 16 dpi. The increase in serum gastrin concentration was revealed 6 days after elevation in abomasal pH, which could be the result of reduced acid secretion. Generally, the present study pointed out that a limited number of M. marshalli could increase serum gastrin concentrations.

Interactions Between Nutrition and Infections With Haemonchus contortus and Related Gastrointestinal Nematodes in Small Ruminants

Interactions between host nutrition and feeding behaviour are central to understanding the pathophysiological consequences of infections of the digestive tract with parasitic nematodes. The manipulation of host nutrition provides useful options to control gastrointestinal nematodes as a component of an integrated strategy. Focussed mainly on the Haemonchus contortus infection model in small ruminants, this chapter (1) illustrates the relationship between quantitative (macro- and micro-nutrients) and qualitative (plant secondary metabolites) aspects of host nutrition and nematode infection, and (2) shows how basic studies aimed at addressing some generic questions can help to provide solutions, despite the considerable diversity of epidemiological situations and breeding systems.

A simulation model to investigate interactions between first season grazing calves and Ostertagia ostertagi

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A deterministic model to address calf—O. ostertagi interactions was developed.

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The model predicts performance and FEC for different infection intensities.

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It performs well when validated against published data.

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It does not account for calf genotypic variation.

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A future aim is to develop a stochastic model to account for between host variation.

A dynamic, deterministic model was developed to investigate the consequences of parasitism with Ostertagia ostertagi, the most prevalent and economically important gastrointestinal parasite of cattle in temperate regions. Interactions between host and parasite were considered to predict the level of parasitism and performance of an infected calf. Key model inputs included calf intrinsic growth rate, feed quality and mode and level of infection. The effects of these varied inputs were simulated on a daily basis for key parasitological (worm burden, total egg output and faecal egg count) and performance outputs (feed intake and bodyweight) over a 6 month grazing period. Data from published literature were used to parameterise the model and its sensitivity was tested for uncertain parameters by a Latin hypercube sensitivity design. For the latter each parameter tested was subject to a 20% coefficient of variation. The model parasitological outputs were most sensitive to the immune rate parameters that affected overall worm burdens. The model predicted the expected larger worm burdens along with disproportionately greater body weight losses with increasing daily infection levels. The model was validated against published literature using graphical and statistical comparisons. Its predictions were quantitatively consistent with the parasitological outputs of published experiments in which calves were subjected to different infection levels. The consequences of model weaknesses are discussed and point towards model improvements. Future work should focus on developing a stochastic model to account for calf variation in performance and immune response; this will ultimately be used to test the effectiveness of different parasite control strategies in naturally infected calf populations.

A review of the epidemiology and control of gastrointestinal nematode infections in cattle in Zimbabwe

In this review, the main gastrointestinal nematodes infecting cattle in Zimbabwe and the epidemiological factors influencing their occurrence are reviewed and discussed. Nineteen gastrointestinal nematode species that belong to seven families have been found to occur in cattle in Zimbabwe. The main genera reported to date are Cooperia, Haemonchus, Trichostrongylus and Oesophagostomum and the dominant species are Cooperia pectinata, Cooperia punctata, Haemonchus placei and Trichostrongylus axei. The mixed infection by several species from the genera is the cause of parasitic gastroenteritis in cattle in Zimbabwe. Production and husbandry practices, season, host age and environment are considered to be the main factors that influence gastrointestinal nematode infection in cattle. The geographical distribution of the gastrointestinal nematodes is also reviewed in relation to the climatic conditions of the country. Various control options are discussed and how they are applicable to the Zimbabwean situation. Based on reports and existing data on the epidemiological features of the gastrointestinal nematode infection in cattle, practical control measures are critically reviewed and recommendations are made for a national control programme.

