ADVERTISEMENT
  • The Membership Club
  • PT Hausa
  • About Us
  • Advert Rates
  • Careers
  • Contact Us
Tuesday, March 2, 2021
Premium Times Nigeria
  • Home
  • COVID-19
  • News
    • Headline Stories
    • Top News
    • More News
    • Foreign
  • Investigations
  • Business
    • News Reports
    • Financial Inclusion
    • Analysis and Data
    • Business Specials
    • Opinion
    • Oil/Gas Reports
      • FAAC Reports
      • Revenue
  • Opinion
  • Health
    • News Reports
    • Investigations
    • Data and Infographics
    • Health Specials
    • Features
    • Events
    • Primary Health Tracker
  • Agriculture
    • News Report
    • Research & Innovation
    • Data & Infographics
    • Special Reports/Features
    • Investigations
    • Interviews
    • Markets
  • Arts/Life
    • Arts/Books
    • Kannywood
    • Lifestyle
    • Music
    • Nollywood
    • Travel
  • Sports
    • Football
    • More Sports News
    • Sports Features
  • Projects
    • Parliament Watch
    • Panama Papers
    • Paradise Papers
    • AGAHRIN
  • Home
  • COVID-19
  • News
    • Headline Stories
    • Top News
    • More News
    • Foreign
  • Investigations
  • Business
    • News Reports
    • Financial Inclusion
    • Analysis and Data
    • Business Specials
    • Opinion
    • Oil/Gas Reports
      • FAAC Reports
      • Revenue
  • Opinion
  • Health
    • News Reports
    • Investigations
    • Data and Infographics
    • Health Specials
    • Features
    • Events
    • Primary Health Tracker
  • Agriculture
    • News Report
    • Research & Innovation
    • Data & Infographics
    • Special Reports/Features
    • Investigations
    • Interviews
    • Markets
  • Arts/Life
    • Arts/Books
    • Kannywood
    • Lifestyle
    • Music
    • Nollywood
    • Travel
  • Sports
    • Football
    • More Sports News
    • Sports Features
  • Projects
    • Parliament Watch
    • Panama Papers
    • Paradise Papers
    • AGAHRIN
Premium Times Nigeria
BUA Group Ad BUA Group Ad BUA Group Ad
ADVERTISEMENT
Coronavirus

Coronavirus

Will coronavirus really evolve to become less deadly?

There is little or no direct evidence that virulence decreases over time.

byThe Conversation
February 3, 2021
5 min read

A recent modelling study painted a reassuring picture of a post-pandemic future in which SARS-CoV-2 transitions, over “a few years to a few decades”, from dangerous pathogen to just another common-cold coronavirus. This predicted loss of virulence, the authors stress, is based on a specific idiosyncrasy of the virus, namely that it rarely causes serious disease in children.

Still, many experts agreed that we should not be in the least surprised by the authors’ conclusion, as all viruses “become more transmissible and less pathogenic over time”. After all, the seductive logic goes, from an evolutionary perspective it makes no sense for a pathogen to harm the host on which it depends for its survival. According to this reasoning, virulence is little more than a temporary evolutionary imbalance.

This comfortable chain of reasoning was rudely broken by the announcement of “a realistic possibility” that the new highly transmissible B117 variant “is associated with an increased risk of death”.

Although the evidence is still accruing, early estimates from Nervtag, the UK’s New and Emerging Respiratory Virus Threats Advisory Group, suggest that B117 may be around 30% more deadly.

But perhaps this is a single exception to an otherwise well-observed rule, and we can still be confident that SARS-CoV-2 will slowly fade away to obscurity. So what is the evidence for this view? And how confident can we be in predicting how evolution will shape the relationship between a pathogen and its host?

Law of declining virulence

It was the bacteriologist and comparative pathologist Theobald Smith (1859-1934) who began the narrative of the “law of declining virulence” in the late 19th century.

Studying tick-borne disease of cattle during the 1880s, Smith realised that the severity of the disease was determined by the degree of prior infection. Cattle that had been repeatedly exposed to the pathogen suffered from much more moderate disease than cattle encountering it for the first time. Smith reasoned that this was because host and pathogen conspired over time towards a mutually benign relationship.

