A campaign to eradicate bovine babesiosis from New Caledonia

In December 2007, Babesia bovis was introduced to New Caledonia through the importation of cattle that had been vaccinated with a live tick fever (babesiosis and anaplasmosis) vaccine. Although the tick Rhipicephalus (Boophilus) microplus is common in New Caledonia, the territory had previously been free of tick-borne diseases of cattle. This paper describes the initial extent of the outbreak, the measures and rationale for disease control, and the progress to date of the eradication campaign. Initially, 22 properties were affected involving approximately 2300 cattle in 'high risk' zones and 1600 in adjoining 'suspect' zones. Rather than slaughtering infected herds or attempting to eliminate the tick vector, the campaign was based on quarantine of affected properties, and aggressive tick control in conjunction with 3-monthly treatments of the high risk cattle with the antiprotozoal drug imidocarb dipropionate. Subsequent surveillance by ELISA and PCR showed a progressive and dramatic decline in seroprevalence among infected herds and the absence of new infections. All 22 properties were considered to be free of Babesia within 12 months of the start of the disease control program. These results indicate that the strategy was effective in eliminating Babesia from infected herds and feasible as an eradication strategy on a moderately large scale. Unfortunately, early in the campaign, babesiosis spread to a herd of feral cattle on a property in the 'suspect' zone, and this reservoir of infection subsequently resulted in the infection (or reinfection) of cattle on several neighbouring commercial farms. The eradication campaign in New Caledonia is currently focussed on destocking the feral cattle - extensive surveillance suggests that this is the only remaining nidus of infection.

In vitro and in vivo evaluation of deltamethrin and amitraz mixtures for the control of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) in New Caledonia

Acaricide resistance is a major problem that hinders the control of the tropical cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), in many parts of the world where cattle production continues to suffer severe economic losses to tick infestation. Deltamethrin and amitraz have been used alone to control R. microplus in New Caledonia for the past decade, and tick populations have developed resistance to both acaricides. A study was conducted to evaluate the effectiveness of deltamethrin and amitraz mixtures, through in vitro laboratory bioassays and in vivo on-animal efficacy trials, for the control of resistant R. microplus on cattle at two dairy farms in New Caledonia. Results of laboratory bioassays using modified larval packet tests (LPT) revealed up to 16.59-fold resistance to deltamethrin, and up to 5.86-fold resistance to amitraz. Significant synergism was observed when amitraz was used as a synergist in deltamethrin bioassays. Amitraz significantly increased deltamethrin toxicity to tick larvae, while deltamethrin was much less effective on amitraz toxicity. Synergism of amitraz by deltamethrin only occurred when the deltamethrin concentration was relatively high. Results of on animal efficacy trials of deltamethrin and amitraz alone and mixtures of both at different concentrations revealed a similar pattern of synergism. Adding amitraz to a deltamethrin formulation led to dramatic increases of percent reduction of both immature and adult ticks. In contrast, adding deltamethrin to an amitraz formulation did not increase control efficacy. Results from this study may lead to the adoption of an acaricide mixture strategy for the control of pyrethroid-resistant R. microplus in New Caledonia and elsewhere.

Accumulation of acaricide resistance mechanisms in Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) populations from New Caledonia Island

Rhipicephalus (Boophilus) microplus has been pesticide-controlled for several decades in the pacific island of New Caledonia. Since 1996, pesticide-control has been based on either deltamethrin (Butox) or amitraz (Taktic) in herds harbouring deltamethrin-resistant ticks. In this island, the first R. microplus deltamethrin- and amitraz-resistances were detected in 1992 and 2003, respectively. Using LPT bioassays, we have undertaken to update data regarding the geographical distribution and the physiological diversity likely to be involved in these resistances. We confirmed that after 17 years of intensive use of deltamethrin, several resistances of moderate levels (<30-fold) have evolved and/or diffused in any part of the island. We also evidenced that amitraz-resistant phenotypes have recently evolved in diverse western tick populations, although none has reached fixation in any tick population yet. According to synergists bioassays, the physiological changes involved in amitraz-resistance in New Caledonia would involve target modification and detoxifying P450 cytochrom oxydase(s). It may also involve detoxifying esterase(s) although this later point will need confirmation on samples bearing higher frequency of resistant phenotypes. Results are discussed with regard to the local evolutionary dynamics of resistance.