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The spread of H5 bird flu -

As H5 bird flu continues to spread among wild birds, poultry, and livestock worldwide, there have been several documented cases of the virus in humans.

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Evolving knowledge -

While the current risk to public health is low, experts are nonetheless working to understand more about the virus and how it spreads.

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What causes bird flu -

H5 bird flu is caused by the highly pathogenic H5N1 virus. It is usually transmitted by wild birds that shed the virus in their poop.

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The possibility of airborne spread -

When there was an H5 outbreak at a maximum security chicken farm in the Czech Republic, however, experts began to wonder about the possibility of airborne spread.

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Lack of data -

The idea that the wind can spread bird flu is nothing new. However, until recently, there was no reliable data on the topic, since it is very difficult to measure.

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Early investigations -

When scientists started to investigate the outbreak at the Czech chicken farm, their only lead was a nearby duck farm, where an outbreak had occurred a week earlier.

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Nearby duck farm -

The duck farm, which was home to 50,000 birds, was very different from the chicken farm in terms of biosecurity.

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Top facilities -

At the chicken farm, the facilities were state of the art. Think filtered water, giant fans to create one-way airflow, and a secure fence to keep wild animals out.

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Lower level facilities -

At the duck farm, by contrast, the birds were kept in buildings with natural ventilation and a minimum level of biosecurity.

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Difference in trajectory -

The bird flu swept through the duck farm much quicker than it did the chicken farm. Indeed, 800 birds died on the first day alone.

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End result -

However, the infection did eventually spread throughout the entire chicken farm, which consisted of two distinct locations.

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Pulling samples -

In order to see what they could learn, investigators took samples of the bird flu found at each of the three locations (the duck farm and the two chicken farm locations).

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Findings -

Three H5N1 strains sequenced from the duck farm were genetically identical to the strains found in the first bird to get sick on each farm.

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Interpreting the results -

According to the researchers, this serves as evidence that the duck farm had been the source of the outbreak at the chicken farm.

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Explaining the spread - Upon learning this, investigators wracked their brains for a physical link between the duck farm and the chicken farm that would explain the spread of disease between the two.

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No physical link -

However, the duck farm was nearly five miles west of the chicken farm, and there was no human connection (such as an employee or a supplier).

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Looking at weather patterns -

After ruling out all other potential reasons for the spread of the virus, investigators began to look at the weather patterns during the week the chickens got sick.

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Perfect conditions -

They found that conditions were, in fact, perfect for the spread of the virus from the ducks to the chickens.

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Cool temperatures and cloud cover -

There had been a steady breeze from the west and sufficient cloud cover to block germ-killing UV rays from the sun. The temperature was also cool, but not freezing, which is optimum for a virus.

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Best explanation -

According to the author of the study, the investigators decided that the best explanation for the outbreak at the chicken farm was an airborne spread of the virus from the duck farm.

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Going forward -

In light of this evidence, experts have called for farmers to consider the airborne spread of bird flu when thinking about how to protect their birds and livestock.

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Current measures -

This is not to suggest that current precautions, such as restricting entry to farms and requiring personnel to wear protective equipment, are not important.

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Layered approach - However, it seems likely that a layered approach to protection will be the best course of action going forward.

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Extra protection -

For example, farmers may consider filtering the air in their barns, as well as continuing with other measures, in order to provide another layer of protection for their animals.

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Transmission in humans -

In terms of bird flu cases in humans, experts believe that airborne spread of the virus may be involved in cases where there is no other identifiable source of transmission.

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Explaining unusual cases -

For example, three veterinarians tested positive for H5N1 antibodies at a recent conference, and only one of them had known exposure to a sick animal.

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General rule - However, it is important to note that the current iterations of the H5N1 virus do not seem to be very effective at infecting humans in general.

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Current risk -

Of course, that may change as time goes on and the virus mutates. For now, however, the risk to the human population is low.

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Another distinction -

Furthermore, it would probably take a lot more of the virus to infect a human than it takes to make a bird sick.

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Low levels of the virus in the air -

Viruses disperse in the air, meaning that they would only be present in the wind in tiny amounts. Therefore, it would seem there is minimal cause for concern.

Sources: (CDC) (CNN)

See also: Why have flu deaths in kids hit a new record in the US?

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