The changes we make to our environment have rippling effects that can literally bite us back in ways that are as convoluted as they are subtle. A prime example is the effect of urbanization (or, perhaps more correctly, sub-urbanization) on the risk – both for ourselves and our canine companions – of contracting Lyme Disease.
Decades of research on the ecology of Lyme disease, much of it carried out at the Cary Institute of Ecosystem Studies (www.caryinstitute.org), has revealed some fascinating connections between habitat modification, wildlife population dynamics, and the movement of Borellia burgdorferi (the bacteria that causes Lyme Disease) through wildlife hosts, tick vectors, and ultimately into our anthropomorphized environment.
- Habitat fragmentation – Our spreading suburban neighbourhoods are lovely patchworks of gently curving streets, manicured lawns, and small copses of trees that were left as green space when the forest was cleared to make way for home construction. If you’re lucky, you might even have a small wooded park or tree-lined lake to enjoy. They are quiet, peaceful places for us – and for some wildlife species too. Mice, crows, deer, and other adaptable generalist species can prosper in these environments, benefiting from the extra food, shelter, and other resources provided by our gardens and landscaping, our trash and compost bins, and even our houses and outbuildings, while at the same time having the shelter of these small patches of forest to retreat to. On the other hand, more specialized species that rely on larger patches of or more pristine forest tend to drop out. The result is burgeoning populations of the generalists and an overall decrease in biodiversity as the specialist species are out-competed.
- Host and parasite population dynamics – among other factors, most external parasites such as the black-legged or deer tick Ixodes scapularis, the vector for Lyme Disease, require a blood meal from their hosts in order to reproduce. As such, the more robust the host populations, the more successfully the tick can reproduce. So it’s not surprising that tick populations – and therefore our own personal tick encounters – are on the rise in step with the rising populations of deer and, even more importantly, white-footed mice.
- Host compatibility – white-footed mice display a couple features that make them especially complicit in the rise of the incidence of Lyme disease in Nova Scotia and other parts of the continent. First of all, it seems that burgdorferi likes to be in white-footed mice. Though the mice don’t seem to exhibit any significant disease from infection with B. burgdorferi, the bacteria can be found in their blood at relatively high levels for relatively long periods of time. Secondly, it turns out that white-footed mice are very permissive hosts for ticks. Studies comparing tick burdens in white-footed mice to tick burdens in other small forest rodents (including many of those wanting specialist species) show that white-footed mice are not nearly as diligent about removing ticks from their skin as they groom. That means more ticks have more time to pick up B. burgdorferi from and transfer it between their host mice and beyond.
The end result from these factors is high numbers of hungry black-legged ticks infected with B. burgdorferi. No wonder, then, that we are seeing more cases of Lyme disease infection in our pets and our families. So what can we do to protect ourselves and our pets?
- AVOID TICK EXPOSURE – This is the first line of defence. For us, that means wearing long-sleeved shirts and long pants tucked into your socks whenever you’re in tick habitat, and doing a thorough tick search immediately upon returning home. For our pets, we are fortunate to have some highly effective and very safe medications available that will kill ticks, should they bite, before they have a chance to transmit Lyme disease. A thorough tick search upon returning home is also appropriate; however, remember that the larval and nymph life stages are very small and easily overlooked, even on us let alone our furry companions.
- VACCINATION – Dog Vaccination technology is advancing rapidly, especially with the use of DNA techniques that allow the creation of vaccines that provide a complete protection with fewer adverse side effects. So though vaccination against Lyme disease is not appropriate for every pet, it can be done more safely and effectively than ever before for those for whom it is indicated.
Lyme disease ecology is not unique in its being a synthesis of environmental, host, and disease agent factors; the ecology of all diseases is a result of such interactions. They are complex and subtle, and to our eyes, it may seem that diseases are acting on their own. But it would behove us to keep our eyes and minds open to these webs of interactions so that we can better recognize, predict, and avoid creating the conditions, through our own actions, that allow diseases like Lyme disease to become a danger to our health and the health of our pets.
Written by Dr. Samantha Sanford