The first confirmed case of tick-borne encephalitis virus in the United Kingdom was recorded in 2022. It all started with a bike ride.
A man in his fifties was mountain riding on the North Yorkshire Moors, an English national park noted for its huge tracts of woods and purple heather. At some point during his journey, a black-legged tick burrowed into his flesh. Five days later, the mountain cyclist got signs of a viral infection, including weariness, muscle discomfort, and fever. He appeared to be on the mend at first, but about a week later, he began to lose coordination. An MRI scan revealed that he had acquired encephalitis or brain swelling. He developed tick-borne encephalitis, or TBE, a potentially fatal disease that experts say is spreading into new regions due in large part to global warming.
Over the last 30 years, the United Kingdom has warmed by about 1 degree Celsius (1.8 degrees Fahrenheit) on average relative to the historical norm. Several tick-borne illnesses are becoming more common as a result of climate change, according to research. Because of the speed with which TBE has spread from nation to country, public health officials are particularly concerned. TBE is deadlier than more well-known tick diseases like Lyme. According to Gábor Földvári, an expert at Hungary’s Center for Ecological Research, the consequences of climate change on TBE are undeniable. “It’s a really common problem which was absent 20 or 30 years ago,” he added.
Climate change boosts ticks, raising disease risk for humans
Ticks can only survive for a few days in temperatures below zero, but they can survive in extreme heat as long as there is enough humidity in the environment. Ticks are becoming more active earlier in the year as the Earth warms and winters get milder. Climate change impacts ticks at all stages of their life cycle, including the egg, six-legged larva, eight-legged nymph, and adult, by prolonging the period ticks actively feed on humans and animals. Even a fraction of a degree of global warming increases tick breeding and disease transmission.
“The number of overwintering ticks is increasing and in spring there is high activity of ticks,” said Gerhard Dobler, a doctor who works at the German Center for Infection Research. “This may increase the contact between infected ticks and humans and cause more disease.”
Tick-borne encephalitis increasing in Europe and Asia
Since its discovery in the 1930s, the virus has primarily been detected in Europe and areas of Asia, including Siberia and northern China. The disease is carried by the same species of tick in these places, but the viral subtype — of which there are dozens — differs by region. Tick bites are the most common cause of encephalitis in areas where the virus is endemic, although the virus can also be contracted by drinking raw milk from tick-infected calves. TBE has not been discovered in the United States, though a few Americans have become infected while vacationing in Europe.
Each year, between 10,000 and 12,000 instances of the disease are reported in Europe and Northern Asia, according to the World Health Organization. Case counts are unreliable in countries where the population is unaware of the disease and local health authorities are not obligated to report cases to the government, therefore the overall number of cases worldwide is likely an undercount. However, specialists say there has been a definite increase since the 1990s, particularly in nations where the condition was previously uncommon. “We see an increasing trend of human cases,” Dobler said, citing rising cases in Austria, Germany, Estonia, Latvia, and other European countries.
TBE can lead to severe symptoms and lasting effects
TBE does not necessarily endanger one’s life. On average, roughly 10% of infections progress to the severe stage of the illness, which frequently necessitates hospitalization. However, once severe symptoms appear, there is no cure for the disease. Depending on the viral subtype, the death rate among people who develop severe symptoms ranges from 1 to 35 percent, with the far-eastern strain being the deadliest. In Europe, for example, out of around 3,700 verified cases, 16 deaths were recorded in 2020.
Up to 50% of severe TBE survivors have persistent neurological issues, such as insomnia and aggression. Many infected persons are asymptomatic or only develop mild symptoms, according to Dobler, thus the true caseload in some areas could be up to ten times higher than reported.
Tick-borne encephalitis (TBE) cases rise due to climate change
While two TBE vaccines are available, vaccine adoption is limited in areas where the virus is new. Neither vaccination covers the three most common subtypes, and a 2020 study urged for the creation of a new vaccine that provides better viral protection. According to Dobler, the TBE vaccine rate in Austria is near 85 percent, yet the number of human cases continues to rise — a symptom, in his opinion, of climate change’s influence on the disease.
Documented cases of the virus have been increasing in recent decades in central and northern Europe, where average annual temperatures have been roughly 2 degrees Celsius above pre-industrial times (3.6 degrees Fahrenheit) for the past decade — evidence, some experts say, that rising global temperatures are conducive to more active ticks. As previously difficult terrain warms to their optimal temperature range, parasitic arachnids have been observed to move further north and higher in altitude. Northern Russia is an excellent example of where TBE-infected ticks have spread. Ticks have increased 20-fold in previously tick-free mountains in Germany, Bavaria, and Austria in the last decade.
Tick-borne virus spreading due to warming temperatures
Documented cases of the virus have been increasing in recent decades in central and northern Europe, where average annual temperatures have been roughly 2 degrees Celsius above pre-industrial times (3.6 degrees Fahrenheit) for the past decade — evidence, some experts say, that rising global temperatures are conducive to more active ticks. As previously difficult terrain warms to their optimal temperature range, parasitic arachnids have been observed to move further north and higher in altitude. Northern Russia is an excellent example of where TBE-infected ticks have spread. Ticks have increased 20-fold in previously tick-free mountains in Germany, Bavaria, and Austria in the last decade.
The virus’s spreading shadow throughout Europe, Asia, and now areas of the United Kingdom highlights the hazards of tick-borne disease. The first domestically acquired case of TBE, a British bicyclist, survived, but the experience serves as a warning to the region: while the virus is still rare, it may not be for long.