Sesquiterpene lactone containing extracts from two cultivars of forage chicory (Cichorium intybus) show distinctive chemical profiles and in vitro activity against Ostertagia ostertagi

The study investigated direct anthelmintic effects of sesquiterpene lactones (SL)-containing extracts from forage chicory against free-living and parasitic stages of Ostertagia ostertagi. Freeze-dried leaves from chicory cultivars 'Spadona' and 'Puna II' were extracted using methanol/water. Total SL were further fractionated by solid-phase extraction and resulting extracts were characterised by high-performance liquid chromatography (HPLC). O. ostertagi eggs from faeces of mono-infected calves were hatched and L1 were used in a larval feeding inhibition assay (LFIA), while cultured L3 were used in a larval exsheathment inhibition assay (LEIA). Adult worms were immediately recovered after slaughter and used for motility inhibition assays (AMIA). Electron microscopy (EM) was performed on adult O. ostertagi exposed to 1000 μg extract mL(-1) of both chicory cultivars. In all assays, decreasing concentrations of SL-containing extracts in PBS (1% DMSO) were tested in replicates with 1% DMSO in PBS as negative controls. HPLC demonstrated similar concentrations of most SL in both extracts. However, Spadona-extract contained significantly higher concentrations of 11, 13-dihydro-8-deoxylactucin (P = 0.01), while Puna II-extract had increased levels of 11, 13-dihydrolactucin (P < 0.0001). In the LFIA, both extracts reduced larval feeding at increasing concentrations, but Spadona-extract showed higher potency confirmed by significantly lower EC50 (P < 0.0001). In the LEIA, neither of the two extracts interfered with the exsheathment of L3 (P > 0.05). In the AMIA, both SL-containing extracts induced a dose-dependent effect but Spadona-extract showed greater activity and exerted faster worm paralysis than Puna II-extract with significantly lower EC50 (P < 0.0001). No cuticular damage was observed by EM in worms exposed to any of the extracts. We have demonstrated that SL-containing extracts from forage chicory can inhibit feeding of free-living larvae and exert direct effects against parasitic stages of O. ostertagi. Our results may contribute to the identification of natural anti-parasitic compounds and to interpret the in vivo anthelmintic effects of forage chicory.

Metagenome plasticity of the bovine abomasal microbiota in immune animals in response to Ostertagia ostertagi infection

Infections in cattle by the abomasal nematode Ostertagia ostertagi result in impaired gastrointestinal function. Six partially immune animals were developed using multiple drug-attenuated infections, and these animals displayed reduced worm burdens and a slightly elevated abomasal pH upon reinfection. In this study, we characterized the abomasal microbiota in response to reinfection using metagenomic tools. Compared to uninfected controls, infection did not induce a significant change in the microbial community composition in immune animals. 16S rRNA gene-based phylogenetic analysis identified 15 phyla in the bovine abomasal microbiota with Bacteroidetes (60.5%), Firmicutes (27.1%), Proteobacteria (7.2%), Spirochates (2.9%), and Fibrobacteres (1.5%) being the most predominant. The number of prokaryotic genera and operational taxonomic units (OTU) identified in the abomasal microbial community was 70.8±19.8 (mean ± SD) and 90.3±2.9, respectively. However, the core microbiome comprised of 32 genera and 72 OTU. Infection seemingly had a minimal impact on the abomasal microbial diversity at a genus level in immune animals. Proteins predicted from whole genome shotgun (WGS) DNA sequences were assigned to 5,408 Pfam and 3,381 COG families, demonstrating dazzling arrays of functional diversity in bovine abomasal microbial communities. However, none of COG functional classes were significantly impacted by infection. Our results demonstrate that immune animals may develop abilities to maintain proper stability of their abomasal microbial ecosystem. A minimal disruption in the bovine abomasal microbiota by reinfection may contribute equally to the restoration of gastric function in immune animals.

The anthelmintic effect of plant extracts on Haemonchus contortus and Strongyloides venezuelensis

