Lyme disease researchers at the University of California, Irvine, have discovered that how a mouse’s immune system responds to different strains of Borrelia burgdorferi could help in the effort to reduce human cases of Lyme disease. Some strains of Lyme disease bacteria are more common than others and finding a shared trait may help in vaccine development so as to eradicate the infection before it even reaches humans.
Human Lyme Disease Vaccine Unlikely
Alan Barbour, lead author of the study printed last month in the journal of the American Society for Microbiology, says “There’s no human vaccine, and there’s not likely to be one.” Instead, Barbour and team are focused on finding a way of reducing the host reservoir of the Lyme disease pathogen so that ticks do not carry Borrelia and do not infect humans with Lyme disease even if they bite.
How Lyme Disease Spreads
This novel strategy for Lyme disease reduction concentrates on one of the major carriers of Lyme disease bacteria in North America, the white-footed mouse. These mice show a different immune system response to varied strains of bacteria that then allow some of the strains to reproduce significantly while others fail to multiply. Mice, unlike humans and dogs, do not develop symptoms of Lyme disease when infected with the bacteria. This allows the bacteria to remain mobile and spread further as new ticks bite the mice carrying Borrelia and, in turn bite other mice, deer, lizards, dogs, humans and other animals.
How Mice May Hold Key to Lyme Disease Prevention
Looking at the increasing number of Lyme disease cases and the emergence of as many as fifteen strains of Borrelia, the research team in California began to ask questions about how best to prevent disease in the absence of a human vaccine. What they found was that the mice fought off infection with some strains, leaving fewer bacteria in body tissues, while absent or lower immune system response resulted in higher density of bacteria and, therefore, an increased chance of ticks taking up the bacteria when feeding on the mice. Importantly, for Lyme disease prevention efforts, those strains eliciting a lower immune system response in the mice were the ones with the highest prevalence in the wild.
Targeted Vaccination of Mice Against Lyme Disease
In a strategy similar to that used to eradicate or reduce rabies, Barbour and his team suggest the placement of vaccine-laced food that would be consumed by the mice and which would target the most common strains of Lyme disease bacteria. The relatively short lifespan of mice in the wild would facilitate substantial reductions in the number of some of these strains of bacteria and have the effect of vastly reducing infection in humans as fewer ticks carry the bacteria to pass on through bites.
Lyme Disease Cases Increase, Healthcare Costs Rise
The increasing numbers of Lyme disease cases in the US is not only due to improved recognition of the infection but also due to the increased spread of ticks and host species and human contact with these courtesy of climate change, migration patterns and urbanisation of rural settings. Some 25,000 cases of Lyme disease are reported in the US each year but this is only considered a small percentage of the actual cases occurring and going unreported or unrecognized. The cost of diagnosing and treating the growing number of Lyme disease patients is thought to already range in the billions and with no human Lyme disease vaccine forthcoming, preventing the further spread of the infection is increasingly a priority for public health officials.
Helping Mice to Help Humans
Knowing more about the way white-footed mice respond to the proteins found in individual strains of Borrelia not only explains why so many varied strains exist in the wild but also allows for development of a mouse vaccine targeting multiple strains of Lyme disease bacteria. Any Lyme disease vaccine that is developed will need to be tested in the laboratory before being deployed in the wild but the hope is that such a development will lead to significant decreases in mice carrying Borrelia and, therefore, fewer human cases of Lyme disease in the longer term.
Baum E, Hue F, Barbour AG., Experimental Infections of the Reservoir Species Peromyscus leucopus with Diverse Strains of Borrelia burgdorferi, a Lyme Disease Agent. MBio. 2012 Dec 4;3(6). pii: e00434-12. doi: 10.1128/mBio.00434-12.