Articles, Blog

How do viruses jump from animals to humans? – Ben Longdon

December 19, 2019

At a Maryland country fair in 2017, the prize pigs were not
looking their best. Farmers reported feverish hogs with
inflamed eyes and running snouts. But while fair officials worried
about the pigs, the Maryland department of health was
concerned about a group of sick fairgoers. Some had pet the pigs, while others had
merely been near their barns; but soon, 40 of these attendees would
be diagnosed with swine flu. More often than not, sick animals
don’t infect humans. But when they do, these
cross-species infections, or viral host jumps, have the potential to produce
deadly epidemics. So how can pathogens from one species
infect another, and what makes host jumps so dangerous? Viruses are a type of organic parasite
infecting nearly all forms of life. To survive and reproduce, they must move
through three stages: contact with a susceptible host,
infection and replication, and transmission to other individuals. As an example, let’s look
at human influenza. First, the flu virus encounters
a new host and makes its way into
their respiratory tract. This isn’t so difficult, but to survive
in this new body, the virus must mount a successful
infection before it’s caught and broken down
by an immune response. To accomplish this task, viruses have evolved specific interactions
with their host species. Human flu viruses are covered in proteins adapted to bind with matching receptors
on human respiratory cells. Once inside a cell, the virus employs
additional adaptations to hijack the host cell’s reproductive
machinery and replicate its own genetic material. Now the virus only needs to suppress
or evade the host’s immune system long enough to replicate to sufficient
levels and infect more cells. At this point, the flu can be passed on to
its next victim via any transmission
of infected bodily fluid. However, this simple sneeze also brings
the virus in contact with pets, plants, or even your lunch. Viruses are constantly encountering
new species and attempting to infect them. More often than not, this ends in failure. In most cases, the genetic dissimilarity
between the two hosts is too great. For a virus adapted to infect humans, a lettuce cell would be a foreign and
inhospitable landscape. But there are a staggering number
of viruses circulating in the environment, all with the potential to
encounter new hosts. And because viruses rapidly reproduce
by the millions, they can quickly develop random mutations. Most mutations will have no effect,
or even prove detrimental; but a small proportion may enable the
pathogen to better infect a new species. The odds of winning this destructive
genetic lottery increase over time, or if the new species is closely related
to the virus’ usual host. For a virus adapted to another mammal, infecting a human might just take
a few lucky mutations. And a virus adapted to chimpanzees, one of our closest genetic relatives,
might barely require any changes at all. It takes more than time and genetic
similarity for a host jump to be successful. Some viruses come equipped to easily
infect a new host’s cells, but are then unable to evade
an immune response. Others might have a difficult time
transmitting to new hosts. For example, they might make the host’s
blood contagious, but not their saliva. However, once a host jump reaches
the transmission stage, the virus becomes much more dangerous. Now gestating within two hosts, the pathogen has twice the odds of
mutating into a more successful virus. And each new host increases
the potential for a full-blown epidemic. Virologists are constantly looking for
mutations that might make viruses such as influenza
more likely to jump. However, predicting the next potential
epidemic is a major challenge. There’s a huge diversity of viruses
that we’re only just beginning to uncover. Researchers are tirelessly studying the
biology of these pathogens. And by monitoring populations to quickly
identify new outbreaks, they can develop vaccines and containment
protocols to stop these deadly diseases.


  • Reply Wallywutsizface August 9, 2019 at 9:33 pm

    But chimps don’t have tails

  • Reply SpeedStriker August 9, 2019 at 10:13 pm

    My deadly killer viruses can't be this cute!

  • Reply Milo Estobar August 10, 2019 at 12:39 am

    so virus are the oldest gambler….

  • Reply Chau Hien August 10, 2019 at 1:03 am


  • Reply Logix Indie August 10, 2019 at 3:20 am

    The process of evolution is a brutal process where different lives compete for survival. We would become better over time, so would our enemies.

  • Reply Edmund Au August 10, 2019 at 3:53 am

    I came because of the cute bacon ?

  • Reply Brian McInnis August 10, 2019 at 4:11 am

    Were you writing this under the impression that humans are vegetables or minerals?

  • Reply USS SNOWBALL August 10, 2019 at 4:54 am

    Omggggg they're sooo cute!!!

