Adaptation of a 96-well plate larval migration inhibition test for measuring the sensitivity of cyathostomins to macrocyclic lactone anthelmintics.

The use of macrocyclic lactone drugs for control of equine cyathostomins is threatened by increasing levels of resistance. Detection of changes in drug sensitivity is important for effective and sustainable management of cyathostomins, however, at present such detection relies on the use of the faecal egg count reduction test, which is known to be an insensitive method. The present study therefore aimed to examine the use of a 96-well plate larval migration inhibition test for detection of resistance to macrocyclic lactone drugs in cyathostomins. We optimised conditions for migration of larvae, and examined the effects of larval storage time on drug dose responses. The modified test was able to define the sensitivity of cyathostomin isolates to ivermectin and eprinomectin in terms of dose response curves, and IC50 and IC95 values. The IC95 showed much greater consistency than the IC50 with larvae that had been stored for different periods prior to the test. Comparisons between two isolates, which had both been defined previously as susceptible using faecal egg count reduction tests, showed more variation at the IC50 compared to the IC95. Limitations of the test included the degree of variation in control-well migration despite optimisation of migration incubation conditions, and the need to incorporate a method to determine the species composition of the larval populations to account for possible species differences in drug sensitivity among cyathostomins. Validation of the technique on reference susceptible and resistant isolates of known species composition is still required.

A survey of macrocyclic lactone efficacy in Australian cyathostomin populations.

The macrocyclic lactone (ML) drugs are central to the control of equine strongyles but recent international reports raise concerns about reduced efficacy of these drugs against cyathostomins. The objectives of the present study were firstly, to evaluate the efficacy of ML drugs against cyathostomins on a cross-section of Australian horse farms, and secondly, to determine the egg reappearance period (ERP) following treatment of horses with MLs. A total of 419 horses on 43 properties were treated orally with ivermectin, abamectin or moxidectin, at recommended dose rates and drug efficacy was determined using the faecal egg count reduction test. Efficacy of 100% at 14days post-treatment was reported on all of the 43 farms. ERP following ivermectin treatment was 6weeks on two properties and ERP following moxidectin treatment was 12weeks on a third property. These ERPs are shorter than those reported at the time of commercial release of these drugs which likely reflects changing drug susceptibility of the cyathostomin populations tested. Ongoing surveillance of drug efficacy and ERPs should be part of an integrated management approach to equine worm control that prioritises the preservation of anthelmintic efficacy.

The influence of reproductive physiology and nutrient supply on the periparturient relaxation of immunity to the gastrointestinal nematode Trichostrongylus colubriformis in Merino ewes.

A pen experiment was conducted to investigate the interaction of early-weaning and nutrient supply on the periparturient relaxation of immunity to the gastrointestinal nematode (GIN) Trichostrongylus colubriformis in Merino ewes. Mixed-age pregnant and non-pregnant (dry) ewes were infected with 8,000 T. colubriformis L(3)/week, and fed either a high or low quality diet. Following parturition, lambs were either removed from their mothers at 2 days of age or allowed to continue suckling. Systemic immunity began to wane during late pregnancy with circulating eosinophils and plasma total antibody (Ab) levels declining from day -37 (relative to the midpoint of lambing) and day -24, respectively. Pregnant ewes fed the low quality diet exhibited an increasing faecal worm egg count (WEC) from day -24 and had higher intestinal worm burdens on day 13, whereas ewes fed the high quality diet had a delayed transient rise in WEC of lower magnitude. Dry and early-weaned ewes remained highly resistant to T. colubriformis at all times. In the post-lambing/lactation period, ewes fed the high quality diet had higher levels of local total Ab and numbers of goblet cells (GC) in the small intestine on days 13 and 41. Lactating/suckled ewes had a lower anti-parasite local immune response as indicated by reduced titres of total Ab, IgG(1), IgM and IgA and lower numbers of mucosal mast cells (MMC), globule leukocytes (GL) and GC in small intestinal tissue compared to their dry and early-weaned counterparts. Early-weaning resulted in rapid recovery of blood eosinophils and total Ab. On day 13 post-lambing, titres of total Ab, IgG(1), IgM, IgA and IgE, and numbers of MMC and GL were greater than those measured in dry and suckled ewes. When fed the high quality diet, ewes had a higher dry matter (DM) intake, maternal weight, fat score, greater fat depth and eye muscle depth, birthed heavier lambs that had higher growth rates, and produced more milk. The physiological status of pregnancy resulted in a higher DM intake but lower measures of fat depth and eye muscle depth, and suckling led to an increase in DM intake but a reduction in body weight and fat score through mobilisation of fat and muscle reserves. Despite the marked effect of diet quality on production traits, some inconsistencies were observed between body composition and apparent parasite resistance, measured by WEC and worm counts, suggesting that the nutritional influence was not necessarily always mediated through changes in body composition. Although reproductive status affected blood leptin levels, diet had no effect within suckled ewes and therefore it was concluded that leptin has no causative role in maintaining the periparturient relaxation of immunity to T. colubriformis.

Selective transport of IgE into ovine mammary secretions.

