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.     

Preliminary Analysis of the Results of Selective Therapy Against Strongyles in Pasturing Horses

Control of horse parasites often omits application of measures to eradicate the free-living stages in pastures and frequently relies on chemotherapy only. Selective therapy was used for Spanish Sport horses grazing either in the same pasture (continuous) or in rotated meadows. In each group, equines exceeding a cutoff value of 300 strongyle eggs per gram of feces received ivermectin or moxidectin. Efficacy of the treatment was assessed by estimating reduction of fecal egg counts and the number of horses shedding parasite eggs (PHR). Coprocultures revealed presence of the cyathostomins Cyathostomum and Gyalocephalus spp. In all treated groups, a 100% value for both reduction of fecal egg counts and PHR against cyathostomins was obtained, and PHR values ranged from 100% to 12%. The longest strongyle egg reappearance period was observed in horses undergoing rotation grazing and receiving ivermectin (9 weeks), compared with a 6-week period recorded for the other treated equines. Our results seem to point that the efficacy of selective therapy in equine herds could be reduced if the horses with fecal egg counts below the threshold value (thus not receiving chemotherapy) remain grazing in the same pastures with the treated ones. It is strongly suggested that interested parties consider performing periodic fecal analyses to monitor fecal egg counts, together with the percentage of horses passing eggs in feces, to improve the effect of this procedure.     

Effect of a diet high in energy and protein on growth,carcase characteristics and parasite resistance in goats

The effects of a high-energy and high-protein diet on growth, parasite resistance and carcase characteristics were studied using local goats with an average initial body weight (BW) of 12.0 (SD = 0.7) kg. Thirty-two animals were allocated to a completely randomized factorial design, with four animals of each sex per treatment. The factors were: two diets (diet H with high content of crude protein (CP) and metabolizable energy (ME), and diet L with low content of CP and ME) and deworming (DW) or non-deworming (NDW). The highest dry matter (DM) intake was obtained for goats fed diet H combined with DW, but there was no significant difference between DW or NDW for goats fed diet H. The goats fed diet L and DW had significantly better total DM intake than NDW goats. The average daily gain of animals fed diet H was 86 and 92 g/day compared to 27 and 40 g/day for diet L, for NDW and DW animals, respectively. Feeding diet H resulted in higher slaughter weight and consequently also higher empty BW, carcase weight and dressing percentage and lower feed conversion ratio. Dewormed animals had significantly higher empty BW than NDW animals. There were significant effects of diet and parasite control on Faecal egg count (FEC: number of parasite eggs per gram of faeces (e.p.g.)), with NDW animals fed diet L having higher FEC than animals fed diet H.     

Sarcoptic mange and production performance of swine: A review of the literature and studies of associations between mite infestation, growth rate and measures of mange severity in growing pigs

Cost-effective control of sarcoptic mange requires knowledge of the effects of the disease on production. This paper presents a critical review of the literature on the association between sarcoptic mange and reduced production performance of swine. One of the difficulties in interpreting inconsistent findings among studies is lack of information about the severity of disease, which is likely to vary considerably. Lack of standard methods and failure to quantify disease severity preclude meaningful interpretation of experimental results in commercial production. Three experiments with growing pigs were conducted to evaluate associations between sarcoptic mite infestation and growth rate, and to assess pruritic behaviour and mite-induced lesions at slaughter as indices of mange severity. Sarcoptic mange was associated with increased pruritic behaviour and the presence of papular dermatitis at slaughter. Pruritic behaviour decreased over time despite reinfestation and may be subject to numerous behavioural influences. Growth rate tended to be slower in mange infested pigs, but a significant effect of mange infestation on average daily gain was found in only one trial, in which the severity of skin lesions at slaughter was greatest. These observations suggest that the production effects of mange infestation of growing pigs are variable. Evaluating dermatitis lesions at slaughter may be an objective means for assessing the severity of mange infestation and for relating experimental results to commercial swine production.     

Causative organisms and somatic cell counts in subclinical intramammary infections in milking goats in the UK

The bacterial causes of subclinical mastitis were determined in samples of milk taken from one half of the udders of 159 goats in three different herds. The mean prevalence of subclinical infection was 33 percent, with prevalences of 26 percent, 39 percent and 42 percent in the three herds. Staphylococcus aureus was isolated from seven (13 percent) of the 53 infected halves, coagulase-negative staphylococci accounted for 47 percent, Corynebacterium species for 31 percent and alpha-haemolytic streptococci for 6 percent of the infected samples. The mean somatic cell count of the uninfected milk samples was 428,000 cells/ml, and 93 percent of uninfected samples had counts less than 1,000,000 cells/ml; the mean cell count of the infected samples was 2,785,000 cells/ml.     

