Ticks: Necessity or nuisance?

Photo: AnastazjaSoroka/Adobe Stock

Ticks play a crucial role in ecosystems and ecological balance, serving as food for various organisms, regulating wildlife populations, and contributing to biodiversity. However, humans often overlook their significance because of the diseases they transmit, raising questions about the necessity of ticks in our world.

Ticks transmit many pathogens, including bacteria, parasites, and viruses, which pose significant threats to human and animal populations globally through vector-borne diseases. These diseases can cause severe consequences for both humans and animals, ranging from mild discomfort to chronic illness and even death.¹ Alongside other arthropod vectors like mosquitoes and sand flies, ticks are pivotal to the spread of these diseases.

Furthermore, ticks enhance their effectiveness as disease vectors by manipulating host behavior and phenotypic traits. A study published in Pathogens discusses how pathogens such as Borrelia and Anaplasma can modify the behavior of tick vectors to increase their chances of survival and reproduction. The investigators found that infected ticks may exhibit increased mobility and blood engorgement, facilitating pathogen transmission to hosts. Additionally, infected ticks may develop greater resilience to environmental stressors such as desiccation and cold temperatures to improve their ability to survive and spread diseases.¹ These behavioral modifications not only increase the likelihood of pathogen transmission but also complicate efforts to control tick populations and mitigate disease risk.

Lyme disease

Originating from Lyme, Connecticut, Lyme disease rapidly became a public health concern. Early research revealed a correlation between the disease and the presence of ticks, particularly the black-legged tick. Understanding Lyme disease transmission required delving into the complex life cycle of ticks and the critical role of host dynamics and environmental factors in determining disease risk. Published in Fundamentals of Ecosystem Science, the study found that higher species diversity in host communities was associated with lower disease risk, as diverse communities provide fewer opportunities for efficient tick hosts to proliferate.² This finding underscored the importance of ecosystem health and biodiversity conservation in mitigating zoonotic disease transmission.

Further investigations into Lyme disease emphasized how environmental factors, such as acorn masting events (cyclic events in which trees produce large amounts of seeds) affect the abundance and distribution of tick populations. Mast seeding events led to surges in tick populations because of increased deer activity, while acorn failures reduced tick populations.²

Chronic wasting disease

In the context of chronic wasting disease (CWD), an infectious disease affecting cervids (mammals in the deer family), ticks may play a role in indirect transmission. In Scientific Reports, the investigators examine whether ticks can harbor prion protein (PrP) CWD, the infectious agent causing CWD, and contribute to disease spread among cervids. PrPCWDs are found in the blood and tissues of infected hosts, suggesting that ticks could pick up these prions while feeding on infected animals and transmit them to healthy individuals.³ The study demonstrates the potential for ticks to ingest and excrete PrPCWD, indicating that ticks may play a role in the natural transmission of the disease.

Takeaways

Moving forward, developing effective disease prevention and control strategies in both human and animal populations requires an understanding of the complexities of tick-borne disease transmission. Ticks undeniably play a role in ecosystems as part of complex food webs and biodiversity. However, the negative consequences of tick-borne diseases on human and animal health pose challenges for disease prevention and control. These factors may outweigh any potential benefits they may provide to the ecosystem, implying that ticks can be more of a nuisance than a necessity.

Ava Landry is a PharmD candidate, who is studying veterinary pharmacy at the University of Connecticut in Storrs.

REFERENCES

1. Benelli G. Pathogens manipulating tick behavior-through a glass, darkly. Pathogens. 2020;9(8):664. doi:10.3390/pathogens9080664
2. Ostfeld RS. Ecology of Lyme disease. In: Weathers KC, Strayer DL, Likens GE, eds. Fundamentals of Ecosystem Science. Academic Press; 2021.
3. Inzalaco HN, Bravo-Risi F, Morales R, et al. Ticks harbor and excrete chronic wasting disease prions. Sci Rep. 2023;13(1):7838. doi:10.1038/s41598-023-34308-3