Before the COVID pandemic, the World Health Organization (WHO) had made a list of priority infectious diseases. These were felt to pose a threat to international public health, but where research was still needed to improve their surveillance and diagnosis. In 2018, “disease X” was included, which signified that a pathogen previously not on our radar could cause a pandemic, reports The Conversation.
Influenza: a ‘known known’
Influenza is largely a known entity; we essentially have a minor pandemic every winter with small changes in the virus each year. But more major changes can also occur, resulting in spread through populations with little pre-existing immunity.
However, there’s a lot we don’t understand about what drives influenza mutations, how these interact with population-level immunity, and how best to make predictions about transmission, severity and impact each year.
The current H5N1 subtype of avian influenza (“bird flu”) has spread widely around the world. It has led to the deaths of many millions of birds and spread to several mammalian species including cows in the United States and marine mammals in South America.
Human cases have been reported in people who have had close contact with infected animals, but fortunately there’s currently no sustained spread between people.
Coronaviruses: an ‘unknown known’
We knew more about coronaviruses than most people might have thought before the COVID pandemic.
We’d had experience with severe acute respiratory syndrome (SARS) and Middle Eastern respiratory syndrome (MERS) causing large outbreaks. Both are caused by viruses closely related to SARS-CoV-2, the coronavirus that causes COVID. While these might have faded from public consciousness before COVID, coronaviruses were listed in the 2015 WHO list of diseases with pandemic potential.
The 25 viral families: an approach to ‘known unknowns’
Attention has now turned to the known unknowns. There are about 120 viruses from 25 families that are known to cause human disease. Members of each viral family share common properties and our immune systems respond to them in similar ways.
An example is the flavivirus family, of which the best-known members are yellow fever virus and dengue fever virus. This family also includes several other important viruses, such as Zika virus, which can cause birth defects when pregnant women are infected, and West Nile virus, which causes encephalitis, or inflammation of the brain.
Pathogen X, the ‘unknown unknown’
There are also the unknown unknowns, or “disease X” – an unknown pathogen with the potential to trigger a severe global epidemic. To prepare for this, we need to adopt new forms of surveillance specifically looking at where new pathogens could emerge.
In recent years, there’s been an increasing recognition that we need to take a broader view of health beyond only thinking about human health, but also animals and the environment. This concept is known as “One Health” and considers issues such as climate change, intensive agricultural practices, trade in exotic animals, increased human encroachment into wildlife habitats, changing international travel, and urbanization.
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