Impact of tsetse control on the age-specific prevalence of trypanosomosis in village cattle in southeast Uganda

The prevalence of trypanosomosis, mean packed cell volume and anti-trypanosomal antibody levels in village cattle of different age groups (< 0.5 year, 0.5-2 years, > 2-5 years and > 5 years) in the areas with tsetse control were compared with those of corresponding age groups in areas without tsetse control in Tororo, southeast Uganda. The prevalence of trypanosomosis in cattle in the age groups of 0.5-2 years, > 2-5 years and > 5 years in the areas with tsetse control was significantly lower than in cattle in similar age groups in the areas without tsetse control (p < 0.5). Trypanosoma vivax was the most predominant Trypanosoma species in the areas with tsetse control, while T. congolense was the most predominant species in the areas without tsetse control. The mean Trypanosoma antibody levels in cattle in the age groups < 0.5 year, 0.5-2 years and > 2-5 years in the areas with tsetse control were significantly lower than those of the similar age groups in the areas without tsetse control (p < 0.5). The mean PCV values for cattle in the age groups 0.5-2 years, > 2-5 years and > 5 years from the areas with tsetse control were significantly higher than those of the similar age groups in the areas without tsetse control. Tsetse control appeared to have a considerable impact on the prevalence of trypanosomosis, distribution of Trypanosoma species, specific antibody levels and the packed cell volume of cattle in the different age groups.

Human nakedness: adaptation against ectoparasites?

Homo sapiens L. has been described as the naked ape, and this nakedness undoubtedly constitutes one of the most striking differences in appearance between man and the apes. Nakedness has been attributed at various times to sexual selection [1], aquatic stage [2], hunting [3], cooling [4], sex [5], neoteny [6] and allometry [7], most proposed explanations logically revealing some aspect of the phenomenon. However, most fail to account for the distinctiveness of man's hairlessness among mammals of the same size. Unfortunately, fossils cannot help us to explain how denudation occurred, and how it helped hominids to survive. In this paper I will present an old hypothesis with a new point of view incorporating more recent evidence.

Advances in flea control

With an increase in our knowledge of flea life cycle and biology, flea control has improved tremendously over the past 10 years. Treatment programs should be tailored to each case. The goal of effective flea control is to eliminate adults and to prevent reinfestation and the development of new generations of fleas. New products are of great benefit to flea-infested and flea-allergic animals and allow a safe and effective way to control fleas. Even if the consistent use of a topical adulticide alone is tempting, rotation and a combination of products should still be used to delay resistance. In addition, environmental flea control is a wise approach, especially in cases of severe infestation or in situations where there is a flea-allergic animal. Finally, in order to avoid failures and resistance, it is important to treat all pets in the household.

Estimating the effects of tsetse control on livestock productivity--a case study in southwest Ethiopia

A tsetse control campaign was started in January 1991 using a synthetic pyrethroid cypermethrin 'pour-on' applied monthly to cattle exposed to high levels of drug-resistant trypanosomes in the Ghibe valley of southwest Ethiopia. In December 1992, a cost-recovery scheme was introduced, and thereafter farmers paid for treatment. An average of 100 village Ethiopian Highland Zebu cattle were monitored monthly from March 1986 to February 1997. Individual animals in this herd were treated with diminazene aceturate (Berenil, Hoechst, Germany) at 3.5 mg/kg when trypanosomes were detected and their packed cell volume was less than 26%. Superimposed on this systematic trypanocidal chemotherapy, control of tsetse resulted in average reductions from 1992 to 1996 of 95% and 75% in the mean relative densities of tsetse and biting flies, respectively, and of 63% in the prevalence of trypanosomal infections in cattle. Despite these reductions, there was no significant increase in the body weight of the cows, calving rate or the mean body weight of calves at 12 months of age. There was, however, an average decrease of 57% in calf mortality (including still births) by 12 months of age, an increase of 49% in the ratio of live calves under 12 months of age to cows over 36 months of age, and an increase of 8% in the body weight of adult males.

Partial cross protection against Ichthyophthirius multifiliis in Gyrodactylus derjavini immunized rainbow trout

Partial cross protection against a skin-parasitic ciliate has been recorded in rainbow trout previously immunized with an ectoparasitic platyhelminth. The susceptibility to infection by Ichthyophthirius multifiliis differed significantly between naive and Gyrodactylus derjavini immunized rainbow trout. Fish partly immune to the ectoparasitic monogenean G. derjavini became less infected and experienced lower mortality than naive fish when exposed to I. multifiliis infections. In vitro studies on immobilization of theronts using decomplemented (heat-inactivated) serum from G. derjavini immune or non-immune hosts showed no immobilization. However, untreated serum from both immune and non-immune fish containing intact complement immobilized theronts (titre 128-256). In addition, non-specific priming of the host response with interleukin (IL-1), bacterial lipopolysaccharide (LPS), concanavalin A (Con A) or mannan did confer a partial resistance to I. multifiliis infection. This will suggest that non-specific factors including complement could be partly responsible for the host response against infections with this ciliate.

