SUCKING LICE

Anoplura-sucking lice- these are obligate parasites feeding exclusively on mammals. There is a alternative taxonomic nomenclature that places the order Mallophaga which are the biting lice, into a suborder of the Anoplura, with sucking lice being placed in the suborder Siphunculata. Sucking lice tend to be larger than biting lice, up to 8mm and have small heads in relation to body size. They are morphologically adapted to an ectoparasitic existance being dorso-ventrally flattened with short stout legs that end in a single large curved claw. The claws of sucking lice can be retracted and touch a process on the tibia. The size and shape of the gap between the claw and tibia is the same as the hosts hair, thus the louse is able to clamp itself onto the host. Lice have lost their wings as an evolutionary adaptation to their ectoparasitic way of life. Sucking lice are generally blind although some posses photosensitive areas. They are extremely host specific with a particular lice species being found on only one host species. Some lice have been found on different hosts but these are generally closely related, such as sheep and goats. This transmission is probably due to lice that have become accidentally detached and being blind, slow moving and needing high ambient temperatures for activity they will attempt to live on any endotherm. If a closely related species is found then survival may ensue. Transmission from host to host often occurs between closely penned animals or densely herded animals, and from mother to offspring in a matter of hours. Piglets have become infested with Haematopinus suis in as little as 10 hours.

Sucking lice feed on their hosts blood taking regular blood meals and are unable to survive away from their host for more than 24-36 hours. Sucking lice will leave a dead host, or one that has a high fever for a more suitable host and this is a crucial factor in transmission of pathogens through livestock herds. The mouthparts are designed for piecing with sharp dorsal, median, and ventral stylets with the ventral stylet being the main penetration organ. The whole proboscis can be withdrawn into a cavity within the head when not in use. Differences between the two sexes are relatively easy to distinguish with females having two pairs of gonopods laying laterally on the ventral surface and males have an elongate genitalia along the midline of the lateral surface. Lice lay individual eggs directly onto the hairs of their host and as Anoplura is a Hemimetabola group (young resemble adults except for size) the nymphs hatch and exist in the same manner the larger adults do. There are three nymphal stages before the adult and lifespan along with development time are related to temperature and humidity.