Biological diversity and distribution
Ticks are classified as class Arachnida, subclass Acari, order Parasitiformes, suborder Ixodida. There are about 878 species divided into four families: Argaside (soft ticks), Ixodidae (hard ticks), Nutalliellidae and Laelaptidae. Each of the last two families contains one single species and their medical importance is low. Ixodidae family is one that contains almost all the species of importance from medical veterinary point of view. Ticks are specialized organisms obligatory hematophagous with temporary parasitic life. They feed on the blood of mammals, birds, reptiles or amphibians and can be found in all regions of the world. Although ticks are present from tropics to subarctic regions, species diversity is higher in tropical and subtropical regions.
Tick body is divided into two primary sections: the anterior capitulum (gnathosoma) and the posterior part of body (idiosoma), on this second component are fixed the legs. Tick larvae have six legs, while nymphs and adults have eight legs. Unfed adult ticks have dimensions ranged between 2 and 20 mm. Gorged females may increase the weight of up to 100 times the initial weight. The components of mouthparts are located in the capitulum. Here are the palps that in ixodids presents numerous chemosensors. The palps don’t enter in the wound. They are designed to push the skin laterally and horizontally during feeding. From the capitulum base, located medial to the palps, two tubular segments called chelicerae starts. At the end of these, can be found two devices highly mobile and very sharp, involved in cutting the skin. The hyostome located median and relatively large, allows them to anchor themselves firmly at the same time constituting the feeding channel. The shape, size and location of the hypostome backward-curving hooks can vary depending on the species and are important criteria in the differentiation and identification of the ticks. Ticks present and well developed salivary glands. Saliva contains proteolytic enzymes, involved in digestion and liquefaction of tissues. It enters the host body through the hypostome. The body is located in the back part of capitulum. In the anterior part of the body are located the legs and the genital pore and in the posterior part, the anus. Genital pore is closed and vaguely at the larval and nymph stages and is open only in adults. In “hard ticks" on the back side a shield is present over the entire surface in males, while in females and preadulte stages it only covers the anterior portion. During feeding, the cuticle, excepting the shield, expands as the response to the ingestion of blood, and body volume increase. The body of Argasidae is fully covered by a flexible cuticle. Articulated legs, consisting of six segments, have a role in locomotion. Haller's organ located on the first pair of legs, detects temperature, air currents, odors and chemicals.
Biological cycle of ixodid ticks (hard-ticks) implies the presence of four developmental stages: egg, larva, nymph and adult. Along the passage through these stages, the feeding stages alternate with free life periods. Time spent on the host extends the duration in about 10% of the entire life cycle. Most hard-ticks hard are less mobile and not actively hunt their host, but rather adopt the strategy "sit and wait" (eng. questing). The Ixodidae ticks lay a large number of eggs (from several hundred to 23,000 per female), after which the female die. Eggs hatch and form larvae that start looking the host. The larvae climb onto the host, attach and feed for a period of 3 to 7 days. Fed larvae emerges from the host, molts and turns in nymph. This will start searching their host. After finding them, will attach and feed over a period of 3 to 8 days. Speaking in percentages, larvae and nymphs take a small amount of blood than females, but their weight may increase of 7 to 20 times, referring cases to increase the weight of even 80 times. After feeding, the nymphs emerge from the host, molt and turn into adults. This pattern of life cycle, where each evolutionary stage must find a host, is called the life cycle with three host. It is not characteristic to all Ixodidae. Several species of the Hyalomma and Rhipicephalus genera, are characterized by the fact that larval stage molt and turns in the nymph on the same host body, the life cycle being with two hosts. The life cycle that has only one host is characterized by the fact that after larval attaching on the host, one that will come off it will be an adult, the shedding and feeding taking place on the same host for all evolutionary stages. This is characteristic of species of the genera Margaropus and occasionally Hyalomma. The feeding process starts slow but becomes extremely rapidly in the past 12-36 hours. Most of the time, half of the weight gained during feeding is carried out in the last hours. This feedingĀ  pattern characterizes larvae, nymphs and females.
At the tick bite site, local necrosis and hemorrhage may occur, followed by inflammatory response often associated with eosinophilia. Although there may be a hypersensitivity reaction, innate inflammatory response and necrosis are sufficient to cause damage to the skin. Injuries caused by ticks can be infected with bacteria of the genus Staphylococcus, causing skin abscesses or pyaemia. The massive infestation with ticks in animals can lead to significant blood loss, reduced productivity, reduced weight gain and restlessness. Hematophagous nutritional behavior, enroll the ticks in the vectors category of various diseases, being able to transmit a high number of pathogens, viruses, bacteria, protozoa and ricketsia. Moreover, some of these disorders, as Lyme disease, tick borne encephalitis, relapsing fever, Rocky Mountain spotted fever, affect human populations. Domestic and wild animals are important by their role as reservoir of pathogens, transported and maintained by animal-tick-people contact.

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