The effect of long-term feeding of fresh and ensiled cassava (Manihot esculenta) foliage on gastrointestinal nematode infections in goats

The benefit of long-term feeding of fresh or ensiled cassava foliage on gastrointestinal parasite in goats was evaluated. Eighteen male goats (15.15 ± 2.83kg and between 4–6months) were randomly allocated into three treatments supplemented with 200g of wheat bran head⁻¹ day⁻¹. All groups were fed ad-libitum on either grass (CO), fresh cassava (CaF) or ensiled cassava foliage (CaS). At the beginning of the trial, each goat was inoculated with 3000 L3 containing ≈50% Haemonchus contortus. Individual LWt, FEC and PCV were measured at weekly intervals for 10weeks. At the termination of the experiment all goats were slaughtered for worm recovery and enumeration. The goats in CaF and CaS had similar weight gains while those in CO lost weight (p < 0.05) through the trial. FEC in CaF and CaS were lower (p < 0.05) than CO during the patency of parasite infections, but there was no difference between CaF and CaS goats. PCV of all groups decreased from above 30% to around 25% at the end of the trial. The compositions of established worm burdens were mainly H. contortus (19–40%) and Trichostrongylus colubriformis (55–76%). TWB did not differ among the groups, however, CaS significantly reduced H. contortus burdens, as compared to CaF and CO (p ≤ 0.005). Thus, ensiled cassava foliage reduced the H. contortus population while the fresh foliage only reduced worm fecundity.     

Ectoparasites of free-ranging pumas and jaguars in the Paraguayan Chaco

Ectoparasites were collected from seven puma (Puma concolor) and seven jaguar (Panthera onca) live-captures (each representing six different animals) in the Paraguayan Chaco from 2002 to 2004. The same five species of ectoparasites were recovered from both host species: the flea, Pulex simulans (total on both hosts combined=30 male, 49 female), and the ticks, Amblyomma cajennense (1 male, 4 female, 46 nymphs, 241 larvae), Amblyomma parvum (42 male, 25 female), Amblyomma tigrinum (1 male, 7 female, 34 larvae) and Amblyomma triste (4 male). There were no statistical differences between the prevalences (percent of hosts infested) for any of these ectoparasite species between the two host species, and only P. simulans showed a significantly higher mean intensity (mean no. of each ectoparasite species per infested host) on one of the host species (jaguar). Clearly, these two large carnivores share similar ectoparasite faunas in the Paraguayan Chaco. However, both carnivores occupy large geographical distributions in the New World and this study, combined with the few previous studies, suggests that their ectoparasite faunas differ slightly in different parts of their respective ranges.     

国产阿维菌素驱杀绵羊内外寄生虫试验

在隔离饲养的条件下,０２ｍｇ／ｋｇ 、０３ｍｇ／ｋｇ 国产阿维菌素片剂和０２ ｍｇ／ｋｇ 气雾剂对绵羊颚虱、绵羊足颚虱、消化道线虫和丝状网尾线虫的驱杀效果均达１００ ％ ;对绵羊虱蝇杀灭率分别为９０６４ ％ 、９４９９ ％ 和８７７１ ％ ;对草原革蜱的杀灭率分别为７４４２ ％ 、８４９１ ％ 和７６３２ ％ ;原园科线虫减少率分别达８３１７ ％ 、９０７６ ％ 、８５６６ ％ 。因此,在放牧条件下,推广使用阿维菌素片剂是防治内外寄生虫病的一种有效手段。     

Ectoparasites of road-killed vertebrates in northwestern South Carolina, USA

Road-killed animals are overlooked as the source of ectoparasites for monitoring vectors of zoonotic pathogens. We demonstrate that by exclusively sampling road-killed animals, a wide spectrum of vertebrate hosts and ectoparasites can be collected. Fifty-one species of ectoparasites were recovered from 35 species of road-killed vertebrates in northwestern South Carolina. Approximately, 11% of the total known terrestrial vertebrate species in the region were examined, which included more than 25% of the known mammal species. Our sampling techniques produced new state and regional records for chewing lice, ticks, and parasitic mites. Most ectoparasites were alive when they were collected, which would allow them to be screened for zoonotic pathogens.     

