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[Myiases of economic importance].

A simplified list of the principal Diptera capable of causing myiasis is followed by a brief presentation of the biology, lesions inflicted, and methods of treatment and control of the myiases of economic importance. Cochliomyiasis caused by Cochliomyia hominivorax is of greatest interest, in view of the damage and losses caused by this disease. A brief account of the outbreak of infestation in Libya illustrates the danger of this parasite. Other important traumatic myiases are described: that due to Chrysomya bezziana, which causes an African myiasis similar to cochliomyiasis, and those due to Lucilia cuprina and related species. Hypodermyiasis (warble fly infestation) and oestrosis (nasal bot fly infestation in sheep) still cause major economic losses in domestic animals, justifying their inclusion in control campaigns. The same applies to stomach bot flies of the family Gasterophilidae. The account of each myiasis includes notes on parasiticides which have been found to be effective. Given the rapidity with which a parasite can now be transported from one continent to another, it is important for Veterinary Services to be well-informed and vigilant.

Animals

Colostral transfer of antibodies specific for Hypoderma lineatum proteins.

Antibodies to Hypoderma lineatum were transferred to calves via colostrum. The antibodies transferred in the colostrum demonstrated specificity to all the H. lineatum first-instar proteins which were resolved by non-denaturing polyacrylamide gel electrophoresis and were capable of mediating a Type I hypersensitivity reaction. The kinetic decline of colostrum-acquired antibodies, the effect upon development of an autologous humoral response to H. lineatum and the host or parasite protective role of these antibodies are discussed.

Animals

[The larval development of the warble-fly Oestromyia leporina Pall. (Deptera, Hyodermah'dae) (author's transl)].

The present paper deals with the larval development of the warble-fly Oestromyia leporina and especially with the development of the first instar larvae (L 1). The hatching from the egg and the modus of infection is described. The migration of the L 1 within the host is reported for the first time as well as the perforation of the skin after the migration period. Exact dates on the duration of the different larval stages are given. Experimental infection reveals a partial immunization of the host against new infections. Some remaining problems of larval biology are discussed. By comparison several facts suggest our present knowledge of the perforation of larval (L 1) Hypoderma bovis probably to be wrong.

Animals

[Cultivation of the warble-fly Oestromyia leporina pall. (Diptera, Hypodermatidae) and its biological prerequisites (author's transl)].

The warble-fly Oestromyia leporina was cultivated for four generations in the laboratory. In the present paper the technic of laboratory mating and the modus of experimental infection of the host are described. The fertility of females is tested by experiments and by dissections. It is shown how the diapause of the puparia can be shortened and how it can be omitted. The successful infection of several species of small mammals demonstrates that O. leporina can be colonized not only on the natural host but also on some common laboratory animals like mice and rats.

Animals

[Histological reactions of the host induced by the larvae of the warble-fly Oestromyia leporina Pall. (Diptera, Hypodermatidae) (author's transl)].

The histological reactions of Mastomys natalensis induced by the larvae of Oestromyia leporina are described from the start of the infection to the complete healing of the evacuated cyst. Against the migrating larva no cellular reactions take place. After the larva settles, the most obvious feature is a non-suppurative inflammation of the surrounding tissue, while a layer of granulation tissue, infiltrated with eosinophils, is built up around the parasite. About 13 days p.i. the number of eosinophils starts to decrease again. No giant cells are present; plasmocytes and lymphocytes are relatively scarce. A few days before the parasite leaves the host, the inner surface of the warble is infiltrated with masses of neutrophils, obviously caused by secondary invasion of bacteria through the warble opening. After the parasite leaves the host, the repair of the tissue takes place within three weeks. The remaining scar tissue contains cells carrying haemosiderin, which disappears entirely about two months later.

Animals

The response of cattle vaccinated with hypodermin A to a natural infestation of Hypoderma bovis and Hypoderma lineatum.

