A big increase in UK deer populations and the growing popularity of outdoor pursuits mean we need to be more aware of the hazard of ticks.
Although there are no long-term studies into tick numbers, zoologist Dr Sarah Randolph an expert in parasite ecology at the University of Oxford, says that there are good reasons to accept anecdotal evidence and surveys that report ticks are now much more abundant in the UK than in the past.
All ticks are blood-feeding parasites of vertebrates, mostly mammals. Around half a dozen of the 23 species that occur in the UK bite humans. The most common species in Europe, including the UK, is Ixodes ricinus, and deer are a favourite host.
Because I. ricinus is the main European vector (transmitter) of the pathogen that causes Lyme disease, this also means an increase in the risk of catching the disease.
Ticks looking for a host may move onto and bite people, which means any pathogens harboured by the tick can be transferred in their infected saliva. And more deer mean more ticks can prosper.
I. ricinus is a three-host tick, which means the larva, nymph and adult female each has to find a different host animal to feed on. Adult females lay up to two thousand eggs at one time, often under a mat of vegetation, where it is moist.
The six-legged larvae that hatch like small mammals, eg, mice, to feed on. Once engorged, they drop to the ground and moult to the eight-legged nymphal stage. The nymphs feed on small to large hosts before dropping off and developing to adults. Adult females prefer hosts bigger than stoat size.
When engorged, female ticks can grow to a length of 11mm. Male ticks feed rarely.
I. ricinus ticks like to live in moisture-retaining vegetation, eg, long grass. They climb to the top of, for example, a blade of grass and wave their front legs (questing) to search for approaching hosts. Sensors in the Haller’s organ on their front legs can detect changes in carbon dioxide levels, humidity and temperature that are clues a host is near. They then attach themselves to an animal brushing past.
‘Ticks particularly like to feed where blood flows close to the skin's surface, such as armpits and groins,' said Museum acarologist Dr Anne Baker.
‘The longer a tick feeds, the more opportunity there is for the pathogens to pass into the host, so rapid and regular post-exposure examination and tick removal are important ways to protect yourself.’
Not all ticks have Lyme pathogens, but areas with thriving wild deer populations have been highlighted as Lyme hotspots, including Richmond Park, the New Forest, the South Downs and the Lake District.
Feeding ticks are at their peak during the spring, most abundant during March-May and in some areas peak again in the autumn. However, they are also present throughout the summer and early winter.
In a research paper in 2011, Dr Randolph found blankets, such as picnic blankets, picked up the greatest number of ticks, particularly around trees.
'It’s important to assess the health risk of ticks as not only the likelihood of them being present in a certain habitat but also the likelihood of people coming into contact with them,' she said.
'The number of visitors to Richmond Park, for example, is around 420,000 a year per square kilometre. And these are often tourists and visitors who live in cities who are perhaps not so aware of the risks of walking in areas where ticks live.’
Ticks use a structure with backward facing teeth to anchor themselves to their host. It’s a myth that you should ‘unscrew’ a tick.
Use tweezers or gloved thumb and forefinger to grasp all of the tick and firmly pull it out. Don’t squeeze the body as this can mean more saliva (and pathogens) being passed on.
Avoid removal methods such as burning, squirting with alcohol or smothering in petroleum jelly as these can cause the tick to regurgitate pathogens. It’s also important not to break off the body and leave behind the mouthparts as this can lead to infection of the wound.
Early Lyme disease presents as flu-like malaise that doesn’t go away. A classic sign of Lyme infection is a circular red rash spreading out from the bite, but this doesn't always happen. It is very treatable with antibiotics and the sooner the treatment starts, the better.
'The problem is often getting a quick diagnosis,' Dr Randolph said. 'If you feel unwell, it’s important to let your GP know you have been in an environment that could have exposed you to ticks.'