Peritrophins of adult dipteran ectoparasites and their evaluation as vaccine antigens

Several peritrophins of larvae of Lucilia cuprina (sheep blowfly) have demonstrated potential as vaccine antigens, and some have been characterised and cloned. These proteins are tightly associated with the peritrophic matrix, a chitinous tube or sac lining the lumen of the gut of most insects. The peritrophins require strong denaturants for their removal from peritrophic matrix. We now report the preliminary characterisation of peritrophins of the adult stage of L. cuprina and Haematobia irritans exigua (buffalo fly). Similar SDS-PAGE profiles were obtained for proteins extracted in SDS or urea from isolated adult peritrophic matrices of both species. Radioiodination of urea-extracted peritrophins improved sensitivity, indicating numerous proteins of 15-75 kDa. Direct radioiodination of L. cuprina peritrophic matrix preferentially labelled high molecular weight complexes and proteins of 80-90 kDa. Two-dimensional gel analyses of a urea extract of adult L. cuprina peritrophic matrix revealed that most proteins were moderately acidic. Antibodies produced against SDS-extracted peritrophins, or against sonicated peritrophic matrices of these two flies were crossreactive. The sera also appeared to recognise SDS-extracted components of Triton X-100 treated and washed adult peritrophic matrix of the mosquito, Aedes vigilax (Skause). This profile altered as the peritrophic matrix matured. In concordance with extracts from the adult L. cuprina and H.i. exigua peritrophic matrices, proteins in the 50-75 kDa region were immunodominant. The vaccine potential of the peritrophins of these Diptera were examined following vaccination of cattle and rabbits with adult H.i. exigua or L. cuprina peritrophins. When the adult life stages of H.i. exigua or two mosquitoes, A. vigilax and A. aegypti (Linnaeus), were fed on the sera or blood of vaccinated hosts, there were no detrimental effects to any life cycle stages of these Diptera.

Important parasites in poultry production systems

Poultry now accounts for 30% of all meat consumed. Parasites are a problem where ever poultry are raised, whether in large commercial operations or in small back-yard flocks, and economic losses can be significant. This paper will briefly review the major protozoan, helminth, and arthropod species in poultry including pathogenesis. Other topics will include the importance of the interaction of other diseases and parasites, and control of the infection by chemotherapy, management, and immunity.

Control of fleas on pets and in homes by use of imidacloprid or lufenuron and a pyrethrin spray

OBJECTIVE

To evaluate imidacloprid and the combination of lufenuron and pyrethrin to control flea infestations in households with pets.

ANIMALS

37 dogs and 19 cats in 34 flea-infested households.

PROCEDURE

Households were assigned randomly to 1 of 2 groups. Pets in group 1 were treated topically with imidacloprid on day 0, then once a month for 90 days. Pets in group 2 were given lufenuron orally on day 0 and at monthly intervals for 90 days and also were treated topically with a pyrethrin spray every 1 to 2 weeks throughout the study. Flea numbers in homes were assessed by use of intermittent light traps, and flea burdens on pets were assessed using visual area counts done once a week during the first month, then every other week.

RESULTS

One application of imidacloprid reduced flea burdens on pets by 96 and 93.5% on days 7 and 28, respectively, compared with day-0 burdens. Following 3 applications, flea burdens on pets and in homes were reduced by 98.8 and 99.9%, respectively. Lufenuron and pyrethrin spray reduced flea numbers on pets by 48.9 and 91.1% on days 7 and 28, respectively. By the end of the study, this combination reduced flea burdens on pets and in homes by 99.2 and 99.7%, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Imidacloprid applied topically or lufenuron administered orally along with a topically applied pyrethrin spray were effective in eliminating fleas on pets and in homes. Flea control can be achieved with topical application of adulticides or oral administration of insect growth regulators without concomitant treatment of the surroundings.

Long-lasting prevention against blowfly strike using the insect growth regulator dicyclanil

OBJECTIVE

To assess a ready-to-use formulation of dicyclanil to prevent blowfly strike on Merino sheep under Australian conditions.

DESIGN

Randomised clinical trials conducted in an environment house and in the field.

PROCEDURE

Two environment house trials were used to measure the protection against flystrike provide by a jetting or a ready-to-use 5% spray-on formulation of dicyclanil over 22 and 31 weeks respectively. Oviposition and strikes were recorded weekly for each sheep. In two field trials the occurrence of strike in Merino sheep treated off-shears or in long wool with dicyclanil or with cyromazine was compared for up to 38 weeks after treatment. Efficacy was assessed by calculating the cumulative percentage of sheep struck.

RESULTS

Under environment house conditions, sheep jetted with dicyclanil at 1.50, 0.75 and 0.30 g per sheep developed 0, 8 and 9 strikes respectively during the 22 weeks of the trial, whereas there were 358 strikes present in the placebo group. Sheep sprayed with dicyclanil at 2.25, 1.50 and 0.75 g per sheep developed 5, 11 and 29 strikes respectively between weeks 15 and 31 after treatment, whereas there were 185 strikes present in the untreated controls. In field trials the cumulative percentage of sheep struck reached 1% between weeks 12 to 13 after sheep had been treated with cyromazine. Sheep treated with dicyclanil reached the 1% limit at week 21 after treatment.

CONCLUSION

Under Australian field conditions, a ready-to-use 5% spray-on formulation of dicyclanil applied off-shears or to long wool protected Merino sheep from blowfly strike for a period of at least 20 weeks.

The pharmacology of halogenated salicylanilides and their anthelmintic use in animals

The halogenated salicylanilides are a large group of compounds developed mainly for their antiparasitic activity in animals. Several halogenated salicylanilides with potent antiparasitic activity have been synthesised of which only closantel, niclosamide, oxyclozanide, rafoxanide and resorantel are commercially available. Closantel and rafoxanide, which represent the most important drugs in the group, are used extensively for the control of Haemonchus spp. and Fasciola spp. infestations in sheep and cattle and Oestrus ovis in sheep in many parts of the world. Niclosamide is used extensively for its anticestodal activity in a wide range of animals. Antiparasitic activity of the halogenated salicylanilides has also been demonstrated against a large number of other internal parasites, in particular haematophagous helminths, and external parasites including ticks and mites, in a variety of animal species. Several cases of toxicity and mortality have been reported for closantel and rafoxanide in sheep and goats. Their unique pharmacokinetic behaviour appears to play an important role in the efficacy and safety of these compounds. The chemical and physical characteristics, mode of action, pharmacokinetics, antiparasitic activity and toxicity of the halogenated salicylanilides in animals are reviewed.

