Scarlet fever reemerging

Supercharged bacterial clones appear responsible for new cases of scarlet fever.

By 1940, antibiotics had nearly eradicated the once-deadly childhood disease. But in 2011, a scarlet fever epidemic in Asia caught health authorities by surprise. A second outbreak occurred in the United Kingdom in 2014. By 2018, the U.K. National Health Service reported a 68 percent increase in the number of cases. “This global reemergence of scarlet fever has caused a more than five-fold increase in disease rate and more than 600,000 cases around the world,” said Stephan Brouwer, a University of Queensland researcher.

An international group of scientists led by the University of Queensland discovered that a viral infection strengthened some strains of the bacteria responsible for scarlet fever, according to their Oct. 6 study in Nature Communications.

The group of viruses carried a gene mutation that allowed them to produce three new toxins called superantigens. When a virus attacked a ball-shaped Group A strep, or Streptococcus pyogenes, the bacterium incorporated the virus’s own DNA into its own in a process called horizontal gene transfer. This allowed the scarlet-fever-causing bacterium and its future clones to produce the toxins, as well.

The toxins give A strep new ways to enter a child’s tissues and escape the white blood cells that are part of the body’s immune defense. The researchers attribute the uptick of scarlet fever to these toxin-producing bacteria. When they used genetic editing to disable the mutated genes, the strains lost their ability to invade animal models in the lab, Live Science reported.

Scarlet fever mostly affects children 2-10 years old and can cause sore throat, fever, headache, swollen lymph nodes, coughing, sneezing, and a telltale red rash. Severe cases can result in toxic shock and organ failure. Before the advent of antibiotics, deadly complications such as brain abscess, meningitis, lung abscess, pneumonia, osteomyelitis (bone infection), and middle ear and soft tissue infections could develop following the illness.

Researchers have not developed a vaccine to prevent scarlet fever. The microbe is beginning to develop resistance to some antibiotics, study co-author Mark Walker told the Australian Broadcasting Corporation.