Exotic Rickettsiae in Ixodes ricinus: fact or artifact?

Area of Science:

• Veterinary Microbiology
• Molecular Biology
• Public Health

Background:

• Pathogenic Rickettsia species are transmitted by Ixodes ricinus ticks, posing risks to humans and animals.
• Tick surveys often detect diverse Rickettsia sequences using the 16S rRNA gene, complicating identification.

Purpose of the Study:

• To address the challenges in interpreting Rickettsia sequences found in ticks.
• To caution against the premature classification of novel or pathogenic Rickettsia species based solely on sequence data.

Main Methods:

• Review of existing literature on Rickettsia detection in Ixodes ricinus ticks.
• Analysis of sequence data interpretation, including potential misidentification of species.
• Examination of alternative sources for rickettsial DNA in tick samples.

Main Results:

• A recent study potentially misidentified Rickettsia helvetica as Rickettsia australis in European ticks.
• Rickettsial DNA in tick lysates can originate from non-pathogenic sources like endosymbionts or environmental contamination.
• Horizontal gene transfer is also a potential source of rickettsial DNA.

Conclusions:

• Caution is advised when reporting new or pathogenic Rickettsia species based on tick-derived sequences.
• Distinguishing between viable pathogens and other DNA sources is crucial for accurate risk assessment.
• Further investigation is needed to understand the origin and implications of diverse Rickettsia sequences in ticks.