The story then takes a distinctly antipodean turn. In 1859, the year Charles Darwin published his Big Idea, European rabbits were introduced to Australia for sport, with devastating consequences for the indigenous flora and fauna. Having turned down Louis Pasteur’s offer of mass délapinsation using fowl cholera as a biological control agent, the Department of Agriculture turned to the myxoma virus that causes the lethal, but highly species-specific disease, myxomatosis in rabbits.

By the 1950s, the myxoma virus was spreading rapidly among the rabbit population. Recognising the opportunities provided by this unique experiment, the virologist Frank Fenner documented how the virulence of the disease decreased over a few years from 99.5% mortality to about 90%. This was taken as strong empirical evidence in support of Smith’s law of declining virulence – and occasionally still is.

RelatedNews

MTN biggest Nigerian company by revenue as pandemic drives data sales

Oyo residents lament as petrol queues resurface

Custodian Investment profit balloons 111% as firm declares N2.6 bn dividend

Trump says he predicts ‘energy disaster’ for America

Black and white photo of the myxomatosis control trial in Australia, 1952.
Myxomatosis control trial, Australia,1952.
Queensland State Archives/Wikimedia Commons

A challenge to the law of declining virulence

At around the same time, a talented young Australian mathematician named Robert May came across the work of his compatriot Charles Birch, an eminent ecologist working on the regulation of animal populations. Together with epidemiologist Roy Anderson, May went on to pioneer the application of mathematical modelling to the ecology and evolution of infectious disease. By the late 1970s, May and Anderson had developed the “trade-off” model for the evolution of virulence – the first conceptual framework in 100 years to challenge the Smith’s general law of declining virulence.

The trade-off model recognises that pathogen virulence will not necessarily limit the ease by which a pathogen can transmit from one host to another. It might even enhance it. Without the assumed evolutionary cost to virulence, there is no reason to believe that disease severity will decrease over time. Instead, May and Anderson proposed that the optimal level of virulence for any given pathogen will be determined by a range of factors, such as the availability of susceptible hosts, and the length of time between infection and symptom onset.

This last factor is a key aspect of the epidemiology of SARS-CoV-2. The long time period between infection and death (if it occurs) means that SARS-CoV-2 has a significant window in which to replicate and spread, long before it kills its current host.

Dangote adbanner 728x90_2 (1)

The trade-off model is now widely accepted. It emphasises that each host-pathogen combination must be considered individually. There is no general evolutionary law for predicting how these relationships will pan out, and certainly no justification for evoking the inevitability of decreased virulence.

There is little or no direct evidence that virulence decreases over time. While newly emerged pathogens, such as HIV and Mers, are often highly virulent, the converse is not true. There are plenty of ancient diseases, such as tuberculosis and gonorrhoea, that are probably just as virulent today as they ever were.

A change in conditions can also drive the trend in the other direction. Dengue fever has afflicted humans since at least the 18th century, but an increasingly large and mobile human population is thought to have driven a marked increase in virulence over the last 50 years or so. Even the seminal case of the rabbit-killing myxoma virus is uncertain. There was little subsequent decline in virulence after Fenner’s early reports, and it may even have risen slightly.

Plausible but not inevitable

Of course, these counter-examples do not in themselves present evidence that the virulence of SARS-CoV-2 will not decline. Declining virulence is certainly plausible as one of many potential outcomes under the trade-off model.

Conversely, mutations might simultaneously heighten both virulence and transmissibility by increasing viral replication rate. Although we will have to wait for more evidence to be certain – and the precise mechanisms may be difficult to pin down – the emerging evidence around the B117 variant currently points more towards increased mortality.

Ed Feil, Professor of Microbial Evolution at The Milner Centre for Evolution, University of Bath and Christian Yates, Senior Lecturer in Mathematical Biology, University of Bath

ADVERTISEMENT

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

The conversation

The Conversation

The Conversation is PREMIUM TIMES syndication partner. We have permission to republish.

  • WhatsApp
  • Tweet
  • Email
  • Print
  • Telegram
  • More
  • Share on Tumblr
  • Pocket

Support PREMIUM TIMES' journalism of integrity and credibility

Good journalism costs a lot of money. Yet only good journalism can ensure the possibility of a good society, an accountable democracy, and a transparent government.

