Incidence of Lyme Disease in Scotland
On average, 5% of ticks in Scotland are infected with Borrelia, and the number of cases of Lyme Disease in humans is has been higher in the last decade: in 1996 there were fewer than 30 new cases in Scotland; in 2014 there were around 230. However, GPs estimate that only 20-40% of cases are referred, and so the numbers are likely to be much higher. Analyses are very rough because the real figures are unknown. Dr. Darrel Ho-Yen, previous head of the national Lyme Disease Testing Service in Scotland, believed that the known number of proven cases should be multiplied by 10 “to take account of wrongly-diagnosed cases, tests giving false results, sufferers who weren’t tested, people who are infected but not showing symptoms, failures to notify and infected individuals who don’t consult a doctor”.
Tests in donated blood have concluded that 4.2% of blood donors have positive Borrelia serology. With the estimated 2015 mid-year population of Scotland standing at 5.373 million, that equates to 225,666 blood donors of Scotland having been infected. The number of infected people is likely to be higher as those who are ill are less likely to give blood. Not everyone who is infected has current symptoms. The prevalence of positive serology amongst blood donors was even higher in the Highlands, being 8.6% around Inverness.
Species of Borrelia in Ticks in Scotland
The species of ticks in the Scotland are very different from those in the USA. The Chief Medical Officer of NHS Scotland (in a personal letter from November 2016) advised that, "in a study, 8% of ticks from 25 sites across Scotland were identified as being infected with B. valaisiana, however, the majority of genospecies were B. afzelii (48%) and B. garinii (36%)".
However, in 2013, Borrelia miyamotoi was discovered in the USA. In 2014, a high seroprevalance of Borrelia miyamotoi antibodies was found in forestry workers in the Netherlands. In 2015, scientists from the Porton Down Public Health Laboratory in England announced the discovery of Borrelia miyamotoi in ticks in England. It is not know how prevalent it is in Scotland but in 2017 it was reported that ticks with Borrelia miyamotoi were found feeding on competitors of a Scottish mountain marathon.
In 2017, Borrelia spielmanii was found in UK ticks, as well as the co-infections Babesia venatorum, Babesia vulpes sp. nov., Babesia divergens/Babesia capreoli, Babesia microti, and Babesia canis.
A recent European study found many other pathogens in ticks.
Although it is commonly understood that transmission of Lyme Disease is via tick bites, there is some question about other transmission mechanisms. Studies have varied and this is an area of controversy, but a study in 1986 concluded that "B. burgdorferi can be transmitted by direct contact without an arthropod vector". It has been found in breast milk, found to survive in urine of mice, and it has been suggested it could contaminate the food chain. There is also some question about whether sexual transmission is likely. A number of studies have found that transmission can take place from insects other than ticks, including mosquitos and fleas. Spirochaetes have been found in human vaginal and seminal secretions.
Although it is commonly stated that a tick must be attached for at least 24 hours before transmission occurs, a recent review "has determined that in animal models, transmission can occur in <16 hours, and the minimum attachment time for transmission of infection has never been established". Recent research concluded that, in the case of borrelia miyamotoi, "transmission can occur within the first 24 hours of nymphal attachment".
Congenital human infection with the tick-borne co-infection, babesia, has been reported.
According to the National Lyme Borreliosis Testing Laboratory, "prior to 2010, LB was a notifiable disease in Scotland and although the NLBTL reported all laboratory confirmed cases, the data published by Health Protection Scotland (HPS) varied and the reporting of clinical cases by medical practitioners was limited".
Co-infections exist in Scotland and are on the rise, partly as a result of the relaxation of the Pet Travel Scheme.