Britain’s long hot summers mean disease-carrying ticks are living longer

Recent heatwaves are allowing disease-carrying ticks to survive for longer periods in the UK, a specialist has warned.

In the past, temperatures were too cool to enable hyalomma ticks to reach full maturity.

Dr Jolyon Medlock, head of medical entomology at the UK Health Security Agency (UKHSA), noted that although cases remain rare, public health authorities are "starting to pick up a bit more".

The hyalomma tick serves as the primary vector for Crimean-Congo haemorrhagic fever, a condition that can prove severe and life-threatening.

These parasites occasionally enter the UK by attaching themselves to birds migrating from Africa and the Mediterranean during their nymph stage.

At this intermediate point in their development, the ticks are approximately the size of a poppy seed.

They transition to adulthood through moulting, a phase where they cast off their hard outer layer.

Dr Medlock said: “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.”

The UKHSA’s Tick Surveillance Scheme was set up in 2005 to map and monitor ticks across the UK.

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.”

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 per cent.

The virus can incubate anywhere from one to nine days following 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, a headache and sore eyes, as well as 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 said: “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.”