Improved efficacy of tetracycline by acaciasides on Dirofilaria immitis

The discovery of Wolbachia, a bacterial endosymbiont that occurs in the filarial parasite and its sensitivity to tetracycline, has fostered a new initiative in the development of suitable antifilarial drugs. The present study is an attempt to investigate whether adding acaciasides (saponins from Acacia auriculiformis) to the standard dose of tetracycline would further improve the efficacy of tetracycline treatment against Dirofilaria immitis microfilariae in vivo. Treatment of microfilaremic adult dogs (body weight range 8-12 kg) with tetracycline at 10 mg/kg/day for 40 days resulted in 72% and 83% reduction in mf count on days 15 and 30, respectively, and the maximum reduction in mf count (91%) was achieved on day 75 post-treatment. However, treatment with tetracycline (10 mg/kg/day for 40 days) followed by acaciasides (10 mg/kg/day for 7 days) resulted in almost 100% clearance of mf at a faster rate on day 45 post-treatment and ensured long-term (until 4 months post-treatment) protection against microfilaremia. Data from polymerase chain reaction analysis reveals that compared to untreated dogs, in treated dogs, there was marked reduction in Wolbachia specific wsp markers in fast depleting mf population. The present data indicate that prior tetracycline treatment enhances microfilaricidal activity of saponins. This effect may be additive or synergistic as the worms are weakened by Wolbachia depletion, and these weakened microfilariae are possibly killed by the saponins.