Description of the condition
Scabies is a common parasitic infection. It is present worldwide, and up to 300 million cases are thought to occur each year (Chosidow 2006). It is caused by a mite, Sarcoptes scabiei variety hominis (Green 1989), also known as the human itch mite. Crusted scabies (or Norwegian scabies) is caused by the same mite, but is associated with very large numbers of mites and tends to occur in immunocompromised hosts, e.g. transplant patients on immunosuppressive therapy, alcoholics, the elderly or other debilitated people.
Sarcoptes scabiei is a mite which depends on humans for survival, and infection occurs by human to human spread (Hengge 2006). Thus, it tends to be more prevalent in areas with poor sanitation or in circumstances where there is frequent close person to person contact, as in overcrowding. In developed countries where sanitation problems and overcrowding are not as prevalent, it tends to spread between family contacts, between residents in residential care, or between patients and staff in hospitals.
Mites crawl on the skin surface at approximately 2.5 cm per minute (Hengge 2006) but can neither fly nor jump. They can survive three to four days off the host, depending on environmental conditions (Green 1989). Mating occurs on the skin surface (Chouela 2002), before the gravid female mites burrow into the skin (Chosidow 2006), where eggs are laid. Several days later, the eggs hatch, and nymphs emerge; three moults are required before the mite reaches maturity (Chouela 2002).
Direct skin to skin contact is required for transmission to occur. Whether transmission can occur via fomites (object or substance capable of carrying infectious organisms, for example, clothing, bedding, etc.) is uncertain, and conflicting opinions exist (Blumenthal 1976; Chosidow 2006; Chouela 2002; Orion 2006). Individuals with classical scabies are typically infected with up to 50 mites (Orion 2006). In immunocompromised hosts, however, crusted scabies can develop, and the individual is likely to be infected with a minimum of several thousand mites. Crusted scabies is thought to be more infective than classical scabies. This higher infectivity is attributed to the higher "volume" of infection, and the increased shedding of skin scales which carry the mites, which some believe could facilitate the spread of infection via fomites (Arlian 1989; Chosidow 2006).
Itch is the most prominent symptom, although this is often limited in immunocompromised hosts with crusted scabies (Scheinfeld 2004). The itch tends to be worse at night (Green 1989). Those affected can develop a cutaneous eruption, consisting of a variety of lesions, over most of the body. Some patients may develop secondary bacterial infections, such as impetigo, as a consequence of the disrupted skin barrier from scratching due to the profound itch. In crusted scabies, patients typically develop a psoriatic type eruption, which can be present on the hands, feet, trunk and face (Orion 2006).
The symptoms experienced are generally attributed to the development of an allergic reaction to the mite or its excreta. Consequently, symptoms are not likely to develop until four to six weeks after primary infection (Green 1989). On subsequent infections, symptoms generally develop within hours to days (Chouela 2002). Additionally, successful treatment does not always result in elimination of symptoms until several weeks later, as patients can continue to have a hypersensitive response to the mite or its products (i.e. post-scabetic itch).
On examination, lesions may be noted in particular in the finger web spaces, on the elbows, in the axilla, on breasts, and on the buttocks and genitalia. Burrows, nodules and vesicles may be seen. In adults, lesions do not generally occur above the neck. In young children and in vulnerable populations, lesions can occur above the neck, and mites can occasionally be observed in the retroauricular fold (Chouela 2002). Skin scales are commonly associated with crusted scabies.
Skin scrapings may facilitate direct observation of mites, eggs, or mite faeces pellets (Chosidow 2006; Hengge 2006). This is achieved by applying a drop of mineral oil to the suspected lesion, then using a scalpel blade to scrape away the oil and the entire lesion, which are transferred onto a slide for microscopic examination (Chouela 2002). Alternatively, a shave biopsy can be performed, whereby the top of the papule is removed and placed on a microscopic slide for further examination (Chouela 2002). The "burrow ink test" on the other hand depends on the burrows absorbing ink (Hengge 2006).
There are several recommended treatments for scabies. These have been extensively discussed in another Cochrane review (Strong 2010). Both oral (e.g. ivermectin, thiabendazole, flubendazole) and topical therapies (e.g. lindane, permethrin, sulfur-containing products, crotamiton, malathion benzyl benzoate) are available (Chouela 2002; Scheinfeld 2004). Oral Ivermectin (Guay 2004), is not widely available and has not been approved in some jurisdictions for the treatment of scabies (Bouvresse 2010). The usual treatments are topical, and typically require application over all of the body for many hours duration. There is no international consensus on the appropriate schedule of treatment, and recommendations in one jurisdiction may not be appropriate in others (Bouvresse 2010). Multiple treatment doses are often recommended over days to weeks. Some patients require symptomatic treatment for the itch, including post-scabetic itch or itch caused by medication. Antihistamines and emollients have been recommended in this regard (Chouela 2002).Topical or systemic antibiotics may be required if secondary skin infection has developed.