For continued free access to the best investigative journalism in the country we ask you to consider making a modest support to this noble endeavour.

By contributing to PREMIUM TIMES, you are helping to sustain a journalism of relevance and ensuring it remains free and available to all.

Donate


TEXT AD: To advertise here . Call Willie +2347088095401...


JOIN THE CONVERSATION

  • Disqus (0)
premiumtimes



PT Mag Campaign AD

Previous Post

Court jails man 25 years for raping teenager

Next Post

Violence erupts at APC registration exercise in Kwara

The Conversation

The Conversation

More News

MTN Office

MTN biggest Nigerian company by revenue as pandemic drives data sales

March 1, 2021
EFCC

EFCC arraigns former Nigerian senator for N419 million scam

March 1, 2021
EFCC (PHOTO CREDIT: @twitter.com/officialEFCC)

EFCC arraigns ex-BPE boss, Dikki, for N1billion bribe

March 1, 2021
Nestlé Nigeria Plc

Nestlé shareholders fund falls 36% as firm plans to pay dividend from retained earnings

March 1, 2021
Olumide Akpata

NBA sets up 20 committees on judiciary, human rights, anti-corruption, others

March 1, 2021
WHO

How WHO is supporting Nigeria’s COVID-19 response – Official

March 1, 2021
Next Post
APC FLag used to illustrate the story.

Violence erupts at APC registration exercise in Kwara

Women protest in Uromi1

Insecurity: Edo women protest alleged attacks by herders

Discussion about this post

Search

#EndSARS: Latest Updates




Polaris Bank


JAIZ Ad


NITDA Ad





Glo Ad

Subscribe to News via Email

Enter your email address and receive notifications of news by email.

Join 1,627,128 other subscribers.

Advertisement






netherland biz school Advert

Zenith Advert
ADVERTISEMENT

Our Digital Network

  • PT Hausa
  • Election Centre
  • Human Trafficking Investigation
  • Centre for Investigative Journalism
  • National Conference
  • Press Attack Tracker
  • PT Academy
  • Dubawa
  • LeaksNG
  • Campus Reporter

Resources

  • Oil & Gas Facts
  • List of Universities in Nigeria
  • LIST: Federal Unity Colleges in Nigeria
  • NYSC Orientation Camps in Nigeria
  • Nigeria’s Federal/States’ Budgets since 2005
  • Malabu Scandal Thread
  • World Cup 2018
  • Panama Papers Game
  • Our Digital Network
  • About Us
  • Resources
  • Projects
  • Data & Infographics
  • DONATE

All content is Copyrighted © 2020 The Premium Times, Nigeria

No Result
View All Result
  • Home
  • COVID-19
  • News
    • Headline Stories
    • Top News
    • More News
    • Foreign
  • Investigations
  • Business
    • News Reports
    • Financial Inclusion
    • Analysis and Data
    • Business Specials
    • Opinion
    • Oil/Gas Reports
      • FAAC Reports
      • Revenue
  • Health
    • News Reports
    • Investigations
    • Data and Infographics
    • Health Specials
    • Features
    • Events
    • Primary Health Tracker
  • Agriculture
    • News Report
    • Research & Innovation
    • Data & Infographics
    • Special Reports/Features
    • Investigations
    • Interviews
    • Markets
  • Arts/Life
    • Arts/Books
    • Kannywood
    • Lifestyle
    • Music
    • Nollywood
    • Travel
  • Sports
    • Football
    • More Sports News
    • Sports Features
  • Projects
    • Panama Papers
    • Paradise Papers
    • Parliament Watch
    • AGAHRIN
  • Opinion
  • PT Hausa
  • The Membership Club
  • Dubawa
    • Dubawa NG
  • About Us
  • Advert Rates
  • Careers
  • Contact Us
  • Digital Store
  • DONATE

All content is Copyrighted © 2020 The Premium Times, Nigeria

Our website uses cookies. By continuing to use this website you are giving consent to cookies being used. Visit our Privacy and Cookie Policy.
loading Cancel
Post was not sent - check your email addresses!
Email check failed, please try again
Sorry, your blog cannot share posts by email.