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Updated: Apr 5, 2026
Extraction of Saliva, Haemolymph, Salivary Glands, and Midgut from Individual Ticks (Acari: Ixodidae)
Published on: October 31, 2025
Ultrastructure of Presumed "Candidatus Rickettsia Andeanae" in Amblyomma maculatum (Acari: Ixodidae)
F A G Ferrari1, J Goddard2, C D Paddock3
1Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, 240 Wise Center Drive, Mississippi State, MS 39762, USA.
Abstract:
Amblyomma maculatum Koch, 1844 (also known as the Gulf Coast tick) is found in parts of the Americas, including the central and southern United States. Its primary importance is as the vector of Rickettsia parkeri, a spotted fever group rickettsia that causes an illness similar to, but milder than, Rocky Mountain spotted fever. A second spotted fever group rickettsia, "Candidatus Rickettsia andeanae," was detected in Gulf Coast ticks approximately 10 yr ago. However, the significance of this organism, including pathogenicity, has not yet been well-characterized. Here, we use transmission electron microscopy to describe bacteria within the tissues of A. maculatum ticks that were positive by polymerase chain reaction assay for "Ca. R. andeanae." In ultrathin sections of unfed A. maculatum adult females, we found evidence of bacteria with morphological features consistent with spotted fever group rickettsiae, including small size (≈0.3 by 0.9 μm), a halo zone (electron-lucent layer around the bacterium), and a trilaminar cell wall. In female ticks, bacteria were present in granular salivary glands and ducts, foregut, Malpighian tubules, nerve trunks, and reproductive tissue. These findings demonstrate evidence of "Ca. R. andeanae" in situ and contribute to our understanding of this novel rickettsia in A. maculatum.
Insights
Gulf Coast ticks carry "Candidatus Rickettsia andeanae," a novel spotted fever rickettsia. Transmission electron microscopy revealed these bacteria within various tick tissues, aiding understanding of this pathogen.
Area of Science:
- Veterinary Entomology
- Microbiology
- Pathogen Discovery
Background:
- Amblyomma maculatum (Gulf Coast tick) transmits Rickettsia parkeri.
- A novel spotted fever rickettsia, "Candidatus Rickettsia andeanae," was previously detected in Gulf Coast ticks.
- The pathogenicity and significance of "Ca. R. andeanae" remain poorly understood.
Purpose of the Study:
- To describe the in situ presence and morphology of "Ca. R. andeanae" within Amblyomma maculatum ticks.
- To investigate the distribution of "Ca. R. andeanae" in various tissues of the Gulf Coast tick.
Main Methods:
- Polymerase chain reaction (PCR) assay to confirm the presence of "Ca. R. andeanae."
- Transmission electron microscopy (TEM) to visualize bacteria within tick tissues.
- Ultrathin sectioning of unfed adult female A. maculatum ticks.
Main Results:
- Bacteria with morphological characteristics of spotted fever group rickettsiae were observed in A. maculatum.
- Observed bacteria exhibited small size (≈0.3 by 0.9 μm), a halo zone, and a trilaminar cell wall.
- These bacteria were found in salivary glands, ducts, foregut, Malpighian tubules, nerve trunks, and reproductive tissues of female ticks.
Conclusions:
- This study provides in situ evidence of "Ca. R. andeanae" within Amblyomma maculatum.
- The findings contribute to the characterization of this novel rickettsia and its presence in the Gulf Coast tick.
- Further research is needed to fully elucidate the pathogenicity of "Ca. R. andeanae."
