Treatment and control of ectoparasites in sheep

Effect of Intensification Practices, Lambing Period and Environmental Parameters on Animal Health, and Milk Yield and Quality in Dairy Sheep Production Systems on Crete

Due to increasing demand, many traditional, grazing-based Mediterranean sheep production systems have introduced intensified feeding regimes, increased investments in infrastructure and drug use to increase milk yields. However, compared to bovine milk production systems, there is limited knowledge about the impact of these intensification practices on animal welfare and health and on the quality of dairy products. The aim of this study was therefore to quantify the effects of management practices and environmental conditions background on udder health, parasitism and milk quantity and quality in Cretan traditional production systems. Milk yields were higher in semi-intensive production systems while concentrations of several nutritionally desirable compounds such as omega-3 fatty acids were found to be higher in milk from extensive systems. Antibiotic and anthelmintic use was relatively low in both extensive and semi-intensive production systems. There was no substantial difference in parasitic burden, somatic cell counts, and microbiological parameters assessed in milk. Recording of flock health parameters showed that animal health and welfare was high in both extensive and semi-intensively managed flocks, and that overall, the health status of extensively managed ewes was slightly better. In contrast, environmental conditions (temperature and rainfall) had a substantial effect on parasitism and milk quality.

Entomopathogenic Fungi and Bacteria in a Veterinary Perspective

Simple Summary

Several fungal species are well suited to control arthropods, being able to cause epizootic infection among them and most of them infect their host by direct penetration through the arthropod’s tegument. Most of organisms are related to the biological control of crop pests, but, more recently, have been applied to combat some livestock ectoparasites. Among the entomopathogenic bacteria, Bacillus thuringiensis, innocuous for humans, animals, and plants and isolated from different environments, showed the most relevant activity against arthropods. Its entomopathogenic property is related to the production of highly biodegradable proteins. Entomopathogenic fungi and bacteria are usually employed against agricultural pests, and some studies have focused on their use to control animal arthropods. However, risks of infections in animals and humans are possible; thus, further studies about their activity are necessary.

Abstract

The present study aimed to review the papers dealing with the biological activity of fungi and bacteria against some mites and ticks of veterinary interest. In particular, the attention was turned to the research regarding acarid species, Dermanyssus gallinae and Psoroptes sp., which are the cause of severe threat in farm animals and, regarding ticks, also pets. Their impact on animal and human health has been stressed, examining the weaknesses and strengths of conventional treatments. Bacillus thuringiensis, Beauveria bassiana and Metarhizium anisopliae are the most widely employed agents. Their activities have been reviewed, considering the feasibility of an in-field application and the effectiveness of the administration alone or combined with conventional and alternative drugs is reported.

In vitro and in vivo effects of chlorpyrifos and cypermethrin on blood cholinesterases in sheep

The combination of the organophosphate (OP) chlorpyrifos (CPF) and the pyrethroid cypermethrin (CPM) is commonly marketed as pour-on formulations for the control of sheep lice, ked, and blowflies. CPF irreversibly inhibits acetylcholinesterases (AChE), while pyrethroids are not AChE inhibitors. However, combinations of pyrethroids with OPs showed a highly synergistic effect on AChE inhibition. Thus, the aim of the current work was to evaluate in vitro and in vivo the inhibitory potency of both pesticides, alone and in combination with AChE and butyrylcholinesterase (BChE) activities in sheep blood. In vitro, IC50 values were similar after CPF or CPF plus CPM incubations. The pour-on coadministration of recommended doses of CPF and CPM did not cause a significant inhibition of AChE and BChE in sheep blood. Only slight percentages of inhibition of their catalytic activities were observed when both drugs were given at 4-fold higher dose rates. The lower systemic availability of topical administration of OPs in sheep may help to explain the lower degree of inhibition of blood AChE and BChE in vivo. The results emerged from this research are a further contribution to the knowledge of the risks of implementing higher dosage regimens of OPs-containing antiparasitic formulations.

