The fatal viruses that the world has learned to live with

The World Health Organization has warned that Covid may never be wiped out entirely but instead become a virus with which the world has to learn to live.

The health agency’s emergencies director Dr Mike Ryan told a press briefing this week that “it is important to put this on the table: this virus may become just another endemic virus in our communities, and this virus may never go away”.

So what other major viruses are affecting communities worldwide?

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Influenza

The question of whether another flu pandemic will strike the world is “not if... but when”, according to global health experts.

“The threat of pandemic influenza is ever-present,” said WHO director-general Dr Tedros Adhanom Ghebreyesus as the UN health agency launched a global influenza-fighting strategy last year. “We must be vigilant and prepared – the cost of a major influenza outbreak will far outweigh the price of prevention.”

Each year brings an estimated billion flu cases, of which between three million and five million are severe, resulting in 290,000 to 650,000 deaths, according to WHO.

Pandemic flu, however, is “a different animal”, says CNN’s chief medical correspondent, Sanjay Gupta.

“Unlike seasonal flu, pandemics occur when a completely new or novel virus emerges,” Gupta explains. “The result is something mankind has never seen before: a pathogen that can spread easily from person to defenceless person, our immune systems never primed to launch any sort of defence.”

HIV

Delivering WHO’s predictions for Covid-19 at a virtual press briefing in Geneva this week, director-general Ryan noted that “HIV has not gone away” but that effective treatments have been developed to allow people to live with the Aids-causing virus.

Contracting HIV was once a death sentence, but people with the infection can now “live a near-normal life” thanks to antiretroviral therapy (ART) treatments that reduce the amount of the virus in the blood to undetectable levels, says the NHS.

A landmark study in 2014 “looked at over 58,000 instances of sex without a condom, where one partner was HIV positive and one was HIV negative”, and found “zero cases of HIV transmission in couples where the HIV positive partner was on effective treatment”, the Terrence Higgins Trust charity reports.

And the results of recent research projects around the world have raised hopes of a cure for HIV, with reports of patients being cleared of the virus.

Sexual health experts say the current coronavirus lockdown restrictions may also offer a “once-in-a-lifetime” to end HIV transmission. Current tests are unable to give definitive results for up to a month after potential exposure to HIV, but while people are having less sex with new partners, testing has chance to catch up with infections.

“If we can now find the remaining people with HIV through testing and put them on treatment, we could remove anyone who is infectious from the population with long-lasting effects,” London-based HIV specialist Alan McOwan told The Guardian.

“We won’t get this two-month window of no sex again.”

Malaria

Malaria remains one of the most dangerous diseases in the world, with an estimated 228 million cases and 405,000 deaths as result of the parasite in 2018, according to WHO.

Nearly half the world’s population is at risk from malaria, in regions including Southeast Asia, Eastern Mediterranean, Western Pacific and the Americas. But by far the worst-affected region is Africa, which accounts for 93% of malaria cases and 94% of malaria deaths.

Partial immunity develops in humans over years of exposure, but young children remain vulnerable. In 2018, under-fives accounted for 67% (272,000) of all malaria deaths worldwide.

However, researchers in Kenya hope they may be able to help bring the disease under control, after discovering a microbe carried by some mosquitos that prevents the insects from being infected with malaria parasites - and by extension, from transmitting the deadly disease to humans.

“The data we have so far suggest it is 100% blockage, it’s a very severe blockage of malaria,” Dr Jeremy Herren, from the Nairobi-based International Centre of Insect Physiology and Ecology, told the BBC.

Ebola

While relatively rare, Ebola has an extremely high fatality rate, at around 50% on average, although this has ranged from 25% to 90% in previous outbreaks.

The 2014-16 Ebola outbreak in West Africa was the biggest since the virus was discovered in 1976, killing more than 11,300 people, according the US Centers for Disease Control.

However, a vaccine, rVSV-ZEBOV, was shown to be effective in a 2015 trial in Guinea, the epicentre of the West African outbreak. This vaccine has been used in the ongoing Ebola outbreak in the Democratic Republic of Congo, which was declared in August 2018, reports Medicins Sans Frontiers.

According to latest figures from the DRC Ministry of Health, nearly 3,500 Ebola cases and 2,277 deaths had been reported as of 19 April.

“In 2020, the number of cases recorded per week has declined dramatically, with just a handful of cases recorded throughout January and February,” says MSF.

But “the outbreak is not yet over and there is a continued need for vigilance”, the international medical charity adds.

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Dengue

Like malaria, dengue is a viral infection spread by mosquitos in certain regions, including Asia, the Americas and the Caribbean.

“The global incidence of dengue has grown dramatically in recent decades,” says the WHO website. About half of the world's population is now at risk, with an estimated 100 million to 400 million infections each year, according to the health agency.

The infection is “usually mild and passes after about a week without causing any lasting problems”, says the NHS. “But in rare cases it can be very serious and potentially life threatening.”

Although the number of dengue cases reported to WHO has soared from 505,430 cases in 2000 to 3,312,040 in 2015, the death rate is far lower than with malaria, at 960 and 4,032 for each of those respective years.