For infectious diseases experts at the World Health Organisation (WHO), the job is never done.

While the immediate dangers of the coronavirus appear to be over three years on from the respiratory disease bursting out of Wuhan, China, and bringing the entire world to a standstill, epidemiologists must remain vigilant for the next virus that has the theoretical potential to explode into a public health emergency.

The organisation has kept a list of “priority pathogens” since 2017, which compiles the diseases that pose the greatest potential threat to humanity and which we are, at present, most in need of more research into in order to ensure we are in a position to tackle them should they begin to spread.

The list, used by governments and public health organisations to guide their planning, will soon be revised again after the WHO brought together 300 scientists in November to reassess the danger represented by 25 viruses and bacteria with a view to reprioritising it.

“Targeting priority pathogens and virus families for research and development of countermeasures is essential for a fast and effective epidemic and pandemic response,” Dr Michael Ryan, executive director of WHO’s Health Emergencies Programme, said at the time.

“Without significant R&D investments prior to the Covid-19 pandemic, it would not have been possible to have safe and effective vaccines developed in record time.”

We can expect an update in the coming months.

The coronavirus tops the present list but, putting that aside since we are all so well acquainted with it, here are the other eight viruses currently of most concern to WHO experts.

Crimean-Congo haemorrhagic fever

An endemic disease frequently found in Africa, the Balkans, the Middle East and Asia, Crimean-Congo hemorrhagic fever is most commonly spread when people are bitten by infected ticks or encounter sick livestock.

The resulting condition can damage the body’s internal organs and cardiovascular system and cause severe bleeding.

The disease has a fatality rate of 10 to 40 per cent and a vaccine for it is licensed in Bulgaria but has not been approved anywhere else as yet.

Ebola and Marburg

Bat and primates carry both of these diseases, part of the filovirus family, which also cause hemorrhagic fevers.

Once a human has been infected, they commonly spread the viruses on to others through their bodily fluids or direct contact or through contact with contaminated surfaces in unsterilised settings.

They typically have a fatality rate of 50 per cent, although this has varied from 25 to 90 per cent in previous outbreaks.

Vaccines have been used for Ebola in Guinea and the Democratic Republic of Congo but are not widely approved.

Lassa fever

Endemic in West Africa, this disease is spread through the urine of faeces of rats and rodents. Humans who contract it can then pass it on through their own excreta or blood or through sexual contact.

Lassa fever is believed to pose a particular danger to pregnant women in the third trimester of pregnancy and can also cause deafness in patients.

The fatality rate is low at 1 per cent, although this rises to 15 per cent in cases where sufferers’ conditions are serious enough to result in hospitalisation. Ribavirin has been used to treat it but there is no vaccine.

MERS

Properly known as Middle East Respiratory Syndrome, this disease amounts to a deep infection of the respiratory tract and is native to the region, where it is carried by camels.

Once contracted by a human, it can be passed on to others by close contact.

Its fatality rate is high at 35 per cent and it has been diagnosed in 27 countries since 2012, according to the WHO, but there is still no vaccine.

Nipah virus

This is recurrent in Asia and carried by fruit bats, as well as domestic animals such as pigs, horses, cats and dogs, and can be transmitted to humans by these carriers, as well as from person to person.

It can cause swelling of the brain (encephalitis), has a 40-70 per cent fatality rate and is currently without a vaccine.

Rift Valley fever

A disease of the blood carried by mosquitoes, who pass it on by biting humans or livestock such as cows, sheep, goats, buffalo and camels, Rift Valley fever has spread from Africa to Saudi Arabia and Yemen.

Although the fatality rate is less than 1 per cent and Rift Valley is mild for most people, around 8 to 10 per cent of patients develop severe symptoms, including eye lesions, encephalitis and hemorrhagic fever.

A vaccine has been developed but is not yet licensed anywhere.

Zika virus

Another disease spread by mosquito bites, which can infect the blood and be transmitted through sex, Zika is rarely fatal but can cause severe brain defects in foetuses and has been known to cause miscarriages and stillbirth.

There is, at present, no vaccine.

‘Disease X’

A space is reserved on the list for an as-yet-unknown virus that could arise in future to cause us problems, as Covid so ably demonstrated in spring 2020.