Responses of artificially reared cat fleas Ctenocephalides felis felis (Bouché, 1835) to different mammalian bloods

The cat flea, Ctenocephalides felis felis (Bouche, 1835) (Siphonaptera: Pulicidae), which is found worldwide and which parasitizes many species of wild and domestic animal, is a vector and/or reservoir of bacteria, protozoa and helminths. To aid in the study of the physiology and behaviour of fleas and of their transmission of pathogens, it would be of value to improve the laboratory rearing of pathogen-free fleas. The conditions under which artificially reared fleas at the University of Bristol (U.K.) and the Rickettsial Diseases Institute (France) are maintained were studied, with different ratios of male to female fleas per chamber (25 : 50, 50 : 100, 100 : 100, 200 : 200). The fleas were fed with bovine, ovine, caprine, porcine or human blood containing the anticoagulants sodium citrate or EDTA. Egg production was highest when fleas were kept in chambers with a ratio of 25 males to 100 females. In addition, the use of EDTA as an anticoagulant rather than sodium citrate resulted in a large increase in the number of eggs produced per female; however, the low percentage of eggs developing through to adult fleas was lower with EDTA. The modifications described in our rearing methods will improve the rearing of cat fleas for research.

Wild deer as potential vectors of anthelmintic-resistant abomasal nematodes between cattle and sheep farms

Gastrointestinal (GI) nematodes are among the most important causes of production loss in farmed ruminants, and anthelmintic resistance is emerging globally. We hypothesized that wild deer could potentially act as reservoirs of anthelmintic-resistant GI nematodes between livestock farms. Adult abomasal nematodes and faecal samples were collected from fallow (n = 24), red (n = 14) and roe deer (n = 10) from venison farms and areas of extensive or intensive livestock farming. Principal components analysis of abomasal nematode species composition revealed differences between wild roe deer grazing in the areas of intensive livestock farming, and fallow and red deer in all environments. Alleles for benzimidazole (BZ) resistance were identified in β-tubulin of Haemonchus contortus of roe deer and phenotypic resistance confirmed in vitro by an egg hatch test (EC₅₀ = 0.149 µg ml⁻¹ ± 0.13 µg ml⁻¹) on H. contortus eggs from experimentally infected sheep. This BZ-resistant H. contortus isolate also infected a calf experimentally. We present the first account of in vitro BZ resistance in wild roe deer, but further experiments should firmly establish the presence of phenotypic BZ resistance in vivo. Comprehensive in-field studies should assess whether nematode cross-transmission between deer and livestock occurs and contributes, in any way, to the development of resistance on livestock farms.

Comparison of traps for the control of sheep blowfly in the U.K

The ability of three commercially available trap types to catch Lucilia (Diptera: Calliphoridae) blowflies was assessed on three sheep farms in southwest England in 2008. The aim was to evaluate their relative value for the control of ovine cutaneous myiasis (sheep blowfly strike) on farms. There was a highly significant difference between the total number of female Lucilia caught per day by the traps, with an Agrilure Trap (Agrimin Ltd, Brigg, U.K.) catching more than the other trap types (Rescue Disposable Fly Trap, Sterling International, Spokane, U.S.A.; Redtop Trap, Miller Methods, Johannesburg, South Africa). However, there was no significant difference between the traps in the numbers of female Lucilia sericata (Meigen) caught. Nevertheless, consideration of the rate at which female L. sericata were caught over time showed that the Agrilure trap did not begin catching until about 30 days after its initial deployment. It subsequently caught L. sericata at a faster rate than the other two traps. The data suggest that the freeze-dried liver bait used in the Agrilure trap required a period of about 30 days to become fully rehydrated and decompose to the degree required to attract and catch L. sericata. Once the bait was attractive, however, the trap outperformed the other two traps in terms of the rate of L. sericata capture. The Agrilure trap would appear to be the most effective of the designs tested for use against sheep blowfly and blowfly strike in the U.K., but care would be needed to ensure that the traps were deployed in advance of the blowfly season so that the bait was suitably aged when trapping was required.

