SA’s three big cities identified as possible sources of future pandemics

Johannesburg, Cape Town and Durban are among the global cities at high risk of seeding the next pandemic, according to a new study led by the University of Sydney in Australia.

The research looks at cities with a high level of contact between animals and humans, combined with poor health care and high global connectedness.

Lead author Michael Walsh said areas where the human pressure on wildlife is high have more than 40% of the world’s most connected cities, measured by airports within 50km.

Between 14% and 20% of the world’s most connected cities at risk of diseases spilling over from animals to humans are likely to fail to detect the new diseases because of poor health infrastructure, said Walsh. This list of 74 includes SA’s three biggest cities.

“The emerging infections that lead to substantive epidemics or pandemics are typically zoonoses that cross species boundaries at vulnerable points of animal-human interface,” said Walsh’s paper, in the journal One Health.

“The sharing of space between wildlife and humans, and their domesticated animals, has dramatically increased in recent decades and is a key driver of pathogen spillover.

“Increasing animal-human interface has also occurred in concert with both increasing globalisation and failing health systems, resulting in a trifecta with dire implications for human and animal health.

“Where spillovers go unidentified this might lead to dissemination worldwide and new pandemics,” said Walsh, from the Marie Bashir Institute for Infectious Diseases and Biosecurity.

The cities at highest risk of spillovers are predominantly in Sub-Saharan Africa and south and southeast Asia.

With this new information, people can develop systems that incorporate human health infrastructure, animal husbandry, wildlife habitat conservation, and movement through transportation hubs to prevent the next pandemic.

Walsh said that though low- and middle-income countries have the most cities in zones classified at highest risk for spillover and subsequent global dissemination, the high risk in these areas is a consequence of diminished health systems.

While not as extensively represented in the zone of highest risk because of better health infrastructure, high-income countries still have many cities in the next two tiers of risk because of the extreme pressures affluent countries exert on wildlife via unsustainable development.

The researchers took a three-staged approach:

• Identify where the sharing of space between wildlife and humans is greatest, and therefore where spillover events would be expected to be most common;
• Identify where areas of high wildlife-human interface coincide with areas of poor health system performance, where chains of transmission after a spillover event are likely to be missed. The infant mortality ratio (IMR) was used as a proxy for health system performance; and
• Identify cities within or adjacent to these areas of spillover risk that are highly connected to the network of global air travel, and therefore may serve as conduits for future pandemics.

“This is the first time this three-staged geography has been identified and mapped, and we want this to be able to inform the development of multi-tiered surveillance of infections in humans and animals to help prevent the next pandemic,” the paper said.

Walsh said though it would be a big job to improve habitat conservation and health systems, as well as surveillance at airports as a last line of defence, the benefit in terms of safeguarding against debilitating pandemics would outweigh the costs.

“Locally directed efforts can apply these results to identify vulnerable points. With this new information, people can develop systems that incorporate human health infrastructure, animal husbandry, wildlife habitat conservation, and movement through transportation hubs to prevent the next pandemic,” he said.

“Given the overwhelming risk absorbed by so many of the world’s communities and the concurrent high-risk exposure of so many of our most connected cities, this is something that requires our collective prompt attention.”

Key measures required included conservation efforts to limit wildlife encounters with humans and their domesticated animals, improved surveillance of animals and improved human health infrastructure to detect spillovers.