Cypermethrin pour-on synergized with piperonyl butoxide: effects on Haematobia irritans (Diptera: Muscidae) natural populations resistant to cypermethrin

Development of pyrethroid resistance in Haematobia irritans in Santa Fe province, Argentina, resulted in an increased use of pyrethroid insecticides, probably due to lack of suitable alternative treatments. We explored the efficacy of mixtures of cypermethrin and piperonyl butoxide (PBO) against pyrethroid-resistant H. irritans. Groups of 25 Holstein cows each, naturally infested with cypermethrin resistant H. irritans were assigned to treated or control groups in April, September, October and December 1997. Cattle in treated groups were medicated with pour-on oil formulations of 5% cypermethrin (dose = 4 mg per kg of body weight) with 5% or 10% PBO in April, and with a mixture containing 5% of both components thereafter. Efficacy was tested for 21 days after treatment. A treatment of 5% cypermethrin pour-on without PBO was evaluated in October 1997. Samples of horn flies were obtained before September, October and December treatments and exposed for 2 h to filter papers impregnated with different cypermethrin concentrations to determine the 50% lethal concentration (LC50). No difference in efficacy was found between cypermethrin pour-on formulations with 5% or 10% of PBO (more than 94% efficacy on day 21 after treatment). Efficacy of 5 % cypermethrin-5% PBO mixture decreased rapidly in the successive treatments (less than 40% efficacy was observed on day 21 after the December treatment), and the period after treatment with an efficacy higher than 95% was 14 days for the treatment carried out in April, 10 days in September; 7 days for the treatment performed in October and 4 days for the December treatment. The LC50 of cypermethrin was 36.6 microg per cm2 in September and increased to 116.6 and 226.1 microg per cm2 in October and December, respectively. It is concluded that the addition of PBO to cypermethrin did not provide a treatment that would give a long term control of pyrethroid resistant-horn flies.

Activity of a deltamethrin shampoo against Ctenocephalides felis and Rhipicephalus sanguineus in dogs

A controlled clinical trial was undertaken to assess the efficacy of an application of a 0.07% deltamethrin shampoo against fleas and ticks in dogs. Twenty beagles, housed in separate cages, were randomly allocated into two groups of 10. The dogs were infested with 50 Ctenocephalides felis and 50 Rhipicephalus sanguineus each, and parasites were counted 24 h (fleas) and 72 h (ticks) later (Day 0). Dogs, when state, were then treated with 25 ml of a shampoo containing 0.07% deltamethrin (Group 1). Dogs in Group 2 were the controls. Fleas and ticks were counted 24 h (Day 1) and 48 h (Day 2) after the shampoo was applied, and the parasites were then removed. All the dogs were reinfested with fleas and ticks on Days 2, 7, 9, 14, 16 and 20. Parasites were counted 24 and 48 h after each reinfestation. Effectiveness against fleas was calculated 24 h after infestation, and against ticks 48 h after infestation. This study showed that the application of 25 ml of shampoo containing 0.07% deltamethrin to beagle dogs weighing between 10.2 and 12 kg was very well tolerated. It controlled the parasites present on the animals at the time of application: with an efficacy of 100% against fleas 24 h after treatment and an efficacy of 95% against ticks 48 h after treatment. The treatment protected against flea reinfestations with an efficacy of 100% during the first week, >98% in the second week and >95% in the third week. It also gave >99% protection against tick reinfestations in the first week and >96% in the second week.

A primary animal health care approach to treatment and control of flea (Ctenocephalides felis) infestation in indigenous goats kept on communal grazing

This paper describes a primary health care approach to an infestation of indigenous goats by the common cat flea, Ctenocephalides felis. The flea species was identified using scanning electron microscopy. The infested goats were kept on communal grazing at Winterveld in the North-West Province. They were penned at night in housing made of wire and corrugated iron. The owner complained that the goats were lethargic. Fleas were found on the goats and flea larvae were found in the kraal. Haematology and blood biochemistry performed on the infested goats revealed no abnormalities; however, infestation caused irritation that made the animals lethargic. Available flea control methods for domestic animals were appraised in terms of cost, availability and ease of administration at a primary animal health care level using participatory extension methods. It was found that a carbamate powder was available, affordable and effective for flea control in this small flock of goats kept under communal grazing conditions. Although the authors had observed fleas on goats kept under similar conditions elsewhere in Mpumalanga and the North-West Province, this was the 1st time that the species had been identified.

Immunological control of arthropod ectoparasites--a review

The control of arthropod ectoparasites of livestock by systemically delivered chemicals was introduced in the 1950s. Their low cost, ease of use, and high level of efficacy ensured dependence upon them for ectoparasite control. However, current societal and scientific concerns regarding dependency upon chemicals have emphasised the need for the evaluation of environmentally safe alternatives for ectoparasite control. Immunological intervention for the control of ectoparasite populations, either through the selection of animals with resistant genotypes or vaccination, is consistent with principles of sustainable agriculture. Unlike the activity of chemicals, currently available ectoparasite vaccines do not induce a rapid knockdown of the parasite population and they do not protect the individual from parasitism. However, if these vaccines are used in an integrated pest-management programme, they have the potential to reduce parasite populations over successive generations and reduce or eliminate the need for chemical application.

Attitudes and practices of Queensland dairy farmers to the control of the cattle tick, Boophilus microplus

OBJECTIVE

To determine practices for the control of cattle ticks on dairy farms in Queensland, the attitudes of farmers to tick infestations and to identify opportunities for and barriers against the introduction of non-chemical methods of tick control.

