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.     

A survey of mutations in the Cochliomyia hominivorax (Diptera: Calliphoridae) esterase E3 gene associated with organophosphate resistance and the molecular identification of mutant alleles

Cochliomyia hominivorax (Calliphoridae) is one of the most important myiasis-causing flies and is responsible for severe economic losses to the livestock industry throughout the Neotropical region. In Brazil, C. hominivorax has been controlled mainly with organophosphate (OP) insecticides, although the inappropriate use of these chemicals can result in the selection of resistant flies. Changes in carboxylesterase activity have been associated with OP insecticides in some arthopodan species. In this work, we isolated and characterized part of the E3 gene in C. hominivorax (ChE7), which contained the same substitutions responsible for the acquisition of OP hydrolase activity in Lucilia cuprina (Calliphoridae). Digestion of the polymerase chain reaction products with a restriction enzyme that specifically recognized the mutation site unambiguously differentiated wild and mutated esterase alleles. The PCR-RFLP assay therefore provided a fast, reliable DNA-based method for identifying C. hominivorax individuals with a mutation in the esterase gene. Further bioassays to determine the association of this mutation with OP resistance in C. hominivorax should allow the development of more effective strategies for managing this species.     

Effects of immunization of Pelibuey lambs with Oestrus ovis digestive tract protein extracts on larval establishment and development

Larval midgut proteins of hematophagous parasites contain strong antigens that can be used for host immunization. This concept has been applied for immunization of Pelibuey sheep against Oestrus ovis L. (Diptera: Oestridae). The aim of this study was to examine the effect of immunization on larval establishment (LE) and development. Immunized lambs (I, n = 6) received two injections of crude gut membrane protein extracts (GMPE) from third instar larvae with Freund's incomplete adjuvant (FIA) on days 0 (Day of first immunization) and 21 (0.4 and 0.45 mg GMPE/lamb, respectively). The control group (C, n = 5) received physiological saline with FIA. Lambs were challenged with first instars on Day 29 (20 larvae) and Day 43 (25 larvae). Blood samples were collected biweekly and IgG titers were analyzed by ELISA. All lambs were slaughtered on Day 90 and number of larvae recovered, larval stage and larval weight were recorded at necropsy. No significant effect of immunization on LE (C = 28.9%; I = 31.0% P > 0.05) was observed. Antibody titers were higher in the immunized group on Day 28 (P < 0.05), but subsequently similar in both groups. Larval physiological age and weight were also significantly (P < 0.05) affected by immunization. Immunization of Pelibuey lambs with GMPE did not affect LE but did delay O. ovis larval development.     

Control of sheep blowfly strike using fly-traps

The use of fly-traps for the control of sheep blowfly strike was examined on 12 commercial sheep farms in south west England in 2003. Two flocks acted as controls, with no prophylactic blowfly strike control. Four flocks of lambs and three flocks of ewes were protected only by blowfly traps, seven of the flocks of ewes and six flocks of lambs were protected by blowfly traps but also had proprietary insecticides applied to them at some stage. There was no difference in the abundance of L. sericata at the various sites. The highest incidence of strike was seen in the two control flocks where 10.9 and 5.8% of the ewes and 10.1 and 9.2% of the lambs were struck. Strike incidence in the flocks that used trapping only and flocks that used trapping plus a chemical preventive was on average five times lower than in the control flocks, but the percentages struck on the sites in the trapping only and trapping plus insecticide groups were not significantly different from each other. The results of this study show that traps can make an effective contribution to blowfly strike control on individual farms.     

World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) guidelines for evaluating the efficacy of ectoparasiticides against myiasis causing parasites on ruminants

These guidelines have been prepared to assist in the planning, conduct and interpretation of studies for the assessment of efficacy of ectoparasiticides against the myiasis causing parasites of ruminants. These guidelines specifically focus on larvicidal efficacy against myiasis causing flies. Information is provided on the selection of animals, dose determination and dose confirmation studies, field studies, record keeping and result interpretation. These guidelines advocate the use of pen facilities for dose determination and dose confirmation studies for defining therapeutic and persistent efficacy. These guidelines are also intended to assist investigators on how to conduct specific experiments, to provide specific information for registration authorities involved in the decision-making process, to assist in the approval and registration of new ectoparasiticides, and to facilitate the world-wide adoption of standard procedures.     

