ECTOPARASITES: CHARACTERISTICS, TYPES AND EXAMPLES - BIOLOGY - 2025

The ectoparasites are organisms that live in the outermost layer of its host; the prefix "ecto" means "outside." In other words, ectoparasites are parasites that are found on the host's skin, not inside its body. The infestation caused by an ectoparasite is called ectoparasitosis.

For example, fleas and lice are ectoparasites. Like all parasites, ectoparasites develop a dependent relationship with their host, from whom they take advantage of to ingest the nutrients that keep them alive. Ectoparasites can be present in animals and plants.

flea

Main features

They are attached to different species

Ectoparasites are characterized by living attached to the body of organisms of other species. Being located there they take advantage of the guest and take their food from it.

They feed on bodily fluids

These parasites feed on the blood or other skin secretions of their hosts.

They are usually located in places that are difficult to access

Ectoparasites are usually located in inaccessible places, so that it is not easy to get rid of them through regular hygiene actions.

They do not contribute anything to their guest

As in the case of all parasites, the relationship that is generated between ectoparasites and their host is one of convenience. Ectoparasites live at the expense of the organism they parasite.

They can be temporary or permanent

Ectoparasites can be classified according to the time they spend parasitizing their host; that is, they can be temporary or permanent.

Temporary ectoparasites can spend certain periods of time away from their host, such as fleas, ticks, and mosquitoes. In contrast, permanent ectoparasites spend all stages of their life cycle on their host, as is the case with lice and mites.

Main types of ectoparasites

Ectoparasites are divided into two main groups: arachnids and insects. This classification is given by structural characteristics.

The class of arachnids includes ticks and mites. The class of insects consists of flies, mosquitoes, fleas, and lice.

Insects (six-legged arthropods)

Insects are characterized by having three different parts of the body: head, thorax and abdomen. They have one pair of antennae on the head, three pairs of legs on the thorax and, in some cases, have wings.

Many ectoparasites in this group, including some species of flies, mosquitoes, and fleas, spend little time on the host.

In contrast, others, such as bluefly larvae and lice, remain on the bodies of hosts for longer periods of time.

- Lice

Lice are common, easily visible insects, approximately 2-4mm in length. Like all insects, lice have 6 legs that are specially adapted to adhere to the skin and hair of the host.

Morphologically, some lice have elongated bodies and others are rounded, similar to crabs but much smaller. The eggs of these insects are called nits and are white in color.

Louse

Lice as adults feed on blood. By doing this they inject saliva into the host's skin, which causes a hypersensitivity reaction. This reaction is evidenced by causing itching of the affected individual's skin (pruritus).

Lice are easily transmitted through fomites such as combs, hair accessories, towels, among others.

- Flies

Flies are flying insects that are widely distributed throughout the world. Many of these are capable of infecting humans through their larvae, which provoke an inflammatory response. Infections occur most frequently in tropical areas.

The infection caused by these ectoparasites varies according to the species of insect. Some flies lay their eggs when there is a wound in the host, later the egg hatches and produces the larva.

Other flies deposit their eggs on the host's mucosa, such as in the nostrils or near the lips. Another group of flies lay their eggs on the intact skin and it is the larva that invades the skin.

- Bedbugs

Chiches are another type of insect with parasitic habits. It is common to find them in beds, where they can easily parasitize their hosts. Morphologically they are oval, brown in color and about 5 mm long.

Bed bugs are usually found in cracks in wood and on mattresses. Their eating habits are nocturnal, while their human hosts sleep, bed bugs feed easily.

The main symptoms of a bed bug bite are inflammation and itching, which are caused by an allergic reaction to toxins in the bug's saliva.

Arachnids (eight-legged arthropods)

Within the group of arachnids are ticks and mites. Morphologically, these parasites are characterized by having two body segments: the head fused with the thorax (cephalothorax) and an abdomen.

Another distinctive feature is its four pairs of legs in the adult stage, which do not have wings or antennae.

- Ticks

Ticks are small ectoparasitic arachnids that feed on the blood of mammals, birds, and some reptiles and amphibians. These arachnids are distributed throughout the world; however, they are more commonly found in hot, humid climates.

They are frequently subdivided into two groups, according to their structural characteristics: hard ticks (family: Ixodidae), which are difficult to squash; and soft ticks (family: Argasidae), which are easy to squash.

Tick

Ticks locate their hosts primarily by smell. Their ovoid bodies fill with blood when they feed.

They have 4 stages in their life cycle: egg, larva, nymph and adult. Because they are hematophagous (that feed on blood), ticks are vectors of diseases that affect humans and other animals.

- Mites

Mites are arachnids that can be easily seen under a microscope. Their bodies are generally round and flattened, although an exception to this general rule are the mites belonging to the genus Demodex, which have an elongated shape.

The mites are found in the stratum corneum of the epidermis and feed on the remains of dead skin cells, such as scales. Some species have alternative feeding habits, such as piercing the skin to suck up lymphatic fluid.

Transmission occurs by personal contact or by sharing fomites such as clothing, especially if there are few hygienic conditions.

The symptoms are similar to those caused by other ectoparasites, the itching is a response of the body to a delayed hypersensitivity reaction to the mite's feces. The mite is found within the stratum corneum of the epidermis.

Examples of ectoparasites in humans

The scabies mite (

Sarcoptes scabiei is a species of mite and is the causative agent of scabies, commonly called scabies. This is a skin disease and is distributed worldwide since it is highly contagious.

The infection occurs when a female digs tunnels in the skin of the host and leaves her eggs as she moves. The eggs hatch and produce larvae that migrate to the surface and develop into infectious adults.

The hair follicle mite (Demodex sp.)

The mites of the genus Demodex are small ectoparasites that live in the hair follicles of mammals and in other nearby areas. They are very small and there are two species that affect humans: Demodex folliculorum and Demodex brevis.

Demodex infestation is common and generally remains asymptomatic, although in some cases they can cause skin diseases, especially in people who have problems with their immune system.

If the immune system is not working properly, these ectoparasites can proliferate and cause demodicosis.

The head louse

P. humanus capitis is an ectoparasite of the group of insects and is the causal agent of pediculosis. These parasites do not have wings so they are forced to spend their entire lives on their host.

Its shape is flattened and its color is translucent; however, they turn red when feeding on human blood. Despite being hematophagous (blood-eating) parasites, these head lice do not transmit disease.

The common flea (

The Pulex irritans species is an example of an ectoparasite that severely affects humans because it is the vector of transmission of various diseases, including the bubonic plague that struck Europe in ancient times.

It is a species that has been successful in its distribution throughout the world. It feeds on the warm blood of various animals such as dogs, cats, pigs, bats, rats, chickens, among others.

The pubic louse (

Pubic crab is an ectoparasite that feeds exclusively on human blood. It is usually found in the pubis of infected people, but its presence has also been reported in other parts of the body, such as the eyelashes. Its distribution is worldwide and its transmission is by contact.

When this louse feeds it causes certain symptoms in the host. The most common symptom is itching, caused by the louse's hypersensitivity to saliva at the parasite's feeding site (pubis). Other symptoms are redness and inflammation.

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