In this study, we have determined whether immunization with hypodermin A (HA), associated with various adjuvants, could provide protective immunity for calves when challenged with a natural hypoderma infestation. Groups of naive calves were vaccinated with HA antigen alone or with adjuvants [Freund's incomplete adjuvant (FIA) or alumina phosphate (AP)]. Subcutaneous injection with HA antigen with or without adjuvant did not significantly protect calves against a natural hypodermosis infestation. The humoral response during the infestation period was evaluated by ELISA. A significant earlier and greater response was induced in groups vaccinated with HA alone and HA combined with FIA. These results indicate that HA, in this vaccination protocol, induces a very incomplete protection in calves exposed to a natural infestation.

Adjuvants, Immunologic

Specific antisera produced by direct immunization with slices of polyacrylamide gel containing small amounts of protein.

Rabbits were injected with slices of polyacrylamide gels containing entrapped insect proteins after separation by electrophoresis. Specific antibodies were produced independently of the nature of the gel (with or without sodium dodecyl sulphate) and of the staining technique (amido black or Coomassie Blue). The procedure appears to be a rapid and simple method for production of antibodies specific to proteins separated in minute quantities from a complex mixture.

Acrylic Resins

Effect of hypodermin A, an enzyme secreted by Hypoderma lineatum (Insect Oestridae), on the bovine immune system.

The absence of any inflammatory reaction around the first instar larvae (L1) of Hypoderma sp. in previously uninfested cattle suggested that these larvae may escape the non-specific defence system of the host. Immunosuppression had been noted during an experimental infestation. The aim of this work was to determine more precisely the potential role of hypodermin A (HA), an enzyme secreted by the larvae, in this immunosuppression. HA was found to have no effect on unstimulated lymphocytes from naive cattle but could influence the response of these cells to mitogens. In calves, injection of HA was accompanied by a decrease in the lymphocyte proliferative response to mitogens. This immunodepression lasted only for the duration of enzyme injections. In cattle, when HA is added, the antigen-dependent proliferative response increased significantly after 1 week of injection and disappeared 2 weeks after the end of the injection period. Finally, the rate of production of anti-HA antibodies increased at the same rate for calves and cows, and achieved a similar level. These results suggest that HA significantly modified the lymphoproliferative response for naive cattle and, to a lesser extent, immune cattle during the time of administration only.

Animals

In vitro and ex vivo responses of bovine lymphocytes to hypodermin C, an enzyme secreted by Hypoderma lineatum (insect oestridae).

The aim of this work was to determine if Hypodermin C (HC), an enzyme secreted by Hypoderma spp. larvae during their migration, is able to depress the lymphocyte response to mitogens and antigens. HC, when added to the lymphocyte culture, was able to influence the response of naive-calf lymphocytes to phytohemagglutinin. Secondly, injections of HC to uninfested and previously-infested cattle did not modify the proliferative response of the lymphocytes of these animals to mitogens. Thirdly, injections of HC to infested cattle did not negatively influence the specific humoral and cellular responses.

Animals

Acquired resistance to Hypoderma lineatum: comparative immune response of resistant and susceptible cattle.

The humoral and cellular immune responses of previously infested and noninfested cattle were compared after a single experimental exposure to 1st-instar Hypoderma lineatum. No correlation was found between the development of humoral antibodies as measured by passive hemagglutination assay and resistance in cattle. However, the most resistant cattle had higher macrophage migration-inhibition activity before and 1 month after infestation than did low- or non-resistant animals, and resistant animals also had greater sensitivity to antigens from larvae as they penetrated the skin. These results suggest that acquired resistance to hypodermatosis involves a cellular component of the immune mechanism.

Animals

Induction of intradermal skin reactions in the bovine by fractionated proteins of Hypoderma lineatum.

