The Role of Autophagy in Chemical Proteasome Inhibition Model of Retinal Degeneration

We recently demonstrated that chemical proteasome inhibition induced inner retinal degeneration, supporting the pivotal roles of the ubiquitin–proteasome system in retinal structural integrity maintenance. In this study, using beclin1-heterozygous (Becn1-Het) mice with autophagic dysfunction, we tested our hypothesis that autophagy could be a compensatory retinal protective mechanism for proteasomal impairment. Despite the reduced number of autophagosome, the ocular tissue morphology and intraocular pressure were normal. Surprisingly, Becn1-Het mice experienced the same extent of retinal degeneration as was observed in wild-type mice, following an intravitreal injection of a chemical proteasome inhibitor. Similarly, these mice equally responded to other chemical insults, including endoplasmic reticulum stress inducer, N-methyl-D-aspartate, and lipopolysaccharide. Interestingly, in cultured neuroblastoma cells, we found that the mammalian target of rapamycin-independent autophagy activators, lithium chloride and rilmenidine, rescued these cells against proteasome inhibition-induced death. These results suggest that Becn1-mediated autophagy is not an effective intrinsic protective mechanism for retinal damage induced by insults, including impaired proteasomal activity; furthermore, autophagic activation beyond normal levels is required to alleviate the cytotoxic effect of proteasomal inhibition. Further studies are underway to delineate the precise roles of different forms of autophagy, and investigate the effects of their activation in rescuing retinal neurons under various pathological conditions.

Donor monocyte-derived macrophages promote human acute graft-versus-host disease

Myelopoiesis is invariably present and contributes to pathology in animal models of graft-versus-host disease (GVHD). In humans, a rich inflammatory infiltrate bearing macrophage markers has also been described in histological studies. In order to determine the origin, functional properties, and role in pathogenesis of these cells, we isolated single-cell suspensions from acute cutaneous GVHD and subjected them to genotype, transcriptome, and in vitro functional analysis. A donor-derived population of CD11c⁺CD14⁺ cells was the dominant population of all leukocytes in GVHD. Surface phenotype and NanoString gene expression profiling indicated the closest steady-state counterpart of these cells to be monocyte-derived macrophages. In GVHD, however, there was upregulation of monocyte antigens SIRPα and S100A8/9 transcripts associated with leukocyte trafficking, pattern recognition, antigen presentation, and costimulation. Isolated GVHD macrophages stimulated greater proliferation and activation of allogeneic T cells and secreted higher levels of inflammatory cytokines than their steady-state counterparts. In HLA-matched mixed leukocyte reactions, we also observed differentiation of activated macrophages with a similar phenotype. These exhibited cytopathicity to a keratinocyte cell line and mediated pathological damage to skin explants independently of T cells. Together, these results define the origin, functional properties, and potential pathogenic roles of human GVHD macrophages.

A humanized mouse model to study mast cells mediated cutaneous adverse drug reactions

Recently a G‐protein‐coupled receptor, MAS Related GPR Family Member X2 (MRGPRX2), was identified as a specific receptor on human mast cells responsible for IgE independent adverse drug reactions (ADR). Although a murine homologue, Mrgprb2, has been identified for this receptor, its affinity for many ADR‐causing drugs is poor making it difficult to undertake in vivo studies to examine mechanisms of ADR and to develop therapeutic strategies. Here, we have created humanized mice capable of generating MRGPRX2‐expressing human MCs allowing for the study of MRGPRX2 MCs‐mediated ADR in vitro as well as in vivo. Humanized mice were generated by hydrodynamic‐injection of plasmids expressing human GM‐CSF and IL‐3 into NOD‐scid IL2R‐γ^−/− strain of mice that had been transplanted with human hematopoietic stem cells. These GM/IL‐3 humice expressed high numbers of tissue human MCs but the MRGPRX2 receptor expressed in MCs were limited to few body sites including the skin. Importantly, large numbers of MRGPRX2‐expressing human MCs could be cultured from the bone marrow of GM/IL‐3 humice revealing these mice to be an important source of human MCs for in vitro studies of MRGPRX2‐related MCs activities. When GM/IL‐3 humice were exposed to known ADR causing contrast agents (meglumine and gadobutrol), the humice were found to experience anaphylaxis analogous to the clinical situation. Thus, GM/IL‐3 humice represent a valuable model for investigating in vivo interactions of ADR‐causing drugs and human MCs and their sequelae, and these mice are also a source of human MRGPRX2‐expressing MCs for in vitro studies.

