TICK-BORNE PATHOGENS - AN OPEN LETTER TO MARTIN ANDERSSON AND RICHARD BIRTLES

An Open Letter to Martin Andersson and Richard Birtles.

Your presentations at the recent Lyme Disease Action conference at the University of Surrey were particularly impressive and obviously the results of countless hours of effort from you and your co-workers. The information regarding the transmission pathways of tick-borne pathogens highlighted the differences of risk to human health from the different species of ticks, and help define optimum strategies for disease prevention. It also demonstrated the variability of tick infection rates on geographic macro and micro scales. Of great interest was the ingenious study of forest enclosures and tick infection rates within and outside the barriers. Deer population size was a driver of tick populations, and rodents a driver for tick infection rates. This suggests that areas with large populations of mammals that provide the final feed for adult female ticks along with high populations of rodents, will have high numbers of infected ticks.

The study of Candidatus Neoehrlichia mikurensis is important in highlighting the fact that ticks carry many different microbes, and new species are being discovered all the time. More than 18 distinct species of Borrelia bacteria have been identified since Willy Burgdorfer first identified the cause of Lyme disease in the early 1980’s. There can be long delays between identification of an organism and general recognition as a disease causing pathogen. It is normal to describe incidence of disease based on national or regional boundaries, however it was well demonstrated in the presentation that absence of reported cases does not mean absence of the disease, and the fact that until you look you will not find. Has the genetic divergence seen in China compared to that exhibited in Europe been used to estimate the length of time that Neoehrlichia has been present in these regions?

Both presentations highlight the fact that ticks do not recognise boundaries marked on maps. It is whether the ecological conditions exist at a specific location that drives the occurrence of infected ticks. Fragmentation of woodland created by urban expansion and people living adjacent to woodlands, parkland and other tick habitat results in large numbers of people and their companion animals permanently living in close proximity to ticks. There could be a higher risk living at 201 Sunnyside Avenue with 2 dogs than an occasional visit to our magnificent countryside.

Clinicians officially have 10 minutes to decide what ails a person, and if Lyme is suspected then it is convenient to enquire whether the person visited a hot spot defined regionally such as, The New Forest, or Dartmoor or Thetford Forest. It may be more relevant to ask; do you live or play near woodland or areas of natural beauty. This is not an easy option to implement when we are so conditioned to arbitrary lines marked on maps. Can a method other than the use of title specific regions be developed to help clinicians assess the risk of infection? Or should the concept of “hot spots” be abandoned and replaced by a greater emphasis on clinical symptoms?

It is hard work and scientific data gathering and analysis as demonstrated by you, that will help educate current and future generations and reduce or avoid the often devastating and sometimes fatal effects of tick-borne diseases.

Michael Cook
Highcliffe
Dorset