Sara Moutailler, Claire Valiente Moro, Elise Vaumourin, Lorraine Michelet, Florence Hélène Tran, Elodie Devillers, Jean-François Cosson, Patrick Gasqui, Van Tran Van, Patrick Mavingui, Gwenaël Vourc’h, Muriel Vayssier-Taussat
Published: March 17, 2016



Ticks are the most common arthropod vectors of both human and animal diseases in Europe, and the Ixodes ricinus tick species is able to transmit a large number of bacteria, viruses and parasites. Ticks may also be co-infected with several pathogens, with a subsequent high likelihood of co-transmission to humans or animals. However few data exist regarding co-infection prevalences, and these studies only focus on certain well-known pathogens. In addition to pathogens, ticks also carry symbionts that may play important roles in tick biology, and could interfere with pathogen maintenance and transmission. In this study we evaluated the prevalence of 38 pathogens and four symbionts and their co-infection levels as well as possible interactions between pathogens, or between pathogens and symbionts.

Methodology/principal findings

A total of 267 Ixodes ricinus female specimens were collected in the French Ardennes and analyzed by high-throughput real-time PCR for the presence of 37 pathogens (bacteria and parasites), by rRT-PCR to detect the presence of Tick-Borne encephalitis virus (TBEV) and by nested PCR to detect four symbionts. Possible multipartite interactions between pathogens, or between pathogens and symbionts were statistically evaluated. Among the infected ticks, 45% were co-infected, and carried up to five different pathogens. When adding symbiont prevalences, all ticks were infected by at least one microorganism, and up to eight microorganisms were identified in the same tick. When considering possible interactions between pathogens, the results suggested a strong association between Borrelia garinii and B. afzelii, whereas there were no significant interactions between symbionts and pathogens.


Our study reveals high pathogen co-infection rates in ticks, raising questions about possible co-transmission of these agents to humans or animals, and their consequences to human and animal health. We also demonstrated high prevalence rates of symbionts co-existing with pathogens, opening new avenues of enquiry regarding their effects on pathogen transmission and vector competence.

Author Summary

Ticks transmit more pathogens than any other arthropod, and one single species can transmit a large variety of bacteria and parasites. Because co-infection might be much more common than previously thought, we evaluated the prevalence of 38 known or neglected tick-borne pathogens in Ixodes ricinus ticks. Our results demonstrated that co-infection occurred in almost half of the infected ticks, and that ticks could be infected with up to five pathogens. Moreover, as it is well established that symbionts can affect pathogen transmission in arthropods, we also evaluated the prevalence of four symbiont species and demonstrated that all ticks were infected by at least one microorganism. This work highlights the co-infection phenomenon in ticks, which may have important implications for human and animal health, emphasizing the need for new diagnostic tests better adapted to tick-borne diseases. Finally, the high co-occurrence of symbionts and pathogens in ticks, reveals the necessity to also account for these interactions in the development of new alternative strategies to control ticks and tick-borne disease.

To which we all said AMEN!

A few notes on the study:  To see a chart showing exactly what coinfections and symbionts they looked at, go to the link for the study.  They looked at 6 strains of borrelia (Lyme), Anaplasma, Ricketssia helvetica, Bartonella, Babesia, and Neoehrlichia mikurensis (Order: Rickettsiales, Family: Anaplasmataceae).  The symbiots looked at were:  Wolbachia, Spiroplasma, Acinetobacter, and Midichloria mitochondri.

While I am unfamiliar with most of the symbionts, Wolbachia concerns me as scientists are actively inserting Wolbachia into mosquitoes and releasing them into the wild in efforts of eradicating Dengue Fever, Chikungunya, yellow fever, and possibly even Malaria.  While scientists claim Wolbachia, a gram-negative bacterium in the family of Rickettsiales, can not infect humans, they can and do infect worms which cause human disease.  Since nematodes have been found in ticks and many Lyme/MSIDS patients have to treat for worms, the question begs to be asked, “Does Wolbachia play a role in Lyme/MSIDS?”  This is a question I plan on writing about, but the answer could very well be, “Yes.”  I certainly pray that more research on Wolbachia in relation to Lyme/MSIDS is done as this could definitely be a fly in the proverbial ointment.

Lastly, I believe recorded coinfection numbers to be abysmally low.  My own LLMD doesn’t even test for them, he feels the tests are that poor.  Also, probably the numbers reflect the most severe cases – leaving many out.  As you are aware, coinfections are notorious for presenting differently than the textbook presentations that most doctors are familiar with. Dr. Horowitz writes and speaks about this often.

Published on Nov 3, 2014
At the “Symposium on Tick-borne Diseases” held May 17, 2014

37:30 You will only find a positive test for Babesia if the level of parasitima in the blood is greater than 5%.  38:05 Medical textbooks also state you should have hemolytic anemia, thrombocytopenia, and renal failure if you have Babesia.  Dr. Horowitz states he has not had one Lyme/MSIDS patient present this way.  

How many doctors are going to think outside their medical textbooks?