Ezh2 Controls Skin Tolerance through Distinct Mechanisms in Different Subsets of Skin Dendritic Cells

Ezh2, a well-established epigenetic repressor, can down-regulate leukocyte inflammatory responses, but its role in cutaneous health remains elusive. Here we demonstrate that Ezh2 controls cutaneous tolerance by regulating Langerhans cell (LC) transmigration across the epidermal basement membrane directly via Talin1 methylation. Ezh2 deficiency impaired disassembly of adhesion structures in LCs, leading to their defective integrin-dependent emigration from the epidermis and failure in tolerance induction. Moreover, mobilization of Ezh2-deficient Langerin^– dermal dendritic cells (dDCs) via high-dose treatment with a weak allergen restored tolerance, which is associated with an increased tolerogenic potential of Langerin^– dDCs likely due to epigenetic de-repression of Aldh in the absence of Ezh2. Our data reveal novel roles for Ezh2 in governing LC- and dDC-mediated host protection against cutaneous allergen via distinct mechanisms.

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Ezh2 regulates LC transmigration across basement membrane via Talin1 methylation

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Ezh2-mediated LC migration is required for cutaneous tolerance induction

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Ezh2 represses Aldh epigenetically in dermal DCs

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Ezh2-deficient dermal DCs exhibit increased tolerogenicity

Biallelic interferon regulatory factor 8 mutation: A complex immunodeficiency syndrome with dendritic cell deficiency, monocytopenia, and immune dysregulation

BACKGROUND

The homozygous K108E mutation of interferon regulatory factor 8 (IRF8) is reported to cause dendritic cell (DC) and monocyte deficiency. However, more widespread immune dysfunction is predicted from the multiple roles ascribed to IRF8 in immune cell development and function.

OBJECTIVE

We sought to describe the effect on hematopoiesis and immunity of the compound heterozygous R83C/R291Q mutation of IRF8, which is present in a patient with recurrent viral infection, granuloproliferation, and intracerebral calcification.

METHODS

Variant IRF8 alleles were identified by means of exome sequencing, and their function was tested by using reporter assays. The cellular phenotype was studied in detail by using flow cytometry, functional immunologic assay transcriptional profiling, and antigen receptor profiling.

RESULTS

Both mutations affected conserved residues, and R291Q is orthologous to R294, which is mutated in the BXH2 IRF8-deficient mouse. R83C showed reduced nuclear translocation, and neither mutant was able to regulate the Ets/IRF composite element or interferon-stimulated response element, whereas R291Q retained BATF/JUN interactions. DC deficiency and monocytopenia were observed in blood, dermis, and lung lavage fluid. Granulocytes were consistently increased, dysplastic, and hypofunctional. Natural killer cell development and maturation were arrested. TH1, TH17, and CD8+ memory T-cell differentiation was significantly reduced, and T cells did not express CXCR3. B-cell development was impaired, with fewer memory cells, reduced class-switching, and lower frequency and complexity of somatic hypermutation. Cell-specific gene expression was widely disturbed in interferon- and IRF8-regulated transcripts.

CONCLUSIONS

This analysis defines the clinical features of human biallelic IRF8 deficiency, revealing a complex immunodeficiency syndrome caused by DC and monocyte deficiency combined with widespread immune dysregulation.

