In keeping with the creepy-crawly theme for early Spring, today’s post highlights a news story from this week about Lyme disease. We probably all know people and pets that have had to deal with the debilitating effects of this disease. Did you know that ticks collected on Long Island in the 1940’s carried the Lyme bacteria? We tend to think Lyme disease is “new,” but it really has been around for a long time. Why does it seem like more and more infections occur now? It’s partly because the infection is being diagnosed and reported more often. But it’s also related to the deer population, which has rebounded from practically nil in Southern New England in the early 20th century. Human behavior is also a factor: we are increasingly building and living in previously rural areas, thereby increasing our contact with ticks.
The study published in the Journal of Infectious Diseases focuses on breaking the transmission cycle of the bacteria (Borrelia burgdorferi) that causes Lyme disease. Black-legged ticks (also called deer ticks) are the vector in this scenario. The life cycle of the deer tick spans two-years; that is, it takes two years to go from egg, through three developmental stages, reproduce, and then die. Throughout those two years, each tick takes a blood-meal on three separate occasions. A deer tick isn’t hatched infected with Borrelia. Infection occurs when the tick larva takes its first blood-meal on a previously infected reservoir host, which is usually a white-footed mouse. After feeding the tick molts to the next stage (called a nymph) and lies dormant until the following spring, at which time it feeds again (likely on a white-footed mouse but also on other mammals including people) and spreads the infection. The tick molts again into an adult and takes another blood-meal (another opportunity to spread infection), then it lays eggs and dies.
So some really smart people thought, “What if we could vaccinate the white-footed mouse population to stop Lyme disease transmission in its earliest stages?” They used a strategy that the USDA has successfully employed to combat rabies disease in wildlife for over ten years: dropping bait containing vaccine that is eaten by the animals. After the mice eat the bait, their immune systems produce antibodies against Borrelia. Later, if they are bitten by infected ticks, the antibodies defeat the bacteria and infection does not occur.
The results of the field study with this vaccine are promising. The study was conducted in New York state, in an area where Lyme disease is prevalent. After the first year of the study, ticks (in the nymph stage) showed a 23% reduction in Lyme infection. By year 5 of the study, the incidence of Lyme had dropped by 75%! The study authors note that in order to collect ticks for testing and obtain blood samples from mice, they had to use bait in live traps. They expect even better results when the vaccine pellets are distributed widely, such as how the rabies vaccine bait program is conducted. They also note this approach is economical: it costs around $20 to treat one acre of land.
In the future, we may each have our own little mouse feeding station in our backyard that we fill with Lyme vaccine pellets. How cute is that? I think this is a win-win approach. We reduce the transmission of the bacteria causing Lyme disease without using pesticides in a cost-effective manner. What do you think? Would you sign up for a tiny mouse house in the corner of your backyard?