Impact of the South-to-North Water Diversion Project on the transmission of Schistosoma japonicum in China

The South-to-North Water Diversion Project (SNWDP) is currently the key, national, water-conservation project in China, designed to optimise the use of water resources and relieve the water shortages in the north of the country. As one of the main water intakes for the project, that of the Eastern Route Scheme (ERS), is a breeding site for Oncomelania hupensis (the intermediate host of Schistosoma japonicum), there is concern that the snail may be carried far to the north, in the water passing through the project. To see if they could survive and breed to the north of their current range in China, O. hupensis were collected in marshland near Nanjing City and transferred to cages, on the banks of fish ponds, in the cities of Zhenjiang (in Jiangsu province, at 32 degrees 10'N), Xuzhou (in the same province but at a latitude of 34 degrees 23'N) and Jining (in Shandong province, at 35 degrees 23'N). Except over the first 6 months in Xuzhou, the snails moved north of their natural distribution did not survive and reproduce as well as those in Zhenjiang, and all those transferred to Jining died out within 1 year. Although the snail populations in Xuzhou survived for 7-8 years and retained their infectivity to S. japonicum, histological and histochemical studies revealed abnormalities in the reproductive organs of these snails. It is concluded that, unless global warming significantly increases the minimum winter temperatures in northern China, the SNWDP is unlikely to result in the northward spread of schistosomiasis japonica.

An Immunohistochemical Assessment of the Cutaneous Immune Response to Louse Infestation in Cattle

Skin samples were taken from 10 experimental cattle exposed naturally, during a period extending over two winters, to Bovicola bovis and Solenoptes capillatus, five becoming infested and five being protected from infestation by repeated treatment with ectoparasiticides. Skin sections were examined histopathologically and immunohistochemically for expression of the immune cell markers CD3, CD4, CD8 and class II antigens of the major histocompatibility complex (MHC). Louse-infested cattle had a mixed infiltration of the superficial dermis and perifollicular regions with eosinophils and mononuclear cells. The skin of infested cattle differed from that of non-infested cattle in showing significantly more cells expressing CD3, CD4 and MHC class II (P<0.05). Many of the MHC class II(+) cells had dendritic morphology, suggesting active antigen presentation within the lesions. Louse infestations have previously been thought to produce a type 1 hypersensitivity response, mediated by Th2 lymphocytes. However, the increased number of lymphocytes and antigen-presenting cells observed in the present study suggests that in chronic infestation there is activation of local cell-mediated (Th1) immunity.

The detection of anthelmintic resistance in nematodes of veterinary importance

Before revised World Association for the Advancement of Veterinary Parasitology (WAAVP) guidelines on the detection of anthelmintic resistance can be produced, validation of modified and new methods is required in laboratories in different parts of the world. There is a great need for improved methods of detection of anthelmintic resistance particularly for the detection of macrocyclic lactone resistance and for the detection of resistant nematodes in cattle. Therefore, revised and new methods are provided here for the detection of anthelmintic resistance in nematodes of ruminants, horses and pigs as a basis for discussion and with the purpose that they are evaluated internationally to establish whether they could in the future be recommended by the WAAVP. The interpretation of the faecal egg count reduction test has been modified and suggestions given on its use with persistent anthelmintics and continuous release devices. An egg hatch test for benzimidazole (BZ) resistance is described. A microagar larval development test for the detection of benzimidazole and levamisole resistance provides third stage larvae for the identification of resistant worms. The sensitivity of these two tests can be increased by using discriminating doses rather than LD(50) values. Details are given of a PCR based test for the analysis of benzimidazole resistance in strongyles of sheep and goats, horses and cattle. Although promising for ruminant trichostrongyles, quantitative determination of gene frequency using real time PCR requires further development before PCR tests will be used in the field. Apart from faecal egg count reduction tests there are currently no satisfactory tests for macrocylic lactone resistance despite the great importance of this subject. Except for treatment and slaughter trials there are no validated tests for fasciolicide resistance or for the detection of resistance in cestodes.

Rapid selection for ivermectin resistance in Haemonchus contortus

Lambs infected with two isolates, one British and one American, of Haemonchus contortus were treated with increasing doses of ivermectin. Eggs from the highest dose that had not eliminated the infection were cultured and larvae used to infect another lamb. After three generations the H. contortus was resistant to 0.2 mg/kg ivermectin. The results stress the ease with which ivermectin resistance can be selected if high selection pressure is applied.

