Impact of previous infestation on dynamics of circulating hypodermin C in cattle artificially infested with Hypoderma lineatum (Diptera: Oestridae).

Four groups of cattle were artificially infested with 50 first instar Hypoderma lineatum after either a primary natural infestation or in the absence of a primary infestation. In two groups the primary infestation had been terminated by the application of either an organophosphate insecticide or a macrocyclic lactone parasiticide. Circulating hypodermin C and specific antibodies were measured for 40 weeks after the artificial infestation. Stage specific mortality of the larvae was also monitored. Previously uninfested cattle exhibited typical antibody and antigen profiles during the infestations. Antibodies were first detected on Week 7p.i., they rose to maximum values between Weeks 24 and 25, then declined as larvae reached the back. A second peak occurred at Week 32 and antibody remained more less constant thereafter. Previously infested groups exhibited a dramatic anamnestic response by Week 3p.i. with antibody levels peaking at Week 8. A second peak was noted between Weeks 24 and 26p.i. after which antibody levels declined and then remained relatively stable. The dynamics of circulating hypodermin C in the previously infested cattle resembled those in the previously uninfested cattle. Mortality of first instars did not differ among the four groups. Similarly mortality of second and third instars, in the warble, did not differ although there was a tendency for higher mortality in the previously infested, untreated group. These results reinforce previous work demonstrating the development of a significant immune response during the primary infestation that is reflected in the rapid and substantial production of antibodies upon re-infestation. It is significant that a challenge model using subcutaneous injection of newly hatched first instars avoids host immune responses in the skin that result in substantial larval mortality. The current data also support the concept that migrating first instars induce significant reduction in host immune response. There is a peak of antibody production as antigen levels peak during first instar migration to the back. As larvae molt to the second instar and antigen production ceases there is a persistence of antibody which suggests release of the immune response from the suppression induced by the first instar secretory antigens.

Estado de la resistencia a insecticidas y mecanismos de resistencia en larvas del municipio Playa, colectadas durante la etapa intensiva contra el Aedes aegypti en Ciudad de La Habana, 2001-2002 / State of the resistance to insecticides and resistance mechanisms in larvae from Playa municipality collected during the intensive campaign against Aedes aegypti in Havana City, 2001-2002

Se determinaron los niveles de susceptibilidad y/o resistencia a insecticidas en larvas de Aedes aegypti, colectadas del municipio Playa, durante la etapa intensiva de la campaña contra el mosquito Aedes aegypti en Ciudad de La Habana, en el presente año. En larvas, se encontró alta resistencia a los insecticidas organofosforados fention y temefos y moderada a fenitrotion, también se detectó alta resistencia al carbamato propoxur. Las larvas resultaron susceptibles a clorpirifos, malation y pirimifos metil. Los resultados a través del uso de sinergistas indicaron que las esterasas desempeñan un papel importante en la resistencia detectada a los insecticidas organofosforados, pero no en la resistencia a propoxur, sin embargo, las monoxigenasas intervienen solamente en la resistencia a fenitrotion. Estos mecanismos se encontraron a elevada frecuencia en las larvas de este municipio. Se confirmó el papel de las esterasas en la resistencia a temefos mediante ensayos de inhibición en gel de poliacrilamida(AU)

Resistencia a insecticidas en larvas y adultos de Aedes aegypti: prevalencia de la esterasa A4 asociada con la resistencia a temefos / Resistance to insecticides in larvae and adults of Aedes aegypti: prevalence of A4 esterasa associated with resistance to temephos