The indiscriminate use of anthelmintics has resulted in the establishment of parasite resistance. Thus, this study aimed to evaluate the in vitro antiparasitic effect of plant extracts on Haemonchus contortus in sheep and the in vivo effect on Strongyloides venezuelensis in Rattus norvegicus. The plant extracts from Piper tuberculatum, Lippia sidoides, Mentha piperita, Hura crepitans and Carapa guianensis, produced at different research institutions, were chemically analyzed and evaluated through the egg hatch test (EHT) and larval development test (LDT) in H. contortus. P. tuberculatum (150 and 250 mg kg(-1) of body weight) was evaluated for its anthelmintic action on R. norvegicus experimentally infected with S. venezuelensis. In the EHT, the LC(50) and LC(90) of the extracts were respectively as follows: 0.031 and 0.09 mg mL(-1) for P. tuberculatum, 0.04 and 0.13 mg mL(-1) for L. sidoides, 0.037 and 0.10 mg mL(-1) for M. piperita, 2.16 and 17.13 mg mL(-1) for H. crepitans and 2.03 × 10(-6) and 1.22 × 10(-12) mg mL(-1) for C. guianensis. In the LDT, the LC(50) and LC(90) were respectively: 0.02 and 0.031 mg mL(-1) for P. tuberculatum, 0.002 and 0.04 mg mL(-1) for L. sidoides, 0.018 and 0.03 mg mL(-1) for M. piperita, 0.36 and 0.91 mg mL(-1) for H. crepitans and 17.65 and 1890 mg mL(-1) for C. guianensis. The extract of P. tuberculatum showed the following substances: piperamides as (Z)-piplartine, (E)-piplartine, 8,9-dihydropiplartine, piperine, 10,11-dihydropiperine, 5,6 dihydropiperlongumine and pellitorine. The major compounds of the oils were thymol (76.6%) for L. sidoides, menthol (27.5%) for M. piperita and oleic acid (46.8%) for C. guianensis. Regarding the in vivo test, neither dose of P. tuberculatum caused any significant reduction (P>0.05) in worm burden and fecal egg counts compared with the control group. We conclude that the extracts of P. tuberculatum, L. sidoides and M. piperita have effective activity when tested in vitro, but the doses of the extract of P. tuberculatum have no effect when employed in in vivo tests.

Evaluation of anthelmintic activity of Iris hookeriana against gastrointestinal nematodes of sheep

The objective of this study was to evaluate the anthelmintic efficacy of Iris hookeriana Linn. rhizome against gastrointestinal nematodes of sheep. A worm motility inhibition assay was used for in vitro study and a faecal egg count reduction assay was used for an in vivo study. The in vitro study revealed anthelmintic effects of crude aqueous extracts and crude ethanolic extracts on live Trichuris ovis worms (P ≤ 0.05) as evident from their paralysis and/or death at 8 h after exposure. The aqueous extracts of I. hookeriana resulted in a mean worm motility inhibition of 54.0%, while ethanolic extracts resulted in a mean worm motility inhibition of 84.6%. The mean mortality index of aqueous extracts was 0.55, while for ethanolic extracts it was 0.85. The lethal concentration 50 for aqueous extracts was 0.45 mg ml− 1 and for ethanolic extracts it was 0.15 mg ml− 1. The in vivo anthelmintic activity of aqueous and ethanolic extracts of I. hookeriana in sheep naturally infected with mixed species of gastrointestinal nematodes demonstrated a maximum (45.62%) egg count reduction in sheep treated with ethanolic extracts at 2 g kg− 1 body weight on day 10 after treatment, closely followed by ethanolic extracts at 1 g kg− 1 body weight on day 10 after treatment (43.54% egg count reduction). The aqueous extracts resulted in a maximum of 31.53% reduction in faecal egg counts on day 10 after treatment with 1 g kg− 1 body weight. Thus ethanolic extracts exhibited greater anthelmintic activity under both in vitro and in vivo conditions; this could be due to the presence of alcohol-soluble active ingredients in I. hookeriana. From the present study it can be suggested that I. hookeriana rhizome exhibited significant anthelmintic activity against gastrointestinal nematodes of sheep and has the potential to contribute to the control of gastrointestinal nematode parasites of small ruminants.

Transcriptional profiling of Ovis aries identifies Ovar-DQA1 allele frequency differences between nematode-resistant and susceptible selection lines

