The Typhoid Mary is a character who carries an infectious disease but doesn't suffer any visible symptoms — in some cases she may actually be immune to it herself — and spreads the disease to everyone she encounters.
Unlike the Plaguemaster and Poisonous Person, the Typhoid Mary isn't a villain. She doesn't intentionally try to spread her infection, and is often unaware that she is infected at all, especially when she is an asymptomatic carrier like the original Typhoid Mary. She is at worst Obliviously Evil, stubbornly refusing to believe she is a carrier, let alone cooperate with public health authorities.
However, villains may try to use the Typhoid Mary as a weapon, deliberately infecting an unsuspecting person with a contagious disease so she can unknowingly spread it to others. If she was in fact the first person who was infected she may be the Patient Zero and possibly be the key to curing it. Thus she can be the target of an all-out manhunt to contain her before everyone around her is infected.
In Zombie Apocalypse works, there may be some overlap with the Zombie Infectee, depending on how the infection spreads. In most cases, however, the Zombie Infectee doesn't pose a danger of infecting others until he actually dies and become a zombie himself. The Typhoid Mary, on the other hand, is highly contagious from the first moment of her infection.
The Trope Namer is the Real Life example of Mary Mallon, the original "Typhoid Mary" who spread typhoid fever to at least 53 other people while refusing to believe she carried the disease at all, because she never became sick from it herself. In biology/epidemiology, this is known as an "asymptomatic carrier" (i.e. carries the disease but shows no symptoms of it).
Not to be confused with the Daredevil villain of the same name. For the metaphorical case of a character who unintentionally brings death and disaster to everyone they come into contact with, see Doom Magnet.
- In the second episode of Memories, a man takes an experimental drug that causes anyone near him to die instantly. He never realizes he's dangerous (and doesn't realize that people are dying instead of just randomly going unconscious), and seems quite upset that everybody's trying to kill him.
- During the Ryugu Shelter arc of 7 Seeds, it is said that the hidden carrier of the Arcia X parasitoids is likely asymptomatic and doesn't even know that they have them and are spreading them around. Turns out the carrier is Maria.
- Italian comic book Dylan Dog had a short story about a girl born into a werewolf family. While not a werewolf herself, she was a carrier of lycanthropy — anyone who came into contact with her internal fluids (including through sex) would be infected.
- Averted in an issue of The New Teen Titans; a young Russian woman is sent to run errands in New York City, while unknowingly infected by her boss to spread disease in America. Unfortunately, she gets progressively sicker as she goes along, and once the Titans catch up to her, she is the only one who can't be cured.
- In one Bad Future of Batman, Damian Wayne faces his greatest challenge as Batman when a Joker virus drives the people of Gotham insane. All except for one baby boy. Barbara Gordon tests the baby and can't find any symptoms of Joker virus at all. Damian visits Gorilla Grodd and demands that he help synthesize a cure for the Joker virus using the baby. Grodd reveals that the baby is actually a carrier of the Joker virus. Cue Joker Barbara killing the baby and opening the doors for the mob of lunatics.
- Jack from Transporter 2 is turned into one by the villains as part of an assassination plot.
- Love Interest Nyah from Mission: Impossible II was going to be used as one by the villains. She knew it, however, and was ready to kill herself rather than spread the disease. Luckily, Ethan got her the cure in time.
- In 28 Weeks Later, Alice is an asymptomatic carrier of the Rage virus, which results in it breaking quarantine. Her son and daughter inherited this immunity from her, which allows the virus to spread to the continent.
- This was the central plot driver in [REC], where no one knew that the little girl didn't actually have tonsilitis, but something far far worse.
- In Kids, one of the characters is a sexually promiscuous teenage boy who doesn't know he's HIV-positive.
- The lab tech in Outbreak unwittingly infects dozens of people in a cinema after an accident in the lab in which he catches the virus. He's exposed to a blood sample from a dead man, who caught the virus from a smuggled monkey.
- Anthony Wong's Villain Protagonist character from Hong Kong exploitation movie The Ebola Syndrome contracts the eponymous sickness, but turns out to be a one-in-a-million case whose immune system fights it off while remaining contagious, and unknowingly spreads it around in South Africa and Hong Kong. Towards the ending, he becomes aware of his condition and starts to spread it willingly, but by then he's been long confirmed to be pure evil.
- In Rise of the Planet of the Apes, Hunsiker displays exactly one symptom of what will eventually be known as Simian Flu: a nosebleed (which frankly, could be anything). He brushes it off and boards a plane, starting Simian Flu on the global pandemic that kills 90% of humanity.
