2. What is a HOST? What is a PARASITE?
Before we even begin, I
want each student to
write down on a piece of
paper what they think a
HOST is and what they
think a PARASITE is.
1-2 minutes, GO!
After you have written down your
thoughts, fold your paper and trade it with
someone else who is done in the class. 30
seconds, GO!
3. NEXT:
Read your piece of
paper, if you think your
paper has a correct
answer raise your hand
and read it out loud.
If it is correct, you and
the person who wrote the
answer will receive *___
pts on your next quiz.
4. Final Answer
(Should go something like this)
A HOST is any organism that allows
another organism or bacteria to live in it
or on it.
The PARASITE is the organism living
off of the HOST.
*Lets think about and discuss some examples
of a parasite/host relationship
5. A More Formal Definition for
Parasites:
Parasite:
Eukaryotes that live on
or in the body
of another eukaryote
species and exploit
that species for
sustenance.
http://www.aber.ac.uk/~mpgwww/Edu/Pa
ra_ism/PaIsmTxt.html this is a useful
sight with definitions and explanations of
symbiotic relationships.
This means the
parasite benefits at the
expense of the host.
The host-parasite
relationship is
typically species
specific.
6. Some Examples:
Fleas on a dog or cat – why is this a
parasite host relationship?
Intestinal worms in horses or cows – why
is this a parasite/host relationship?
7. Relationships Between Parasite and
Host Can Vary:
Like a “Hit and Run” – parasites live on or in the
host for a brief period of time then must move on, they
may or may not kill the host.
Parasites may invade/infest the host in two ways:
Acute Invasions/Infestations
Chronic Invasions/Infestations
8. What a parasite MUST HAVE to
survive:
Nutrition – food! The host
provides nourishment for
the parasite.
Protection from the
environment –The host
provides shelter, warm and
snug!
Ability to Reproduction –
make more! The parasite can
not survive without its host!
9. Parasite Life Cycle:
The life cycle is a never-ending chain of
events that lead to the parasite constantly
reproducing and re-infesting another animal.
YUCK!!!
Let’s take a look at one example of a parasite
life cycle….next slide
10. Example Life
Cycle:
4. Parasite returns to
intestine to lay eggs to be
released again in feces,
continuing its life cycle.
3. The parasite moves to
many different places inside
horse as it grows and feeds
off the animal host,
sometimes making animal
sick.
1. Lets start here,
eggs are released in
feces.
2. The animals eats the
eggs that are now on
the pasture grass.
11. Different Parasites have Different Ways
of Surviving!
EWWWW!!!
Each parasite plays a
role in a food chain/web.
They find their NICHE
in order to survive!!
12. Survival:
Mutual evolutionary
adaptations of parasite and
host may lead to a parasite
becoming less damaging and the
host becoming more resistant!
This means that both the host
and parasite change over time!!!
Just like many other organisms
on the planet!
Below: example of
evolution of horse.
13. What is the Niche of a Parasite?
You must first know what a niche is.
the role of an organism within its natural
environment that determines its relations with
other organisms and ensures its survival – in
other words, the organisms JOB! What does it
do to survive?
14. Parasites Niche:
The parasite must find a place within the host
to survive.
A particular parasite may occupy a specific
site and utilize certain host resources and
this defines its niche.
So a niche is a description of the parasites
requirements, not of host attributes.
15. Common Types of Parasites:
Roundworms
Tapeworms
Hook worms
Heart worms
Amoeba
Flies, Fleas, Lice,
Mites,Ticks, and
Spiders.
Each causes different
symptoms and different
infections.
As host is treated for
parasite, both can build up
immunities. The host to the
parasite and the parasite to
the treatment.
That is why new methods of
treatment must constantly be
created!!
16. Parasites in a food chain or food web:
6 Links of the Chain
1. Contact and Entry Into Host
2. Gaining a suitable niche
In the host (where it lives to
gain nutrition)
6. Development in environment
or intermediate host.
3. Continued survival in Host.
May have to move to
different areas within
host body.
5. Escape from host,
released back into
environment.
4. Reproduction
17. Entry into/on Host
Three Routes of entry
1. Host can eat eggs that are on grass or other plant
life, or if parasite is on grass or other plant life, it
can crawl on to host.
18. Entry into/on Host Continued:
2. Skin Contact
Biting insects, passes in to blood stream or,
Parasite can penetration through skin.
3. From the mother to the baby while in the
womb.
19. Parasite Finds its Niche in Host:
Must evade host
defenses and,
Must Migrate =
Movement
Through tissue
Through systems,
from organ to organ
Most must return to
intestines to be
released in feces.
Human lesions
from hookworm
migration
20. Examples of Specific Niche Needed for
Protection and Nutrition
The babesia parasite
is only found within
red blood cells
Human head lice only
reproduce on humans and
prefer areas of skin with lots
of hair, like the head
21. Contact with Host: Starts and Restarts Life
Cycle!