A Novel Human Systemic Lupus Erythematosus Model in Humanised Mice

Mouse models have contributed to the bulk of knowledge on Systemic Lupus Erythematosus (SLE). Nevertheless, substantial differences exist between human and mouse immune system. We aimed to establish and characterise a SLE model mediated by human immune system. Injection of pristane into immunodeficient mice reconstituted with human immune system (humanised mice) recapitulated key SLE features, including: production of human anti-nuclear autoantibodies, lupus nephritis, and pulmonary serositis. There was a reduction in the number of human lymphocytes in peripheral blood, resembling lymphopenia in SLE patients. Concurrently, B cells and T cells were systemically hyperactivated, with a relative expansion of CD27⁺ and CD27⁻IgD⁻ memory B cells, increased number of plasmablasts/plasma cells, and accumulation of effector memory T cells. There was also an increased production of human pro-inflammatory cytokines, including: IFN-γ, IL-8, IL-18, MCP-1, and IL-6, suggesting their role in SLE pathogenesis. Increased expression of type I IFN signature genes was also found in human hepatocytes. Altogether, we showed an SLE model that was mediated by human immune system, and which recapitulated key clinical and immunological SLE features. The advancements of humanised mice SLE model would provide an in vivo platform to facilitate translational studies and pre-clinical evaluations of human-specific mechanisms and immunotherapies.

Mapping the human DC lineage through the integration of high-dimensional techniques

Dendritic cells (DC) are professional antigen-presenting cells that orchestrate immune responses. The human DC population comprises two main functionally specialized lineages, whose origins and differentiation pathways remain incompletely defined. Here, we combine two high-dimensional technologies-single-cell messenger RNA sequencing (scmRNAseq) and cytometry by time-of-flight (CyTOF)-to identify human blood CD123⁺CD33⁺CD45RA⁺ DC precursors (pre-DC). Pre-DC share surface markers with plasmacytoid DC (pDC) but have distinct functional properties that were previously attributed to pDC. Tracing the differentiation of DC from the bone marrow to the peripheral blood revealed that the pre-DC compartment contains distinct lineage-committed subpopulations, including one early uncommitted CD123^high pre-DC subset and two CD45RA⁺CD123^low lineage-committed subsets exhibiting functional differences. The discovery of multiple committed pre-DC populations opens promising new avenues for the therapeutic exploitation of DC subset-specific targeting.

Isolation of Human Skin Dendritic Cell Subsets

Dendritic cells (DCs) are specialized leukocytes with antigen-processing and antigen-presenting functions. DCs can be divided into distinct subsets by anatomical location, phenotype and function. In human, the two most accessible tissues to study leukocytes are peripheral blood and skin. DCs are rare in human peripheral blood (<1 % of mononuclear cells) and have a less mature phenotype than their tissue counterparts (MacDonald et al., Blood. 100:4512-4520, 2002; Haniffa et al., Immunity 37:60-73, 2012). In contrast, the skin covering an average total surface area of 1.8 m(2) has approximately tenfold more DCs than the average 5 L of total blood volume (Wang et al., J Invest Dermatol 134:965-974, 2014). DCs migrate spontaneously from skin explants cultured ex vivo, which provide an easy method of cell isolation (Larsen et al., J Exp Med 172:1483-1493, 1990; Lenz et al., J Clin Invest 92:2587-2596, 1993; Nestle et al., J Immunol 151:6535-6545, 1993). These factors led to the extensive use of skin DCs as the "prototype" migratory DCs in human studies. In this chapter, we detail the protocols to isolate DCs and resident macrophages from human skin. We also provide a multiparameter flow cytometry gating strategy to identify human skin DCs and to distinguish them from macrophages.

Human skin dendritic cells in health and disease

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Human skin dendritic cells (DCs) are heterogenous and functionally specialised.

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Factor XIIIa+ dermal dendrocytes are resident dermal macrophages.

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Dermal CD14+ cells, previously defined as DCs, are monocyte-derived macrophages.

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Dynamic changes occur in the composition of recruited ‘inflammatory’ DCs and resident DCs in inflamed skin.

Dendritic cells (DCs) are specialized antigen presenting cells abundant in peripheral tissues such as skin where they function as immune sentinels. Skin DCs migrate to draining lymph node where they interact with naïve T cells to induce immune responses to microorganisms, vaccines, tumours and self-antigens. In this review, we present the key historical developments and recent advances in human skin DC research. We also integrate the current understanding on the origin and functional specializations of DC subsets in healthy skin with findings in inflammatory skin diseases focusing on psoriasis and atopic eczema. A comprehensive understanding of the dynamic changes in DC subsets in health and disease will form a strong foundation to facilitate the clinical translation of DC-based therapeutic and vaccination strategies.

