Lice are small wingless, insects that have plague the life of humans and animals for many years. Their size range from 0.4 to 10 mm in general. They are important disease vectors and household pests in many parts of the world. They feed on blood of a wide range of vertebrates, and have the ability to chew human clothes.
Classification and Importance of Lice in the WorldLice belong to the order Phthiraptera which is divided into two sub-order, the Anaplura (sucking Lice) and Mallophaga (chewing and biting lice). There are disagreement about the taxonomic rank of different groups of lice. There are more 3200 described species of louse in the world. Most species are ectoparasites of wild birds and other mammals. All known species in the Anaplura sub-order are obligate blood feeders and ectoparasites of placental mammals. Species in the Mallophaga group are more of ectoparasites and have the ability to chew skin, feathers and fur of their hosts.
There are approximately 550 described species of sucking lice as reported by Durden and Musser in 1994. All sucking lice are classified in about 50 genera and 15 families.
In the Mallophaga sub-order, there are about 2650 described species. Most species in this category are associated with birds. For most authors, Mallophagan species can be classified into three suborders including Amblycera, Ichnocera and Rhyncophthirina (Lance, ).
Medical Importance of Lice
Sucking lice are responsible for the transmission of diseases to human. The most well know louse is the human body louse, Pediculus humanus humanus. Both chewing and sucking lice have a high degree of specificity with their hosts. All of these species are parasites of placental mammals. In some case the interaction between lice and their host is really a case of parasitism with the potential to transmit pathogens to the host.
Sucking Lice Implication in Veterinary and Public Health
Sucking lice of medical importance are mainly classified in the families Pediculidae and Pthiridae. There are three species of lice that affect humans including, the body louse (Pediculus humanus humanus), the head louse (Pediculus humanus capitis) and the crab louse or pubic louse (Pthirus pubis). Members of the families Haematopinidae, Hoplopleuridae, Linognathidae, Pedicinidae, and Polyplacidae are the only sucking lice that have veterinary importance. Lice can pasitize a wide variety of domestic and wild animals.
The body lice is responsible for the transmission of three important pathogens to humans including epidemic typhus, trench fever and louse-borne relapsing fever.
Chewing Lice Implication in Veterinary and Public Health
Within the chewing lice, only the dog biting louse (Family Trichodectidae) is important in public health. From a veterinary stand point, five families of Mallophaga have importance including Trichodectidae, Philopteridae, Gyropidae, Menoponidae and Boopiidae. Many chewing lice affect poultry and other birds. The chicken body louse for instance is the most common lose that affect poultry.
Bio-ecology of Lice
Lice are hemimetabolous insects with three distinct stages including eggs, nymphs and adults. The egg stage take s approximately 4 to 5 days depending on the species. After hatching, the nymph undergo tree different nymphal instars. Each instar last from 3 to 8 days. The third nymphal molts to give rise to the adult. Lice have exceptional rate of reproduction, with many species completing 10 to 12 generations per year. There are also some parthenogenic species of lice (reference).
Sucking lice are solenophages (vessel feeders) and rely heavily on blood feeding for their development. They Puncture the skin of their host and reach for a blood vessel to acquire blood. Special muscles, the cibarial and pharyngal muscles are responsible for the sucking of the blood.
Chewing lice on the other hand use their mandibles to chew and scratch the skin of their hosts. Other have the ability to severe parts of their bird hosts.
Lice Prevention and Control Strategies
Lice control and prevention require an elaborate plan of action, especially if the louse population is already establish.
- Durden, L. A., and Musser, G. G. (1994a). The sucking lice (Insecta, Anoplura) of the world: a taxonomic checklist with records of mammalian hosts and geographical distributions. Bull. Am. Mus. Nat. Hist. 218, 1-90.