Opinion: The science of Lyme disease
I am writing to simply ensure that we, as Block Island residents, are fully informed about our collective desire to reduce Lyme disease on the island via substantial reduction of the deer herd population. Most islanders are convinced that by drastically reducing the deer herd on the island we will virtually assure an equivalent reduction in Lyme disease incidence. The vast majority of us take this for granted, and assume that this correlation between Lyme disease and deer herd population has been confirmed and fully examined. This correlation and the facts surrounding this very difficult situation are not nearly as clear cut as we all would like. At the very least, we should understand and consider the following facts, issues and topics before moving forward with such an extreme course of action (details related to each follow the list):
The measured incidence of Lyme disease in the U.S. has gone up 1,200 percent (12 times) since 1999, currently growing at 15 to 20 percent per annum — Block Island is not unique in this rapid growth;
In communities that have initiated public testing programs (such as Block Island), the growth rate of incidence has spiked significantly;
Deer do not carry or transmit the bacteria responsible for Lyme disease, small rodents such as mice, rats and birds have this honor — ticks do not get infected by the deer;
Many scientists and researchers do not agree that deer herd reduction will result in a decrease in Lyme disease incidence;
Two (2) Yale University professors are currently conducting research on Block Island related to understanding why Block Island’s measured incidence rate is so high. Their theory is related to the small mammals on Block not solely the deer herd population;
Virtually all scientists and researchers agree that if any reduction is possible from deer herd reduction, the deer population must be reduced to less than 10 deer per square mile before any meaningful reduction in Lyme disease will likely be seen. This translates to a 90 percent or greater reduction for Block Island — removing nearly 1,000 deer from the island herd;
Monhegan Island in Maine is very different from Block Island, and we cannot reasonably expect the same results;
A large increase in Lyme disease incidence is virtually assured for 2 to 3 years after a “successful” deer herd reduction program; and
After a “successful” deer herd reduction program, the other local large mammals (dogs, cats, cattle, horses, etc) will see a significant increase in tick bites and Lyme disease (when susceptible).
The measured incidence of Lyme disease in the U.S. has gone up 1,200 percent (12 times) since 2000. This is very important to consider when examining the issue overall. Although Block Island’s measured incidence has gone up dramatically over the past decade, the incidence rate across the U.S. and, in particular, the northeast has also gone up dramatically. Much of this increase can be attributed to general awareness and better testing capabilities. Clearly there are other factors to consider; however, we must examine Block Island’s sharp increase in incidence against a proper statistical background.
Additionally, when public testing has been encouraged or programs developed, the incidence rate virtually always spikes beyond the expected results. This is primarily due to awareness. It is widely assumed by the scientific and medical establishment that the vast majority of Lyme disease infections are not tested or more importantly not acknowledged by those infected. This is an important concept to understand when viewing rising statistics of measured incidence as the actual act of testing/measuring has increased many fold during the same period of time.
Deer do not carry or transmit the bacteria responsible for Lyme disease. This very critical fact is typically not well understood by most people affected by Lyme disease. Deer ticks become infected in their early life when, as nymphs, they attach to small mammals such as mice and rats. Certain small mammals are much better carriers of the bacteria than others, as a result the local diversity and populations of small mammals in any given area are very much directly related to the infection rate of ticks in that area.
Block Island appears to have a very high infection rate of deer ticks due to the types of small mammals available. In fact, this theory is currently being researched on Block Island by two Yale’s professors, Maria Diuk-Wasser and Durland Fish. They hope to determine how the unique population of small mammals on Block Island is contributing to the high Lyme disease incidence rate and if a process called “dilution” could be applied to Block Island to help control the tick infection rate and therefore the disease incidence in humans.
Many scientists and researchers do not agree that deer herd reduction will result in a decrease in Lyme disease incidence. If one were to spend any time researching the various studies, theories and research surrounding this issue, it quickly becomes clear that the scientific community is split on this issue. Many researchers, as referenced above, are focused on the small mammal populations and believe that deer can easily be replaced by other large mammals present in the area. Clearly, when no other large mammals are available (as on Monhegan Island), reduction in the deer herd becomes more obvious and viable. Remember the deer or other alternative large mammals only act as hotels and food sources for the ticks and do not infect them. However, a high density of available large mammal population does increase the overall tick population without doubt.