- In Cabin Fever Patient Zero, Porter is an asymptomatic carrier of an otherwise highly infectious strain of a flesh-eating disease. An amoral scientist uses him as a lab rat to help find a cure so he (the scientist) can get rich.
- Lenie Clark of Peter Watts' Rifters Trilogy series carries βehemoth back to the surface world. However she isn't a proper example, since she spreads it deliberately.
- The protagonist of Peeps carries a parasite that transforms anyone he gets too intimate with into a vampire. Now that he knows, he's careful not to spread it, but he had already infected a number of people before he found out he had it.
- Geoffrey Allen from The Changeling Plague. He gets a retrovirus engineered to cure his cystic fibrosis. Since it was specifically designed for his DNA, it has only positive effects on him. But unbeknownst to him, he's also spreading to other people...
- The novel Code Orange revolves around a teen who fears he may be a carrier of smallpox.
- Wild Cards: In Down and Dirty, Croyd 'The Sleeper' wakes up with the ability to spread a new strain of the Wild Card virus; one where people who have already been transformed with Wild Card can be re-infected and changed all over again. Croyd keeps moving and spreading the virus because he has entered the paranoid stages of his meth addiction, and can't trust anyone.
- Stephen King's The Stand has several unwitting Typhoid Marys but "Joe Bob" Brentwood is the most important as he unintentionally spreads the superflu beyond any chance of containment.
- The rabies-spreading Rant Casey, of, well... Rant. In fact, the book compares him to Typhoid Mary several times. However, he seems to actually want to spread the disease... unless he doesn't... it's a little complex when you don't know there's technically
twoTHREE of him.
- In the Temeraire series, the British government exploits this by infecting a French dragon with a highly contagious plague and sending it back to its home base to spread the disease.
- Miss Sneezy's story in Haunted 2005 is about an island facility where examples of this trope from all over the country live in sterile, high-security isolation. And yes, she is one of them.
- In Wyvern by A.A. Attanasio, one character finds that every village he stays at is struck by fever, although he never gets sick himself. He is finally taken in by a Buddhist monastery, and although the monks get sick, they teach him how to treat the illness. Finally, he administers the cure to himself, and from then on nobody else gets sick by having contact with him.
- The zombie plague in World War Z does not have any asymptomatic carriers, but some infected people were killed and had their organs harvested and sold on the black market. This spread the infection across the world, well past any precautions set up to stop mobile zombies. There are rumors that this was deliberate, as China — the source of the outbreak — wanted to make sure that no other country would survive unscathed while they struggled.
- Thura in the Redwall book Salamandastron; probably his partner-in-crime Dingeye as well, but he never got the chance to show symptoms.
- In the Paradox Trilogy, Devi becomes one after being infected with the Stoneclaw virus. The virus works by corrupting plasmex; Devi has so little plasmex herself that it will take months to kill her, but she can still spread it to others, who die almost immediately.
- In The Initiate Brother, a plague is spread to the ranks of a barbarian army by Shimeko, a former Botahist Sister who is having something of a Crisis of Faith. It's debated by other characters whether or not she filled this role knowingly or not, though the fact that she was a healer suggests she'd have to have realised it.
- In the Jacob's Ladder Trilogy, Perceval is unknowingly infected with a deadly strain of influenza and then set up to be taken prisoner by the enemy kingdom of Rule so she'll spread it to her captors. Perceval is horrified when she later learns that she was used as an unwitting biological weapon.
- In Clive Barker's short story "The Life of Death," an English woman ventures into a crypt that was sealed after the Black Death, and becomes a carrier of the disease. She spreads it to a number of coworkers and friends, who die, and to countless others as well. She is then murdered and raped by an acquaintance who turns out to be a Serial Killer, and he becomes a carrier in her stead.
- In "The Moral Virologist" by Greg Egan, a Mad Scientist designs a deadly disease that only kills people who have multiple sexual partners, but is as contagious as the common cold or the flu. Since he has never had sex himself, being both a fundamentalist Christian and unmarried, he spreads it through the population by infecting himself and engaging in some Platonic Prostitution.
- Flight from Tomorrow, by H. Beam Piper. A future dictator escapes a revolution with a time machine to the twentieth century where he plans to be a Conqueror from the Future. However he turns out to be a Walking Wasteland because future mankind has become acclimatized to high levels of radiation after a series of atomic wars. The military track him and carpetbomb the valley he's in, then fill it with concrete from one mountainside to the next.
