Practice English Speaking&Listening with: 6 Sleeper-Agent Pathogens That Can Make You Sick

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lets face it nobody likes being sick, and for the most part our bodies protect us from all kinds of pathogens,

Infectious disease causing things like viruses, bacteria, parasites, even fungi

your skin and mucous membranes are physical barriers to keep out nasty microbes

plus some immune cells can scan for any foreign molecule and attack. That's your innate immune response.

then you have you're adaptive immune response kicking into gear with other cells that make

antibodies and specialized cells to target specific pathogens,

that way if the pathogen ever infects you again, your body should be ready to fight it off

but not always, some pathogens are tricky, they can go dormant in tough conditions

or even hide in your body without you knowing, and reactivate to cause latent infection

so because I'm sure you want to know about this, here are six of the sleeper agent pathogens

that can come back to haunt you. Let's start with varicella zoster, the virus responsible for varicella

also known as chicken pox. Today most kids are vaccinated for chicken pox

but if you were born before the 1990's, you probably are familiar with this itchy, red, blister type rash

I know I am. It's a super contagious infection, spread by skin contact

or by inhaling droplets from someone else's sneeze or cough

our immune systems are tough, so after about a week or so, the blisters will scab and fall off

but the virus isn't necessarily gone, anyone who's had chicken pox could have a latent

infection called herpes zoster, which you might know as shingles. Basically, the varicella zoster virus

becomes inactive and hides in your ganglia, clusters of nerves that are found all along your central nervous system

We don't really understand how, but basically the virus simplifies it's replication cycle.

Instead of making lots of copies of itself, it only replicates a few important proteins

as you get older, your immune system get weaker, so the antibodies and specialized immune cells don't respond as well to pathogens

Varicella zoster can take advantage of this and reactivate in some people,

start multiplying, and cause a latent secondary infection that's pretty different from chickenpox

Since the viruses were hiding in clusters of neurons, the shingles rash usually infects

the skin along the nerves branching from the spinal cord, causing painful blistered stripes

instead of pox marks, but there is a shingles vaccine if you weren't

vaccinated for chicken pox as a kid and it's treatable with antivirals and pain medications.

Another contagious rash causing virus is the measles virus which

also causes a fever and flu-like coughing and sneezing.

It's so infectious that around ninety percent of people

near an infected person will become

infected if they aren't immune and the virus can survive

in tiny airborne droplets for up to two hours.

