To stand any chance of cutting the rising rates of Lyme disease in the US and Canada we need to look to the population of white-footed mice. This is because these animals are super-hosts of Lyme disease bacteria, meaning that while ticks can overwhelm and kill moose and other animals they appear to have little effect on these mice, allowing them to carry on with their lives and act as a key disease reservoir.
Lyme disease is thought to affect around 300,000 people a year in the US, although most cases fail to be reported to the CDC resulting in inaccurate official counts. Where Lyme disease is quickly recognised, diagnosed, and treated with antibiotics it is usually a temporary infection with no lasting effects. However, where a person goes undiagnosed and/or untreated Lyme disease can cause damage to a wide range of tissues in the body and, in some cases, cause lingering effects even after the infection is treated.
Mice Central to Lyme Disease Control
Those who live in areas where white-footed mice are present are at particular risk of contracting the infectious disease, with new research from Sarah Lawrence University showing that these mice can carry hundreds of ticks without any increase in adverse effects over and above those hosting just a few ticks. Not only does this research suggest the importance of looking at how mice are able to resist the effects of ticks, it also highlights the need to roll out the oral bait vaccine developed specifically with mice in mind.
This vaccine was designed so that mice who fed on the vaccine-laced food would then go on to develop antibodies to the Lyme disease bacteria, leading to the death of any bacteria to which the mouse was later exposed. As such, mice who carry hundreds of infected ticks could clear those ticks of Borrelia burgdorferi and make them less of a hazard when the ticks go on to get their second blood meal from a human, dog, cat, horse or other animal vulnerable to Lyme disease.
Mice the Perfect Super-Hosts for Lyme Disease Bacteria
The researchers at Sarah Lawrence expected to find that an abundance of ticks would negatively affect the white-footed mice and actually help control mouse populations. However, it appears that the mice are incredibly resilient to the effects of playing host to the ticks. A recent mass moose die-off has been blamed on a winter tick population boom as these ticks literally drain the blood of the moose. The same thing has not happened with mice.
Mice and Ticks and Population Control
Of course, in many cases, ticks carry more than just Lyme disease bacteria, meaning that a tick that has fed on a mouse vaccinated against Borreli burgdorferi may still cause infection and illness in any human or other animal it subsequently bites. These ticks may carry bacteria responsible for Bartonella, Babesia, Ehrlichiosis and other conditions that are often co-infections with Lyme disease.
Still, controlling mouse populations and using them as a way of eradicating Lyme disease bacteria could be a key component in the strategy for Lyme disease prevention. Mice have done well from land development for human use as the fragmentation of forests has led to a decline in predators such as coyotes, foxes and owls, as well as reduced competition from other small animals that need larger areas of unbroken land. Increased acorn harvests, as well as climate change, have also been favourable to white-footed mice in recent years.
Forest Management and Vaccination for Lyme Prevention
Research carried out by biologists at Bard College revealed that in areas of forest smaller than 3 acres there were an average of 3 times as many ticks compared to larger areas of forest. What’s more, in smaller areas as many as 80% of ticks were infected with Lyme disease bacteria. Limiting forest fragmentation and vaccinating mice using the oral bait vaccine could dramatically reduce the population of ticks and the proportion of ticks infected with Lyme disease bacteria. The oral bait vaccine reduced infection by 70% after four years in one study and as a human Lyme disease vaccine is still not available this seems the best option so far for controlling the disease.