Air pollution exposure linked to higher COVID-19 cases and deaths – new study

The global death toll from COVID-19 has now passed half a million. To slow the spread of the disease, we need to better understand why some places have higher numbers of cases and deaths than others.

One factor that could partially explain this is air pollution. Research has shown that long term exposure to pollutants such as fine particulate matter (often called PM2.5, as these are particles smaller than 2.5 micrometres), nitrogen dioxide (NO₂) and sulphur dioxide (SO₂) can reduce lung function and cause respiratory illness. These pollutants have also been shown to cause a persistent inflammatory response even in the relatively young and to increase the risk of infection by viruses that target the respiratory tract.

The pathogen that causes COVID-19 – SARS-CoV-2 – is one such virus. Several studies have already suggested that poor air quality can leave people at greater risk of contracting the virus, and at greater risk of serious illness and death. A study of the US found that even a small increase in PM2.5 concentrations of 1 microgram per cubic metre is associated with an 8% increase in the COVID-19 death rate. Our new research looked at the relationship between COVID-19 cases and exposure to air pollution in the Netherlands and found that the equivalent figure for that country could be up to 16.6%.

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The unusual case of the Netherlands

After analysing data for 355 Dutch municipalities, we found that an increase in fine particulate matter concentrations of 1 microgram per cubic metre was linked with an increase of up to 15 COVID-19 cases, four hospital admissions and three deaths.

The first confirmed COVID-19 case in the Netherlands occurred in late February and by late June over 50,000 cases had been identified. The national spread of COVID-19 cases shows a greater number in the south-eastern regions.

Unusually, these hotspots of disease transmission are in relatively rural regions where there are fewer people living close together. The Dutch media offered one potential explanation. In late February and early March each year, these areas hold carnival celebrations which attract thousands of people to street parties and parades – 2020 was no exception, so does that explain the rapid spread of COVID-19 there?

While it’s likely that the carnival celebrations played a role, the pattern of cases across these regions suggest other factors may be at least as important.

The south-eastern provinces of North Brabant and Limburg house over 63% of the country’s 12 million pigs and 42% of its 101 million chickens. Intensive livestock production produces large amounts of ammonia. These particles often form a significant proportion of fine particulate matter in air pollution. Concentrations of this are at their highest in air samples from the south-east of the Netherlands.

The correlation between these indicators of air pollution and cases of COVID-19 is clear to see, but is it just a coincidence?

Pollutants associated with COVID-19

Our analysis used COVID-19 data up to June 5 2020, capturing almost the entire known course of the Dutch epidemic. The relationship we found between pollution and COVID-19 exists even after controlling for other contributing factors, such as the carnival, age, health, income, population density and others.

To put our results in context, the highest annual average concentration of fine particulate matter in a Dutch municipality is 12.3 micrograms per cubic metre, while the lowest is 6.9. If concentrations in the most polluted municipality fell to the level of the least polluted, our results suggest this would lead to 82 fewer disease cases, 24 fewer hospital admissions and 19 fewer deaths, purely as a result of the change in pollution.

Read more: What we do and don't know about the links between air pollution and coronavirus

The correlation we found between exposure to air pollution and COVID-19 is not simply a result of disease cases being clustered in large cities where pollution may be higher. After all, COVID-19 hotspots in the Netherlands were in relatively rural regions. Still, region-level data can only get us so far. Within regions, pollution levels and COVID-19 cases can vary considerably from place to place, making it hard to estimate the precise relationship between the two.

Being able to study this link among individual people would allow us to more precisely eliminate the influence of age and health conditions. But until this kind of data is available, the evidence of a relationship between pollution and COVID-19 can never be conclusive.

Matt Cole, Professor of Environmental Economics, University of Birmingham; Ceren Ozgen, Assistant Professor in Economics, University of Birmingham, and Eric Strobl, Professor of Economics, Université de Berne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bats are hosts to a range of viruses but don't get sick – why?

