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Thinking about the next pandemic keeps many researchers busy.

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Peter Zelei Images / Getty Images

Thinking about the next pandemic keeps many researchers busy.

Peter Zelei Images / Getty Images

Just three years ago, on January 30, 2020, the head of the World Health Organization made a groundbreaking statement: A “novel coronavirus” first identified in China had spread to the point where it was now a “public health emergency.” of International Importance (PHEIC).”

The virus now known as SARS-CoV-2 – which causes the disease COVID-19 – is still spreading. But for those who study infectious diseases, talking about possible next pandemics is a necessity.

Hidden Viruses: How Pandemics Really Start

NPR has a series on spillover viruses — that’s when pathogens from animals get to humans. Researchers used to think that spillovers were rare events. Now it is clear that they happen all the time. That has changed the way scientists search for new deadly viruses. To learn more, we traveled to Guatemala and Bangladesh, to Borneo and South Africa.

Send your questions about spillovers to goatsandsoda@npr.org with “spillovers” in the subject line. We’ll answer questions in a follow-up post when the series ends in mid-February.

That is why the World Health Organization maintains a list of viruses and bacteria with pandemic potential. Jill Weatherhead of Baylor College of Medicine says prioritizing diseases is generally based on two factors: their ability to spread and people’s ability to treat them.

The list helps guide scientists, governments and organizations as they invest energy and funds to study the pathogens most likely to wreak the greatest havoc on humans. The WHO is developing “blueprints” with strategic goals and research priorities for each disease on the list.

These are the diseases on the current list. A revised list is expected in the coming months: by the end of 2022, the World Health Organization convened more than 300 scientists to review and update the list.

Note: Disease detection infrastructure varies in different parts of the world, as does the fact that mild cases of a disease may not be known or reported. The mortality rate is based on the best available data.

Nipah virus

Which animals carry it: fruit bats, including flying foxes, and domestic animals such as pigs, horses, cats, and dogs

How it spreads: The Nipah virus can be transmitted to humans through animals or contaminated food. It can also be transmitted directly from person to person.

Its toll: 40% to 75% mortality rate. The virus can also cause encephalitis, or swelling of the brain.

Medical tool box: No vaccine is available for humans or animals. Monoclonal antibody therapies are under development.

Pandemic Potential: Outbreaks occur in parts of Asia almost every year, but there are known ways to prevent the virus from spreading. Prevention efforts include avoiding exposure to bats and sick animals, avoiding the consumption of fruits that bats may have nibbled on, and not drinking certain raw juices from fruits that bats feed on. The risk of international transmission can be reduced by thoroughly washing and peeling those fruits and fruit products before eating them.

Crimean-Congo haemorrhagic fever

Which animals carry it: sign, cattle

How it spreads: People usually get the virus through contact with ticks or infected livestock. Getting the virus from another person requires close contact with blood or other bodily fluids from an infected person.

Its toll: 10% to 40% mortality rate. The disease is endemic, meaning it occurs regularly, in Africa, the Balkans, the Middle East and Asia. The virus causes severe outbreaks of viral hemorrhagic fever, a condition that can damage the body’s organ and cardiovascular systems and is often accompanied by severe bleeding.

Medical tool box: Although a vaccine is in use in Bulgaria, no research has been published on how well it works, and it is not licensed anywhere else. Other vaccines are in development, and an antiviral called ribavirin appears to help treat infections.

Pandemic Potential: It’s hard to tell when an animal is infected and should be avoided, and the WHO says ticks carrying the virus are numerous and widespread. The threat can be reduced by avoiding tick bites and wearing gloves and other protective clothing around livestock.

Lassa fever

Which animals carry it: rats and other rodents

How it spreads: The virus is endemic to parts of West Africa. Rats shed the virus and humans pick it up when exposed to the rodents’ urine and feces, either through direct contact or eating contaminated food. It can also spread between people through direct contact with an infected person’s secretions (blood, urine, feces), through sexual contact, and in medical settings through contaminated equipment.

Its toll: 1%, but up to 15% in severe hospital cases. It can be fatal to humans and fetuses in the third trimester of pregnancy. In addition to death, a common complication is deafness, which can be permanent.

Medical tool box: There is no vaccine, but ribavirin appears to help treat infections.

Pandemic Potential: Because the primary method of transmission is exposure to a particular type of rat, the likelihood of the disease spreading is most likely limited to the countries where the rat lives.

