Don’t call it a comeback

By Emily Margosian, Senior Editor, September 1, 2025

Natural disaster, climate change, shifting health norms, and global travel. All are contributing factors to the emergence and re-emergence of disease.

“It’s always worthwhile to remind dermatologists of our role as sentinels,” said Scott A. Norton, MD, MPH, MSc, FAAD, adjunct professor of dermatology and pediatrics at the George Washington University School of Medicine and Health Sciences. “We are often among the first to see diseases that are uncommon, emerging, or re-emerging. In our residencies, we’re trained to think of diseases found worldwide, and that someday we may see them in our own communities. It’s good to remind ourselves that worldwide diseases can occur anywhere so that we stay vigilant.”

Amid a rapidly evolving health landscape, experts highlight emerging and re-emerging diseases that may make their way into dermatology practices.

Disease emergence drivers

Many factors are involved in the emergence of new disease or the re-emergence of “old” previously eliminated disease. Some stem from natural processes such as the evolution of pathogens over time, but many are a result of human behaviors and practices. “Many emerging diseases are neither new nor infectious,” noted Dr. Norton. “Influences on emerging diseases include expanded geographic ranges of pathogens, vectors, and hosts (PVH), human behaviors and societal changes, vaccine hesitancy, antimicrobial resistance, and population migration.”

International travel has been on a long-term upward trend since the 1950s. As people become more mobile, so does the spread of disease, according to Carolyn Goh, MD, FAAD, a member of the AAD’s Emerging Diseases Task Force. “Typically, that’s the infectious disease model — people travel where certain diseases are endemic, then return home and spread it.”

Population growth, migration, and interaction with new zoonoses have also contributed to the emergence and re-emergence of disease in recent years. “Population migration due to economic, political, and safety reasons is also a driver,” said Dr. Norton. “For example, Chagas disease. We already had the insect vector in the United States but not the pathogen. We’ve also seen a similar situation with cutaneous leishmaniasis that is increasingly common in Mediterranean refugee camps.”

Climate change also impacts disease emergence by altering the environment in which pathogens, hosts, and vectors interact. “We’re seeing certain mosquitoes and therefore certain mosquito-borne diseases occupy different and expanding ranges as the climate changes,” said Dr. Goh.

“We are often among the first to see diseases that are uncommon, emerging, or re-emerging. In our residencies, we’re trained to think of diseases found worldwide, and that someday we may see them in our own communities. It’s good to remind ourselves that worldwide diseases can occur anywhere so that we stay vigilant.”

“Climate change allows species to expand ranges,” agreed Dr. Norton. “For example, the Lone Star tick is moving northward, and it can transmit diseases that previously did not occur in some northern states. We also see invasive species occupy new geographic ranges, such as the Asian long-horned tick. Man-made environmental disruption, such as deforestation, allows PVH to expand into new areas and allows people to enter previously less-populated areas, where they now have greater exposure to the natural life cycles of these organisms.”

Human behavior also plays a central role in disease emergence, particularly a rise in vaccine hesitancy and health care access gaps. “When some groups decline vaccination, it decreases herd immunity and creates a reservoir of disease,” said Dirk Elston, MD, FAAD, professor and chair of the department of dermatology and dermatologic surgery at the Medical University of South Carolina in Charleston, in a previous DermWorld article. Read more about cultural factors that contribute to re-emergence of infectious disease.

“When we’re talking about something like measles that re-emerges, it heavily has to do with changes in vaccination rates,” said Dr. Goh.

“Certainly, measles should now be on everyone’s mind, as U.S. cases are no longer confined to the American Southwest, places like New Mexico and West Texas,” agreed Dr. Norton. “We’re seeing measles cases all around the country and at the highest incidence in decades. If vaccination rates drop in the U.S., for whatever reasons, we’re likely to see a lot more childhood illnesses, which is scary from a public health perspective.”

Old bugs, new tricks: Re-emergent disease

As the global health care landscape continues to evolve, dermatologists should be alert to disease outbreaks in previously eliminated or controlled diseases.