Bats harbour many diverse viruses, including coronaviruses. Indeed, Sars, Mers and COVID-19 – which are all caused by coronaviruses – are thought to have emerged from bats. These diseases can be deadly to humans, yet bats seem to be unaffected by them.

Like all animal species, bats possess their own range of pathogens – viral, bacterial and fungal. Organisms are part of an interconnected system of other living things that evolved to exploit and be exploited in turn. Bats have therefore evolved with a set of viruses that infect them and continuously circulate through the bat population.

SARS-CoV-2, the virus that causes COVID-19 is a member of a family of viruses called the coronaviridae (coronaviruses). Coronaviruses, or “CoVs”, infect a variety of animals, with human infections ranging from HCoV-229E, which causes some cases of the common cold, to MERS-CoV, which is fatal in up to 30% of cases.

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Since the original SARS-CoV outbreak in 2002, coronaviruses closely related to SARS-CoV have been discovered in bats from countries all over the world. Scientists in China studying Chinese horseshoe bats in 2013, identified several SARS-like CoVs that use the same ACE2 receptor to bind to cells as the current SARS-CoV-2. These viruses were similar enough to SARS-CoV that they were termed SARS-like coronaviruses. New viruses have been added to this group since then. So there is a significant diversity of coronaviruses circulating in bats, which may increase the probability that one of these viruses has the potential to become a zoonotic infection – in other words, can jump to humans.

Bats are excellent hosts for viruses in general and coronaviruses as a group have been particularly successful at infecting and diversifying within bats. The highly social nature of many bat species leads to the constant exchange of viral pathogens between bats – and this may act to drive viral diversification within a population.

Unique among mammals

With so many potentially dangerous viruses circulating among them, why do the bats themselves not die off from these constant infections? Clearly, bats can maintain a balance between control of a viral infection and the excessive inflammatory response that can kill other hosts. Perhaps the answer lies in their unique feature among mammals – flight.

Read more: Bat flu can spread to humans: should we be worried?

The physiological requirements of flight have affected the bat immune system. Flight causes bats to have elevated metabolic functions and raises their core body temperature about 38°C. This means that bats are often in a state that, for humans, would be considered a fever. Researchers in the UK have suggested that this may be a mechanism to help bats survive viral infections.

Viral infections can harm the host, in part, by causing an out-of-control inflammation response called a “cytokine storm”, which can be a fatal complication in several respiratory diseases, including COVID-19. If bats adaptation to flight also allows them to tolerate high body temperatures better, it means they can tolerate at least some potential damaging effects of the inflammation response better than other mammals.

In addition to traits that allow bats to tolerate a high body temperature, bats may also have other adaptations that mark their immune system as unusual or unique among mammals.

A sting in the tale

In 2018, scientists in China and Singapore identified a mutation in a gene that helps to control the antiviral response in bats during a viral infection. The mutation is in a gene called the stimulator of interferon genes (STING), which is common to all mammals and has a crucial role in triggering the inflammation response during a viral infection.

The mutation identified in bats has been shown to reduce the production of specific inflammation-causing proteins, called interferons, during a viral infection.

It may seem counter-intuitive that reduced production of an antiviral component could be better for the host, but it appears that damping down the inflammation response may allow the bats to avoid the damage caused an excessive immune response – the previously mentioned cytokine storm.

Adaptation to flight and mutation in STING both serve to control and tolerate inflammation. But these changes are probably only part of how bats have adapted to persistent viral infections in a way that other species have not.

Although we have known for a long time that bats are a potential source of novel viruses, research into bat immunity remains at the cutting edge of science, and new research is emerging all the time. It is likely that further discoveries will be made and that each new piece of data will enhance our understanding of bats, viruses and provide insights into our own immune systems.

Keith Grehan, Postdoctoral Researcher, Molecular Biology, University of Leeds

This article is republished from The Conversation under a Creative Commons license. Read the original article.