Bad news!
"Scientists have discovered that avian influenza viruses have a gene that makes them incredibly resistant to heat, rendering our body's natural defense system – fever – powerless in fighting infection. In fact, higher temperatures actually help the viruses replicate. ..."
"A gene in avian flu viruses protects them against heat generated by a human’s fever, essentially neutralizing one of the body’s prime defenses; higher temps even help the viruses replicate, according to Cambridge and Glasgow university scientists."
From the editor's summary and abstract:
"ditor’s summary
Birds operate at body temperatures several degrees higher than those of mammals, and, like mammals, birds are infected by influenza viruses. Influenza viruses can move between animal hosts, often reassorting their gene segments as they transition. Knowing that the body temperature of humans often elevates when sick, Turnbull et al. investigated whether virus gene segments originating from hot-blooded birds may give the virus an advantage in feverish mammals. They found that a viral polymerase containing an avian origin PB1 subunit indeed allowed the virus to replicate at higher temperatures in vitro and in a hyperthermic mouse model. ...
Structured Abstract
INTRODUCTION
Influenza A viruses circulate in diverse species of birds and periodically spill over to cause severe or fatal infections in humans. Avian influenza A viruses are adapted to replicate in the gastrointestinal tract of birds at ~40° to 42°C. By contrast, human-adapted seasonal influenza A viruses tend to cause mild symptoms and thrive in the cool upper respiratory tract at ~33°C but struggle to replicate in cells cultured at 40°C. Notably, the normal body temperature of avian hosts exceeds that of a typical human fever. ...
RATIONALE
We sought to harness the strain-specific temperature sensitivity of influenza viruses to assess the antiviral potential of febrile temperature in vivo. We hypothesized that elevated temperature can inhibit the replication of human-origin influenza A viruses, whereas avian viruses, adapted to higher temperatures in birds, may be able to resist this defense.
RESULTS
To avoid false comparison, we wanted to engineer viruses that were identical apart from their ability to replicate at different temperatures. Taking advantage of the segmented viral genome, we found that avian-origin PB1 proteins (a component of the viral polymerase) enabled viral replication at higher temperatures.
Notably, the 1918, 1957, and 1968 pandemic influenza viruses all acquired an avian-origin PB1 that enabled temperature-resistant replication, and they were associated with more-severe disease compared with their seasonal descendants.
We used a human-origin laboratory-adapted virus (PR8) that is avirulent in humans for our in vivo experiments. PR8 causes severe disease in mice but, like seasonal influenza A viruses, it replicates poorly at 40°C.
We made a series of chimeric PB1 proteins and mapped two amino acid substitutions that conferred avian-like temperature resistance to PR8.
This allowed us to generate two similar viruses for comparative experiments: one that replicated poorly at 40°C and one “avianized” mutant that replicated effectively at this temperature.
In mice housed under standard conditions, the parental virus and the avianized mutant both caused severe disease.
However, when we simulated a fever in mice by elevating the ambient temperature to increase core body temperature, the mice were protected against the parental virus and experienced relatively mild symptoms. By contrast, the avianized temperature-resistant virus caused severe disease in mice, despite their higher body temperature.
CONCLUSION
Because the avianized mutant that replicates effectively at 40°C in vitro was the only virus that caused severe disease in the presence of a simulated fever, we conclude that elevated temperature itself can be a potent antiviral defense in vivo. ..."
Bird flu viruses are resistant to fever, making them a major threat to humans (original news release) "Bird flu viruses are a particular threat to humans because they can replicate at temperatures higher than a typical fever, one of the body’s ways of stopping viruses in their tracks, according to new research led by the universities of Cambridge and Glasgow."
Avian-origin influenza A viruses tolerate elevated pyrexic temperatures in mammals
