#33 – HMPV: the Common Respiratory Virus Nobody Knows

00:00:07: Overall, six to seven percent of all hospitalizations with acute respiratory infections are because of human methanomavirus.

00:00:46: Yeah hello and welcome to this week's episode of Virological!

00:00:50: This was recorded on September twentieth of twenty-twenty-six in Austria.

00:00:56: so Today we're going to talk about a respiratory virus, and I'm gonna start focus on respiratory viruses again because the season starts.

00:01:07: And so this time we are talking about the human metanomavirus or HMBV.

00:01:14: that's a pneumovirus which broadly speaking is a paramexorvirus.

00:01:19: it closely related to avian metanumovirus but then also to respiratory syncytial virus or RSV, which is another pretty nasty human respiratory virus that can cause troubles in kids and all the adults.

00:01:36: And a little bit further away from genetic relatedness we have other baromix viruses like mumps or measles so they're kind of distantly-related.

00:01:52: Basically, all pyromixoviruses is a negative-sense RNA virus.

00:01:58: It has one single stranded RNA genome of negative polarization.

00:02:04: The virion is pretty ugly.

00:02:07: it's kind of roundish but they can also be elongated and its about hundred fifty to six hundred nanometers in diameter doesn't look really nice.

00:02:18: The virus encodes for a number of proteins that make up the virion.

00:02:22: I'm just going to go through the structural proteins here, which are in the virions.

00:02:28: inside we have the RNA genome and it's protected by nuclear protein then associated with phosphobrotein but also with polymerase called L In this case.

00:02:40: Then we've got matrix protein on the insides lipid envelope.

00:02:45: The matrix protein stabilizes the virion and in the envelope we have a small protein that's called SH.

00:02:52: And then two spike proteins, one is called G and other one is F. F stands for fusion.

00:03:00: The G-protein is receptor binding protein.

00:03:03: even though it might not completely necessary to be infectious It binds to heparin, sulfate and other glycosaminoglycans.

00:03:15: So these are basically just polysaccharides that the virus recognizes in binds.

00:03:21: And F can also bind into a protein do an integrine.

00:03:24: That's another surface protein on cells.

00:03:29: This human metanema virus is special in a way for paramexor viruses A lot of paramexo viruses.

00:03:36: they fuse at the cell membrane.

00:03:40: But it seems that human metonymovirus actually gets taken up into the endosome, like influenza virus and then fuses with the endostomal membrane once the endo-some get acidified.

00:03:54: so endosomes are these little vesicles that cells use to bring stuff in to their cells And then fusion happens there basically when the genome is released and replication starts once they endosomal and viral membrane fused.

00:04:11: A little bit about the history of the virus, it was discovered only in two thousand one in the Netherlands In samples from kids with respiratory infections.

00:04:22: The person who discovered the virus is Bernhard Van den Hogen.

00:04:26: I hope i pronounced that right.

00:04:28: probably not.

00:04:29: my Dutch is very good.

00:04:31: And at Erasmus Medical Center And for the various horology aficionados out there, Bernadette is Ronfoshie's wife.

00:04:42: So it was only discovered in two thousand one but... ...it was likely circulating in humans for quite some time already Even that first paper where they described to Discovery.

00:04:53: They really looked at samples Back in time, basically I think the oldest temple was from nineteen fifty-eight and people back then already had antibodies against metanumovirus.

00:05:05: So it's not like you jumped into humans in two thousand one but i think that hypothesis still is.

00:05:12: at some point in history this virus probably branched out of avian metanomovirus.

00:05:19: so potentially there were zoonosis where avian metaneumovirus made it into humans and then established itself, became human metaneumeovirus.

00:05:29: And there are estimates based on phylogenetic clock analysis... ...and the estimate is that might have happened about two hundred years ago.

00:05:39: You always had to take this estimate with a grain of salt.

00:05:44: The virus was pretty established in humans And there's actually two genetic lineages, lineage A and lineage B that circulate.

00:05:52: They don't seem to be much different in terms of disease but they're genetically different.

00:05:58: Yeah so how do you get infected with this virus?

00:06:00: It is typically spread via respiratory secretions.

00:06:04: This can be a form of respiratory droplets But also direct contact with infected individuals and it can be transmitted by objects.

00:06:15: we call this fomite transmission, so yeah similar to many other respiratory viruses.

00:06:23: It does cause mild-to severe respiratory infections.

00:06:26: it can also unfortunately lead to death but it depends a little bit on which patient is infected.

00:06:33: for the milder disease what you typically see is a runny nose nasal congestion sore throat beasing and fever.

