Increasingly, there is need for methods to control cattle tick (Boophilus microplus) infestations by the use of non-chemical technology. This need is brought about by a mixture of market forces and the failure or inadequacy of existing technology. A recombinant vaccine has now been developed against the tick. This vaccine relies on the uptake with the blood meal of antibody directed against a critical protein in the tick gut. The isolation of the vaccine antigen, Bm86, and its production as a recombinant protein is briefly described. The vaccine has been tested in the field, has been taken through the full registration process and is now in commercial use in Australia. A related development has occurred in Cuba. The potential for improvement of the current vaccine and for the development of similar vaccines against other haematophagous parasites is discussed.

The development of new acaricides is a long and very expensive process. Worryingly, there is increasing resistance to available acaricides worldwide leading to the real possibility that our dwindling supply of effective acaricides will be exhausted unless action is taken to increase the number of new acaricidal products and reduce the rate of resistance development. In 1995, eight major animal health pharmaceutical companies formed the Veterinary Parasite Resistance Group (VPRG) to act as an expert consultative group to guide the FAO in resistance management and collaborate in the prudent use of acaricides. In this paper, members of the VPRG discuss the problems and processes in acaricide development, resistance in the field to commonly used acaricides and the different considerations when targeting the cattle and pet market, and give their view of the future for tick control from the perspective of the animal health industry.

There is now abundant evidence that vaccination with defined protein antigens is able to induce significant immunity to tick infestation. In a limited number of cases, this immunity has been duplicated by vaccination with recombinant antigens, a critical step on the pathway to commercial vaccine production. The existence of two commercial vaccines has allowed a number of field studies showing that the existing products can make an important contribution to an integrated approach to the control of ticks in the field. Under most circumstances however, the use of a tick vaccine as the single, stand alone control technology is likely to require more efficacious vaccines than those currently available. Increases in efficacy are most likely to come through the discovery of additional, effective vaccine antigens. The number of antigens with demonstrated effect is increasing, though only slowly, while the number of potential antigens that remain to be evaluated is increasing more quickly. There is limited, though convincing, evidence that some of these antigens will show effective cross-species protection, though in a poorly understood and unpredictable way. The groundwork has been laid; the potential of the field is still to be effectively exploited.

Here we describe the purification and characterization of a vitellin (VT) degrading cysteine endopeptidase (VTDCE) from eggs of the hard tick Boophilus microplus. A homogeneous enzyme preparation was obtained by chromatographic fractionation on ion-exchange and gel filtration columns and an autolysis step. This step consisted of incubation of a semipurified enzyme (after the first ion-exchange chromatography) at pH 4·0 that dissociated the enzyme from VT, to which VTDCE is naturally tightly associated. The enzyme purity was confirmed by capillary and native gel electrophoresis, and SDS–PAGE suggested the enzyme is a dimer of 17 and 22 kDa. VTDCE was active upon several synthetic substrates, with a preference for a hydrophobic or a basic residue in P1, and a hydrophobic residue in P2. VTDCE also hydrolysed haemoglobin, albumin, gelatin and vitellin. VTDCE is inactive in the absence of DTT and was totally inhibited by E-64, indicating it is a cysteine endopeptidase. Our results suggest that VTDCE is a major enzyme involved in yolk processing during B. microplus embryogenesis.

The tick Boophilus microplus is a 1-host tick that causes important losses to bovine herds, and protective antigens are being investigated in order to develop vaccines that avoid the use of acaricides. Paramyosins are multi-functional invertebrate muscle proteins, whose roles may include host immunomodulation, and seem to be a prominent candidate in a schistosomiasis vaccine. We report here the cloning, expression and characterization of a B. microplus paramyosin (BmPRM). Sequence analysis of the full length coding sequence cDNA shows high identity to other arthropod paramyosin sequences, and the predicted molecular weight, pI and secondary structure are consistent with a typical paramyosin. Western-blot expression analysis indicates the presence of BmPRM in all tissues and developmental stages tested, but not in saliva. The recombinant protein (rBmPRM) was shown to bind both IgG and collagen. Possible implications of these activities with host evasion mechanisms are discussed.

An aspartic proteinase precursor, herein named BYC (Boophilus Yolk pro-Cathepsin) was isolated from eggs of the hard tick, Boophilus microplus. As judged by electrophoresis on sodium dodecyl sulfate polyacrylamide slab gel (SDS–PAGE), purified BYC presented 2 bands of 54 and 49 kDa, bearing the same NH2-terminal amino acid sequence. By Western blot analysis, BYC was also found in the haemolymph, indicating an extraovarian site of synthesis. Several organs were incubated in culture medium with [35S] methionine, and only the gut and fat body showed synthesis of BYC polypeptides. Protein sequencing of both the NH2-terminal and an internal sequence obtained after cyanogen bromide (CNBr) cleavage of BYC revealed homology with several aspartic proteinase precursors. Incubation at pH 3·5 resulted in autoproteolysis of BYC, which produced the mature form of the enzyme, that displayed pepstatin-sensitive hydrolytic activity against haemoglobin. Western blot analysis using anti-BYC monoclonal antibodies showed proteolytic processing of BYC during embryogenesis and suggested activation of the enzyme during development. A role of BYC in degradation of vitellin, the major yolk protein of tick eggs, is discussed.

