Scabies Life Cycle

Introduction

The order Sarcoptiformes, class Arachnida, and subclass Acari all include the Sarcoptes scabiei. Scabies was one of the first human ailments for which a cause could be found. The perpetrator is the mite Sarcoptes scabiei, which is found in the epidermis of numerous mammals, including humans. This mite was first known as Acarus scabiei DeGeer, 1778, before changing its name to S. scabiei (Latreille 1802).

Over the past 40 years, research has substantially advanced our understanding of the biology of the mite, interactions between the parasite and the host, and tactics used to circumvent the host's defences.

What is Scabies?

The mite Sarcoptes scabiei var. hominis is the parasite that causes scabies, and crusted scabies are more communicable than classic scabies due to a higher mite load. Aristotle and the Old Testament both contain the first descriptions of scabies. The Greek words "sarx," which denotes flesh, "koptein," which denotes to cut, and "scabere," which denotes to scratch, are combined to form the name Sarcoptes scabiei. Ectoparasites are the cause of scabies, which was first identified as an infestation in 1687 by Bonomo. In the same year, Renucci in Paris used light microscopy to confirm the mite's role in the disease in vivo.

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Image: Kid s leg skin being subject to scabies

Scabies is usually found in unsanitary and congested areas, however, it can afflict people of all ages and socioeconomic statuses regardless of cleanliness standards. Inflammatory and hypersensitive responses to mites and mite products mediate the majority of illness symptoms. Controlling the disease requires treating the affected individual as well as anyone else they have come into contact with.

However, this process is frequently slowed down by incorrect or delayed diagnosis, poor treatment compliance, and improper use of topical medications like permethrin, lindane, or benzyl benzoate. In addition to concerns over the toxicity of such medications, parasite resistance seems to be increasing. Oral ivermectin is an option that has been successfully used in community control programs. Future medicines could potentially benefit from plant derivatives like tea tree oil, neem, and turmeric.

Life Cycle of Scabies

In general, 30 minutes after initial contact, the scabies mite burrows into the skin's epidermis. It is an obligate parasite. The adult mite digs into the stratum corneum at a rate of 0.5 to 5.0 mm per day and leaves feces in its wake; Additionally, female mites lay eggs. When the eggs hatch into larvae in 2 to 3 days, the larvae leave the burrow to grow on the skin's surface. The females develop into adult egg-laying creatures in 10 to 11 days. The average adult female lives about 5 weeks in total. Mites are easily distinguished from their less developed six-legged larval forms, by their adult counterparts, which have eight legs. Larval mite types have the ability to burrow while they are developing on the surface of the skin. Scabies mites can remain alive and continue to infest humans at room temperature (21°C and 40%–80% relative humidity) for an average of 24–36 hours and for as long as 19 days in a cool, humid environment. With more time away from a host, a mite's capacity to spread infection declines. Adult mites identify a new host through smell and thermotaxis.

The Egg – Stage 1

The female parasite lays 2 to 3 eggs every day under the skin after fertilization. The eggs are oval in shape and can reach a length of 0.15 mm. The eggs hatch in 3 to 4 days under ideal circumstances, as well as 10% of the eggs, develop into adult itch mites.

Image 2: Scabies mite on human’s hand

The Larvae – Stage 2

The mite's larvae travel to the skin's surface when the eggs hatch and burrow into the stratum corneum, the epidermis. As a result, moulting pouches which are invisible burrows are created. After hatching, the larvae show just three pairs of legs and live for three to four days. The larva later goes through a moult and becomes a nymph. 

The Nymph – Stage 3

The nymph has four pairs of legs at this stage. Before becoming adult mites, the nymphs moult into considerably larger nymphs. The moulting pouches are where you'll typically find the nymphs and larvae of itch mites. The nymphs have an adult appearance and can also be seen in hair follicles.

The Adult – Stage 4

The adult stage of the nymph is characterized by the appearance of spherical, sac-like, eyeless itch mites. The length of the female adult mites can reach 0.45 mm. The size of adult male mites is double that of females. Mites only mate once during the course of their existence. After the male mite has gotten inside the female mite's moulting pouch, mating of mites takes place. The female mite stays fertilized following mating throughout her remaining life.

These fertilized female mites leave their moulting pouches behind and rove the skin's surface in search of an appropriate location to burrow permanently. The mature mites cling to the skin using pulvilli that resemble suckers and are connected to the two pairs of anterior legs.

After locating the ideal location, the female mite burrows into the skin and lays her eggs there. The fertilized female can remain in the host for up to one or two months after she has wormed into the skin. During their adult stage, male mites are hardly ever observed. To feed, they dig shallow pits until they locate a female's burrow, at which point they begin mating.

Conclusion

Other parasite species, such as those that afflict cats, dogs, pigs, and other mammals besides Sarcoptes scabiei, exist. One of the earliest human diseases to be discovered by mankind is scabies, cases of which have been documented for the past 2,500 years. Since this illness is spread through intimate personal contact, there are over 300 million cases recorded each year.

FAQs

Q1. What signs and symptoms indicate scabies?

Ans: Severe nighttime itching is one of the early signs of scabies. In places like the elbows, armpits, wrists, waist, and so on, a small, itchy rash resembling a pimple will appear. As the female mites migrate beneath the skin, there are occasionally very little burrows visible on the skin's surface.

Q2. What is the lifespan of scabies mites?

Ans: A scabies mite can only live for 48 to 72 hours without a host. The irritating mite, however, can survive for up to two months on the host.

Q3. Can I contract scabies from animals or pets?

Ans: The disease is non-communicable and does not spread from one species to another.

Q4. What are crusted (Norwegian) scabies?

Ans: The severe type of scabies known as "crusted scabies" can affect those with weakened immune systems.

Q5. How is an infestation of scabies diagnosed?

Ans: An infestation of scabies is identified by the distinctive shape and pattern of the rash, as well as the presence of burrows.