eggs

bird-flu-flare:-cattle-in-5-states-now-positive-as-texas-egg-farm-shuts-down

Bird flu flare: Cattle in 5 states now positive as Texas egg farm shuts down

bird flu, CDC, Chickens, dairy cows, eggs, health, hens, Highly pathogenic avian influenza, influenza, Science, USDA / /

flare-up —

The risk to the general public remains low, federal officials say.

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Chicken eggs are disposed of at a quarantined farm with bird flu in Israel's northern village of Margaliot on January 3, 2022.

Enlarge / Chicken eggs are disposed of at a quarantined farm with bird flu in Israel’s northern village of Margaliot on January 3, 2022.

The flare-up of highly pathogenic bird flu continues to widen in US livestock after federal officials confirmed last week that the virus has spread to US cows for the first time. The virus has now been detected in dairy cows in at least five states, a single person in Texas exposed to infected cows, and an egg farm in Texas, all spurring yet more intense monitoring and biosecurity vigilance as the situation continues to evolve.

As of Tuesday, seven dairy herds in Texas, two in Kansas, and one each in Idaho, Michigan, and New Mexico had tested positive for the virus. The affected dairy herd in Michigan had recently received cows from one of the infected herds in Texas. It remains unclear if there is cow-to-cow transmission of the flu virus.

The virus—a highly pathogenic H5N1 avian influenza or HPAI—has been devastating wild birds worldwide for the past several years. Throughout the devastating outbreak, the flu virus has spilled over to various species, including big cats in zoos, river otters, bears, dolphins, seals, squirrels, and foxes. While cows were an unexpected addition to the list, federal officials noted last week that affected dairy farms had found dead wild birds on their farms, suggesting that wild birds introduced the virus to the cows, not an intermediate host.

On Monday, the Centers for Disease Control and Protection reported that a person in Texas who had contact with infected dairy cows had tested positive for the HPAI. The person’s only symptom was eye redness. The CDC said the person was treated with an antiviral for flu and was recovering. It is the second case of HPAI found in a person in the US. The first case was in a person in Colorado who was directly exposed to poultry infected with the virus. In that case, the person’s only symptom was fatigue over a few days. The person recovered. The CDC considers the risk of HPAI to the general public to be low.

Low risk

Meanwhile, the virus continues to spread to less-surprising animals: chickens. On Tuesday, Cal-Maine Foods, Inc., the country’s largest producer of fresh eggs, reported that HPAI was detected in one of its facilities in Texas. The facility is located in Parmer County, which sits at the border of Texas and New Mexico. It’s unclear if the egg facility is close to any of the affected dairy herds. Cal-Maine, following the US Department of Agriculture biosecurity protocols, immediately shut down the facility. Approximately 1.6 million hens and 337,000 pullets—young hens—were culled. Cal-Maine said the hens represented about 3.6 percent of the company’s total flock.

Since the outbreak began in wild birds, the virus has led to the deaths of over 82 million commercial and backyard birds in the US, with 48 states affected and over 1,000 outbreaks reported. The infections have spurred increases in egg and poultry prices.

It’s unclear if the virus will have the same effect on milk or beef, but so far, it appears that it will not. In the infected herds, the virus appears to only be affecting a small percentage of animals, particularly older animals, and they generally recover. As the USDA puts it there’s “little to no associated mortality reported.” Milk from sick cows is always diverted from the milk supply, but even if milk contaminated with HPAI were to make it into the supply, the virus would be destroyed in the pasteurization process.

Still, the continued, widespread outbreak and spillovers of HPAI in various species highlight the ever-present risk that influenza viruses could mix together, combining genetic fragments of different strains (genetic reassortment) to create a new strain that could spark outbreaks or even a pandemic in humans. In the current outbreak among dairy cattle, federal researchers were quick to check the genetic sequence of the HPAI, finding that, so far, the strain lacks mutations in key genetic regions that would signal the virus has become more infectious to humans. For now, the USDA and the CDC report that the risk to the public is low.

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big-evolutionary-change-tied-to-lots-of-small-differences

Big evolutionary change tied to lots of small differences

Biology, eggs, evolution, live birth, Science, snails / /

Cracking the eggs —

Lots of genes changed as a species of snail went from laying eggs to live births.

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Image of a dark, grey-black snail shell.

Enlarge / An example of a Littorina species, the common periwinkle.

The version of evolution proposed by Charles Darwin focused on slow, incremental changes that only gradually build into the sort of differences that separate species. But that doesn’t rule out the potential for sudden, dramatic changes. Indeed, some differences make it difficult to understand what a transitional state would look like, suggesting that a major leap might be needed.

A new study looks at one major transition: the shift from egg-laying to live births in a set of related snail species. By sequencing the genomes of multiple snails, the researchers identified the changes in DNA that are associated with egg-laying. It turns out that a large number of genes are associated with the change despite its dramatic nature.

Giving up eggs

The snails in question are in a genus called Littorina, which are largely distributed around the North Atlantic. Many of these species lay eggs, but a number of them have transitioned to live births. In these species, an organ that coats eggs with a protein-rich jelly in other species instead acts as an incubator, allowing eggs to develop until young snails can crawl out of their parent’s shells. This is thought to be an advantage for animals that would otherwise have to lay eggs in environments that aren’t favorable for their survival.

The egg laying species are so similar to their relatives that they were sometimes thought to just be a variant of an egg-laying species. All of which suggests that live birth has evolved relatively recently, giving us a good opportunity to understand the genetic changes that enabled it.

So, a large international team of researchers sequenced the genomes of over 100 individual snails, both egg-laying and live birth. The resulting data was used to analyze things like how closely related different species are, and what genetic changes are associated with live birth.

The results suggest that there are two separate clusters of species that reproduce through live births. Put differently, on an evolutionary tree of these snail species, there’s a branch full of egg-laying species separating two groups that give birth to live snails. Typically, this structure is viewed as an indication that live births evolved twice, once for each of the two clusters.

But that doesn’t seem to be the case here, for reasons that we’ll get into.

Lots of variations

Separately, the researchers looked for regions of the genome that are associated with giving live births. And they found lots of them—88 in total. These 88 regions were identified in both clusters of live-birth species, and the DNA sequences within them were very similar. This suggests that these regions had a single origin and were maintained in both these lineages.

One possibility to explain this is that a population of live-birth animals reverted to egg-laying at some point in their evolution. Alternatively, hybridization between egg-layers and live-birthers could have let these variations spread within an egg-laying population and ultimately re-enable live births when enough of them were present in individual animals, producing a separate live-birth lineage.

The 88 regions identified as underlying live births have very little genetic diversity, suggesting that a specific genetic variant in each region is so advantageous that it swept through the population, displacing all other versions of the stretch of DNA. They have, however, picked up some distinct variations that are rare outside the egg-laying populations—enough to allow the researchers to estimate the age when these pieces of DNA came under evolutionary selection.

The answer varies depending on which of the 88 segments you’re looking at, but it ranges from about 10,000 to 100,000 years ago. That range suggests that the genetic regions that enable live births were put together gradually over many years—exactly as the traditional view of evolution suggests.

The researchers acknowledge that at least some of these regions are likely to have evolved after live births were already the norm and simply improve the efficiency of the internal incubation. And there’s no way to know how many variants (or which) need to be present before live births are possible. However, the researchers now have an extensive list of genes to look into to understand things better.

Science, 2024. DOI: 10.1126/science.adi2982  (About DOIs).

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