The immunobiology of myiasis infections--whatever happened to vaccination?

The current state of myiasis vaccine technologies are reviewed mainly in the primary research genera of Lucilia and Hypoderma. The importance of myiasis flies as primary causes of morbidity and mortality in agricultural species and man has not diminished despite the existence of good control strategies. However, the development of vaccines against myiasis infections has been relatively quiescent for more than 10 years despite the rapid development of genomic and proteomic analysis and of skills in data interpretation. The value of vaccine research in an era of chemical primacy is analysed. In fact, recent findings of drug resistance and the impact of animal welfare concerns should mean a renewed interest in alternative controls. The reasons that this has not been true to date are explored and new possibilities discussed.

Antigen characterization from second instars of oestrid bot flies for the detection of anti-Cephenemyia stimulator antibodies by ELISA in roe deer (Capreolus capreolus).

A study to determine the most appropriate antigen for use in the serodiagnosis of Cephenemyia (Diptera: Oestridae) infestation in roe deer (Capreolus capreolus) was carried out using immunoenzymatic tests. Serum samples from 43 roe deer from northern Spain were obtained post-mortem and corresponding numbers of bot fly larvae established. Three antigen complexes were tested, including Cephenemyia stimulator Clark excretory/secretory antigens (CsES), C. stimulator somatic antigens (CsSA) and Oestrus ovis L. (Diptera: Oestridae) excretory/secretory antigens (OoES). In addition, the composition of each antigen was analysed using an electrophoresis system. Cephenemyia stimulator larvae were found in 25% of roe deer; the mean intensity of infection was 24.3 larvae per infested animal. In the antigen analysis, CsSA showed four exclusive bands of molecular weight (17-19, 62, 65 and 67-70 kDa). A positive correlation between immunoglobulin G (IgG) values and total number of larvae was found with CsES and CsSA. The highest sensitivity value, negative predictive value and negative likelihood ratio were obtained using CsES. The highest specificity value, positive likelihood ratio and kappa value were achieved with CsSA. The predictive values of the enzyme-linked immunosorbent assay (ELISA) using CsES and CsSA reached statistical significance and seroprevalence values were 26-44%. The use of ELISA with CsES and CsSA seems promising in the non-invasive diagnosis of Cephenemyia infestation in roe deer.

The presence of anti-Hypoderma antibodies in udder milk samples, and correlation with selected parameters of dairy performance.

Hypodermosis is responsible for significant economic losses and remains a current problem in animal husbandry. This study determined the extent of Hypoderma spp. invasion in north-eastern Poland in dairy herds. The extent of the invasion, determined on the basis of positive results of an ELISA assay (Bovine Hypodermosis Milk Screening of Institut Pourquier), varied in herds. Statistical analysis performed on the results of milk productivity and content of basic components revealed a decrease in the milk yield and changes in milk protein in animals revealing positive, doubtful and negative results. Statistically significant differences were absent as regards the content of milk fat or milk total solids. The milk yield and the content of particular milk components were determined using the AT4 method, as part of a control program carried out by the Polish Federation of Cattle Breeders and Dairy Farmers (PFHBiPM).

Histopathology of experimental myiasis in mice as a result of infestation and experimental implantation of Dermatobia hominis larvae.

A laboratory model of myiasis as a result of Dermatobia hominis (L.) larvae was developed using mice as hosts. Mice in three groups were each infested with one newly hatched larva and skin biopsies processed for histopathology at 4, 12, and 20 d postinfestation (dpi). Mice in three other groups were each subjected to implantation of one larva collected from an infested (donor) mouse at 4, 12, and 20 dpi. Skin lesions of these receptor mice were then assessed at 10, 14, and 6 d postimplantation (dpimp), respectively. The inflammatory process in infested mice at 4 dpi was discrete, consisting of a thin necrotic layer around the larva, edema, many neutrophils, few eosinophils, mast cells, and proliferation of fibroblasts. At 12 dpi, there was a thicker necrotic layer, edema, many neutrophils and eosinophils, few mast cells, neoformation of capillaries, proliferation of the endothelium and fibroblasts, and early stages of fibrosis. These histopathological characteristics together with fibrosis were observed over a large area of the lesion at 20 dpi. Mice submitted to larval implantations demonstrated similar skin histopathology to that seen in the infested rodents, 10 dpimp corresponding to 12 dpi and 6 or 14 dpimp to 20 dpi. In all mice, the progressive acute inflammatory process followed a sequence linked to factors such as size of larvae and presence of secretory-excretory products. Both infested mice and those implanted experimentally with D. hominis larvae were shown to be suitable models for the study of the parasite-host relationship in this important zoonotic myiasis.

