SCABIES HOMEPAGE

Image from: http://www.biosci.ohio-state.edu/~parasite/pictures/scabies_mite.gif

 

Introduction

Scabies is a common skin condition seen worldwide. Notorious for the itch caused by the irritation of the skin, the scabies mite dates back to times of antiquity. Also known as the “itch mite,” scabies affects people of any gender, age, ethnicity, and socioeconomic status. Symptoms such as unbearable itching, rash, and lesions are common characteristics of the clinical presentation of the illness. A more serious manifestation of the illness known as Norwegian Scabies is particularly common in immunocompromised individuals. Treatment consists primarily of scabicidal creams.

 

Agent

Scientific Name: Sarcoptes scabiei var. humanus

Classification: Anthropod

 

Synonyms

Scabies

Itch mite

 

History of Discovery

Dating back to over 2500 years ago, scabies was known from the time of the Greeks and Romans through the Middle Ages as the “itch.” Although the disease was acknowledged by numerous cultures over several eras, the cause of the infliction was never clearly determined. Then, in 1687, Giovanni Cosimo Bonomo discovered the scabies mite as the cause of the “itch”, making scabies one of the first diseases with a known cause.

 

Clinical Presentation in Humans

The activities and secretions of the mites in the skin cause the irritation and intense itching of the effected areas. The proteins released by the mites create a delayed (type IV) hypersensitivity which results in the skin disease presented. Symptoms that characterize scabies include itching, rash, small red papules—often excoriated, and lesions which represent the burrows of the mites. The intense itching and scratching often leads to bleeding and scab formation which promotes secondary bacterial infection.

Scabies rash on the hand. Burrows visible.

Image from: http://web.ukonline.co.uk/ruth.livingstone/little/scabies4.jpg

The preferred sites of infestation are the interdigital and popliteal folds, the groin, and the inframammary folds. In infants and young children, lesions of the palms, soles, ankles, wrists, face, scalp and trunk are commonly involved. In men, the penis and scrotum may experience highly inflammatory papules and nodules.

Scabies burrows between fingers.

Image from: http://web.ukonline.co.uk/ruth.livingstone/little/scabies5.jpg

 

Characteristic distribution of scabies lesions and rash.

Image from: http://www.aafp.org/afp/20040115/341_f4.jpg

Norwegian scabies is a more serious manifestation of the illness. Symptoms include dermatitis with scaling and crusting, however, itching is minimal. This condition is seen most commonly in immunodeficient individuals with conditions such as T-cell leukemia, AIDS, and transplant patients. These patients may be infested with thousands to millions of mites making this condition highly contagious .

Individual with Norwegian Scabies.

Image from: dermatology.wustl.edu/.../ caseofmonth/10-97.html

 

Image from: http://dermatology.wustl.edu/dermsub/caseofmonth/PageMill_Images/10-97eNorwegian-Scabies.jpg

 

Transmission

Scabies mites are transmitted by direct skin-to-skin contact with infected persons or their clothing/bedding. Scabies is often referred to as a sexually transmitted disease not because it is transmitted sexually but because it is associated with close, direct contact. Scratching is responsible for the transmission and spread of mites over different parts of the body. Scabies can also be transmitted from the environment of an infected person such as their house, couch, or bedding because mites are capable of surviving outside of the host in those conditions for 24-36 hours.

 

Reservoir

Domestic animals can transmit scabies; however, they carry a different strain of the mite. The scabies that animals carry have distinct host preferences so that infection acquired from domestic animals is of a short duration.

 

Vector

None

 

Incubation Period

Normally, the incubation period is 2 to 6 weeks.

For individuals sensitized from prior exposure, incubation can take as little as 1 to 4 days.

 

Morphology

The scabies mite is a small, round bodied, eight-legged parasite barely visible to the human eye. Adult females measure slightly less than 0.5mm in length and are larger than males.

