RESUMEN
The efficacy of amitraz on cattle ticks was assessed by susceptibility tests, spraying and dipping trials. Tests on the susceptibility of three tick species, Rhipicephalus appendiculatus, Amblyomma variegatum and Boophilus decoloratus to amitraz (technical grade-purity 98.6% w/w) showed all 15 tick strains tested to be highly susceptible, with LC50 ranging between 0.001% and 0.03%, and LC99, between 0.01% and 0.07%. Spraying trials were carried out on calves infested with R. appendiculatus, A. variegatum and B. decoloratus. Amitraz wettable powder [as Taktic total replacement (TR)] was tested against B. decoloratus, and amitraz emulsifiable concentrate (as Taktic EC) against the other two species. Both formulations showed instant action, with ticks detaching from the calves between 30 min and 8 h after spraying. More than 50% of the detached engorged females failed to lay eggs. The remainder laid few eggs, and these had a low hatching rate of 0-2%, compared with 90-98% in the controls. The detached nymphs failed to moult, and the males and non-engorged females also detached, were immobilized and finally died. In the dipping trials, cattle heavily infested with ticks (mean tick counts of about 800) were dipped once weekly in amitraz (Taktic TR). Weekly tick counts showed that the reinfestation rate was reduced to zero after the ninth dipping. The results of the three trials complement each other, showing that amitraz is at present effective in the control of African tick species on cattle in Tanzania.
Asunto(s)
Insecticidas , Garrapatas/efectos de los fármacos , Toluidinas , Animales , Bovinos , Insecticidas/farmacología , Insecticidas/uso terapéutico , Tanzanía , Control de Ácaros y Garrapatas/métodos , Infestaciones por Garrapatas/tratamiento farmacológico , Infestaciones por Garrapatas/prevención & control , Infestaciones por Garrapatas/veterinaria , Toluidinas/farmacología , Toluidinas/uso terapéuticoRESUMEN
Resistance to Rhipicephalus appendiculatus, Amblyomma variegatum and Amblyomma hebraeum was investigated in the laboratory by infesting rabbits with adults of each of the three species followed by homospecific or heterospecific secondary infestations. Significantly lower female engorged weights and egg mass weights were taken as evidence of protective immunity. Following a single infestation with adults, rabbits developed homospecific protective immunity (resistance) to only R. appendiculatus and A. hebraeum; primary infestation with A. variegatum did not protect against secondary infestation with the same species. There was no cross-resistance (heterospecific protective immunity) between the species except for one-way protection between R. appendiculatus and A. variegatum; primary infestation with R. appendiculatus protected against secondary infestation with A. variegatum, but not vice versa. The results from ELISA did not indicate any correlation between serum antibodies to soluble antigens from salivary gland extracts and protective immunity. Post-infection sera from rabbits infested with each of the three species reacted strongly to their respective salivary gland extracts. Despite the high reactivity of A. variegatum serum with salivary gland antigens from all three species, A. variegatum-infested rabbits did not show any homospecific or heterospecific-immunity; on the other hand, although R. appendiculatus serum did not react positively to A. variegatum antigens, infestation with R. appendiculatus protected against a subsequent A. variegatum infestation.