- Naples '44, by Norman Lewis, details a plan by the Allies to send prostitutes behind German lines who were infected with severe cases of syphilis. Venereal disease had infected the Allied armies in Italy but not the German military, who ran their own brothels. Unfortunately the mission was cancelled and the women were released so they could continue to infect Allied soldiers.
- Star Trek:
- Star Trek: The Original Series:
McCoy: All the others are clear. He doesn't have it. He's a carrier. Remember your ancient history? Typhoid Mary? He's immune, as she was, but he carries the disease and spreads it to others.
- The episode "The Way to Eden" featured Dr. Sevrin, carrier of the Synthecoccus Novae virus who was more crazy in the coconut than malicious. While the episode didn't have any reported infections, this was because Federation citizens were immunized against the disease. The problem was that Sevrin wanted to go live on a primitive planet whose inhabitants were susceptible to the disease and did not have any immunities. Kirk orders him to be arrested and isolated which causes Severin's followers to get very angry.
- Spock in the episode "Miri", although he never actually spreads the disease he passively carries, simply because everyone else around him is infected too.
- In the Star Trek: The Next Generation episode "I Borg", Geordi proposes using the captured Borg drone Hugh as a carrier for a computer virus meant to destroy the Borg Collective. Picard eventually decides against it on moral grounds—he had come to see Hugh as a person rather than a nameless Borg drone—for which he is roundly chewed out by Admiral Nechayev in "Descent". However, the sense of individuality that Hugh gained from his exposure to the Enterprise crew did infect his cube, which resulted in the Collective severing its connection (in much the same way a computer security guy would unplug a computer actively being hacked).
- In the backstory to the Star Trek: Voyager episode "Child's Play" the Brunali genetically engineered a child, Icheb, to carry a pathogen fatal to the Borg in the hopes of eliminating the Collective. It did succeed in killing the Borg aboard the cube that assimilated him, but wasn't transmitted beyond it.
- Star Trek: The Original Series:
- An episode of House had an old lady volunteer at the hospital handing out teddy bears and unwittingly spreading echovirus. She barely had any symptoms, and healthy adults were unaffected, but it was lethal to newborns.
- In Dark Angel, Original Cindy's girlfriend was turned into one and eventually died from it.
- The X-Files:
- Given an I'm a Humanitarian twist in episode "Our Town", a town of cannibals catches Cruetzfeld-Jakob disease by serving up an infectee at a ritual banquet.
- In episode "Jump The Shark" is about a biological terrorism plot based on sending out two Typhoid Maries. (Unusually for the trope, they are both fully aware and willing participants).
- Played straight in "El Mundo Gira", when an undocumented laborer mutates to secrete an enzyme that causes anyone who touches him to be overwhelmed by lethal fungal infections within minutes.
- In Stargate SG-1, before the Ori gain the ability to attack Earth directly, they try infecting an SG team member with a virus. He then spreads it to the rest of his team, and once they return to Earth they bring the disease back with them. The man who was originally infected turns out to be immune to the disease, ensuring he doesn't die before he spreads it to as many people as possible.
- An incompetent intern spends the whole week nearly killing patients until JD has a heart-to-heart with him and tells him that medicine isn't for him. But on his way out, the intern absent-mindedly picks up and bins a dropped medical tissue, then shakes hands with a recently-cured (and very beloved) patient, which gives her the infection that ultimately kills her.
- In another episode, three people die after organ transplants because the donor unknowingly had rabies.
- The organ donor variant has also been used on Law & Order and NCIS, usually with black market human tissues and cancer.
- In an episode of ER, a staph infection spreads throughout the department, and Jeannie teams up with one of the doctors from the infectious disease department to figure out who's doing it. They both immediately know that it's from someone not washing their hands adequately after going to the bathroom, but are initially flummoxed by realizing none of the infected patients have the same doctor or nurse in common. Shortly afterward, the doctor notices all the charts have the same handwriting on the top page, letting Jeannie figure out the person doing the infecting is Jerry, the desk clerk.
- The Trope Namer appears in 1000 Ways to Die.
- Natalie Luca in The Blacklist.
- One season one episode of Mission: Impossible had a village full of people who were being trained by an East Bloc government to perfectly blend in with western society. The people all believed that they were being trained as deep-cover spies. In truth, their handlers planned to infect them all with the plague before shipping them out to their assignments. Rollin gets infected while disposing of the plague samples, and then comes into unprotected contact with the plot's leaders after getting captured. After Dan succeeds in extracting the team, they leave to find a hospital to get Rollin treated and the rest of their number tested, leaving the villains unaware that they might have caught the plague from Rollin.
