A practical protocol to prepare paraffin-embedded whole tick histology sections

Ticks are important ectoparasites that are capable of transmitting multiple classes of pathogens and are currently linked with many emerging tick-borne diseases worldwide. With increasing occurrences of tick-borne diseases in both humans and veterinary species, there is a continuous need to further our understanding of ticks and the pathogens they transmit. Whole tick histology provides a full scope of the tick internal anatomy, allowing researchers to examine multiple organs of interest in a single section. This is in contrast to other techniques that are more commonly utilized in tick-borne disease research, such as electron microscopy and light microscopy of individual organs. There is a lack of literature describing a practical technique to process whole tick histologic sections. Therefore, the current study aims to provide researchers with a workable protocol to prepare high quality paraffin-embedded whole tick histology sections. Amblyomma americanum adults were used as an example species for this study. After a series of pilot experiments using a combination of various fixatives, softening agents and processing techniques, we elected to compare two common fixatives, 10% neutral-buffered formalin (NBF) and Bouin's solution for whole ticks. Equal numbers of A. americanum unfed adults (n = 10/fixative) were processed identically and their whole tick histology coronal sections were individually scored. Higher scores were assigned to whole tick sections that contained more internal organs that are crucial for tick-borne disease research (e.g. salivary glands and midgut), high integrity of tissues and exoskeleton on the section, and good fixation and staining quality of the tissues. The mean total scores for Bouin's-fixed ticks were significantly higher compared to NBF-fixed ticks (p = 0.001). To further assess our preferred technique, we also demonstrated the feasibility of producing high quality whole tick sections for three other common tick species of medical importance (Rhipicephalus sanguineus, Ixodes scapularis, and Dermacentor variabilis) using Bouin's solution. While this technique may require further optimization for other tick species, we described a feasible protocol that uses commonly available tools, reagents and standard histologic equipment. This should allow any investigator to easily make adjustments to this protocol as needed based on their experimental goals.