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The Growth of Tick Borne Diseases

The number of US counties with blacklegged ticks, known as being responsible for most Lyme Disease cases, has more than doubled over the last twenty years. The northeast corridor of the US is no longer the only “hotbed” for blacklegged tick action.

And to make matters even worse, Lyme Disease is no longer the only threat. New diseases are being discovered from a variety of tick species throughout the US and Canada; the reported infections are growing exponentially and there are cases where people obtain multiple diseases from a single tick bite.

Map data from CDC; reported cases in 2017.

Disease Growth

The chart below visually represents the growth of tick borne disease in the United States from 2009 to 2017 (tip: toggle off Lyme Disease in the legend to see the other diseases in closer detail). You can see the reported cases have a rather unique trend: a substantial increase followed by a slight decrease year over year.

All data is from the CDC. We elected to display data beginning in 2009 because this is when the CDC started recording both confirmed cases and probable cases. As you may know, confirming Lyme Disease is sometimes difficult – especially if the infamous bulls-eye rash doesn’t appear.

As you can see, Lyme Disease is the most common and continues to increase, but Rocky Mountain Spotted Fever and Anaplasmosis are an increasing problem, growing 244% and 396% respectively between 2009 – 2017.

While the diseases listed in this chart are the most common, there is a much longer list of diseases from ticks, many of which are rare but can be deadly. One that I would like to call out is the Powassan Virus, which is still rare (a reason we didn’t include it in the chart due to the small number of reported cases) but drastically increasing. Powassan Virus can cause a severe brain infection; 1 in 10 people with this severe virus die, and half of those who survive have lifelong complications. There are no vaccines to prevent or medicines to treat it. The only thing you can do is practice basic tick prevention.

Are You at Risk?

If you live in the Northeast US, you probably already know that there is a risk of tick bites when venturing outdoors. Using data from the CDC, we averaged the total number of confirmed and probable cases of Lyme Disease from 2009 – 2017. Here are the results.


You can see Pennsylvania has the most reported cases by a large margin. Does this mean Pennsylvania is the worst state for Lyme Disease? Technically speaking, yes – more people from Pennsylvania get the disease than any other. However, your chance of getting the disease is much higher in other states.


Incidence rates (reported cases per 100,000 people) are a better way to determine the number of reported cases based on the number of people in that state. When looking at the average incidence rates throughout the same time frame, it shows a much different story. Residents of Vermont and Maine are most at risk for Lyme Disease, followed by New Hampshire, Delaware, Connecticut, and then Pennsylvania. This is because, while Pennsylvania has more reported cases, there are a lot more people living in Pennsylvania than Vermont or Maine.

Infographic: Tick Borne Diseases

In this infographic, we visually explain the geographical distribution of tick diseases in the United States, what type of ticks carry deadly diseases, and what you can do to prevent a bite.

Types of ticks infographic

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