“The incidence of some viral diseases tends to spike every now and then. For example, Zika and Chikungunya each had summers marked by explosive occurrence rates,” said Dr. Norton. “A few years back, we had a lot of Zika cases, now we have very few. Chikungunya will probably become established in the Caribbean, and there’s a good chance it will become established in America’s Deep South where the mosquito vector for it can thrive.”

Mpox

While the mpox public health emergency has ended, many states continue to see transmission and are urging physicians to continue recommending mpox vaccination and other prevention measures for their patients. In 2024, the rates of infection were about two times higher than they were in 2023.

According to the CDC, there have been four reported cases of clade I mpox in the United States. Access Academy resources on mpox, including guidance on recognizing mpox infection, resources on treatment and pain, and an mpox registry to gather information on dermatologic manifestations of the disease.

Syphilis

Syphilis was once considered a nearly eliminated disease in the U.S. but over the last decade, syphilis rates continue to rise. In 2022, the most recent year for which statistics are available, more than 200,700 cases of syphilis were reported in the United States, an 80% increase since 2018.

“While we may think of syphilis as a disease of the past — it never went away. It’s important to remember that it’s still out there and that it’s really a disease of the present, and increasingly a disease of the future,” said Kenneth A. Katz, MD, MSc, MSCE, FAAD, a dermatologist at Kaiser Permanente in a previous DermWorld article. Read more about how dermatologists can play a key role in the diagnosis and management of syphilis, as well as national prevention and control efforts.

Dengue

One of the most common mosquito-borne diseases worldwide, dengue case numbers have recently stirred concern among public health officials. “Dengue is a serious disease that’s been found in the tropics forever, but it now seems to be spreading into the subtropics as places like South Florida report their own indigenous cases,” said Dr. Norton.

“Vector-borne diseases, specifically mosquito-borne illnesses like dengue, are continuing to surge globally,” agreed Eva Parker, MD, DTMH, FAAD, assistant professor of dermatology at Vanderbilt University Medical Center. “Cases of dengue are increasingly documented in the Caribbean, a frequent travel destination for people from the United States. However, more and more cases are also being reported in places like Texas and Florida as well.”

In the United States, public health authorities in Puerto Rico and the U.S. Virgin Islands declared dengue outbreaks in 2024 that continue into 2025. Local transmission of dengue was reported in 2024 in California, Florida, and Texas. According to the CDC, Florida has reported local dengue transmission in 2025.

Focus on fungus

Several fungal conditions are also on the rise globally, driven by factors like climate change, antimicrobial resistance, and increased immunosuppression in vulnerable populations.

Drug-resistant tinea

While dermatophytosis is a common and often minor skin infection caused by dermatophyte fungi, over the past decade, severe or antifungal-resistant dermatophytoses have become a global public health concern, including in the United States.

The AAD has assembled resources on Trichophyton indotineae and other severe or antimicrobial-resistant dermatophytes. These resources include information sheets on disease recognition, diagnosis, and treatment options, but do not constitute a clinical guideline. Report suspected cases of antifungal-resistant dermatophytosis. The AAD/ILDS emerging diseases registry helps to gather information on severe or antimicrobial-resistant dermatophytosis cases.

Learn more about managing dermatophytosis amid increasing resistance to antifungal therapies.

Coccidioidomycosis

According to a recent JAMA article on climate change and health, record-high numbers of coccidioidomycosis (Valley Fever) occurred in California in 2023 (doi:10.1001/jama.2024.27274). Study authors attribute this to an ongoing pattern of extreme dry and wet weather amid the state’s ongoing drought, creating ideal conditions for spread of the windblown spores of Coccidioides.

Currently endemic in the U.S. in Arizona, California, New Mexico, West Texas, and Utah, the fungus is projected to be endemic by 2100 also in Idaho, Montana, Nebraska, North Dakota, South Dakota, and Wyoming. “Dermatologists should remain vigilant for coccidioidomycosis, which CDC modeling shows is currently substantially underdiagnosed even in endemic areas,” recommended Dr. Katz in a recent issue of DermWorld. “Important for dermatologists: approximately 40% of patients develop symptoms; approximately 50% of patients with pulmonary infection have erythema nodosum; and up to 10% of patients have disseminated infection, including in the skin.”