Passive Contact:
Animals come to the eggs or larva that can not move
Active Contact:
Some parasites move to areas where they are more
likely to come into contact with an animal. E.x. ticks on
trees, grass, bushes will crawl or jump on to animal.
Fleas actually detect vibration and carbon dioxide and
will move towards it because it means that a potential
host is near by
One species of roundworm larvae crawl up vegetation
onto the leaves to increase their chances of being eaten
22. Survival in Host
Evade the immune system
long enough to reproduce.
Methods to avoid the
immune system:
Live inside cells of the host
Mimic host substances so
they are not recognized
Live in the gastrointestinal
tract of the host out of
reach of the immune system
Form a protective cyst
which cannot be penetrated
by the host immune system
Roundworms in Intestines
24. Escape from Host
The larva, eggs, or cysts have to have a way
to leave the host
Most common way is through the feces
Can also leave through urine, saliva, semen,
milk, mucous membranes, or blood
25. Development in Intermediate Host
Some parasites require
another host to complete
their life cycle, this is called
an Intermediate Host.
This particular parasite has
the cow or sheep as the
direct host and a snail as
the indirect host
An intermediate host often
helps to increase the
spread of the parasite and
protect the parasite from
spending too much time in
the environment.
26. Development in Environment
Generally hotter weather
leads to faster
development/reproduction.
Colder weather leads to
longer environmental
survival, parasites can lay
dormant during cold
weather.
28. One Last Point:
No definition of parasitism is ever going to be
completely satisfactory, if we try hard enough we
can always find an exception and there are always
going to be grey areas where parasitism, mutualism
and commensalism overlap.
It has been estimated that more than 50% of all
known species are parasitic at some stage of their
life cycle.
If the above statement is true, can you think of a time
when you acted like a parasite????
29. Importance of Life Cycles
If you understand the life cycle of a parasite it
answers a lot of important questions
Who is infested?
What stage of the life cycle is parasite in and how does
this affect the host? (
It is an acute or chronic condition?
What time of year is parasite most common in
environment?
What kind of infestation/sickness does this organism
cause?
Where are the vulnerable points of the life cycle for the
best treatment and prevention?
31. Drug Resistance
Resistance is a real problem
In Texas we have multiple species of parasites that
have developed resistance to many treatments
Reasons resistance develops
Parasites with genomes that allow them to survive
treatment can pass this DNA to their offspring. Thus, in
following generations, the whole population becomes
resistant.
Can be difficult to get drugs to the parasite depending
where they are in the body
32. Research in Parasite Treatment
Current Drugs
Treatment is sometimes difficult, often times
parasites and their hosts have similarities that
may make the treatment drug harmful to the
host as well.
Example: the only proven method to kill adult
heartworms in the dog is to use arsenic, a highly
toxic compound that is potentially deadly to the host
(dog) as well.
33. Research in Parasite Treatment
Extra Information:
New Drugs
Constant need for new drugs for resistant parasites
Common problem with fleas. Companies are coming out with new
products every few years because the old products are ineffective
Special concerns with drugs given to food producing animals because
of potential accumulation of drugs in tissues for human consumption
Animal Research
Many parasites are host specific, so animal research does not
translate well to human parasites. In animals, testing can only be
done in susceptible species.
Even if a parasite infects different species, it often behaves differently
in the different hosts
34. Research in Parasite Treatment
Vaccines
So far have had limited success
Parasites have complex antigens that are difficult
to characterize
Vaccine research is expensive and it is difficult to
get funding
There are some new vaccines for parasites on
the horizon but only time will tell if these prove
to be effective treatments
Please notice on many slides there will be additional teacher information in the notes section.
Be sure to keep time limits and encourage all kids to write something. Then get them to trade and be ready to share!!!
*Teachers should fill in point value with what they think is appropriate or change the reward to a program used in your class.
Teacher can also erase the “See Notes” comment on slide.
Parasitism. Classical definition - intimate relationship between two organisms in which one (the parasite) lives on, off or at the expense of the other (host). This implies that one of the partners benefits, the other is harmed.
http://www.aber.ac.uk/~mpgwww/Edu/Para_ism/PaIsmTxt.html
*Take time here to let students give you their ideas/examples or ask questions about parasite/host relationships. 3-5 minutes These are very basic answers. The following is more specific with terms they need to know:
Parasites can be called: Eukaryotes that live on or in the body of another eukaryote species and exploit that species for sustenance. The host-parasite relationship is typically species specific
Ask students what “species specific” means. Let them come up with examples to be sure they understand.
Answer: Limited to or found only in one species.
NOTE: Bacteria and viruses are also parasites in the technical sense, but by convention most people to parasites as eukaryotes.
Allow students time again to give you their thoughts, if they are not correct, prompt them to rethink their answer with well guided questions and see if they can come up with a correct response.
