IN SPRING/SUMMER 2015 we co-ordinated a nationwide survey of ticks biting dogs that involved over 1,400 participating veterinary practices. This was known as “The Big Tick Project”.
Here we describe the planning, scale and logistics of the operation which triggered an overwhelmingly enthusiastic response from veterinary practices – and as such we believe it is a model for surveys on this scale.
Introduction
Recent studies have suggested that tick abundances are increasing throughout northern Europe; the cause is most likely to be a combination of increases in host abundance, particularly deer, habitat change and a warming climate.
Warmer and wetter winters and milder wetter summers, in particular, may allow the expected highly seasonal pattern of tick activity to be extended with ticks becoming active earlier in the year and feeding for a longer period of time, giving more continuous periods of exposure (Dautel et al, 2008).
In Great Britain the distribution of ticks was estimated to have expanded in the last 10 years by 17% and the abundance of ticks to have increased at 73% of locations surveyed (Scharlemann et al, 2008). For the last two years we have recorded biting ticks throughout winter in the UK.
What this means in terms of increased disease risk is difficult to determine at present because surveys of tick-borne disease are logistically difficult to undertake, expensive and not usually undertaken on a sufficiently large scale.
Previous work on the prevalence of pathogens in 800 Ixodes ticks collected from 3,500 dogs in the UK showed that only 0.74% of the ticks collected were infected with Anaplasma phagocytophilum but 2.4% were infected with Babesia (largely B. gibsoni type) and 2.3% were infected with Borrelia (Smith et al, 2012). We wanted to confirm these findings and obtain more compelling evidence for the prevalence of disease pathogens in dogs by repeating this survey approach on a much larger scale throughout the UK. Given the changes in the pet passport scheme, routine surveillance is also urgently needed to assess the introduction of exotic tick species into the UK (Hansford et al, 2015).
Since the prevalence of tick-borne pathogens is expected to be relatively low, based on previous studies in the UK, large sample sizes would be required to produce statistically meaningful results. We therefore designed a survey, named “The Big Tick Project” that we anticipated would recruit up to 250 veterinary practices, which would contribute to the survey for 10 weeks between April and June 2015.
If the 250 practices checked five dogs per week, equating to 1,250 dogs over a 10-week sample period, and if at least 10% of the dogs were carrying a tick, we would obtain in the region of 1,000-2,000 samples, which would be a large enough sample to detect pathogens at the frequencies detected in our previous studies.
Here we describe how The Big Tick Project was planned and undertaken – and how it unfolded.
The plan
Veterinary practices from throughout England, Scotland and Wales were recruited through an intensive media and publicity campaign, including input from TV presenter Chris Packham, co-ordinated by Liz Peplow of Sourced Communications, an outdoor direct to consumer disease awareness campaign and the support of the MSD sales team. Together, this generated a great deal of media interest and raised the pro le of the survey from the start.
Participating veterinary practices were asked to register their interest by e-mailing a contact name and their practice details. Once enrolled, they were then sent the Big Tick Project box which contained everything they needed: 40 questionnaires, stamped addressed envelopes, tick removers, test tubes and protocols; all branded “Big Tick Project”.
Dr Susan McKay of Companion Consultancy organised the registrations and sent out the Big Tick Project box to the veterinary practices involved; and also followed up with the practices if they had registered but not yet started sending in completed questionnaires.
The protocol asked registered veterinary practices to examine five dogs for ticks each week, using a specified standard grooming procedure and then complete a questionnaire relating to the clinical history of each dog. It was important that questionnaires were completed and returned for dogs that were found not to have ticks, so that a true prevalence figure could be calculated. It was important that these dogs were selected at random (dogs brought for vaccination, etc.) and which were not known to be carrying ticks when selected.
Each week, each participating veterinary practice sent tick samples by post to the University of Bristol, where they were identified to species, life-cycle stage and sex. Once the main tick collection period was completed, the aim was to extract DNA from the ticks and run genus-specific PCRs to detect pathogen DNA from the extracts. PCR products of the positive samples would then be purified and then sent for DNA sequencing.
The practice
Packs of ticks began to arrive at the University of Bristol within days of the campaign being launched and numbers rapidly built up through May (Figure 2). At its peak, over 450 envelopes were arriving a day, particularly on Mondays, in bulging mail sacks.
