The Aedes aegypti mosquito species, shown here obtaining a blood meal, is a vector for the dengue virus.
A paper by a team of scientists from University of Florida, published recently in Science, shows how the four strains of the dengue virus circulating in Bangkok, Thailand, have changed in response to immunity in a population over a period of two decades. Being scientists, they attribute this to the natural process of evolution by natural selection, but, as any self-respecting Creationist (if any such exist) will tell you, because nothing changes genetically without their putative designer god's intelligent intervention, these changes must be because this divine malevolence is trying to find ways around the resistance to the virus our immune system is providing - an immune system which it also designed to protect us from is nasty little creations, allegedly!
We want to understand if or how immunity is driving extinction or persistence of particular lineages of dengue virus circulating in this one place. To do that, we characterized the immune signature of dengue viruses isolated in Bangkok over a long period of time.
We found that there is a pattern like influenza, where we get different viruses every year that are driven by natural selection for viruses that evade the human immune response to the population. We have shown that that this is also happening with dengue.
This of course, is a classic evolutionary arms race, just as is predicted and expected by the theory of evolution by natural selection, but which, if we are to believe Creationists, can only mean their putative creator god is indulging in yet another bizarre arms race with itself, almost as though it suffers from a multiple personality syndrome. But it gets even more bizarre. There are four different versions (or serotypes) of the virus, named by scientists as DENV1 through DENV4, each of which appears to be competing with the others! As well as variation between strains, there are also smaller variations within strains.We found that there is a pattern like influenza, where we get different viruses every year that are driven by natural selection for viruses that evade the human immune response to the population. We have shown that that this is also happening with dengue.
Professor Derek Cummings, senior author
Professor of biology
University of Florida, Gainesville, FL, USA.
Professor of biology
University of Florida, Gainesville, FL, USA.
It's as though there are four independent, competing designers, each responsible for just one strain of the virus, as well as a fifth designer responsible for the human immune system, and they're all competing with one another. The thought that this is one and the same, supposedly highly intelligent, designer simply beggars belief.
Our findings suggest that the dengue viruses are moving away from the viruses that generated immunity in the population in the past. It’s sort of like the flu story, dengue is evolving to escape the immunity that is in the population at any particular time. But it seems to be happening at a slower pace with dengue than influenza.
The scientists analysed the genomes of the viruses in 1,944 archived blood samples from Bangkok. The samples were preserved from people known to be ill with dengue and they represent all four dengue virus strains from every year between 1994 and 2014. The team genetically sequenced more than 2,000 virus samples. They then tested a subset of these samples that represented a time series of each strain. From this they were able to characterise the antigenic relationship of the strains to each other through time. This showed how well (or badly) an immune response to one strain protects against another strain.Professor Henrik Salje, co-author
Assistant professor
Department of Biology and Emerging Pathogens Institute
University of Florida, Gainesville, FL, USA
Assistant professor
Department of Biology and Emerging Pathogens Institute
University of Florida, Gainesville, FL, USA
These results were then plotted on a chart to make a map showing how far from the original strain(s) and from one another, the viruses had moved over time.
This scatter plot depicts the movement of antigenic distance within and between each DENV serotype. Yellow circles date to 1994, green to 2004, and purple to 2014.
The results also show a clear inverse relationship between the level of antigenic diversity in a given year and epidemic levels. When Thailand experienced large epidemic outbreaks, antigenic diversity was low. But in years when epidemic levels were lower than average, the antigenic diversity was higher. They also showed that the assumption that infection by one strain of the virus would also protect people against the other strains was not strictly true, since reinfections are now known to have occurred. The reason for this is that the virus evolves to evade the antibodies produced by an earlier infection, or to put that in evolutionary terms, those viruses that survive and get passed on are those which are able to infect despite the presence of antibodies to earlier strains in the population. In this way the presence of genetic variations which enable this evasion tend to increase in the population of that strain.
Classic evolution by natural selection.
In the abstract to their published paper in Science the team say:
Variations in disease enhancementA very clear case then of how a virus can evolve according to the changes in its environment and how strains diversify when in competition for the same resource and in the presence of antibodies produced by their competitors. As with SARS-CoV2, Creationists are left to explain this in terms of intelligent design by their favourite putative god, rather than to attribute it to a natural process not involving any gods, their favourite included. For reasons which have never been explained they prefer to present this god as the malevolent and rather stupid entity behind these parasites and the resultant arms races with itself.
Secondary Dengue virus (DENV) infections can be dangerous if levels of antibodies from prior infection are inadequate to clear the virus. This RNA flavivirus exploits the presence of lower levels of heterotypic antibodies to infect immunoglobulin Fcγ receptor–bearing cells. Many RNA viruses also exhibit antigenic variation, which classically allows evasion of immune responses. Katzelnick et al. investigated whether antigenic variation in DENV has a biological function in a virus that courts immune responses to enhance replication (see the Perspective by Rohani and Drake). Using antigenic cartography on a panel of more than 400 DENV1-4 subtype samples isolated in Bangkok, Thailand, the authors found that antigenic variation in virus populations oscillated between similarity and dissimilarity across subtypes over time, with outbreaks correlating with periods of antigenic dissimilarity within serotypes. This pattern may be at least in part a result of the conflicting evolutionary pressures of immune evasion and immune enhancement. — CA
Abstract
Infection with one of dengue viruses 1 to 4 (DENV1-4) induces protective antibodies against homotypic infection. However, a notable feature of dengue viruses is the ability to use preexisting heterotypic antibodies to infect Fcγ receptor–bearing immune cells, leading to higher viral load and immunopathological events that augment disease. We tracked the antigenic dynamics of each DENV serotype by using 1944 sequenced isolates from Bangkok, Thailand, between 1994 and 2014 (348 strains), in comparison with regional and global DENV antigenic diversity (64 strains). Over the course of 20 years, the Thailand DENV serotypes gradually evolved away from one another. However, for brief periods, the serotypes increased in similarity, with corresponding changes in epidemic magnitude. Antigenic evolution within a genotype involved a trade-off between two types of antigenic change (within-serotype and between-serotype), whereas genotype replacement resulted in antigenic change away from all serotypes. These findings provide insights into theorized dynamics in antigenic evolution.
Katzelnick Leah C.; Coello Escoto Ana; Huang Angkana T.; Garcia-Carreras Bernardo; Chowdhury Nayeem; Maljkovic Berry Irina; Chavez Chris; Buchy Philippe; Duong Veasna; Dussart Philippe; Gromowski Gregory; Macareo Louis; Thaisomboonsuk Butsaya; Fernandez Stefan; Smith Derek J.; Jarman Richard; Whitehead Stephen S.; Salje Henrik; Cummings Derek A. T.
Antigenic evolution of dengue viruses over 20 years
Science 2021 374 (6570); 999-1004; DOI: 10.1126/science.abk0058
© 2021 The Authors. Published by American Association for the Advancement of Science.
Reprinted with kind permission under license #5193010127296.
One wonders what it would think of their portrayal of it, if it were real.
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