  • Reply Ahhh Suke Suke August 10, 2019 at 4:56 am

    Kinda, inaccurate. Those pigs were destroyed, not immunized lol

  • Reply Software Sadhu August 10, 2019 at 4:57 am


  • Reply JV August 10, 2019 at 5:06 am

    That vaccine sound so cute

  • Reply Vonilla August 10, 2019 at 5:43 am

    I mean, we ARE animals but okay

  • Reply Funneh cake 2 August 10, 2019 at 5:48 am

    Well viruses infectes humans one by one….

  • Reply Erice Dela Cruz August 10, 2019 at 6:15 am

    I'm from Philippines mahal ko kayo

  • Reply Vit Gra August 10, 2019 at 7:03 am

    Pigshit! I want swine flu, cannot get it.

  • Reply Calvin Stuart August 10, 2019 at 7:33 am

    Goodness the amount of snot flying all over the place was crazy. No wonder viruses can always get into us.

    This video was awesome. Love Ted-Ed.

  • Reply Perikles_la Anonymoose August 10, 2019 at 7:52 am

    Amazingly drawn and animated

  • Reply Joel Mathmath August 10, 2019 at 11:24 am

    Oh no! Those cute piglets are too adorable to be sick. 🙁

  • Reply Bob bob August 10, 2019 at 11:29 am

    Anyone else surprised by the high amount of videos made even though they all have stellar animations

  • Reply T Pham August 10, 2019 at 12:05 pm

    Is there viruses in quails because I hope there isn’t

  • Reply Joey Ridzwan August 10, 2019 at 1:53 pm

    Oh addison.. read me a bedtime story please.

  • Reply Scarlett Assasinator August 10, 2019 at 2:15 pm

    So if there's already a zombie deer disease,is it possible that a zombie apocalypse might happen??

  • Reply Blockling News August 10, 2019 at 4:24 pm

    Can I know who made the animation ? It's so adorable !

  • Reply Wan Lopes August 10, 2019 at 4:43 pm


  • Reply Tamy August 10, 2019 at 4:52 pm

    But viruses are non motile….

  • Reply Shivangi Shrivastav August 10, 2019 at 5:30 pm

    The animation in this video tho…… It's soooooooooo cute UWU especially the pigs ♥️

  • Reply Knosis August 10, 2019 at 5:50 pm

    Great video TED-Ed. I am surprised that you did not mention the HIV jump from chimpanzees to humans

  • Reply S V D August 10, 2019 at 6:33 pm

    Pet the pigs!!!
    Everything is so cuteee…

  • Reply Ann Sm August 10, 2019 at 6:34 pm

    What a beautiful fluid animation! Congratulations ??

  • Reply ChloChloa August 10, 2019 at 7:24 pm

    That little pig's sneeze- Awwwww..

  • Reply Mr. Ordinary August 10, 2019 at 7:40 pm

    Omg look at those cute piggy snouts and that doggie and agsgsg I can't the animation is too damn cuuuute :3

  • Reply Michael Daniels August 10, 2019 at 8:00 pm

    I feel worse for the pigs than the humans.

  • Reply Wilcon Barro August 10, 2019 at 9:09 pm

    Then why does rabies virus infect many species?

  • Reply Beatriz Gongora August 10, 2019 at 9:56 pm

    Simple, it's because we eat animals…

  • Reply вrчαnprσ lσngσѕ August 10, 2019 at 10:39 pm

    Fun fact
    Theres a virus that kills bacteria
    And very friendly to human bateriophages

  • Reply kid thatlikememe August 11, 2019 at 1:04 am

    The animation is so cute and adorable GJHJIKHLITFHYHDCRHRUNJFG

  • Reply qwerty uiop August 11, 2019 at 7:00 am

    piggy flu

  • Reply Ali Maged August 11, 2019 at 8:46 am

    Imاتابعكم from ??

  • Reply Harvey Lu August 11, 2019 at 8:55 am

    Im so gonna isolate myself aways from everything

  • Reply Abdul Samad August 11, 2019 at 1:11 pm

    which software they are using for video making ?

  • Reply Chisomo Banda August 11, 2019 at 2:20 pm

    Wait so viruses are the original hackers???