DESIGN

A survey of 199 dairy farmers from tick-infested parts of Queensland was undertaken by 20 dairy advisers and stock inspectors from October 1996 to June 1997. The sample was a proportional, random selection of dairy farms from four regions. A personal interview was conducted with each farmer and answers to 134 questions were obtained.

RESULTS AND CONCLUSIONS

Most farmers were not concerned by cattle ticks on their own farms, although they believed that ticks are important to the dairy industry. They were most concerned about the development of chemical resistance by cattle ticks. Inadequate facilities and lack of motivation appeared to be the factors most limiting to improving the methods of control. Most farmers claimed to have only small numbers of ticks at worst. Although a control program recommended by the Queensland Dairyfarmers' Organisation was well regarded by farmers, few had adopted it. Many farmers saw no need to implement a strategic control program.

Pesticide use and residues on Queensland wool

OBJECTIVE

To determine practices for control of louse infestation and blowfly strike in Queensland sheep flocks that are associated with organophosphorous and synthetic pyrethroid residues on wool.

DESIGN

Information on residues was obtained from a survey of Queensland wool clips. Information on pesticide use was obtained from a trace-back postal survey. The association between pesticide use and residues was assessed using generalised linear models, controlling for potential confounding by flock location.

PROCEDURE

Between 1995 and 1997 Queensland wool clips were randomly sampled. Samples were tested for the presence and amount (mg per kg of greasy wool) of organophosphorous and synthetic pyrethroid pesticides. A questionnaire seeking information on flock characteristics and pesticide use was sent to the manager of each flock from which a wool sample was tested.

RESULTS

The median amount of OP and SP residue was 0.8 and 0.25 mg/kg, respectively, and 91 and 95% of wool samples contained < 8 mg/kg of OP and SP residues, respectively. The frequency of OP pesticide use for louse control was significantly (P = 0.005) associated with mean OP residue amount, and the timing of SP use for louse control, in relation to shearing, was significantly (P < 0.001) associated with mean SP residue amount.

CONCLUSION

Most Queensland wool clips have acceptable amounts of residues after the use of OP and SP pesticides, but wool growers can further reduce residues by effectively controlling louse infestation with pesticide applications early after shearing and the use of non-chemical methods of ectoparasite control.

Predicting insecticide resistance: mutagenesis, selection and response

Strategies to manage resistance to a particular insecticide have usually been devised after resistance has evolved. If it were possible to predict likely resistance mechanisms to novel insecticides before they evolved in the field, it might be feasible to have programmes that manage susceptibility. With this approach in mind, single-gene variants of the Australian sheep blowfly, Lucilia cuprina, resistant to dieldrin, diazinon and malathion, were selected in the laboratory after mutagenesis of susceptible strains. The genetic and molecular bases of resistance in these variants were identical to those that had previously evolved in natural populations. Given this predictive capacity for known resistances, the approach was extended to anticipate possible mechanisms of resistance to cyromazine, an insecticide to which L. cuprina populations remain susceptible after almost 20 years of exposure. Analysis of the laboratory-generated resistant variants provides an explanation for this observation. The variants show low levels of resistance and a selective advantage over susceptibles for only a limited concentration range. These results are discussed in the context of the choice of insecticides for control purposes and of delivery strategies to minimize the evolution of resistance.

Efficacy of zeta-cypermethrin as pour-on or spray formulations for the control of buffalo fly (Haematobia irritans exigua) in cattle

OBJECTIVE

To determine the efficacy of zeta-cypermethrin in controlling buffalo fly (Haematobia irritans exigua).

DESIGN

Five field trials in northern and central Queensland.

PROCEDURE

Zeta-cypermethrin pour-on at 2.5 mg/kg, spray at 62.5 ppm, deltamethrin pour-on and pour-on vehicle were applied to groups of 20 cattle. Buffalo fly counts were conducted three times before treatment and 3, 7, 14, 21, 28 and 35 days after treatment.

RESULTS

In central Queensland where synthetic pyrethroid resistance in buffalo fly populations was rare, 2.5 mg/kg of zeta-cypermethrin pour-on gave good control of buffalo fly for 4 weeks and was better than a deltamethrin product. A zeta-cypermethrin spray used at 62.5 ppm gave 14 days control. In far-north Queensland where resistance to synthetic pyrethroids and heavy rain was common, the maximum period of efficacy of zeta-cypermethrin pour-on was reduced to 2 weeks.

CONCLUSION

In areas where there is low resistance to synthetic pyrethroids among buffalo flies, zeta-cypermethrin pour-on can be expected to give good control for 4 weeks.

Mortality of horn fly (Diptera: Muscidae) larvae in bovine dung supplemented with loline alkaloids from tall fescue

Larvae of arthropod ectoparasites of livestock, such as the horn fly, Haematobia irritans (L.), may be exposed to acyl-loline alkaloids in dung of ruminant livestock ingesting herbage of the tall fescue (Festuca arundinacea Schreb.)-endophyte association [Neotyphodium coenophialum (Morgan-Jones & W. Gams) Glenn, Bacon & Hanlin comb. nov.]. Biological activity of alkaloid-supplemented bovine dung was assayed by growth, development, and survival of 1st instars of horn fly. An extract from tall fescue seed, containing N-formyl loline (NFL), N-acetyl loline (NAL), and loline (59:21:20 by mass, respectively) caused 100% mortality of horn fly larvae when dung was supplemented at > or = 100 micrograms/g. Probit analysis of data corrected for natural mortality indicated a LD50 of 30 micrograms/g (95% fidicial limits: 20-49 micrograms/g). When horn fly larvae were introduced to dung supplemented with up to 50 microM of acyl-loline derivatives, mortality of larvae varied significantly between alkaloids (P < 0.0001). Probit analysis indicated that NFL [LD50: 34 microM (95% fidicial limits: 3-53 microM)] was more toxic than NAL [LD50: 46 microM (0-83 microM)], and that loline hydrochloride was not toxic.

