The efficacy of ivermectin against larvae of the screw-worm fly (Chrysomya bezziana)

An in vitro technique for screening systemic insecticides against larvae of the screw-worm fly, Chrysomya bezziana is described. Susceptibilities of screw-worm larvae of different ages to ivermectin (MK-933) were determined. Based on 24 h larval mortality, the LD50 of 1-,2-,3-,4- and 5-day larvae was 0.01, 0.02, 0.03, 0.2 and 0.4 ppm of ivermectin. LD50 based on adult emergence following treatment of 4- and 5-day larvae was 0.02 and 0.05 ppm. The LD99.9 for 4-day larvae based on 24 h larval mortality and adult emergence was 11.0 and 0.15 ppm respectively and for 5-day larvae, was 44.3 and 0.4 ppm respectively. Pen and field trials with cattle infested with screw-worm fly demonstrated the potential of ivermectin as a systemic insecticide. Dosages of 50, 100 and 200 micrograms/kg, of ivermectin administered subcutaneously to experimentally infested cattle gave complete control for 6, 12 and 14 days respectively. Ivermectin at 200 micrograms/kg caused 100% mortality of screw-worm larvae up to 2 days old at the time of treatment with 70, 64 and 21% mortality of 3-, 4- and 5-day old larvae at the time of treatment. The residual protection from a single dose of 200 micrograms/kg was 16 to 20 days. When bull calves were treated with ivermectin at a dose of 200 micrograms/kg at the time of castration and branding, none of the 77 treated animals sustained a screw-worm strike in the scrotal area compared with 47 strikes (44%) in the 106 control cattle.     

Use of insecticides to control screw-worm fly strike by Chrysomya bezziana in cattle

Some insecticides to control and prevent screw-worm fly strike by Chrysomya bezziana in calves and adult cattle were tested in field trials on cattle in Sabah, East Malaysia. Ivermectin injected subcutaneously in newborn calves at 200 mu/kg provided 10 days protection from screw-worm fly strike, which allowed navels to dry. Ivermectin, 1% dichlofenthion plus gentian violet and 3% lindane plus pine oil smear were all effective in preventing re-strike of treated wounds in adult cattle. A single subcutaneous injection of ivermectin at 200 mu/kg was effective, whereas it was necessary to re-apply the dichlofenthion and lindane smear preparations every 48h.     

The efficacy of insecticides against the screw-worm fly (Chrysomya bezziana)

A number of insecticides used for ectoparasite control in the livestock industry were screened for their efficacy against larvae of the screw-worm fly, Chrysomya bezziana, using in vivo and laboratory tests. Proprietary screw-worm fly treatments (after exposure to outdoor conditions for up to 10 days) were also tested against eggs and adults of C bezziana. Three of these were also evaluated on naturally acquired screw-worm infestations. Residual protection was generally of short duration. Among the organophosphorus compounds, the most effective formulations contained relatively high concentrations (3 to 4% al) of coumaphos, 2.5% fenchlorphos or low concentrations (0.05 to 0.5% al) of diazinon, chlorfenvinphos and fenthion methyl. Two chlorinated hydrocarbon insecticides containing 3% lindane and 5% dieldrin were very effective but are now prohibited for use in Australia. Preparations had serious deficiencies when used under field conditions, especially for treating large, deepseated myiases for which systemic insecticides are recommended. A comparison of methods demonstrated that a laboratory test could supersede live animal experimentation, at least for the initial screening of potential insecticides.     

The effect of the bont tick (Amblyomma hebraeum) on the weight gain of Africander steers

The effects of the bont tick Amblyomma hebraeum on the productivity of cattle need to be quantified in order to design economically optimal control programs. Liveweight gains (LWGs) of three groups of Africander steers, maintained in the same pasture and exposed to zero, medium or high numbers of larvae, nymphs and adults of the tick, were measured. Larvae and nymphs had no significant effect on LWG but adults had a large, statistically significant effect (P less than 0.05). The tick-free group had an average LWG of 20 kg more than the heavily infested group after 3.5 months. No mortality was recorded from ticks or tick-borne diseases during the experiment. There was no relationship between the number of engorging adult female ticks counted and loss of LWG of individual animals. The latter suggests that exposure to ticks as well as engorgement by female ticks causes losses. The loss per adult female that completed engorgement was estimated, by relating the LWGs of individual animals to their tick infestations, to be 4 +/- 2 g per adult female tick. An alternative estimate, made by comparing the average LWG and tick infestations of each treatment group, was equal to 10 +/- 4 g. This latter estimate includes the effect of challenge (and rejection) as well as tick feeding and so was accepted as giving the best estimate. Screw-worm fly (Chrysomya bezziana) struck an average of 7.5% of the cattle infested with ticks in any week but the effects on the productivity of the cattle were minimized by immediate treatment. There was a significant, positive correlation between the incidence of screw-worm fly strike and the numbers of adult ticks counted on the experimental animals. The results provide data for calculating losses caused by A. hebraeum in different parts of its geographical range.     

