Evening Science | How strong is H5N1? Does China have a vaccine?

New research provides answers to how long influenza viruses A(H5N1) and A(H1N1)—hereafter abbreviated as A(H5N1) and A(H1N1), respectively—can survive and remain contagious on surfaces (just read the last paragraph).

Overseas researchers studied the persistence of highly pathogenic avian influenza A(H5N1) and pandemic influenza A(H1N1)pdm09 from cattle and humans in unpasteurized milk and showed that both viruses remain infectious for several hours on milking equipment materials. These findings highlight the risk of A(H5N1) transmission to humans through contaminated surfaces during the milking process.

The researchers diluted the virus 1:10 in raw milk and phosphate-buffered saline (PBS), the latter as a control, and dropped small drops of diluted virus milk or PBS on stainless steel or rubber-lined test pieces in a simulated environmental chamber. Virus samples were then collected after 0, 1, 3, and 5 hours and tested for infectious virus. To simulate the environmental conditions in an open milking room in the Texas High Plains in March-April 2024, the researchers also conducted a persistence study using 70% relative humidity.

The study found that A(H5N1) remained infectious after 1 hour in unpasteurized milk dilutions on stainless steel and rubber liners; while infectious virus in PBS dilutions dropped below the detection limit after 1 hour (Figure A below).

This finding suggests that unpasteurized milk containing the AH5N1 virus may still be infectious on materials in milking machines.

To evaluate whether a less virulent influenza virus could be used as a surrogate to study viral persistence on milking unit materials, the researchers also compared the attenuation of A(H5N1) and A(H1N1) viruses on rubber linings and stainless steel surfaces over a 1-hour period (Figure B). The attenuation rates of both viruses on these two surfaces were similar, suggesting that A(H1N1) could be used as a surrogate for A(H5N1) bovine virus to study the persistence of viral infectivity in milk.

Further studies found that in unpasteurized milk, A(H1N1) was infectious for at least 3 hours on rubber linings and at least 1 hour on stainless steel (Figure C). These results indicate that influenza viruses are stable in unpasteurized milk and that influenza A viruses deposited on milking equipment may still be infectious after 3 hours.

From the process point of view, milking workers may be at risk of infection in several links:

① The figure below shows the principle of the milking machine. Before using the milking machine, the dairy worker will manually squeeze the cow to stimulate the cow to continue lactating after the first few times of lactation. This process is called "pre-milking", and milk aerosol may be generated during the process;

② The milking machine collects milk through negative pressure, so the milking machine will automatically release when the cow's milk production is insufficient. Since milking usually occurs above the level of the human eye, there is a possibility that milk may come into contact with the eyes or respiratory mucosa when the milking machine falls.

In summary, the results of this study suggest that dairy farm workers are at risk of contracting A(H5N1) after contacting contaminated surfaces during milking. Therefore, to reduce the transmission of A(H5N1) from cows to humans, farms should provide workers with personal protective equipment, such as masks and goggles, during milking. In addition, contaminated rubber inflatable pads in milking machines may be the cause of virus transmission between cows on dairy farms. Therefore, it is necessary to disinfect the pads after milking each cow, which can reduce the transmission of influenza viruses between farm animals and help contain the current outbreak.

Of course, compared with the transmission of influenza A (H5N1) virus by milk, the bigger problem with contact with raw cow's milk in China is the risk of infection with Brucella and brucellosis. Although both pathogens can be prevented by vaccines (my country has an approved H5N1 influenza vaccine and a brucellosis vaccine), these two vaccines are not common. Therefore, it is safest to avoid contact with unsterilized raw cow's milk as much as possible.

willing

=Pill=

Disclaimer: This article was created out of personal interest, only to help more ordinary people have a clearer understanding of vaccines. The content and views do not represent any organization, unit, or institution, and it has not accepted any form of sponsorship. All pictures are from public online platforms. If the content is incorrect, please do more self-criticism (not).