The World Health Organization tracks several emerging viral threats at any given time, and the landscape shifts frequently. As of late 2025 and into early 2026, the most prominent concerns include mpox clade Ib, H5N1 avian influenza spreading in new animal populations, Marburg virus outbreaks in East Africa, and Oropouche virus expanding its geographic range. None of these are brand-new discoveries, but each has recently behaved in ways that raised global alarm.
Mpox Clade Ib: The Most Recent Emergency
In August 2024, the WHO declared a Public Health Emergency of International Concern over a new strain of the mpox virus called clade Ib, which surged in the Democratic Republic of the Congo and spread to neighboring countries. This was a more aggressive form than the clade IIb strain that circulated globally in 2022. The emergency designation was lifted in September 2025, but the virus hasn’t disappeared.
Since the emergency was lifted through November 2025, 43 new confirmed clade Ib cases were reported across six WHO regions outside areas with sustained community transmission. In most settings, the death rate is below 1%, but deaths have occurred among young children, pregnant women, and people with weakened immune systems in African countries. The WHO considers the risk moderate for men who have sex with men and low for the general population in most countries.
H5N1 Bird Flu in Mammals
H5N1 avian influenza has existed for decades, but recent spillovers into dairy cattle and sporadic human infections have put it back on the WHO’s watch list. The virus primarily spreads from infected poultry to humans through direct contact or airborne exposure in places where live birds are kept, slaughtered, or processed. Research has shown that even processing chickens that appear healthy but carry the virus generates infectious droplets and aerosols capable of infecting mammals.
Sustained human-to-human transmission of H5N1 has not been confirmed, which is the critical threshold that would trigger a pandemic. But the virus’s ability to jump into new mammalian hosts, including cows, raises concern that it could adapt further. The WHO published guidance in June 2025 on options for using H5 vaccines during the current pre-pandemic period, and several countries maintain small stockpiles of H5N1 vaccine candidates that could be scaled up if needed.
Marburg Virus Outbreaks in East Africa
Marburg virus, a close relative of Ebola, caused outbreaks in Tanzania (early 2025) and Ethiopia (ending January 2026). The Ethiopian outbreak resulted in 19 total cases, 14 of them confirmed, with a case fatality rate of 64.3% among confirmed cases. All five probable cases also died. The outbreak was concentrated in southern Ethiopia before being declared over in late January 2026.
Marburg is not new, but it is rare and extremely lethal. Nineteen outbreaks have been recorded globally, nearly all in African countries including the DRC, Rwanda, Ghana, Guinea, and Uganda. There is no approved vaccine or specific treatment, which is why the WHO keeps it on its priority pathogen list. The virus spreads through direct contact with the blood or bodily fluids of infected people or animals, particularly fruit bats, which are the natural reservoir.
Oropouche Virus Reaches New Regions
Oropouche virus, spread by biting midges, emerged as a growing concern in 2024 when cases appeared in countries and regions where it had not previously circulated. The disease causes fever, headache, joint and muscle pain, chills, nausea, vomiting, and rash, with symptoms appearing 3 to 10 days after a bite. Most people recover, but the expansion of the virus into new areas caught public health systems off guard.
Diagnosis is a significant challenge. Testing requires specialized laboratory techniques, and there are no commercially available rapid tests. This means cases in lower-resource settings can go undetected, making it difficult to track how far the virus has actually spread.
The WHO’s Priority Pathogen List
The WHO maintains a formal list of diseases with epidemic potential that lack adequate vaccines, treatments, or diagnostics. This list drives global research funding and preparedness planning. The current priority diseases are: COVID-19, Crimean-Congo hemorrhagic fever, Ebola and Marburg virus diseases, Lassa fever, MERS and SARS coronaviruses, Nipah and related viruses, Rift Valley fever, Zika, and “Disease X,” a placeholder for an unknown pathogen that could cause a future pandemic.
The inclusion of Disease X reflects a core lesson from COVID-19: the next major threat may come from a virus we haven’t identified yet. For the pathogens already on the list, a persistent gap remains in diagnostic tools. Outside of COVID-19, there are no commercially validated rapid tests for any of these high-priority diseases. That means outbreak detection still depends heavily on laboratory infrastructure that many affected countries lack.
How to Stay Informed
The WHO publishes Disease Outbreak News updates on its website whenever a new cluster or outbreak is detected. These reports include case counts, affected regions, and risk assessments. For travelers, the WHO maintains country-specific advisories covering dengue, Zika, chikungunya, and other mosquito-borne infections, along with vaccination requirements for international travel.
If you’re tracking a specific virus, the WHO’s outbreak news page is the most reliable real-time source. National health agencies, like the CDC in the United States or the ECDC in Europe, also issue their own alerts that may be more relevant to your location.