Sheep and goat immune responses to nose bot infestation: a review.

Oestrus ovis L. (Diptera: Oestridae) is a cosmopolitan agent of myiasis in sheep and goats. The parasitic phase begins after adult females deposit first-stage larvae (L1) into the nostrils of hosts; these larvae develop into L2 and L3 in the nasal and sinus horn cavities. Sneezing and nasal discharges are the major clinical signs in infected animals. The pathogenesis of O. ovis infection is caused by: (a) the trauma resulting from the mechanical action of spines and hooks during larval movement on mucosal membranes, and, more importantly, (b) an allergenic reaction provoked by molecules excreted/secreted by larvae, of which salivary antigens are those mainly recognized by the host's immune system. The recruitment of immune reactive cells increases gradually from the nasal to sinus cavities in infected hosts. Mast cells, eosinophils, macrophages and lymphocytes are always more numerous in infected than non-infected animals. Humoral (antibody) systemic response of immunoglobulin G (IgG) usually reaches seroconversion 2-4 weeks post-first infection and the highest levels are observed during the development of L2 and L3 larvae. Local antibody responses include specific IgG, which has been found to negatively correlate with larval survival and development. Hypersensitivity reaction, immunomodulation, immunization trials and mixed infections of O. ovis and helminths are discussed.

A Lucilia cuprina excretory-secretory protein inhibits the early phase of lymphocyte activation and subsequent proliferation.

The development of a protective immune response in sheep towards the presence of the larval stage of Lucilia cuprina has not been reported in the field. Upon investigation of the effects of larval excretory/secretory material on ovine T lymphocyte proliferation, we isolated a 56 kDa protein capable of inhibiting lymphocyte proliferation by at least 70%, compared with that in the presence of mitogen alone. This protein inhibited proliferation induced through cross-linking of the T-cell receptor as well as proliferation induced pharmacologically through the stimulation of the protein kinase C (PKC) pathway. The protein, named blowfly larval immunosuppressive protein (BLIP), was shown to bind directly to lymphocytes. Further investigation revealed that the BLIP prevented a proportion of lymphocytes from entering the first division following stimulation, by affecting the early events in lymphocyte activation. Subsequently, the BLIP reduced CD25 expression on T lymphocytes, reduced IL-2 mRNA expression, in addition to IFN-gamma, IL-4, IL-10 and IL-13 mRNA expression. Conversely, TNF-alpha and TGF-beta gene expression was up-regulated in response to the BLIP. These effects suggest suboptimal activation of T lymphocytes in the presence of the BLIP, and we propose that the BLIP presents an effective immune evasion tactic for the larvae of L. cuprina.

Lymphadenopathy and expression of nodal mast cells and eosinophils in the myiasis by human bot fly.

Wistar rats (Rattus norvegicus) infested with Dermatobia hominis (L. Jr., 1781) had their axillary lymph nodes removed and histopathologically processed. Follicular hyperplasia in the germinal center was noted from 2 d postinfestation (dpi), exhibiting a high number of centerblasts, mitotic and apoptotic cells, and a thin parafollicular area. The paracortex showed hyperplasia rich in dendritic cells, immunoblasts, and endothelial venules, with diapedesis seen from 4 dpi onward. Hyperplasia of the medullar sinus also was first observed at this point, as well as dilated lymphatic sinus, lymph, macrophages, neutrophils, mast cells, and eosinophils. Medullar strings were expanded and filled with immunoblasts, mitotic cells, and plasmocytes. Lymphadenitis was not observed. The expression of mast cells was similar for both myiasis-affected and control rats but increased significantly (mastocytosis) at 7 and 15 d postlarval emergence (dple). Eosinophilia was observed at 4, 10, 15, 20, and 28 dpi as well as at 2, 7, and 15 dple, particularly on the last three observations of dpi and the earliest dple. This experimental approach allowed progressive tissue reactions in the lymph nodes to be monitored during myiasis, particularly those involving mast cells and eosinophils. These reactions abated and complete repair was observed at 60 dple.

