Scabies is a highly contagious parasite infection caused by the mite Scarcoptes scabiei which result in an extremely itchy rash with distinct features. It is spread by direct skin to skin contact with someone who has scabies. It can also be sexually transmitted. As the mites can survive few days from the human hosts, some people can get it from beddings and furnishes.
After mating the male mite dies and the female mite is the cause of the disease. The female mite burrows into the skin and lays its eggs which turn into adult mites in 10-14 days. The female mite can lay about 3 eggs daily throughout its lifespan of 1-2 months. A typical human host carries 10-12 mites. Each female mite is about 0.4 x 0.3 mm borderline visible to the naked eye. The male mite is half the size of the female mite.
Scabies infection is more of a nuisance to the host due to the extreme itch, it rarely leads to mortality. Complications include secondary bacterial infection leading to impetigo, furunculosis, cellulitis and sepsis (spread of infection throughout body organs).
For primary scabies, the incubation period is 3-4 weeks, subsequent re-infections the symptoms often appear after 3-4 days. It tends to affect clusters of people especially those in institutions (prison, nursing homes and hospitals).
1.Itch: Itch is mediated by delayed type IV hypersensitivity reaction to the mites, eggs and mite feces. Itch is extremely worse at night especially over the trunk and limbs area.
2.Rash: there will be small red papules (lumps) and sometimes pustules (filled with pus), blisters and vesicles usually associated with skin excoriations and crusting.
The rash generally is distributed sides and webs of the fingers, flexor aspects of the wrists, extensor aspects of the elbows, axillary folds (armpits areas), periumbilical areas (near belly button), waist, extensor surface of the knees, lower half of the buttocks, adjacent thighs and the feet.
In males, the scrotum, penile shaft and glans penis may also be involved. In females, the skin adjacent to the nipples may be affected. Usually the back is relatively not involved. Head is spared except in very young children.
3.Itchy nodules: firm red nodules of 0.5 cm or larger may occur over the armpits, groins and the penis shaft area.
4.Mite burrows: A short elevated red or brown or gray, straight or tortuous S-shaped lines found at the wrist and between the fingers is characteristic feature of scabies. The burrows vary from 2 to 15 mm long and may contain mites, eggs and mite feces under microscopic examination.
5.Norwegian Scabies: Very contagious form of scabies which presents with extensive skin crusting, thickened skin scaling and poorly defined red patches over the elbows, knees, palms and soles. The crusts and scales may contain hundreds of mites and may have an odor. It is more common in immune-compromised individuals like those with AIDS/HIVinfection, elderly in institutions (prison, nursing homes and hospitals), leprosy patients, lymphoma and also in patients with Down syndrome.
6.Secondary infection: Complications of scabies may cause secondary bacterial skin infections like impetigo (yellow crusty pustules), cellulitis (subcutaneous connective tissue infection) and furuncolosis (recurring boils).
Diagnosis of scabies
Diagnosis is often made by the typical clinical presentation, features and positive contact history. Presence of burrows is also definitive of scabies. Confirmation can be done by the identification of the mites and eggs from skin scrapings.
Treatment of scabies
Treatment should be aimed at eradication of the mites with topical agents which are applied once to cover the whole body surface from neck downwards for adults and washed off after 8-24 hours depending on the agent used. In children, the scalp and head areas should also be applied with the agents. Repeated treatment one week later is recommended to kill the eggs that might have hatch.
Household family members and close contacts should all be treated. Common topical agents used include topical permethrin 5% cream, Malathion and benzyl benzoate. They are relatively safe with minimal side effects like skin irritation.
After eradication of scabies, patients may develop persistent itch anddermatitis which may improve with topical steroids.
Oral antihistamines can be given for itch control. Antibiotics can be given to treat secondary skin bacterial infections. Symptoms usually improve within days although the skin may still have mild itch/rash due to skin irritation from the dead mites.
Intra-lesional steroid injections can be used to treat the scabies nodules
Eradication of scabies mites
Bed sheets, pillow cases and clothing should be soaked in hot water and washed thoroughly followed by sunning. Non washable items should be sealed in a plastic bag and stored above 20° C for 1 week. Alternatively they can be frozen below -20° C for 12 hours.
