Mites of livestock

Mites are small crawling animals related to ticks and spiders. Most mites are free-living and harmless. Other mites are parasitic, and those that infest livestock animals cause many diseases that are widespread, reduce production and profit for farmers, and are expensive to control. Mites are invertebrates, arthropods with a chitinous exoskeleton and jointed limbs. Within the Arthropoda, they belong in the subclass Acari (or Acarina) and species belonging to the Acari are informally known as acarines. Although both acarines and insects (class Insecta) are studied in the fields of veterinary and medical parasitology, acarines are separated from insects by structure, feeding, lifecycles, and disease relations. Both livestock and companion animals are susceptible to mite infestation and although this article will focus on livestock, the two are similar. Humans also may become infested by contagion from these domestic animals (a zoonosis). Infestation by mites usually causes skin diseases known as mange, scab, demodecosis, or in general as acariasis. The causation, economic impact, and control of these diseases in livestock are described in this article. Mites that cause disease in honey bees are described in Varroa destructor.

Classification, lifecycles, anatomy, and feeding

Classification

Over 48,000 species of mites are described, and an estimated half-million more are yet to be discovered. Acarines parasitic on livestock animals are classified to family level in the list below. The taxonomy of the Acari is complex, several versions exist, and their phylogeny is considered to be paraphyletic (originating from several ancestral lines). The Acari are a subclass of the class Arachnida. Within the Acari are two superorders: the Acariformes and the Parasitiformes. The list below (Outline classification) is simplified for this veterinary article by omitting the superorders, orders, and suborders; this emphasizes the pragmatic taxonomic level of families, together with vernacular names. Within this list, the Parasitiformes include the blood-sucking mites of birds, the hard ticks, and the soft ticks, whilst the Acariformes include the psoroptic and sarcoptic mites, the trombiculids, and the demodectic mites. The identification of many types of mites is work for a specialist. However, the mites parasitic on vertebrate animals can readily be identified to at least the level of genus by nonspecialists if the clinical context of host species and site of infestation on skin or other organs is used. Also, the two main families of ticks are added to the list of acarine families because these common parasites are closely related to mites, and as larvae may be confused with them at infestations. The third tick family, the Nuttalliellidae, consists of one rare species. Ticks require separate accounts because they have distinctly different feeding mechanisms and relations to disease. Distinguishing acarines from insects (subphylum Hexapoda) is similarly important because the term 'insect' is often used in popular text and speech for various small crawling animals. The generalized anatomy of an acarine as shown in the diagram below can be compared with that of an insect as in typical parasitic flies of domestic animals.

Outline classification Phylum: Arthropoda (insects, acarines, crustaceans, arachnids etc.) Subphylum: Chelicerata (acarines, scorpions, horseshoe crabs, solfugids, etc.)

Class: Arachnida (mites, ticks, spiders, scorpions, etc.)

Subclass: Acari (mites and ticks) [Superorders, orders and suborders omitted]

Family: Psoroptidae (psoroptic mites) Family: Psorergatidae (itch mites) Family: Sarcoptidae (sarcoptic mites) Family: Cytoditidae (air-sac mites) Family: Laminosioptidae (fowl cyst mites) Family: Analgidae (feather mites) Family: Trombiculidae (trombiculid or chigger mites) Family: Demodicidae (follicle mites) Family: Dermanyssidae (blood-sucking mites of birds) also Family: Argasidae (soft ticks) also Family: Ixodidae (hard ticks)

Lifecycles Mites have a lifecycle in which larvae hatch from the eggs, then feed and molt into nymphs. Several stages of nymphs may follow (another term for stages in this context is instar). The final molt produces an adult female or male. The early form of the female is described as pubescent (ready for mating) and may be equipped with protuberances that couple with matching sockets on the male during fertilization. Such coupled mites are a natural occurrence in skin-scrape samples of mites for diagnosis. Once mated, the female continues to develop and lay eggs; or in the typical case of Psoroptes for example, females produce one large egg at a time. In most parasitic mites, the entire lifecycle takes place on the host, with all stages present simultaneously (an exception is the trombiculid mites where the nymphs and adults are free-living). This type of lifecycle, with all active stages resembling each other in structure and feeding mechanism, is called incomplete metamorphosis (or hemimetabolism). A metamorphosis is a distinct change of body shape. When the larval stages of an invertebrate animal are completely different from the adult stage, as with caterpillars changing into butterflies, a complete metamorphosis occurs (holometabolism).

Anatomy and morphology

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