Chatper 4 : Invertebrates

Abstract:

This chapter talks about hard ticks and vector mites, diurnal fleas and flies, diurnal mosquitoes, nocturnal mosquitoes, nocturnal bugs and soft ticks, and ectoparasites. Invertebrates comprise > 2 million species, mainly molluscs, helminths, and arthropods (with insects, spiders, and crustaceans). Hard ticks, vector mites, fleas, vector flies (Glossina and Chrysops), and some mosquitoes (Aedes, Culicoides, and Simulium) mainly seek hosts during the day, while other mosquitoes (Anopheles, Culex, Lutzomyia, and Phlebotomus), bugs, and bedbugs seek hosts at night. Developmental stages are eggs, larvae (three leg pairs), nymphs, and adults (four leg pairs). Ixodids can carry viruses, bacteria, and protozoa to humans. By area, ixodid ticks can be sources of viruses from at least three genera that cause flulike illness, viral hemorrhagic fever (VHF), or encephalitis. Vector fleas attempt to regurgitate the bacterial bolus that blocks their feeding. Muscids are effective mechanical vectors of enteric bacteria, protozoa, and helminths. Tabanids are suspected or confirmed mechanical vectors of some systemic bacteria. An obstacle to ecological understanding is one's inability to reliably distinguish zoonotic Trypanosoma brucei from anthroponotic T. brucei gambiense and T. brucei rhodesiense. Old World Phlebotomus can carry viruses and protozoa to humans, New World Lutzomyia bacteria and protozoa. Mainly nocturnal vectors include triatomine bugs, Cimex bedbugs, and Ornithodoros soft ticks. Temporary ectoparasites are fly larvae and sandfleas that leave hosts after weeks. Residual ectoparasites are lice (Pediculus and Phthirus) and scabies mites that maintain themselves by continued autoinfection.