Local and systemic cytokine responses during larval penetration in cattle experimentally infested with Hypoderma lineatum (Diptera: Oestridae)

Local and systemic cytokine responses were studied in 3 groups of cattle, with 4 animals each, experimentally infested with Hypoderma lineatum (De Villers) first instars (L1). The first group was undergoing a primary infestation (G-1), the second group was undergoing a secondary infestation (G-2) and the third group was infested for their third consecutive year (G-3). Cattle were infested with 25 L1 deposited on the skin. Blood and skin samples were taken at 0, 6, 12, 48, 96 and 144 h post-infestation (h.p.i.). Interleukin 10 (IL-10), IL-4 and interferon gamma (IFN-γ) production was studied by immunohistochemistry and sandwich ELISAs. IL-4⁺ cells showed a significant increase at 6 h.p.i. in both reinfested groups (G-2 and G-3) when compared with G-1. In all groups the number of IL-4⁺ cells decreased significantly at 48 h.p.i. IL-10⁺ cells increased in G-1 at 6 and 48 h.p.i., whereas in both reinfested groups increased at 12 h.p.i. with a peak at 48 h.p.i. IFN-γ⁺ cells showed a significant increment at 6 h.p.i. in all groups, followed by a rapid descent at 12 (G-1 and G-2) and 48 h.p.i. (G-3). Penetration of the skin by H. lineatum did not have any significant effect on IFN-γ serum concentrations and, except for IL-10 there were no correlation between local production and serum concentrations of cytokines. The increase of both Th1 (IFN-γ) and Th2-type cytokines (IL-4 and IL-10) indicates that bovine T-cell response during the first phases of the infestation by H. lineatum is apparently a Th0 response.     

Ectoparasites: future challenges in a changing world

Ectoparasites are ubiquitous, often highly damaging and in most cases cannot be permanently eradicated; hence, they must usually be managed at a local scale with insecticides or endectocides. However, the growth in resistance, the slow rate of development of new actives, coupled with environmental and health concerns associated with the continued use of some of the existing neurotoxic insecticides, suggest that more sophisticated approaches to their management need to be identified. These approaches need to allow ectoparasite populations to be maintained at acceptable levels, while conserving the compounds that remain available. The development of integrated approaches, in which cascades of management tactics are deployed, with parasiticides available as one component to be used in requisite circumstances, may be the most appropriate route to achieving this aim. An essential element of such an approach is the clear articulation of the purpose of intervention and rational justification of the time-point and manner in which it is attempted. However, for this to be possible, considerably better information is required about the effects of ectoparasite abundance on animal welfare and productivity, in addition to the greater availability of effective alternative control tools. To this end, recent work undertaken at the School of Biological Sciences at the University of Bristol, into the use of biological control agents, off-host trapping and the selective treatment of more highly susceptible individuals or classes of host, is reviewed here.     

Ovine cutaneous myiasis: Effects on production and control

Ovine cutaneous myiasis ('fly strike') remains a major sheep health problem in many areas of the world. Myiasis risk is the result of a complex interaction of factors, such as fly and host abundance, host susceptibility, climate and, critically, husbandry and management strategies, all of which change seasonally in space and time. Given the complexity of the interacting factors, changes in myiasis incidence are hard to predict, as accordingly are the optimal husbandry responses required to manage the problem. Here the important risk factors are briefly reviewed and the future changes in myiasis incidence under conditions of anticipated climate change are considered. It is concluded that future work should focus in particular on evaluating the optimum use of integrated management, such as the combination of insecticide and trap use, in different environments under a range of farming regimes.     

A Case of a Dermatobia hominis Infection in a Dog in The Netherlands

Abstract— The first case of a Dermatobia hominis infection in a dog in the The Netherlands is described. The dog was imported from Brazil. The life cycle of the parasite and the therapeutic measures are emphasized.
Zusammenfassung— Beschrieben wird der erste Fall einer Dermatobia hominis —Infektion bei einem Hund in den Niederlanden. Der Hund wurde aus Brasilien eingeführt. Der Lebenszyklus des Parasiten und die therapeutischen Maßriahmen werden behandelt.
Resumen  En el presente artículo se describe el primer caso de infección causada por Dematobia hominis en Holanda. El perro habia sido importado desde Brasil. Se describe la vida del parásito y las medidas terapéuticas.