Fueron estudiadas 2 cepas de Aedes aegypti provenientes de 2 Consejos populares con altos índices de infestación de este vector, producto de la necesidad de hacer un control efectivo de larvas y adultos en el municipio Guanabacoa. Se determinaron los niveles de susceptibilidad y/o resistencia a insecticidas organofosforados, piretroides y un carbamato. Los resultados de los bioensayos en larvas mostraron completa susceptibilidad a los insecticidas organofosforados malation, clorpirifos, pirimifos metil y al carbamato propoxur en ambos consejos populares, sin embargo, se observó alta resistencia a temefos y a fention, no se observó resistencia a fenitrotion en uno de los consejos populares, pero sí en el otro. En el estado adulto, a la dosis recomendada por la Organización Mundial de la Salud o por los fabricantes de los productos, se observó resistencia a malation, fenitrotion y propoxur, sin embargo, se obtuvieron mejores resultados con los piretroides, con porcentajes de mortalidad por encima de 90 por ciento. Según los resultados obtenidos, utilizando el sinergista S S S tributil fosforotritiado (DEF) y piperonil butóxido, se demostró que las enzimas esterasas y oxidasas de función múltiple desempeñaron un papel importante en la resistencia a temefos y a fention. Por medio de ensayos bioquímicos se demostró que la amplificada actividad de estas enzimas se encontró a elevada frecuencia en ambos consejos populares, al igual que la enzima glutation transferasa (GST) en uno de los 2 Consejos Populares. Mediante electroforesis en gel de poliacrilamida se observó que en ambos consejos populares prevaleció la amplificada actividad de esterasas A4(AU)

Effect of treatment on the dynamics of circulating hypodermin C in cattle naturally infested with Hypoderma lineatum (Diptera: Oestridae).

An antigen capture ELISA, using a murine monoclonal antibody recognising recombinant hypodermin C (rHyC), was used to evaluate the influence of early treatment with eprinomectin (Eprinex) or fenthion (Spotton) on the kinetics of circulating hypodermin C in calves naturally infested with Hypoderma lineatum. No viable larvae were collected from treated animals, whereas a variable number of warbles were found in control animals. Treatment provoked a decrease in circulating HyC levels that was significant 9 days post-treatment (p.t.). Circulating antigen levels in the treated cattle remained detectable for approximately 99 days p.t. In contrast, control animals had no detectable antigen at 64 days p.t., 42 days earlier than in the treated animals. These results suggest that larvae were either gradually killed, resulting in slow release of antigen or they were encapsulated, leading to the slow liberation of antigen. Kinetics of circulating HyC did not differ among the two insecticide treatments. Antibodies persisted, in all groups, throughout the 120-day study. These results suggest that the antigen capture ELISA will be useful as a technique for detecting successful treatment of cattle grub infestations and for the detection of new infestations in previously infested cattle.

Relative cost-effectiveness of treatment of feedlot calves with ivermectin versus treatment with a combination of fenbendazole, permethrin, and fenthion.

OBJECTIVE: To compare growth performance, animal health characteristics, and carcass characteristics of feedlot calves treated with ivermectin topically with that of feedlot calves treated with a combination of fenbendazole orally and permethrin and fenthion topically. DESIGN: Clinical trial. ANIMALS: 14,184 British crossbred steer calves (mean weight, 286 kg [630 lb]) in 30 pens at a commercial feedlot in Nebraska. PROCEDURE: On arrival at the feedlot, calves were randomly assigned to be treated with ivermectin topically or with a combination of fenbendazole orally and permethrin and fenthion topically (control). At the time of assignment to treatment groups, fecal samples were collected from 5% of the calves. Growth performance, carcass characteristics, and health information were recorded. RESULTS: Geometric mean fecal egg counts at the time of arrival at the feedlot were not significantly different between groups. Final weight, weight gain, average daily gain, and the dry matter intake-to-gain ratio were significantly improved for calves in the ivermectin group. The percentage of carcasses classified as quality grade choice was higher for the ivermectin group than the control group; however, the percentage of carcasses classified as yield grade 1 and the dressing percentage were higher for the control group than for the ivermectin group. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that topical administration of ivermectin to feedlot calves is relatively more cost-effective than administration of a combination of fenbendazole orally and permethrin and fenthion topically.