00:06:44: So that's kind of typically what you see.

00:06:46: But there are patient groups, they're at much higher risk and it includes babies in infants specifically prematurely born babies but also older adults above the age of sixty-five.

00:07:02: COPD patients asthma patients the virus can lead to asthma exacerbation And then of course immunocompromised patients Specifically kids.

00:07:15: Most hospitalizations happen between six and twelve months of age, so that's when the infections seem to be pretty dangerous.

00:07:23: And what can happen here is the virus can lead to pneumonia, bronchiolitis... ...and specifically bronchiolisis.

00:07:31: something happens often in kids.

00:07:34: So, bronchialitis means the bronchioles are inflamed.

00:07:38: The bronchiols are very thin basically airways before the alveoli.

00:07:46: The alveolus is where gas exchange happens and then the bronchiose are right before that, when they're inflamed because of infection.

00:07:56: it's really hard to get air into their alveolae which can lead to hypoxia.

00:08:03: so basically low oxygen levels and this is very severe.

00:08:09: So specifically in kids that virus.

00:08:11: a big problem.

00:08:13: What I forgot to mention is the incubation time of the virus which seems to be three two six days.

00:08:18: So most people get symptomatic, three-to-six days after they got exposed.

00:08:25: so how big a problem are these human weather pneumovirus infections?

00:08:30: As i mentioned it can lead to severe disease but the problems with the virus infection also very common.

00:08:36: The estimate that its second most common respiratory tract illness in kids under five In otherwise healthy children, about ten to twelve percent of all acute respiratory illnesses are caused by human metonymovirus.

00:08:55: Overall six-seven percent of our hospitalizations with acute respiratory infections is because of the human metonymovirus.

00:09:05: and if you look at... age group under five, about eight to fifteen percent of all pneumonia cases in that age group are due to human metonymovirus.

00:09:17: It's a relatively big problem.

00:09:18: it is almost comparable with RSV which you know as the biggest issue where we have now vaccines and monoclonal antibody treatments.

00:09:26: but human metoneumovirus would need that attention too.

00:09:31: The virus circulates worldwide.

00:09:33: typically epidemics occur during winter or early spring And yeah, as I said it's a very common infection.

00:09:42: Once kids are five years old basically all of them have been infected.

00:09:46: and the problem is you don't get long-lasting immunity against reinfection.

00:09:51: people get re-infected over time.

00:09:53: the virus can keep circulating in means that basically there's a lot of exposure to the virus and that also explains why older adults can still get infected, then they can develop more severe disease because their immune system is not as strong anymore instead of younger healthy adults.

00:10:16: Maybe it's also worth mentioning that there was a big outbreak in China at the end of twenty-twenty four, beginning of Twenty-Twenty five.

00:10:23: Some people might remember that There were headlines about that.

00:10:27: I think People are worried that there is new virus causing a pandemic again which certainly wasn't the case but they had relatively large wave and That certainly caused concerns because A lot of people who're not familiar with this virus didn't know that the virus existed.

00:10:45: so Typically this virus infects humans, but there have been infections also in chimpanzees and gorillas.

00:10:51: And that can be problematic because of course these are endangered animals... ...but human methanomavirus can cause pretty severe diseases to the animal and kill them.

00:11:01: so it has been recorded One of the reasons why people have to be very careful when interacting with wild chimpanzees or wild gorillas, because there's always a risk that we infect them and then these viruses can burn through their populations.

00:11:17: Yeah!

00:11:17: The other issue is that we assume metonymoviruses where there are no treatment and they're not vaccines.

00:11:23: Vaccines are in development and I think treatments There are no vaccines in phase one and phase two clinical trials.

00:11:32: A lot of them were actually combination vaccines where companies try to combine an RSV vaccine with the human-veteran pneumovirus vaccine, also partially with Barrow influenza virus three vaccines.

00:11:45: that would be great because those viruses affect kids quite a bit And if you have a combination vaccine against them this will be great.

00:11:55: Again, for RSV we already have vaccines that are typically given to pregnant women than to basically passively protect the babies once they're born.

00:12:07: But something like this does not exist in human metanumamorous yet.

00:12:11: so hopefully next few years will have same set of countermeasures as we have them with RSV right now.

00:12:19: That's it for today short episode about relatively common respiratory virus that can do a lot of damage, but then a lot people are not the bearer.

00:12:30: So as always if there's any comments questions or suggestions please write an email to Virological at podcastvex.com and If you want support us You can also do it on Steady.

00:12:43: Thanks for listening in And until next week Bye!

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