Acarology Lecture 3 PDF

Acarology “516 ZOO” Lecture 3 Dr. Osama B Mohammed & Dr. Jawahir ALGhamdi Family ARGASIDAE Soft ticks have a leathery and unsclerotized body with a textured surface, which in unfed ticks may be characteristically marked with folds or grooves. The integument is inornate. The palps appear somewhat leg...

Acarology “516 ZOO” Lecture 3 Dr. Osama B Mohammed & Dr. Jawahir ALGhamdi Family ARGASIDAE Soft ticks have a leathery and unsclerotized body with a textured surface, which in unfed ticks may be characteristically marked with folds or grooves. The integument is inornate. The palps appear somewhat leg-like, with the third and fourth segments equal in size. The gnathosoma is located ventrally and is not visible from the dorsal view in nymphs and adults. When present, the eyes are present in lateral folds above the legs. The stigmata are small and anterior to the coxae of the fourth pair of legs. The legs are similar to those of hard ticks; the pulvillus is usually absent or rudimentary in nymphs and adults but may be welldeveloped in larvae. (a) (b) An argasid tick (a) Dorsal view of female. (b) Ventral view of female (reproduced from Arthur, 1963). The soft ticks have a multi-host life cycle. The larval stage feeds once before moulting to become a first-stage nymph. There are between two and seven nymphal stages, each feeding and leaving the host before moulting to the next stage. The adult females lay small batches of eggs after each short feed, lasting only a few minutes. Unlike the Ixodidae, these ticks are drought-resistant and capable of living for several years. They are found predominantly in deserts or dry conditions but live close to their hosts. Three genera are of veterinary importance: Argas, Otobius, and Ornithodoros. THE MITES 1. The ectoparasitic mites of mammals and birds inhabit the skin, where they feed on blood, lymph, skin debris , or sebaceous secretions, which they ingest by puncturing the skin, scavenge from the skin surface, or imbibe from epidermal lesions. 2. Most ectoparasitic mites spend their entire lives in intimate contact with their host, so transmission from host to host is primarily by physical contact. 3. Infestation by mites is called acariasis and can result in severe dermatitis, known as mange, which may cause significant welfare problems and economic losses. 4. Some mites may be intermediate hosts of anoplocephalid cestodes, including Anoplocephala, Moniezia and Stilesia. Ventral shields of a generalised mesostigmatid mite. The important features for mite identification: 1. Parasitic mites are small, most being less than 0.5 mm long, though a few blood-sucking species may attain several millimeters when fully engorged. 2. The body is unsegmented but can show various sutures and grooves. 3. The body is divided into two sections: A. Gnathosoma B. Idiosoma. -The idiosoma may be soft, wrinkled and unsclerotised. 4. Many mites may have two or more sclerotized dorsal shields and two or three ventral shields: the sternal, genitoventral, and anal Shields. 5. The genitoventral shield, located between the last two (posterior) pairs of legs, bears the genital orifice. The gnathosoma is a highly specialised feeding apparatus bearing a pair of sensory palps and a pair of chelicerae, the latter sometimes bearing claw-like, or stylet-like chelae at their tips. Between the chelicerae is the buccal cone, both of which fit within a socket-like chamber formed by enlarged coxae of the palps, ventrally and laterally and by a dorsal projection of the body wall, called the rostrum. Longitudinal section through the gnathosoma of a generalised mite. ▪ In the mesostigmatic mites, the fused expanded coxal segments of the palps at the base of the gnathosoma are known as the basal capituli, from which protrudes the hypostome. ▪ The palps are one- or two-segmented in most astigmatic and prostigmatic mites, and five- or six-segmented in the Mesostigmata. ▪ The last segment of the palps usually carries a palpal claw or apotele. Nymphal and adult mites have four pairs of legs arranged in two sets of anterior and posterior legs. Larval mites have three pairs of legs. The first pairs of legs are often modified to form sensory structures and are frequently longer and slender. At the end of the tarsus may be a pretarsus that may bear an ambulacrum, usually composed of paired claws, and an empodium, which is variable in form and may resemble a pad, sucker, claw or filamentous hair. In some parasitic astigmatic mites, the claws may be absent and replaced by stalked pretarsi, which may be expanded terminally into bell or sucker-like pulvilli. In many mites, particularly astigmatic ones, gas exchange occurs through the integument. In other mites, gas exchange takes place through one to four pairs of stigmata, found on the idiosoma. The presence or absence of stigmata is used for taxonomic purposes. Eyes are usually absent and, hence, most mites are blind. Where they are present, however, in groups such as the trombidiformes, the eyes are simple. Hairs, or setae, many of which are sensory in function, cover the idiosoma of many species of mite. The number, position and size of the setae are extremely important in the identification of mite species. ▪ Although, like the ticks, mites are obligate parasites, they differ from them in the important respect that most species spend their entire life cycle, from egg to adult, on the host so that transmission is mainly by contact. ▪ The life cycle of many parasitic species may be completed in less than 4 weeks and in some species as little as 8 days. ▪ Female mites produce relatively large eggs from which a small, six-legged larva hatches. ▪ The larva moults to become an eight-legged nymph. ▪ There may be between one and three nymphal stages, known respectively as the protonymph, deutonymph and tritonymph. ▪ In many groups of mites, particularly the Astigmata, one of these nymphal instars, usually the deutonymph, is usually a facultative inactive, dispersal or protective stage, and may be omitted from the life cycle altogether. The tritonymph then moults to become an eight-legged adult. Thanks..