Hi everyone, and welcome to Biology Professor. Today, I want to talk to you about the life cycle
of a pretty terrible parasite called hookworm. Now, hookworm is a parasite, specifically a
kind of helminth, which means a worm, which we can tell from its name. So hookworm is a parasite that
infects upwards of 800 million people per year globally, so certainly a serious parasite for many
people's experiences. The worm is particularly noteworthy because it actually penetrates right
through unbroken skin of the host. So a lot of times, various pathogens will actually need a
cut in the skin to be able to enter through the skin. Hookworm doesn't need that. It can actually
burrow right through healthy unbroken skin. And ultimately it lives in the small intestine where
it attaches to the intestinal walls, sometimes for years, and sucks the host's blood. Now this leads
to some pretty severe side effects resulting from anemia, that is the blood is sucked,
blood is where a lot of our body's iron is stored, and so hosts get anemia, which is
an iron deficiency and the anemia then goes on to cause its own problems, including delayed
growth and delayed mental development or mental impairment. Now, we said hookworm is a parasite,
parasite is actually a form of symbiosis, which is where two organisms live in really close contact
with each other. In particular, parasitism is what we call a plus/minus form, that means that of the
two organisms involved in that symbiotic event, so the two organisms here being the hookworm
and its host, one of those organisms benefits from the symbiosis, the benefitter here would
be the hookworm, and then the other organism is harmed and of course in the case of all events of
parasitism, the one being harmed is the host. If you are interested in symbiosis and about
learning more about parasitism and other forms of symbiosis, including mutualism and commensalism,
please see my video on the different types of symbiosis. But to continue here, let's
now talk about the lifecycle of hookworm. Now a hookworm infection begins with an egg. Now eggs,
hookworm eggs are shed in human feces, so an infected host has hookworms inside them, their
feces will contain huge, huge numbers of hookworm eggs. And this is actually the diagnostic stage,
meaning that you can take a fecal sample from a person and actually see under a microscope all of
the different eggs in the feces, and so that's how a hookworm infection is typically diagnosed. Now,
these eggs, if they make it into soil, they can actually hatch in the warm soil into the
next developmental stage which is larvae, and they need warm soil to do this and this is why hookworm
is typically thought of as a tropical disease because it's those tropical temperatures that
allow the favorable conditions necessary for the eggs to hatch into larvae. Now this early
larval form has a particular name, it's called the rhabditiform stage of the larvae. Now, over
the course of a couple of weeks, the rhabditiform form larvae will mature into a more mature form,
the larval stage here is called filariform, and these larvae can actually survive approximately
three to four weeks in the soil. And that is when conditions are particularly favorable,
so when temperature and moisture conditions are right. Now, it is these filariform larvae that
can actually burrow through the host skin. So here we have a picture, a drawing, of a human foot and
these larvae can actually burrow right through the skin. Now the larvae are going to be able to
burrow through whatever skin is most in contact with the soil, which of course is where they're
living, and so typically this is done when a human goes barefoot and has their bare foot in contact
with the soil. Now once this larvae enters the human body, it goes through a really circuitous
route. First, it enters the bloodstream, from the bloodstream it moves to the heart, from the heart
it can travel through the body to the lungs, and then the larvae actually gets coughed up,
so it gets coughed up from the lungs, up to the pharynx, and then it gets swallowed,
and goes to the stomach. And the larvae that survives the stomach acid conditions make it to
the small intestines, and it is here in the small intestine where the larvae mature into adults.
So the larvae mature into adult worms. These adult worms are the ones that then attach to the lining
of the small intestine and suck blood. They can stay there for years and during the time that
they are alive within the body, they're constantly laying eggs, huge huge numbers of eggs that then
get excreted from the human body in the feces and then the cycle can continue. Now, luckily hookworm
has been all but eradicated in most developed nations and this is for a few different reasons.
First, we have anti-helminthic drugs, so these are drugs that fight worm infections. We can also take
iron pills to counteract the anemia that comes from the blood loss. And then we can also break
this this chain of transmission by doing sort of two main things: encouraging people to wear
shoes and making sure that everybody has shoes, this is of course a bigger problem in various
developing nations, and also we can break this chain of transmission in another place as well
and that's right here: making sure that the human feces that contains the eggs does not
actually get into soil. And of course this can be done when countries have proper sanitation
and public health infrastructure, and that's why we don't really hear about hookworm in the United
States anymore but certainly it is a bigger problem in many other parts of the world and
you can see that from the number who are infected. Now, if you are interested in learning about other
types of parasite life cycles, please see my other video which is on the life cycle of the parasite
that causes the the disease schistosomiasis, and that's another kind of worm parasite so
check that one out if you're interested. Thanks for watching Biology Professor! :)