Topical application of crude ethanol extracts (CEs) of the leaves of 43 of 51 Jamaican plants produced varying degrees of multiple acaricidal effects on engorged Boophilus microplus Canst., including mortality (M), inhibition of oviposition (IO) and inhibition of embryogenesis (IE). Acaricidal indices (AI) ranged from 50 to 100 for the CEs of 29 plants, 38 to 47 for 9 plants and from 0 to < 25 for 13 plants. The most active CEs, in decreasing order of activity (AI values in parentheses) were those of: Simarouba glauca (100), Symphytum officinale (99), Nicotiana tabacum (95), Hibiscus rosa-sinensis (93), Ervatamia divaricata = Ricinus communis (82), Salvia serotina (80), Stachytarpheta jamaicensis (79), Blighia sapida = Ocimum micranthum (76), Spigelia anthelmia (75), Cycloptis semicordata (74), Mormordica charantia (71), Bontia daphnoides (69), Azadirachta indica (68), Capsicum annum = Catharantus roseus = Petiveria alliacea (66), Gliricida sepium (64), Lippia alba (62), Cuscuta americana = Erythrina corallodendrum (61), Piper amalago (60), Cannabis sativa = Cecropia peltata (58), Dioscorea polygonoides (56), Artocarpus altilis (53), Crotalaria retusa (51), Citrus aurantium (50).

The biological activity against Boophilus microplus of extracts of the berries, bark, leaves and twigs of Pimenta dioica was examined and compared with that of eugenol, methyl eugenol and four commercial acaricides, namely dimethoate, farnesyl methyl ether, carbaryl and diazinon. The berry essential oil was more effective at inhibiting oviposition and causing mortality of the ticks than all the extracts, the commercial acaricides and methyl eugenol. At a dose of 1.0 mg/g it was 33, 12, 6, and 3 times as effective in inhibiting oviposition as the non-polar extracts of the leaves, bark, twigs and berries, respectively. The potency of the berry essential oil is attributable to eugenol, a phenyl propanoid derivative, which accounts for over 65% of the oil content.

Boophilus microplus is Brazil's outstanding livestock ectoparasitic pest (annual losses, US$ 1B), affecting, to varying extents, all its States, with a national herd of some 130 M cattle. The country's 8.5 M sq km and 23,000 km of land frontier with 10 tick infested countries complicate any concepts of national campaigns. Whereas Brazil is increasingly climatically suitable for B. microplus from south (three generations annually) to central (four) to north (potentially up to five), direct problems caused are incidentally decreased due to greater use of Bos indicus cattle at lower stocking rates; five tick population survival mechanisms are suggested. Voluntary, empirical chemical tick control remains the tradition, with little government involvement. Formamidine and synthetic pyrethroid acaricides dominate the market, due to former tick resistance to arsenicals, organochlorines and organophosphates, and market forces. Plunge dips, various sprayers, and “pour-on” formulations are used; first suspicions of tick resistance to synthetic pyrethroids have been reported. Various ecologically based “improved” tick control schemes produced promising results experimentally, but require a complementary vaccine against babesiosis/anaplasmosis before wide recommendation. Intensive use of synthetic pyrethroid acaricides has created tick-borne diseases and heightened demand for a live, frozen “vaccine”, in its pre-commercialization phase in Brazil. A strategic research and development approach has been adopted for widespread improvement to cattle ticks and tick-borne disease control in Brazil.

Risk-benefit considerations have stimulated efforts to develop technology to overcome the limitations of procedures that place excessive reliance on the use of acaricides for the control of ticks affecting cattle. One of the alternatives to acaricides is the selection and use of breeds of cattle with a natural propensity for developing acquired resistance to ticks. The literature on aspects of the modes of expression and mechanisms of resistance of cattle to ticks, is reviewed along with information on the successful efforts in Australia to develop productive Bos indicus ï Bos taurus breeds with the ability to develop high levels of resistance. The use of cattle resistant to ticks is discussed in relation to other factors that should be considered in the design of a programme for tick control.

The relative efficacy of 25 acaricides, applied topically to the engorged adults of B. microplus was in the following order: chlorfenvinphos > tetrachlorvinphos > dimethoate > chlorpyrifos > fenitrothion > dicrotophos (LC50 = 0.000897−0.00244%) > naled > propoxur > crotoxyphos > pirimiphos ethyl > coumaphos > dioxathion (LC50 = 0.00425−0.00534%) > trichlorphon > lindane > carbaryl > allyxycarb > diazinon (LC50 = 0.00737−0.0149%) > promecarb > ethion > chlorpyriphos methyl > chlormebuform (LC50 = 0.021−0.0593%) > clenpyrin > chlordimeform > pirimiphos methyl > phosphamidon (LC50 = 0.1566™0.275%).

The order of toxicity is different from their relative efficacy against the larvae of the same population of the tick. Applied implications of the results are discussed.