Unusually aggressive lone star ticks, common in the south-east, are spreading to areas previously too cold for them

Blood-sucking ticks that trigger a bizarre allergy to meat in the people they bite are exploding in number and spreading across the US, to the extent that they could cover the entire eastern half of the country and infect millions of people, experts have warned.

Lone star ticks have taken advantage of rising temperatures by the human-caused climate crisis to expand from their heartland in the south-east US to areas previously too cold for them, in recent years marching as far north as New York and even Maine, as well as pushing westwards.

The ticks are known to be unusually aggressive and can provoke an allergy in bitten people whereby they cannot eat red meat without enduring a severe reaction, such as breaking out in hives and even the risk of heart attacks. The condition, known as alpha-gal syndrome, has proliferated from just a few dozen known cases in 2009 to as many as 450,000 now.