Gastrointestinal nematodes are a major cause of disease in grazing livestock; however, individual animals differ in their response to infection. To identify genes whose expression correlates with resistance status, transcriptional profiling of resistant and susceptible sheep was undertaken. Transcription profiles were taken at three time points during the growth of lambs. The number of genes differentially expressed increased as animals were exposed to longer nematode challenge. Almost 300 genes, with a variety of functions, were differentially expressed overall, although genes more highly expressed in resistant animals typically had major histocompatibility complex (MHC) II, free radical scavenging or smooth muscle-specific functions. The Ovar-DQA1 gene was 8.4-fold more highly expressed in resistant animals. This was due in part to a higher frequency of DQA1 null alleles in susceptible animals. The null allele of DQA1 was also associated with susceptibility in a separate selection flock, presenting the hypothesis that failure to present parasite antigens to immune cells led to nematode susceptibility. To test this hypothesis, commercial rams from three breeds were genotyped for the null allele of DQA1. The homozygous null allele was associated with susceptibility in only one of the three breeds tested indicating that the null allele does not cause susceptibility to intestinal parasites per se but is probably in linkage disequilibrium with additional polymorphisms in the MHC region. A combination of these polymorphisms may contribute to susceptibility in some populations. The extent of linkage disequilibrium between polymorphisms may vary from breed to breed or population to population.

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.

Low-level parasitic worm burdens may reduce body condition in free-ranging red deer (Cervus elaphus)

Regulation of ungulate populations by parasites relies on establishing a density-dependent relationship between infection and vital demographic rates which may act through the effect of parasites on body condition. We examine evidence for parasite impacts in 285 red deer (Cervus elaphus) harvested during 1991 and 1992 on the Isle of Rum. In the abomasa, prevalence of nematodes was 100% and the most abundant genus observed were Ostertagia species, however, mean intensity of infection was low (less than 1000) relative to other studies. Additional species, also present in low numbers, included Nematodirus spp., Capillaria spp., Cooperia spp., Monieza expanza, Oesophagostomum venulosum and Trichuris ovis. Lungworm (Dictyocaulus spp.) and tissue worm (Elaphostronygylus cervi) larvae were also observed in faecal samples. There was no evidence for acquired immunity to abomasal nematodes. Despite low levels of infection, both adult male and female deer showed significant negative correlation between indices of condition (kidney fat index, dressed carcass weight and larder weight) and intensity of Ostertagia spp. infection. However, there was no evidence that pregnancy rate in females was related to intensity of infection. For calves, there was no relationship between body condition and intensity of infection. The apparent subclinical effects of low-level parasite infection on red deer performance could alternatively be due to animals in poorer nutritional state being more susceptible to infection. Either way the results suggest that further studies of wild populations are justified, in particular where high local host densities exist or alternative ungulate hosts are present, and, where experimental treatments are tractable.

The effect of dietary polyunsaturated fatty acids (PUFA) on infection with the nematodes Ostertagia ostertagi and Cooperia oncophora in calves

Diet-induced changes in the polyunsaturated fatty acid (PUFA) content of immune cells influences the immune phenotype that develops following infection. The aim of this study was to examine the effect of manipulating dietary PUFA supply on tissue fatty acids composition and immunity to a mixed infection with an abomasal and an intestinal nematode parasite in calves. Calves (n=24) were allocated into two treatment groups and fed 25 g/day of either fish oil (n-3 group) or a binary mixture of palm/rapeseed oil (normal group) as a supplement in milk replacer. Within each treatment group eight calves were infected with 2000 L3 Ostertagia ostertagi and Cooperia oncophora, three times per week for 8 weeks, the remaining calves were pair-fed uninfected controls. Faecal egg counts (FEC) were carried out twice weekly. At slaughter, the whole gut was removed intact for worm counts and tissue samples were taken for fatty acid analysis. Samples of abomasum, duodenum and mid-gut were also collected for immunohistological analysis. FEC were not significantly influenced by oil supplement but tended to remain higher in the palm/rapeseed oil-fed group (normal infected). The number of intestinal immature worms was significantly (p<0.05) higher in the n-3 group. Mucosal mast cell (MMC) and eosinophil numbers were significantly increased (p<0.05) by infection and were significantly lower (p<0.05) in the intestinal tissue of the fish oil supplemented and infected group (n-3 infected group). These results suggest that feeding an n-3 PUFA-rich supplement (fish oil) can influence cellular mediators of immunity to nematode infection. This is the first report of the establishment of patency and the subsequent development of immunity to a mixed infection with O. ostertagi and C. oncophora in calves undergoing early rumen development. The trend in the FEC, MMC and eosinophil numbers in the n-3 group suggests that decreasing the dietary n-6/n-3 PUFA ratio may be a worthwhile immunonutritional strategy for potentiating the immune response to nematode parasite infection in the calf.