Comparative cost-effectiveness of ivermectin versus topical organophosphate in feedlot yearlings.

A replicated-pen field trial was performed under commercial feedlot conditions in western Canada to determine the cost-effectiveness of administering ivermectin to yearling beef cattle upon entry to the feedlot after the grazing season, and to establish the level of trichostrongylid gastrointestinal parasite infection in this population, as estimated by fecal egg counts. Six thousand eight hundred and eighty-three, mixed breed, yearling steers were randomly allocated upon arrival at the feedlot to one of 2 experimental groups as follows: Ivermectin, which received topical ivermectin (0.5%) at the rate of 1.0 mL/10 kg body weight; or Fenthion, which received topical fenthion (20%) at the rate of 12 mL/295 kg body weight. There were 15 pens in each experimental group. Final weight, weight gain, average daily gain, and dry matter intake to gain ratio were significantly (P < 0.05) improved in the Ivermectin group as compared with the Fenthion group. There were no significant (P > or = 0.05) differences in initial weight, days on feed, or daily dry matter intake between the experimental groups. The geometric mean fecal egg counts at the time of allocation were 14.7 eggs/5 g and 16.6 eggs/5 g for the Ivermectin and Fenthion groups, respectively (P > or = 0.05). There were no significant (P > or = 0.05) differences in morbidity or mortality between the experimental groups. In the economic analysis, the significant improvements in feedlot performance in the Ivermectin group resulted in a net economic advantage of $4.20 CDN per animal.

Evaluation of flea control programmes for cats using fenthion and lufenuron.

Four groups of six cats were kept in carpeted pens similarly infected with Ctenocephalides felis. One group was left untreated, but the other groups were treated every 28th day with either an insecticide (fenthion at 30 mg); or an inhibitor of insect development (lufenuron at 133 or 266 mg) or with both. A sudden upsurge in the numbers of fleas occurred on the control cats after 50 days. At this time, the three control strategies had reduced the counts by 91.3, 72.5 and 98.6 per cent, respectively. Thereafter, welfare considerations demanded the limitation of the flea burden on the control cats, but conditions were shown to be favourable for flea development throughout the study. The mean numbers of fleas on the treated groups after six months were 1.2, 11.0 and 0.4 respectively. After this, in addition to the fleas acquired in the pen, the cats were each infected weekly with five fleas to mimic roaming animals introducing extraneous fleas into the home. This produced no obvious effect on the counts and the mean values three months later were 0.5, 11.0 and 0.2, respectively. None of the strategies eradicated the flea population but they all reduced the numbers considerably and worked equally well whether or not small numbers of new fleas were introduced into the system. Significantly lower flea counts were maintained in the early and later stages of the study by the strategies including the insecticide.

CGA-72662--a new sheep blowfly insecticide.

The efficiency of 2-cyclopropylamino-4, 6-diamino-s-triazine CGA-72662 (proposed common name: cyromazine) for the control of blowfly strike was tested in fly cage and field trials on sheep. The safety to sheep and physico-chemical properties of the compound as they relate to blowfly control were also assessed. When the sheep were thoroughly jetted with a solution of CGA-72662 containing 1g of active ingredient per litre, the mean incidence of fly strike in 7 field trials was reduced from 16.5% to 1.5% over a period of 9 weeks. The incidence of strike in the treated sheep in 2 insectary tests, which imposed levels of fly activity far in excess of that usually encountered in the field, was reduced from 93% and 73% in untreated sheep to 2% and nil respectively over a period of 8 weeks. Jetting with CGA-72662 solutions 100 times greater than the recommended concentration did not produce any side effects in sheep. Three treatments at twice the recommended concentration during the first trimester did not affect pregnant ewes nor their progeny. The compound was safe to use in combination with common anthelmintics and with sheep dips used for control of lice. CGA-72662 was stable in solution. No stripping occurred in dips and it persisted on wool for a considerable period. A satisfactory alternative to the organophosphorus insecticides has been found in CGA-72662, since it provided a substantial increase in residual protection against blowfly strike with a high degree of safety.

