Lice are obligate ectoparasites of every avian and most mammalian species. They are only a few millimeters long and like [[Fleas|fleas]], are wingless but unlike fleas are dorsoventrally flattened.
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Lice are host specific, permanent parasites which cause [[Pediculosis|pediculosis]]. The louse saliva and faeces contain allergenic substances which cause irritation, rubbing, licking and skin damage leading to decreased host productivity.
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Mammalian lice species have a single pair of claws on the ends of stout legs, whereas avian lice species have a double claw on each leg.
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There are two main groups of veterinary importance, the Mallophaga (chewing lice) and Anoplura (sucking lice)