Prevalence and diagnosis of parasites of the stomach and small intestine in horses in south-west England

Parasites were extracted from the stomach and small intestine of 118 horses at slaughter. The most abundant species was the tapeworm Anoplocephala perfoliata. Maximum likelihood analysis was used to investigate the relationship between the number of worms and their total weight, and the ability of an antibody-based elisa to diagnose the level of infection. The total weight of tapeworms increased towards a maximum as the number of worms increased, suggesting a population density-dependent constraint on the weight. The number of A perfoliata present could be predicted approximately from the results of the elisa. Although wide variation in elisa optical densities confound interpretation in individual animals, tests on groups of animals could provide a useful reflection of overall levels of infection.

Anthelmintic resistance – looking to the future: a UK perspective

The full extent of anthelmintic resistance in nematodes of farm animals is not known. Resistance can be detected with a faecal egg count reduction test and two in vitro tests, the egg hatch and larval development tests. The sensitivity of these two in vitro tests can be increased by using discriminating doses rather than calculating LD50 values. Only benzimidazole resistance can be detected with PCR based tests because the molecular mechanisms of resistance to levamisole and the macrocyclic lactones remain unknown. Resistance detection is important because it enables the appropriate management strategies to be put in place. The development of resistance is delayed by keeping sufficient parasites in refugia (not exposed to anthelmintic), but the necessary management details have not yet been validated in the field. It is probably too late to use combination products to delay the development of resistance, except in cattle but quarantining animals to prevent introduction of resistant helminths onto a farm is important. Dilution of resistant worms with susceptible ones is only at the preliminary research stage and the application of non-chemical methods of control to delay resistance is not yet a practical option. Extensive research is required to manage resistance, especially in the control of resistance in Fasciola hepatica.

Efficacy of two cyclooctadepsipeptides, PF1022A and emodepside, against anthelmintic-resistant nematodes in sheep and cattle

Resistance against the major currently available anthelmintics has reached a critical level in many small ruminant herds world-wide, and is increasingly becoming a problem in horses and cattle. Therefore, new products with different modes of action are urgently needed. Recently, such a new class of compounds, the anthelmintically active cyclooctadepsipeptides, was described. Here, the effects of cyclooctadepsipeptides on benzimidazole-, levamisole- and ivermectin-resistant populations of Haemonchus contortus in sheep as well as an ivermectin-resistant Cooperia oncophora population in cattle were studied. Experimentally infected sheep and cattle were used. Animals were treated orally, subcutaneously, or intravenously with cyclooctadepsipeptides. The anthelmintic effects were assessed by means of fecal egg count reductions and/or worm count reductions. Both, PF1022A and emodepside were found to be fully effective against these parasite populations. These findings confirm that this new class of compounds acts by a different mode of action compared to the above-mentioned anthelmintics.

Resistance to benzimidazole and macrocyclic lactone anthelmintics in cattle nematodes in Argentina

In April 2003, persistent scouring and ill-thrift that was reported in calves form an intensive beef rearing operation in central Argentina despite treatments with benzimidazole and ivermectin. In order to conduct a controlled faecal egg count reduction test on this herd, 40 calves 5-8-months-old were selected on the basis that they had a nematode eggs per gram (epg) of faeces count greater than 150. Animals were divided into four groups (1-4) of 10 calves. Calves of groups 1-3 were treated, respectively, with subcutaneous injection of ivermectin (200 mcg/kg), ricobendazole (4 mg/kg) and levamisole (7.5 mg/kg), while calves of group 4 remained as untreated controls. The egg count reductions carried out 10 days later were lower than 15% in calves treated with ivermectin and ricobendazole, but 100% in animals receiving levamisole. Pooled post-treatment faecal cultures showed larval percentages of 92 and 95 for Haemonchus and 8 and 5 for Cooperia in the faeces of calves treated with ivermectin and ricobendazole, respectively. This is the first reported case of Haemonchus parasiting cattle showing simultaneous resistance to avermectins and benzimidazole type anthelmintics.