The Battle Against Flystrike - Past Research and New Prospects Through Genomics

Flystrike, or cutaneous myiasis, is caused by blow fly larvae of the genus Lucilia. This disease is a major problem in countries with large sheep populations. In Australia, Lucilia cuprina (Wiedemann, 1830) is the principal fly involved in flystrike. While much research has been conducted on L. cuprina, including physical, chemical, immunological, genetic and biological investigations, the molecular biology of this fly is still poorly understood. The recent sequencing, assembly and annotation of the draft genome and analyses of selected transcriptomes of L. cuprina have given a first global glimpse of its molecular biology and insights into host-fly interactions, insecticide resistance genes and intervention targets. The present article introduces L. cuprina, flystrike and associated issues, details past control efforts and research foci, reviews salient aspects of the L. cuprina genome project and discusses how the new genomic and transcriptomic resources for this fly might accelerate fundamental molecular research of L. cuprina towards developing new methods for the treatment and control of flystrike.

Effect In Vitro of Antiparasitic Drugs on Microbial Inhibitor Test Responses for Screening Antibiotic Residues in Goat's Milk

Microbial inhibitor tests are widely used to screen antibiotic residues in milk; however, these tests are nonspecific and may be affected by various substances capable of inhibiting the growth of the test microorganism. The objective of this study was to determine the effect of antiparasitic drugs in goat's milk on the microbial inhibitor test response. Raw antibiotic-free milk from Murciano-Granadina goats was supplemented with eight concentrations of seven antiparasitic substances (albendazole, 10 to 170 mg/kg; closantel, 1 to 140 mg/kg; diclazuril, 8 to 45 mg/kg; febendazole, 10 to 140 mg/kg; levamisole, 40 to 440 mg/kg; diazinon, 8 to 45 mg/kg; and ivermectin, 40 to 200 mg/kg). Twelve replicates for each concentration were analyzed with three microbial inhibitor tests: BRT MRL, Delvotest SP-NT MSC, and Eclipse 100. The results were interpreted visually (negative or positive). Using a logistic regression model, the concentrations of the antiparasitic drugs producing 5% (IC5), 10% (IC10), and 50% (IC50) positive results were determined. In general, the Eclipse 100 test was less sensitive to the effect of antiparasitic substances; the inhibitory concentrations of almost all the drugs assayed were higher than those for other tests. Conversely, the BRT MRL test was most affected, with high levels of interference at lower antiparasitic drug concentrations. Closantel and diazinon interfered with all microbial tests at lower concentrations than did other drugs (IC5 = 1 to 26 and 12 to 20 mg/kg, respectively), and higher concentrations of levamisole and diclazuril (IC5 = 30 to 240 and 50 to 117 mg/kg, respectively) were required to produce 5% positive results. These findings indicate that microbial inhibitor tests can be affected by elevated concentrations of antiparasitic drugs in goat's milk.

Insecticidal Activity of Some Traditionally Used Ethiopian Medicinal Plants against Sheep Ked Melophagus ovinus

Twelve medicinal plants and a commercially used drug Ivermectin were examined for insecticidal activity against Melophagus ovinus sheep ked at different time intervals using in vitro adult immersion test. The findings show that at 3.13 µL/mL, 6.25 µL/mL and 12.5 µL/mL concentration of Cymbopogon citratus, Foeniculum vulgare and Eucalyptus globulus essential oils respectively, recorded 100% mortalities against M. ovinus within 3 hour of exposure. Significantly higher insecticidal activity of essential oils was recorded (P = 0.00) when compared to 10  μ g/mL Ivermectin after 3-hour exposure of M. ovinus at a concentration of ≥1.57  μ L/mL, ≥3  μ L/mL, and ≥12.7  μ L/mL essential oils of C. citratus, F. vulgare, and E. globulus, respectively. Among essential oils, C. citratus has showed superior potency at a three-hour exposure of the parasite (P = 0.00) at a concentration of ≥0.78  μ L/mL. Strong antiparasitic activity was recorded by aqueous extract of Calpurnia aurea (80% mortality) at a concentration of 200 mg/mL within 24 h among aqueous extracts of 9 medicinal plants. The results indicated all the four medicinal plants, particularly those tested essential oils, can be considered as potential candidates for biocontrol of M. ovinus sheep ked.