Ticks on livestock in Barbados

Cattle, sheep, goats, and horses in most areas of Barbados were examined for ticks. About 68% of the cattle, mostly Holstein dairy cows, and 23% of the sheep, mostly purebred or crossbred black belly sheep, were infested with the southern cattle tick, Boophilus microplus (Canestrini), a vector of bovine babesiosis and anaplasmosis. About 13% of the horses were infested with the tropical horse tick, Anocentor nitens (Neumann), a vector of equine babesiosis. Cattle owners used a variety of acaricides as dusts, sprays, or washes on their cattle for the control of ticks.     

Susceptibility to two pyrethroids in Boophilus microplus (Acari: Ixodidae) populations of northwest Argentina. Preliminary results

Cattle are treated 6-12 times yearly to control Boophilus microplus ticks in the east zone of the Argentinean infested region, while 1-4 treatments are applied for tick control in the west zone. In the 1970s resistance to organo-phosphate acaricides was found in the east zone, but not in the west zone. However, a shift to synthetic pyrethroids (SP) was made through all infested regions. Currently, indications of resistance to SP in the east zone, but not in the west zone, are provoking to a switch to formamidine acaricides. During 1998 a total of 147 B. microplus engorged females were collected from 20 beef cattle ranches from the west zone of the Argentinean infested region. Individual progenies of these ticks were tested ('larval packet test') with cypermethrin and deltamethrin, and their LC 50 and LC 90 were compared to those estimated for the Milagro susceptible strain. No evidence of resistance to these SP was found. Due to sampling restraints the results are presented as preliminary. Nevertheless, a shift away from use of SP for control of B. microplus in the west zone appears to be unjustified and should be independent of the resistance circumstances observed in the east zone of the Argentinean tick infested region.     

Hypodermosis control and simultaneous treatment for fascioliasis in steinfurt,Germany

For decades, about 30% of the young cattle in the Steinfurt district of the North German Basin were infested with Hypoderma bovis. Compulsory treatment with rotenone between 1934 and 1963 failed to control infestation. When systemic organophosphorous insecticides became available a 3-year scheme was instituted in which all the 6–24-month-old cattle were treated annually, between 15 November and 15 December, with trichlorfon spot-on.At first, the treatment was not compulsory and warble infestation was occasionally found in cattle purchased outside the district. Later, the treatment was made compulsory and since 1966 warble infestation has not been detected in the district.     

Development of a novel self-medicating applicator for control of internal and external parasites of wild and domestic animals

Four trials, three in the United States and one in South Africa, were conducted to evaluate the potential value of a novel self-medicating applicator in the passive control of gastrointestinal nematodes in cattle and deer, and of files and ticks on cattle using oil-based treatments. The results of the trials demonstrated that this applicator is an effective and practical device for the passive treatment of both deer and cattle for trichostrongyle infections using the endectocide, moxidectin (Cydectin. Fort Dodge Animal Health, USA), of cattle for hom fly (Haemotobia irritans) infestations using the insecticide, cyfluthrin (CyLence, Bayer AG, Germany) and of cattle for tick infestations (in particular Amblyomma hebraeum and Rhipicephalus appendiculatus) using the acaricides deltamethrin and amitraz (Delete All, Intervet, South Africa).     

Factors affecting the detachment rhythm of engorged Boophilus microplus female ticks (Acari: Ixodidae) from Charolais steers in New Caledonia

As in most parts of the world where the cattle tick Boophilus microplus is established, resistance of ticks to acaricides occurs in New Caledonia. In order to implement laboratory resistance tests on larvae, engorged females collected in suspected farms are necessary. Investigations on the detachment schedule of the engorged females were conducted to explain certain field situations such as the lack or scarcity of engorged females on highly infested cattle driven from the pasture to the pen in the morning. Three experiments on Charolais steers naturally infested on pastures showed that: (1) engorged female burdens at sunrise are similar whether the steers spend the night in pasture or in a pen; (2) compared with steers maintained in a pen, morning detachment of females increases when the steers stay on the pasture or move from the pasture to the pen; (3) detachment rhythm of engorged females on steers staying the morning in a pen, is not influenced by feeding activity or exposition of steers to sun; (4) detachment occurs earlier for females attached on anatomical sites exposed to sun, and earlier from these sites for the steers in pasture or walking than for steers in a pen.     

