Pandemiology Watch (September 17-23, 2025)
Emerging outbreaks
On September 18, 2025, the World Health Organization reported four fatal cases of Nipah virus in Bangladesh between January 1 and August 29. The cases were confirmed in separate districts across Barisal, Dhaka, and Rajshahi divisions. Nipah virus, a zoonotic disease primarily carried by fruit bats, can spread from animals to humans and between people through close contact, and has a high case fatality rate of around 72%.
Ebola
Democratic Republic of the Congo
On September 22, Africa Centres for Disease Control and Prevention (Africa CDC) reported a total of 105 suspected Ebola cases, including 65 new since the previous update on September 14. In addition, 38 cases have been confirmed overall, with 13 new confirmations. A total of 24 deaths have been reported, with no new deaths since the last update.
MPOX
Africa
Sierra Leone: The latest update from the World Health Organization shows 5,291 confirmed mpox cases as of September 14, a surge of 25 cases since September 7. According to a report from Africa CDC on September 14, these cases are linked to clade 2b, with 6.5% of confirmed cases in children under 15 years of age and 51% in males. Testing shows a 77.1% positivity rate.
Uganda: As of September 14, 2025, Uganda reported 6689 confirmed mpox cases, according to the World Health Organization. This is an increase of 29 cases since September 7.
Guinea: As of September 14, 2025, The World Health Organization has reported 942 cases in 2025 and one death in Guinea. This is an increase of 27 cases since September 7. According to Africa CDC, Testing shows a 43% positivity rate. The outbreak is linked to clade 2b.
MEASLES
U.S.
As of September 17, 2025, Center for Disease Control reports a total of 1,491 confirmed measles cases in the U.S. in 2025. 12 % of cases have required hospitalization (181 cases of 1,491), and three deaths have been reported.
On September 16, 2025, Cook County Department of Public Health confirmed a measles case in a 4-year-old unvaccinated child who became ill after likely contracting the virus during international travel. The child is receiving care, and her condition is being monitored.
Canada.
As of September 8, 2025, Canada has reported 4,902 measles cases where 70% occurred in children, according to the Public Health Agency of Canada. Ontario accounts for 49% of the total, followed by Alberta with 38%. 88% were unvaccinated, and 8 % required hospitalization. Genotype D8 remains the most frequently detected strain. 1 death has been reported.
Looking closer at the epicenter, Ontario has emerged as the province most affected by the outbreak, with Alberta also reporting a high number of cases. According to the World Health Organization, the outbreak began in October 2024 with an internationally imported case at a large gathering in New Brunswick, which then spread to Ontario, among other provinces. The Guardian reported on June 6, 2025, that much of the transmission in Ontario has been concentrated in communities with lower vaccination coverage, including some Mennonite groups, where limited access to healthcare and vaccine hesitancy contributed to rapid spread.
POLIO
As of September 17, the Global Polio Eradication Initiative reports 12 WPV1-positive environmental samples in Afghanistan. In Algeria, one cVDPV1 case, one cVDPV1-positive environmental sample, and one cVDPV2-positive environmental sample have been detected. Yemen has reported six cVDPV2-positive environmental samples.
H5N1
U.S.
As of September 5, Centers for Disease Control and Prevention has not reported any cases of person-to-person transmission of H5N1 in the United States. The total remains at 70 confirmed cases and one death.