 

Image from: http://www.onedreamdesign.com/canine/buyimage.shtml

The production of a lytic secretion and the movement of the legs allow the mite to penetrate the skin. It is estimated that the mite crawls 2-3 mm each day as it burrows.

 

Life Cycle

 

Image from: www.dpd.cdc.gov/.../ Scabies_LifeCycle.gif

The adult mite enters the upper layers of the epidermis, digging a convoluted burrow. The female deposits eggs in the burrows as she continues to excavate through the skin. The eggs incubate in the burrows and hatch into larvae after 3 to 4 days. The larvae then dig out new burrows in which they molt for 4 days into mature mites. Some adults are scratched off and transmitted to the next host.

 

Diagnostic Tests

The only definitive way to diagnose scabies is by identifying a mite, its eggs, or its fecal pellets in the skin.

Skin scraping is the most common procedure used to diagnose scabies. Burrows and unexcoriated papules are located with the help of a hand lens. A scalpel blade is used to scrape the skin. The scraping material is then transferred to a glass slide for review under the microscope.

Photomicrograph of a skin scraping that contains a scabies mite, eggs, and feces.

Image from: http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/2471.jpg

Curettage is a less common diagnostic test found particularly helpful only in the cases of infants, anxious patients, as well as AIDS/HIV patients.

 

Management and Therapy

For adults the most employed medication for treatment is Elimite—the 5% permethrin cream. Another option is Lindane—a 1% cream of gamma benzene hexachloride, however, it is more dangerous due to its potential neurotoxicity.

For infants less than 2 months, 10% crotamiton, N-ethyl-o-crotonotoluidide or a 6% sulfur ointment is recommended to treat the mites.

The treatment should be applied to the skin over the entire body from the top of the head to the bottom of the feet. The medication should be applied and washed off after 8 to 12 hours. If mites are still present, the treatment should be repeated again in one week.

For persons suffering from Norwegian scabies the 5% cream permethrin (Elimite) is recommended. For individuals who are immunocompromised it may be necessary to combine the medication with Ivermectin. Crust removal is possible with a keratolytic agent (3-6% salicyclic acid in petrolatum) or sulfur ointment.

Proper treatment of fomites are essential. All clothes and bedding should be washed and dried for at least 10 minutes at 122 ◦F, dry cleaned, or stored in closed plastic containers for a week.

Antihistamines or topical 1% hydrocortisone cream may be helpful in addressing the itching.

 

Epidemiology

There are an estimated 300 million cases of scabies in the world and approximately 1 million cases in the United States each year. Scabies is seen in both sexes and across all age groups, races, and socio-economic status, regardless of personal hygiene. However, scabies is often seen in crowded living conditions with poor hygiene.

 

Country Information

Scabies is a disease common to global community. It is found in both developed countries and developing countries.


Public Health and Prevention Strategies

Prevention strategies include avoiding contact with infected individuals, and good personal hygiene.

Due to the high concentration of people and constant physical contact between health care professionals and patients, hospitals and nursing homes are public venues vulnerable to the transmission of scabies. Awareness to such outbreaks should facilitate an immediate response to address the spread of scabies and it should be controlled by requiring all persons in the area be treated with scabicidal cream and upkeep personal hygiene.

 

Useful Web Links

Scabies FAQ: http://www.cdc.gov/ncidod/dpd/parasites/scabies/factsht_scabies.htm

Scabies life cycle: http://www.dpd.cdc.gov/dpdx/HTML/Scabies.asp?body=Frames/S-Z/Scabies/body_Scabies_page1.htm

DermNet: http://dermnetnz.org/arthropods/scabies.html

 

References

Fleischer, Alan. The Clinical Management of Itching. New York: The Parthenon Publishing Group, 2000.

Markell, Edward K. and David John and Wojciech Krotoski. Markell and Voge’s Medical Parasitology. Philadelphia: Saunders, 1999.

Raza, Aly and Howard I Maibach. Atlas of Infections of the Skin. New York:Churchill Livingstone, 1999.