Scabies Life Cycle

Introduction

Scabies is a kind of skin irritation or inflammation caused by the parasite Sarcoptes scabiei. The Sarcoptes scabiei falls under the order Sarcoptiformes, the class Arachnida and the subclass Acari. This parasite enters the epithelial tissue during the night hours and causes severe skin irritation that makes the host rigorously scratch the infected area. Scabies is transmitted through physical contact, as the parasite passes from one individual to the other. This parasite is also known as the ‘itch mite’, that passes through close contact with an infected person. The parasite Sarcoptes scabiei measures up to 0.35 mm in length, which is not visible from the naked eye.

Let’s look at the life of scabies to get a better understanding.

Life Cycle of Scabies

1) The Egg – Stage 1 –

After fertilization, the female parasite deposits 2 to 3 eggs daily under the skin. The size of the eggs are oval in shape and measure up to 0.15 mm in length. Under favourable conditions, the eggs hatch in three to four days and about 10% of the eggs transform into adult itch mites.

2) The Larvae – Stage 2 –

After the eggs hatch, the larvae mite migrates to the skin’s surface and burrows itself into the stratum corneum; the outermost layer of the skin. This creates moulting pouches, which are invisible burrows. The larvae after hatching have only three pairs of legs and last for about three to four days. Later, the larva moults and transforms into a nymph.

3) The Nymph – Stage 3 –

In this stage, the nymph has four pairs of legs. The nymphs moult into much larger nymphs before it transforms into adult mites. The nymphs and larvae of itch mites are mostly found in the moulting pouches. The nymphs look similar to adults and are also found in hair follicles as well.

4) The Adult – Stage 4 –

When the nymph enters the adult stage, they appear to be round, sac-like eyeless itch mites. The female adult mites measure up to 0.45 mm in length. The male adult mites measure twice the size of the females. Mating process in mites occurs only once in their lifetime. The process of mating in mites occurs after the male mite has penetrated into the moulting pouch of the female mite. After mating, the female mite is fertilized for the rest of her remaining life.

These fertilized female mites detach their moulting pouches and roam on the surface of the skin until they find a suitable spot for burrowing permanently. The adult mites grab on to the skin through sucker-like pulvilli, which is attached to the two pairs of anterior legs.

After the female mite finds the desired spot, she burrows into the skin, laying the eggs in the process. After the fertilized female has burrowed into the skin, she can survive up to 1 to 2 months in that host. The male mites are hardly seen during their adult stage. They make shallow pits to feed, till the time they find a female’s burrow and start mating.

Conclusion

Apart from the parasite Sarcoptes scabiei, there are other species that affect other mammals like cats, dogs, pigs, etc. As the scabies cases have been reported for the past 2,500 years, it is one of the earliest human diseases known to mankind. Since the transmission of this disease is close, physical contact, approximately 300 million cases are reported every year.

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