Scientific experiments with the herpesvirus such as the one that causes Marek’s disease in poultry have confirmed, for the first time, the highly controversial theory that some vaccines could allow more-virulent versions of a virus to survive, putting unvaccinated individuals at greater risk of severe illness. The research has important implications for food-chain security and food-chain economics, as well as for other diseases that affect humans and agricultural animals.
“The challenge for the future is to identify other vaccines that also might allow more-virulent versions of a virus to survive and possibly to become even more harmful,” said Andrew Read, an author of the paper describing the research, which will be published in the July 27, 2015 issue of the scientific journal PLoS Biology. Read is the Evan Pugh Professor of Biology and Entomology and Eberly Professor in Biotechnology at Penn State University.
“When a vaccine works perfectly, as do the childhood vaccines for smallpox, polio, mumps, rubella, and measles, it prevents vaccinated individuals from being sickened by the disease, and it also prevents them from transmitting the virus to others,” Read said. These vaccines are a type that is “perfect” because they are designed to mimic the perfect immunity that humans naturally develop after having survived one of these diseases. “Our research demonstrates that another vaccine type allows extremely virulent forms of a virus to survive — like the one for Marek’s disease in poultry, against which the poultry industry is heavily reliant on vaccination for disease control,” said Venugopal Nair, who led the research team in the United Kingdom where the experimental work related to this study was carried out. Nair is the head of the Avian Viral Diseases program at the Pirbright Institute, which also hosts the OIE Reference Laboratory on Marek’s disease. “These vaccines also allow the virulent virus to continue evolving precisely because they allow the vaccinated individuals, and therefore themselves, to survive, Nair said.
Less-than-perfect vaccines create a ‘leaky’ barrier against the virus, so vaccinated individuals sometimes do get sick, but typically with less-virulent symptoms. Because the vaccinated individuals survive long enough to transmit the virus to others, the virus also is able to survive and to spread throughout a population. “In our tests of the leaky Marek’s-disease virus in groups of vaccinated and unvaccinated chickens, the unvaccinated died while those that were vaccinated survived and transmitted the virus to other birds left in contact with them,” Nair said. “Our research demonstrates that the use of leaky vaccines can promote the evolution of nastier ‘hot’ viral strains that put unvaccinated individuals at greater risk.”
The theory tested by the research team was highly controversial when it first was proposed over a decade ago. The team’s experiments now show, for the first time, that the modern leaky vaccines, widely used in the agricultural production of poultry, can have precisely the effect on evolution of more-virulent strains of the virus that the controversial theory predicted.
Marek’s disease used to be a minor disease that did not do much harm to chickens in the 1950s, but the virulence of the virus has evolved and today it even is capable of killing all the unvaccinated birds in poultry flocks, sometimes within 10 days. “Even though the Marek’s disease virus is much nastier now than it was in the 1950s, it is becoming increasingly rare and now it causes relatively minor problems in the poultry industry because almost every chicken in agricultural production worldwide is vaccinated against the disease,” Read said. If you can vaccinate all the individuals in a population against a virus, it does not matter if the virus has become super virulent so long as the vaccine continues to be effective.”
The virus for Marek’s disease is very virulent, but the virus causing avian influenza can be even worse. “The most-virulent strain of avian influenza now decimating poultry flocks worldwide can kill unvaccinated birds in just under three days,” Read said. The vaccine against avian influenza is a leaky vaccine, according to Read. “In the United States and Europe, the birds that get avian influenza are culled, so no further evolution of the virus is possible,” Read said. “But instead of controlling the disease by culling infected birds, farmers in Southeast Asia use vaccines that leak — so evolution of the avian influenza virus toward greater virulence could happen.”
The research has implications for human health, as well. The World Health Organization recently reported laboratory-confirmed cases in China of human infection with the avian influenza virus, including a number of deaths. “We humans never have experienced any contagious disease that kills as many unvaccinated hosts as these poultry viruses can, but we now are entering an era when we are starting to develop next-generation vaccines that are leaky because they are for diseases that do not do a good job of producing strong natural immunity — diseases like HIV and malaria,” Read said.
“Vaccines for human diseases are the least-expensive, most-effective public-health interventions we ever have had,” Read said. “But the concern now is about the next-generation vaccines. If the next-generation vaccines are leaky, they could drive the evolution of more-virulent strains of the virus.” He said it is critical now to determine as quickly as possible that the Ebola vaccines that now are in clinical trials are not leaky — that they completely prevent the transmission of the Ebola virus among people. “We do not want the evolution of viral diseases as deadly as Ebola evolving in the direction that our research has demonstrated is possible with less-than-perfect, leaky vaccines,” Read said.
The Latest on: More-virulent viruses
via Google News
The Latest on: More-virulent viruses
- Laramie County health officer, Gov. Mark Gordon orders closings, restrictions of some businesseson March 20, 2020 at 4:00 am
CHEYENNE – Laramie County Health Officer Stanley Hartman issued an order Thursday morning closing some public places, including bars and restaurants, in light of the confirmed COVID-19 cases in the ...
- Trump campaign turns focus from Biden to a more virulent threat to his reelectionon March 20, 2020 at 4:00 am
The Trump campaign has pivoted to promoting the president’s work on tackling the coronavirus and fact-checking the media as it adapts to an election season turned upside down by a deadly pandemic.
- Novel coronavirus test provides fast, accurate resultson March 19, 2020 at 10:37 pm
"As we have all seen in the news, identifying individuals infected with this virus within a few hours and initiating the quarantine protocol ... so much about it now because there are changes in the ...
- The biggest questions our readers have about coronaviruson March 19, 2020 at 1:38 pm
Multiple genetic mutations are required for a virus to evolve into something more virulent or threatening. Current research suggests the two major strains of coronavirus affecting humans differ by ...
- An Endless Arms Race: Viruses as Humanity’s Natural Predatoron March 17, 2020 at 7:09 pm
As humans bolster their immunity to viruses, the enemy becomes still more virulent. And new virus strains can appear as a reaction to the development of vaccines. “It’s just like an arms race ...
- A seven-gene-deleted African swine fever virus is safe and effective vaccine in pigson March 16, 2020 at 2:03 pm
while it is not known if they could convert to more virulent strains during their replication in pigs. In the present study, Chen and his colleagues used the Chinese ASFV HLJ/18 as a backbone and ...
- ‘Xenophobia around virus can be more virulent than virus itself’on March 15, 2020 at 10:48 am
The xenophobia, which has already manifested, could become more virulent than the virus itself and the global economy could teeter. This could even impede the capacity for organised, rational response ...
- The virus of fear more dangerous than any bacteriaon March 13, 2020 at 11:00 pm
Please note: The virus of fear is more virulent than any bacteria. Please refrain from allowing it to infect your body or mind, as fear is the last frequency we ...
- Coronavirus: Scientists isolate virus responsible for deadly Covid-19 outbreakon March 13, 2020 at 4:23 am
In the current outbreak, the mutations have led to two main strains of the virus emerging. The one most closely associated with the outbreak in Wuhan is more prevalent, and it is reportedly more ...
- Viruses and the Jewish Microbe Hunterson March 11, 2020 at 11:59 am
In 1798, the English physician Edward Jenner showed that deliberate inoculation with the pustules of relatively benign cowpox (“vaccination,” from Latin vacca, cow) protected the person from attack ...
via Bing News