Copro-antigen capture ELISA for the detection of Teladorsagia (Ostertagia) circumcincta in sheep: improvement of specificity by heat treatment

A copro-antigen capture ELISA for the detection of Teladorsagia circumcincta infection in sheep was developed and evaluated. Experiments with faeces from worm-free sheep, that had been spiked with known concentrations of excretory–secretory (E–S) antigen indicated that a positive signal was generated with 180 ng of E–S/ml. A nested design, based on 8 infected and 8 worm-free sheep, was employed to assess the stages during sample preparation contributing to variation in signal from the assay. This showed that 87% of the variance in the optical density readings (ODs) was directly explained by infection status. Variation between individual sheep within infection groups, and between samples at various stages in the assay, collectively accounted for the remaining variance. Initial evaluation of specificity using faeces from animals carrying a range of monospecific infections indicated cross-reactivity with Haemonchus contortus and Nematodirus spathiger. However, by treating the supernatant from faeces for 20 min at 100 °C, the cross-reactive signal was eliminated whilst the specific signal was largely preserved. Heat treatment of faeces from 12 non-infected sheep, 12 sheep with T. circumcincta and 6 with H. contortus resulted in sensitivity being increased from 66·7 to 85·7%, and specificity from 62·5 to 87·5%. OD values showed a significant positive relationship with adult worm burdens, although at low infection intensities there was some overlap between infected and worm-free animals. We discuss the application of CC-ELISAs in facilitating selective chemotherapy of sheep, as a means of avoiding the development of anthelmintic resistance in pastoral regions where sheep are farmed on a large scale.

Relationship between lice infestation and leather damage in cattle

The relationship between lice infestation and leather damage was investigated in a trial involving 61 cattle, half of which were treated with ectoparasiticides for lice control either in their first or second year. Hides from the lice-free and lousy calves were removed manually at an abattoir, tanned and inspected for lice-related damage, commercially referred to as light spot and/or fleck. In both the first- and second-year animals there was a significant difference between the hides of the lousy and lice-free animals, confirming that the chewing louse Bovicola bovis is a cause of winter light spot. There was also a difference between the two groups in the levels of scratch damage. After the infested animals had been treated with fenvalerate and eprinomectin to kill all the lice, the damage to the hides had not been fully reversed 13 weeks later.

Field evaluation of a test for praziquantel resistance in Schistosoma sp

A simple rapid test for detecting praziquantel resistance in Schistosoma sp., involving change in shape of miracidia on exposure to praziquantel, was evaluated in China. Tests on miracidia hatched from eggs collected from naturally infected goats were run in a field laboratory in Jiangxi Province and a research laboratory in Shanghai. The mean values in the two laboratories were not significantly different, but the variation between individual samples in the two laboratories suggests that a delineating dose will be required for routine diagnosis of resistance. Confirmation that resistance would have been detected in Schistosoma japonicum must await the isolation of a resistant isolate. The tests suggested that the infection in the goats was susceptible to praziquantel as did chemotherapy of water buffaloes with 25mg/kg. This gave a 95% cure rate on the first treatment and 100% with a second treatment, similar to that found previously in human patients.

Adult worm tegumental damage and egg-granulomas in praziquantel-resistant and -susceptible Schistosoma mansoni treated in vivo

The effect of treatment with praziquantel (PZQ) on the tegument of adult Schistosoma mansoni worms and on liver egg-granulomas has been examined in mice infected with PZQ-resistant and -susceptible parasite isolates. Two PZQ-resistant S. mansoni isolates, one selected by passage in the laboratory under drug pressure and one from Senegal established from eggs excreted by an uncured patient, were compared with PZQ-susceptible control isolates. Scanning electron microscopic observations on the tegument of Schistosoma adult worms treated in vivo with PZQ showed that more severe damage was inflicted by PZQ on susceptible worms than on drug-resistant worms. Observations on the pathology of Schistosoma egg-granulomas in the liver of infected mice after treatment with PZQ indicated that eggs from susceptible control isolates were more sensitive to PZQ than those from drug-resistant isolates.

Sustainable use of anthelmintics in grazing animals

It is suggested that the major factor in avoiding the development of anthelmintic resistance is the percentage of worms that do not encounter the anthelmintics (worms in refugia). This in turn is determined by the numbers of larvae on pasture, the percentage of animals treated and whether any stages in the host can avoid the action of anthelmintic. To maintain anthelmintic efficacy the percentage of worms in refugia must be sufficiently large. In cattle, this should involve treating only first-year animals and using a different pasture each year for calves. For sheep, only animals that have to be treated should be dosed with anthelmintic and clean grazing strategies that involve the use of anthelmintics should be avoided. For horses, reliance should be placed on the removal of faeces from pasture and only treating when the animals' condition requires it. Without a change in anthelmintic use there is the likelihood of increasing numbers of cases for which no anthelmintic is effective and animal welfare may be compromised.

