Health Experts Warn of Rising Infectious Disease Threats to Watch in 2026

Emerging and reemerging infectious diseases are becoming a growing global concern, with health experts warning that some illnesses once thought to be under control are now resurfacing. Increased travel, low vaccination rates, and the overuse of antibiotics are all contributing factors allowing diseases to spread more easily and persist longer.

According to Dr. Amish Adalja with the Johns Hopkins Center for Health Security, many of these threats never truly disappeared. Instead, he says the tools used to control them are now being underutilized.

At the top of his list of infectious diseases to watch in 2026 is measles. As of early January, at least 171 confirmed measles cases have already been reported in the United States this year. That follows more than 2,200 confirmed cases nationwide in 2025. Health officials warn the U.S. is likely to lose its measles elimination status later this month.

Avian influenza remains another major concern. These viruses naturally circulate among birds but can spread to other animals and, in rare cases, humans. Adalja notes that the 1918 influenza pandemic began as an avian flu outbreak that evolved into a global crisis.

Third on the list are filoviruses, a family of viruses that includes Ebola and Marburg. These viral hemorrhagic fevers continue to cause outbreaks across parts of Africa and are spreading to new countries, making containment especially challenging.

Mpox is also a concern in 2026. The illness causes flu-like symptoms and a rash and spreads through close contact or contaminated items such as bedding. While a vaccine is available, Adalja says many people at highest risk are not getting vaccinated.

Rounding out the list are insect-borne illnesses, including Oropouche virus spread by mosquitoes and biting midges, and anaplasmosis, a tick-borne disease that is expanding across the U.S. Experts say while many people are familiar with Lyme disease, anaplasmosis can be more severe and often goes unrecognized.

Health officials continue to emphasize vaccination, prevention, and awareness as key tools in limiting the spread of these diseases.

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