- Wonder Woman: In "The Pluto File", Robert Reed's The Falcon is an unknowing carrier of bubonic plague.
- Mike Barnes from the Midnight Caller episode "After It Happened" is HIV-positive, but he continues to have promiscuous, unprotected sex, thinking that if he doesn't acknowledge his disease, he won't die from it.
- Invoked in one episode of Murder, She Wrote, in which a character named Ellen wryly refers to herself as "the Typhoid Mary of murder" - she herself is not murdered, but people around her are, and Ellen has a tendency to be accused of involvement even though she's completely innocent. Jessica, amused, tells Ellen that she can't be "the Typhoid Mary of murder" because that's Jessica's title.
- The 4400:
- In "Carrier", Jean DeLynn Baker, an unbalanced woman who disappeared in 1999, grows spores on her hands over night. These spores release a toxin that kills everyone else in her hometown of Granite Pass, Oregon, including her parents. Jean can't control her ability, which thereafter manifests whenever she becomes angry or upset. She eventually comes to believe that she is on a Mission from God to purify humanity.
- In "Tiny Machines", Danny takes a promicin shot and soon develops the ability to spread promicin like a plague. He himself is immune to its effects. In the following episode (and Series Finale) "The Great Leap Forward", his mother Susan is the first person to die but far from the last. When he brings her to St. Ambrose Hospital, Danny's presence causes half of the people there to die from promicin exposure while the other half survive and go on to develop abilities. NTAC and the government initially believe that the outbreak is confined to the hospital but it becomes readily apparent that it is spreading throughout Seattle like a contagion. It even reaches the NTAC building itself. Hundreds of people die within hours. By the time that the outbreak is contained eight days later, the confirmed death toll stands at 9,000.
- In The Gamer's Alliance, while staying in Alent, Rhylian learns that she is a symptomless carrier of the Blood Fever and has thus infected several of her elven kin with the fatal disease throughout her journey.
Waldheim: My lady... everything I suspected — everything I feared — has proven to be correct. It wasn't Nesa that infected Killian or Nalaen, or that poor elf in Vanna, or... probably countless others elsewhere. And now, an ever-growing number here in Alent. It was you. It... is you.
Rhylian: No. You're wrong, Waldheim. How can this be? I've never been sick, how can...? No...
Waldheim: I'm sorry, Rhylian. But these samples... the exact strain of the virus in Nalaen's and Killian's blood is the same one that's in your blood. I suspect you contracted the disease long ago, certainly before you left Sanae. But instead of suffering the sickness that affects most... you instead became an infectious, symptomless carrier. And I can see in your eyes that you've suspected it yourself for some time, but have been too afraid to face the truth.
- In the play Damaged Goods by Eugene Brieux, a man diagnosed with syphilis ignores his doctor's warnings to put off his announced marriage for a few years, and is able to keep his disease a secret until his child is diagnosed with it.
- Metal Gear:
- In Metal Gear Solid, Solid Snake is unknowingly infected with FOXDIE to kill the members of FOXHOUND and the ArmsTech President Kenneth Baker.
- This becomes a plot point in Metal Gear Solid 4: Guns of the Patriots when Snake's accelerated aging and the age of the virus itself causes it to mutate; given a few more months, FOXDIE will stop caring whether its targets matches its targeting parameters, and Snake will become a one-man plague. He is then infected with a second strain of the FOXDIE virus which helps cancel out the old virus and will not have enough time in Snake's body to mutate itself, as Snake is estimated to have one year left at most.
- On a wall in Left 4 Dead 2, some wall graffiti purports that some people are carriers of the zombie infection. It's loosely implied that the survivors might be carriers, not immune, as they had assume. This is confirmed in the comics for "The Sacrifice": the original Left 4 Dead survivors learn that they've been spreading the infection across the country and may have inadvertently doomed everyone who helped them in the previous campaigns. They then decide the only responsible way to save themselves is reach an isolated island and live off the land.
- The above may have inspired both the character of Yerema in Dead Island and The Reveal that the player characters are also uninfected-looking carriers in Dead Island: Riptide.
- Another Zombie Apocalypse example is the Dead Rising series: the plague was brought to America by orphaned children (who, in turn, were brought to America by Carlito Reyes) who were infected by the viral agent, then placed in a government adoption program. Then, all hell broke loose, (at least) Willamette and Fortune City went to hell, and the rest is history.
