Viruses up their game in arms race withimmune system14 August 2017

In an evolutionary arms race with its host rabbits, thevirus has evolved the deadly ability to suppress therabbit's immune system. Credit: Kansas State University

In a classic example of the evolutionary arms racebetween a host and a pathogen, the myxomavirus—introduced to control the rabbit population inAustralia in 1950—has developed a novel anddeadly ability to suppress the immune response ofits host rabbits. New research shows that virusescollected in the 1990s are much more effective atshutting down the immune systems of rabbits thathave never been exposed to the virus than areviruses from the 1950s.

"When a host develops resistance to a virus, thevirus will often evolve ways to evade the host's immune response," said Andrew Read, Evan PughProfessor of Biology and Entomology and EberlyProfessor of Biotechnology at Penn State and anauthor of the study. "Instead of hiding from the rabbit's immune response, the myxoma virus hasevolved ways to directly suppress it, leading to thedevelopment of a virus that is even more deadly tonon-resistant rabbits."

A paper describing the new study appears theweek of August 14, 2017, in the journal Proceedings of the National Academy of Sciences.The research suggests that efforts to artificiallyincrease resistance to a virus through selectivebreeding, genetic engineering, orimmunization—unless they completely preventtransmission of the virus—could accelerate the armsrace, producing even more virulent viruses.

Wild European rabbits were introduced to Australiain the 19th century and quickly spread, wreakinghavoc on the land and devastating crops. Themyxoma virus was initially extremely effective inreducing the population of these invaders. Thestrain of virus that was introduced developed in adifferent species of rabbit in South America.Scientists at the time were interested inunderstanding how the virus would evolve in thisnew, European, host.

"This system has been studied since the 1950s asa classic example of an evolutionary arms race,"said Peter Kerr of the University of Sydney,Australia and lead author of the paper. "The rabbitsevolved resistance, the virus evolved ways tocombat that resistance, and this continued in aback-and-forth, ever escalating way. We wanted toknow how that arms race has continued since itwas last studied in the early 1980s."

The research team compared viruses collected inthe 1990s to the original strain introduced toAustralia in 1950. "We can compare how nasty avirus is in what we call a 'common garden'," saidRead. "In this case, laboratory rabbits that have notbeen exposed to myxoma virus provide thatcommon garden—they have not developedresistance to mxyomatosis so we can compare howthey respond to viruses from different eras."

Many of the viruses from the 1990s were extremelyvirulent, but the laboratory rabbits infected withthem did not develop the usual symptoms

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associated with myxoma infection, including skinlesions and high fever. Instead, these rabbitsdeveloped a profound immune system depression,leading to massive bacterial infection and acutecollapse syndrome, similar to sepsis.

"The rabbits infected with virus from the 1990s didnot have a typical inflammatory response to theinfection or develop fevers," said Isabella Cattadori,associate professor of biology at Penn State and anauthor of the paper. "This is further evidence thatthe virus is severely suppressing the immuneresponse in these rabbits. The evolutionary armsrace has produced a virus that instead of trying toevade the host's immune response, directly attacksit."

The myxoma virus was introduced to control thepopulation of rabbits in Australia in 1950, initiating anevolutionary arms race between the virus and the rabbit'simmune system. Credit: JJ Harrison

Although the original strain of myxoma virus

introduced to Australia in the 1950s had some abilityto suppress its host's immune system, this abilityhas increased over time and the acute collapsesyndrome that it causes developed sometime afterthe studies in the 1980s.

"Our study shows that the evolutionary arms racebetween an infectious agent and its host's immunesystem can continue to escalate to produce newmore dangerous viruses," said Read. "We need tobe aware of this in areas like agriculture, and evenhuman vaccinations, where we are artificiallyenhancing resistance. If our methods do notcompletely prevent transmission of the viruses wecould be accelerating the evolution of more deadly viruses."

Provided by Pennsylvania State University

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APA citation: Viruses up their game in arms race with immune system (2017, August 14) retrieved 31August 2021 from https://phys.org/news/2017-08-viruses-game-arms-immune.html

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