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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