Experimental efficacy of a vaccine against Rhipicephalus australis.

Despite several decades of chemical use the cattle tick, Rhipicephalus australis, still represents an important threat for breeders of tick susceptible cattle under tropical conditions. The intense use of acaricides has lead to the development of multi-resistant strains of ticks and alternative means of control need to be developed to maintain control. A vaccine against ticks, based on the Boophilus microplus Bm86 protein, is one of the promising alternative means of tick control. In this investigation, an experimental vaccine was developed based on the orthologous R. australis Bm86 sequence identified from local R. australis strains and a recombinant protein expressed in Escherichia coli. The efficacy of this vaccine against a local strain of R. australis was assessed under controlled conditions. Vaccinated cattle presented 40.3% fewer ticks than unvaccinated cattle and tick reproductive performance was also affected by the vaccine. Ticks that engorged on vaccinated animals laid 51.2% less egg mass and tick fertility decreased by 18.8% compared to the control group. The use of the vaccine reduced the tick population by 74.2% at each generation. The tick vaccine can be used in an integrated tick control program.

Evaluation of three adjuvants with respect to both adverse effects and the efficacy of antibody production to the Bm86 protein.

Cattle tick infestations remain an important burden for farmers in tropical area like in New Caledonia. With the development of acaricide resistance, tick vaccines should be an attractive alternative to control ticks but their efficacy needs to be improved. In this study three adjuvants were studied in an experimental tick vaccine with a Bm86 protein to assess their performance in terms of antibody productions and adverse reactions following vaccinations. The water-in-oil adjuvant ISA 61 VG led to higher antibody titers compared to a water-in-oil-in-water adjuvant ISA 201 VG and an aqueous polymeric adjuvant Montanide Gel 01. Vaccinations with these three adjuvants did not produce severe general reaction but an increase in skin thickness was observed especially with both oil-based emulsions. These results indicated that the water-in-oil adjuvant is the most interesting to use for this vaccine but local adverse reactions remain an issue.

Lack of Efficacy of Albendazole against Dicrocoelium dendriticum Infection in a Sheep Farm in France.

Dicrocoeliosis is a common parasitic disease in European sheep farming. The prevalence of infection by this parasite can reach almost 70% in areas where the environment is favorable to intermediate hosts. In France, only one drug is currently available for the treatment of dicrocoeliosis: albendazole at a dose of 15 mg/kg in a single administration. However, a control coproscopy following a routine treatment led us to suspect that the efficacy of albendazole against Dicrocoelium dendriticum had diminished. Therefore, we carried out an efficacy test on 15 animals by treating them with albendazole at a dose of 15 mg/kg and performing a coproscopy on D0 and a control coproscopy 14 days later. We obtained a 39% reduction in the excretion of D. dendriticum eggs. This shows a reduction in the expected efficacy of albendazole, which is normally more than 90% in other studies involving this molecule at a dosage of 15 mg/kg. These results are of major concern as albendazole is currently the only drug available in France to treat dicrocoeliosis.

Real-time PCR on skin biopsies for super-spreaders' detection in bovine besnoitiosis.

BACKGROUND: Bovine besnoitiosis, an emerging disease in Europe that can be transmitted by vectors, is caused by the apicomplexan Besnoitia besnoiti. Bovine besnoitiosis is difficult to control due to the complexity of its diagnosis in the acute stage of the disease, poor treatment success and chronically asymptomatic cattle acting as parasite reservoirs. When serological prevalence is low, detection and specific culling of seropositive cattle is feasible; however, economic considerations preclude this approach when serological prevalence is high. The aims of this study were to evaluate the accuracy of detection of super-spreaders in highly infected herds and to test their selective elimination as a new control strategy for bovine besnoitiosis. METHODS: Previous real-time PCR analyses performed on skin tissues from 160 asymptomatic animals sampled at slaughterhouses showed that the tail base was the best location to evaluate the dermal parasite DNA load. All seropositive animals (n = 518) from eight dairy or beef cattle farms facing a high serological prevalence of besnoitiosis were sampled at the tail base and their skin sample analysed by real-time PCR. A recommendation of rapid and selective culling of super-spreaders was formulated and provided to the cattle breeders. Subsequent serological monitoring of naïve animals was used to evaluate the interest of this control strategy over time. RESULTS: Among the 518 seropositive animals, a low proportion of individuals (14.5%) showed Cq values below 36, 17.8% had doubtful results (36 < Cq ≤ 40) and 67.8% had negative PCR results. These proportions were grossly similar on the eight farms, regardless of their production type (beef or dairy cattle), size, geographical location or history of besnoitiosis. Within two weeks of the biopsy, the rapid culling of super-spreaders was implemented on only three farms. The numbers of newly infected animals were lower on these farms compared to those where super-spreaders were maintained in the herd. CONCLUSIONS: Real-time PCR analyses performed on skin biopsies of seropositive cattle showed huge individual variabilities in parasite DNA load. The rapid culling of individuals considered as super-spreaders seems to be a new and encouraging strategy for bovine besnoitiosis control.

Efficacy of halofuginone lactate against experimental cryptosporidiosis in goat neonates.

Preliminary results obtained in calves, lambs and goat kids infected by Cryptosporidium sp. have indicated a partial prophylactic efficacy of halofuginone lactate when administered at 100 µg/kg body weight (BW). In this study, the efficacy of halofuginone lactate was evaluated in goat neonates experimentally inoculated with Cryptosporidium parvum oocysts per oral route. The trial consisted in 2 replicated experiments carried out successively at 2 months of interval. Twenty-two 2- to 4-day-old kids were experimentally inoculated once, 2-3 days after the arrival in premises, with 10(6)C. parvum oocysts per oral route and were allocated into 2 groups. Animals of group 1 acted as untreated control whereas animals of group 2 received halofuginone lactate for 10 days from the infection day to day 9 post-infection (DPI) at a daily oral dose rate of 100 µg/kg BW. Individual oocyst shedding was monitored by daily examination of faecal smears stained by carbol fuchsin and scored semi-quantitatively (0-5) until 19 DPI. Daily diarrhoea scores, weight gain and mortality were recorded. In the first experiment, oocyst excretion started 1 DPI in the control group, was highest on 4 DPI (mean score 3.6) and became undetectable from 16-19 DPI. In the treated group, oocyst shedding started 1 day later, showed lower scores compared to control on 4, 5, 6, 7 and 10 DPI and vanished from 16 to 19 DPI. No significant difference was seen for weight gains between groups. Five kids died in the control group compared to 1 kid in the treated group. In the second (replicated) experiment, oocyst excretion started 2 DPI in the control group, was highest on 4 DPI (mean score 4.5) and became undetectable 18 and 19 DPI. In the treated group, oocyst shedding started 2 days later, peaked on 13 DPI (mean score 2.3) and persisted until the end of the experiment. No significant difference was seen for weight gains between groups. Ten kids died in the control group compared to 3 kids in the treated group. The results demonstrated the efficacy of halofuginone lactate when given as a prophylactic treatment at 100 µg/kg BW during 10 days in reducing oocyst shedding, diarrhoea and mortality in goat kid cryptosporidiosis.