- The Elder Scrolls III: Morrowind: One Tribunal Temple quest has you deal with a woman blessed by the Tribunal who has caught the Corprus disease. She doesn't believe you because her "blessed" state means she isn't showing any symptoms. However, she can still spread the disease to others. You need to convince her to leave for the Corprusarium, or kill her.
- During the Mogloween 2011 event in DragonFable, The Hero meets a little boy named Andy. Poor Andy is the only person who managed to escape from a Zardbie outbreak, but not unscathed. For some reason the bite he suffered hasn't mutated him into a Zardbie, but anyone who kisses him (happens twice because girls find him too adorable) or anyone he bites (such as a Gorillaphant) becomes a Zardbie. A bad situation becomes worse when one of the people Andy unwittingly mutates is needed to make the Zardbie cure...
- Zero from the Mega Man X series is the original carrier of The Virus that turns Reploids into bloodthirsty Mavericks. Not only is he immune to its effects (when The Virus becomes a semi-regular enemy in X5) but, in an aversion of Gameplay and Story Segregation, it actually empowers him. Plus, according to the story bridging the X series with the Mega Man Zero series, that kind of immunity was what made scientists try to study Zero's body, and finally create a cure.
- In Trauma Team Rosalia is one of these to a degree. Even after she was killed, her blood had seeped into the ground, into the flowers, and then made the monarch butterflies become carriers of her Rosalia Virus disease. Those butterflies then spread the disease through their shed scales.
- Touhou's resident Plague Master Yamame Kurodani is actually a friendly youkai who doesn't use her powers without reason, but her Power Incontinence causes her to spread disease anyway. As a result, she overlaps with this trope.
- The Awakening expansion to Dragon Age: Origins brings the Messenger, an intelligent darkspawn who seems to be the only one of the bunch not obsessed with slaughter, rape, or experiments of uncertain morality. If he survives the events of the game, he disguises himself and wanders the land helping travelers in need; unfortunately, he's still a darkspawn, so those he helps sometimes become infected with the taint.
- In Battleborn, Beatrix's Patient Zero ability turns a targeted ally for a short time into a contagion carrier that enfeebles enemies they come in contact with but doesn't suffer any ill effects themselves. They instead have their speed buffed. When an ally isn't targeted, she uses the ability to turn herself into such a carrier instead. While it's normally a choice between making an ally or Beatrix herself into a contagion carrier, the Self Medicated augment though allows it so that both a targeted ally and herself become carriers.
- This is invoked by the player in Pandemic and Plague Inc.. Early on, you want people to spread your disease, but not get sick from it. Not that it prevents Madagascar from shutting down everything.
- Hatoful Boyfriend:
- The "Bad Boys Love" storyline elaborates this as the backstory for Fujishiro Nageki the mourning dove, who unwittingly carried a virus harmless to birds but fast-acting and lethal to humans. Upon learning of this, Dr. Shuu experimented with turning him into a bio-weapon against humanity, which drove Nageki to suicide.
- In the same route, we also learn that Ryouta, who already had a slightly weak immune system and weak stomach, got unknowingly experiemented on by Shuu, to make him a good carrier for the virus. He eventually implanted Nageki's liver into Ryouta, having him turn into his next Typhoid Mary.
- Deconstructed in The Zombie Hunters. The Infected contract The Virus through exposure to any zombie bodily fluids through an orifice or wound, but only being bitten or vomited on causes imminent zombification. Otherwise Infected can live full, asymptomatic lives, as the virus will remain dormant. However, they can infect others through their own bodily fluids, and will inevitably reanimate after death. On the Island Military Base humanity's remnants inhabit, Infected are both segregated from and forbidden from romancing the uninfected. Infected are also required to wear identifying armbands and ID tags, pass through checkpoints, and obey curfews while among uninfected, and the unskilled are exploited as highly-expendable Disaster Scavengers (the eponymous Zombie Hunters). All residents are tested regularly, and anyone who goes off-island has to pass through quarantine and decontamination.
- In Sinfest, Squigley is accused of being this for swine flu, as he's a pig.
- Bio-Augmentation is common in Schlock Mercenary, but several characters realize only too late that this process can be tampered with to turn them into unwitting bio-weapons.
- Hark! A Vagrant has a strip parodying the Trope Namer. In this case, she didn't return to cooking after being made aware she was a carrier... far worse.
