More than 14% of the world’s population may have had Lyme disease, an analysis released on Monday found.
The research, published in BMJ Global Health, is the result of a review of nearly 90 studies. It offers an unprecedented picture of the frequency of tick-borne disease.
“As far as I know, this is the first global seroprevalence work that has been done,” said Dr. Peter Krause, principal investigator at the Yale School of Public Health who was not involved in the new study. . Seroprevalence refers to the measurement of antibodies in the blood.
For the analysis, the researchers compiled studies that looked at the frequency of antibodies to the bacterium Borrelia burgdorferi, which causes Lyme disease, in humans. Of more than 158,000 people involved in these studies, around 23,000 had the antibodies, suggesting they were currently infected or had been so in the past.
Lyme disease is the most common tick-borne disease in Europe and North America, but it is not evenly distributed around the world.
The new study showed that Central Europe had the highest share of residents with Lyme disease – 21% – compared to about 9% in North America. This is similar to Krause’s own research, which found that 11% of people sampled in New England in 2018 tested positive for Borrelia burgdorferi antibodies. Most Lyme disease cases in the United States are in the Northeast and upper Midwest.
The new analysis included participants from Asia, Australia, the Caribbean, Europe, and North and South America. The Caribbean had the lowest proportion of people with Lyme disease, at just 2% – an expected finding, given that the region is made up mostly of island nations.
“There are areas where the disease doesn’t exist,” Krause said.
But Lyme disease has become more prevalent over time: About 8% of people studied from 2001 to 2010 had Lyme disease antibodies, according to the new study. From 2011 to 2021, the share was 12%.
In the United States, confirmed cases of Lyme disease increased by 44% from 1999 to 2019, according to the Centers for Disease Control and Prevention.
The new analysis offers some explanations for the trend. Deer ticks, which transmit Lyme disease to humans, prefer warm, humid climates. Rising global temperatures have resulted in longer summers and shorter winters, allowing ticks to become more abundant and widespread. Humans are also encroaching on forest areas, where ticks typically live.
A third reason, Krause said, is that deer populations have increased, giving ticks more opportunities to feed and reproduce.
“Wherever deer are, tick numbers are exploding,” he said.
Lyme Disease Symptoms
According to the CDC, about 70 to 80 percent of people who get Lyme disease develop a bulls-eye rash at the site of the tick bite. The rash usually appears three to 30 days after the bite and can spread up to 12 inches wide. It may feel hot to the touch, but usually doesn’t itch or hurt.
Other symptoms include fever, chills, headache, fatigue, and muscle or joint pain shortly after a tick bite; these can also affect people who do not develop a rash. A small minority of people may not have symptoms, Krause said.
But in more severe cases, people may develop severe headaches, stiff neck, nerve pain, dizziness, heart palpitations, shortness of breath, arthritis, or sudden weakness or paralysis of one side of the face in the days or months following a bite.
“There are people who have had even longer bouts of fatigue and they don’t feel well or have brain fog, and we don’t have a full understanding of that,” Krause said.
Antibodies to the bacteria Borrelia burgdorferi can persist for at least 16 months, according to one study, and up to 10 or 20 years, according to another.
Although 14% might seem like a high infection rate to those unfamiliar with Lyme disease, Krause said the estimate didn’t shock him.
“It’s not like, ‘Oh my God, there’s so much more disease than we thought,'” he said. “These numbers are a bit higher than I would have thought, but it’s not a breakthrough finding.”
The rise and fall of a Lyme disease vaccine
The best way to avoid a tick bite is to simply stay out of places where they are prevalent: wooded, bushy areas with tall grass. If you’re visiting this type of environment, Krause said, apply insect repellent and wear long sleeves with long pants tucked into socks.
“If you enter a wooded area, you need to do tick checks later,” he said.
People who get bitten by a tick can ask for antibiotics, but Krause said they don’t always eliminate symptoms.
“What appears to be the case – at least there is reasonable evidence for this – is that although the Lyme organism is killed with antibiotics, the organism itself does not break down very well. It sort of hangs around in a dead form,” he said.
He added: “We really need a vaccine. That’s probably the best hope for us to really get it under control.”
The Food and Drug Administration approved a vaccine called LYMErix in 1998 that was shown to be effective in preventing Lyme disease in clinical trials. But GlaxoSmithKline, the developer of this vaccine, pulled it from the market in 2002.
“It worked, but the company stopped using it because it took three injections and there was a group of people who claimed, incorrectly, that it caused arthritis,” Krause said.
Krause said another Lyme vaccine could be available in a few years. A candidate from Pfizer showed promise in early trials.
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