I’ve had a few discussions with people over the past week about geographic variation in disease risk. It’s a great subject because it’s an important and often overlooked issue. Whether it’s animals being imported, animals moving with their owners, animals accompanying owners on vacation and animals being moved between regions within the county, movement between regions can involve picking up or moving diseases in parallel.
From a veterinary standpoint, the challenge is identifying issues that you wouldn’t normally consider, because the disease is rare or non-existent in your practice area. The first step is querying travel history (something that is done variably well). The next is figuring out what that means. We don’t have great resources that say “if you go here with your dog, this is what you need to be concerned about”. I get questions about travel risks all the time and it’s taken a lot of effort to get up to speed with risks in different regions (and I still have a lot of gaps). We’ve published the odd (crude) map to help out, but getting good quality information, ideally based on surveillance data, and assimilating it into a central resource is a challenge (a goal of ours, for sure, but a slow process given time and money limitations).
Regardless, we’re getting more information all the time and getting that out in the open is important. Dr. Michelle Evason wrote a post on her K9 Lifetime Study blog about the leptospirosis data we’re working on, and I thought that was worth putting up here too. It’s a fairly high level map of a few years of leptospirosis cases in dogs in Canada, based on data from IDEXX Laboratories. There are various limitations with any test dataset so it’s not a perfect representation of this disease. However, it provides some useful data. Lepto’s a nasty disease and also a vaccine preventable disease. So, understanding where it’s common is important for thinking about it (making a diagnosis) and when discussing vaccination programs.
The incidence is adjusted for human population, on the assumption that dog ownership trends are similar across the country. We do that so that we don’t see bias towards big cities. If we just plot the number of cases, place with a big dog population but low incidence of disease could have more cases than a true high risk area with a lower population and hide the real risk.
This bacterium lives is different wildlife hosts (e.g. raccoons, rodents) and is passed in urine, and is survives well in moist, temperate climates. Unsurprisingly, we see lepto concentrated in much of Ontario and east, particularly in southern regions, as well as coastal British Columbia. Risks varying within those regions and lepto vaccination discussions require some assessment of risk (although I consider lepto vaccination a core vaccine in most of these green (and all of the blue) regions on this map.