Structure-activity relationships of acetylcholine derivatives with Lucilia cuprina nicotinic acetylcholine receptor α1 and α2 subunits in chicken β2 subunit hybrid receptors in comparison with chicken nicotinic acetylcholine receptor α4/β2

Insect nicotinic acetylcholine (ACh) receptors (nAChRs) are the targets of several insecticide classes. In the present study, we report the gene identification and cloning of nAChR α1 and α2 subunits (Lcα1 and Lcα2) from the sheep blowfly Lucilia cuprina. Xenopus oocytes voltage clamp experiments as hybrids with the chicken β2 nAChR (Ggβ2) subunit resulted in ACh-gated ion channels with distinct dose-response curves for Lcα1/Ggβ2 (effective concentration 50% [EC50 ] = 80 nM; nH  = 1.05), and Lcα2/Ggβ2 (EC50  = 5.37 μM, nH  = 1.46). The neonicotinoid imidacloprid was a potent agonist for the α-bungarotoxin-sensitive Lcα1/Ggβ2 (EC50 ∼ 20 nM), while the α-bungarotoxin-resistant Lcα2/Ggβ2 showed a 30-fold lower sensitivity to this insecticide (EC50  = 0.62 μM). Thirteen close derivatives of ACh were analysed in EC50 , Hill coefficient and maximum current (relative to ACh) determinations for Lcα1/Ggβ2 and Lcα2/Ggβ2 and the chicken Ggα4/Ggβ2 nAChRs, and comparisons relative to ACh allowed the definition of novel structure-activity and structure-selectivity relationships. In the case of N-ethyl-acetylcholine, the EC50 of the chicken Ggα4/Ggβ2 rose by a factor of 1000, while for both Lcα1/Ggβ2 and Lcα2/Ggβ2, potency remained unchanged. Further derivatives with insect nAChR selectivity potential were acetyl-α-methylcholine and trimethyl-(3-methoxy-3-oxopropyl)ammonium, followed by acetylhomocholine and trimethyl-(4-oxopentyl) ammonium. Our results may provide guidance for the identification or design of insect-specific nAChR agonists using structure-based or in silico methods.

Emerging parasitic diseases of sheep

There have been changes in the emergence and inability to control of a number of sheep parasitic infections over the last decade. This review focuses on the more globally important sheep parasites, whose reported changes in epidemiology, occurrence or failure to control are becoming increasingly evident. One of the main perceived driving forces is climate change, which can have profound effects on parasite epidemiology, especially for those parasitic diseases where weather has a direct effect on the development of free-living stages. The emergence of anthelmintic-resistant strains of parasitic nematodes and the increasing reliance placed on anthelmintics for their control, can exert profound changes on the epidemiology of those nematodes causing parasitic gastroenteritis. As a consequence, the effectiveness of existing control strategies presents a major threat to sheep production in many areas around the world. The incidence of the liver fluke, Fasciola hepatica, is inextricably linked to high rainfall and is particularly prevalent in high rainfall years. Over the last few decades, there have also been increasing reports of other fluke associated diseases, such as dicroceliosis and paramphistomosis, in a number of western European countries, possibly introduced through animal movements, and able to establish with changing climates. External parasite infections, such as myiasis, can cause significant economic loss and presents as a major welfare problem. The range of elevated temperatures predicted by current climate change scenarios, result in an elongated blowfly season with earlier spring emergence and a higher cumulative incidence of fly strike. Additionally, legislative decisions leading to enforced changes in pesticide usage and choices have resulted in increased reports and spread of ectoparasitic infections, particularly mite, lice and tick infestations in sheep. Factors, such as dip disposal and associated environmental concerns, and, perhaps more importantly, product availability have led to a move away from more traditional methods of pesticide application, particularly dipping, to the use of injectable endectocides. This has coincided with increased reports of sheep scab and lice infestations in some countries. Reduction in the use of organophosphate dips appears to have to some extent contributed to reported increased populations of ticks and tick activity, a consequence of which is not only of significance to sheep, but also many other hosts, including increased human zoonotic risks.

Sheep psoroptic mange: an update

Psoroptic mange is one of the most severe skin conditions of sheep. This highly contagious disease is responsible for huge economical losses in many sheep-raising countries. It is also a significant welfare concern. Our understanding of the biology of Psoroptes ovis and of the host-parasite relationship during psoroptic mange made remarkable progress during the last decade. These data combined with the availability of powerful molecular tools have opened new avenues of research. Clearly, there is still a long way to go before a vaccine becomes a reality. Additionally, other diagnostic tools and control methods should be further investigated such as breeding for genetic resistance and the use of biocontrol agents.