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.

Contrasting consequences of different defence strategies in a natural multihost-parasite system.

Hosts counteract infections using two distinct defence strategies, resistance (reduction in pathogen fitness) and tolerance (limitation of infection damage). These strategies have been minimally investigated in multi-host systems, where they may vary across host species, entailing consequences both for hosts (virulence) and parasites (transmission). Comprehending the interplay among resistance, tolerance, virulence and parasite success is highly relevant for our understanding of the ecology and evolution of infectious and parasitic diseases. Our work investigated the interaction between an insect parasite and its most common bird host species, focusing on two relevant questions: (i) are defence strategies different between main and alternative hosts and, (ii) what are the consequences (virulence and parasite success) of different defence strategies? We conducted a matched field experiment and longitudinal studies at the host and the parasite levels under natural conditions, using a system comprising Philornis torquans flies and three bird hosts - the main host and two of the most frequently used alternative hosts. We found that main and alternative hosts have contrasting defence strategies, which gave rise in turn to contrasting virulence and parasite success. In the main bird host, minor loss of fitness, no detectable immune response, and high parasite success suggest a strategy of high tolerance and negligible resistance. Alternative hosts, on the contrary, resisted by mounting inflammatory responses, although with very different efficiency, which resulted in highly dissimilar parasite success and virulence. These results show clearly distinct defence strategies between main and alternative hosts in a natural multi-host system. They also highlight the importance of defence strategies in determining virulence and infection dynamics, and hint that defence efficiency is a crucial intervening element in these processes.

Expression of circulating leucocytes before, during and after myiasis by Dermatobia hominis in experimentally infected rats.

Expression of circulating white blood cells was investigated in rats (Rattus norvegicus) experimentally infected with larvae of Dermatobia hominis, the human bot fly. Leucocytes were counted prior to infection (control group) as well as at 6, 10, 15, 20 and 28 days post-infection (dpi) and at 7, 15, 30 and 60 days post-larval emergence (dple). Total leucocyte numbers did not differ markedly among the groups. Significant differences were registered when values from control and animals harboring each larval stage of D. hominis were compared; with crescent rank: L1-, L2-, control and L3-infected groups. Leucocyte numbers were significantly higher in the control, 15, 20 or 28 dpi groups than in the 6 dpi animals. Higher counts were observed in control, L2- or L3-infected rats than L1-infected animals. Neutrophils, eosinophils and both large and small lymphocytes were also counted and analyzed. Basophils and monocytes were insufficient in number to permit statistical studies. These results stimulate the continuity of the studies about the host-parasite relationship in the dermatobiosis.

Tree swallows (Tachycineta bicolor) nesting on wetlands impacted by oil sands mining are highly parasitized by the bird blow fly Protocalliphora spp.

Oil sands mining is steadily expanding in Alberta, Canada. Major companies are planning reclamation strategies for mine tailings, in which wetlands will be used for the bioremediation of water and sediments contaminated with polycyclic aromatic hydrocarbons and naphthenic acids during the extraction process. A series of experimental wetlands were built on companies' leases to assess the feasibility of this approach, and tree swallows (Tachycineta bicolor) were designated as upper trophic biological sentinels. From May to July 2004, prevalence and intensity of infestation with bird blow flies Protocalliphora spp. (Diptera: Calliphoridae) were measured in nests on oil sands reclaimed wetlands and compared with those on a reference site. Nestling growth and survival also were monitored. Prevalence of infestation was surprisingly high for a small cavity nester; 100% of the 38 nests examined were infested. Nests on wetlands containing oil sands waste materials harbored on average from 60% to 72% more blow fly larvae than those on the reference site. Nestlings on reclaimed sites suffered mean parasitic burdens about twice that of those on the reference site; and for comparable parasitic load, they exhibited greater pathologic effects (e.g., decreased body mass) than control nestlings. The heavy blow fly infestation on oil sands-impacted wetlands suggests that oil sands mining disturbs several components of the local ecosystem, including habitat characteristics, blow fly predators, and host resistance to parasites.