The Prevalence of Bovine Hypodermosis in Kars Province,Turkey

A total of 1276 cattle from 76 farms in 8 villages were examined by palpation of the skin for evidence of hypodermosis. The effects of age, sex, breed, and colour of cattle on hypodermosis were investigated. The overall prevalence was 31.9%. The mean number of warble fly larvae on infested animals was 8.46. Hypodermosis infestations were encountered in all the villages visited. Within a herd, the intensity of infestion decreased with the age of cattle. Infestation rates of warble fly larvae were lower in native cattle, in females, and in piebald animals.     

The use of irradiated embryos of Chrysomya bezziana for the detection of the Old World screw-worm fly

Irradiation of Chrysomya bezziana embryos 1 h before hatching with doses less than or equal to 7 kilorad (kr) had a significant effect on percentage egg hatch, weights and survival of larvae. Doses greater than or equal to 1 kr allowed larval development to the end of the 3rd instar stage in vitro, but prevented normal pupal development. Cattle with wounds infested with 1st instar larvae derived from irradiated embryos had 3rd instar larvae present after 3 d but these failed to pupate. Thus it would be feasible to use such larvae for wound infestation for the enhanced detection of screw-worm fly in areas where the release of fertile flies is undesirable.     

Chemical control of Haematobia irritans with 0.5% topical ivermectin solution in cattle.

A field trial was conducted to evaluate the efficacy of a topical formulation of ivermectin administered at the dose of 500 micrograms/kg against horn flies (Haematobia irritans) in cattle. Eighty-eight cattle in four herds naturally exposed to horn flies were used in the trial. Replicates were formed of two herds. Within replicates, one herd was randomly allocated to the untreated control and the other to the ivermectin treatment group. Horn fly counts were taken on the treatment day (Day 0) and on Days 7, 14, 21, 28, and 35 post-treatment. There were no horn flies on any cattle in the treatment group, whereas all the control cattle were continuously infested by horn flies on each examination day.     

Protection of pastured cattle from black flies (Diptera: Simuliidae): Improved weight gains following a dermal application of phosmet

In two experiments, a pour-on application of phosmet at 25 mg kg^?1 reduced the harassment of cattle by black flies for up to 5–6 weeks posttreatment. During this period, the treated groups either gained more weight or loss less weight than their controls. The untreated groups made compensatory gains when teh black fly activity decreased or ceased. No significant differences existed between the average daily gains of a treated group and its control either for the posttreatment-periods of 9 and 15 weeks or for the experimental periods of 15 and 20 weeks in the two experiments.Black fly toxemia was not seen in indigenous cattle or in naive steers brought into a black fly infested area 1–2 weeks before the onset of black fly activity.     

Bovine hypodermosis in north-eastern Algeria: prevalence and intensity of infestation]

Between 1989 and 1997 different factors related to warble fly infestation (prevalence, intensity, climate, breed) were studied in north-eastern Algeria. Mean prevalence during the period was 76%. This figure was obtained from a cattle market survey of four different regions (Jijel, Constantine, Guelma, and El Tarf). One-hundred percent of the herds were found to be infested in El Tarf and 61% of animals were infested. Within a herd, the intensity of infestation decreased with the age of the cattle. The mean number of warbles per animal decreased as reinfestations occurred. The peak of the emergence of warbles observed between January and March was progressively delayed in the older animals. Two species of Hypoderma were present in cattle in Algeria (H. bovis and H. lineatum) with a predominance of H. lineatum (63%) in the semi-arid area (Batna) and a majority of H. bovis (75%) in humid area (Jijel). Warbles appeared earlier in Batna (October) than in Jijel (November). The Prim'Holstein breed was more susceptible to the warble fly infestation than Montbeliard or local breeds. The implementation of a control programme for hypodermosis in Algeria is urgent. Control can be achieved through a mass treatment of cattle. This approach must take into account the factors described in this study which influence the epidemiology of the disease.     

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.     

Progress in the British hypodermosis eradication programme: the role of serological surveillance.

The British warble fly eradication programme has resulted in the numbers of infested cattle falling from an estimated four million in 1978 to zero in 1991. In 1982, when about 705 herds were infested the disease was made notifiable, and serological surveillance was begun in 1988. In spring 1991, 227,000 blood samples were tested by using the ELISA technique and no warbled animals were found. In addition no clinical cases were reported during 1991.     

