Which virus will cause the next pandemic?
The COVID-19 pandemic took much of the world by surprise. But not everyone. For years, epidemiologists and other experts have warned that we have been setting ourselves up for a global pandemic.
Most of the diseases experts worry about originate in animals. In fact, 75% of newly emerging diseases are zoonotic. COVID-19 – thought to have originated in pangolins sold at wet markets in China – was no different. But like COVID-19, zoonotic diseases are becoming riskier to humans because of our own actions.
Our effect on the climate, encroachment on wildlife habitats and global travel have helped circulate animal-borne diseases. Combined with urbanisation, overpopulation and global trade, we’ve set up an ideal scenario for more pandemics to come.
World Health Organization (WHO)’s concerns
In 2018, the World Health Organization (WHO) listed several infectious diseases that pose a serious threat to public health, most of which have no vaccines yet and few medicines, with the aim of galvanising research into them. It called one of them ‘Disease X’ – a future disease that humans had never seen before that would cause a pandemic. COVID-19 has proven to be disease X,
We will now describe 10 viruses that may cause the next pandemic. Most but not all are viruses.
1. Nipah virus
What animals carry it: fruit bats (including flying foxes), and domestic animals such as pigs, horses, cats and dogs.
How it spreads: Nipah virus can be transmitted to humans from animals or contaminated foods. It can also be transmitted directly from human to human.
Mortality: 40% to 75% fatality rate. The virus can also cause encephalitis, or swelling of the brain.
2. Crimean-Congo haemorrhagic fever
What animals carry it: ticks, livestock.
How it spreads: Humans usually get the virus from contact with ticks or infected livestock. To get the virus from another person requires close contact with blood or other bodily fluids from an infected person.
Mortality: 10% to 40% fatality rate. The disease is endemic, meaning it occurs regularly, in Africa, the Balkans, the Middle East and Asia. The virus causes severe outbreaks of a viral haemorrhagic fever; a condition that damages several the body’s organ systems (including cardiovascular) and often leads to severe bleeding.
3. Lassa fever
What animals carry it: rats and other rodents
How it spreads: The virus is endemic in parts of West Africa. Rats excrete the virus, and humans pick it up when exposed to the rodents’ urine and faeces, either through direct contact or eating contaminated food. It can also spread between humans through direct contact with an infected person’s secretions (blood, urine, faeces), through sexual contact, and in medical settings via contaminated equipment.
Mortality: 1%, but up to 15% in severe hospitalised cases. It can be deadly for people and foetuses in the third trimester of pregnancy. Besides death, a common complication is deafness, which can be permanent.
4. Rift Valley fever
What animals carry it: mosquitoes. The insects can transmit the virus to both humans and their own offspring. Livestock such as cattle, sheep, goats, buffalo and camels can also get infected.
How it spreads: It spreads to people through contact with blood, other body fluids or tissues of infected animals.
Mortality: Although the fatality level is less than 1% and the disease is mild for most people, about 8% to 10% of people infected develop severe symptoms – including eye lesions, encephalitis and haemorrhagic fever.
5. Zika
What animals carry it: mosquitoes.
How it spreads: In addition to mosquito bites, the virus can spread from a pregnant person to a foetus. The disease can also be transmitted through sex and probably through blood transfusions.
Mortality: It is rarely fatal, but Zika can cause severe brain defects in foetuses, including microcephaly. It has also been linked to miscarriage, stillbirth and other birth defects.
6. Ebola and Marburg virus disease
What animals carry them: bats and nonhuman primates are believed to carry the viruses, from the filovirus family, that cause these haemorrhagic fevers.
How they spread: Both viruses are believed to spread in the same way. After the initial spillover 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 from 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.
Mortality: The average fatality rate is about 50%, though rates have varied from 25% to 90% in past outbreaks.
7. MERS (Middle East respiratory syndrome)
What 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.
Mortality: The reported fatality rate, according to the WHO, is 35%.
8. SARS (severe acute respiratory syndrome)
What 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 spillover event from animal to human, SARS can spread from person to person 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 infectious people.
Mortality: less than a 1% fatality rate
9. Influenza
Pandemic influenza is different from ‘ordinary’ seasonal flu, which for most people is an unpleasant illness but runs its natural course (sometimes referred to as ‘self-limiting’) and is not life-endangering.
Pandemic flu can occur when a new influenza virus emerges which is markedly different from recently circulating strains and to which humans have little or no immunity.
The 1918 Spanish flu pandemic was an exceptionally deadly global influenza pandemic caused by the H1N1 influenza A virus. Estimates of deaths range from 17 million t o 50 million, and possibly as high as 100 million, making it one of the deadliest pandemics in history.
The influenza virus can originate in wild waterfowl which transmit infection to domestic birds and poultry, and they then pass it on to animals and/or humans.
10. Bubonic plague
Historically, the most well-known and devastating pandemics were those of the bubonic plague (caused by the flea-borne bacterium Yersinia pestis). The first bubonic plague pandemic, known as the Plague of Justinian, was active for 21 years, 521 to 542 AD. It killed up to 30 % of the world’s population.
The second bubonic plague, known as the Black Death, ravaged Europe, North Africa, and Asia from 1346 to 1353; and is estimated to have caused up to 200 million deaths – as many as 60 % of the population of Europe at the time
The disease still affects rodents and can be transmitted from rodents to humans today. In fact, modern outbreaks of the disease were seen in 1994 in India, in 2003 in Algeria, in 2006 in the Democratic Republic of Congo and in 2008 and 2014 in Madagascar – but were limited deaths (100-150).
What about Disease X?
The WHO says it does not rank diseases in any order of potential threat, but it continues to acknowledge the possibility that an as-yet-unknown disease (‘Disease X’) could cause another serious pandemic. COVID-19 was Disease X. There could be another.
In her work with bat viruses, for example, Raina Plowright of Cornell University says that even in the small proportion of bat species that have been studied, the animals carry thousands of viruses, “and we have no clue how many present risk,” she says. “We don’t have the technology to take a sequence and say with certainty whether it can infect humans or can transmit from human to human. We’re blind, really.”
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 that transmitted efficiently?”
The Future
In the history of humanity, the COVID-19 pandemic is relatively mild by comparison with many others, including bubonic plague that had a much higher mortality. We might not be so lucky next time. This is why we need to make plans. Now.
Summary
We have discussed which virus will cause the next pandemic, and given 10 possibilities. We hope it has been informative.