Ivermectin treatment did not increase slaughter weight of first-year reindeer calves

To investigate if antiparasitic treatment of reindeer calves during the summer could increase their carcass weight during the slaughter period in autumn and winter, 529 reindeer calves were allocated to three groups, weighed, and marked with individually numbered plastic ear tags in early July, 1995. One of the groups was left untreated, another was treated with ivermectin injection at 200 micrograms/kg, and the third with pour-on ivermectin at 500 micrograms/kg. Following slaughter, carcass weights were received from 231 animals, and there was no difference between the treatment groups.

Lack of relay toxicity in ferret hybrids fed carbaryl-treated prairie dogs

Carbaryl (1-napthol methylcarbamate) is being considered for control of fleas on prairie dogs (Cynomys spp.) used in black-footed ferret (Mustela nigripes) recovery in the western United States. The potential for relay toxicity in ferrets was determined by feeding carbaryl treated prairie dogs to black-footed ferret x Siberian polecat (M. eversmanni) hybrids. Adult prairie dogs were treated topically with 2.5 g of commercial 5% carbaryl dust sold as flea powder. After 14 days prairie dogs were killed and fed to ferrets. Potential for relay toxicity was evaluated by analyzing ferret blood cholinesterase (CHe), prairie dog brain Che, and hepatic carbamate concentration. There was no difference between pre- and post-exposure blood CHe activity, nor did treated prairie dog brain CHe differ significantly from controls. Post-exposure blood CHe did not exhibit reactivation after dilution in aqueous buffer. Hepatic carbaryl concentrations were less than detection limits (50 ppb). Based on these results, we conclude that short-term use of carbaryl for flea control on prairie dogs does not pose a hazard of relay toxicity in black-footed ferrets.

Antifeeding effect of several insecticidal formulations against Ctenocephalides felis on cats

Evaluation of insecticidal activity of flea products is generally based on counting live fleas in the animal's coat 24 and 48 hours following artificial infestation. This approach, however, does not allow to specify whether the fleas have had the opportunity to bite and take a bloodmeal prior to their death. To address this question, 30 cats were alloted to six groups of five animals. Each cat was housed in a separate cage. At Day 0, each group of cats received a single treatment as follows: Group 1: spot-on application of imidacloprid: cats < 4 kg: 40 mg/cat, cats > or = 4 kg: 80 mg/cat (Advantage). Group 2: spot-on application of fipronil: 50 mg/cat (Frontline spot-on). Group 3: spray application of fipronil: 7.5 mg/kg b.w. (Frontline spray). Group 4: foam application of permethrin 40/60: 50 mg/kg b.w. (Defencat). Group 5: aerosol spray application of dichlorvos + fenitrothion: one second/kg b.w. (NuvanTop). Group 6: control group: cats were left untreated. One hour after treatment, each cat was infested with 50 unengorged young adult fleas, Ctenocephalides felis, deposited along the dorsal midline. One hour later, each cat was carefully combed using a fine-toothed comb (13 teeth/cm). Collected fleas were swatted to deteci blood in their abdomen. To the manufacturers respective product use instructions and efficacy claims, reeinfestations were made at Days 3, 7, 14 in all groups; at Days 21 and 30 in Groups 1, 2, 4, 6; at Days 35 and 42 in Groups 3 and 6. The cats were combed one hour after each reinfestation. The results indicate that the topical application of imidacloprid or fipronil does not prevent fleas from biting and feeding within the first hour after infestation prior to being killed while the topical application of dichlorvos/fenitrothion and permethrin let to a better than 80% decrease of the number of engorged fleas for three and seven days post treatment, respectively.

Comparative activity in dogs of deltamethrin- and diazinon-impregnated collars against Ctenocephalides felis

OBJECTIVE

To compare effectiveness of deltamethrin- and diazinon-impregnated collars against fleas (Ctenocephalides felis) in an experimental infestation.

ANIMALS

30 Beagles.

PROCEDURE

Dogs were housed in separate cages. Dogs were infested with 50 fleas each, and fleas were counted 24 hours later. Dogs were then fitted with a collar containing 4% deltamethrin (group 1) or 15% diazinon (group 2). Dogs in group 3 were controls. Fleas were counted 24 and 48 hours after collars were applied, and fleas were then removed. Dogs were reinfested with fleas on days 7, 14, 28, 60, 90, 120, 150, and 210. Fleas were counted 24 and 48 hours after each reinfestation.

RESULTS

48 hours after applying collars, flea counts were not notably decreased. Effectiveness in groups 1 and 2 was 24 and 29%, respectively. Infestation on day 7 was controlled, to a comparable extent, by both insecticides (effectiveness approx 85%). Effectiveness > 97% was obtained after collars had been worn for 14 days. Between days 14 and 91, both collars had comparable effectiveness (> 93%) that did not differ significantly. After day 91, effectiveness of the collar containing diazinon decreased sharply, whereas that of the collar containing deltamethrin remained > 90% until day 152.

CONCLUSIONS AND CLINICAL RELEVANCE

The collar containing deltamethrin controlled flea populations on dogs beginning 14 days after application and continuing until day 150. The collar containing diazinon controlled infestation for 90 days. Deltamethrin-impregnated collars are a new formulation that can be introduced into a program to easily control fleas.

Efficacy of imidacloprid for removal and control of fleas (Ctenocephalides felis) on dogs

OBJECTIVE

To evaluate efficacy of a 9.1% (w/w) imidacloprid solution, applied topically, to remove fleas from dogs and the duration of residual flea control when dogs were exposed to continuing flea infestation.

