Human body lice vector a number of deadly bacterial diseases. Resistance to current pediculicides has caused clinical failures. An uncertain economy and increased strife have increased homelessness and infestations. New pediculicides with novel actions and information on resistance mechanisms are critical needs for the effective and sustainable control of louse vectors. The body louse has the smallest insect genome annotated to date with a substantially reduced number of metabolic defensive (detox) genes implicated in insecticide resistance. Thus, it is an efficient model to study ivermectin- and spinosad-induced tolerance proactively prior to evolution of resistance. Ivermectin and spinosad are the newest pediculicides being commercialized and as natural products are prone to detoxification via xenobiotic metabolism. The induction of metabolic detox genes by ivermectin and spinosad using the non-invasive induction assay with an inbred and wildtype strain of body lice reared on the in vitro feeding system reduces stochastic variation and allows the efficient identification of inducible detox genes involved in the metabolism of these insecticides, providing temporary protection termed 'tolerance.' Some of these detoxification pathways will result in resistance once constitutive over expression occurs and can be developed as 'proactive' monitoring tools with this information. Specifically, resistance to ivermectin and spinosad will occur by oxidative metabolism (P450), glutathione conjugation (GST), and efflux via ABC transporters (ABCT) driven by the over expression of some of the genes identified herein. The transcription levels of 11 P450, 11 ABCT and 8 GST genes will be initially monitored using quantitative real-time PCR (transcriptional profiling) and correlated to the level of tolerance induced by sub-lethal exposure to pediculicides (functional profiling by the tolerance screen). Induced detox genes that result in tolerance will be further transcriptionally profiled at all developmental stages (developmental screen). Induced detox genes that result in tolerance and are expressed at all stages will be functionally profiled in vivo using RNAi and in vitro using heterologous expression (baculovirus expression of P450s and Xenopus oocyte expression for ABCTs) techniques. Tissue specific protein expression of induced detox genes that result in tolerance at all stages of development and metabolize pediculicides will be determined by immunohistochemical analysis.
Human lice transmit a number of bacterial diseases to people and are likely capable of mechanically transmitting many more, such as MRSA and hepatitis viruses. Resistance to commercial products used to treat lice infestations has occurred and control failures have been reported worldwide. New anti-lice products, novel target sites and information on resistance mechanisms are all necessary for the effective and sustainable control of human lice.
