An outbreak of the deadly Ebola virus in the Democratic Republic of Congo and Uganda has prompted the World Health Organization to declare a global health emergency.

About 80 deaths have been attributed to the disease in Ituri Province of the D.R.C., where the outbreak was first identified. There are believed to be nearly 250 cases in the province, but, so far, laboratory testing has definitively linked only eight cases to the virus. Cases have also been confirmed in neighboring Uganda.

The type of Ebola virus behind the latest outbreak, known as Bundibugyo, is rare has fewer field tests available, and has no targeted vaccine or treatment, potentially compounding the difficulty of containing the outbreak.

Here’s what to know about Ebola.

What is Ebola?

Ebola is an illness caused by a group of viruses, known as orthoebolaviruses, first discovered in 1976 in the countries now known as South Sudan (formerly part of Sudan) and the Democratic Republic of Congo (formerly known as Zaire) in a region near the Ebola River. The most common species is the Zaire Ebola virus.

Ebola outbreaks have mostly occurred in sub-Saharan Africa, according to the U.S. Centers for Disease Control and Prevention. Four of the six known species of Ebola viruses cause illness in humans and can be fatal. Among them is Orthoebolavirus bundibugyoense, leading to Bundibugyo virus disease, the form of Ebola that prompted the latest global health emergency declaration.

Ebola is among a group of illnesses characterized as viral hemorrhagic fevers. These can affect the work of organs, damage the cardiovascular system and broadly diminish the body’s ability to function.

People with Ebola may first experience so-called dry symptoms such as fever, aches, pains and fatigue before progressing to wet symptoms, including diarrhea, vomiting and bleeding, according to the C.D.C.

Ebola diseases can be contracted through contact with the body fluids of an infected, sick or dead person and with contaminated objects like clothing, bedding, needles and medical equipment.

Health care providers and those caring for someone with Ebola face the highest risk of infection, but the viruses that cause Ebola pose little risk to travelers or the general public, according to the agency.

To control disease outbreaks, the health authorities rely on clinical care, surveillance, contact tracing, quarantines for infection prevention, safety controls in health facilities and safe burials, among other public health protocols.

What to know about the history of Ebola outbreaks

In the 21st century, there have been a number of outbreaks of Ebola viruses that killed dozens of people, with the worst occurring from 2014 to 2016.

• 2025: Last year, health officials in the D.R.C. officially declared the country’s 16th Ebola outbreak since 1976. There were 53 confirmed cases and 45 deaths. Earlier that year, Uganda also reported 12 confirmed cases and four deaths from Ebola.

• 2022: Uganda confirmed an outbreak that ended in early 2023, with 142 confirmed cases and 55 confirmed deaths, and cases were also reported in the D.R.C.

• 2020: The D.R.C. reported 130 cases, 55 of which ended in death.

• 2019: A severe outbreak led to nearly 3,500 cases in the D.R.C., with nearly 2,300 deaths.

• 2014: An Ebola epidemic in West Africa began in 2014 and ended in 2016. It was the largest such epidemic in history, with cases in southeastern Guinea, Liberia and Sierra Leone. More than 28,600 people fell ill and more than 11,300 died. There were also cases reported in the D.R.C., Mali, Nigeria, Senegal, Spain, Britain and the United States.

• 2007: About 130 people in Uganda fell ill with the Bundibugyo virus, and more than 40 people died. In the D.R.C., there were more than 260 cases related to the Zaire species of the Ebola virus, and more than 70 percent of cases resulted in death.

• 2003: Two outbreaks in the Republic of the Congo led to about 180 cases and 170 deaths.

• 2001: Two small outbreaks occurred in the Republic of the Congo and in Gabon, each affecting about five dozen people and resulting in the deaths of most of those who fell ill.

• 2000: About 425 people fell ill during an outbreak in Uganda; more than half died.

There were also a number of notable outbreaks of the virus after its discovery in 1976, before the turn of the century.

• 1996: Two small outbreaks in Gabon afflicted more than 90 people and more than 60 people died. There were also two cases in South Africa.

• 1995: Several hundred people fell ill with Ebola in the D.R.C. More than 250 people died.

• 1994: More than 50 people in Gabon’s rainforest fell ill, and scientists initially believed they had yellow fever, but later attributed the illnesses to an Ebola virus.

• 1979: An outbreak in what is now South Sudan affected nearly 35 people, killing more than 20.

• 1976: Two strains of Ebola virus affected nearly 600 people in South Sudan and the D.R.C., leading to the deaths of more than 430 people.

Are there vaccines?

There is no vaccine or specific treatment for the Bundibugyo species, as outbreaks have been rare.

The Bundibugyo species was first identified in 2007 after a mysterious illness broke out in Bundibugyo District in Uganda, which borders the D.R.C. Diagnostic samples submitted to the C.D.C. in the United States revealed the existence of a previously unknown type of Ebola virus. In 2012, another such outbreak was identified in the D.R.C.

Fatality rates during the past two outbreaks of this form of Ebola have ranged from 30 percent to 50 percent, according to the W.H.O. While there is no licensed vaccine or specific treatment for the Bundibugyo species, early care can save lives, health experts say.

The incubation period for this species of Ebola virus ranges from two to 21 days, and individuals are usually not infectious until symptoms manifest. But because the early symptoms — like fever and fatigue — resemble those of other illnesses, including malaria, early detection can be difficult.

Vaccines have been developed for the Zaire species, but they are not effective in preventing disease caused by other Ebola virus species.

In January, scientists at the University of Oxford announced an effort to develop and test vaccines to protect against multiple lethal viruses, including Bundibugyo. And the W.H.O. says that “candidate products are in development” to address the species of Ebola without current vaccines, including Bundibugyo.

Have U.S. spending cuts impeded the response?

The U.S. Agency for International Development has played a major role in containing previous outbreaks, but last year it was shuttered by the Trump administration. It is unclear how that might have affected the response to this outbreak. Atul Gawande, who served as assistant administrator for global health at U.S.A.I.D. during the Biden administration, suggested on social media on Sunday that the latest outbreak went undetected for weeks because American agencies had withdrawn from work that had previously helped detect outbreaks sooner.

The C.D.C. said in a statement that it had “mobilized response activities” upon receiving confirmation of the outbreak and has “been actively working to support” the needs of the health ministries in D.R.C. and Uganda.

In 2014, when the W.H.O. declared a Public Health Emergency of International Concern amid the world’s most severe Ebola outbreak, the C.D.C. in the United States collaborated with other American agencies, health ministries in the affected countries, and national and international agencies and partners to help end the epidemic.

The United States withdrew from the W.H.O. in January, cutting off regular communication with that organization. The C.D.C. learned of the outbreak only on Thursday, according to officials.