A ten-year review of commercial vaccine performance for control of tick infestations on cattle

Ticks are important ectoparasites of domestic and wild animals, and tick infestations economically impact cattle production worldwide. Control of cattle tick infestations has been primarily by application of acaricides which has resulted in selection of resistant ticks and environmental pollution. Herein we discuss data from tick vaccine application in Australia, Cuba, Mexico and other Latin American countries. Commercial tick vaccines for cattle based on the Boophilus microplus Bm86 gut antigen have proven to be a feasible tick control method that offers a cost-effective, environmentally friendly alternative to the use of acaricides. Commercial tick vaccines reduced tick infestations on cattle and the intensity of acaricide usage, as well as increasing animal production and reducing transmission of some tick-borne pathogens. Although commercialization of tick vaccines has been difficult owing to previous constraints of antigen discovery, the expense of testing vaccines in cattle, and company restructuring, the success of these vaccines over the past decade has clearly demonstrated their potential as an improved method of tick control for cattle. Development of improved vaccines in the future will be greatly enhanced by new and efficient molecular technologies for antigen discovery and the urgent need for a tick control method to reduce or replace the use of acaricides, especially in regions where extensive tick resistance has occurred.     

Toxicity of cypermethrin and diazinon to Haematobia irritans (Diptera: Muscidae) in its American southern range

Synthetic pyrethroids are considered currently less effective than organophosphate insecticides for controlling Haematobia irritans on cattle in its American southern range. To test the validity of this hypothesis, horn fly populations from 95 cattle herds in central-northern Argentina and southern Brazil were evaluated to determine 50% lethal concentrations (LC(50)) to cypermethrin and diazinon, respectively. Horn flies were exposed to filter papers and glass vials treated with cypermethrin and diazinon, respectively, and LC(50) values were determined using probit analysis. Two and 78 fly populations showed LC(50) values indicating susceptibility and resistance to cypermethrin, respectively, in comparison to historical LC(50) values obtained when the horn fly populations were susceptible to cypermethrin. Five fly populations had an undetermined resistance status to cypermethrin. The diazinon tests showed no obvious indications of H. irritans resistance. Thirty nine percent of farmers still rely on pyrethroids to control horn fly populations on cattle which represents a decreasing proportion from a few years ago when horn fly control was carried out using pyrethroids almost exclusively. Organophosphates could provide control for horn flies resistant to pyrethroids; however, the reliance on chemicals alone to control H. irritans is not considered a proper approach for the future.     

Field assessment of synthetic attractants and traps for the Old World screw-worm fly, Chrysomya bezziana

The performance of newly developed trapping systems for the Old World screw-worm fly, Chrysomya bezziana has been determined in field trials on cattle farms in Malaysia. The efficacy of non-sticky traps and new attractants to trap C. bezziana and non-target flies was compared with the standard sticky trap and Swormlure. The optimal trap was a modified LuciTrap(?) with a new attractant mixture, Bezzilure-2. The LuciTrap/Bezzilure-2 caught on average 3.1 times more C. bezziana than the sticky trap with Swormlure (P<0.05) and provided selectivity for C. bezziana against Chrysomya megacephala and Chrysomya rufifacies with factors of 5.9 and 6.4, respectively. The LuciTrap also discriminates with factors of 90 and 3.6 against Hemipyrellia sp. and sarcophagid flesh flies respectively, compared to the sticky trap. The LuciTrap/Bezzilure-2 system is recommended for screwworm fly surveillance as it is more attractive and selective towards C. bezziana and provides flies of better quality for identification than the sticky trap.     

Goats as alternative hosts of cattle ticks

The objective of this study was to compare the presence on goats and cattle of adult ticks that usually infest cattle. To this end ticks collected from sets of five goats were compared with those collected from sets of five cattle at 72 communal dip-tanks in the eastern region of the Eastern Cape Province. Amblyomma hebraeum was present on goats at 25 and on cattle at 39 dip-tanks, and a total of 61 goats and 138 cattle were infested. Adult Rhipicephalus (Boophilus) microplus was present on goats at 48 and on cattle at 69 dip-tanks, and a total of 113 goats and 242 cattle were infested. The lengths of 84 of 148 female R. (Boophilus) microplus collected from the goats exceeded 5 mm or more, indicating that they could successfully engorge on these animals. The differences between the proportions of dip-tanks at which A. hebraeum or R. (Boophilus) microplus was present on goats and cattle and also between the proportions of goats and cattle that were infested were significant (Chi-square test, P < 0.01). Adult Rhipicephalus appendiculatus was present on goats at 70 and on cattle at 67 dip-tanks, and a total of 296 goats and 271 cattle were infested. The proportion of dip-tanks at which cattle were infested did not differ significantly from the proportion of tanks at which goats were infested (Fischer's exact probability test, P = 0.44), but the proportion of infested cattle was significantly lower than the proportion of infested goats (Chi-square test, P < 0.05). Adult Rhipicephalus evertsi evertsi was present on goats and cattle at all 72 sampling localities, and a total of 334 goats and 316 cattle were infested. The proportion of infested cattle was significantly lower than the proportion of infested goats (Chi-square test, P < 0.05). These results underscore the necessity of including goats in any tick control programme designed for cattle at the same locality.