Helminth control used by trainers of thoroughbreds in England

A telephone survey was conducted of the methods used to control parasitic worms at 106 thoroughbred training yards. Most of the horses were allowed access to grass and were therefore at risk of infection. The control methods relied primarily on the use of anthelmintics and appeared reasonably successful because only 44 per cent of trainers reported observing clinical signs of nematode infections. They dosed their horses frequently, 40 per cent treating every four to six weeks and 25 per cent treating every seven to eight weeks. New arrivals on yards were usually treated with anthelmintic but the strategies used would be unlikely to prevent the introduction of anthelmintic-resistant nematodes on most yards or to deal with encysted cyathostomes. Trainers were responsible for the design of most control schemes, and only 42 per cent of them based their choice of anthelmintic on veterinary advice.

Widespread insecticide resistance in head lice to the over-the-counter pediculocides in England, and the emergence of carbaryl resistance

BACKGROUND

Increasing resistance to insecticides used for the control of head lice infestation has been documented over the last decade. Treatment failure and tolerance to insecticides have been validated in a number of studies undertaken in several U.K. centres.

OBJECTIVES

To establish the extent of insecticide resistance in head lice and acetylcholinesterase activity in the presence of carbaryl in head lice.

METHODS

Head lice were collected from school children in four centres across England (Exmouth, Loughborough, Leeds and South Shields), and tested in their response to the insecticides permethrin, phenothrin, malathion and carbaryl. Data were compared with information collected in Bristol and Bath in 1998 and with susceptible body lice. The activity of louse acetylcholinesterase was measured with and without carbaryl in head lice collected in Bristol, Leeds, Loughborough and in body lice. The efficacy of a 1% carbaryl lotion was compared in children in Bristol and Leeds.

RESULTS

Compared with body lice, head lice from all six centres were significantly different in their response (P < 0.0001) to permethrin, phenothrin and malathion after 2-h exposure tests. There were significant differences in louse acetylcholinesterase activity in body lice, and head lice collected in Loughborough and Bristol in the presence or absence of carbaryl (P < 0.001), indicating enzyme inhibition. However, the difference for lice from Leeds was not significant (P = 0.363) suggesting that the enzyme was resistant to carbaryl. Eighty-nine per cent of children treated in Leeds with carbaryl were cured compared with 100% in Bristol.

CONCLUSIONS

The data suggest head lice resistance is present in many parts of England to over-the-counter products containing synthetic insecticides (permethrin, phenothrin and malathion). They further suggest that resistance is starting to develop to carbaryl in head lice in Leeds and that extensive use of this product would lead to significant resistance.

Biological characteristics of praziquantel-resistant and -susceptible isolates of Schistosoma mansoni

If there is a change in the biological characteristics of schistosomes associated with the development of resistance to praziquantel, this could affect the transmission and pathology of the diseases they cause. To investigate this possibility, the host-parasite relationships of five praziquantel-resistant and five praziquantel-susceptible isolates of Schistosoma mansoni were compared in Biomphalaria glabrata snails and outbred CD(1) albino mice. Whether praziquantel-resistant or -susceptible, all the laboratory-selected isolates gave similar results in B. glabrata. However, the snails infected with any of three field-collected isolates from Senegal, each of which has been shown to be praziquantel-resistant, shed fewer cercariae and survived longer than the snails infected with the drug-susceptible or laboratory-selected, drug-resistant isolates. There were no differences between isolates in terms of their infectivity to mice. However, mice infected with any of four of the five drug-resistant isolates shed more eggs in their faeces than mice carrying the drug-susceptible parasites, and mice infected with any of the resistant isolates also had larger numbers of eggs in their tissues. Although granuloma sizes were generally similar for all isolates, the praziquantel-resistant isolates may be more pathogenic in mice than the susceptible ones because of their relatively high egg productions.