Rooms should be thoroughly cleaned with normal household products. Fumigation is not required. Carpeted floors and upholstered furniture should be vacuumed. The vacuum bag should then be discarded and furniture covered by plastic or a sheet during treatment and for 7 days after.
Treatment of Norwegian scabies
Patients can be treated with 1 doses of ivermectin 200mcg/kg to be given 2 weeks apart. Patient should also use topical agent like permethrin weekly until the crusts and scales are gone. Scrubbing with chlorhexidine may also help remove the crusts.
Patients with Norwegian scabies who stay in institution should be isolated till eradication of scabies to reduce the transmission.
Bedbugs are blood sucking parasites from the insect family of Cimicidae. Bedbugs are flat oval shaped about 5 mm long. Before feeding it is brownish in color after feeding it elongates and widens and appears dull red in color.
Bedbugs like to stay in cracks and crevices associated with mattresses and cushions and bed frames. The females lay their eggs here which will hatch in 10-14 days. They are seldom found on the quiet surfaces of chairs and beds. They usually hide in the day and feed at night.
Bedbugs are attracted by warmth and carbon dioxide, they usually feed at night. Prior to feeding, they inject an anticoagulant to prevent blood clotting and anesthetic containing saliva. They usually feed for 5-10 minutes when the person is lying quiescently during sleep. The bedbugs usually bite on exposed skin areas. They may leave a feeding trail of bites.
Clinical features of bedbugs bites
Most individuals do not develop a reaction to bedbug bites. A bedbug bite is usually appears as a punctum (hole at site of bite) without surrounding reaction. If a reaction does occur it will form a 2-5 mm red bump which is very itchy. It some rarer cases, the bites may form urticarial or bullous(blisters).
The bedbug bites may leave a linear trail of feeding track marking “breakfast”, “lunch” and “dinner”.
The bedbug bites may cause secondary bacterial infection and cause impetigo (yellow crusty pustules) and cellulitis (subcutaneous connective tissue infection).
The bedbug bites usually resolve spontaneously within a week. However if there is excoriations or secondary infections it may take several weeks to heal.
Diagnosis of bedbug bites
Bedbug bites may be difficult to distinguish from other insect bites. Differential diagnosis include scabies, bites by other arthropods like fleas and delusional parasitosis ( psychiatric delusion of body manifested with bugs).
Treatment of bedbug bites
Bedbug bites generally do not require treatment and the reactions will resolve by itself. Good personal hygiene should be maintained. Itch can be controlled by oral antihistamines and topical steroid creams.
Eradication of bedbugs
Firstly one must determine the presence of bedbugs. If present then pest control experts will use chemical insecticides to destroy the bedbugs.
Non-chemical control will involve vacuuming, heat treatment, laundering and freezing articles. Washing and drying of clothes and linen in a dryer with hot settings is sufficient to kill the bedbugs.
Pediculosis (lice) is parasites divided into 3 categories: Pediculus humanus capitis (head louse), Pediculus humanus humanus (body louse) and Pediculosis pubis (genital louse).
What is Pediculosis capitis?
Head lice commonly affect children more than adults. It can be transmitted through direct contact and via sharing of towels, combs, bed and clothing.
Head lice are gray white about 3-4 mm and moves from hair to hair by gripping it with their legs. They do not jump or fly. Their mouth parts can suck blood. The female lifespan is about 1 month and it lays about 7-10 eggs daily. The eggs (nits) will hatch in 8 days and the nymphs will mature in another 8 days. The adult lice can survive up to 55 days without a host.
Clinical presentation of head lice
Head lice manifestation usually does not cause symptoms. The allergic reaction to the lice saliva may cause itch and irritation of the scalp. Scratching can cause crusting and scaling of scalp.
Complications include secondary bacterial infection and dermatitis.
Diagnosis of head lice
Diagnosis is confirmed by the visualization of live lice. Using a nits comb (teeth of 0.2mm apart) comb the hair and identify the live lice.