  • Reply Wan Fahmy August 11, 2019 at 2:21 pm

    Just like hiv. Primate to human..

  • Reply Jesse Biliran August 11, 2019 at 2:27 pm

    The animation is too frickn cute.

  • Reply Mykell Sumira August 11, 2019 at 4:38 pm

    I want to know why its more difficult to make a tight fist when you wake up… can you do a video on that please

  • Reply Rushell Dizon August 11, 2019 at 7:15 pm

    Hello! It would be very interesting if you feature anything related to Lorenzo's oil or even just ALD. It will give me great joy if you consider my suggestion. Nonetheless, keep creating great content. ?

  • Reply Daniel Björkman August 11, 2019 at 9:11 pm

    You drew the chipanse with a tail. Hope you catch this next time 🙂

  • Reply Mario Alavez August 11, 2019 at 9:13 pm

    thats an unfortunate depiction of the animal-industrial complex

  • Reply Sun 99 August 11, 2019 at 10:19 pm

    They flyyyy~

  • Reply Movie Time August 11, 2019 at 11:54 pm

    Chang ur intro I don’t like it

  • Reply Christina Key August 12, 2019 at 2:26 am

    This is why I hate being sick. Rude Mico organisms crashing in my body tearing up everything and not paying rent or sharing on the bills!!! Free loaders!!!

  • Reply Jenna Sliman August 12, 2019 at 3:48 am

    This wholesome animation makes me so happy ❤❤

  • Reply Fais MZ August 12, 2019 at 5:06 am

    Why do viruses and radioactive materials were often imagined/pictured as "green colors"? Why not blue? Red? Magenta?

  • Reply Aurobindo Ghosh August 12, 2019 at 5:54 am

    by contact, by air or by water

  • Reply Gamer Kron August 12, 2019 at 10:02 am

    This is why you vaccinate your kids.

  • Reply nuanphan chaumsuk August 12, 2019 at 12:38 pm

    The dog is sooo cute ☺

  • Reply Anju Singh August 12, 2019 at 1:20 pm

    The animation is so good

  • Reply Cindy Cute August 12, 2019 at 4:28 pm

    Please add albanian captions in videos
    Also thank u for teaching us such a great things

  • Reply Jesus rocks August 12, 2019 at 11:17 pm

    Nooooo not the piggies!

  • Reply nia August 13, 2019 at 1:08 pm

    Whos the narrator?

  • Reply Troy Nall August 13, 2019 at 2:26 pm

    They jump with their powerful tiny legs.

  • Reply Ananya Shetty August 13, 2019 at 3:12 pm

    This is such a kawaii episode!!!!

  • Reply Олег Козлов August 13, 2019 at 6:03 pm

    Ive met a bird
    I named it Enzo
    I opened a window
    And in flew Enzo

  • Reply Infinity Dragon August 13, 2019 at 9:34 pm

    Where's my Safe Space? All these Viruses are being mean to me!

  • Reply Asmita J. August 14, 2019 at 6:59 am

    I've always been such a paranoid hypochondriac, and I'm 20 and it's weird but I got goosebumps watching this. Although I'm morbidly obsessed with biology even though I'm going to be an accountant. But the animated pigs were so adorable!

  • Reply lika August 14, 2019 at 12:16 pm

    If you are from English speaking country please reply, I found this website, that publishes articles and per published article the author gets 100$, but your article can only published if you are native English speaker, I saw this as a great way to earn money, but I'm from non English speaker country, so if anyone is interested, please reply (I have explained it horribly I know??)

  • Reply chinchin 1 August 14, 2019 at 3:42 pm

    but the question is why does it replicates , why does a virus has the urge to survive?

  • Reply Ahil Kannan August 15, 2019 at 12:15 am

    Do a video about anti-virus.

  • Reply David Chavarria Carbajal August 15, 2019 at 1:31 pm

    The dog was so cute

  • Reply Dinesh Desai August 16, 2019 at 2:26 am

    Adding to this there are certain virus that remain in sleeping mode in the cold countries and they get activated when the person moves to the place having higher temperature. One need to take care of this effect too.

