The emergence of COVID-19 has produced the worst pandemic in living memory, but barely two years later, countries are now grappling with the appearance of monkeypox, which the World Health Organisation (WHO) has declared a public health emergency of international concern.
Disease outbreaks are now happening at an increasing rate with fewer years between them and more outbreaks that spread across several continents.
"There's clear research evidence now that, particularly for viruses, the number of pathogen emergence events that lead to outbreaks, epidemics and pandemics has increased over the last century," said University of Tasmania disease ecologist and epidemiologist Dr Scott Carver.
Why are disease outbreaks becoming more common?
Dr Carver said there were many reasons outbreaks were becoming more common, including increased human contact with wild animals due to deforestation, population growth, climate change, the wild animal trade and expansion of farming land.
Some scientists believe zoonotic spillover events (when a disease-causing organism in animals jumps into humans) have likely triggered every viral pandemic since the start of the 20th century.
As humans push further into wilderness areas, they are also more likely to be exposed to new diseases. Source: AP
It noted factors that could increase the risk of a pandemic include the growing number of laboratories handling dangerous pathogens, which could boost the likelihood of a disease-causing organism being released accidentally, and also the possibility of a country developing a biological weapon. But it pointed to an increase in spillovers as causing the faster emergence of new infectious diseases.
"New infectious diseases have been emerging at a quickening pace due to increased zoonotic transmission from animals, driven by population growth, climate change, habitat loss, and human behaviour, and these diseases are spreading faster with increased global travel," the paper said.
It's likely both COVID-19 and monkeypox were caused by spillovers, potentially linked to bats and rodents, respectively.
This month, scientists revealed in the another , and possibly connected to shrews. No deaths have yet been recorded and it's unclear whether the virus can be transmitted between people.
"As devastating as the COVID-19 pandemic is, there is a reasonable likelihood that another serious pandemic that may be worse than COVID-19 will occur soon — possibly within the next decade," the paper warned.
Scientists are concerned spillovers are not being properly addressed to stop diseases from emerging in the first place. Instead, countries are focusing on improving their monitoring of infectious diseases and developing vaccines.
China banned the sale and consumption of wild animals after the emergence of COVID-19. Source: Getty / Getty Images
"This supports the suggestion that zoonotic [emerging infectious diseases] represent an increasing and very significant threat to global health," the study noted.
The study found the incidence of emerging infectious disease events had increased since 1940, and around 60.3 per cent of these emerging diseases had an animal source. Among these, 71.8 per cent came from wildlife.
Many people in Australia may remember warnings about H1N1, known as swine flu, which was first detected in the United States in 2009. More than 37,000 cases were confirmed in Australia and 191 people died from the disease.
There is a reasonable likelihood that another serious pandemic that may be worse than COVID-19 will occur soon — possibly within the next decade.
More recently Zika virus, which is spread by mosquitoes, almost derailed the 2016 Olympic Games in Brazil. While it's generally not a deadly disease, it can cause complications among pregnant women and congenital abnormalities in babies.
While H1N1 and Zika were not declared pandemics, which the WHO loosely defines as a new disease that spreads across the world, they still had serious health consequences for many people.
The 2016 Rio Olympics was almost derailed by the spread of Zika.
How exactly does an animal infection get into humans?
Humans can be exposed to pathogens in various ways, including having direct contact with an infected animal. For example, being scratched or bitten, or touching infectious tissue or fluids while butchering meat.
People can also breathe in airborne particles from the urine of rodents or bats; or eat or drink contaminated water, soil or food. Mosquitoes, ticks and fleas can pass on the disease if they feed on infected wildlife and then bite humans.
Many humans don't have direct contact with wild animals but infections can involve a more domesticated "host animal" such as a pig, being exposed and then passing the disease on to humans.
This is becoming an increasing problem as humans move further into relatively untouched wilderness areas due to logging operations or the expansion of farmlands.
Dr Carver said one of the classic examples of this was seen in Malaysia when the expansion of pig farms into more natural areas saw the emergence of Nipah virus in 1999, which infected more than 300 people and killed more than 100. Nearby fruit bats were attracted to mango trees planted close to the pig farms and dropped their faeces into piggeries.
"That led to the viruses that these fruit bats had — this Nipah virus — spilling over into the pigs and then ultimately to humans," he said.