Experimental concurrent infection of sheep with Oestrus ovis and Trichostrongylus colubriformis: effects of antiparasitic treatments on interactions between parasite populations and blood eosinophilic responses.

The purpose of this experiment was to determine if an earlier infection with Oestrus ovis would down regulate an infection with Trichostrongylus colubriformis when the larvae of O. ovis were expelled from the nasal cavities of sheep by a specific treatment. Three groups of five lambs were used: group 1 was artificially infected with O. ovis larvae and later with T. colubriformis, group 2 received O. ovis larvae and later was treated with ivermectin 14 days before being infected with T. colubriformis. Group 3 was infected with T. colubriformis only. The criteria examined were: the effects on nematode egg excretion, worm fecundity, nematode burdens and the kinetics of blood eosinophils. Significant decreases of nematode egg excretion, worm fecundity, nematode burdens were observed in group 1 compared to group 3. However, no changes were observed in either group 2 or 3. In group 2 it was noted that antiparasitic treatment induced a rapid decrease in blood eosinophils to a range close to the non-infected control group and this was associated with the removal of the down regulation effects of nematode burdens. This experiment showed that there is no cross immunity between O. ovis and T. colubriformis and that eosinophils may act against any parasite without specific priming.

Seroprevalence of Oestrus ovis (Diptera, Oestridae) infestation and associated risk factors in ovine livestock from southwestern Spain.

This survey was carried out to determine the seroprevalence of nasal infestation by sheep bot fly, Oestrus ovis L., and to identify the risk factors associated with the disease in flocks in southwestern Spain. In total, 5,878 sera samples of adult sheep were collected at random in 551 farms from four provinces in the southwestern Spain: Badajoz, Cáceres, Córdoba, and Sevilla. Sera were tested by enzyme-linked immunosorbent assay for O. ovis antibodies, by using a crude L2 larval as antigen. The seropositive mean prevalence was 69.30%, and mean percentage of optical densities was 61.83%. There were significant differences between the provinces studied; C6rdoba and Sevilla were the provinces with more infested animals and higher seroprevalences. The correlation between seroprevalence and percentage of antibodies by farms was significant. There were only 18 farms free of seropositive animals, and 115 of the total 551 farms had all sampled animals seropositive, an indication of the high importance of this parasitosis in the investigated areas. Altitude, latitude, flock size, and ovine population density were the potential risk factors associated with the detection of O. ovis antibodies. Those animals breeding in regions located at low altitudes (<500 m), meridian latitudes (<39.5 degrees N), and on farms with medium-to-large flock size (>250 sheep) and high ovine population density (>100 sheep per km2) were more likely to be seropositive. These findings confirm that these studied factors should be considered as potential risk factors to the presence of O. ovis in ovines from southwestern Spain.

Skin immune responses in cattle after primary and secondary infections with Hypoderma lineatum (Diptera: Oestridae) larvae.

Cellular immune responses were examined in the skin of cattle after primary and secondary experimental infections with Hypoderma lineatum larvae. Skin biopsies were taken at 0, 6, 12, 48 and 96 h post-infection (h.p.i.). In primary infected animals the penetration of Hypoderma larvae was characterized by moderate inflammatory responses. The pattern of cellular changes in previously infected animals suggested an allergic or rheumatic process, probably as a consequence of the development of a type III hypersensitivity reaction against the second or successive reinfections. Perivascular infiltration with CD3(+) T lymphocytes was marked in infected groups, but especially in previously infected animals, with a significant increase with respect to uninfected controls at 48 h.p.i. B cells remained close to control values during primary infection, while they increased significantly 12 h.p.i. in reinfected animals. IgG(+) plasma cells were also very abundant during secondary infections, with significant differences from primary infected and uninfected animals from 6 h.p.i. onwards. These results suggest that secondary infections allow cellular responses which may be effective in killing some of the entering larvae, resulting in a degree of resistance.

Regulation of Oestrus ovis (Diptera: Oestridae) populations in previously exposed and naïve sheep.