- Lick your face clean, 5p
- Stand Still, Stay Silent: The Rash works like this while it's incubating, according to this in-universe document. This is the reason for which some areas require a two-week quarantine for all non-immunes who wish to enter. While it's technically a Zombie Apocalypse example as well, the overlap with Zombie Infectee is averted due to only a minority of patients actually transforming, and the rest simply dying.
- Awful Hospital: Fern herself might be a carrier of The Parliament of the Old Flesh's Synthetic Plague.
- Wilde Life: This is why animal people aren't supposed to eat humans—normal people can be carriers for "the Madness," a supernatural ailment that drives animal people insane and then turns them into monsters.
- Parodied in the South Park episode "Pink Eye," where Kenny's case of being a zombie was misdiagnosed as conjunctivitis. He goes through the episode without anyone (except Chef, eventually) noticing that he's causing the "pink eye" epidemic. It was Halloween, so they thought he was just dressed as
a zombieEdward James Olmos.
- In The Powerpuff Girls, the Amoeba Boys catch a cold and accidentally cause a city-wide epidemic when the virus mutates within their bodies. Although they are villains (or at least try to be), they did not spread the cold on purpose, and so are this instead of plague masters.
- The Trope Namer: Mary Mallon was a woman who worked as a chef in New York in the early 20th century. Everywhere she worked, her employers and the other household staff would all fall ill with typhoid fever, after which she would leave and find new employment. She was ultimately caught in 1907 and forcibly quarantined, given the nickname "Typhoid Mary" by the Journal of the American Medical Association, and revealed that she did not wash her hands before cooking. She was given the option to have her gallbladder removed, or she would have to agree to never become a cook again. She was released 3 years later and forbidden from cooking. She changed her name and went right back at it, leaving a swath of typhoid fever infections in her wake. She was arrested again in 1915, and remained in quarantine until she died 23 years later in 1938. Autopsies showed her gallblader was full of live typhoid bacteria. Her treatment in quarantine was unusual in that other repeat offenders, including other food handlers and people who had more outbreaks to their name than her, got off with nary a reprimand and a promise not to do it again; the government threw the book at her because she explicitly refused to stop working as a cook, backing them into a corner.
- This is one of the more serious problems faced by health workers trying to contain the 2014 Ebola virus epidemic. In the early stages the symptoms are so minor as to be barely distinguishable from the common cold, making every victim an asymptomatic carrier for the first couple of days. Most diseases eventually evolve to a point where they have a long period of little or no symptoms, as obvious symptoms and/or early death of the infected hinder the transmittal of the disease.
- Men with many STDs and bladder infections. As of yet, there is no method for detecting HPV (the virus that causes cervical cancer) in men. About 80% of the adult population are thought to be infected, although that may have changed due to the vaccination. Gonorrhea may not cause any symptoms at all in men, but can cause infertility in women (and, we now know, in men as well), and babies born to infected women can become blind from infection to the eyes, if left untreated.
- Even women tend to be asymptomatic more often than not. While men are more likely (although not guaranteed) to have a pus-like urethral discharge with chlamydia and gonorrhea that causes itching and burning, women may not know they have it (or had it) until they go for a routine OB/GYN exam or seek treatment for infertility, as they are less likely to have the "classic" symptoms associated with those diseases. And there are couples who have been bouncing Trichomonas back and forth for decades, without even realizing it. This is why it's important to practice safe sex: limit the number of partners you have, use a fresh condom every time (and use it correctly), wash "down there" before and after sex, and get tested (and if necessary treated) for STIs before having sex with a new partner.
- Children who catch COVID-19, as a general rule, show little to no symptoms. However, the disease becomes more likely to be serious when people grow older and/or have other health issues, so a seemingly healthy child can transmit the disease to a person who is more vulnerable to it.
- Most people who carry the Epstein-Barr virus (Mononucleosis) can actually be just this - to the point where almost everybody over the age of 35 has antibodies that can target the Epstein-Barr virus. This is evidently true with a lot of herpes-family viruses as well.
- This can actually be the case of tuberculosis, this is called latent Tuberculosis. It's suspected of being way more common than one thinks. So much, even Edgar Allan Poe may have been one.
- Many animals can be vectors for illnesses which do not affect them, but can be deadly for other species, such as humans. Bats in particular tend to be a common vector for serious infectious viruses like ebola, rabies, and SARS because they have extremely effective immune systems that minimize inflammatory symptoms at all times, but this in turn causes viruses within them to adapt much quicker to keep up, effectively causing bats to become a petri-dish of super-viruses.