Tetracycline treatment and sex-ratio distortion:: a role for Wolbachia in the moulting of filarial nematodes?

Filarial nematodes harbour intracellular bacteria of the genus Wolbachia. These bacteria are though to be beneficial to the host nematode. Indeed, tetracycline treatments reduce the population of Wolbachia in filarial worms and hake detrimental effects on the nematode. Even though various, antibiotic-curing experiments have been performed on filariae, the actual role of Wolbachia in the biology of these nematodes is not yet clear. To address this issue, we designed a first experiment on a model filaria (Brugia pahangi). maintained in the gerbil (Meriones unguiculatas). In this experiment, timing of tetracycline treatment x as set on the basis of the larval stage of the nematode. This first experiment showed that 2 weeks of treatment started after the L-4-L-5 moult of males, but before the moult of females, led to significant sex-ratio distortion of the nematodes. We thus hypothesised that tetracycline interferes with the moult in B. pahangi. To test this hypothesis designed a second experiment in which antibiotic treatments ere started (1) before the moult of both sexes, (2) after the moult of males but before the moult of females. or (3) after the moult of both Treatment I determined a reduction of worm recovery with no sex bias. Treatment 2 led to a male-biased sex-ratio. Treatment 3 had no effect on either worm recovery or sex-ratio. These results, thus support the hypothesis that tetracycline treatment interferes with the L-4-L-5 moult of B. pahangi. The nematodes recovered from the treated and control animals were examined for the presence of Wolbachia using both immunohistochemistry and real-time PCR. In general. nematodes from treated animals showed a dramatic reduction in Wolbachia content. In one group, Wolbachia depletion, as observed at the end of the treatment, was followed by a rebound to 'normal' values 160 days later. Prospects for antifilarial therapy using Wolbachia-targeted tetracycline treatments should thus take into account the possibility of Wolbachia rebound. (C) 2002 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights resened.