The deer population must be reduced to less than 10 deer per square mile before any meaningful reduction in Lyme disease will likely be seen. Even the most adamant scientists on the side of deer reduction are clear that in order to be an effective strategy, the deer herd population must be reduced to less than 10 deer per square mile. To put this in perspective, Block Island is roughly 9.75 square miles with approximately 900 to 1,250-plus deer depending on what source you use.
In order to meet the minimum threshold for reduction to be potentially effective, we would need to kill or remove approximately 1,000 deer from the herd. And this does not account for population growth each and every year. Clearly, it would take many years to complete such a strategy and with the deer herd growing by approximately 200-plus per year, we are looking at killing or removing close to 2,000 deer to meet the minimum effective threshold density. Please stop and take a moment to consider this number. First off, it’s difficult to imagine purposefully killing 2,000 of any innocent animal, however; more importantly, it would be virtually impossible.
Monhegan Island in Maine is very different from Block Island, and we can not reasonably expect the same results. The total deer herd population on Monhegan Island was 52 prior to their efforts to remove the deer. It took them three years of concerted effort to successfully remove the entire herd of 52 from the island. Even when considering this relatively small task, when comparing to our herculean one, what is critical to realize is that virtually all the deer habitat on Monhegan Island is and was owned by a single entity — Monhegan Associates (a trust which owns 380 of the total 513 acres on the island — as compared to Block’s 6,230 acres).
With this huge advantage, the hired hunters basically had access to virtually all of the area inhabited by deer. This is not the case on Block as much of the land inhabited by the deer is diversely owned, private land and many of these private owners will not allow hunting on their land. This inconvenient fact must be understood to truthfully determine viability of such a plan. With this being the case, it becomes nearly impossible to even imagine a 5-plus year program being successful at meeting the minimum reduction to 10 deer per square mile — or reduction to less than 100 deer total.
A large increase in Lyme disease incidence is virtually assured for 2 to 3 years after a “successful” deer herd reduction program. An important part of any deer reduction strategy must be coupled with the knowledge and resulting plan on how to deal with one of the better known side effects — a corresponding increase in human tick bites and resulting Lyme disease for two to three years after completing the deer herd reduction. This has been witnessed in virtually all studies (including Monhegan Island). We need to be prepared for this marked increase and its impact on the island and its tourism-based economy. Even if we aren’t successful in meeting the minimum reduction threshold, we will more than likely still suffer this side effect with any material reduction in the deer herd.
After a “successful” deer herd reduction program, the alternative large mammals (dogs, cats, cattle, horses, etc) will see a significant increase in tick bites and Lyme disease (when susceptible). Since Block Island is unlike Monhegan Island in that we have a much more diverse large mammal population, we need to be cognizant of this side effect. During the 5-plus years required for any deer reduction program, our dogs, cats, horses and cattle will become much more likely to be infested by ticks — this is without question. We need to have a plan in place to guard against this unwanted side effect.
Lyme disease is most certainly a major issue for Block Island and for much of the northeast. We are only beginning to fully track its actual incidence rates through proper testing and awareness. Before we undertake any drastic measures to decrease the incidence rate on Block Island, we first should understand the viability of these potential measures and what their potential side effects are.
The people of Block Island should realize that to reduce the deer herd to less than 10 per square mile will be extremely difficult and would almost certainly take more than five years to even attempt. It is quite likely that such an effort will miss the required reduction goal and thus likely not have a notable impact on Lyme disease. In fact, it appears that it may be more likely to have a negative impact on the residents. Clearly we should get the facts, understand the risks, the viability and potential side effects.
Perhaps the first place to start is to have a meeting and conversation with the Yale professors who are currently doing research on this very topic here on Block Island. Last but not least, we should never take lightly the killing of 2,000 innocent animals without fully understanding the situation and being 99 percent certain that such a brutal effort will produce the desired results.
Knowledge is power.
Peter Capuciati lives on Mohegan Trail.