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Avian flu viruses are surrounded by mineral layers and are therefore infectious to humans
In the past few years, bird rib viruses have been transmitted to humans several times and experts have warned vigorously of an impending pandemic if the pathogens become transmissible between humans. According to a recent study, the fact that the viruses can infect humans is due to a type of eggshell that the pathogens build up in the birds' bodies. Accordingly, an interpersonal transfer is unlikely.
The cause of the infections in humans "could be an eggshell-like mineral layer that the viruses get from birds due to the high calcium concentration in the intestines of birds", reports the journal "Angewandte Chemie" in a press release on the current study results of Chinese scientists. In their study, the researchers at Zhejiang University (Hangzhou, China) were able to demonstrate that the mineralized viruses are significantly more infectious, and at the same time more robust and heat-stable than the native viruses.
Avian flu viruses are also a threat to humans
Avian flu is a highly contagious disease among birds and can wipe out entire populations, but so far there have been relatively few outbreaks that have spread to humans. However, experts believe that the viruses are a serious threat to human health. Because in close contact with sick birds or their excretions an infection can occur. Infections among humans, on the other hand, remain limited, which suggests that these viruses cannot directly infect humans, reports the specialist magazine "Angewandte Chemie".
Mutations are not the cause of infections in humans
In the worst case, if avian influenza viruses can also be transmitted between people, a pandemic threatens. Such interpersonal transferability could occur through mutations of the viruses, so far the assumption so far. The infections that have already occurred in humans have also been attributed to mutations of the viruses by doctors, which, however, is a misjudgment according to the current study results. The findings show that bird flu viruses isolated from sick people have the same gene sequences as the pathogens from birds. The previous assumption that the viruses could cross the species limit through mutations or recombination with other pathogens must be corrected.
Structure of a mineral protective cover
According to the Chinese researchers, the cause of bird flu infections in humans is not a mutation, but the formation of a kind of eggshell around the pathogen. In the bird's intestine, the viruses build up a mineral protective layer under the calcium-rich conditions, the scientists explain. "Using experiments in a solution modeled on the bird's intestine, the researchers have now been able to show that 5 to 6 nm thick shells are formed from a calcium phosphate mineral around H9N2 and H1N1 viruses," reports the specialist magazine "Angewandte Chemie". These mineralized viruses had proven to be significantly more infectious - and more lethal - than native viruses in cell culture as well as in mice.
Effects of the mineral protective layer
According to the experts, the mineral shell changes the electrical surface potential of the virus, which means that the mineralized virus adsorbs to the surface of future host cells much more effectively. The mechanism of absorption into the cell is also different. Because the virus normally docks onto receptors on the cell surface and is then smuggled into the cell. This is prevented by the mineral layer of the viruses, but apparently at the same time it stimulates very effective absorption in other ways. Finally, the mineralized viruses within the cell reach the so-called lysosomes, whose slightly acidic environment dissolves the mineral coatings and releases the viruses.
Since avian influenza viruses primarily affect the respiratory tract in humans and then move mainly in body fluids that have insufficient calcium concentrations for mineralization, the pathogens lack the protective shell here and are therefore less infectious. Overall, the findings can explain why people are more likely to contract birds than infected people, the scientists emphasize. The researchers hope that new approaches to combating bird flu can also be derived. (fp)