I recently attended the ASFWB meeting in Summerside, PEI and had the honour of taking home the 2nd place prize student presentation for my talk “What’s in your gut, leftovers or lunch? Determining if tick gut contents are blood meal remnants or a result of interrupted feeding.” At Mount Allison University in Sackville, NB our lab receives hundreds of ticks per year as part of the surveillance program conducted by my supervisor, Dr. Vett Lloyd. While cataloging our wild-caught, unfed, unengorged ticks we noticed that some blood was visible in the gut of the ticks. After consulting with an entomologist we were told that since ticks use a blood meal to acquire the nutrients necessary to molt to the next life stage, some blood will remain in the gut after the molting process is complete. I found this explanation unsettling, and after reviewing the images in our tick bank, I figured out why. Our surveillance program relies heavily on community involvement and many of the ticks submitted are removed from pets and people. Unengorged ticks that were found attached and feeding on a mammalian host, ie: had lunch in their gut, were virtually indistinguishable from ticks that had leftovers in their gut. If we couldn’t visually distinguish them, could we quantitatively distinguish between ticks that have previously fed and ticks that have molted but not yet fed? This is when I posed the question to my ticks – What’s in your gut, leftovers or lunch?
Ixodes scapularis, commonly known as deer ticks, transmit the Lyme disease causing spirochete bacterium Borrelia spp. during a blood meal. As ticks extract proteins from host blood, the salivary glands undergo physiological changes to allow secretion of excess liquid into the host. Simultaneously, Borrelia alters its gene expression to travel to the salivary glands. Transmission occurs with secretion of liquid containing Borrelia back into the host after 24-48 hours of feeding. Thus, ticks removed within 24 hours of attachment are not considered capable of transmitting Borrelia. If a tick is displaced before it completes feeding, movement of Borrelia to the salivary glands will have begun. Therefore, the bacteria may be able to infect a second host immediately upon feeding. This study examined whether the amount of blood in a tick gut indicates feeding status. I. scapularis were collected using passive and active surveillance in NB, NS and PEI and imaged using a dissecting scope. Various area and length measurements were taken for 122 unattached unengorged ticks and slightly engorged feeding ticks. Coxal, scutal, engorgement and blood meal indices were calculated using measurement ratios as estimations of tick size and engorgement. All variables were analyzed for differences between attached and unattached ticks using a t-test. Engorgement was the only index to reveal a significant difference between the estimated sizes of the attached and unattached groups; however, it was determined not to be biologically relevant. The inability to distinguish between the sources of blood in the gut indicates a potential problem in assessing the risk of bacterial infection based on tick engorgement. Unfed ticks and early stage re-feeding ticks are indistinguishable, but re-feeding ticks have the potential for more rapid transmission of Borrelia.
If you wish to contribute to my research and many other projects in our lab, please visit the following website for instructions on how to submit your tick: