Scabies outbreak in Brazil may be linked to indiscriminate ivermectin use

In August, researchers at Brazil's Federal University of Alagoas published a warning that would soon feel prophetic. They had identified a troubling possibility: the parasite that causes scabies might be developing resistance to ivermectin, the antiparasitic drug that had become ubiquitous across the country during the pandemic. By late 2021, that warning was no longer theoretical. At least 264 people in six cities around Recife, in Pernambuco state, had sought medical care for a mysterious skin condition—intense itching that worsened at night, followed by open sores that persisted even with antihistamines. Health authorities were investigating. The timing and the symptoms pointed toward one conclusion: the outbreak the researchers had predicted might already be happening.

The path to this moment began with a false promise. When early studies suggested ivermectin might work against COVID-19, consumption of the drug skyrocketed—nearly tenfold in Brazil. The medication had never been proven effective against the virus, and subsequent research confirmed it didn't work. But the damage was already done. Ivermectin had become part of what supporters called the "COVID kit," a collection of unproven treatments that circulated widely, encouraged at the highest levels of government, including by President Jair Bolsonaro, who repeatedly advocated for its distribution even as evidence mounted against it.

The research team at the Federal University of Alagoas—led by pharmacotherapy researchers Alfredo Oliveira-Filho and Sabrina Neves, along with students Lucas Bezerra and Natália Alves—had connected the dots. They reviewed documented cases of ivermectin resistance, isolated outbreaks, and consumption data. Their conclusion was stark: widespread misuse of the drug created ideal conditions for the scabies parasite, Sarcoptes scabiei, to evolve resistance. "The article raises the hypothesis that we could face problems with resistant scabies outbreaks because of irrational ivermectin use," Neves explained. "The outbreak is real—there's been a rapid increase in cases of itchy skin lesions and other symptoms."

What made this possibility so alarming was the stakes. If the parasite had indeed become resistant, treatment would become difficult across any population. The disease could spread widely, and the tools to stop it would be compromised. Neves emphasized that irrational use of antiparasitic drugs, antibiotics, and antifungals posed particular dangers. "When we use medications like ivermectin incorrectly, we risk inducing the parasite to become resistant to the very drug that should treat the disease it causes," she said.

At the time of reporting, health authorities had not yet confirmed that the Recife outbreak was scabies, let alone drug-resistant scabies. Neves noted that other causes were being tested and ruled out. But the alert had already spread. Health services across Brazil's states had been notified of the symptoms to watch for—intense itching, skin lesions, nocturnal worsening—so they could report similar cases if they appeared. In São Paulo, another scabies outbreak had already surfaced in coastal communities, severe enough that an infant required hospitalization. The researchers' August warning, once a cautionary hypothesis, was becoming a public health crisis unfolding in real time.