In the last year and a half, there has been a fourfold increase of scabies in the Netherlands. What we see globally is that two populations are the most affected: children in low- and middle-income countries, and groups in high-income countries, which include students, sexually active people, the homeless and people working in health care. Where does this epidemic come from and what can we do about it? Professor Henry de Vries, dermatologist-venereologist with expertise in skin infections and sexually transmitted diseases, shares his view on the epidemic, the action plan crafted by the Amsterdam Public Health Service (PHS) and his experience doing scabies research in Ethiopia.

Scabies is an ectoparacite, which means that the scabies mite does not reside in humans but on humans. The scabies mite lives in the highest layer of the epidermis. In the epidermis it lives off dead skin cells and digs passageways through them. The scabies mite does not get deeper than this top layer. For this reason, it does not cause an infection but an infestation. As the scabies mite digs tunnels, it triggers a T-cell mediated eczematous reaction (resulting in redness, itching, scaling). The allergen to which the immune system eventually responds is not the scabies mite itself but the mite's feces.

Scabies is transmitted following a minimum of 15 minutes of skin-to-skin contact. It usually occurs by sharing a sleeping space. After infection, the symptoms which are the result of the first T-cell mediated response to scabies mites take a fairly long time to develop: about four to five weeks after the first exposure. Second exposures result in faster onset of symptoms because of T-cell memory.

Linking the epidemic to social trends

“Scabies has been prevalent in high-income countries for many years. The key populations are sexually active people, homeless people, students and people working in health care."
Prof. Henry de Vries
Dermatologist-venereologist with expertise in skin infections and sexually transmitted diseases

In the last year and a half, there has been a fourfold increase in scabies. This rise started in 2021 during the COVID-19 lockdown period. According to Prof. de Vries, it is difficult to assign a cause to this increase. Prof de Vries: “In the case of the lockdown, you would say: everyone is inside with the same people for a significant amount of time, this is likely the cause for the epidemic. However, suppose we would have seen a decrease in numbers - we would most likely also blame this on the lockdown, because there was less contact outdoors. Often, we link epidemics to social trends. Just look at the past: The STD epidemic in the 1960s was blamed on promiscuous women who got hold of oral contraceptives, in the 1970s the STD epidemic was blamed on the gay liberation movement. Human sexuality is much more complex than these simplistic assertions”.

Crusted scabies

A notable variant of scabies is crusted scabies, in which there is significant multiplication of the scabies mite in the epidermis in a short period of time. Although not curative, scratching is an effective reflex to keep the number of mites under control. When the scratching reflex is suppressed by an underlying disease, scabies mites can multiply exponentially. This is the case in patients with an underlying immune disorder, which results in a suppressed inflammatory response and as a result no itch. Crusted scabies is also seen in paraplegic patients, and in patients with severe intellectual disabilities in which the scratch reflex is absent.

Crusted scabies is characterized by a crusted lesions with a gray color over extensive surface areas. The highly contagious scab flakes are loaded with numerous mites and eggs, and can move through the air over considerable distances. This can result in airborne transmission, and skin-skin contact is no longer required for scabies to be transmitted from one person to the next. This forms a clear risk for healthcare workers.

“Treatment of crusted scabies is extremely challenging”, Prof de Vries stresses, “it can take several months, and contact management is often very complex. The hospital hygienist has an important role, people previously discharged from the affected ward must be tracked down and treated.”

Prof de Vries: “In the current outbreak it is feared that transmission will occur from the student population to health care facilities with the risk of increasing numbers of crusted scabies outbreaks. Scabies is currently common among students, students are often employed in health care facilities, if scabies spreads from them to patients with immune dysfunction, paralysis or severe intellectual disabilities there is a danger of crusted scabies in these institutions.”

PHS action plan

The Public Health Service (PHS) in Amsterdam started a scabies clinic after the number of infections quadrupled. Here they conduct source-and-contact tracing. Prof. de Vries: "What we see is that students often do not follow up the treatment instructions properly. Suboptimal treatment can lead to treatment failure and cause re-infections in earlier contacts, also called ping-pong infections. Other errors are not notifying all potential sources and contacts, treatment of partners and contacts at different moments, or insufficient compliance with medications. Guidance is of great importance here, which is why we have created a step-by-step plan that clearly explains how to manage scabies properly."

In addition to source-and-contact testing, PHS Amsterdam has developed a PCR test for scabies. The main purpose of this PCR test is to facilitate diagnostics. Prof. de Vries: "Currently scabies diagnostics are challenging, and dermatological experience with the disease is necessary. We currently evaluate the PCR test in a comparative study with the reference tests in the Netherlands (the dermatoscope and the light microscope). This study is expected to be completed this year."

In addition, Prof. de Vries is working with the Dutch Society for Dermatology and Venereology (NvDV) on a multidisciplinary scabies guideline for public health workers, medical specialists and general practitioners. Part of this guideline involves developing better educational materials to convey key information to patients.

Research in Ethiopia

Ethiopia is a low- and middle-income country where scabies is endemic. Henry de Vries worked on scabies in Ethiopia together with Wendemagegn Enbiale Yeshanh, a PhD student, studying mass drug administration. Residents of areas where scabies and lymphatic filariasis (a parasitic infection leading to lymphoedema) are hyper endemic were administered medication effective for both pathogens in mass drug administration campaigns.

Prof. de Vries: “Here we looked at the effect of mass drug administration. What becomes clear is that this method is effective in treating and preventing scabies, however, the mass drug campaigns must be repeated regularly otherwise the infection incidence returns to initial levels. A positive outcome of the study is that scabies does not show any drug resistance. In instances that there was drug failure, it was generally due to incompliance or environmental influences.” Follow-up research in Ethiopia is on the agenda, the start date is not known yet.

Is mass drug administration an option for the Netherlands? According to Prof. de Vries, this is not the case. In high-income countries like the Netherlands with a good infrastructure, a strategy employing stringent source-and-contact tracing, and diagnostic efforts are far more effective options to curb this outbreak. Another recurring topic is mandatory notification. According to Prof. de Vries, this is not achievable in the short term, since legal actions are required, moreover the consequential privacy breaches do not outweigh the benefits in this case.

Read more about the research of Henry de Vries and colleagues in Ethiopia:

Who is Henry?

Bio Art & Design (BAD) Award

In 2022, Prof. de Vries won the Bio Art & Design (BAD) Award together with artist Kuang-Yi Ku. With this, they realized a project called "Atlas of Queer Anatomy," which is on display in the Beyond Binaries and Borders exhibition at MU Hybrid Art House in Eindhoven until April 16, 2023. Medical education is in need of revision because it is quite outdated, White centered, heteronormative, and one-sided to say the least. In this project, Prof. de Vries and Kuang-Yi offer an ironic reflection on the still widely used classic anatomy textbook "Atlas of Human Anatomy" drawn by medical illustrator and surgeon Frank H. Netter that first appeared in 1957.

Text: Esmée Vesseur