Parasitic Diseases Quiz

Parasitic Infestations

• Parasitic infestations include pediculosis, scabies, myiasis, tungiasis, cutaneous larva migrans, and onchocerciasis.

Pediculosis

• Pediculosis is an ectoparasitosis caused by blood-sucking, wingless insects (lice).

• Human infestations are caused by Pediculus humanus capitis (head lice), Pediculus humanus corporis (body lice), and Phthirus pubis (pubic lice).

• Pediculosis capitis is commonly found on the head and is also known as head lice.

• Pediculosis corporis affects the body or clothes.

• Pediculosis pubis is caused by Phthirus pubis and affects the pubic area.

• Pediculosis Capitis is common in children.

• It is spread by head-to-head contact and shared combs/hats.

• Often seen in epidemics among school-age children.

• Also common in homeless people.

• Lice live on the scalp and suck blood.

• They firmly attach their eggs (nits) to the hair shaft.

• The head louse is about 3-4 mm long.

• Clinical features in Pediculosis capitis include pruritic eruption on the back of the scalp and nape, excoriations, and secondary infections.

• Hairs may become matted from repeated scratching.

• Lice are sometimes identified when combing the hair.

• Nits are commonly found in the retro-auricular region.

• Look for nits on hair shafts and lice on the scalp to diagnose Pediculosis capitis.

• Effective treatments for Pediculosis capitis include pyrethrins and synthetic permethrin (1% and 5% cream).

• Malathion 0.5% lotion—an effective treatment but can irritate the eyes.

• Lindane, or gammabenzene hexachloride, is widely used but has a high potential neurotoxicity.

• Crotamiton (Eurax) is also a treatment option.

• Nits are a continuing problem to manage.

• Many schools ban children with nits.

• If present, retreatment is reasonable a week or so later.

• Combing with a fine-toothed comb aids in treatment.

• Pediculosis corporis: Same pediculicides as for Pediculus humanus capitis can be used.

• Lice can survive in clothing for a month without blood meals.

• Disinfect clothing and bedding (boiling, hot ironing).

• Pediculosis pubis: Found in the pubic region and hairy areas of the legs, abdomen, chest, axillae, and arms.

• Spreading is through close physical contact.

• Commonly transmitted through sexual contacts.

• Lice and nits are present in the hair, with symptoms similar to that of body lice.

• Patients often report moving lice in pubic hair often accompanying pruritus.

• Nits are typically found on pubic hair but may sometimes be found elsewhere on the body.

• Feeding sites on the body may become distinctive blue-gray hemorrhagic macules.

• These macules, often called maculae cerulenne, are commonly found on the sides of the trunk and inner thighs.

• Malathion lotion and permethrin cream/shampoo are the preferred treatment choices for Pediculosis pubis.

• Malathion sticks well to the hair to help prevent re-infection.

• Lindane lotion/shampoo is also effective.

• Treatment application should be repeated a week later.

Scabies

• Scabies is a highly pruritic skin infestation caused by Sarcoptes scabiei var hominis.

• It's a host-specific mite.

• Prevalence higher in children and active individuals.

• Spread occurs through direct contact with an infected person (not from inanimate objects).

• Mites can survive outside a host for up to 3 days.

• Mites burrow into the epidermis (top layer of skin) after prolonged contact with an infected individual.

• The S. scabiei female mite burrows through the stratum corneum at the rate of about 2 mm per day.

• The female lays 2 or 3 oval eggs daily and the life cycle of the mites lasts 30 days, all within the epidermis.

• The mites feed on dissolved skin tissue.

• The feces of the mites are left behind within the skin's layers and cause irritation.

• On initial infestation, a delayed type IV hypersensitivity reaction occurs over 4–6 weeks.

• Symptoms include intense pruritus or itching, sometimes worse at night.

• Lesions appear differently in adults and infants.

• Adults: Lesions typically appear on the wrists, interdigital web spaces of the hands, feet, axillae, elbows, waist, buttocks, and genitalia.

• Infants and children: Lesions may appear on the face, scalp, neck, palms, and soles.

• Primary lesions include small papules, vesicles, and burrows.

• Burrow are pathognomonic for S. scabiei and are linear, slightly raised.

• Treatment options include scabicidal agents, antipruritic medication(e.g. sedating antihistamine), and antimicrobial medication if a secondary infection is present.

• Topically applied scabicidal agents are usually repeated after 7 days.

• Permethrin 5% cream is often the preferred option for infants and children.

• Lindane 1% lotion or cream, sulfur 6% in petrolatum, and crotamiton (Eurax) 10% cream or lotion are also used.

• In some cases, an oral ivermectin treatment is given.

Myiasis

• Myiasis refers to infestation of body tissues by larvae (maggots).

• Different types of myiasis include the following,

  • facultative/traumatic wound myiasis: Eggs of certain flies which have larvae in suppurating tissues.
  • obligate cutaneous myiasis: Creeping eruptions and furuncular myiasis.

• Furuncular myiasis presents with boils or pustules that have a central punctum.

