300,000 Americans are diagnosed with Lyme disease each year, not 30,000 as previously thought. The CDC announced this new estimate in August 2013 during the 13th International Conference on Lyme Borreliosis and other Tick Borne Diseases (ICLB). The event was held in Boston and co-chaired by Dr. Linda Bockenstedt , Yale University School of Medicine.
Prior to the ICLB conference, JEOL USA provided Dr. Bockenstedt with SEM images of her deer tick specimens, both whole and cross-sectioned. Dr. Bockenstedt does not use SEM in her lab, so seeing the micrographs gave her a different perspective.
Images inform studies of ticks
Dr. Bockenstedt explains: "We use 2-photon intravital microscopy to image how ticks feed and movement of the Lyme disease spirochete Borrelia burgdorferi between the tick and the mouse host in real time, so we need to understand the anatomy of the tick mouthparts very well. Other labs study migration of the spirochetes from the midgut (the largest empty black space in the cross section above) to the salivary glands during tick feeding. Our interest in the EM images is primarily in the hypostome area (the region with the spade-like serrated mouthpart ), particularly the dorsal and ventral aspects and how they move in relation to each other, as well as the chelicera (the paw-like appendages on either side of the hypostome). Having the close up structures revealed by EM helps inform us about what we are seeing when we image the active process of tick feeding in real time."
One meal = one growth stage
Deer ticks can be difficult to detect when they attach themselves to mammals, and people often don't realize they've been host to one. "The larva are very small and after feeding enlarge to the size of a poppy seed. The nymphs are about the size of a pen tip and after engorgement are the size of a sesame seed. The adults are about the size of a sesame seed prior to feeding (or a bit bigger if female) and enlarge to the size of a raisin after feeding. These Ixodes species ticks feed only once per development stage," Dr. Bockenstedt says.
Transmitting the infection
Only the deer tick - or the spirochetes they transmit through feeding - causes Lyme disease. "The spirochetes that cause Lyme disease are only transmitted by Ixodes species ticks, no other insect or arthropod. Larvae do not harbor the spirochetes but pick them up after feeding on an infected rodent. They can remain infected throughout their lifespan after molting to nymphs and adult ticks. Nymphs are the most common tick form that transmit infection to humans because they have more promiscuous feeding patterns than the adult ticks, which prefer deer. Also, adult ticks are larger than the nymphs and more easily recognized and removed before spirochetes are transmitted, which takes at least 24 hours of tick attachment."
"Our lab is mainly studying the pathogenesis of tick-borne disease in animal models. Although we have focused our efforts on Lyme disease, we hope to apply our imaging techniques to study the biology of other tick-borne pathogens responsible for human disease, including the red blood cell parasite Babesia microti and the newly recognized relapsing fever spirochete Borrelia miyamotoi."
Dr. Bockenstedt describes some of the images from the SEM
"I was fascinated by the overall changes in topography of the tick — the spikes and barbs that come out of some regions (fourth image, left), the armor-like plates and the corrugation in the area of the body (bottom image) that may facilitate its expansion during feeding.
The cheliceral sheath (1st image) has a rough surface resembling papilla.
The appearance of the spiracular plates (3rd image), the aperture through which respiration (gas exchange) occurs, can help identify tick species. Ticks are very susceptible to desiccation, so this structure also limits water loss during gas exchange.