Dogs may help scientists understand how prevalent Valley fever actually is, new research says

Arizona health officials reported nearly 11,000 cases of Valley fever in 2023, the most recent year for which data are available.

Valley fever is a lung infection caused by a fungus that grows in the soil and is most common in Arizona, California and other parts of the southwestern United States.

But new research suggests dogs may be able to help give us a better sense of how prevalent the disease actually is.

Jane Sykes, professor of small animal internal medicine at the University of California, Davis, joined The Show to talk about what she found, including what this research says about what dogs can tell us about Valley fever that we don’t already know.

Full conversation 

JANE SYKES: Yeah. So, as you may be aware, Valley fever is a disease that’s considered to be emerging in people. And certainly concerns about changes in our climate and contributing to increasing Valley fever in people. And so there’s been a lot of concern, and certainly some modeling efforts to suggest that, by 2035, even as much as half of the Western United States may have Valley fever.

And, unfortunately, currently, the reporting of Valley fever is not required for all states and people. And so we have states that we know that are endemic for the fungus — like Texas, for example, where there’s no reporting information available. Whereas with dogs, you know, we have been able to collect the results of antibody tests, serology tests — which is the main way the disease is diagnosed in dogs — that have been archived at this very, narrow set of laboratories that actually performs this specialized testing. And so that’s allowed us to capture results for dogs right across the entire country, including in these states that don’t report human disease. And so we’ve been able to get really good information from hundreds of thousands of dog test results from these regions. And because dogs don’t travel as much as people — actually, even if we were able to get that information for people, it would be more complicated by travel than it is in dogs.

MARK BRODIE: So basically what you’re saying is we have better information on how many dogs have Valley fever and where they are than we do for humans.

SYKES: Exactly, that’s right.

BRODIE: So, how are we able to use that? Like, are you able to look at the results from dogs and say, “OK, there’s X number in, say, Texas. So, we can maybe extrapolate that out and say there might be X number of human cases in that state.”

SYKES: Exactly. And, and so one of the findings from our study is that, where we do know human disease happens — like in California and Arizona, where there is quite good reporting information for people — we were able to compare the results of the dog test results to human reported data, and show that there was a very strong correlation between those case numbers. And we normalize the dog data to population, so per 10,000 households. The other thing that makes dog information useful is that there are a lot of dogs in the United States. And, you know, it’s now estimated that about 45% of U.S. households have at least one dog. So, when, when we were able to use the households as a denominator, you know, that helps to control for population numbers. And very close correlation between case numbers in people in California and in Arizona, which suggests that probably is the same for other states, where we don’t have human information. And, so, our future work is looking at those areas where we don’t have information in humans and trying to extrapolate as to what’s likely based on the dog data.

BRODIE: How reliable do you think that might be able to be in places like, maybe, Texas or Oregon or Washington State, where there have started to be more cases of Valley fever? Like, do you think you’ll be able to look at the number of dogs and maybe have to increase the number of dogs that are tested in those places to try to get a gauge of what the human situation might be?

SYKES: Yeah, and interestingly, in Washington, before human cases were recognized in Washington state, the Washington State Disease … Veterinary Diagnostic Laboratory noted that there had been cases in dogs and also a horse in Washington before disease was recognized in people. And they now have a requirement, the state requirement, for reporting of animal cases. And, you know, when we looked at our data, there were a number of states that seemed to have really quite a higher incidence of dog disease when compared with other states that probably had, you know, kind of low incidence of disease because of travel. You know, states like, East Coast states, where we really know the fungus isn’t present. But there were some Western states that had really a huge jump in incidents relative to those other states where we really don’t think the fungus exists. And some of those states were states that we really don’t recognize as being endemic for Valley fever in humans at this point in time. And I think that’s a sign that the fungus is present in those locations.

BRODIE: That’s interesting. So it’s possible that Valley fever might be more widespread than we think it is, and the way we might be able to figure that out is through dog infections.

SYKES: Exactly, yeah. So, states like Colorado, Wyoming, Idaho, Oregon all had, you know, these higher incidences that might be a sign that the disease is occurring in people in those regions, not as a result of travel to endemic states.

BRODIE: So, I know that one of the issues with Valley fever, especially as it relates to humans, is that there are some number of doctors who just don’t know to even look for it or test for it because … a lot of people can have it and never, it never manifests itself. They never show symptoms, anything like that. Is that also the case with dogs? Like, are vets ready and knowledgeable enough to test for it if they know a dog is from a particular area and maybe has particular symptoms?

SYKES: Yeah … we have the same problems for dogs as as existing people, and it is underrecognized in some parts of the country. And sometimes I get calls from veterinarians working in Florida, for example, who have just diagnosed the disease in a dog that’s been traveling to Arizona. So, there are some vets that are aware of it, and some that are not. And, unfortunately, we do see cases referred to us here at UC Davis, oftentimes that have been treated with antibacterial drugs, antibiotics, when they need anti-fungals. Because no one’s thinking about Valley fever. So, this is a really good opportunity to increase awareness of the disease and have people be looking out for it in these states where we think it might be present.

BRODIE: So, I would imagine then that for someone who does the kind of work that you do, having a more accurate gauge of how many dogs and people are actually infected with Valley fever would probably be pretty helpful.

SYKES: Very much so. Yes. Yes. And the other thing about dogs that we’ve found is that one of the risk factors for Valley fever in dogs is digging in the dirt. And, you know, dogs have this tendency to dig. It brings them very close to the soil. And so it means that they’re … often getting infected, and more susceptible to infection maybe than people in the same region. And so that makes them good what we call sentinels for the disease. Kind of like the canary in the coal mine, if you will.

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