One of the steps that gives epidemiologists the shakes has now occurred. H5N1 has been able to infect a few pigs.
Bird flu in pigs on a hobby farm. News From The States
The pigs were roaming with the poultry, which caught it presumably from a wild bird. The animals have been euthanized, the farm quarantined, and the owners given protective gear. So far nothing further.
Why are pigs a big deal? Let’s review virology 101. In very layman terms. For more, you can start with wiki and follow the linked references.
Viruses can’t do anything on their own. They are total parasites, barely qualifying as “life” outside a host cell. They break into cells using receptors on the cell surface that serve other purposes in health, and hand off their DNA or RNA (both sorts of virus exist; flu is an RNA virus) to the cell’s machinery to copy. Then the copies break out of the cell wall and go infect more cells. This usually kills the host cell.
Most viruses hand over their genetic codes WHOLE. But flu came up with an analog of the assembly-line concept. It breaks its genome into 8 pieces, hands each one to a different organelle in the host cell, and they all churn out copies of these pieces. Then the pieces reassemble themselves before breaking out of the cell wall. They must have some lock-and-key segments on the ends of these bits.
This is naturally somewhat prone to error, but is efficient enough to make flu one of the more easily transmissible viruses. Still, most flu pandemics burn themselves out in a couple of years, to be replaced by some other strain.
The current highly pathogenic bird flu has been circling the globe as a panzootic [demos = people, zoos = animals] for nearly thirty years. It is breaking a lot of what we thought were rules. It is endemic in wild birds and causes outbreaks in domestic birds and a growing list of mammal species. Some seabirds, and seals and sealions, have been severely affected. If a domestic flock catches it, the entire flock must be euthanized, and incinerated to stop the spread. [It is going to kill them anyway, and they will suffer]
Lots of animals have flus particular to their species. Bats, pigs, horses, and dogs, have strains of influenza A specific to them, as do humans, and other species can sometimes catch these. Practically all of the possible combinations of H (1-16) and N (1-11) antigens have been observed in wild birds, they are the natural reservoir. H17 and H18 have only been discovered in bats.
Bird-adapted strains of the virus can be asymptomatic in some aquatic birds but lethal if they spread to other species, such as chickens.[14]
wikipedia
Flus are quite specific in which cell-surface receptor they use, and this is part of what keeps them in their respective species silos. What sets pigs apart, and makes them so worrisome, is that their cells have receptors that can accept different types of flu. They can catch bird flus and human flus as well as pig flus.
The Big Bad happens when any animal catches two types of flu at once, which is perfectly possible. When they split their genomes for reproduction in the host cell, there is a non-zero chance that some of the newly made viruses will reassemble using each others’ bits.
This “reassortment event” is the quick and dirty way for a bird flu to acquire human-infecting abilities, without endless experiments with random mutations. Just mix and match with a human flu.
This event could occur in a human that catches the bird flu, but there have only been a few dozen of those in the US. If this bird flu gets loose in a BIG pig raising operation, hell breaks loose. The 1918 flu pandemic started on an American hog farm.
Keep your guard up. If you keep pet pigs, keep them the hell away from any birds. Mother Nature is not on anybody’s side.