Efficiency and safety of methidathion applied as a pour-on systemic insecticide for control of cattle lice.

Methidathion applied to cattle as a pour-on insecticide for control of lice (predominantly Linognathus vituli, but also Haematopinus eurysternus and Damalinia bovis) caused a reduction in the lice population of approximately 98% to 99% in laboratory trials at the minimum recommended dose of 4 mg/kg and a 98.8% to 100% efficiency was achieved in field trials. In a comparative efficiency trial in the laboratory methidathion at 3.5 to 5 mg/kg reduced the lice population by 98.8% to 99%, fenthion by 98.5% at 4.5 mg/kg and famphur by 99.7% at 16.5 mg/kg. Methidathion was tolerated by calves aged 15 to 20 weeks at dose rates up to 40 mg/kg indicating an approximate 7 fold safety margin, but 1 of 4 calves treated at 50 mg/kg died following treatment. Treatment with fenthion at 50 mg/kg, 7.4 times the average recommended rate, famphur at 75 mg/kg, 3 times the average rate and chlorpyrifos at 85 mg/kg, 5 times average rate, caused reductions in whole blood cholinesterase activity of 52%, 27% and 47% respectively which were similar to the reductions in cholinesterase activity found in calves treated with methidathion at similar levels above the recommended commercial dose rates. It was found that 2 day old calves were more sensitive to treatment with methidathion than calves 9 or 16 days old. A further 11,900 cattle of varying age, breed and sex were treated with methidathion under field conditions at the recommended rate of 4 to 8 mg/kg, and 534 cattle were treated at 24 mg/kg without any signs of toxicity.

Laval implant sutdies with Lucilia cuprina.

Semi-field studies, using the larval implant technique, show that sheep may be protected against resistant larvae of Lucilia cuprina by thorough jetting with chlorfenvinphos, diazinon, dichlofenthion and fenthion ethyl, but not bromophos ethyl, for the normal duration of waves of bodystrike in New South Wales. The standard method of assessing implant data is to be preferred to analyses based on average protection due to the extra time required for the latter procedure.

[Comparative evolution of blood antibodies in cattle infested with hypodermosis and treated with different insecticides (author's transl)]. / Evolution des anticorps circulants chez les bovins traités contre l'hypodermose

Immunological response to hypodermosis is studied by a passive hemagglutination method in three groups of cattle naturally infested during the spring of 1972. In the autumn, one group was treated with fenthion and another with niclofolan, a drug generally used for distomatosis, but also efficient in hypodermosis and free from side-effects. The third group served as a control. Two kinds of immunological response are observed after use of the insecticide. In the group treated with fenthion, there is a rapid drop in antibodies during the 3 days following treatment; this increases for the next 2 months up to a very low level, which is stable for 3 months (fig. 3, 4, 5). During the same period, antibodies in the control group increase regularly to reach a maximum in April or May (fig. 1, 2). The immunological response of the host is closely related to the antigenic stimulation of the larvae. In the group treated with niclofolan, the slow drop in antibodies suggests that there is a parallel drop in the number of larvae during the month following treatment. A study of the other group shows that larvae are affected in the 24 hours following fenthion administration. This agent, as well as all organophosphorous compounds, are well-known to act efficiently on larvae and have anaphylactic-type side-effects on the host. The massive degradation of larvae should have induced an important antigenic reaction, but no increase in the antibodies of the host is observed; there is a even rapid drop in the number of larvae immediately after treatment. This fact is investigated further by experiments on guinea pig: the role of antigen-antibody complexes is studied by passive anaphylaxis. It appears that shock reactions, following use of organophosphorous insecticides, have a true-hyper-sensitivity origin, and are increased by the intrinsic toxicity of the first instar larvae.