Pathophysiology of abomasal parasitism: is the host or parasite responsible?

Nematode larvae developing within the glands cause local loss of parietal cells and mucous cell hyperplasia whereas reduced acid secretion, increased serum gastrin and pepsinogen concentrations and generalized histological changes are associated with parasites in the abomasal lumen. Parietal cells with dilated canaliculi and/or degenerative changes typical of necrosis are present soon after the transplantation of adult worms, and abomasal secretion is also affected. Anaerobic bacteria survive in greater numbers as the pH rises, with bacterial densities becoming similar to ruminal populations at an abomasal pH of 4 and above. Failure to lyse bacteria may affect adversely the nutrition of the host. The parasites may initiate the pathophysiology through the release of excretory/secretory (ES) products which either act directly on parietal cells or indirectly through enterochromaffin-like (ECL) cells by provoking inflammation or by disrupting the protective mucosal defence system. Parietal cell dysfunction is proposed as a key event which leads to loss of mature chief cells and mucous cell hyperplasia, as well as hypergastrinaemia. Inflammation increases circulating pepsinogen concentrations and may also contribute to increased gastrin secretion. Stimulation of mucosal proliferation and differentiation of parietal cells in the isthmus by the raised serum gastrin levels will be beneficial by generating a new population of active parietal cells and adequate acid secretion.

A model for study of lungworm (Dictyocaulus sp.) and gastrointestinal nematode infection in young red deer (Cervus elaphus)

A model of sub-clinical parasitism in young red deer, using concurrent trickle infections of lungworm (Dictyocaulus sp.) and mixed gastro-intestinal (GI) nematodes of deer-origin was evaluated. 20 parasite-free deer calves were artificially reared indoors from 4 days of age. A further five calves were naturally reared on pasture with their dams, treated with anthelmintic and brought indoors at 3-4 months. At 4-4.5 months of age they were individually housed and allocated to five groups (n=5). Groups were dosed 3 x per week, for 9 weeks with 0, 100 and 500, 200 and 1000 (2 groups), 400 and 2000 infective larvae of lungworm and mixed GI nematodes, respectively, cultured from deer faeces. Liveweight and voluntary feed intake measurements and faecal and blood samples were taken weekly. In the fourth week following cessation of trickle infection, deer were euthanased and lung and GI nematodes recovered. Both lungworm and GI nematode infections became patent at Week 4 of infection. Maximum group arithmetic mean faecal egg counts were 100-190 epg. Maximum group arithmetic mean faecal lungworm larval counts were 58-123 lpg. Group arithmetic mean nematode counts at slaughter ranged from 439-806 for GI nematodes and 31-73 for lungworm, respectively. Despite low nematode counts, reduced liveweight gain, voluntary feed intake and serum albumin concentration, elevated serum pepsinogen, gastrin and globulin concentrations and elevated peripheral eosinophil counts and slight haemoconcentration, but no clinical signs, were observed. The reduction in liveweight gain was related to the reduction in voluntary feed intake (r2=0.83; p<0.088). Naturally-reared deer had similar liveweight gains, voluntary feed intake and nematode counts to artificially-reared deer. Thus, methods of infection to produce concurrent sub-clinical lungworm and GI nematode burdens for study of sub-clinical parasitism in young deer have been defined.

Pathophysiology of infection with gastrointestinal nematodes in domestic ruminants: recent developments

