Isolation and characterization of a trypsin-like enzyme from the buffalo fly, Haematobia irritans exigua

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.

The role of HiTI, a serine protease inhibitor from Haematobia irritans irritans (Diptera: Muscidae) in the control of fly and bacterial proteases

Blood-sucking arthropods are vectors responsible for the transmission of several pathogens and parasites to vertebrate animals. The horn fly Haematobia irritans irritans (Diptera: Muscidae) and the tick Boophilus microplus are important hematophagous ectoparasites that cause losses in cattle production. A serine protease inhibitor from a thorax extract of the fly H. irritans irritans (HiTI) was previously isolated, characterized and cloned. In the present study we described the expression, purification, and characterization of the recombinant HiTI (rHiTI) and its possible role in the control of different endogenous and bacterial proteases. rHiTI was successfully expressed using the pPIC9 expression vector with a yield of 4.2 mg/L of active rHiTI. The recombinant HiTI purified by affinity chromatography on trypsin-Sepharose had a molecular mass of 6.53 kDa as determined by LS-ESI mass spectrometry and inhibition constants (Kis) similar to those of native HiTI for bovine trypsin and human neutrophil elastase of 0.4 and 1.0 nM, respectively. Purified rHiTI also showed inhibitory activity against the trypsin-like enzyme of H. i. irritans using its possible natural substrates, fibrinogen and hemoglobin; and also inhibited the OmpT endoprotease of Escherichia coli using fluorogenic substrates. The present results confirm that HiTI may play a role in the control of fly endogenous proteases but also suggest a role in the inhibition of pathogen proteases.

Purification, characterization, and cloning of a serine proteinase inhibitor from the ectoparasite Haematobia irritans irritans (Diptera: Muscidae)

The fly Haematobia irritans irritans is one of the most important ectoparasites in cattle production, due to its ability to suck large amounts of blood. This report describes the purification and characterization of a serine proteinase inhibitor (HiTI) present in H. i. irritans head and thorax extracts. The HiTI purified by affinity chromatography on trypsin-Sepharose has a molecular mass of 7029Da by MALDI-TOF mass spectrometry. HiTI inhibited bovine trypsin, human neutrophil elastase, and a trypsin-like enzyme purified from H. i. irritans abdomen with dissociation constants of 0.57, 1.30, and 0.20nM, respectively. The HiTI partial amino acid sequence allowed its classification into the BPTI-Kunitz-type family. An HiTI cDNA fragment was cloned in the pGEMT vector using RT-PCR. The translated amino acid sequence of HiTI cDNA confirmed a unique Kunitz-type-domain protein. Our results suggest that HiTI could control some endogenous enzyme, e.g., the H. i. irritans trypsin-like protein.

Purification and characterization of a trypsin-like enzyme with fibrinolytic activity present in the abdomen of horn fly, Haematobia irritans irritans (Diptera: Muscidae)

This work describes the purification and characterization of a trypsin-like enzyme with fibrinolytic activity present in the abdomen of Haematobia irritans irritans (Diptera: Muscidae). The enzyme was purified using a one-step process, consisting of affinity chromatography on SBTI-Sepharose. The purified protease showed one major active proteinase band on reverse zymography with 0.15% gelatin, corresponding to a molecular mass of 25.5 kDa, with maximum activity at pH 9.0. The purified trypsin-like enzyme preferentially hydrolyzed synthetic substrates with arginine residue at the P1 position. The Km values determined for three different substrates were 1.88 x 10(-4), 1.28 x 10(-4), and 1.40 x 10(-4) M for H-alpha-benzoyl-Ile-Glu-Gly-Arg-p-nitroanilide (S2222), DL-Ile-Pro-Arg-p-nitroanilide (S2288), and DL-Phe-Pip-Arg-p-nitroanilide (S2238), respectively. The enzyme was strongly inhibited by typical serine proteinase inhibitors such as SB

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.

Identification and characterisation of the excreted/secreted serine proteases of larvae of the old world screwworm fly, Chrysomya bezziana

Serine proteases are the major proteolytic activity excreted or secreted from Chrysomya bezziana larvae as demonstrated by gelatin gel analyses and the use of specific substrates, benzoyl-Arg-p-nitroanilide and succinyl-Ala-Ala-Pro-Phe-p-nitroanilide. Serine proteases were identified through their inhibition by 4-(2-aminoethyl)-benzene sulphonyl fluoride and classified as trypsin- and chymotrypsin-like on the basis of inhibition by tosyl-L-lysine chloromethyl ketone and tosyl-L-phenylalanine chloromethyl ketone, respectively. Like most insect serine proteases, the C. bezziana enzymes were active over broad pH range from mildly acidic to alkaline. The excreted or secreted serine proteases were purified by affinity chromatography using soybean trypsin inhibitor. A different subset of the serine proteases was isolated by salt elution from washed larval peritrophic matrices. Amino-terminal sequencing identified both trypsin and chymotrypsin-like sequences in the excreted or secreted pool with the latter being the dominant protease, whereas trypsin was the dominant species in the peritrophic matrix eluant. These results suggest that trypsin was possibly preferably adsorbed by the peritrophic matrix and may act as a final proteolytic processing stage as partially digested and ingested polypeptides pass through the peritrophic matrix. Immunoblot analysis on dissected gut tissues indicated that the anterior and posterior midguts were the main source of the serine proteases, although a novel species of 32 kDa was predominantly associated with the peritrophic matrix. Proteases are a target for a partially protective immune response and understanding the complexity of the secreted and digestive proteases is a necessary part of understanding the mechanism of the host's immunological defence against the parasite.

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

The digestion of blood by the buffalo fly (Haematobia irritans exigua) was monitored for 6h at 33 degrees C after a single meal. Following the meal, the concentration of soluble protein within the midgut increased to a peak at 2 hours then decreased steadily over the next 4h. The magnitude of the increase in soluble protein at 2h indicated a release of protein from another source; most likely from lysed red blood cells. The immunoglobulin (IgG) fraction of the blood meal was digested rapidly (50% within one hour of feeding) and fully digested within 4h. This is indicative of its accessibility to digestive enzymes within the midgut. In contrast, when flies had continuous access to blood, the concentration of IgG in the midgut remained at a more constant level. The loss of antigen-binding activity of a specific antibody was more rapid than complete degradation of the IgG, with 70% of binding activity lost within one hour of feeding. The level of trypsin activity in the midgut increased from pre-feeding levels to reach a peak at 2h before returning to basal levels after 6h. The pattern of trypsin activity follows closely that of the concentration of soluble protein in the midgut (r=0.88). The activity of leucine aminopeptidase in the midgut also increased immediately after feeding and remained elevated for 4 h before declining to a basal level after 6h. The rapid digestion of IgG and subsequent loss of antibody activity suggests that for a specific anti-buffalo fly antibody to be effective it would need to be able to either evade the digestive system or induce a rapid response.