Each envelope had to be opened, the questionnaires led and any ticks placed in a tube with a number that cross-checked to the questionnaire and later placed in a deep freeze. At its peak, a production line of three people were required full-time to handle the volume of mail and the bulk were opened over the summer by our enthusiastic team of visiting French intern students (Claire Le Roy, Mathilde Fayolle-Baussian and Charlotte Dumas)
The initial plan to run the campaign for only 10 weeks until June was quickly abandoned because of the overwhelming response from veterinary practices; we ceased sending packs out at the end of July but we were still getting isolated envelopes submitted and phone calls asking if we wanted ticks in December 2015.
By the end of August we had received envelopes from 1,171 veterinary practices, more than 14,000 dogs had been examined and questionnaire responses received and in excess of 6,300 ticks had been sent in from across the country.
The scale and enthusiasm of the response from veterinary practices was extraordinary and demonstrated that this issue was clearly something of considerable concern to pet owners and veterinary professionals throughout the UK.
All the ticks collected have now been identified, and identifications of some of the more unusual specimens confirmed by Keyleigh Hansford at Public Health England. Of particular note is that 13 cases of the brown dog tick, Rhipicephalus sanguineus, were detected, all in travelled dogs that had recently visited the Mediterranean region.
The import and potential establishment of this species is of particular concern following changes to the pet passport scheme in 2012 (Hansford et al, 2015) and emphasises the importance of appropriate treatment against ticks for dogs that are travelling, and that this should be applied before they leave the UK.
The huge number of paper questionnaire responses are now being digitised by a team of first and second year Bristol biology undergraduate students (Beth Savagar, Saloni Bhuptani, Kitty Sherwood, Sarina Saddiq and Zoe McLoughlin).
DNA is being extracted from the ticks by teams of third and fourth year undergraduates as part of their research training (Andrew Bird, Nancy Matthews, Laura Harber, Issy Sykes, William Turner, George Van Horn,Roisin McDonough and Jay Towne) and PCR and sequence analysis is now under way in Bristol (with additional thanks to Drs Chris Helps and Severine Tasker at the Acarus laboratories, Langford Diagnostic Services).
Establishing confidence in the results
The sheer volume of the data has resulted in a somewhat slower release of the results than had been anticipated initially, but it is important to make sure that we have a high level of confidence in the results before they are made public.
For example, one of the commonest problems encountered was that some practices did not understand why they should complete a history and send in a questionnaire for dogs that did not have ticks.
As a result, some practices sent only positive samples. The university has therefore taken this into account and adjusted the data accordingly to make it as reliable as possible. The negative samplesare important for two reasons. First, because you need to know how many dogs did not have ticks to allow you to calculate a true prevalence. Second, the statistical comparison of the characteristics of dogs that did have ticks with dogs that did not have ticks will allow us to identify the factors that are associated with a higher risk of tick infestation.
As a result, substantial work will be needed with the data to ensure that it is robust before we can undertake statistical analysis.
Clearly the Big Tick Project has been a huge and highly successful undertaking – it has involved input from a very large number of people and has engaged veterinary professionals and pet owners alike. As such we believe it is a model for surveys on this scale.
We hope to have available and ready to publish in July, during Tick Awareness Month, and would like to take this opportunity to thank all those veterinary practices that participated with such enthusiasm.
References
- Dautel, H., Dippela, C., Kaemmer, D., Werkhausen, A. and Kahl, O. (2008) Winter activity of Ixodes ricinus in a Berlin forest. I J Med Microbiol 298: 50-54.
- Hansford, K. M., Pietzsch, M. E., Cull, B., Medlock, J. M., Wall, R. (2015) Overwintering of the brown dog tick in residential properties in England – raising awareness. Vet Rec 177: 156.
- Scharlemann, J. P. W., Johnson, P. J., Smith, A. A., Macdonald, D. W. and Randolph, S. E. (2008) Trends in Ixodid tick abundance and distribution in Great Britain. Med Vet Entomol 22: 238-47.
- Smith, F. D., Ballantyne, R., Morgan, E. and Wall, R. (2012) Estimating Lyme disease risk using pet dogs as sentinels. Comp Immunol Microbiol Infect Dis 35: 163-167.