Fleas need the body of dog and cat for shelter and it bites it to eat its blood. This is why the animal itches. Then the flea lays its eggs on the animal and when the animal bites at the flea it eats the eggs. The eggs then hatch in the dog and are released in the feces. Once it the larva become an adult flea again it jumps on to a new host to start the cycle all over again.
Same with worms, they need the animal to live and to reproduce more eggs.
Acute – when a parasite causes an acute infestation or invasion, it must move on to a new host quickly before it kills the host or is killed by the host.
Chronic – in this case, the parasite survives for long periods without killing its host right away or being killed by host.
Parasites have special adaptations to accomplish these requirements. Allow students to discuss or ask questions about things in their life that may be relevant to this. Such as, fleas on their dog/cats – what are they eating?
This is the life cycle of one type of human parasite. Parasite eggs that pass in the feces hatch into free living larvae and can survive for a short time in moist, warm soil. These larvae can then invade a host via skin (in this case penetrating bare feet). Once inside the intestines of the host, the worms mature and lay eggs to perpetuate the cycle. Note that this particular parasite has no intermediate host.
Tick shown on lower left, tapeworm top middle, and roundworm on the far right.
Evolutionary adaptations! Sounds like a big statement, take this time to ask students what this means. They have had exposure to adaptations, so they should be able to generate thoughts as to why this also applies to parasites and their hosts. Why would each need to change? Prompt students to think about how environmental factors may change and therefore so do the species living within them in order to survive. Medications for parasite treatment may also cause the parasite to change and mutate over time, becoming more resistant to the current medications.
Allow students time to discuss or ask questions about niche and understand it completely before moving on.
Have students explain or discuss the Niche of the three pictures on slide. Use terms like heterotroph, autotroph, predator, prey, consumer, producer…
Go to this link for more detailed information on niche: http://peer.tamu.edu/curriculum_modules/Ecosystems/module_1/whyitmatters2.htm
http://www.aber.ac.uk/~mpgwww/Edu/Para_ism/PaIsmTxt.html
Where would the tick live on the deer? What would it do to survive? Let students discuss this and this will help them see that the parasite finds a niche for itself on/in the animal to ensure its survival.
Roundworms – dogs, cats, sheep, cows, humans! Basically almost all mammals can get some type of roundworm!
Tapeworms – basically all mammals again
Hook worms – all mammals
Heartworms – dogs, cats
Dysentery carrying amoeba – most commonly contracted by people eating contaminated food and drinks by poor hygiene. (people not washing hands after going number 2!!)
Flies – all mammals, and many other kinds of animals
Fleas - all mammals and many other animals
Bugs, lice, mites, ticks – all animals
Ask as a class discussion question: What do you think the effects of over-grazing might be? What do you think the effects of leaving a pasture idle for a long time might be?
Ans.: More exposure to parasite eggs and greater degree of infestation. Depending on the species of parasite, you might break the life cycle, because the eggs or larvae would die. They can't survive indefinitely outside a host and at some point they must invade the primary host in order to sustain the cycle."
Intermediate Hosts are very common and essential to the survival and spread of the parasite. They allow the parasite to travel further in environment and be in the environment with less chance of dying before it reaches a new host. It will not reproduce on the intermediate host, it is a step used by the parasite to ensure survival until a new host is found.
Example of Intermediate hosts and their response to parasite:
Rats, infected with the intermediate stages of a tapeworm called Spirometra grow larger than uninfected rats. The tapeworm larva produces an analogue of vertebrate growth hormone-is the growth boost harming the host or is it good for the host? Similarly many molluscs, when infected with the intermediate stages of Digenetic flukes develop thicker, heavier shells, which could be deemed an advantage. On closer investigation some of the classic examples of mutualism seem more like an armed standoff than mutual benefit. Given the right conditions many organisms which harbour symbiotic algae - like for example green hydra will digest the algae and carry on quite happily. Many trees have associated with their roots fungal mycorrhiza. The fungi get organic nutrients from the plant via the phloem, and in nutrient poor soil the trees seem to benefit by increased nutrient uptake, particularly phosphate by the fungus. But if soil nutrient levels are good it appears much more like a parasitic invasion by the fungus with the tree attempting to wall off infected cells. Depending on external conditions, the association switches between mutualism and parasitism.
http://www.aber.ac.uk/~mpgwww/Edu/Para_ism/PaIsmTxt.html
Ask students why they think it is useful to know the life cycle of a given parasite species. Knowing the life cycle and all the different stages and where the parasite likes to go in the host allows for better treatment and prevention methods. The medications are made to treat the parasite based on where it is in its life cycle.
Next slide will discuss further!
http://www.aber.ac.uk/~mpgwww/Edu/Para_ism/PaIsmTxt.html
Answer: When you lived in the womb of your mother.