Protein species found in crude extracts of Hypoderma lineatum (Villers) 1st-instar gullet-stage larval homogenates were fractionated by chromatography and further identified by conventional polyacrylamide gel electrophoresis (PAGE) and SDS/PAGE techniques. Seven major fractions were resolved by ion exchange chromatography. Conventional PAGE of the crude antigen preparation revealed a minimum of 14 protein species, while SDS/PAGE revealed 3 major protein species. The ability to elicit cutaneous reactivity by isolated proteins was determined by the intradermal skin test. An immediate-type hypersensitivity reaction was elicited in the skin of vaccinated and previously infested animals by the components of the 4 protein fractions tested. Only one protein fraction, fraction 4, elicited an apparent delayed reaction at 48 h in vaccinated and previously infested animals. A non-specific background reaction was elicited in control animals by the fractionated proteins and was most notable between 1- and 4-h post-injection.

Animals

Effect of dose and route of application on the action of decamethrin against cattle grubs.

The efficacy of pour-on or orally administered decamethrin against bovine hypodermosis was investigated on naturally infested yearlings. Treatment at dose rates of 1, 2 or 10 mg per kg body weight were ineffective, but the highest dose had a long-term lethal effect on warbles. The severe side effects which followed the high dose suggest that this drug is unsatisfactory for systemic grub control. Investigations on the dynamics of circulating anti-Hypoderma antibodies in the post-treatment period showed that there is some sub-lethal activity of decamethrin on the larval physiology even at the lowest doses.

Administration, Oral

New methods of applying drugs for the control of ectoparasites.

A brief history of the development of methods used to apply drugs (commonly called insecticides or acaricides) to domesticated animals for the control of ectoparasites is presented. The focus is on methods used in the United States for treating cattle, sheep and goats, and swine. Details of the evolution of treatment methods are presented for lice, flies, cattle grubs, keds, ticks, and other arthropods. In general, treatment methods have undergone some change over the years; while, in contrast, treatment materials have changed considerably. Three trends in treatment methods become obvious - (1) Gradual reduction in the amount of treatment material applied dermally from spray or dip to pouron, to spoton, and to insecticide-impregnated ear tags, (2) Increasingly wider use of animal systemic insecticides administered orally or percutaneously to control a variety of ectoparasites, and (3) The development of new methods (sustained release devices) to lengthen the residual effectiveness of treatments. Unfortunately, lengthened residual effectiveness may lead to resistance of important ectoparasites to the treatment materials.

Animals

Immunization of cattle against hypodermatosis (Hypoderma lineatum (deVill.) and H. bovis (L.)) using H. lineatum antigens.

The feasibility of immunizing calves against Hypoderma lineatum and H. bovis with a crude H. lineatum larval extract or culture-derived antigen was investigated. Larval survival was followed through pupation. Grub appearance in the backs of both of the immunized groups was found to be 50% of that in the control groups. First appearance of H. bovis was significantly retarded in both immunized groups; however, H. lineatum was unaffected. Duration of H. bovis dropping was also shorter in animals receiving crude extract than in controls while duration of dropping of H. lineatum was not influenced by immunization. Survival of H. lineatum larvae to pupation was significantly reduced in animals immunized with crude larval extract, but not in those receiving culture-derived antigen. H. bovis survival was reduced by both treatments.

Animals

Lymphocyte responsiveness in cattle previously infested and uninfested with Hypoderma lineatum (de Vill.) and H. bovis (L.) (Diptera: Oestridae).

Cattle exposed to their third consecutive warble (Hypoderma lineatum and H. bovis) infestation had significantly reduced apparent and accumulative grub populations and produced significantly fewer grubs than animals exposed to their first infestation. These resistant animals had enhanced reactivity to mitogens (concanavalin A (con A) and pokeweed) upon reinfestation and a strong antigen-specific response at 2 months post-infestation. Their responsiveness to con A and antigen was also enhanced at 7 months post-infestation when grubs appeared in the backs, and the response to antigen continued at 10 months post-infestation. Responsiveness to mitogens in previously uninfested animals was similar to the control response throughout the infestation apart from the suppression of the con A response at 7 months post-infestation. These animals finally responded to antigen at 10 months post-infestation. These results suggest that acquired resistance to hypodermosis has a cellular basis with participation of both B- and T-cell components.

Animals