A New Guide for Tick Researchers on Working With Mice
By Andrew Porterfield
Insect pests can be associated with either plant or animal hosts, but most entomologists aren’t equally comfortable working with vertebrates and plants. For research on ticks such as blacklegged ticks (Ixodes scapularis) and the western blacklegged tick (I. pacificus), the primary vectors of Lyme disease, handling mouse hosts can be challenging for the uninitiated.
To make matters worse, much of the information available on handling small mammals is scattered across literature, tutorials, protocols, and other sources. To help resolve these issues, Erika Machtinger, Ph.D., assistant professor of veterinary entomology at Pennsylvania State University, and Scott Williams, an entomologist with the Connecticut Agricultural Experiment Station, wrote a practical guide for trapping and handling mice in the genus Peromyscus, the most common host of Lyme disease ticks. Their guide appears in a new special collection on protocols in medical and veterinary entomology published last week in the Journal of Insect Science.
Because Peromyscus plays such a vital part in the spread of tick-borne disease, live-trapping the mice can help with surveillance research on ticks. When removed from captured animals, the ticks provide insight on their abundance as well as species, life stages, and vectored pathogens.
But using vertebrates can be problematic, certainly more so than working with plants. “It is important to remember that there are quite a few regulations involved with vertebrate research, both on an institutional level, and, if working with wildlife, a government level,” says Machtinger. “Some entomologists may have a background in animal science, wildlife, veterinary science, or similar, or maybe had experiences like working on a farm. For some who have had more experience working in plant systems, behavior, or other basic sciences, that may not be the case. I think this is more of a roadblock for entomologists who may not know where to start.”
The guide starts with experimental design, covering permits and dealing with safety risks as well as offering advice on design protocols and determining the personal protective equipment needed. Trap usage (the authors recommend H.B. Sherman traps, the most frequently used type for rodent studies), placement, tagging, and collection are also covered.
Trap setup is presented in detail, as these steps will ensure that the right test animals are captured and that they will represent the fauna in the field. Overnight setup (Peromyscus species are nocturnal), using the right number of traps for a field study, setting up grids, and placement in areas with the highest density of mice are all important considerations. Even with the best preparation, however, capture rates can range from zero to 50 percent, depending on area, season, and trapping efforts.
Sometimes, the authors note, it is advisable to work with a veterinary expert or experienced animal researcher, especially for medical procedures like anesthesia, euthanasia, tissue sampling, and other handling. Often this will be required by IACUC protocols, which at least demand that researchers demonstrate their proficiency in working with mice, Machtinger warned.
“Animals, wild animals in particular, can throw curveballs at you and you need to be really comfortable handling them,” she says. “When we are training undergraduates, I can’t tell you how many mice escape because they squeak or jump, or wriggle, and the students think they are going to hurt them. When you are properly trained on restraint, the handling process becomes much smoother and you get a feel for how to manipulate the animal.
“This also helps in animal welfare, too. The faster you can get through the procedure, the better it is for the animal!”
Ultimately, of course, the goal is to get access to ticks. Most ticks are found on the ears and faces of captured mice. Counts of visible ticks allow for comparisons of tick concentration between individual mice, but will underestimate the total number of ticks on a mouse. To arrive at an absolute tick abundance number, tick drop-offs (obtained by suspending the mice in a mesh cage above water) can yield even unseen parasites.
Trapping rodents is often taught by mentors, or researchers end up teaching themselves. Improving on that, this guide provides a practical protocol for working with mice (and accompanying ticks), and links to more detailed resources for in-depth, complex, or mixed-species trapping.
Journal of Insect Science
Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.