Human dermal CD14⁺ cells are a transient population of monocyte-derived macrophages

Dendritic cells (DCs), monocytes, and macrophages are leukocytes with critical roles in immunity and tolerance. The DC network is evolutionarily conserved; the homologs of human tissue CD141^hiXCR1⁺CLEC9A⁺ DCs and CD1c⁺ DCs are murine CD103⁺ DCs and CD64⁻CD11b⁺ DCs. In addition, human tissues also contain CD14⁺ cells, currently designated as DCs, with an as-yet unknown murine counterpart. Here we have demonstrated that human dermal CD14⁺ cells are a tissue-resident population of monocyte-derived macrophages with a short half-life of <6 days. The decline and reconstitution kinetics of human blood CD14⁺ monocytes and dermal CD14⁺ cells in vivo supported their precursor-progeny relationship. The murine homologs of human dermal CD14⁺ cells are CD11b⁺CD64⁺ monocyte-derived macrophages. Human and mouse monocytes and macrophages were defined by highly conserved gene transcripts, which were distinct from DCs. The demonstration of monocyte-derived macrophages in the steady state in human tissue supports a conserved organization of human and mouse mononuclear phagocyte system.

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Human dermal CD14⁺ cells are a transient population of macrophages

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Dermal CD14⁺ cells are derived from circulating blood monocytes

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Human CD14⁺ cells are homologous to murine CD11b⁺CD64⁺ monocyte-derived macrophages

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Human and mouse mononuclear phagocyte network organization is conserved

Penumbral mismatch is underestimated using standard volumetric methods and this is exacerbated with time

BACKGROUND AND AIMS

The mismatch between perfusion weighted images (PWI) and diffusion weighted images (DWI) using MR is increasingly being applied in patient selection for therapeutic trials. Two approaches to the calculation of the mismatch volume exist--the commonly used volumetric and the more precise co-registration method, the latter of which considers lesion topography. That there are differences in the mismatch volume analysed by each method and that these are time dependent was hypothesised.

METHODS

Patients within 48 h of ischaemic stroke onset had baseline MR PWI/DWI mismatch and T2 outcome volumes at 3 months. Volumetric mismatch volume was defined as PWI minus DWI lesion. Co-registration mismatch volume was defined as the PWI defect lesion not overlapped by the co-registered DWI lesion.

RESULTS

72 patients of median age 74.0 years were studied. Median baseline MR was at 5.9 h (IQR 3.0, 20.4 h) after stroke onset. Consistent underestimation of the mismatch volume occurred using the volumetric method (volumetric median 9.3 ml, IQR 0, 63 ml; co-registration median 20.1 ml, IQR 3.2, 69.8 ml; p<0.0001). This difference increased with time from stroke onset (p = 0.006).

CONCLUSIONS

Volumetric analysis consistently underestimates the PWI/DWI mismatch volume compared with the more precise co-registration method. This effect increases with time.

Activated dectin-1 localizes to lipid raft microdomains for signaling and activation of phagocytosis and cytokine production in dendritic cells

Lipid rafts are plasma membrane microdomains that are enriched in cholesterol, glycosphingolipids, and glycosylphosphatidylinositol-anchored proteins and play an important role in the signaling of ITAM-bearing lymphocyte antigen receptors. Dectin-1 is a C-type lectin receptor (CLR) that recognizes beta-glucan in the cell walls of fungi and triggers signal transduction via its cytoplasmic hemi-ITAM. However, it is not known if similar to antigen receptors, Dectin-1 would also signal via lipid rafts and if the integrity of lipid raft microdomains is important for the physiological functions mediated by Dectin-1. We demonstrate here using sucrose gradient ultracentrifugation and confocal microscopy that Dectin-1 translocates to lipid rafts upon stimulation of dendritic cells (DCs) with the yeast derivative zymosan or beta-glucan. In addition, two key signaling molecules, Syk and PLCgamma2 are also recruited to lipid rafts upon the activation of Dectin-1, suggesting that lipid raft microdomains facilitate Dectin-1 signaling. Disruption of lipid raft integrity with the synthetic drug, methyl-beta-cyclodextrin (betamD) leads to reduced intracellular Ca2+ flux and defective Syk and ERK phosphorylation in Dectin-1-activated DCs. Furthermore, betamD-treated DCs have significantly attenuated production of IL-2, IL-10, and TNFalpha upon Dectin-1 engagement, and they also exhibit impaired phagocytosis of zymosan particles. Taken together, the data indicate that Dectin-1 and perhaps also other CLRs are recruited to lipid rafts upon activation and that the integrity of lipid rafts is important for the signaling and cellular functions initiated by this class of innate receptors.

