I asked a few questions in another thread from 2003, and parts of my questions were answered but not the one in my subject line here.
There are some vaccines against bacterial infections, like TB, but not for things like strep. I’ve had strep a dozen times, but you get chicken pox once and you’re done.
The TB vaccine is not really used much and may be minimally-effective. The more common bacterial vaccine is for tetanus.
Viruses are not really living things. They consist of a protein shell containing the data (usually in RNA form) needed to make more of that type of virus. They have no progressive metabolic processes, just an injection mechanism to force the host to produce more viruses. They have no real life cycle outside of parasitic replication. Defeating them is a matter of disabling their ability to replicate, which could, theoretically, be as simple as clogging their injection point.
Bacteria, by contrast, are unmistakably living things, which have their own metabolic processes and usually reproduce on their own. It is typically the reproductive process where stuff like antibiotics cause bacteria to fail, because a large fraction of bacteria do not attack the living host but create other issues (like toxic by-product generation). In fact, the human microbiome includes a staggering contingent of symbiotic bacteria without which we would be dead.
Bacteria have a lot of cell wall proteins, and most of them are commonplace, so identifying one surface protein to mark can be a major challenge. It might not even be possible in some cases to distinguish a harmful bacterium from a harmless or important type. It is a far greater challenge to defeat dangerous bacteria a priori than with much simpler viruses.
Here is an article explaining some of the difficulties in developing vaccines for bacteria:
Until you get shingles
We discussed this a while back - chicken pox is one of those things that you can get more than once (not even counting shingles):
Sometimes they’re challenging to develop for various reasons, but the numerous vaccines against bacterial pathogens include ones for meningococcal disease, (Strep) pneumococcal pneumonia, Haemophilus influenzae, tetanus, diphtheria and pertussis.
Article explaining why it’s been tough developing vaccines against targets like Staph aureus and Pseudomonas. Antigenic diversity, complexity of effective immune responses and lack of good animal models for vaccine studies are cited.
I believe the germ’s genetic code has something to do with it.
Viruses that run on DNA have surface antigens which are fixed, and thus the body’s immune system can create antibodies to neutralize the germ.
RNA based viruses (and bacteria?) create variable surface antigens which change faster than an immune system to keep up.
The TB vaccine is not really used much in the USA because (1) There is a national shortage of TB vaccine in the USA, and (2) The USA does not have a high level of TB.
TB vaccine is highly effective in preventing TB in young children. “May be minimally-effective” is true, but those are weasel words. It also “May be effective”. Nobody thought about making statements about the effectiveness of BCG twenty years ago: what changed was the lack of supply in the USA, and the possibility of new mRNA vaccines.
BCG is an attenuated virus vaccine. Unlike COVID mRNA vaccines, which have demonstrated safety in billions of people, BCG is not a ‘safe’ vaccine. It’s given to people who work with TB infected people (in health care, or indigent care), and it’s used in areas with high levels of endemic TB.
BCG is mostly used in the U.S. as immunotherapy for early stage bladder cancers.
It may also have application for treating other non-infectious disorders.
Diphtheria, hemophilus influenzare and pertussis are also bacterial diseases.
That’s the only thing I ever saw it used for. I have no idea who figured out this might work, or why, but for some (usually) men, it does, with minimal side effects beyond local discomfort.
Before doing clinicals in 1994, all of us pharmacy students had to have TB tests, at the school’s expense. All but two, who were friends of mine, were able to use the PPD, but they had to get chest x-rays because they had emigrated from Uganda and Hong Kong in the 1970s, and had to get a BCG vaccine to enter the country. People who have had a BCG will usually register a false-positive for a PPD. AFAIK, all the tests for the 86 of us were negative.
I find this fascinating. Enough so that I did a little digging. Since the OP has mostly been answered, I hope it’s OK to post this synopsis on the origin/evolution of viruses:
'The exact origin of viruses remains a topic of scientific debate. Several hypotheses have been proposed, but none have been definitively proven.
Hypothesis 1: Ancient Cells
This hypothesis suggests that viruses originated from ancient cells that existed before the Last Universal Common Ancestor (LUCA). Over time, these cells may have lost their ability to replicate independently and became dependent on host cells for survival. (this has the makings of a good sci-fi story)
Hypothesis 2: Escape from Host Cells
This hypothesis proposes that viruses originated from genetic elements that escaped from host cells. These elements, such as plasmids or transposons, could have acquired the ability to replicate and spread between cells, eventually evolving into viruses.