ANIMALS

32 adult mixed-breed dogs.

PROCEDURE

Dogs were allocated to 4 groups of 8 dogs each; dogs of 3 groups received a single dose of imidacloprid, and those of the fourth group received excipient. Each dog was infested with 100 adult fleas on study days -3, -1, 6, 13, 20, 27, and 33. Treatments were applied on day 0. Each dog was examined for live fleas on days -2, 1, 7, 14, 21, 28, and 34. Posttreatment efficacy was determined by comparing the mean number of live fleas remaining on the treated dogs with the mean number of live fleas remaining on the control dogs.

RESULTS

All 3 imidacloprid dosages provided flea control > or = 96.9% one day after treatment. Maximal efficacy of all 3 dosages (99.1 to 100%) was observed at 7 days after treatment. Flea control with 3.75 mg of imidacloprid/kg of body weight ranged from 94.4 to 96.9% for days 14 to 28 and decreased to 91.6% by 34 days after treatment. Flea control with 7.5 and 10.0 mg of imidacloprid/kg was 97.8 to 100% through day 28. At day 34, dosages of 7.5 and 10.0 mg of imidacloprid/kg were 97.6 and 96.9% efficacious, respectively.

CONCLUSION

7.5 or 10.0 mg of imidacloprid/kg are equivalent and superior to 3.75 mg/kg for flea control over the course of a 34 day posttreatment period.

CLINICAL RELEVANCE

Monthly imidacloprid application of 7.5 to 10 mg/kg will rapidly kill existing and reinfesting flea infestations on dogs and break the flea life cycle by killing adult fleas before egg production begins.

Novel vaccines for ectoparasites

Novel vaccines against ectoparasites have the potential to be cost-effective new technology for pest control that avoids some of the real and perceived problems with insecticide and acaricide usage. Nevertheless, their development is in its infancy. A vaccine against the cattle tick Boophilus microplus, the world's first vaccine against an ectoparasite, is in field use in Australia. Considerable effort had gone into the development of a vaccine against the sheep blowfly Lucilia cuprina, while other vaccines are at an earlier stage of development. The identification of critical antigens and their production as effective recombinant proteins remains the greatest hurdle. Characteristics of the few known antigens and the mode of action of the protective immune response are discussed. Development of further vaccines will depend on recognition of likely antigenic targets. The efficacy of such vaccines will depend on the characteristics of the target species, in particular its digestive biology and the way in which the novel vaccine impacts on the parasite population.

Sheep dip chemicals and water pollution

The Tweed River Purification Board's objective of reducing the numbers and significance of water pollution incidents by a proactive approach based on persuasion and education is described. This has consisted of prioritising potential pollutant sources which have then been investigated in detail followed by discussion and agreement with dischargers as to remedial measures. The paper describes in detail the Board's investigation of pollution from the organophosphate (OP) sheep dips, Diazinon and Propetamphos, and their effects on surface waters throughout its area. Examination of historical incidents and a preliminary survey of sheep farms in the Ettrick Water catchment in 1989 confirmed the potential for serious pollution. Comparison of OP concentrations in the Ettrick with strategic sites throughout the catchment confirmed the widespread nature of the problem and led to visits to every sheep farmer in the Board's area in 1990 and 1991, when 795 dippers were investigated. The study involved risk assessments of the location of dippers and the spent dip disposal practice which confirmed that poor siting, inadequate disposal and particularly poor management of the dipping operation were responsible for the pollution problems observed. Practical advice on the management of dipping and disposal of spent dip was given individually to farmers. The success of the project in reducing pollution is reflected in a significant and sustained reduction in OP concentrations in environmental samples. The future of ectoparasitic treatments for sheep, the potential for antidotes to spent sheep dip and legal obligations relating to its safe disposal is also considered.

Ecological implications of control strategies: arthropods of domestic and production animals

The control of arthropods of veterinary importance represents a disturbance for the ecosystem and its animal community. This disturbance can influence the densities of target and non-target organisms and their associated indirect interactions in the food web, leading to reductions in the species richness and diversities in the communities involved. Finely tuned control affecting the target organism alone can have unexpected consequences, depending on the relationships between the target and other organisms within the food web. Broad-spectrum control methods will have more wide ranging and less predictable consequences. Modifications within the community caused by arthropod control can take place over generations and may not be immediately apparent. Most modern techniques of control are designed to minimize environmental impact by concentrating specifically on the target organism. The effects of control of arthropod pests of domestic and production stock must be seen against a background of more general effects caused by rural development which acts to modify the environment continuously over a long time span.

Screwworm eradication program in Central America

The Screwworm Eradication Program has been extremely successful in its efforts to achieve its goal of eradication of screwworms through Central America and establishment of a permanent biological barrier in the eastern half of Panama. Following eradication of screwworms from Mexico in 1991, eradication was achieved in Belize in 1992, in Guatemala in 1993, and in El Salvador in 1994. Honduras has been free of screwworms since January 1995, and the number of cases in Nicaragua has dropped, as of April 1995, to about 4% of the average number of cases found during the period June-August 1993.

Overview of the current international trade in ornamental fish, with special reference to Singapore

The value of international trade in ornamental fish in 1992 was US$247 million, based on import statistics, or US$140 million, based on export statistics. Between 1983 and 1992, annual growth of imports and exports averaged 21% and 16%, respectively. More than 100 countries are involved in this trade. The top five exporting countries in 1992 were Singapore (32%), Hong Kong (11%), the United States of America (USA) (11%), the Netherlands (7%) and Germany (6%). The top five importing countries were the USA (26%), Japan (17%), Germany (9%), the United Kingdom (9%) and France (7%). The bulk of ornamental fish trade internationally are freshwater in origin and farm-bred. Marine ornamental fish species and invertebrates are mainly wild-caught. An estimated one billion ornamental fish are exported annually, involving one thousand species or more. Mass-cultured fish species - e.g. guppy, tetra, angel, swordtail, platy, goldfish, koi - have long been established in the market and will continue to constitute the major market share. The author discusses the results of a trial on quality enhancement of the shipment of guppies, and makes recommendations on treatment to minimise stress and disease transmission.

