The skin or more broadly the Integumentary system is the largest organ in the human body. It protects us, keeps vital fluids from seeping away, aids in expelling wastes, regulates temperature, and plays a very important role as a tactile organ through which we sense the external world. It is a snug fitting, all weather, protective habitat- comparable in some ways to a safe, well planned, sturdily constructed home. This is all good, but in the course of the evolutionary journey we took to become the human beings we are today, other animals tagged along and evolved with us and found other uses for the human skin. These tiny critters have also come to call the human skin, home. And like it or not, we have had to share and still share our skins with these fellow travelers that mooch off us and have at times killed large numbers of us during outbreaks. We call these critters parasites or bugs and despise them and want to be rid of them- so far, we have not succeeded. In fact, they have been with us and “on us” for such a long time, that scientists have utilized their DNA and their evolutionary history as an aid in understanding our own evolution. It is therefore important to know the most common parasites on the human skin.
Close-up of a body louse feeding
The most common ectoparasites
1. Human lice: Essentially, there are three types of lice species commonly found on the human body. Together or alone, they can cause symptoms leading to the condition called Pediculosis.
a. The Head louse: this little creature is the most recognizable and widespread. Scientific name Pediculus humanus capitis. It prefers to hide, chew on, lay eggs called nits and in general “nitpick” around hairy areas on the human body especially the head, hence the name. It particularly affects children and adults deficient in the personal hygiene department. An infestation can cause intense bouts of itching sensations on the scalp. Transmission is typically person to person.
b. The body louse, Pediculus humanus humanus, is very similar to the head louse and responsible for spreading nasty diseases like typhus. This critter has adapted to us so well, that it even lays its eggs on clothes, having abandoned the protection of the hair on the human head, it prefers to dwell on the human trunk proper. Its effects were often called the vagabond’s disease. It tends to spread quickly in crowded, hygiene deficient and unsanitary conditions. It can spread through infested articles of clothing and linen as well as via direct contact.
c. Pubic lice, Crab lice or Latinized, Pthirus pubis. These critters tend to live in and around the pubic area or in other hairy areas of the body with coarse body hair including the eyelashes and armpits. They are spread from person to person usually during sexual contact and can cause intense bouts of itching in the pubic region and other areas. Infestation can also spread via shared articles of clothing and linen.
2. Itch mites or Sarcoptes scabiei: These nasty critters can cause agonizing bouts of itching sensations on the skin and are responsible for the skin disease known as scabies. They affect a host of mammals and produce symptoms on the skin similar to allergic reactions on the skin and worse in full blown scabies. Mode of transmission is usually though skin contact between a carrier and an unaffected person.
3. Demodex species: most infections are by two species of mites, D. folliculorum hominis and D. Brevis, also known as the eyelid mite, because some of these critters have a strange fondness for the hair follicles and particularly the ones around the eyes. Though, it tends to affect all areas around the face, including the outer canals of the ears, this critter makes it home in the hair follicles and or sebaceous(fat) glands on the skin and can cause great irritation leading to a condition known as “demodicosis,” it can also affect your pets, especially dogs.
4. Human flea or the flea, or in scientific Latin, Pulex irritans, John Donne wrote about it but despite its name, it is not restricted to humans and is quite the parasitic player, affecting and capable of living on a host of mammals. This bug is comparatively a late comer to the human body and to the "all you can eat buffet" that is the human skin. The body lice mentioned above was already firmly in our midst two million years ago when the Gorillas and we were perhaps still kissing and it is thought the flea is a recent addition to the human skin, its association with us more likely in the thousands of years than the millions. Nevertheless, this newcomer has a nasty bite and can cause a great deal of discomfort. Infection is by several vectors as it can jump from host to host.
Pubic Lice or Crab Lice
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