Diversity of Ectoparasites in Sheep Flocks in Sa~o Paulo,Brazil

The occurrence of ectoparasites in sheep flocks is frequently reported but seldom quantified. Sheep production used to be a predominantly family activity in the state of Sa~o Paulo (Brazil), but it began to become a commercial activity in the past decade. Thus, information about the ectoparasites existing in sheep flocks has become necessary. The present data were obtained by means of questionnaires sent to all sheep breeders belonging to the `Associaça~o Paulista de Criadores de Ovinos' (ASPACO; Sa~o Paulo State Association of Sheep Breeders). Response reliability was tested by means of random visits paid to 10.6% of the respondents. Most of the properties (89.5%) reported the presence of one or more ectoparasites. Screw-worm (Cochliomyia hominivorax) was the most frequent ectoparasite (72.5%), followed by bot fly larvae (Dermatobia hominis, 45.0%), ticks (Amblyomma cajennense) and Boophilus microplus, 31.3%) and finally lice (Damalinia ovis, 13.8%). Combined infestations also occurred, the most common one being screw-worm with bot fly larvae (36.0%) followed by bot fly larvae with ticks (13.9%), screw-worm with ticks (9.3%), bot fly larvae with lice (6.9%), and ticks with lice (5.0%). The most common triple combination was screw-worm, bot fly larvae and ticks (12.8%). Breeds raised for meat or wool were attacked by bot fly larvae and ticks more often than other breeds. Lice were only absent from animals of indigenous breeds. The relationships among these ectoparasites are discussed in terms of sheep breeds, flock size, seasonality and the ectoparasitic combinations on the host.     

山羊子宫内膜炎病理模型的制备

长期以来,对子宫内膜炎的研究大多采用自然病例,由于发病时间和疗效判定标准不尽一致,所以试验结果很难比较.通过实验室建立山羊子宫内膜炎病理模型,保证其发病程度和症状的一致,从而为研究该病的诊断、治疗及防治方法创造良好条件.     

Evidence for multiple anthelmintic resistance in sheep and goats reared under the same management in coastal Kenya

Four experiments, two with sheep and two with goats, were carried out to determine the efficacy of ivermectin, fenbendazole, levamisole, closantel and some of their combinations by faecal egg count reduction tests. In the first experiment, injectable ivermectin, oral ivermectin, fenbendazole and levamisole were tested in 6-month-old lambs, and their reduction percentages were 77%, 13%, 42% and 92%, respectively. In the second experiment, with yearling sheep, the reduction percentages were 35% for injectable ivermectin, 32% for fenbendazole, 99% for levamisole, 48% for closantel, 92% for injectable ivermectin combined with fenbendazole, 99% for injectable ivermectin combined with levamisole, and 100% for fenbendazole combined with levamisole. In the study with 18-month-old goats given the same dose rates as those recommended for sheep, the reduction percentages were 73% for injectable ivermectin, 25% for fenbendazole, and 78% for levamisole. Another group of 14-month-old goats was treated with dose rates 1.5 times those recommended for sheep and the reduction percentages were 93% for levamisole, 92% for injectable ivermectin, and 97% for a combination of levamisole and ivermectin. In all experiments with sheep and goats the gastrointestinal nematode parasites identified by larval cultures were Haemonchus contortus, Trichostrongylus spp. and Oesophagostomum spp. The gastrointestinal nematodes of both sheep and goats on this farm are resistant to ivermectin and fenbendazole, whereas levamisole is still effective in sheep, but not in goats. The results are discussed in relation to the farm as a source of breeding stock to smallholder farmers and its potential to spread anthelmintic resistance.     

Enterotoxaemia in goats

Enterotoxaemia of sheep and goats occurs worldwide, but the condition in goats is poorly understood. The disease in goats is mostly caused by Clostridium perfringens type D, although the role of the toxins of this microorganism in the pathogenesis of the disease is not fully understood. The disease occurs in three forms, peracute, acute and chronic, the cardinal clinical sign of the acute and chronic forms being diarrhoea. The main biochemical alterations are hyperglycaemia and glycosuria, while at necropsy the disease is often characterized by haemorrhagic colitis. The typical histological changes observed in the brain of sheep with enterotoxaemia are not considered to be a common feature of enterotoxaemia in goats. Although the pathogenesis of caprine enterotoxaemia has not yet been properly defined, it is usually accepted that the presence of C. perfringens type D in the small bowel, together with a sudden change to a diet rich in carbohydrates, is the main predisposing factor for the disease. Vaccination seems to be poorly effective in preventing caprine enterotoxaemia, which might be due to the fact that the enteric form of the disease is partially independent of circulating C. perfringens toxin. More studies are needed on caprine enterotoxaemia, especially of its pathogenesis and immunity, in order to develop more efficient control measures for this disease.     

野生动物园动物寄生虫调查

对某野生动物园的近25种以上的动物进行了寄生虫调查,调查采用随机抽样的方法检查了近700头份样品,发现了16种左右重要寄生虫,其中危害严重的有片形吸虫、血矛属线虫、狮弓首蛔虫、鞭虫、长角血蜱等。