Resistance to benzimidazole anthelmintics in equine strongyles. 1. Frequency, geographical distribution and relationship between occurrence, animal husbandry procedures and anthelmintic usage

A survey was conducted to determine whether benzimidazole resistant populations of equine strongyles are present in New South Wales and north central Victoria; what is their frequency and geographical distribution; which species are involved; and whether different methods of parasite control could be related to the occurrence and frequency of anthelmintic resistant populations. Resistant populations of strongyles were found over wide areas of New South Wales and in north central Victoria. There was no relationship between geographical location and the occurrence of benzimidazole resistance. The species involved were small strongyles of the sub-family Cyathostominae. There was a direct correlation between the occurrence of resistance (including the level at which it is present) and the frequency of use of benzimidazole anthelmintics. Examination of management practices showed that resistance is not an important problem on farms where different chemical classes of anthelmintics were used in a slow rotation programme; combination anthelmintic therapy (for example, benzimidazole/piperazine/organophosphates) was used and anthelmintic treatment was given at intervals of not less than 16 weeks. Tentative suggestions are made for the control of small strongyles in the light of an emerging resistance problem.

Resistance to benzimidazole anthelmintics in equine strongyles. 2. Evidence of side-resistance, and susceptibility of benzimidazole-resistant strongyles to non-benzimidazole compounds

The susceptibility of a known thiabendazole-resistant population of small strongyles to anthelmintics of both benzimidazole and non-benzimidazole groups, was determined. In the first study, 42 horses infected with thiabendazole-resistant small strongyles were allocated to 6 groups. Treatment groups received one of the following anthelmintics: mebendazole, febantel, febantel plus trichlorphon, morantel tartrate, or a combination of thiabendazole, piperazine and trichlorphon. Morantel tartrate and the thiabendazole/piperazine/trichlorphon combination produced highly significant (p less than 0.001) reductions in faecal strongyle egg counts 20 days post-treatment. Mebendazole, febantel and febantel plus trichlorphon failed to reduce strongyle egg counts significantly. Larval culture and differentiation indicated that in all cases of anthelmintic failure, small strongyles of the sub-family Cyathostominae were involved. Eighteen horses from groups in which treatment had failed were re-allocated to 3 groups. Treatment with either morantel tartrate or haloxon was highly efficient in reducing faecal strongyle egg counts. In the final study, fifty-four horses, infected with benzimidazole-resistant small strongyles were allocated to 10 groups. On day zero, each treatment group received one of the following anthelmintics: thiabendazole, cambendazole, mebendazole, oxibendazole, piperazine, thiabendazole/piperazine, cambendazole/piperazine, mebendazole/piperazine or oxibendazole/piperazine. Oxibendazole, piperazine and the benzimidazole/piperazine combinations produced highly significant reductions in faecal strongyle egg counts 20 days post-treatment (p less than 0.001). When administered alone, benzimidazole anthelmintics failed to reduce strongyle egg counts significantly, with the exception of oxibendazole. Larval culture and differentiation indicated that in all cases of anthelmintic failure, the species involved were small strongyles of subfamily Cyathostominae. There was no significant increase in benzimidazole resistance level (based on in vitro assay) as a result of drug treatment, over one generation.