Impact of an orally administered insect growth regulator (lufenuron) on flea infestations of dogs in a controlled simulated home environment

OBJECTIVE

To evaluate the ability of lufenuron to control cat flea (Ctenocephalides felis felis) populations on dogs under conditions simulating a naturally infested home environment.

DESIGN

2 treatment and 2 control groups of dogs. Treated dogs received lufenuron in tablet form monthly, and controls received excipient. Dogs had unrestricted access to indoor (carpeted) and outdoor (grassy) environments in which self-propagating flea populations had been established.

ANIMALS

17 adult female Beagles.

PROCEDURE

Dogs were monitored for 77 days after initial infestation with fleas and 70 days after initial treatment. Efficacy of the drug was calculated on the basis of absolute reduction in flea counts and as a percentage of control.

RESULTS

Lufenuron administration caused a statistically significant (P < 0.05) reduction in flea burdens in treated dogs, compared with controls. Initiation of treatment 7 days after infestation resulted in 75% control of F1-generation and 97% control of F2-generation fleas over a 70-day posttreatment period.

CONCLUSIONS

Lufenuron was highly effective in reducing flea populations on dogs. The time required for control will vary with the duration (generation time) of the flea reproductive cycle and, hence, the geographic area in which the product will be used. The experimental results are most relevant to use of the product for control of an existing flea population in the Midwest.

A case of tungiasis

Tunga penetrans is a burrowing flea that is prevalent in Central and South America, the Caribbean, tropical Africa, India, and Pakistan, and rarely is imported to the United States. Tungiasis results from the cutaneous infestation of humans by the gravid female flea, T. penetrans. We report a case of tungiasis in a female who had been on a missionary expedition along the Brazilian Amazon River. The clinical presentation, life cycle, differential diagnosis, military and historical aspects, and treatment are discussed.

Resistance and the control of sheep ectoparasites

For about 100 years Australian woolgrowers have used a variety of chemicals to control blowflies, lice and other ectoparasites of sheep. While the chemicals have changed considerably the application technology has not changed very much at all. Chemicals registered for use on sheep have paralleled the evolution of synthetic insecticides with the unfortunate consequence of the development of resistance in the Australian sheep blowfly, Lucilia cuprina, following closely behind. Organochlorine (dieldrin) resistance peaked at about 70% in 1958 when unacceptable residues in meat and wool forced their withdrawal. Organophosphate (OP) resistance appeared in 1965. With no alternative insecticide classes until 1979, OP resistance reached near fixation levels by the early 1970s and has remained unchanged. OP resistance has reduced the protection period from over 16 weeks to about 6 weeks. Moreover, resistance has decreased the effectiveness of many flystrike dressings to unacceptably low levels. OPs are still very effective against sheep body lice, Bovicola ovis but control is hampered by inadequate application via plunge or shower dipping. Synthetic pyrethroid (SP) pour-on products were released in 1981 but resistance developed by 1985 and many woolgrowers were unable to eradicate lice with pour-on products. Highest Resistance Factors at this time were only about 26 x but this was sufficient to prevent pour-ons working efficiently. By 1991 a population from Hartley in NSW was found to be 642 x resistant to cypermethrin with side-resistance conferred to the other SPs. SP resistance was partially suppresible by piperonyl butoxide but field trials suggested that the resulting improvement in efficacy was not sufficient to be commercially attractive. OPs remain very effective if applied correctly and the release of ivermectin and 2 benzoylphenyl urea products significantly improves the prospects for resistance management. However the increasing environmental concern about the persistence of chemical residues in wool has stimulated interest in biological control of sheep lice by Bacillus thuringiensis.

The cat, the flea, and pesticides

Recent advances in our knowledge of cat flea biology and the discovery of new nontoxic control methods have greatly simplified and improved flea control. Instead of relying on adulticides for the bulk of flea control, the veterinarian now focuses on the immature stages, particularly the larvae and the eggs. By doing this, environmentally "friendly" flea control methods are employed that are much safer for the veterinarian, the pet owner, and the cat.

Species of flea found on cats and dogs in south west England: further evidence of their polyxenous state and implications for flea control

Fleas were collected from 60 dogs and 32 cats living in south west England. Ctenocephalides felis felis and Ctenocephalides canis were found on both dogs and cats, with a marked preponderance of C felis felis on both species. More female fleas than males were found. There was no apparent tendency for C canis to be found more often in rural areas than in suburban areas. The survey confirmed the polyxenous nature of both species of flea. The significance of this state is discussed in relation to flea control, and the author concludes that it is unlikely that all significant flea species could be completely eliminated from the environment of pet animals.