It is also advised that close contacts of those with scabies should be treated concurrently (Chouela 2002; Paasch 2000; Scheinfeld 2004), as they may be infected without yet manifesting symptoms, and so act as a reservoir of infection. Treating the contacts may prevent reinfection of the index case following treatment. Although the treatments used are generally safe, allergies to treatment are possible, and adverse events including death have been reported (Nolan 2011). The logistics required to treat all contacts simultaneously are considerable (Scheinfeld 2004; Stoevesandt 2012). For example, this would be very difficult to co-ordinate in an institutional setting where, along with the index case, other patients, family members, and all staff who had contact with the index case are all advised to also have treatment.
Description of the intervention
Following contact with an index case, where the contact has not been infected with scabies previously, symptoms often take up to four to six weeks to develop. During this long incubation period, the contact may act as a reservoir for onward infection to their contacts (Green 1989), or may cause re-infection in the index case (Buehlmann 2009). Therefore, treatment is recommended for contacts of the index cases, simultaneously to treating the index case, even in the absence of symptoms, for two reasons. FIrstly, early treatment will reduce the chance that the contact will develop symptoms of scabies infestation. Secondly, the contact may not have any symptoms in early infection, but may still be able to transmit the infection.
There has been some success with the provision of scabies treatment for the whole community, in settings where there is a high prevalence of scabies (Carapetis 1997). Such community initiatives have assisted in the eradication of scabies, and require screening, health education regarding the risk of scabies infestation, provision of drug treatments, and advice and support with non drug treatments (Kanaaneh 1976). Consequently, guidelines have been developed in some areas that recommend community-wide treatment to control scabies (Currie 2000).
This review will focus on localised secondary preventative measures, where scabies treatment is used to prevent the spread of infestation or to prevent re-infestation. It is generally recommended that along with the index case, contacts of the index case should be considered for prophylactic treatment (Chouela 2002; Scheinfeld 2004). This recommendation is made for several reasons:
infection may have been transmitted to contacts who may remain asymptomatic but develop symptoms at a later stage,
untreated contacts may act as a reservoir of infection and may re-infect the index case, and
untreated contacts may be a source of onward transmission of infection to others.
Onward transmission to others would be particularly problematic in healthcare or residential settings, where infection may be spread to vulnerable patients. Additionally, where employees are infected, they may require restriction from work until treatment has been initiated to limit the chance of onward transmission. This has implications for the staffing levels and the workforce in general (Bouvresse 2010).
Generally, contacts of the index case are prescribed treatment (either the same treatment as the index case, or a shorter regimen, or a different treatment), and are provided with advice regarding washing of clothes and bedding (Buehlmann 2009).
How the intervention might work
Treating the contacts of the index case potentially limits the development of infection (both asymptomatic and symptomatic) in the contacts of the index, and restricts onward transmission of infection to others, and re-infection of the index case (Chouela 2002). This is particularly important in settings where there are a large number of people in close proximity to each other or in settings where there are vulnerable populations, such as nursing homes, residential care homes, or other healthcare settings.
Why it is important to do this review
Prophylactic treatment continues to be recommended for all types of contacts, including family contacts, residential or institutional contacts, and healthcare exposures. The level of exposure of the contact to an index case in these settings, however, is subject to considerable variation: shaking hands; cuddling a baby for a prolonged period; assisting a nursing home resident with bathing and dressing; sexual contact; holding hands; and children playing sports together.
It is not clear whether prophylaxis is more appropriate than a "wait and see" approach (Chouela 2002), whereby contacts are educated regarding the possibility of infection, and advised to seek medical attention should they develop symptoms suggestive of infection.
Concerns regarding prophylaxis include:
considerable commitment on the part of the exposed contacts of index cases of scabies and their required willingness to take treatment (Buehlmann 2009),
recommending prophylaxis where the contact may not be able to describe the level of contact they had with the index case, or may not be able to consent to treatment (Ejidokun 2007),
recognised side-effects associated with some of the treatments recommended, some of which are serious (Bouvresse 2010),
the stigma associated with a diagnosis of scabies, which may lead to non-compliance and a reluctance to disclose the diagnosis to close contacts (Heukelbach 2006), (as society frequently associates scabies with poor hygiene and poverty),
considerable cost associated with providing medical treatments to contacts (e.g. a whole family, other patients and staff in a residential care setting) (Vorou 2007), and
frequently, there are logistic difficulties in identifying all contacts of an index case (e.g. a child with scabies infestation may attend school, after school care, and other recreational activities) (Buehlmann 2009).
The results of this review will particularly influence occupational health policy and practice in the treatment of contacts of scabies in the healthcare and residential care settings, and may possibly be wider reaching, for example, school and prison workers.
This review will summarise the effectiveness and safety of prophylactic treatment in various settings, and will be updated as further new evidence becomes available.