Luckily the MMR vaccine is really good

at preventing the spread of measles but

that doesn't mean that measles infections

still don't happen in the US and around

the world, and in rare cases the measles

virus can have a mutation that lets it

cross the blood-brain barrier which

normally keeps everything but essential

nutrients from getting to the brain once

the virus is in the brain tissue the virus enters

a latent period, but we still don't know how exactly

it's likely that the mutations also help

the virus stay undetected by antibodies

it could be 7 to 10 years until a latent

infection shows up with the virus

causing subacute sclerosing

panencephalitis or sspe this disorder

affects the central nervous system and

can quickly get worse from mild

cognitive dysfunction to motor

difficulties and eventually coma and

death even though it's rare this severe

disease is just one more reason why

routine vaccinations are important

otherwise the risks could be fatal but

if you want to talk about real bad

there's also human immunodeficiency

virus or HIV which specifically in fact

certain immune cells you know the ones

that are supposed to be fighting the

disease and this virus destroys

someone's immune cells their immune

system gets really weak and they can

develop acquired immunodeficiency

syndrome which can make any infection

very dangerous even something like the

common cold HIV doesn't necessarily

cause AIDS right away or even ever in

some people because it's really tricky

HIV can easily mutate some of its

identifying protein markers for example

which let's escape the adaptive immune

system plus HIV is a retrovirus which is

an RNA virus that makes DNA copies of

itself that can be integrated into the

DNA of host cells in this case immune

cells this happens the incorporated

viral DNA

is called a provirus and it only

replicates a little bit not enough to do

too much harm during this late stage

most hiv-positive people don't have any

symptoms of illness depending on their

age genetics and general health and

antiretroviral therapy can help keep the

virus from progressing to more serious

stages, but HIV can also hide in viral

reservoirs certain tissues like lymph

nodes or the spleen that aren't affected

by antiretroviral treatments which can

only kill the virus in the blood stream

right now. In tissue reservoirs the virus

can replicate at low levels without

being wiped out so a person stops there

antiretroviral treatment for example HIV

can come back out of those viral

reservoirs with vengeance and the person

usually will develop AIDS some people

have a genetic mutation in certain

immune cell receptors that keeps HIV

from infecting them so researchers want

to figure out how to translate that into

a treatment but other scientists are

looking at ways to coax the virus out of

these tissue reservoirs so that they can

be killed through drug therapies so

while HIV is extremely dangerous

transmission is preventable AIDS is

preventable and HIV positive people can

live long and relatively healthy lives

viruses aren't the only pathogens that

can hide though mycobacterium

tuberculosis is a bacterial species that

causes the disease tuberculosis or TB

it's pretty contagious you can get

infected if someone cost or sneezes and

you inhale those tiny bacteria filled

droplets and it is not a fun time those

bacteria usually infect your lungs and

all that coughing leads to flem and

eventually bleeding so different immune

cells target the lung tissue and

cluster together to form granulomas

which are like biological traps that

keep the bacteria from spreading the low

oxygen environment inside the granulomas

causes the bacteria to only activate a

few necessary genes, stop replicating and

exist in a dormant state in fact it's

estimated that a third of the population

is infected with TB bacteria but most

never have any symptoms or are ever

contagious out ten percent of TB

positive people have latent reactivation

of the bacteria and we're not exactly

sure why. It probably has to do with a

careful balancing act between the

pathogen and the host's immune system

since the risk increases in

immunocompromised people like HIV

positive individuals, infants or the elderly

TB is preventable through the BCG

vaccine in children but it may not be as

effective in adults there's a treatment

to a very strict regimen of drugs for

several months but because bacteria can

develop drug resistance new treatments

are still being researched basically M

tuberculosis can turn the immune systems

response against itself so the

granulomas aren't a prison but safe

havens for survival bacillus anthracis

on the other hand is a really tough

bacterium that makes its own safe haven

although it usually spreads to humans

from contaminated animals this bacterium

is most famous for being a potential bio

weapon. A mysterious white powder could be

infectious spores that cause the disease

anthrax even though these bacteria

don't hide in your own body like our

previous examples to cause a latent infection

anthrax is worth mentioning because

these spores are a latent form of

certain bacteria they protect the

bacterial DNA in a hardened protein

shell. Spores can survive for long

periods of time in lots of environments

extreme heat extreme cold certain

chemical treatments even some radiation

anthrax spores for example have even

infected new hosts after being frozen in

icy animal corpses for nearly a century

once inside the warm nutrient-rich

environment of the living host, the spores

reactivate and grow into full-fledged

bacteria that keep replicating bacterial

spores can infect a host through

inhalation ingestion or any wounds in

the skin and depending on the route of

the infection anthrax symptoms can

include blisters and ulcers fever or

swelling of tissues and organs there is

a preventable anthrax vaccine but it's

only give it to people who work in

high-risk environments such as

laboratory workers animal handlers or

military personnel it isn't the common

infection so there isn't a huge risk to

the general population anthrax is also

treatable with antibiotics if they're

given early enough and taken four months

and anything that dies from anthrax can

become hosts for the hardy latent spores

making this bacterium a sleeper agent

that's in it for the long haul

finally we have this strange parasite

Toxoplasma gondii. It can affect most

mammals and cause a disease called

toxoplasmosis, but this parasite only sexually

reproduces in cats. oocysts are

resilient eggs that contain a dormant

parasite called a sporozoite. these oocysts

are microscopic and can survive in all kinds of

environments where they can get eaten by

intermediate hosts such as rats or birds

inside any host the dormant parasites

are released from their eggs and become

tachyzoites which move into muscles

and neural tissue through the

bloodstream there the tachyzoites

become bradyzoites and form

fluid-filled cysts. When cats eat

infected rats or birds for example the

parasites can mate and reproduce in

their intestines making lots of oocysts

that get pooped out to continue the

cycle humans are only an intermediate

host so the parasites won't sexually

reproduce and someone who is infected

can still seem healthy during a latent

period while the parasites hideout

in cysts but like many latent infections

when the immune system gets weaker with

age or illness the cysts can actively

cause severe disease Latent toxoplasmosis

has been linked with severe neurological

disorders including depression

schizophrenia Alzheimer's and

Parkinson's disease and if a mother

becomes infected the parasite can affect

unborn babies unfortunately there is no

current treatment for toxoplasmosis only

prevention which doesn't mean that you

should get rid of your cats but just be

careful around their poop and stay away

from potentially contaminated food or

water sources so most of the time the

best we can do is try to stay healthy

and trust our immune systems to do their

job and defend us against pathogens

plenty of scientists and doctors are

doing their best to find treatments that

work for these and other extra tricky

diseases thanks for watching this

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