Infection with gastrointestinal nematodes, particularly Ostertagia species in domestic ruminants, continues to represent an important cause of impaired productivity in temperate parts of the world. The mechanisms responsible for such losses include changes in feed intake, gastrointestinal function, protein, energy and mineral metabolism, and body composition, and were described in detail at the last Ostertagia Workshop (Fox, M.T. 1993. Pathophysiology of infection with Ostertagia ostertagi in cattle. Vet. Parasitol. 46, 143-158). Since then, research into the pathophysiology of infection has focused on three main areas: mechanisms of appetite depression; changes in gastrointestinal function; and alterations in protein metabolism. Studies on the mechanisms responsible for appetite depression in Ostertagia-infected cattle have continued to support a close association between impaired feed intake and elevated blood gastrin concentrations. Alternative explanations will have to be sought, however, to account for the drop in feed intake associated with intestinal parasitism in which blood gastrin levels normally remain unaltered. Such work in sheep, and more recently in laboratory animals, has shown that central satiety signals are associated with inappetance accompanying intestinal infections, rather than changes in peripheral peptide levels. Changes in gastrointestinal function have also attracted attention, particularly the mechanisms responsible for increases in certain gut secretions, notably pepsinogen and gastrin. Elegant experimental studies have established that the gradient in pepsinogen concentration between abomasal mucosa and local capillaries could alone account for the increase in blood concentrations seen in Type 1 ostertagiosis. Additional factors, such as increases in capillary permeability and in surface area, probably contribute to such responses in cases of Type 2 disease. The increase in blood gastrin concentrations that accompanies Ostertagia infections in cattle is associated with the concurrent rise in abomasal pH. However, in sheep, additional factors appear to contribute to the hypergastrinaemia which may occur independent of parasite-induced changes in gastric pH. Alterations in protein metabolism have been well documented in ruminants harbouring monospecific infections with either abomasal or intestinal nematodes. More recently, however, the effects of dual abomasal and intestinal infections have been investigated and demonstrated that the host is able to compensate for impaired abomasal digestion provided that the intestinal parasite burden does not occupy the main site of digestion and absorption in the latter organ. An alternative method of improving the host's protein balance, dietary supplementation, has been shown not only to improve productivity, but also to enhance the innate resistance of susceptible breeds of sheep to Haemonchus and to accelerate the development of immunity to Ostertagia in lambs.

Production responses following strategic parasite control in a beef cow/calf herd

Strategic parasite control has been reported to improve performance in a beef cow/calf herd that does not demonstrate clinical parasitism. This study was conducted to determine if strategic anthelmintic treatment at turnout and at midsummer would improve growth and reproduction. Two cow/calf groups of similar composition were grazed on separate, but equivalent pastures in the spring, and at midsummer, they were moved to new pastures. The treated group was given fenbendazole at tumout (cows) and at midsummer (cows and calves). The control group was not treated. The study was repeated in the following year. Across both years of the study, parasite egg counts were substantially reduced in both the treated cows (P < 0.005) and treated calves (P < 0.0001). The calves in the treated group significantly (P < 0.0001) outgained the control calves in both years of the study by 19.3 kg and 13.2 kg, respectively. Average daily gain (ADG) after adjusting for birth weight and birth date for treated calves was 0.13 kg greater than for control calves (0.83 vs 0.70) for the 2-year study (P < 0.0001) There was also a significant (P = 0.0357) increase in the reproductive performance of the cows. The pregnancy rate averaged across years was 94% for the treated cows compared to 82% for the control animals.

Implications of nutrition for the ability of ruminants to withstand gastrointestinal nematode infections

Resistance and resilience of the ruminant host to gastrointestinal (GI) parasitic nematode infections are influenced by many factors, including nutrition. This review examines the effects of host nutrition on the ability of ruminants to withstand GI nematode infections. Firstly the effects of infection on host metabolism are summarised briefly. An important factor in the pathogenesis is a reduction in feed intake by the host. Gut nematodes also increase endogenous protein losses, which result in net loss of amino acids to the parasitised host, though energy and mineral metabolism are also perturbed. The indications are that the major nutritional change is in protein metabolism. Resilience (the ability of an animal to withstand the effects of infection) can be enhanced markedly by increasing metabolisable protein supply and to a lesser extent metabolisable energy supply. Resistance to GI nematodes (ability of host to prevent establishment and/or development of infection) is also influenced by diet, particularly metabolisable protein supply. While there do not appear to be any effects of host nutrition on establishment of infective larvae, the rate of rejection of adult worms can be enhanced by improved nutrition. The exact nutritional requirements or the mechanisms involved are not known. It appears that the effects of improving nutritional status on host resilience are more clearly defined than effects on host resistance. The implication of changes in host resistance with nutritional state for host productivity need to be better described. Understanding the role of nutrition in improving both resistance and resilience of the host to GI parasites will be important if producers are to make better use of host acquired immunity and reduce dependence on pesticides for prophylaxis.