Susceptibility of Schistosoma japonicum to praziquantel in China

To look for possible evidence of the development of resistance in Schistosoma japonicum to praziquantel, we conducted a field study in China. During the non-transmission period of schistosomiasis a random sample of 2860 individuals from six villages in three provinces of China were examined using a parasitological stool examination. Of the 372 stool-positive subjects, 363 subjects were treated with a single oral dose of 40 mg/kg of praziquantel. Six to Seven weeks after treatment, of 334 subjects examined using the same stool examination, stool-negative results were found in 319 patients which represents a 95.5% parasitologic cure rate. Fifteen subjects still excreting eggs were treated a second time with the same dose of praziquantel. All stool samples, including those from participants re-treated with praziquantel, were re-examined 12 weeks after the first treatment and no stool-positive subjects were found. The results indicate that there was no evidence for reduced susceptibility of S. japonicum to praziquantel despite its extensive use in the main endemic areas of China for more than 10 years. The in vitro responses to praziquantel of cercariae, miracidia and eggs of S. japonicum compared with S. mansoni demonstrate that the cercariae, miracidia and eggs of S. japonicum are more sensitive to praziquantel than those of S. mansoni. More sensitive worms would be less likely to develop resistance and this could explain why no evidence for resistance was found in S. japonicum in China.

In vitro responses of praziquantel-resistant and -susceptible Schistosoma mansoni to praziquantel

The resistance status of five praziquantel-susceptible and five praziquantel-resistant isolates was confirmed by chemotherapy in CD(1) mice with 3 x 200mg/kg micronised praziquantel. Micronised praziquantel had higher efficacy than two other praziquantel formulations (prepared without milling). The five resistant isolates were less responsive to praziquantel than the five susceptible isolates (59-74% reduction in worm burden in resistant isolates compared with 92-100% in susceptible isolates). Observations were made on the in vitro responses of different stages of 10 isolates to praziquantel. There were different in vitro responses to praziquantel at the egg, miracidial, cercarial and adult stages of Schistosoma mansoni between praziquantel-resistant and praziquantel-susceptible isolates. There were differences in the response of resistant and susceptible isolates following exposure of freshly hatched miracidia to 10(-6)M praziquantel for 1 min and observing the percent change in shape. Using this test it should be possible to determine whether failed therapy in patients infected with S. mansoni is due to the presence of praziquantel-resistant worms. Similarly, by exposing freshly shed cercariae to 4 x 10(-7)M praziquantel and observing the percent of tail shedding over 80 min it should be possible to monitor for the presence of praziquantel-resistant worms in snails collected in the field.

The future of veterinary parasitology

Current evidence suggests research in veterinary parasitology is in decline despite its importance. This is particularly true in the UK where research funds have been diverted into BSE. Decline in interest in veterinary parasitology is at least in part due to the success of major pharmaceutical companies in producing a range of effective and safe anti-parasitic drugs. Research is needed because of the effects of parasites on animal welfare and the economic costs of parasites. However, there is little information on the actual costs of animal parasites. Another major reason for research is the development of drug resistance in protozoa, helminths and arthropods of veterinary importance. This is a serious problem particularly for sheep and goats in the southern hemisphere. A prioritised list of research requirements is suggested: (i) new drugs; (ii) resistance management; (iii) vaccines; (iv) breeding for resistance; (v) improved diagnostics; (vi) zoonoses; (vii) global warming and parasites. There is a major political challenge to raise the profile of veterinary parasitology and thus the funding essential for its advancement and the continued welfare and productivity of animals.

Drought and flock isolation may enhance the development of anthelmintic resistance in nematodes

A survey of anthelmintic resistant nematodes was conducted in sheep and goat flocks in Greece using in vivo and in vitro tests. Faecal egg count reduction tests in Macedonia were all greater than 99% indicating very high sensitivity of the nematodes to anthelmintics. In vitro tests showed benzimidazole resistant Teladorsagia circumcincta in 17 out of 106 flocks on small islands. On the mainland there were only three cases of benzimidazole resistance out of 310 flocks and animals had recently been introduced to the flocks. Flocks on the islands are isolated and there are higher temperatures than on the more mountainous mainland, where flocks tend to intermingle. It is concluded that drought and isolation are likely to be the major factors accounting for the development of anthelmintic resistance in nematodes in the island flocks.