Immunoglobulin (Ig) E is actively transported into ovine colostrum. Here we examine the degree of selectivity and the mechanism by which this transfer occurs in sheep. Results indicate that during colostrogenesis in sheep, transfer of immunoglobulins was most selective for IgG1 and IgA followed by IgE, IgM and IgG2. In milk, selectivity was greatest for IgA, followed by IgM, IgE, IgG1 and IgG2. The neonatal Fc receptor (FcRn) and poly immunoglobulin receptor (pIgR) mediate the transport of IgG1 and IgA across the ovine mammary epithelium respectively. In primates and rodents, the low-affinity IgE receptor, Fc epsilonRII, functions to transport IgE across the intestinal epithelium. We therefore investigated the expression of the low-affinity IgE receptor (CD23), pIgR and FcRn transcripts in the ovine mammary gland. The expression profiles of FcRn, pIgR and CD23 mRNA reflected concentrations of their Ig ligands in mammary secretions. These findings suggest a role for CD23 in transport of IgE across the mammary epithelium of sheep.

The periparturient relaxation of immunity in Merino ewes infected with Trichostrongylus colubriformis: endocrine and body compositional responses.

The temporal association between the periparturient rise in worm egg count of grazing Merino ewes to infection with Trichostrongylus colubriformis and the underlying causal mechanisms was investigated in an experiment that incorporated two levels of pregnancy (pregnant or unmated), two levels of infection (infected with 6000 T. colubriformis L(3)/week or uninfected) and, following lambing, three levels of lactation (non-lactating/"dry", early-weaned 2 days after parturition, or suckled). In addition to parasitological and host immune responses reported in a previous paper (Beasley et al., 2010), a range of endocrine and body compositional changes were monitored from day -50 to day 42, relative to the midpoint of lambing (day 0). By day -19, pregnant ewes had begun to mobilise fat and eye muscle, and after 42 days of suckling had lost 31% and 8%, respectively, of their existing depots. In comparison to non-pregnant (dry) ewes, the endocrine profiles of late-pregnant ewes were characterised by low levels of cortisol and prolactin and high levels of progesterone and oestradiol. Lactating ewes had lower levels of cortisol and leptin and higher levels of prolactin compared to both dry and early-weaned ewes. The mobilisation of fat and protein reserves throughout lactation in suckled ewes was closely associated with leptin and cortisol profiles, and provided strong evidence of an underlying nutritional basis for the periparturient relaxation of immunity. Both leptin and cortisol concentrations were also associated with both parasite burden and the immune status of the ewe. It is suggested that lower blood cortisol levels in suckled ewes contribute to a Th1 biased immune response that leads to an increased susceptibility to gastrointestinal nematodes. The results provide a detailed characterisation of the physiology underlying the periparturient relaxation of immunity to T. colubriformis, from which further investigations will aim to expose potential causal factors.

The periparturient relaxation of immunity in Merino ewes infected with Trichostrongylus colubriformis: parasitological and immunological responses.

The temporal association between the periparturient rise (PPR) in worm egg count (WEC) of grazing Merino ewes to infection with Trichostrongylus colubriformis and the underlying causal mechanisms was investigated in an experiment that incorporated two levels of pregnancy (pregnant or unmated), two levels of infection (infected with 6000 T. colubriformis L(3)/week or uninfected) and, following lambing, three levels of lactation (non-lactating/"dry", early-weaned 2 days after parturition, or suckled). The 128 ewes in the experiment were monitored for a range of parasitological and host systemic and local immune responses from days -50 to 42, relative to the midpoint of lambing (day 0). Unmated/non-lactating (dry) ewes remained largely resistant to T. colubriformis infection with WEC remaining below 200 eggs per gram (epg) throughout the experiment. For infected ewes, the PPR in WEC commenced during late pregnancy and peaked at 1552epg on day 42. There was evidence of a relaxation of immunity that preceded the rise, as demonstrated by a reduction in circulating eosinophils and plasma total antibody (Tab) and lower titres of Tab and IgG(1) in the small intestine in pregnant ewes. Circulating eosinophils and plasma Tab remained low in suckled ewes, and at the local level, lactating ewes also had lower titres of Tab, IgG(1), IgM, IgA and IgE as well as fewer mast cells (MC), globule leucocytes (GL) and goblet cells (GC) in intestinal tissue. These effects were associated with higher worm burdens. Weaning at 2 days after lambing resulted in a rapid amelioration of immunological responsiveness and a reduction in WEC, worm burden and parasite establishment rate. A rapid increase in circulating eosinophils and Tab titre followed by an improvement in components of the local immune response was also observed. Over the 6-week period following lambing, weaned ewes exhibited higher titres of Tab, IgG(1), IgM, IgA and IgE as well as higher numbers of MC, GL and GC present in the small intestinal tissue, compared to lactating ewes. The results provide a detailed characterisation of the periparturient relaxation of immunity to T. colubriformis, and highlight possible causative factors that deserve further investigation.

Intraocular lens implants: a biocompatibility review.

The natural aging process of the eye inevitably leads to the formation of a cataract, resulting in an increasing loss of vision. A cataract is the clouding of the natural lens in the eye and represents a major physical impairment. Modern surgical techniques allow for removal of the clouded lens and replacement with a prosthetic intraocular lens. This article reviews the intraocular tissue response to the implant, which frequently leads to postoperative complications for the patient.