Expanding vector ranges usher new disease

The ranges of many pathogens, hosts, and vectors of disease have seen recent expansion, said Dr. Norton. “An interesting example is that for decades, the state of Michigan had few cases of Lyme disease because the specific bacterium that causes Lyme, Borrelia burgdorferi, was uncommon there, even though the tick vector and the mammalian hosts were abundant. Now we are seeing cases of Lyme disease in Michigan, and in the next few years may see large focal clusters and outbreaks similar to the ones we saw in New England 25 to 35 years ago.”

Other tick species have begun to crawl northward in the United States, including the Asian long-horned and the Lone Star ticks. “The Asian long-horned tick was first detected in the U.S. roughly 10 years ago. This tick carries diseases that can be devastating to cattle, but we now believe it can also carry human diseases as well,” said Dr. Norton. “The Lone Star tick was typically found in the southeastern United States, but it is now expanding its range rapidly all the way up to New England. As these tick populations increase, they can serve as additional vectors for existing tick-borne diseases as well as the potential to carry and spread several tick-borne diseases that weren’t present in our country before.”

Increasingly deemed a pest across areas of South America, there are growing fears among the livestock and agriculture industries that screwworms (Cochliomyia hominovorax), the flesh-eating larvae of a parasitic fly, could once again spread north into parts of the United States. According to the USDA, “When New World Screwworm (NWS) larvae burrow into the flesh of a living animal, they cause serious, often deadly damage to the animal. NWS can infest livestock, pets, wildlife, occasionally birds, and, in rare cases, people.”

“Screwworm infestation might be causing the most loss of sleep among veterinary health officials,” said Dr. Norton. “This is a form of myiasis, where fly larvae live, feed, and develop inside the vertebrate host. Screwworms are expanding northward from South America into Central America over the past few years. Entomologists worry that if screwworms arrive in the United States, it will be a very bad day for wild animals, domestic animals, farm animals, and humans.”

According to Dr. Norton, dermatologists should be on alert for sightings of screwworm myiasis but also be prepared to counsel patients amid potential misinformation. “Dermatologists may indeed see the earliest cases of screwworm myiasis in the United States, but as public awareness of a potential screwworm problem rises, we will likely see patients who are worried that they have personally been infested with the fly larvae. That can become problematic, similar to widespread fears of cutaneous anthrax in late 2001.”

Dermatologists as public health sentinels for emerging diseases

Historically, dermatologists have served as critical watchdogs for emerging diseases, recognizing unusual skin findings that signal new or re-emerging infections, identifying travel- or vector-related dermatoses early, and reporting suspicious patterns that could indicate broader public health threats. “Dermatologists have the very fundamental skill of observation,” said Dr. Goh. “As an attending, I remember it was often quoted that while NIH dermatologists do a lot of bench research, often the basis of their work starts with the observations of general dermatologists.”

“It’s important to be in touch with one’s state or county board of health, because there are many diseases that have mandatory reporting requirements. Each state has its own list, and there’s a federal list as well. Not all conditions on the lists are necessarily new and not all are infectious. We don’t know what the next outbreak will be,” said Dr. Norton. “At the national level, public health authorities continue to be concerned about influenza viruses and coronaviruses. Right now, those probably have the highest likelihood of creating another pandemic.”

According to Dr. Goh, after the COVID-19 pandemic the Academy realized the need for a permanent task force to keep members informed about emerging diseases and outbreaks. “That’s how the Emerging Diseases Task Force was born. We were noticing all these cutaneous manifestations that seemed to be related to COVID infections. That sparked a desire to develop a registry and leverage our collective knowledge and experiences in the field to learn more. After COVID-19, we then saw mpox emerge — and now re-emerge — which led to the creation of an additional registry to document and utilize the observations of dermatologists. We continue to address new challenges posed by measles and drug-resistant tinea.”

The Academy has curated and developed scientific resources to help you recognize, manage, and report emerging diseases. Visit the AAD Emerging Diseases Resource Center for regular updates with disease alerts and new resources.

Additional DermWorld Resources