Hotter UK summers are allowing disease-carrying ticks to live longer and reach adulthood, according to an expert. Previously, UK summers were not warm enough for Hyalomma ticks to make it all the way to adulthood, but this is now changing.
While still rare, it is something health officials are “starting to pick up a bit more”, says Dr Jolyon Medlock, head of medical entomology at the UK Health Security Agency (UKHSA). Hyalomma ticks are the primary vectors of Crimean-Congo haemorrhagic fever, a serious and potentially fatal virus.
How ticks arrive in the UK
These ticks sometimes show up in the UK by holding onto birds that migrate from the Mediterranean and Africa when the ticks are still young. This is the middle part of a tick's life when they're about as small as a poppy seed. Ticks move to the next stage of their life by moulting, where they shed their hard outer shell.
Dr Medlock told the Press Association: “They would normally come in on migratory birds as a nymph, and then fall off, and they wouldn’t be able to moult. It’s not warm enough. What we’re seeing now in heatwave years is that they can moult through to the adult stage, and we then could be able to pick up records of adults through our tick surveillance.
“These have happened less than probably five times in the last 10 years or so, but it’s something that we and colleagues across northern Europe are starting to pick up a bit more. It doesn’t mean the tick will survive, and it doesn’t necessarily mean it’s an infection risk.”
Surveillance and reporting
The hard-bodied ticks are common in Asia, Europe, and North Africa. The UKHSA’s Tick Surveillance Scheme was set up in 2005 to map and monitor ticks across the UK. Last year, gov.uk issued a Mosquito and tick incidents message, which reads: "Hyalomma ticks can vector pathogens of human and animal health importance. We monitor the importation of this species in the UK using our Tick Surveillance Scheme, along with research projects which look for ticks imported into the country on migratory birds.
"Our data show that Hyalomma marginatum ticks enter the country regularly on migratory birds. Another important species called Hyalomma lusitanicum also enters the country on imported animals, such as dogs. You can report Hyalomma ticks to us using our Tick Surveillance Scheme."
Dr Medlock said there have been records of Hyalomma nymphs on migratory birds from observatories over the last 50 years. He added: “In their native area, they’re vectors of Crimean-Congo haemorrhagic fever virus, which is a relatively common virus that occurs in the Balkans that started to emerge in Spain recently. So these are the sort of climate-sensitive tick-borne disease pathogens that we might see.”
Disease risk and seasonal shifts
According to the World Health Organisation, Crimean-Congo haemorrhagic fever is endemic in Africa, the Balkans, the Middle East and Asia, with a fatality rate of up to 40%. The virus can incubate for one to nine days after a tick bite.
It can also be transmitted through contact with infected animal blood or tissues. The onset of symptoms is sudden and can include fever, dizziness, neck pain, headache, sore eyes, nausea, vomiting, mood swings, and confusion.
Elsewhere, milder winters and hotter summers may also lead to a “shift in the seasonality” of ticks more broadly in the UK, according to Dr Medlock. He told PA: “The simple way of collecting ticks is to go and drag a blanket through the undergrowth, and if it’s a hot, humid day, they’re running around quite quickly.
“If you’ve got mild winters, then they will remain active throughout the winter. Usually they say 7C is the critical temperature for activity, I’ve seen them active at 3C. So as we have milder winters and hotter, drier summers, we’ll see a shift in the seasonality of ticks.”
