In 2009, two farmers checked in to the Heartland hospital in Missouri within days of each other with fever, nausea, diarrhea, and rapidly declining white blood cell counts. Doctors sent their blood samples to the Centers for Disease Control, which discovered that both farmers had contracted a previously unknown virus from a tick bite. The CDC named it the Heartland virus. Five years later, a lab technician testing samples for a suspected Heartland case identified another novel virus, dubbed Bourbon.
Before Heartland and Bourbon, only 14 new tick-borne pathogens had been spotted since 1900. The new discoveries support suspicions that zoonotic pathogens—viruses or bacteria that leap from animals to humans, as SARS-CoV-2 is believed to have done—are more numerous than we realized.
Can researchers who spot a new virus actually do anything to keep it from getting out of control? I spoke with Erin J. Staples, a CDC epidemiologist who led the response to Heartland and created a tracking registry that has documented 50 infections so far.
Q: How often do doctors or scientists find novel viruses in humans?
A: I would say [for tick-borne disease], most scientists and researchers will not discover a new virus in their career. So I consider myself fortunate to have worked on some relatively new ones.
Q: Do new virus discoveries usually happen by accident? Or because someone was looking for them?
A: It’s probably a little bit more of the former than the latter. We were looking for Heartland and found the Bourbon virus. But there are other programs that people have implemented to try to develop some sort of surveillance project. They look at acute febrile illness, meaning someone who developed a fever all of a sudden; test for known pathogens; and then when there’s nothing else there, they move on to using different techniques like next-generation sequencing.
Q: It’s been about 10 years now since the Heartland virus was discovered. Do you think it really is a new virus, or was it always there and doctors didn’t pick it up?
A: Virologists looked at the virus’s genomic sequence. Changes in the sequences can tell you about the virus’s evolution and how long it might have been present. So they definitely know that the virus has been present in the US for decades, if not longer.
In addition, we’ve retrospectively identified some cases that occurred prior to the first two cases. We think it has been causing some low-level amount of disease for a while.
Q: Do you think there are other novel viruses infecting people around the US going undetected?
A: Yes, and Bourbon virus is a good example of that. So I do think there are yet-to-be-discovered bacteria or viruses similar to ones we know about but that are unique enough that they’re their own.
Among patients with encephalitis [brain inflammation] of unknown cause, you’re thankful if you can get 20%, 30%, to actually get a diagnosis. It’s that 70% of the unknown cases that we’re still challenged by. Could they all be due to viruses or bacteria? Probably. We’ve made a huge amount of progress in terms of figuring out what causes people to get unwell in terms of bacteria, parasites, and viruses. But there’s still obviously things yet to be discovered—new, emerging, and old ones that have been there that we have not appreciated.
Q: There aren’t any plans for a vaccine for the Heartland virus, or any specific antivirals. So why is it useful just to know it exists?
A: We often get that question. And you’re correct, right now we do not have an effective antiviral.
As a clinician, it’s important because when you have a person who is sick, you need to figure out what’s going on. For instance, because Heartland virus looks like ehrlichiosis [a tick-borne bacterial infection], people are often given antibiotics. For certain people, antibiotics can cause side effects. They can also cause resistance to develop. Cutting down on the use of therapeutics that aren’t going to help can be very beneficial. In some other situations, it is helpful to the family. There was unfortunately a very severe case of Heartland virus where the patient was not getting better. Allowing the family to know that the diagnosis was actually caused by a virus there was no way to treat, and there’s nothing else the physicians could do, allowed the family to make a tough decision to let their loved one go.
Q: How did you start identifying more cases of the Heartland virus for the registry?
A: There was obviously the need to identify and diagnose additional human disease cases. We developed a lot of protocol to allow us to have people tested while we were working on developing the test.
We had to explain to patients: “You might have this new disease, which they’re working on a test for. We’re going to test you for it.” And in general, everybody was quite willing to give us a blood sample so we could evaluate and determine.
The additional cases we identified allowed us to improve our diagnostic tests and have samples to use as positive controls, which is very important.
All of that was going on over the process of a few years. At the same time, we also had our entomologists and ecologists working to understand a little bit better and validate exactly how people were being infected. If we’re going to tell people about a new virus, we definitely need to figure out how to tell them how not to get infected with the virus.
To date, we’ve got at least 50 individuals in the United States that we’ve identified, and we’re probably going to be pushing that number up. We have numbers on our website. We also have a map that tells you where we’ve identified individuals that were known to be infected. Any time there’s a new state where an individual was believed to be infected, we highlight that on our map to ensure that people are aware of where this disease is occurring. Recently, Iowa had their first case.
Q: Do the Heartland or Bourbon viruses have pandemic potential?
A: Based on what we know right now, we do think they are limited in geographic scope. Definitely some of our tick-borne diseases have large-scale outbreak potential. That’s one of the reasons we perform surveillance: to understand where it is and make sure we’re not seeing anything unique or different. And we try to make sure everybody can be aware and stay as healthy as possible and take prevention measures, including using your insect repellent when you’re outdoors.
Q: Do you think the current covid-19 pandemic could have been prevented if it had been picked up sooner?
A: When you’re trying to figure out a new virus and understand it, trying to contain it when it is something that is so infectious and transmissible, I think it would have been hard to do.
Q: Do you think we’ll see another pandemic in our lifetimes? And what can the scientific community do to prevent that from happening?
But things that we do as humans—like the ease of global travel, which didn’t exist in the last pandemic—can definitely help disease spread. Again, there are definitely a lot of potential undiscovered viruses and bacteria out there. How they circulate, how they affect us, and how they can be transmitted will definitely impact whether or not and to what degree we will see human disease.