Use of guniea pigs to assay anthelmintic resistance in ovine isolates of Trichostrongylus colubriformis

Guinea pigs infected with Trichostrongylus colubriformis were used to develop an assay for anthelmintic resistance by determination of worm burdens following treatment with test anthelmintics. To achieve comparable efficacy with the recommended dose of thiabendazole and levamisole in sheep, dose rates in guinea pigs had to be increased two to four fold. For example, thiabendazole at 100 mg/kg in guinea pigs was 96.6 per cent effective against a thiabendazole susceptible (GS) strain of T colubriformis, but had no effect against a thiabendazole-resistant (VRSG) strain. In sheep 50 mg/kg of thiabendazole would have a similar efficacy against each strain respectively. Morantel tartrate at 10 mg/kg in guinea pigs was 99 to 100 per cent effective against the GS strain but only 54 per cent effective against a morantel resistant (PF4) strain. A slope ratio assay was used to calculate the relative potency of anthelmintics by comparing efficacies against resistant strains with efficacy against the GS strain. Resistance of the VRSG strain to thiabendazole was confirmed with a relative potency for this drug of 0.047 in guinea pigs. The PF4 strain was resistant to both thiabendazole and levamisole which had relative potencies of 0.168 and 0.255 respectively. The advantages of this statistical treatment together with the cost and time savings of the guinea pig model over a conventional critical anthelmintic assay in sheep are discussed.

Five generations of selection with benzimidazole and non-benzimidazole anthelmintics against benzimidazole resistant strains of Haemonchus and Ostertagia spp in sheep

Benzimidazole resistant strains of Haemonchus contortus and Ostertagia spp were subjected to selection pressure over five laboratory generations with the recommended dose rates of either cambendazole, oxfendazole or morantel. A change in response, with larger residual worm burdens remaining after treatment at the fifth generation, was shown for both cambendazole and oxfendazole against both species of nematode. No change in response against either species are shown for morantel. The results are discussed in terms of the problem associated with inefficient removal of the adult parasites after treatment.

Anthelmintic efficacy of low-dose phenothiazine against strains of sheep nematodes susceptible or resistant to thiabendazole, levamisole and morantel tartrate: effect on patent infections

The anthelmintic efficacy of low-dose phenothiazine therapy, administered as a 1:40 phenothiazine: molasses mixture, was tested against patent infections of strains of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia spp susceptible or resistant to thiabendazole (an other benzimidazoles), levamisole and morantel tartrate. Phenothiazine reduced faecal egg output for both susceptible and resistant strains of all three nematodes. In daily doses of 0.25 g per sheep per day and above it completely inhibited larval production in susceptible strains. Against resistant strains, there was a reduced efficiency with 82.3 per cent inhibition of egg hatch at the 0.25 g per sheep per day level. Phenothiazine treatment had no significant effect on worm numbers for either susceptible or resistant worms. It is suggested that benzimidazole-resistant strains may be cross-resistant to phenothiazine.

Changes in response of a benzimidazole resistant strain of Haemonchus contortus from sheep after passing through calves

A benzimidazole resistant strain of Haemonchus contortus was passaged through lambs only or from lambs to calves and back into lambs. Changes in response to thiabendazole were monitored by using an egg hatch test at each animal passage and by a controlled experiment on adult worms at the final passage in lambs. An increased level of resistance was shown for the isolate during its passage through calves by the egg hatch test, although this was not supported on the adult worms in sheep using a single dose rate of 66 mg/kg of thiabendazole.

Trichostrongylus colubriformis and Ostertagia sp resistant to levamisole, morantel tartrate and thiabendazole: infectivity, pathogenicity and drug efficacy in two breeds of sheep

Merino and Border Leicester cross Merino sheep, nine months old, were infected with 10,000 third stage larvae of both Trichostrongylus colubriformis (PF4) and Ostertagia circumcincta/O trifurcata (PF5), known to have varying degrees of resistance to levamisole, morantel tartrate and thiabendazole. Crossbred sheep carried heavier Ostertagia sp worm burdens but there was no difference in susceptibility between the two breeds of sheep to infection with T colubriformis. The anthelmintic efficacy of thiabendazole, at 50 mg/kg, against T colubriformis was 81.8 per cent and 92.4 per cent for Merinos and crossbreds respectively while levamisole, at 6.75 mg/kg, was 12.3 per cent and 18 per cent effective. Thiabendazole removed 92.3 per cent and 83.8 per cent of Ostertagia sp in Merinos and crossbreds respectively. However, worm burdens in levamisole treated sheep were not significantly different from controls. No significant breed differences were found in 24 h faecal egg outputs. It is suggested that breed differences previously described in four-month-old sheep may have been due to differences in the rate of development of immune responsiveness. This disparity was no longer detectable in the immunologically mature sheep used in this study.

