Ectoparasites: Characteristics, Types and Examples

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

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

flea

Main characteristics

They are annexed to different species

The 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.

They eat bodily fluids

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

They are usually located in hard to reach places

Usually the ectoparasites are located in places that are not easily accessible, 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 the ectoparasites and their host is of convenience. The ectoparasites live at the expense of the organism to which they parasitize.

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 pass 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.

The 2 main types of ectoparasites

The 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.

1- Insects (six-legged arthropods)

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

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

On the contrary, others, such as blue fly larvae and lice, remain on the bodies of the guests for longer periods.

- Lice

Lice are common insects, easily visible, with a length between 2 and 4 mm approximately. 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 the body elongated and others rounded, similar to crabs but much smaller. The eggs of these insects are called nits and are white.

Louse

Adult lice feed on blood. By doing this they inject saliva into the host's skin, which causes a hypersensitivity reaction. This reaction is evidenced by itching of the skin of the affected individual (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 more frequently in tropical areas.

The infection caused by these ectoparasites varies according to the species of insect. Some flies deposit 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 mucous membranes of the host, such as in the nostrils or near the lips. Another group of flies lay their eggs on 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 and about 5 mm in length.

Normally, bedbugs are found in cracks in wood and mattresses. Their eating habits are nocturnal, while their human hosts sleep bed bugs eat easily.

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

2- 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 are its four pairs of legs in the adult state, and that have no wings or antennae.

- Ticks

Ticks are small ectoparasite arachnids that feed on the blood of mammals, birds and some reptiles and amphibians. These arachnids are distributed all over the world; however, it is more common to find them in warm and humid climates.

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

Tick

Ticks locate their guests mainly 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 (blood feeds), ticks are vectors of diseases that affect humans and other animals.

- Mites

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

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 the lymphatic fluid.

Transmission occurs through 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; 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.

The 5 examples of ectoparasites that affect humans

1- The scabies mite ( Sarcoptes scabiei )

Sarcoptes scabiei It is a kind 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 its eggs as it moves. The eggs hatch and produce larvae that migrate to the surface and become infectious adults.

2- The mite of the hair follicles (Demodex sp.)

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

Infestation with Demodex 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 does not work properly, these ectoparasites can proliferate and cause demodicosis.

3- The head louse ( Pediculus humanus capitis )

P. humanus capitis It is an ectoparasite of the group of insects and is the causative agent of pediculosis. These parasites have no 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 they feed on human blood. Despite being hematophagous parasites (that eat blood) these head lice do not transmit diseases.

4- The common flea ( Pulex irritans)

The species Pulex irritans It is an example of an ectoparasite that seriously affects humans because it is the vector of transmission of various diseases, including the bubonic plague that hit Europe in the past.

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

5- The pubic louse ( Pthirus pubis )

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

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

References

1. Anderson, A.L., & Chaney, E. (2009). Pubic lice (pthirus pubis): History, biology and treatment vs. knowledge and beliefs of US college students. International Journal of Environmental Research and Public Health , 6 (2), 592-600.
2. Becerril, M. (2011). Medical Parasitology (3rd ed.). McGraw-Hill.
3. Bogitsh, B., Carter, C. & Oeltmann, T. (2013). Human Parasitology (4 ^th ). Elsevier, Inc.
4. Dantas-Torres, F., Oliveira-Filho, E. F., Soares, F. A. M., Souza, B. O. F., Valença, R. B. P., & Sá, F. B. (2008). Ticks infesting amphibians and reptiles in Pernambuco, Northeastern Brazil. Brazilian Journal of Veterinary Parasitology = Brazilian Journal of Veterinary Parasitology: Official Orgao Do Brazilian College of Veterinary Parasitology , 17 , 218-221.
5. There is, R. J. (2009). Scabies and pyodermas - Diagnosis and treatment. Dermatologic Therapy , 22 (6), 466-474.
6. Hopla, C.E., Durden, L. a, & Keirans, J. E. (1994). Ectoparasites and classification. Revue Scientifique et Technique (International Office of Epizootics) , 13 (4), 985-1017.
7. Kittler, R., Kayser, M., & Stoneking, M. (2003). Molecular Evolution of Pediculus humanus and the Origin of Clothing. Current Biology , 13 , 1414-1417.
8. Klompen, J. S. H., Black, W.C., Keirans, J. E., & Oliver, J. H. (1996). Evolution of Ticks. Annual Review of Entomology , 41 (1), 141-161.
9. Levinson, W. (2014). Review of Medical Microbiology and Immunology (13 ^th ). McGraw-Hill Education.
10. Long, S., Pickering, L., & Prober, C. (2012). Principles and Practice of Pediatric Infections Diseases (4 ^th ). Elsevier, Inc.
11. Nuttall, G. H. F. (1918). The biology of phthirus pubis. Parasitology , 10 (3), 383-405.
12. Rather, P. A., & Hassan, I. (2014). Human Demodex Mite: The Versatile Mite of Dermatological Importance. Indian Journal of Dermatology , 59 (1), 60-66. http://doi.org/10.4103/0019-5154.123498