Parasite/Host Relationships

Copyright 2010. PEER.tamu.edu

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!

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.

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

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/Para_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.

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?

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

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!

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

1. Lets start here, eggs are released in feces.

2. The animals eats the eggs that are now on the pasture grass.

3. The parasite moves to many different places inside horse as it grows and feeds off the animal host, sometimes making animal sick.

4. Parasite returns to intestine to lay eggs to be released again in feces, continuing its life cycle.

Example Life Cycle:

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!!

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.

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?

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.

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!!

Parasites in a food chain or food web: 6 Links of the Chain

6. Development in environmentor intermediate host.

1. Contact and Entry Into Host

4. Reproduction

5. Escape from host,released back into

environment.

3. Continued survival in Host.May have to move to different areas within

host body.

2. Gaining a suitable nicheIn the host (where it lives to

gain nutrition)

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.

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.

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

Human head lice only reproduce on humans

and prefer areas of skin with lots of hair, like the

head

The babesia parasite is only found within red

blood cells

Examples of Specific Niche Needed for Protection and Nutrition

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

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

Reproduction Produce

numerous numbers of offspring

Most of which will not complete their life cycles

Tapeworm eggs

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

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.

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.

So Why are Life Cycles So Important

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????

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?

Prevention/Treatment A thorough understanding of the life

cycle helps in the control and prevention of parasites

Know when and how to expose parasites to the maximum dose of medication

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

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.

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

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

References http://cal.vet.upenn.edu/projects/

dxendopar/parasitelists/pdlist.html http://www.dpd.cdc.gov/DPDX/default.htm www.nih.gov http://users.rcn.com/jkimball.ma.ultranet/

BiologyPages/S/Symbiosis.html http://www.peteducation.com/article.cfm?

c=2&aid=757