Digestion of host immunoglobulin and activity of midgut proteases in the buffalo fly Haematobia irritans exigua

A Review of Australian Tick Vaccine Research

Tick vaccine research in Australia has demonstrated leadership worldwide through the development of the first anti-tick vaccine in the 1990s. Australia’s Commonwealth Scientific and Industrial Research Organisation’s (CSIRO) research led to the development of vaccines and/or precursors of vaccines (such as crude extracts) for both the cattle tick and the paralysis tick. CSIRO commercialised the Bm86 vaccine in the early 1990s for Rhipicephalus australis; however, issues with dosing and lack of global conservation led to the market closure of Tick-GARD in Australia. New research programs arose both locally and globally. The Australian paralysis tick Ixodes holocyclus has perplexed research veterinarians since the 1920s; however, not until the 2000s did biotechnology exist to elucidate the neurotoxin—holocyclotoxin family of toxins leading to a proof of concept vaccine cocktail. This review revisits these discoveries and describes tributes to deceased tick vaccine protagonists in Australia, including Sir Clunies Ross, Dr Bernard Stone and Dr David Kemp.

Proteases and pseudoproteases in parasitic arthropods of clinical importance

Parasitic arthropods feed on blood or skin tissue and share comparable repertoires of proteases involved in haematophagy, digestion, egg development and immunity. While proteolytically active proteases of multiple classes dominate, an increasing number of pseudoproteases have been discovered that have no proteolytic function but are pharmacologically active biomolecules, evolved to carry out alternative functions as regulatory, antihaemostatic, anti-inflammatory or immunomodulatory compounds. In this review, we provide an overview of proteases and pseudoproteases from clinically important arthropod parasites. Many of these act in central biological pathways of parasite survival and host-parasite interaction and may be potential targets for therapeutic interventions.

A peritrophin mediates the peritrophic matrix permeability in the workers of the bees Melipona quadrifasciata and Apis mellifera

The permeability of the peritrophic matrix, essential for its function, depends on its chemical composition. The objective was to determine if the permeability of the peritrophic matrix varies along the midgut and in the presence of anti-peritrophin-55 antibody in Melipona quadrifasciata and Apis mellifera bees. The thickness of the peritrophic matrix in both species varies between the anterior and posterior midgut regions in workers. In A. mellifera dextran molecules with 40 kDa cross the peritrophic matrix, whereas those ≥70 kDa are retained in the endoperitrophic space. In M. quadrifasciata the peritrophic matrix permeability was for molecules <40 kDa. Bees fed on anti-peritrophin-55 antibody showed an increase in peritrophic matrix permeability, but survival was not affected. In the bees studied, the peritrophic matrices have morphological differences between midgut regions, but there is no difference in their permeability along the midgut, which is affected by peritrophin 55.

An insight into the sialome, mialome and virome of the horn fly, Haematobia irritans

BACKGROUND

The horn fly (Haematobia irritans) is an obligate blood feeder that causes considerable economic losses in livestock industries worldwide. The control of this cattle pest is mainly based on insecticides; unfortunately, in many regions, horn flies have developed resistance. Vaccines or biological control have been proposed as alternative control methods, but the available information about the biology or physiology of this parasite is rather scarce.

RESULTS

We present a comprehensive description of the salivary and midgut transcriptomes of the horn fly (Haematobia irritans), using deep sequencing achieved by the Illumina protocol, as well as exploring the virome of this fly. Comparison of the two transcriptomes allow for identification of uniquely salivary or uniquely midgut transcripts, as identified by statistically differential transcript expression at a level of 16 x or more. In addition, we provide genomic highlights and phylogenetic insights of Haematobia irritans Nora virus and present evidence of a novel densovirus, both associated to midgut libraries of H. irritans.

CONCLUSIONS

We provide a catalog of protein sequences associated with the salivary glands and midgut of the horn fly that will be useful for vaccine design. Additionally, we discover two midgut-associated viruses that infect these flies in nature. Future studies should address the prevalence, biological effects and life cycles of these viruses, which could eventually lead to translational work oriented to the control of this economically important cattle pest.

Insecticide resistance in the horn fly: alternative control strategies

The horn fly, Haematobia irritans (Linnaeus 1758) (Diptera: Muscidae) is one of the most widespread and economically important pests of cattle. Although insecticides have been used for fly control, success has been limited because of the development of insecticide resistance in all countries where the horn fly is found. This problem, along with public pressure for insecticide-free food and the prohibitive cost of developing new classes of compounds, has driven the investigation of alternative control methods that minimize or avoid the use of insecticides. This review provides details of the economic impact of horn flies, existing insecticides used for horn fly control and resistance mechanisms. Current research on new methods of horn fly control based on resistant cattle selection, semiochemicals, biological control and vaccines is also discussed.