Larvae of Oestrus ovis (Insecta: Diptera: Oestridae) are common parasites of nasal and sinus cavities of sheep and goats. During larval development, a specific immune reaction is initiated by the host with a humoral local and systemic response and the recruitment of eosinophils and mast cells in the upper airways mucosae. Nevertheless, the roles of these responses in the regulation of O. ovis larvae populations in sheep are not yet known. The aim of this study was to compare the establishment and the development of larvae as well as some inflammatory or immune parameters between different groups of half-sibling sheep: (i) a primed group experimentally infected twice before a challenge infection, (ii and iii) two groups infected once only and previously treated with a long-lasting corticoïd before the challenge (one group) or not (the other group). A fourth group of non-infected animals was added in the experimental design. The larval establishment rate was 23% in the corticoïd treated group compared to about 10% in the two other infected groups. Moreover, the larval development appeared more rapid in the corticoïd treated group than in the two other infected groups suggesting that the inflammatory response is involved in the regulation of O. ovis populations. By contrast, no differences in the establishment rates were shown in the primed group compared to the naïve group (without corticoïd treatment) despite evidence of higher eosinophilia, serum specific IgG, and immediate hypersensibility to excretory-secretory products of larvae. The specific lymphocyte proliferation was reduced in the primed group compared to the naïve one suggesting that an immuno-suppression occurs following repetitive O. ovis infections.

Dynamics of antibodies against hypodermin C in reindeer infested with the reindeer warble fly, Hypoderma tarandi.

Serum samples from 25 reindeer (Rangifer tarandus tarandus) were assayed for antibody against hypodermin C (HyC) using an ELISA. Nineteen animals were calves (born in 1998, 1999 or 2001) and six were adults (3-10 years old at first blood collection). The samples were collected over periods of 4 months (calves born in 2001) or 27 months (adults and calves born in 1998 and 1999), the latter encompassing three Hypoderma tarandi infestation seasons. The calves received antibodies against HyC from their mothers, either by placental transfer or through the ingestion of colostrum. The low level at 3 h postpartum compared to the high level 3 days after birth in one calf suggests that the antibodies are transferred through colostrum. The levels of antibody of maternal origin decreased rapidly and reached low levels by mid-July, which coincides with the onset of the major Hypoderma ovipositioning season in this region. The calves thus did not appear to be protected by antibody against HyC when they were exposed to H. tarandi infestation for the first time. Antibody levels increased following infestation and reached a maximum during November or December, which coincides with when the H. tarandi larva stops migrating after it has reached the site under the skin of the back of the host and develops further. Levels declined thereafter and reached a nadir during the following summer. After the subsequent re-infestation, the increase in levels occurred at least 1 month earlier than with the first infestation. Levels remained elevated throughout the year after repeated infestations. This implies that the antibodies persist after the annual exit of mature larvae from the animal, and after larvae have been killed by application of ivermectin. Levels in adults, however, declined significantly with age, and levels were significantly lower in animals that were 4-11 years old than in 1-year-old animals during the same 1-year period. This supports the contention that the functional capacity of the immune system declines gradually with age. The study demonstrated that HyC is potentially useful for serological diagnosis of hypodermosis in reindeer, but the persistence of antibodies complicates interpretation of antibody-based surveillance programme data in all cases other than first-time exposure.

Analysis of the humoral immune response to Oestrus ovis in ovine.

Antibody responses (IgG, IgM and IgA) against Oestrus ovis were analyzed in sheep and in first year grazing lambs from Sardinia (Italy) by an indirect-enzyme-linked immunoassay test and L2 O. ovis excretory/secretory antigens. Serum samples from 208 sheep were obtained prior to be slaughtered, and then heads were removed and cut open along their longitudinal axis to collect the parasites from the nasal cavities, turbinates and sinus. Besides this, blood samples were monthly collected from the lambs of G-1 (maintained under field conditions) and the lambs of G-2 (kept housed since birth to avoid Oestrus infestations) throughout a year. In the sheep, a positive significant correlation was observed between the number of first instar O. ovis larvae and the values of IgM, and between the second instar larvae and the IgG optical densities. In the lambs, all classes of antibodies increased significantly from July in G-1. The highest values of IgG were reached in September (IgG) and decreased in November-December. The IgM response peaked in November, and very low values of IgA were observed during the study. Matching these data with chronobiology of O. ovis in this region, we conclude that the first infection occurs on May, stimulating the production of humoral antibodies. The reduction of the IgG antibody levels starting from October means the beginning of the diapause while the IgM response seems to be associated to the presence of L1 in the nasal cavities. The data obtained led us to forecast an early treatment of the ovine on June-July, which should keep away from the maturation of O. ovis L1 larvae, avoiding the development of clinical lesions and interrupting the life cycle of this parasite.

