Study uncovers new method of controlling tick populations

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An engorged brown dog tick feeds on a host.

Researchers at the Hebrew University of Jerusalem in Israel have discovered endosymbiotic bacteria to be essential in the reproductive processes of ticks. The study, led by Yuval Gottlieb, a professor at the Koret School of Veterinary Medicine at Hebrew University, found that L-proline is produced by Coxiella-like endosymbionts (CLE), suggesting CLE to be essential during states of high metabolic demand, like oogenesis and embryotic development.¹ These findings not only demonstrate the overall importance of nutritional symbionts on their hosts but could contribute to better control over tick populations and, in turn, tick-borne diseases.²

“Here, we show that B vitamins and L-proline, both of which contribute to tick reproductive fitness, are produced by CLE,” the authors of the study wrote on its significance.² “These findings demonstrate the importance of symbiont-derived metabolites for the host’s persistence and shed light on the complex bacteria-host metabolic interaction, which can be channeled to manipulate and control tick populations.”

Ticks are blood-feeding arthropods, so their diet is naturally deficient in essential B vitamins. As a result, ticks rely on endosymbiotic bacteria as a dietary supplement. The study specifically looked at the brown dog tick, Rhipicephalus sanguineus, its Coxiella-like symbiotic bacteria, and whether additional metabolites, like L-proline, were involved in this nutritional symbiosis.¹

The group tested the effects of antibiotic treatment on molting duration and suppression of CLE titers in emerged adults by performing antibiotic and saline treatments on engorged nymphs. They found the saline-injected nymphs molted significantly earlier than those injected with antibiotics, and tests revealed significant suppression of CLE titers in antibiotic-treated ticks, compared to the control group.²

Further tests found that the titer of L-proline was higher in saline-treated ticks, which supported the idea that CLE synthesizes L-proline. They compared the titers of L-proline and its precursor, L-ornithine, in organs with and without CLE. Free L-proline titer was more prevalent in the CLE-hosting organs of saline-treated ticks than in antibiotic-treated ticks. Titers of L-ornithine were significantly lower in the same organs of saline-treated ticks, implying that L-ornithine is converted to L-proline in those organs.²

Next, the group allowed adult female ticks to mate and feed on rabbit hosts for 3 weeks. Despite similar feeding times among all treatment groups, CLE-suppressed ticks consistently weighed significantly less than control ticks. Ticks rescued post-feeding and treated with B vitamin and B vitamin + L-proline recorded egg mass weight and hatching rates most similar to the control group. These findings suggest that CLE is essential for tick fecundity and demonstrate the importance of B vitamins and L-proline, especially during embryonic development.²

“This study underscores the importance of nutritional symbionts in the health and reproduction of ticks,” Gottlieb said in a news release.¹ “Our findings can open new possibilities for developing strategies to control tick populations and mitigate tick-borne diseases.”

Tick-borne diseases are a major issue, with the US Centers for Disease Control and Prevention approximating that 50,000 people visit emergency rooms each year due to tick bites, a number that has more than doubled since 2004.³ Tick bites can lead to illnesses including Lyme disease, Rocky Mountain spotted fever, and anaplasmosis, through transmission of harmful pathogens. The effects of these diseases can range from joint pain to death, if not properly treated.¹

References

1. Bacteria Inside Ticks Might Offer New Approach to Disease Prevention, According to New Hebrew University Study. News release. A. Lavin Communications. August 14, 2024. Accessed August 14, 2024. https://apigateway.agilitypr.com/distributions/history/d3b44e4f-f0aa-4298-be7c-4e88e44f6fc4?recipientId=b17db3b3-7218-4a70-b990-9eca5c2c50ce
2. Cibichakravarthy B, Shaked N, Kapri E, Gottlieb Y. Endosymbiont-derived metabolites are essential for tick host reproductive fitness. ASM Journal. 2024;9(7). https://doi.org/10.1128/msphere.00693-23
3. Marx G, Spillane M, Beck A, Stein Z, Powell A, Hinkley A. Emergency Department Visits for Tick Bites ­­­— United States, January 2017–December 2019. MMWR Morb Mortal Wkly Rep. 2021;70:612–616. DOI: http://dx.doi.org/10.15585/mmwr.mm7017a2