An epidemic of Ebola in eastern Democratic Republic of Congo has prompted Rwanda to close its border with DRC.
Here are some facts about the virus, which has claimed around 15,000 lives in a known history of 43 years.
Ebola haemorrhagic fever was first identified in 1976 after Belgian-led scientists probed a string of unexplained deaths in northern DRC, then known as Zaire.
The disease was named after a river nearby.
The virus that causes Ebola is believed to reside in bats, which do not themselves fall ill but can pass it on.
Chimpanzees, gorillas, monkeys, forest antelope and porcupines can become infected, and humans who kill and eat these animals can catch the virus through them. Infected humans, in turn, contaminate other people through contact with their body fluids.
DIFFICULT TO CONTAIN
Four viral strains are known to cause disease in humans: Zaire, Sudan, Bundibugyo and Tai Forest.
The symptoms are severe: high fever and muscle pain followed by vomiting and diarrhoea, skin eruptions, kidney and liver failure, internal and external bleeding.
The average fatality rate is around 50 percent, the World Health Organization (WHO) says. The latest outbreak has a mortality rate of around two-thirds.
It is difficult to contain, especially in urban environments, being transmitted through close contact with the blood, body fluids, secretions or organs of an infected person.
People who are infected do not become contagious until symptoms appear, which is after an incubation period of between two and 21 days.
Patients and people who have been in contact with them are routinely isolated.
Medical personnel have to be meticulously protected with disposable full-body plastic suits, masks, goggles, gloves and disinfecting sprays.
The worst Ebola epidemic started in December 2013 in southern Guinea and spread to neighbouring West African countries Liberia and Sierra Leone.
It claimed the lives of more than 11,300 people from the nearly 29,000 registered cases, according to WHO estimates, before being declared over in December 2015.
More than 99 percent of victims were in Liberia, Guinea and Sierra Leone, although cases occurred elsewhere through international travel, sparking panic.
The current epidemic was declared on August 1, 2018 in DRC's North Kivu province, on the border with Uganda, and spread to neighbouring Ituri in DRC.
Since then it has claimed more than 1,800 lives in those areas, and there are fears that it will cross the DRC's porous borders.
Two infected Ugandans -- a boy and his grandmother -- died in June 2019.
Since July, two people have died in the major DRC city of Goma, on the busy border with Rwanda. A third infection in the city was announced Thursday, as the border was shut.
The WHO on July 18 declared the outbreak a "public health emergency of international concern," a rare designation only used for the gravest epidemics.
It is the 10th outbreak in the country.
At present there is no licensed drug to prevent or treat Ebola although a range of experimental drugs are in development.
After the outbreak that started in August 2018, health authorities there began issuing the rVSV-Zebov vaccine on a large scale for the first time.
Developed by the US pharma group Merck, the vaccine is unlicensed but has been shown to be safe and effective, and the WHO has called for its deployment to be expanded.
WHO experts have also recommended introducing another experimental vaccine, the MVA-BN, developed by Johnson&Johnson.
SOURCES: AFP, WHO, US Centers for Disease Control and Prevention (CDC), European Centre for Disease Prevention and Control (ECDC).