Hypothesis 3: RNA World Hypothesis
This hypothesis suggests that viruses originated in the RNA world, a hypothetical period in early Earth’s history when RNA was the primary genetic material. RNA molecules may have self-replicated and evolved into primitive viruses that could infect early cells.
Hypothesis 4: Hybrid Origin This hypothesis proposes that viruses may have originated from a combination of different sources, such as ancient cells, genetic elements, and RNA molecules.’
Here’s a bit more information about the competing hypotheses of viral origins:
We tend to lump different families of viruses into one big overarching group but the realms of viruses are so different that if they were considered independent domains of life. There may not be a singular modal origin for all visuses but it is clear that at least some families are, in fact, free floating RNA or derivatives of organelles which escaped from cells and became capable of replication by infecting host cells. We tend to think of viruses as pathogens but there are plenty of viruses that do no harm and may even sometimes provide benefit to their hosts. No area of biology—even neuroscience—is as complicated an has so many “unknown unknowns” as virology and viral immunology.
Stranger
Thank you, Stranger, for that link.
Also, there are several different groups of viruses, with the groups being basically more different from each other than elephants and rutabagas. There is likely more than one completely different origin.
(Try to wrap your head around this)
Excluding ribozyvirians, RNA viruses of groups III–V are believed to share common ancestry.[2][3] +ssRNA viruses form the basal, ancestral lineage of these viruses from which dsRNA viruses and –ssRNA viruses appear to have evolved from on multiple occasions.[3][66] The two orders of RT viruses in the class Revtraviricetes, Blubervirales and Ortervirales, are believed by virologists to have evolved from two different families of retrotransposons on separate occasions.[114] ssRNA-RT viruses all belong to Ortervirales and thus share common ancestry.[3][72] dsDNA-RT viruses, on the other hand, are found in both orders and therefore represent two separate lineages of dsDNA-RT viruses.[72][98] Ribozyvirians constitute a lineage of –ssRNA viruses unrelated to other RNA viruses.[3]
Most ssDNA viruses likely originate from plasmids that, on multiple occasions, recombined with other genomes to obtain the structural proteins needed to form virions.[2][3] The evolutionary history of dsDNA viruses is the most complex as they appear to have emerged independently on numerous occasions. Two major lineages of dsDNA viruses exist: the realm Duplodnaviria and the realm Varidnaviria, the latter of which also contains ssDNA viruses that are descended from dsDNA viruses. The opposite is true in the realm Monodnaviria, which contains dsDNA viruses descended from ssDNA viruses. There are also two minor realms, Adnaviria and Singelaviria,[22] that exclusively contain dsDNA viruses. Lastly, there are dsDNA virus families unassigned to higher taxa that are unique from existing realms and which likely constitute small realms.[2][3]
Of the replication-expression systems used by viruses, only Baltimore group I (dsDNA) is typically used by cells.[2] The other groups may be remnants of the primordial stage of life before the emergence of modern-like cells, during which the dsDNA system used by extant cells had not yet become uniform. The ancestors of RNA viruses in particular may have emerged during the time of the RNA world. And although virus realms are evolutionarily independent from each other, the replicative proteins encoded by viruses in the four major realms (Duplodnaviria, Monodnaviria, Riboviria, and Varidnaviria) are built on the core RNA recognition motif, one of the most common nucleic acid-binding domains in nature. Therefore, the replication-expression cycles most likely diversified before the separation of large dsDNA replicators, which became the ancestors of cellular life, from other types of replicators, which became selfish genetic elements and gave rise to viruses.[3]
I seem to have failed to complete expressing that thought; that should read:
… but the realms of viruses are so different that if they were considered independent domains of life the would be un different kingdoms.
“Virus” is more of an extremely broad functional description rather that a distinct classification, and as a world-class virologist explained to me (over a game of Pandemic a few years before COVID-10), we really have no idea how many types of viruses exist in the world because research are almost exclusively focused an viruses that are pathogenic or present a cross-species ‘spillover’ threat to humans, livestock, and agriculture, and there are vastly more individual virions than living organisms on the planet even compared with bacteria and archea.
I also asked her if she thought that extraterrestrial life would have some analogue to viruses (because we share an interest in astrobiology), and she responded that if the use proteins and encode heritable data in some analogue of a genome, then they almost certainly have their own counterpart to viruses even if they aren’t specifically DNA and RNA.
Stranger