Parasitic Infestations

Scabies

Scabies is a prevalent skin condition that effects people of all classes and ethnicities all over the world.  Scabies is an ancient affliction, estimated to have infected humans for the last 2,500 years. 

The WHO considers scabies to be a water-related disease because of the connection between bathing and personal hygiene to prevention or control of its spread.  The tick that causes scabies, however, is not dependent on water for transmission or for any part of its life cycle.

Etiology Female sarcoptes scabiei. the scabies mite is an eight-legged arthropod with round body.  It is barely visible to the human eye, and females (larger than males) are less than 0.5 mm in length.

Life Cycle Adult mites burrow into the upper layer of the epidermis.  Females lay eggs in the burrows. Eggs hatch after 3-4 days into larvae, which dig new burrows closer to the skin surface. 

There, the larvae mature into adult mites in about 4 days.  The adults can then either stay in that host or be scratched off and transmitted to a new host.  Adult females can live in the host for up to a month.

Transmission Mostly through prolonged close contact with other people that are infected with the mite; quick contact (as in a hug or a handshake) is unlikely to spread the mite.  Scabies is classified as a sexually transmitted disease.  Scabies can also be transmitted through contact with the bedding or clothing of infected persons—mites can survive up to 24 hours outside the skin.

Reservoir Domesticated animals, but usually different strains have distinct host preferences so infections that are contracted from animals may cause irritation and itching, but are usually short-lived.

Clinical picture Incidence: 300 million cases/year. IP: 2-6 weeks Diagnosis is typical with distribution, 1ry lesions (burrows, vesicles, papules) and 2ry lesions (due to scratch)

Itching esp. by night. Scalp & face are not affected. Interscapular area is usually spared.

Clinical Varities 1- Scabies in infant: 2- Scabies in a clean: Atypical distribution(head,neck,plams,soles). Extensive burrows. Frequent vesicles, 2ry infection & eczematization) 2- Scabies in a clean: Burrows are difficult to seen due to frequent bathing.

3- Scabies incognito: 4- Animal scabies: Clinical picture is modified due to the use of topical steroides. 4- Animal scabies: Short IP (2-4 days). Absence of burrows. Not transmitted from human to human. Self-limited.

5- Nodular Scabies: Itchy indurated reddish-brown nodules. Affects scrotum & penis usually. Persistent for weeks or months after ttt leading to persistent itching.

Complications 2ry infection. Eczematization. Acaraophobia: occurs in neurotic individuals after successful ttt due to fear of still infested.

Diagnosis Itching mainly by night. Burrows. Distribution of lesions. Group infection. Microscopic demonstration of the parasite.

Treatment A- Prophylactic: B- Systemic: Early diagnosis, isolation & ttt. Mass ttt for all contacts. Disinfection of clothes and linens. TTT of the domestic animals. B- Systemic: Antihistamines for itching. Antiobiotics for 2ry infection.

C- Topical scabicides: Sulphur oint 3-10% for 3 nights. Benzyl benzoate 25% for 1 night. Gamma benzene hexachloride 1% for 1 night, avoided in pregnant & children (neurotoxic). Permethrin 2.5-5%: safest, 1 night ttt. Crotarmiton 10% 3 nights less effective. D- IL steroides in scabetic nodules.

Pediculosis

Pthirus Pubis (Pubic or crab louse). Pediculus Humanus: PH Capitis (head louse). PH Corporis (body louse). Pthirus Pubis (Pubic or crab louse).

Pediculi are ectoparasites, they live on top of their hosts instead of inside of them. They are small, six-legged insects with claws adapted to clinging onto their host's hairs or clothes. Pediculi mouth-parts are adapted to sucking the host's blood, and in the case of capitis, they are also adapted to eating dermal parts of the host's scalp, neck and eyelids.

Pediculosis capitis

Clinical Picture Symptoms that may appear are itchiness of the neck, scalp and ears. In more severe cases secondary bacterial infections can develop which may lead to febrile episodes as well as enlargement of the cervical and nucal lymph nodes.

Human to human transmission is the only way pediculosis is transmitted. Diagnosis is by Identification of louse and nits.

Treatment Permethrin 1%: the drug of choice 10 min. and washed off. Malathion 0.5%: applied for 12 hrs. Gamma benzene hexachloride 1% shampoo: washed off after 10 min. Crotarmitone 10%:applied for 30 min. Fine-toothed comb for remaining nits. Antiobiotics for 2ry infection.

Pediculosis Corporis

Body lice infest the seams of clothing and take blood meals at night Body lice infest the seams of clothing and take blood meals at night. Nits are found in the seams, not on human hairs. Maculae ceruleae, the hemosiderin-stained purpuric spots where lice have fed, suggest the diagnosis of body louse infestation.

Treatment Destruction of lice by boiling or ironing of clothes and bedding. Malathion or DDT dusting powder for clothes. Frequent bath.

Pediculosis Pubis (Crab)

Pubic lice and nits generally are plainly visible throughout the pubic hair, extending onto adjacent hairy areas of the body. Eyelash nits are a manifestation of pubic louse infestation, not head louse infestation.

Itching is the main symptom, 2ry infection is common. Treatment: Transmission is by sexual contact mainly and to less extent from bedding. Itching is the main symptom, 2ry infection is common. Treatment: Permethrin 1%: 10 min and washed off Gamma benzene hexachloride 1% applied for 8 hrs

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