The rare Ebola virus behind the current outbreak, explained

The rare Ebola virus behind the current outbreak, explained

Bundibugyo virus is a rare species of Ebola virus that has only been associated with two other known outbreaks.

By Claire Maldarelli edited by Lewis asked.

Global health officials are follow up an Ebola outbreak caused by a rare species of orthoebolavirus called Bundibugyo virus that has so far killed more than 130 people and infected more than 500 others, with other cases likely.

First alerted by the epidemic in the Democratic Republic of Congo (DRC) on May 5, the World Health Organization (WHO) has since declared it to be “a public health emergency of international concern,” the organization’s highest official alert.

Infection in Bundibugyo has a mortality rate of up to 50 percent. Here’s what scientists know and don’t know about this virus and why it’s so concerning to experts.

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What is Bundibugyo virus and how does it differ from other forms of Ebola viruses?

Orthoebolaviruses are Ebola-causing members of a family of viruses called filoviruses, which also includes Marburg virus. Scientists currently know of four species of orthoebolaviruses that cause disease in humans. These include Ebola virus (formerly called Zaire virus), the species responsible for the largest and most severe Ebola outbreaks, as well as Soudan virus, Taï forest virus and Bundibugyo virus.

Compared to the Ebola virus, Bundibugyo is a relatively rare species of orthoebolavirus, explains Elke Mühlberger, professor of virology, immunology and microbiology at Boston University. Before the current outbreak, there have been only two other known outbreaks of Bundibugyo virus: one in Uganda in 2007, when the species was first identified, and another in the DRC in 2012.

Symptoms of Bundibugyo virus infection resemble those of other orthoebolaviruses. At first, they include severe headache, high fever, body aches, and fatigue. As the infection progresses, people may develop intense vomiting and diarrhea, which can be life-threatening. Orthoebolaviruses are also known to cause hemorrhagic fever, in which the virus infects specific immune cells, triggering a massive inflammatory response that can lead to internal bleeding and organ failure.

Is the Bundibugyo virus more deadly than other Ebola viruses?

Filoviruses generally have high mortality rates in humans. Data from past outbreaks shows that the disease caused by the Ebola virus has a mortality rate of up to 90 percent if left untreated and between 50 and 60 percent with medical care; this includes both supportive treatment, vaccines and antibody therapies.

Bundibugyo virus, on the other hand, appears to cause milder but still serious illness. Its mortality rate ranges from 30 to 50 percent, According to the WHO. “It seems a bit cynical to say it’s benign, because if a third of patients die, that means it’s still very dangerous,” says Mühlberger. Some virologists also caution that the death rate is based on just two outbreaks with far fewer infections than Ebola, making it difficult to know whether the current outbreak will show similar rates.

One of the main reasons these viruses are so deadly is that they are incredibly capable of evading the body’s immune defenses, particularly our innate immune system, says Steven Bradfute, an immunologist at the University of New Mexico Health Sciences Center. Normally, the innate immune system’s job is to provide a rapid, nonspecific response to an invading pathogen and alert other, more specialized immune cells to prepare for combat. Bradfute says some research suggests the Ebola virus is more effective at blocking this innate immune response than the Bundibugyo virus, which could be one reason the latter has a lower mortality rate.

“THE [orthoebolaviruses] have some proteins that are effective in blocking this early innate response. And different changes in these proteins that are found in different [orthoebolaviruses] might not be as effective at blocking that, and that might lead to a less pathogenic infection,” says Bradfute.

Do any treatments exist?

Currently, there is no treatment for Bundibugyo virus. The two main defenses that communities have against viruses, including highly pathogenic ones like those that cause Ebola, are vaccines and monoclonal antibody treatments. Vaccines aim to prevent infection in the first place, and antibody treatments strengthen the immune response to infection by neutralizing and preventing viruses from entering cells.

There are two antibody treatments and a vaccine for Ebola, says Erica Ollmann Saphire, an immunologist at the La Jolla Institute of Immunology in California, but they are unlikely to have a significant effect on Bundibugyo, she says. When the genetic sequence of Bundibugyo was first published in 2008shortly after the initial 2007 outbreak in Uganda, the virus was shown to be more than 30 percent genetically distinct from all other known orthoebolaviruses, making it different enough to constitute its own species and meaning that vaccines designed to treat other orthoebolaviruses were likely less effective. “Bundibugyo is the closest to [Ebola virus] compared to all others [orthoebolaviruses]but it’s different enough that [the vaccine for Ebola virus] may not induce sufficient cross-reactive protection,” explains Saphire.

Researchers are developing vaccines specifically against the Bundibugyo virusand early candidates have proven to be very effective in animal trials. But so far, big pharmaceutical companies have shown little interest in further testing these vaccines in humans, because they likely would not be profitable, Saphire says. Scientists are also working to create vaccines that could protect against multiple orthoebolaviruses simultaneously, which could be much more effective in preventing outbreaks.

“These epidemics are very difficult to predict and you never know what the next virus will be,” explains Mühlberger. “Everyone in this field is well aware that we need antivirals and vaccines that protect you against a whole host of these viruses. »