AVIAN INFLUENZA
- 16 hours ago
- 4 min read
Tavishi
Oops... kinda fell of the face of the Earth. I'm in the middle of the British countryside doing a brief placement at a zoo? Anyways. I am BACK. Trust, there will be a post about my zoo experience veeeeery soon. However, I have been cooking this post for a few weeks now, so this has to come first:
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Everyone has a few go-to, half-assed, overused jokes. Every time I see a "road work ahead" sign, I say, "I sure hope it does!".
My brother's go to crappy joke is, "The bird flu? They tend to do that." (You have to say it out loud to get it.)
Sidebar 1: I'm really bad at telling jokes sometimes. I tend to overexplain them. Sorry to my flatmate Mary. And Jasmine. And actually all of my friends.
Anyways, on the topic of bird flu, there's a huge avian influenza outbreak right now, and it's affecting both humans and wildlife (see: One Health!) My brother is going into human medicine, and I'm going into veterinary medicine. Avian influenza is where our interests meet, except he could give fewer shits about epidemiology and pathology. I, on the other hand, am really really interested in all things disease. And! Avian influenza is now in pinnipeds!
Avian influenza has been around for a while, but there is currently an outbreak in the US, which has widely affected birds, humans, and other mammals. What's particularly fascinating to me about avian influenza is not only its reach, but the variety of species it can infect.
Avian influenza is, as you might guess, a type of flu, which is a general type of infection caused by a group of influenza viruses. The influenza viruses are classified into four genera: Alphainfluenzavirus, Betainfluenzavirus, Gammainfluenzavirus, and Deltainfluenzavirus.
In less fancy terms, Flu A, B, C, and D. Now, each of these four species has a bunch of different strains. When you get a flu shot, you're getting protected against influenzas A and B. The Spanish flu was caused by influenza A. Influenzas C and D are considered more irrelevant, because of their limited spread. Influenza C is known for infecting SEALS though (C for seal). Influenza D has not yet been found to infect humans.
Why is this relevant to bird flu? Well, bird flu is a strain of influenza A, specifically H5N1. Yet again, because viral nomenclature is incredible and elegant, it's intentional. What makes each viral strain unique is what proteins it has on its outside- think of it like house decorations. That's what the name of each strain signifies. The H stands for the hemagluttinin protein, and the N for the neuraminidase protein. The numbers mean what type of each of those aforementioned proteins there are- in the case of avian influenza, H5 and N1.
These proteins define the identity of the virus. Hemagluttinin binds to sialic acid receptors on host cell surfaces, allowing virus intrusion, where it later replicates. Neuraminidase permits the viral replicates to break free from host cells. Slight differences in each of these proteins allow for genetic variation and thus, differences in who and where each virus can infect.
In birds, the hemagluttinin 5 specifically binds to α-2,3 sialic acid receptors, primarily found in the upper respiratory tract and intestines. However, in humans, these receptors are found in the lower respiratory tract. As a result, bird and human pathologies differ. As yet, we are of the understanding that H5N1 is transmitted between birds, and from birds to mammals. However, recently, H5N1 has been found to be passed from mammal to mammal in select species: most prominently, pinnipeds.
Transmission of viruses between birds is via infected aerosols and bodily fluids. Additionally, infected birds tend to present asymptomatic until later stages of infection. Now, up till this point, most mammals who were infected, were thought to have been infected via feces or consumption of contaminated birds- as seen with foxes.
However, pinnipeds don't. really eat birds. Gray seals have been known to eat birds on occasion, especially the occasional pesky seagull, but its not enough to explain the phenomena of seal outbreaks as yet.
Outbreaks of H5N1 have been found in species including the Northern elephant seal, Southern elephant seal, harbor seal, gray seal, caspian seal, and more. Most recently, about 3 months ago, infection had been found in elephant seals and California sea lions along the California coast. Nearly three years prior, a major outbreak eliminated a huge portion of the Southern elephant seal population.
This spring, when avian influenza infected seals were found, the Marine Mammal Center closed operations for a few days to prevent this from potentially spreading to people. However, they're back in operations now, and working on a solution to prevent the highly endangered Hawaiian monk seal from having its population decimated via avian influenza.
The biggest attempt to conserve the species is via vaccination of Hawaiian monk seals, an effort used prior to prevent a phocine distemper virus outbreak.
In seals, avian influenza presents with neurological and respiratory systems. Whereas the central nervous system is most commonly affected, the lungs are also a significant source of H5N1 infection. Neurological symptoms are similarly consistent with later symptoms in birds. While most birds remain asymptomatic, they do present with confusion and poor coordination in later stages of disease.
In necropsies of infected seals, mengitis and encephalitis were found, as well as prominent neutrophilic infiltrate (see: sign of inflammation...) Blood and infection was also present throughout the body, with many lesions concentrated around the alveoli of the lungs.
What mostly remains a mystery? Exact methods of transmission. The goal here is to prevent avian influenza from causing the extinction of any one species, as well as to keep it from becoming a global pandemic (oops I need to not fearmonger). I am not an epidemiologist, but epidemiology does occasionally pique my interest. However, my academic interests lean more towards pathology and medicine, and I find myself more interested in the how and why disease manifests. As someone really interested in wildlife medicine, avian influenza is an excellent case study of interventional medicine in conservation of free-ranging wild species. Plus, seal pathology. VERY much my thing.
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