Rift Valley fever

Which animals carry it: mosquitoes. The insects can transmit the virus to humans as well as to their own offspring. Livestock such as cattle, sheep, goats, buffaloes and camels can also become infected.

How it spreads: It spreads to humans through contact with blood, other bodily fluids, or tissues from infected animals.

Its toll: Although the mortality rate is less than 1% and the disease is mild for most people, about 8% to 10% of infected people develop severe symptoms, including eye lesions, encephalitis, and hemorrhagic fever.

Medical tool box: Although a vaccine has been developed, it is not yet approved or available.

Pandemic Potential: Rift Valley fever has spread from Africa to Saudi Arabia and Yemen. Flooding appears to be contributing to more Rift Valley fever as more virus-infected mosquitoes buzz after heavy rainfall. Rapid case detection, including rapid lab testing of people with symptoms, has contained recent outbreaks.


Which animals carry it: mosquitoes

How it spreads: In addition to mosquito bites, the virus can spread from a pregnant person to a fetus. The disease can also be transmitted through sex and probably through blood transfusions.

Its toll: Rarely fatal, Zika can cause serious brain abnormalities in fetuses, including microcephaly. It has also been linked to miscarriage, stillbirth, and other birth defects.

Medical tool box: No treatment or vaccine

Pandemic Potential: So far, it has been largely confined to areas where Zika-carrying mosquitoes live.

Ebola and Marburg virus disease

What animals do they carry: Bats and non-human primates are believed to carry the viruses, from the filovirus family, that cause these hemorrhagic fevers.

How they spread: Both viruses are believed to spread in the same way. After the initial defection from an animal, humans spread the viruses to other humans through direct contact with blood or other bodily fluids of a person who is symptomatic or who has died of the disease. The viruses can also spread through objects or surfaces contaminated with bodily fluids and through semen from people who have recovered from the disease.

Their toll: The average mortality rate is about 50%, although the rate has ranged from 25% to 90% in previous outbreaks.

Medical tool box: Vaccines have been used for Ebola in Guinea and the Democratic Republic of Congo. Monoclonal antibodies approved by the Food and Drug Administration in 2020 may also help treat Ebola. Vaccines against the Marburg virus are under development.

Pandemic Potential: These viruses can spread quickly in healthcare settings, especially when proper sterilization is not used. However, the disease only spreads when a person is symptomatic, making it easier to manage.

MERS (Middle East Respiratory Syndrome)

Which animals carry it: camels

How it spreads: After the initial spillover event from camels to humans, this coronavirus can spread from person to person through close contact with an infected person.

Its toll: The reported fatality rate is 35% according to WHO.

Medical tool box: Several vaccines are in development, but none have been approved.

Pandemic Potential: Since 2012, 27 countries have reported infections. Unlike SARS-CoV-2, the coronavirus that causes MERS grows deep in the airways, making it much less likely to be transmitted through sneezing and coughing.

SARS (severe acute respiratory syndrome)

Which animals carry it: Palm civets were largely blamed for the 2003 outbreak. Bats and possibly other wildlife also carry it.

How it spreads: After the initial animal-to-human spillover event, SARS can spread from human to human through close contact with an infected person. It is believed to usually spread through droplets from coughs and sneezes and sometimes through surfaces touched by contagious people.

Its toll: less than 1% mortality rate

Medical tool box: No treatment or vaccine has been approved.

Pandemic Potential: Unlike SARS-CoV-2, which can spread before people know it is contagious, this SARS virus is usually only spread by people with known symptoms, making it much easier to contain through public health measures such as quarantine . The 2003 outbreak was brought under control after about 8,000 cases and 700 deaths in 29 countries.

Disease X

The WHO says it does not rank diseases in order of potential threat, but recognizes the possibility that a hitherto unknown disease could trigger a serious pandemic.

For example, in her work with bat viruses, Raina Plowright of Cornell University says that even in the small fraction of bat species that have been studied, the animals carry thousands of viruses, “and we have no idea how many are at risk.” say. “We don’t have the technology to take a sequence and say for sure whether it can infect humans or transmit from person to person. We are really blind.”

Not to mention that variants pose threats, she says. “Just the tiniest genetic change can have a profound effect. What if we had [a pathogen] with a 50% fatality rate dispatched efficiently?”

Sheila Mulrooney Eldred is a freelance health journalist based in Minneapolis. She has written about COVID-19 for many publications, including The New York TimesKaiser Health News, Medscape en The Washington Post. More than sheilaeldred.pressfolios.com. On Twitter: @milepostmedia.

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