Explosion of scabies due to increasingly resistant parasite

by Lorraine Williamson

MADRID – The explosion of scabies cases in Spain has been linked by experts to increased resistance of the parasite to the most commonly used treatments. 

That is why the Spanish health system is starting to review protocols on suspicion that permethrin creams have lost their effectiveness. El País writes about the five-month-long crusade of a Spanish couple with a young son against their enemy: Sarcoptes scabiei, the mite that causes scabies. The intense itching this disease causes can be just the beginning of a long battle. 

Scabies is a public health problem 

With tens or hundreds of thousands of cases per year, like that of the couple mentioned, scabies has become a public health problem in Spain, all experts agree. However, exact numbers are not known because scabies is not required to be reported. 

What is known are the figures for the number of medicines sold for scabies in Spain. That has skyrocketed from just over 200,000 in 2017 to nearly 1.4 million last year. This is evident from data from the specialised consultancy firm Iqvia. 

A new resistant variant of parasite 

A growing number of doctors believe a new permethrin-resistant variant of the parasite — the cream treatment given to those affected in the first place — is to blame for the rise in infections. 

Patients who use treatment incorrectly 

However, others focus on the fact that many patients misuse these creams, causing them to fail to heal. In any case, the problem has reached such proportions that the health system has begun to review its protocols to deal with the disease. 

Shared illness 

“We have been seeing scabies for two or three years. I think it has more to do with the misuse of treatments. The cream should be applied well all over the body and allowed to work. And all members of a household must do it because this is a shared disease. If someone skips, everyone will have it again after a short time. In addition, all clothes must be washed well, including bed linen and sofa covers…”, explains Francisca Gómez Molleda, a general practitioner at the Dobra Health Centre in Torrelavega (Cantabria). 

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Scabies does not itch at first 

Cristina Galván is a dermatologist and Vice President of the International Alliance for Scabies Control (IACS). “The problem is that the scabies don’t itch at first. In fact, you won’t notice it at all for the first four or six weeks. The parasite will dig its tunnels in the skin, and lay eggs…, but it won’t start biting you until the immune system response kicks in after that time,” she explains. 

This delay, experts say, is key to the difficult control of outbreaks. “Sometimes what happens is that only those who are itchy are treated properly. Others think they are fine and they don’t need it. Eventually, they get the same scabies, but by the time they notice, they’ve already infected others. And it never ends that way,” adds Galván. 

The parasite has not yet been shown to have developed resistance to permethrin. However, experts say it needs further investigation. 

Ana Pulido, a dermatologist at the Gregorio Marañón Hospital (Madrid), believes that “certain scientific evidence is beginning to emerge that points to the development of resistance mechanisms” by the parasite. This “forces us to rethink the treatment regimen” with the use of “oral ivermectin and other topical alternatives such as sulphurous petroleum jelly” in patients who “do not improve despite properly following therapeutic advice”. 

Major changes in five years 

The data on sales of scabies drugs provided by Iqvia to El País illustrates the major changes that have taken place over the past five years. Billing for prescription and public-funded treatments has increased eightfold, from about €3 million a year to about €25 million. 

Also read: Explosion of scabies infections in Spain 

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