Induction of humoral immune response to multiple recombinant Rhipicephalus appendiculatus antigens and their effect on tick feeding success and pathogen transmission

BACKGROUND: Rhipicephalus appendiculatus is the primary vector of Theileria parva, the etiological agent of East Coast fever (ECF), a devastating disease of cattle in sub-Saharan Africa. We hypothesized that a vaccine targeting tick proteins that are involved in attachment and feeding might affect feeding success and possibly reduce tick-borne transmission of T. parva. Here we report the evaluation of a multivalent vaccine cocktail of tick antigens for their ability to reduce R. appendiculatus feeding success and possibly reduce tick-transmission of T. parva in a natural host-tick-parasite challenge model. METHODS: Cattle were inoculated with a multivalent antigen cocktail containing recombinant tick protective antigen subolesin as well as two additional R. appendiculatus saliva antigens: the cement protein TRP64, and three different histamine binding proteins. The cocktail also contained the T. parva sporozoite antigen p67C. The effect of vaccination on the feeding success of nymphal and adult R. appendiculatus ticks was evaluated together with the effect on transmission of T. parva using a tick challenge model. RESULTS: To our knowledge, this is the first evaluation of the anti-tick effects of these antigens in the natural host-tick-parasite combination. In spite of evidence of strong immune responses to all of the antigens in the cocktail, vaccination with this combination of tick and parasite antigens did not appear to effect tick feeding success or reduce transmission of T. parva. CONCLUSION: The results of this study highlight the importance of early evaluation of anti-tick vaccine candidates in biologically relevant challenge systems using the natural tick-host-parasite combination

INDIRECT FLUORESCENT-ANTIBODY TEST FOR EXPERIMENTAL AND EPIZOOTIOLOGICAL STUDIES ON EAST COAST FEVER (THEILERIA-PARVA INFECTION IN CATTLE) - EVALUATION OF A CELL-CULTURE SCHIZONT ANTIGEN FIXED AND STORED IN SUSPENSION

A schizont antigen for the indirect fluorescent antibody test against Theileria parva was prepared from a T parva-infected bovine lymphoblastoid cell line by fixing the cells in suspension with a mixture of acetone and formaldehyde. The antigen was stored in suspension in phosphate buffered saline for one and a half years at -60 degrees C without loss of activity; the antigen could also be lyophilised. The fluorescence of the intracellular schizonts was bright and specific with T parva positive bovine control serum and absent with negative bovine control serum and Theileria mutans positive bovine control serum. Fluorescence of the lymphoblastoid cell itself was observed with Trypanosoma brucei positive control serum and some bovine test sera: this fluorescence, which masked the intracellular schizonts, was eliminated by absorbing the sera in the supernatant of sonicated lymphocytes obtained from bovine lymph nodes. The antigen was evaluated with sera from cattle experimentally infected with T parva. In an epizootiological study on East Coast fever in the Coast Province of Kenya, there was good correlation between the serological responses of cattle to T parva schizont antigen and the distribution of Rhipicephalus appendiculatus ticks.status: publishe

A NEW METHOD FOR FIXATION AND PRESERVATION OF TRYPANOSOMAL ANTIGENS FOR USE IN THE INDIRECT IMMUNOFLUORESCENCE ANTIBODY-TEST FOR DIAGNOSIS OF BOVINE TRYPANOSOMIASIS

A new method for fixation of trypanosomes for use in the indirect immunofluorescent antibody test (IFAT) is described. The method involves fixation of live trypanosomes, in suspension, using a mixture of 80% cold acetone and 0.25% formalin in saline. The fixed trypanosomes were stored in suspension at -60 degrees C, 4 degrees C or at room temperature for at least one year without loss of antigenicity. Using trypanosomes prepared this way as antigens in IFAT, species-specific antibodies were detected within 2 weeks of infection in sera of cattle infected with T. brucei or T. vivax. Thereafter, antibodies recognizing antigens common to the two species as well as T. congolense were detected. The antibody levels to common antigens of the three species declined 2-3 months post-infection, leaving only the species-specific antibodies. The sera obtained from T. congolense infected animals, did not react with T. vivax or T. brucei antigens. The non-specific fluorescence commonly associated with this assay was eliminated by prior absorption of the test sera with normal bovine lymphocyte lysate. This treatment of serum did not affect the specific antibodies to trypanosomal antigens. Analysis of bovine sera prepared from cattle in Kisiwani and Muhaka, along the Kenya coast, using the fixed trypanosomes revealed that some animals had antibodies to one trypanosome species only while others had antibodies to 2 or all 3 trypanosome species.status: publishe