a parasite centered on the nests of its wild bird hosts, this species has become a major pest in commercial poultry houses. Ornithonyssus bursa and O. sylvarium cause similar problems to poultry production. Mites as transmitters of microorganisms Parasitic mites are less commonly involved than ticks and parasitic insects in transmitting pathogenic microorganisms to livestock species because fewer types of them feed directly on blood. However, the dermanyssid mites blood-feeding on birds can be transmitters (same as the term vector in this context) of microorganisms. Dermanyssus gallinae has been shown to transmit between chickens the virus causing St Louis encephalitis (the main transmitters of this virus to humans are Culex mosquitoes). Dermanyssid mites are also implicated in the transmission to poultry birds of the bacterial agent of avian spirochaetosis, Borrelia anserina, but the main transmitters of this bacterium are argasid ticks. (Trombiculid mites are notorious as transmitters of Orientia tsutsugamushi, the bacterium that causes scrub typhus in humans in Southeast Asia.) Control of infestations Pesticide treatments Psoroptes mites infesting sheep are controlled by application of synthetic chemicals formulated for killing mites and ticks (acaricides, or more generally ectoparasiticides). These can be applied as aqueous washes in dipping baths, or as pour-on preparations in an oily formulation that spreads over the skin. Dip baths used to be commonly used for applying acaricides to sheep (also cattle). However, alternatives such as hand-held sprayers and pour-on applicators are now often used to reduce costs and risk of contamination associated with running a dip tank. Formamidine and synthetic pyrethroid acaricides such as amitraz and flumethrin, respectively, are often used. A more direct way of treating some types of mite are antiparasitic drugs that act systemically through the internal circulation of the animal rather than topically on the skin. The avermectin drugs such as ivermectin are used as acaricides against deeply feeding mites such as Sarcoptes and Demodex species. The drugs are delivered orally or parenterally. They can also be effective against surface-feeders such as Psoroptes species. Botanical pesticides derived directly from plants such as the neem tree (source of the active ingredient, azadirachtin) are an alternative to commercial chemical pesticides. Biological control, management, and hygiene Fungi such as Metarhizium anisopliae and Beauveria bassiana that are naturally pathogenic to mites are subjects of research as an alternative to chemical pesticides. The fungi infest the surface of the cuticle and penetrate into it, smothering the mites.