Public Health

2024 dengue fever outbreak, dengue symptoms, a new study on bird flu in cows and state fair safety


AMA Update covers a range of health care topics affecting the lives of physicians, residents, medical students and patients. From private practice and health system leaders to scientists and public health officials, hear from the experts in medicine on COVID-19, medical education, advocacy issues, burnout, vaccines and more.

What is dengue fever? Is dengue fever deadly? How long does dengue fever last? Can dengue fever kill you? Is dengue fever in Florida? Also, a bird flu 2024 update.

Our guest is AMA's Vice President of Science, Medicine and Public Health, Andrea Garcia, JD, MPH. AMA Chief Experience Officer Todd Unger hosts.


  • Andrea Garcia, JD, MPH, vice president, science, medicine & public health, American Medical Association

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Unger: Hello, and welcome to the AMA Update video and podcast. Today, we have our weekly look at the headlines with the AMA's Vice President of Science, Medicine, and Public Health Andrea Garcia. I'm Todd Unger, AMA's chief experience officer. Good to see you again, Andrea.

Garcia: Good to see you, too.

Unger: Well, the last couple of weeks we've talked a lot about how climate change is driving extreme temperatures and the health impact of all of this heat. But this week, we've got something new that's driving concern and headlines, and that is dengue fever. Andrea, tell us what's going on there.

Garcia: Well, Todd, last week, we saw the CDC issue a health advisory, or a HAN, to physicians, public health authorities and the public, warning of an increased risk for dengue virus infections in the U.S. this year. This is really coming in response to an alarming number of cases we've seen abroad already in the first six months of 2024.

Countries in the Americas have reported more than 9.7 million dengue cases. That's twice as many as we saw in all of 2023. And in the U.S., Puerto Rico has declared a public health emergency this past spring because they've reported more dengue cases in the first five months of 2024 than all of last year. And those were during the dry season when dengue cases are typically at their lowest.

Unger: Andrea, have we seen any cases like this in the continental U.S.?

Garcia: Well, the CDC has said there's currently no evidence of a dengue outbreak in the continental U.S. We do see travel-related cases here. And since January, 745 dengue cases have been identified among U.S. travelers who became infected abroad.

That's higher than expected for this time of year, given that dengue cases typically increase during the warmest months, and we know those are yet to come. Public health officials are expecting to see the virus in more temperate regions, including the southern-most portions of the United States. The mosquito responsible for dengue is found in several states, including Texas, Florida and California. So far this year, Florida has already reported 10 cases from local spread and that is across four different counties.

Unger: So in effect, although we're not talking about necessarily the heat, this is an outcome of climate change, so to speak. Andrea, in terms of how it spreads, we know that dengue fever is spread through mosquitoes. But take us through a little bit more in detail about the mechanism there.

Garcia: So dengue is spread by the bite of an infected Aedes species mosquito, primarily Aedes aegypti, but it can also be spread by the Aedes albopictus mosquito.

Travelers infected abroad can then bring the virus back to their communities, where local mosquitoes bite them and then transmit the disease to others. According to the WHO, dengue is one of the world's most neglected tropical diseases. Three out of four cases are mild or asymptomatic, and that makes the illness really difficult to track.

Unger: And when you say Aedes, I don't think you mean the decade. That's A-E-D-E-S, for those of you who have not heard that term before. Andrea, talk to us about the seriousness of the cases that we're seeing right now.

Garcia: So most cases aren't serious, but there can be severe cases that lead to internal bleeding, organ failure or even death. Infections usually begin after an incubation period of about five to seven days, starts with a fever, and then it's accompanied by other symptoms, including nausea, vomiting, rash, muscle aches, joint and bone pain, pain behind the eyes, headache, or low white blood cell counts.

Unlike other diseases, where fever reduction is a sign that someone's getting better, for dengue, this is when the critical phase begins, and it typically lasts for 24 to 48 hours. There are several warning signs that indicate progression to severe disease. Those include abdominal pain or tenderness, persistent vomiting, bleeding from the nose or gums, and lethargy or restlessness.

Severe disease develops in about one out of 20 people with symptomatic dengue. And infants, pregnant people, adults over 65 years of age, and people with certain medical conditions are at an increased risk.

Unger: All right. Andrea, do we know what is driving this dramatic increase, you have to say, in the number of cases?

Garcia: Well, as you briefly mentioned, this is likely yet another byproduct of climate change. Soaring global temperatures have really accelerated the life cycles and expanded the ranges of mosquitoes that are responsible for dengue, helping spread that virus to roughly one in every 800 people on the planet in the last six months alone.