Nipah virus is thought to have emerged after bat droppings landed in pig farms.
"So having increased contact with animals, particularly unusual contacts with unusual wildlife ... can lead to pathogens that people would not normally be exposed to making it into them, or potentially making it into our domestic or agricultural animals, that then might make it into humans."
Climate change is also playing a role, although it is not as significant.
"Droughts place stresses on wildlife and other animals to have to seek out sources, for example, of water ... and that can drive their behaviours to move into areas where they wouldn't normally move into," Dr Carver said.
Some experts are now calling for action to reduce the likelihood of spillover events so the risk of pandemics is also reduced.
What can we do to help prevent future pandemics?
Dr Carver said research showed the cost of acting on things like deforestation, agricultural expansion, restoration of natural habitats, biosecurity measures, climate change and the wildlife trade, could be much cheaper than responding to disease outbreaks.
"The good news is that because we understand the sorts of factors that are associated with pathogens ... we also understand ... things we can do to help mitigate those," he said.
These activities also have other benefits including decreasing carbon emissions, conserving water supplies and biodiversity, and protecting the rights of Indigenous peoples to their lands.
But rather than prioritising the prevention of spillovers, authorities including those in the US, are instead directing action towards better development of vaccines, early detection of diseases and the prevention of laboratory accidents.
Several health experts are now calling for a more proactive approach to tackling pandemics, including addressing spillovers.
Disease are spreading more quickly thanks to air travel. Source: AAP
They also called for the trade of live wild animals to be banned or better regulated, improved biosecurity for farmed animals, and a focus on improving the health and economic security of people living in areas deemed hotspots for the emergence of diseases, as people in poor health can be more susceptible to infection from disease-causing organisms.
The scientists noted analysis of disease outbreaks over the past four centuries indicated the yearly probability of pandemics could increase several-fold in the coming decades, largely due to human-induced environmental changes.
"For around US$20 billion ($28.2 billion) per year, the likelihood of spillover could be greatly reduced," they wrote.
"This is the amount needed to halve global deforestation in hotspots for emerging infectious diseases; drastically curtail and regulate trade in wildlife; and greatly improve the ability to detect and control infectious diseases in farmed animals.
"That is a small investment compared with the millions of lives lost and trillions of dollars spent in the COVID-19 pandemic."
The six experts hoped "three landmark international endeavours" will help to prevent spillovers and prevent future pandemics.
Droughts can force wildlife into more populated areas as they search for water. Source: AAP
In June, it was announced a new to provide funding to low and middle-income countries and regions, for strengthening health systems.
Around US$1.3 billion ($1.9 billion) has already been raised from countries including the US, European Commission, Italy, Indonesia, China and the United Kingdom. Australia has also pledged to contribute but no decision has yet been made on the amount.
"If realised, this could provide funding at levels that infectious-disease experts have been recommending for decades — around $5 per person per year globally," the six experts write.
The second action is the negotiation of an international instrument to strengthen the global health response.
The World Health Assembly, part of the WHO, is negotiating a legally-binding convention, agreement or other international instruments, for new processes that would potentially support the early detection of outbreaks, provide for better collaboration and information sharing among countries, and easier access to vaccines.
Thirdly, the United Nations Convention on Biological Diversity, of which Australia is a member, is negotiating a framework to reduce and reverse biodiversity loss. Its next meeting is due to be held in December.
"Designed in the right way, these three international endeavours could foster a more proactive global approach to infectious diseases," the US experts note.
"This opportunity — to finally address the factors that drive major disease outbreaks, many of which also contribute to climate change and biodiversity loss — might not present itself again until the world faces another pandemic."
In Australia, SBS News asked Health Minister Mark Butler whether he believed action should be taken to prevent spillover events. Mr Butler said in a statement his department was preparing advice on the establishment of an Australian Centre for Disease Control (CDC), which was a Labor election commitment.
During the 2022 federal election campaign, the Labor Party said the proposed CDC would lead the federal response to future infectious disease outbreaks, ensure pandemic preparedness and work to prevent chronic as well as infectious diseases.
"There were many lessons learned during the COVID pandemic about the importance of emergency planning and a coordinated national response capability," Mr Butler said.
"A CDC will help to leverage these lessons and prepare for future pandemics and other public health challenges."
