The ectoparasites or external parasites they are the parasites that inhabit the skin of their hosts or on it. Good examples of these organisms are fleas, lice, ticks and mites, although some authors consider that, in the broadest sense, mosquitoes and other blood-sucking insects, which depend on their hosts for life, should also be included in this category.
Broadly speaking, a parasite is defined as any organism that lives in or on another organism that is known as a “host”. At the expense of and to the detriment of their host, parasites obtain the food they need to survive and complete their life cycle.
It could be said that there are two types of parasites: endoparasites and ectoparasites. While ectoparasites are those that live on or on the surface of their hosts, endoparasites penetrate said surface and enter the interior of the organism, so they can also be extracellular or intracellular.
Many parasites cause disease in their hosts, especially endoparasites, although ectoparasites can be indirect transmitters or vectors of endoparasites that are pathogenic for the organism on which they live..
Endoparasites are usually much smaller than ectoparasites, since they are microscopic organisms, commonly unicellular or multicellular. Ectoparasites, on the other hand, are usually larger and more complex organisms, such as some small invertebrate animals.
Ectoparasites are parasites that inhabit or on the surface of the organism that hosts them. They can parasitize different types of organisms, such as animals and plants, at the level of their epidermis.
These parasites cause irritation or annoyance to their hosts, but not necessarily a disease or pathological condition. However, among the “hidden” symptoms that some authors describe for ectoparasites, the following stand out:
From another point of view it can also be said that ectoparasites negatively affect the fitness, the "performance" or "fitness" of their hosts, which implies that they are less successful, especially in reproductive terms and with respect to the survival of their offspring.
Since they are not always pathogenic organisms by themselves, ectoparasites are often ignored from a clinical point of view, especially when it comes to animal or human hosts..
However, some ectoparasites are important vectors or vehicles for the transmission of other parasites (endoparasites) or pathogenic organisms, which can be detrimental to the health of the host organism..
The transmission of parasites and / or pathogens by ectoparasites usually occurs when they feed on their host, either through saliva or feces..
Depending on the close relationship they establish with the host, ectoparasites can be obligate or facultative: if they depend exclusively on their host to survive, then they are obligate parasites, but whether or not they can live without their host, they are facultative parasites..
Additionally, ectoparasites can be permanent or intermittent, which means that they can parasitize their hosts uninterruptedly throughout their life cycle or whose parasitism is interrupted and resumed several times throughout their life cycle..
In nature there are many ectoparasites that parasitize a wide variety of species, so they are rather cosmopolitan, however there are others that are specific, which means that they only parasitize organisms of a particular species; this is the case with many lice.
Just as is true for most parasites in nature, ectoparasites are usually physically smaller than the organisms they parasitize..
In addition, which is also usually true for other types of parasites, ectoparasites have much higher reproduction rates than their hosts, which is why they have a greater probability of success in achieving the parasitosis they cause..
Most of the ectoparasites belong to the group of invertebrate animals, although two groups of vertebrate ectoparasites are also recognized.
These two groups of multicellular "worm-like" organisms include some important ectoparasites:
Among the most important ectoparasites of aquatic animals are those belonging to this group of animals. Although they can be eradicated relatively easily on fish farms, some species of fish are highly susceptible to ectoparasitosis of crustaceans, especially salmonids..
The most common ectoparasitic crustaceans belong to the subclasses Copepoda, Branchiura and Malacostraca:
The most important and abundant ectoparasites of vertebrates and invertebrates in nature are found in this group of arthropod animals. Some of the most important groups are:
The main vertebrate ectoparasites belong to the following groups:
Columbicola columbae it is an ectoparasitic organism belonging to the order Mallophaga of the class Insecta. It is a sucking louse that parasitizes the feathers of pigeons, specifically of four particular species:
Pediculus humanus It is another kind of insect belonging to the Pediculidae family (order Phthiraptera, class Insecta) that parasitizes the human scalp, especially during childhood; arguably the "most popular" lice.
Cimex lectularius, Better known colloquially as “bed bug” it is an important ectoparasite belonging to the Cimicidae family, of the group of Hemiptera of the class Insecta.
It mainly affects humans, as it is usually found in the beds of some homes with poor hygiene, where it feeds on the blood of its hosts. However, it has been shown that it is not a species-specific parasite, as it can affect some domestic animals equally..
Many domestic mammals such as dogs, cats, cows, and sheep can be infested with some hematophagous (blood-sucking) ectoparasites of the Ixodidae and Argasidae families of the Arachnida class, commonly referred to as ticks..
Dogs, for example, are commonly affected by organisms of the species Rhipicephalus sanguineus (Ixodidae), especially in those canids that live in hot climates.
These ticks, in addition to feeding on the animal's blood, are important transmitters of different pathogens such as bacteria Ehrlichia canis, causing a condition known as ehrlichiosis, which can also be suffered by humans.
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