Efficacy of lufenuron against developmental stages of fleas (Ctenocephalides felis felis) in dogs housed in simulated home environments

Twenty-four, adult, female Beagles were arranged by body weight from greatest to least and allocated to 2 groups of 12 dogs, using random numbers. Dogs were housed collectively in 2 adjacent metal buildings, each divided into 4 rooms measuring 2.1 x 3.7 m. Each room was paneled and carpeted and had an access door to the outside with a connecting run that measured 2.1 x 9.1 m. Each run had a surface consisting of 5 cm of pea gravel overlaying 5 cm of sand, and was partially covered by an awning that provided shade at its proximal end. For placement in room/run units, dogs in each of the treated and control groups were alloted to 4 subgroups of 3 dogs each. Each subgroup of dogs was placed in a separate room/run unit. Units containing treatment or control subgroups were alternated to avoid placing identically treated subgroups adjacent to each other. Dogs of subgroups A, C, E, and G were treated with lufenuron monthly at a minimal target dosage of 10 mg/kg of body weight; those of subgroups B, D, F, and H were treated with excipient tablets. Dogs were treated on study days 7, 37, 68, and 98. Each dog was infested with 100 newly emerged, unfed, insectary-reared, adult Ctenocephalides felis on each of study days 0 and 2. Thereafter, infestations on all dogs were dependent on continued development of fleas either in the indoor or outdoor environment. Numbers of fleas on each of the treated and control dogs were determined, using a nondestructive counting technique on days 6, 14, 21, 28, 35, 56, 70, 84, 98, 112, and 119.(ABSTRACT TRUNCATED AT 250 WORDS)

Jigger infestation in children in a rural area of Rivers State of Nigeria

During a survey in April 1991 to determine the immunisation status of 218 children resident in a rural riverine community, 49 (22.48) were found to have been infested with Tunga penetrans. Itching and ulceration were the commonest symptoms. The feet were infested in all children, none of whom was taken to a health facility. 42.86% of infested children received complete doses of DPT. Parents reported no complications of infestation. Tungiasis is an important infestation in rural dwellers. The need for adequate childhood immunisation and use of protective clothing and shoes are highlighted.

Integrated control of ectoparasites

Integrated control of ectoparasites of veterinary importance is being implemented on a limited basis at present. However, several forces are accelerating a global shift to integrated pest management (IPM). These accelerating forces include the following: reduction in new chemical compounds registered for use on livestock and poultry universal development of resistance to pesticides heightened environmental sensitivities to exclusive dependence on pesticide-based control need for strategies which increase profits for the producer while decreasing costs to the consumer. Integrated pest control requires many technologies for incorporation into specific pest management systems. Individual components include new chemicals, formulations and delivery systems, biological control, mechanical control, immunological control, genetic control, and regulatory control. Computer simulation models based on a quantitative ecological database are invaluable in devising and monitoring IPM approaches to controlling ectoparasites which affect livestock and poultry. IPM strategies have been developed for pests of veterinary importance, but eventually these must be incorporated into total livestock production systems. For implementation, a number of major impediments to IPM must be overcome. These problems can best be solved through a vigorous technology transfer programme. In addition to face-to-face meetings between producers and extension agents, the implementation of IPM can be further encouraged at producer group meetings, through education of animal health professionals, by the publication of articles in producer magazines, and by radio and television broadcasts to the agricultural sector. Research focusing on the development of cost-effective and environmentally-compatible IPM systems is necessary for future progress.

Nematocera (Ceratopogonidae, Psychodidae, Simuliidae and Culicidae) and control methods

The biology, veterinary importance and control of certain Nematocera are described and discussed. Culicoides spp. (family Ceratopogonidae) transmit the arboviruses of bluetongue (BT), African horse sickness (AHS), bovine ephemeral fever (BEF) and Akabane. Some other arboviruses have been isolated from these species, while fowl pox has been transmitted experimentally by Culicoides. These insects are vectors of the parasitic protozoans Leucocytozoon caulleryi and Haemoproteus nettionis, and the parasitic nematodes Onchocerca gutturosa, O. gibsoni and O. cervicalis. They also cause recurrent summer hypersensitivity in horses, ponies, donkeys, cattle and sheep. Farm animals can die as a result of mass attack by Simulium spp., which are also vectors of Leucocytozoon simondi, L. smithi and the filariae O. gutturosa, O. linealis and O. ochengi. Venezuelan equine encephalomyelitis (VEE) and Rift Valley fever (RVF) have been isolated from simuliids, and vesicular stomatitis virus New Jersey strain has been replicated in Simulium vittatum. Simuliids are well known as vectors of O. volvulus, the cause of human onchocercosis (river blindness). The family Psychodidae includes the genera Phlebotomus and Lutzomyia (subfamily Phlebotominae), vectors of Leishmania spp. in humans, dogs and other mammals. Vesicular stomatitis virus Indiana strain has been regularly isolated from phlebotomine sandflies. Mass attack by mosquitoes can also prove fatal to farm animals. Mosquitoes are vectors of the viruses of Akabane, BEF, RVF, Japanese encephalitis, VEE, western equine encephalomyelitis, eastern equine encephalomyelitis and west Nile meningoencephalitis, secondary vectors of AHS and suspected vectors of Israel turkey meningoencephalitis. The viruses of hog cholera, fowl pox and reticuloendotheliosis, the rickettsiae Eperythrozoon ovis and E. suis, and the bacterium Borrelia anserina are mechanically transmitted by mosquitoes. These insects also induce allergic dermatitis in horses. They transmit several filarial worms of both animals and humans, and are of great medical importance as vectors of major human diseases, including malaria, yellow fever, dengue fever and many more diseases caused by arboviruses.

[Fleas and methods of control]

Over 2,000 species of fleas parasitize mammals and birds. A simplified study of their morphology indicates for the main identification criteria. After listing the main families of fleas, the author outlines the identification of species most often encountered by veterinarians. Knowledge of the different types of flea parasitism and their life cycles is essential for effective control measures. Control is justified by the direct and indirect pathogenic roles of fleas (transmission of plague, tularaemia, myxomatosis, Dipylidium caninum). Effective agents are organochlorine compounds, organophosphorus compounds, pyrethroids and insect growth regulators, available in various formulations to destroy parasitic fleas on animals or in the environment. A novel method is to administer a systemic growth regulator to dogs and cats, which persists in the bloodstream and inhibits the reproduction of fleas which feed on a treated animal. Advantages and disadvantages of each formulation are presented.