The louse has three pairs of legs joined to its thorax – with hooked feet to grip the hair of its host , so it can remain in place – and two large spiracles in the middle part of the thorax and the lateral edges [ 2 ] .
The abdomen is divided into nine segments with spiracles at the lateral edges . The male louse has a rounded rear end , with visible sclerotised genitals on the ventral side . In females , the rear end is bilobed and divided into two sections .
Internally , on the ventral surface , there is a structure known as the mycetome , which has specialised cells used to break down red blood cells . The mycetome also contains symbionts , which ensure the female is fertile . They are passed on to the next generation via the ovary [ 2 ] .
The female louse can lay around 200 – 300 eggs ( also known as nits ) during their month-long life span [ 3 ] . The eggs are adhered to the shaft of the hair at one end and at the other end is a lid ( operculum ) [ 2 ] ( Figure 2 ). The life cycle takes approximately 2 – 3 weeks . The eggs hatch immature lice ( nymphs ), and there are three nymphal stages before the final adult stage of this hemimetabolous cycle [ 4 ] . All stages need to feed on blood , so they remain on the host .
Treatment
Most ectoparasiticides , such as fipronil , imidacloprid and selamectin , are effective against sucking lice [ 5 ] . Treatment should be repeated around a week later to catch any hatching nymphs . The dog ' s environment and bedding should be washed to eradicate any lice that have fallen off its body . In addition , any other dogs that have been in contact with the infested dog should be treated .
Mallophaga
T . canis is host-specific to wild canids and dogs ( Figure 3 ). The lice are wingless , dorsoventrally flattened , light-yellow arthropods of around 2 mm in length [ 2 ] . The head is wider than the thorax , making it distinguishable from L . setosus . The mouth parts are ventrally located and are designed for gripping hair and for chewing and biting . The main food source for these lice is skin debris , specifically keratin and sebum [ 2 ] . They usually infest areas around the head , neck and tail , as well as wound edges and body cavity openings [ 5 ] .
Figure 2 . Egg of a sucking louse , seen with an electron microscope [ 2 ] . Figure 3 . T . canis , seen with an electron microscope [ 2 ] .
L . setosus is found only on canids and transmission usually occurs through direct contact with the infested animal . It is possible for eggs and adults to be transferred on fomites , such as grooming equipment , but contact would need to occur within a few days because the lice cannot survive off the host for long [ 4 ] . In some instances , phoretic transfer on flying insects has been observed .
Infestation is not common in dogs kept in hygienic environments . Clinical signs of infestation include pruritus , scratching and self-trauma . If present in large numbers , lice can cause anaemia [ 5 ] .
Lice are easy to detect on the skin and hair of dogs , especially in areas of thicker hair , such as around the eyes and ears . Eggs become more visible as the hair to which they are attached grows [ 2 ] .
The thorax is divided into three segments , although the two caudal segments are partially conjoined . The louse has three pairs of legs , which are joined to the thorax and have claws at the tips . The segmented abdomen has six pairs of spiracles on the lateral edges [ 2 ] .
The clinical significance of this louse is that it is a vector for the tapeworm Dipylidium caninum , which will infect the host if the louse is ingested [ 4 ] . Infestation can also cause alopecia , irritation and pruritus , mainly in dogs that are very young , old or in poor health .
In the cat , the main louse of concern is F . subrostratus ( Figure 4 , page 47 ). It mainly affects old or sick cats , especially those of long-haired breeds . The louse is easily identified by its triangular , pointed head [ 6 ] .
46 Veterinary Nursing Journal