Some physiological responses associated with reduced wool growth during blowfly strike in Merino sheep.

OBJECTIVE: To examine the effect on wool growth of physiological changes associated with experimental flystrike in superfine Merino wethers. DESIGN: An animal house study comparing experimentally fly struck sheep with non-infected control groups that were pair fed or fed ad libitum. PROCEDURE: Sheep in the blow fly larval challenge group were each artificially infected with 500 first instar larvae per day for 8 days. Infections were terminated with insecticide on day 10. For all sheep, live weight change, feed intake and body temperature were monitored and blood collected for analysis of haematology, cortisol, serum haptoglobin, serum amyloid A and the pro-inflammatory cytokines, TNFa, IL-1 b, IL-6 and IL-8. Wool growth and staple strength were examined 4 months after infection. RESULTS: Experimental fly strike included moderate fever, depressed feed intake, and elevated cortisol, IL-6, serum amyloid A and haptoglobin. Staple strength was significantly decreased in struck sheep and did not differ between wool from sites adjacent to and remote from strike lesions. CONCLUSIONS: The results suggest that depression in feed intake alone is not sufficient to account for the decline in staple strength seen during fly strike. Cortisol, IL-6 and metabolic consequences of the acute phase response are likely to be major contributors to the systemic effects of blowfly strike on wool.

Histological and immunohistochemical characterization of Hypoderma lineatum (Diptera: oestridae) warbles.

Hypoderma larvae are tissue invading parasites which spend several months migrating within the host tissues before completing their development in the sub-dermal tissues of the back. Subcutaneous stages of the parasite produce an inflammatory reaction in the skin called "warbles", as well as holes through which larvae breathe. In order to elucidate the microscopical structure of the warbles, three hides from warbled cows were collected in a slaughterhouse in Lugo (NW, Spain) between March and May 2012. A total of 60 skin samples, including warbles at different phases of development, were chosen for histopathological and immunohistochemical examination. Microscopic lesions were classified into three groups, according to the predominance and distribution of different cell populations. In warbles containing living or recently dead larvae with apparently well preserved cuticle (type 1), plasma cells were observed in high number. However, macrophages and lymphocytes were the predominant cells in granulomas (type 2) formed in relation to remnants of the dead parasite, containing or not remains of the altered cuticle. Scars (type 3) were characterized by granulation tissue. Immunohistochemistry showed that B lymphocytes and IgG(+) cells were predominant in the lesions, as long as the cuticle of the larvae is intact. On the other side, CD3(+) lymphocytes increased once cuticle is destroyed and a granuloma is formed. Macrophages, revealed by CD68(+), MAC387(+) and lysozyme immunolabelling, were detected in all types of lesions, but they were more abundant in type 2 and scarce in scars. These cells appeared isolated around the intact larvae or forming aggregates around its remains in the granuloma. Moreover, a strong immunolabelling against MAC387 antibody was registered in the squamous epithelium covering the breathing pore. This finding may be associated with the expression of calprotectin, a molecule involved on the healing process of the skin after larvae outcome. Our results suggest the predominance of a humoral response inside the warble as long as larvae are intact. Once they are destroyed, cellular response occurred, isolating and destroying the remains of the larvae until healing process completes and scars with low numbers of inflammatory cells appear.

The immunology of myiasis: parasite survival and host defense strategies.

Infestations by dipterous larvae that feed on dead or living vertebrate tissues for a variable period are known as myiases; these infestations reduce host physiological functions, destroy host tissues and cause significant economic losses to livestock worldwide. Recent advances in understanding the specific and nonspecific immune responses of hosts to infestation by myiasis-causing larvae and the immunological strategies evolved by larvae against the host are reviewed here. The practical implications of immunological knowledge for diagnostic and vaccination strategies are also discussed, with a view to developing environmentally sustainable control methods to be used as an alternative to chemical treatments.