Rising temperatures are enabling disease-carrying ticks to survive for longer periods in the UK, according to an expert. Previously, the climate was insufficiently warm for Hyalomma ticks to reach full adulthood.
While still uncommon, it is something health officials are "starting to pick up a bit more", according to Dr Jolyon Medlock, head of medical entomology at the UK Health Security Agency (UKHSA). Hyalomma ticks are the principal carriers of Crimean-Congo haemorrhagic fever, a serious and potentially deadly virus.
How ticks reach the UK
These ticks occasionally arrive in the UK by latching onto birds migrating from the Mediterranean and Africa while still in their juvenile stage. This represents the intermediate phase of a tick's life cycle, during which they are roughly the size of a poppy seed.
Ticks progress to the next stage of their development through moulting, whereby they shed their hard outer casing. 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 risks
The UKHSA's Tick Surveillance Scheme was established in 2005 to chart and track ticks throughout the UK. Last year, gov.uk released a Mosquito and tick incidents message, which states: "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 noted that records of Hyalomma nymphs on migratory birds from observatories have existed for the past 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."
Virus and seasonality
According to the World Health Organisation, Crimean-Congo haemorrhagic fever is endemic in Africa, the Balkans, the Middle East and Asia, carrying a fatality rate of up to 40%. Following a tick bite, the virus can take anywhere between one and nine days to incubate.
The virus can also be contracted through contact with infected animal blood or tissues. Symptoms can emerge suddenly and may include fever, dizziness, neck pain, headache, sore eyes, nausea, vomiting, mood swings and confusion.
Elsewhere, milder winters and hotter summers could also bring about a "shift in the seasonality" of ticks more broadly across 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."