Vaccination against ectoparasites

Ectoparasites of livestock are of great economic and social importance but their effective control remains difficult. The feasibility of vaccination as a novel control measure was established over a decade ago with the commercial release of a recombinant vaccine against the cattle tick Boophilus microplus. Since then, research has continued on ticks and other ectoparasites. While some ectoparasite species will undoubtedly be refractory to immunological control, for others there has been a steady accumulation of knowledge of partially protective antigens, now accelerating through the application of genomic technologies. Nevertheless, progress towards usable, commercially available vaccines has been limited by a number of factors. The number of highly effective antigens is still very small. Although some classes of antigen have been investigated in more detail than others, we have no systematic knowledge of what distinguishes an effective antigen. Much hope has been placed on the potential of multi-antigen mixtures to deliver the efficacy required of a successful vaccine but with little experimental evidence. The application of current knowledge across parasite and host species needs to be explored but little has been done. In most cases, the path to commercial delivery is uncertain. Although many constraints and challenges remain, the need for vaccines and our capacity to develop them can only increase.

Development of vaccines against sea lice

A review of efforts to develop a vaccine against sea lice is presented together with analysis of the rationale behind the approaches and potential future directions. Vaccines against the caligid copepod, Lepeophtheirus salmonis, have the potential to be a cost-effective means of controlling the infection and avoid many of the disadvantages of medicine treatments. However, research towards such vaccines is in its infancy and approaches so far used have met with little or no success. Most strategies for sea louse vaccines have adopted methods used for vaccines against other ectoparasites. A vaccine against the cattle tick (Boophilus microplus) is in field use while other vaccines such as the sheep blowfly (Lucilia cuprina) vaccine are at an earlier stage of development. These haematophageous parasites ingest host antibody as part of a large blood meal which can target antigenic sites in the gut. However, the assumption that arachnid and insect physiology are directly comparable with that of sea lice is not proven, and this may partly explain the slow progress this approach has had with sea lice. Success in developing a louse vaccine will depend upon a better understanding of louse digestive biology, particularly an evaluation of whether the cattle tick model is applicable to the development of a louse vaccine. If the louse gut is to be targeted immunologically, critical antigens will need to be identified and evaluated, bearing in mind that an economic vaccine must include recombinant proteins or be a DNA vaccine. Alternatives to the louse gut as a target are also worth consideration. Antibodies could target critical host-parasite interactions that are amenable to disruption, although no such targets have been identified.

Survival, ovarian development and bloodmeal size for the horn fly Haematobia irritans irritans reared in vitro

Horn flies, Haematobia irritans irritans (Linneaus) (Diptera: Muscidae) were reared in vitro using cattle, pig, horse, rabbit, sheep, goat or chicken blood. The highest survival, bloodmeal size and rate of ovarian development were recorded for both female and male flies fed cattle blood. Flies fed pig, rabbit, sheep and goat blood showed intermediate survival. Flies fed chicken blood showed the lowest survival rates, ingested the smallest bloodmeals and did not develop ovaries. The relationship between dietary factors and host specificity of the horn fly, and the efficiency of vertebrate blood source of several animals for laboratory colonization of horn fly are discussed.

Immunological control of ectoparasites: past achievements and future research priorities

Recombinant vaccines are available for the control of the tick Boophilus microplus, while progress has been made in the development of vaccines against Lucilia cuprina and Chrysomya bezziana. Literature suggests that the control of other ectoparasites is feasible, either through the duplication in a vaccine of naturally acquired immunity or through 'concealed' antigen vaccines. Major deficiencies in our current knowledge however point to possible research opportunities for the future. The identification of protective antigens from all species is proceeding slowly, particularly for the antigens of naturally acquired immunity. Our capacity to produce effective recombinant antigens has progressed greatly, though there remains a major difficulty where some or all of the protective effect is due to immunogenic oligosaccharide. Our understanding of protective mechanisms is limited. The delivery of the appropriate immunological response remains difficult. Nevertheless, some of the most critical areas of ignorance are in basic biological issues: factors which affect the susceptibility of particular pest species to immunological attack and the implications of vaccine-induced effects for pest and disease control under field conditions. Increasingly too, effective pest control is likely to demand the integration of a variety of control technologies. The study of this integration is in its infancy.