Tracking Pathogen-Carrying Ticks and the Diseases They Spread

​Ticks spread a lot of disease in the U.S. If we understand where ticks live, can we stop the spread of tick transmitted disease in its tracks? A new study published by scientists at the CDC claims that maybe we can. Read on to find out exactly how researchers are trying to reduce illness spread by ticks through surveillance and monitoring.

Blacklegged or deer ticks are feared and recognizable in the U.S. due to their association with Lyme disease. Photo credit: Erik Karits (https://unsplash.com/@erik_karits?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText)

Pathogens transmitted to humans by ticks can cause severe illness, even death. Additionally, allergic responses to tick bites, such as alpha-gal syndrome, can severely impact people’s quality of life. In the U.S., tick transmitted diseases account for over 75% of reported illnesses spread by vectors (animals such as insects and ticks that spread pathogens to other animals). In fact, cases of tick transmitted disease more than doubled from 2004-2016 according to the CDC.
 
Some of the problems created by ticks are new and/or poorly understood by the medical community. Scientists recently found a new, invasive tick that has the potential to spread germs to humans and animals. However, public health professionals still have questions about native ticks as well, such as the blacklegged (deer) tick.

​WHERE DO TICKS LIVE?
 
Recently, medical entomologists at the CDC published a survey outlining places in the U.S.  where people may encounter blacklegged ticks and their associated pathogens. This is important, because previously, knowledge about where ticks and their illnesses occurred was limited to local data. We did not know the full range. Additionally, what data did exist was not always publicly accessible. No single database existed, and unfortunately, a lot of data has been lost over the years.

Disease surveillance programs use distribution maps to help understand risk of infection based on location. In this map, researchers separated distribution based on tick species and pathogen. Image credit: Fleshman et al. 2022 (https://academic.oup.com/jme/advance-article/doi/10.1093/jme/tjac049/6588091?login=false)

To produce maps visualizing where ticks and pathogens exist, authors compiled tick surveillance data from 2004-2021 by analyzing surveillance records, published research, and archives from public health websites. The results give us the most current idea of where blacklegged ticks reside in the U.S. as well as where exposure risk is highest for some common illnesses. 
 
The CDC data also revealed that Lyme disease (caused by two types of bacteria) is the most widely reported illness- found in 476 counties, 29 states, and the District of Columbia. Authors noted that pathogen distribution is narrower than tick distribution, and disease cases are likely underreported. For instance, many people do not know that they have Lyme disease and are misdiagnosed. 
 
The authors of this paper are filling huge knowledge gaps, especially for areas where ticks are occurring for the first time. However, this study only focused on two species of blacklegged ticks and seven pathogens that cause the following diseases: Lyme disease, hard tick relapsing fever, anaplasmosis, babesiosis, Powassan virus disease, and ehrlichiosis. There are still other species of ticks that can cause other diseases in the U.S. not focused on in this publication.
 
However, not all ticks can transmit pathogens to people. For pathogen transmission to occur, the correct tick species infected with enough pathogen must bite a person. Then, the tick must bite long enough to transmit the pathogen successfully. How long pathogen transmission takes depends on the tick and pathogen in question. Additionally, pathogens and diseases are typically associated with specific ticks. For instance, as of now, scientists have only found Powassan virus in three species of ticks including the blacklegged ticks.
 
FINAL THOUGHTS
 
The authors hope to continue updating the map to keep the public and healthcare providers aware of tick “hot spots.” This is important, because as mentioned above, exposure to ticks could pose a risk to humans. Knowing where ticks exist can help people assess how thoroughly they should check for ticks on their bodies after spending time in habitats likely to harbor ticks (such as woody and excessively grassy areas).
 
Bite prevention is the best way to keep safe. Ideally, you should perform a “tick check” when you have been outdoors for a long period of time even if surveillance data indicates you are probably in the clear. Prevention is the best treatment for disease!

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