Exploring how environmental factors might relate to the presence of pathogen-carrying ticks
The work of understanding why some ticks carry pathogens and others do not, while not straightforward, is important.

A new paper published in PeerJ explores the location of pathogen-carrying ticks. It also highlights the significance of big data in biology.
The environment, including things like temperature, rainfall, humidity, and the type of plants, affects where ticks can live, how active they are, and their chances of surviving. Ticks are known for spreading diseases to humans by carrying harmful bacteria. Two types of ticks, black-legged (Ixodes scapularis) and the lone star (Amblyomma americanum), are common in the central and eastern parts of the United States and can transmit these pathogens.
While there have been studies that look at environmental data to predict where ticks might live, none has compared the environment for both the ticks and the diseases they carry. Researchers Abdelghafar Alkishe, Marlon E. Cobos and A. Townsend Peterson wanted to know whether the pathogens have environmental needs distinct from those of their tick hosts.
Using a database developed by the National Ecological Observatory Network (NEON), they looked at the distribution of two types of ticks: the black-legged and the lone star. The data covered sites across nine states in central and eastern United States and they drew information on almost 88,000 individual ticks. They also used the database to examine whether the pests were carrying any of nine bacteria commonly found in the two species.
The researchers then looked at temperature records and the level of moisture in the air around the time the ticks were collected. They were trying to determine how environmental conditions affected both the spread of ticks and the spread of the bacteria.
They used two different methods to test this: a univariate analysis – which looks at one environmental factor at a time – and a more complex statistical test called permutational multivariate analysis of variance, or PERMANOVA.
For the lone star tick, the researchers tested for three pathogens: Borrelia lonestari, Ehrlichia chaffeensis, and E. ewingii. The univariant test showed that the spread of all three bacteria was affected by at least one environmental factor, such as temperature or humidity. In the PERMANOVA test however, only the pathogen E. ewingii showed a significant difference between its environmental needs and those of its host.
For the black-legged tick, the researchers looked for six pathogens: A. phagocytophilum, Babesia microti, Borrelia burgdorferi sensu lato, B. mayonii, B. miyamotoi, and Ehrlichia muris-like. Univariate analysis found that all but the B. miyamotoi bacteria had environmental preferences that were different from those of the ticks.
The PERMANOVA test, on the other hand, showed two pathogens, B. microti and B. burgdorferi, differed from the ticks in how they respond to the environment. B. microti had a smaller range of environmental tolerance compared to the tick, while B. burgdorferi had a larger one.
Overall, this study highlights the importance of large-scale data, especially when it comes to tracking where pathogens exist and where they don’t. This information can clarify the spread of diseases and the environmental conditions that support it.
Citation
Alkishe, A., Cobos, M. E., & A. Townsend Peterson. (2024). Broad-scale ecological niches of pathogens vectored by the ticks Ixodes scapularis and Amblyomma americanum in North America. PeerJ, 12, e17944. https://doi.org/10.7717/peerj.17944