No abstract

Ticks are important ectoparasites of domestic and wild animals, and tick infestations economically impact cattle production worldwide. Control of cattle tick infestations has been primarily by application of acaricides which has resulted in selection of resistant ticks and environmental pollution. Herein we discuss data from tick vaccine application in Australia, Cuba, Mexico and other Latin American countries. Commercial tick vaccines for cattle based on the Boophilus microplus Bm86 gut antigen have proven to be a feasible tick control method that offers a cost-effective, environmentally friendly alternative to the use of acaricides. Commercial tick vaccines reduced tick infestations on cattle and the intensity of acaricide usage, as well as increasing animal production and reducing transmission of some tick-borne pathogens. Although commercialization of tick vaccines has been difficult owing to previous constraints of antigen discovery, the expense of testing vaccines in cattle, and company restructuring, the success of these vaccines over the past decade has clearly demonstrated their potential as an improved method of tick control for cattle. Development of improved vaccines in the future will be greatly enhanced by new and efficient molecular technologies for antigen discovery and the urgent need for a tick control method to reduce or replace the use of acaricides, especially in regions where extensive tick resistance has occurred.

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.

Glycoproteins located on the luminal surface of the plasma membrane of tick gut epithelial cells, when used to vaccinate cattle, are capable of stimulating an immune response that protects cattle against subsequent tick infestation. One such tick gut glycoprotein, designated Bm86, has been purified to homogeneity and the amino acid sequences of peptide fragments generated by endoproteinase Lys-C digestion have been determined. We report here the isolation and characterization of a cDNA that encodes Bm86. The nucleotide sequence of the cDNA contains a 1982-base-pair open reading frame and predicts that Bm86 contains 650 amino acids including a 19-amino acid signal sequence and a 23-amino acid hydrophobic region adjacent to the carboxyl terminus. The main feature of the deduced protein sequence is the repeated pattern of 6 cysteine residues, suggesting the presence ofseveral epidermal growth factor-like domains. A fusion protein consisting of 599 amino acids of Bm86 and 651 amino acids of /3-galactosidase was expressed in Escherichia coli as inclusion bodies. Ticks engorging on cattle vaccinated with these inclusion bodies were significantly damaged as a result of the immune response against the cloned antigen.The tick Boophilus microplus is a major ectoparasite of cattle in many parts of the world. A single female cattle tick takes up as much as 1.5 ml of bovine blood, increasing its body weight to =250 mg. It has been estimated that cattle in tropical areas of Australia may become infested with 1000 tick larvae per day, resulting in greatly reduced productivity. In addition, B. microplus is the vector of hematoprotozoal parasites such as Babesia bovis. Chemicals have been used extensively to control ticks and have been partially successful, but this approach suffers from certain drawbacks such as environmental and residue problems, the high incidence of acaricide resistance that has developed in tick populations in the field, the need for frequent administration, and high cost.Recently it was shown that cattle immunized against a Construction and Screening of cDNA Library. RNA was extracted (3) from adult B. microplus (picked from cattle 15 days after infestation), cDNA was synthesized from 4 ,ug of poly(A)+ RNA (4), and cDNA fragments larger than 800 base pairs (bp) were ligated to Agtll (5) to generate a library of 8 x 105 recombinant clones. Oligodeoxynucleotide probes (Table 1) were based on the sequences derived from peptides generated by endoproteinase Lys-C digestion of Bm86 (1).Three nitrocellulose filters were prepared from five 150-mm plates each containing 105 plaques. After prehybridization in 0.6 M sodium pyrophosphate/0.005% heparin (Sigma) at 40°C for 4 hr, hybridization was carried out for 16 hr at 40°C in the same solution with the radioactive oligonucleotide probe. Two of the filters were hybridized with the 63-mer probe while the third was hybridized with a mixture of the 50-, 51-, and 72-mer probes. The filters were washed in 0.3 M NaCl/0.03 M sodium citrate, pH 7.5/0.1% SDS at 45°C a...

Babesia spp. are tick-borne, intraerythrocytic hemoparasites that use antigenic variation to resist host immunity, through sequential modification of the parasite-derived variant erythrocyte surface antigen (VESA) expressed on the infected red blood cell surface. We identified the genomic processes driving antigenic diversity in genes encoding VESA (ves1) through comparative analysis within and between three Babesia species, (B. bigemina, B. divergens and B. bovis). Ves1 structure diverges rapidly after speciation, notably through the evolution of shortened forms (ves2) from 5′ ends of canonical ves1 genes. Phylogenetic analyses show that ves1 genes are transposed between loci routinely, whereas ves2 genes are not. Similarly, analysis of sequence mosaicism shows that recombination drives variation in ves1 sequences, but less so for ves2, indicating the adoption of different mechanisms for variation of the two families. Proteomic analysis of the B. bigemina PR isolate shows that two dominant VESA1 proteins are expressed in the population, whereas numerous VESA2 proteins are co-expressed, consistent with differential transcriptional regulation of each family. Hence, VESA2 proteins are abundant and previously unrecognized elements of Babesia biology, with evolutionary dynamics consistently different to those of VESA1, suggesting that their functions are distinct.