But it's not just rising temperatures. Climate-induced droughts can prompt people to stockpile water, which creates more mosquito habitats, and then it also escalates hurricanes and floods that produce standing water while simultaneously forcing people from their homes and increasing their exposure to mosquitoes. There was a Washington Post article that noted that, without drastic action to control the virus and slow climate change, research is suggesting that some two billion additional people across the globe could be at risk for dengue in the next 50 years. 

Unger: Well those are pretty incredible numbers. And as you outlined before, in terms of symptoms, especially the more serious side, not good. Is there any kind of treatment available?

Garcia: Unfortunately, there are no antiviral medications approved to treat dengue and no vaccines for adults or people without a previous dengue infection. The only vaccine approved for use here in the U.S. is for children aged 9 to 16 years old who have had a previous dengue infection and who live in frequent or continued continuous dengue transmission area.

So think like American Samoa, Puerto Rico, U.S. Virgin Islands. But the supply of that vaccine is expected to run out after August of 2026. That's because the manufacturer is going to stop making it due to low demand. In May, the WHO expanded the use of a second vaccine, but that manufacturer withdrew its application from the FDA last summer because of data collection issues.

There's a third vaccine being developed by the NIH. It's still in clinical trials, and it won't be available in the U.S. for at least a few years. I think it's also worth noting that this disease is complicated because it's caused by four distinct but closely related dengue viruses. Infection with one dengue virus generally produces lifelong protection against infection from that specific virus but only partial and short-term protection against the others. And there's evidence that suggests the risk of severe complications may increase with sequential infections from a different type.

Unger: So Andrea, what should physicians be doing in response to this latest development?

Garcia: So the CDC is urging physicians to be on the lookout for dengue among people who have a fever and who've been in areas with dengue transmission within the last 14 days of the start of their illness. This disease is easy to miss, and since dengue hasn't been a problem here, awareness among physicians is likely low.

If physicians do suspect dengue, they need to order the appropriate diagnostic tests for acute dengue infection and of course report those cases to public health authorities. We can also do our part by using EPA-approved repellents, wearing loose-fitting long-sleeve pants and shirts to prevent getting bitten by mosquitoes in the first place. The CDC also suggests using air conditioning and window screens when possible and dumping and draining containers outside that hold water. And if you do develop symptoms, be sure to seek medical care.

Unger: All right. That is a great update on that and all good information, especially as we head into the hotter months. Andrea, let's switch gears a bit and do a quick check in on bird flu. Anything new happening there?

Garcia: Well we do continue to see rising cases. Last week we reported that we had been seeing 118 herds in 12 U.S. states with bird flu. This week, that number has grown to 132 herds. I think something worth talking about briefly are those agricultural fairs as we head into the holiday weekend.

Millions of people in the U.S. attend fairs each year, especially around the fourth and throughout the summer months. The CDC's recommendations around fairs previously focused on reducing the risk of spreading swine-origin flu viruses between pigs and people. Those recommendations have now been expanded to include cattle. The best thing people can do is avoid animal exposures at these fairs and remember to wash your hands frequently.

Unger: All right. There was also a new study that I read about that was promising news for containing the virus. Andrea, can you tell us a little bit more about that?

Garcia: Well, one of the big questions that scientists have been wrestling with is how this virus spreads from one animal to another. And there was a detailed article in The New York Times around a small experiment that was carried out in Kansas and Germany, which has offered some new information. Now, I think it's important to note these findings haven't been posted online or published in a peer-reviewed journal yet.

But what that experiment found is that the virus is mainly infectious via contaminated milking machines. And this certainly poses logistical problems for dairy farmers. But it would mean the virus is easier to contain than if it were spread through respiratory droplets.

According to a scientist involved in the study, this offers hope that the outbreak could theoretically be halted before it evolves into a form that can spread readily between humans. There are certainly caveats, though. These results are from two experiments that involved a very small number of cows.

The scientists also studied an early strain of the virus, and we know that virus has been mutating as it has moved from animal to animal. And researchers can't say whether a more recent strain would behave more like a respiratory disease. Certainly, though, Todd, this is something we'll continue to pay attention to.

Unger: Well, that's something we'll continue to watch carefully in the coming weeks. Andrea, that's all we have time for this week. I want to say thanks again for being here and sharing this important information.

I do want to add that we also have a lot of vaccine updates following the CDC's Advisory Committee on Immunization Practices meeting last week, but we'll be diving into more details on that on Monday with the AMA's ACIP liaison, Dr. Sandra Fryhofer. So make sure to tune in for that.

If you found this discussion valuable, you can support more programming like it by becoming an AMA member at And due to the Fourth of July holiday, this is going to be our last episode until Monday. Of course, you can always find all our videos and podcasts at

Please enjoy your Fourth of July holiday. Stay safe out there. Take care.

Disclaimer: The viewpoints expressed in this video are those of the participants and/or do not necessarily reflect the views and policies of the AMA.

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