• A serosanguinous (blood tinged) discharge accompanies such sores.

• Rapid resolution occurs when larvae are removed.

• Signs or symptoms may include rapid resolution following extraction, lymphangitis.

• Creeping eruption presents as a line of red, slightly raised tortuous lines.

• It may resemble cutaneous larva migrans infection.

• Treatment of myiasis types depends on the specific form.

Tungiasis

• Tungiasis is a disease caused by the tunga penetrans flea.

• The flea penetrates into the skin, resulting in a small, round, painful, and itching swelling.

• Secondary bacterial infection is likely to happen if not carefully dealt with.

• Prevention can occur by maintaining house and environment cleanliness and by wearing shoes.

• Treatment includes mechanical removal of the flea with a pin, followed by antiseptic dressing.

Cutaneous Larva Migrans

• Cutaneous larva migrans (CLM) is a parasitic skin infection caused by hookworm larvae, most often in tropical and subtropical locations.

• It is characterized by a snake-like or linear track that follows the larva's movement.

• The track is often itchy and elevated.

• It is common in areas with warm environments (tropical, subtropical) and often found in those who are close to animals, like farmers and gardeners.

• The eruption arises where the larvae penetrate the skin.

• The bites usually cause mild to intense itching followed by a non-specific eruption.

• The rash is often snake-like stretching up to 3-4 cm from the penetrating site.

• Usually a self-limiting infection, where humans are not the definitive host.

• Thus, the larvae die in most cases, and lesions resolve within 4–8 weeks without treatment.

• Treatment is not necessary in most cases, but if treated, helminthics like tiabendazole, mebendazole, albendazole, and ivermectin can be used.

• Additional treatments include liquid nitrogen cryotherapy or carbon dioxide laser treatment, antihistamines, topical corticosteroids, and antibiotics if a secondary bacterial infection is present.

Onchocerciasis

• Onchocerciasis is a chronic, progressive skin, eye, and neurological disease.

• It's caused by the filarial nematode Onchocerca volvulus.

• Often called “river blindness.”

• Initial infestations often happen in childhood, with little to no apparent symptoms for a varying length of time.

• Neurologic manifestations are common in children.

• The disease is transmitted to humans through the bite of a female blackfly (Simulium spp).

• Characteristics of the skin disease include widespread, itchy, eczema-like rash that progresses into vesicles and pustules.

• Chronic papular onchodermatitis presents as itchy plaques.

• The characteristic presentations in Onchocerciasis include acute or chronic onchodermatitis (itchy, eczematous rash with macules and papules), subcutaneous nodules (oncocercoma), lymphadenopathy, and sowda (sever pruritus).

• Later symptoms may include lizard skin—dry, scaly skin resembling ichthyosis, hanging groin—a sac of atrophic skin, scarring, atrophy, elephantiasis, and leopard skin (depigmentation in the skin).

• Eye disease occurs when microfilariae in the cornea and back of the eye die, often resulting in inflammation and bleeding.

• Early symptoms include itching, redness, pain, and photophobia.

• Continued inflammation can cause keratitis, sclerosis, blurring of vision, night blindness, glaucoma, visual field loss, and eventually blindness.

• Diagnoses are aided by identifying microfilariae in skin snips, a chain reaction, and seeing adult worms in excised nodules.

• To confirm, blood or eye analysis can also be used.

• Preventative measures are key to fighting the transmission through the bite of black fly.

• Such measures include using insect repellents, wearing long-sleeved shirts, and pants.

• Ivermectin (oral) kills microfilariae, but not adult worms.

• It should be administered every three months.

• Other potential treatments for the disease include suramin and moxidectin.

Papular Urticaria

• Papular urticaria is a papulovesicular reaction to insect bites, more common in children.

• It's also known as persistent insect bite reaction.

• Children get it more often due to a lack of desensitization to insect bites.

• Adults can still get it, especially those traveling to new areas or environments.

• A reaction develops a few months to years after the initial bite.

• The initial bite is often unnoticed.

• Papules are itchy red bumps present, often in clusters.

• The bumps most often occur on the legs and other exposed areas like forearms and face.

• They can range from 0.2 to 2 cm in diameter and have small central punctuate marks.

• Crops of fluid-filled blisters are possible.

• New lesions and new bites can sometimes trigger itching in others.

• Complications can include infected insect bites leading to cellulitis and rarely bacteremia.

• Scratching can also lead to secondary infections like impetigo.

• Localised vasculitis is also a possible complication.

• Papular urticaria is typically diagnosed clinically.

• Biopsy results sometimes can help with the diagnosis.

• Histological presentations include mild dermal oedema, erythrocyte extravasation, and eosinophils.

• Vasculitic markers in tissue might occasionally be present.

• Preventative measures include protective clothing, and insect repellents.

• Insect repellents and avoiding insect bites is part of the treatment too.

• Symptoms can sometimes be alleviated by topical steroid creams.

• Antibiotic or antiseptic creams can also aid in treating the presence of secondary infections in the skin.