Trichostrongylus colubriformis and Ostertagia sp resistant to levamisole, morantel tartrate and thiabendazole: isolation into pure strain and anthelmintic titration

Strains of Trichostrongylus colubriformis (designated PF4) and Ostertagia sp (O circumcincta/O trifurcata, designated PF5), with varying degrees of resistance to levamisole, morantel tartrate and thiabendazole were isolated into pure culture. Detailed dose response studies showed that both T colubriformis and Ostertagia sp were highly resistant to levamisole and morantel with low level resistance to thiabendazole. The effective dose required to remove 80 per cent worm burdens (ED80) was calculated for each anthelmintic. For T colubriformis the ED80 for levamisole and thiabendazole were 12.6 and 40.1 mg/kg respectively. For Ostertagia sp, the ED80 for levamisole, thiabendazole and morantel were 20.4, 45.2 and 35.8 mg/kg respectively. The implications of these results are discussed with reference to alternative means of chemical control.

The efficacy of fenbendazole and albendazole against immature and adult stages of benzimidazole-resistant sheep trichostrongylids

The efficacy of two recently introduced benzimidazole anthelmintics, albendazole and fenbendazole, was determined for six-day, 10-day and adult stages of resistant strains of Haemonchus contortus and Trichostrongylus colubriformis. Albendazole, at 3.8 mg/kg reduced H contortus worm counts by 92.4, 70.8 and 67.1 per cent while fenbendazole, at 5.0 mg/kg, reduced worm burdens by 51.7, 95.5 and 93.4 per cent against six-, 10- and 25-day-old parasites respectively. For T colubriformis, the corresponding reductions with albendazole were 97.7, 95.8 and 64.9 per cent and for fenbendazole 29.0, 66.3 and 33.4 per cent. Compared with susceptible strains of H contortus and T colubriformis, for which therapeutic doses of benzimidazole anthelmintics are generally highly active against all stages of development, the present results show that these drugs do not have a uniform level of activity against all developmental stages of resistant strains.

Trichostrongylus colubriformis and Ostertagia circumcincta resistant to levamisole, morantel tartrate and thiabendazole: occurrence of field strains

Field strains of Trichostrongylus colubriformis and Ostertagia circumcincta, designated PF4 and PF5 respectively, were recovered from a farm on which the sole use of levamisole over a preceding 12 year period led to the development of anthelmintic resistance. The results of field observations and preliminary critical trials in both Merino and crossbred sheep showed that both species have varying degrees of resistance to three major anthelmintics; levamisole, morantel tartrate and thiabendazole. Mean worm count reductions for adult T colubriformis (PF4) for therapeutic doses of morantel tartrate, thiabendazole and levamisole in crossbreds were 45.7 per cent, 97.3 per cent and zero respectively, and for Merinos 80.7 per cent, 88.3 per cent and 92.0 per cent respectively. Against O circumcincta the corresponding reductions for crossbreds were 51.4 percent, 95.4 per cent and 20.3 per cent and for Merinos, 52.5 per cent, 73.1 per cent and 29.8 per cent. There was no statistically significant difference in the responses of both parasite species to either levamisole or morantel. This result suggests that resistance to the two chemically unrelated drugs may be co-inherited.

The effect of single and divided dose administration on the efficacy of fenbendazole against adult stages of benzimidazole resistant sheep trichostrongylids

Sheep infected with benzimidazole resistant strains of Haemonchus contortus and Trichostrongylus colubriformis were used to compare the anthelmintic efficacy of fenbendazole given as a single dose or administered in a divided dose regime over five days. Statistical analysis showed no significant difference between the two methods of administration for H contortus. On the other hand, divided dose fenbendazole was significantly less effective than single doses against adult T colubriformis at dose rates of 5 and 7.5 mg/kg. In the case of H contortus a highly significant correlation coefficient between post treatment egg counts and worm counts (r = 0.789) was obtained. This suggests that reduction in faecal egg output following drug treatment would provide a useful field indication of anthelmintic performance of fenbendazole (and possibly related compounds) against benzimidazole resistant strains of this parasite.