  • Reply never function August 17, 2019 at 4:23 am

    3:29 that'd a monkey, but I'm sure u knew that 🙂

  • Reply 4c00h August 17, 2019 at 6:07 pm

    Can we make a polymorphic virus that hunts other viruses?

  • Reply Eran Dromy August 18, 2019 at 6:32 am

    Which studio did the animation??

  • Reply wongwanchap August 18, 2019 at 1:40 pm

    The last scene is kind of misleading.. vaccine is not a cure, but a prevention.

  • Reply Nadeille Dure August 19, 2019 at 1:06 am

    The amount of germaphobes increases by 89%

  • Reply Mary christine Jimenez August 19, 2019 at 10:01 am

    Zombie deer:hoho

  • Reply Oskar Denis Baharudin August 19, 2019 at 1:56 pm

    Shouldn't it be "virii" ? 🙂

  • Reply 5 haman August 20, 2019 at 8:07 am

    I really miss Hungarian subtitles?:'(

  • Reply Ally Brooke Is Taking Me Higher August 20, 2019 at 8:27 pm

    I love this. Animation is amazing. When the piggies got healthy again, I was so happy. ❤

  • Reply Grammar Police August 21, 2019 at 6:18 am

    I love the animation!

  • Reply Aaisha QwertyQawerty August 21, 2019 at 10:13 am

    خسارة لم أفهم شيئا !!!! ? لاتوجد ترجمة عربية لماذا ؟؟…. توجد ترجمة إنجليزية وصينية فقط . !!!

  • Reply Waheda Khan August 21, 2019 at 6:38 pm

    Hi Ted-Ed, please share a lesson on why does hair turn grey. Thank you.

  • Reply TERTIVS FABIVS August 22, 2019 at 6:27 pm

    Both the animation and the BGM in this video are fantastic. The music that starts when the explanation of how viruses infect and spread made me feel I was especially good!

  • Reply jchinel August 25, 2019 at 11:09 am

    I HATE THAT KILL IT!!!!!!!!!!!!!!!!!!!!!!!

  • Reply Slimey Piston August 25, 2019 at 1:27 pm

    Ted-ed lessons are amazing!
    Unfortunately i'm just 13 and i don't have any money to donate to Ted-ed's Patreon 🙁

  • Reply MhysaMisa August 25, 2019 at 5:38 pm

    This needs to go viral!

  • Reply khandoker alvy August 27, 2019 at 10:58 am

    Don't put hog in your video because all Muslim hate hog .anyway good content very helpful

  • Reply Yaash04 August 27, 2019 at 3:02 pm

    Why are the pigs so cute

  • Reply Atharva Shrivastava August 29, 2019 at 2:52 am

    I know it takes 7 DNA points

  • Reply poopy cup August 29, 2019 at 10:53 am

    After I finish understanding all Ted Ed videos, I will become even more of a genius than Einstein.

  • Reply Thị Minh Anh Phạm August 30, 2019 at 10:48 am

    intruders alert!

  • Reply CrYStY67 August 30, 2019 at 7:56 pm

    Can u guys make a video about what happens during depression?

  • Reply Pyre Squire August 31, 2019 at 8:31 am

    Why so cute

  • Reply AlwaysOn Forever August 31, 2019 at 1:36 pm

    4:40 i love the squeaky sound ?

  • Reply Trenza September 1, 2019 at 11:57 pm

    I have a question, (sorry for bad english, feel free to correct me) why bacteria and virus evolved to become patogene? Why natural selection let this kind of organism evolve rather than the others?

  • Reply Max September 3, 2019 at 6:10 pm

    I love how the piggies looks

  • Reply Sanjeev Chaudhary September 4, 2019 at 7:28 pm

    animation is itself a fun to watch on ted ed….???

  • Reply cynthia teoh September 6, 2019 at 2:44 pm

    Did you guys have to make another CUTE animation? Wasn't able to pay much attention! lol

  • Reply Uber Cena September 15, 2019 at 5:02 pm

    Virus: Infects my body

    Me: I didn't consent to that

  • Reply Reach Kung fu September 25, 2019 at 12:00 am

    Amazing animation,please keep this kinda animation up!!!

  • Reply Khalil Khalil December 12, 2019 at 2:43 am

    So we have a 50% chance to get a disease from a banana

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