Nits (eggs) may be examined under woods light which make them look pale blue in color. Finding of nits without lice does not mean lice manifestation; nits may persist for months after treatment.
Treatment of head lice
Treatment involves chemical and non-chemical treatments. Chemical treatments involve topical insecticides like permethrin, pyrethrins), Malathion, lindane and benzyl alcohol. They should be applied thoroughly on the scalp and repeated after one week. Permethrin is unsuitable for children below age of 2 months. Benzyl alcohol is unsuitable for children below age of 6 months. Malathion is unsuitable for neonates and infants
Non-chemical treatment involves wet combing with the nits comb on wet hair that is smoothen with hair conditioner. Work through the hair in sections and comb down the hair shaft towards the scalp to try and remove the stubborn nits. It should be repeated every 3-4 days for several weeks until no more live lice is found.
Physical agents to suffocate the lice like dimeticone, a silicon-based material is believed to work against the lice by coating them and disrupting their ability to manage water. Other agents like olive oil, coconut oil, butter, petroleum jelly may not work as well.
Hair shaving has been anecdotally reported as a method to eradicate lice.
Treatment of close contacts
Housemates and school mates should be examined and treated if head lice are present. After the first treatment of wet combing they are fit to go back to school.
Washing of clothing by infected person during the 2 days before therapy in hot water (at least 60 degrees Celsius) and/or drying the items on a high-heat dryer cycle is recommended. Items that cannot be washed may be dry-cleaned or stored in a sealed plastic bag for 2 weeks. Vacuuming of furniture and carpeting on which the infested person sat or laid down is also recommended. Fumigation of house with insecticides is not recommended.
What is pediculosis corporis (Body Lice)?
Body lice tend to occur in poorer people who stay in overcrowded conditions with poor personal hygiene. The lice are found mainly in the trunk of the body. The body lice are slightly larger than head lice.
Body lice will feed off the skin and they live in the clothes and lay eggs in the seams. The body lice can survive 3 days without a blood meal before the feed on the skin again. They may be responsible for the spread of diseases like typhus and trench fever.
Clinical manifestation of body lice
Patients usually complain about itch. Red wheals may occur from fresh bites. Skin changes are most noticeable around the waist and armpit areas. There may be post-inflammatory pigmentation and excoriations on the trunk.
Diagnosis of body lice
Identification of the body lice and their eggs on clothing is diagnostic of body lice. Differential diagnosis includes scabies and eczema.
Treatment of body lice
The infected person should have a thorough shower. All the clothing and linen should be washed with hot water (at least 60 degree Celsius), dry cleaned or discarded. Ironing clothes in particular over the seams area is also effective to kill the lice.
Nits involving the body hair can be treated with topical agent like application of permethrin 5% cream once to the entire body for 8-10 hours. Topical steroids may also help relief localized itch. All household contacts should also be treated.
What is Pediculosis Pubis?
It is a sexually transmitted disease whereby the genital area is infested with crab louses i.e. Phthirus Pubis.
Clinical presentation of Pediculosis Pubis
There will be presence of the brown adult lice and eggs (nits) over at the pubic hair area. Sometimes the body hair, eyebrows and eyelashes may also be affected. Patient will experience itch due to the hypersensitivity reaction to the lice.
There will be small hemorrhagic spots seen over the genitalia skin. Over at the lice feeding sites, there may be small blue macules seen.
Diagnostic test of Pediculosis Pubis
Identification of the lice or eggs from the pubic hair area will confirm the diagnosis.
Treatment for Pediculosis Pubis
1.Malathion 0.5% lotion should be applied over the affected area and washed off after 12 hours.
2.Permethrin 1% cream can be applied to affected areas and washed off after 10 minutes. It can be used in pregnant and breastfeeding women. It is however not available in certain countries.
Follow up management
Patients should be reviewed 1 week later. Re-treatment is commenced if there are still lice or eggs found. Contaminated bed sheets and clothes should be washed in hot water.
Sexual partners within the last one month should be examined and treated if infected.