Scabies: a neglected parasitic disease we already know how to treat

Mites living in your skin are just the start of the problems that come with having scabies.

The highly infectious parasitic condition is linked with extreme itchiness, bacterial infections and kidney damage, plus debilitating social and economic consequences.

But we’re not addressing the problem. Although a drug of known safety and efficacy is available, scabies still affects more than 100 million people across the world who can’t break free of illness and reinfection cycles.

This week the Coalition for Operational Research on Neglected Tropical Diseases and the International Alliance for the Control of Scabies met to refocus efforts to reduce the impact of scabies across the world.

Scabies: mites living in your skin

Scabies is a skin disease caused by infestation with a highly infectious microscopic mite, Sarcoptes scabiei. Less than 1mm in size, the mite burrows into the skin, and leads to intense itching and visible sores. Sleep interruption and social stigmatisation result.

Intense scratching triggered by scabies infection also allows bacteria (Streptococcus pyogenes and Staphylococcus aureus) to become established in the skin.

Scabies is usually treated with a topical cream: in Australia, permethrin is the common choice.

In addition to the infected person, household contacts are often infested with scabies, and so the whole household should be treated at once. However, uptake of treatment in household members is often very low and so re-infestation is common. In settings where the prevalence is high, it is very difficult to avoid re-infestation from other community members, especially among children.

Scabies is a huge global problem

Scabies affects more than 100 million people worldwide. It is especially common in the Pacific region: in Fiji, half of all primary school aged children have scabies, as well as one in five adults. Up to one third of people living in remote Australian Indigenous communities are infected.

While scabies itself is a distressing health issue, the greatest impacts occur as a result of associated bacterial infections. Scabies commonly leads to impetigo (skin sores), and severe skin and soft tissue infections and sometimes even invasive bacterial infection and life-threatening toxic shock syndrome can follow.

The body’s immune response to Streptococcus pyogenes bacteria can cause kidney damage and possibly rheumatic heart disease.

Scabies is therefore a cause of considerable illness and is also linked to some deaths.

Scabies qualifies as a Neglected Tropical Disease

Efforts are increasing for scabies to be added to a list of conditions classified as Neglected Tropical Diseases.

The Neglected Tropical Disease global movement began in the early 2000s in response to the Millennium Development Goals. A Department of Neglected Tropical Diseases was soon established at the World Health Organisation (WHO) to coordinate and support policies and strategies specifically for the control of neglected tropical diseases.

Seventeen conditions currently make up the Neglected Tropical Diseases list, including onchocerciasis (river blindness), lymphatic filariasis (parasitic worms in the lymph system), bacterial eye infections known as blinding trachoma, schistosomiasis (blood parasites acquired through water) and soil transmitted intestinal worms.

Although not currently on the list, scabies has many features that warrant its inclusion. These include its high prevalence in low to middle income countries and in disadvantaged communities, the social stigma it causes, the chronic morbidity associated with the disease and known success of mass drug administration as a control strategy.

Mass drug administration for disease control

Mass drug administration is the centrepiece of ambitious global plans to eliminate several major Neglected Tropical Diseases. More than 700 million people receive mass drug administration every year through large regional and global programs supported by the World Health Organization and partners. At the community level, drugs are delivered by specially trained distribution teams.

The oral drug ivermectin is the most frequently delivered agent, used in highly successful programs for control of lymphatic filariasis and onchocerciasis.

The 2015 Nobel Prize for Medicine was awarded to William Campbell and Satoshi Omura for their discovery of ivermectin and in recognition of the contribution of the drug in improving global public health.

A new approach for scabies eradication

Could mass drug administration for scabies work? Mass permethrin treatment for scabies was successful in Panama and Australia. However, this cream is not ideal for use in public health initiatives because it is messy to apply and adherence can be low, and because the tubes are bulky and difficult to transport.

But scabies can also be killed effectively with ivermectin, an oral medication that comes in tablet form.

A clinical trial conducted in a Fijian community found a single round of ivermectin mass drug administration was able to virtually eliminate scabies: prevalence was reduced from 32% to less than 2%. This reduction in scabies was associated with a 67% drop in the prevalence of scabies-linked bacterial impetigo.

These results provide robust initial evidence to encourage investigation of ivermectin based mass drug administration as a means to control scabies in highly endemic populations on a larger scale. The trial further strengthens the claim for scabies to be considered as a WHO-listed neglected tropical disease.

Let’s get rid of scabies

There are several crucial elements that will lead to successful control of scabies and the alleviation of suffering for those afflicted by the disease. Integration with programs already in place for other neglected tropical diseases (especially those that use ivermectin mass drug administration), recognition and support by WHO, and strong advocacy are essential.

The International Alliance for the Control of Scabies was formed in 2012 and is the key global advocacy body for scabies. The Alliance is a network of professionals, including clinicians from high-prevalence areas, public health physicians, policy makers, and researchers, all of whom are committed to the control of human scabies infestation, and to promoting the health and well-being of all those living in affected communities.

Further research into the effect of ivermectin based mass drug administration on the severe bacterial complications of scabies is warranted.

Also, operational research into acceptability and cost effectiveness of mass drug administration will have an impact through strengthening the case for placing scabies alongside other neglected tropical diseases that are targeted for global elimination.

Andrew Steer receives funding from the National Health and Medical Research Council of Australia and the National Heart Foundation of Australia.