More than 14 per cent of people worldwide have contracted tick-borne Lyme disease, according to blood analyses.
When an infected tick bites an animal like a deer or human, it can pass on a bacterium called Borrelia burgdorferi, the primary cause of Lyme disease. Symptoms including fever, headache, rash and weakness can appear days to weeks after a tick bite. Most cases of Lyme disease can be treated with antibiotics, but without intervention, the pathogen can cause long-lasting damage and inflammation throughout the body.
Since it was first identified in 1975, Lyme disease has become the most common tick-borne zoonotic disease worldwide. To devise better strategies for prevention, we first need a clearer understanding of its prevalence.
To that end, Yan Dong at Kunming Medical University in China and his colleagues combed databases for previous studies. They narrowed their search to 89 studies carried out between January 1984 and December 2021. These included blood samples from a total of more than 150,000 people.
The researchers then looked specifically at the presence of antibodies against B. burgdorferi in the blood, which indicate a current or prior Lyme disease infection. Their results revealed that the global rate of Lyme disease infection is 14.5 per cent.
The analysis pinpointed three regions with the highest rate of Lyme disease: central Europe (20.7 per cent), eastern Asia (15.9 per cent) and western Europe (13.5 per cent). The lowest rates were in the Caribbean, southern Asia and Oceania (all under 5 per cent), while North America had an infection rate of just over 9 per cent.
Those at the highest risk of infection were men aged 50 and older who live in rural areas in the northern hemisphere and have occupations that involve being outdoors or in close contact with animals.
The review also showed that Lyme disease infections have become more common over time. A warming climate can both enable ticks to spread to new regions and extend their lifespans, increasing the opportunity for them to pass on pathogens.
“Our results indicate that the prevalence of [B. burgdorferi] in 2010–2021 was higher than that in 2001–2010,” the authors write. They note that longer summers, warmer winters and changes in precipitation could all play a role in tick distribution.
Vaccines against Lyme disease are currently in different stages of testing, but none has yet been approved for use in humans.
Journal reference: BMJ Global Health, DOI: 10.1136/bmjgh-2021-007744
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