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Each animal can be a host of many parasites; thus?

There are many parasitic organisms on earth


It has been estimated that more than 50% of all living plants and animals are?

parasitic at some stage during their life cycle


In this course we will concentrate on 3 major groups of parasites

1. Protozoa- flagellates, amebas, malarial organisms
2. Helminths - parasitic worms such as the flukes, tapeworms, and roundworms
3. Arthropods - insects and arachnids that are ectoparasites and carriers (vectors) of diseases


Why do we study parasites?

• Parasites provide unique examples of biological phenomena not found in free-living organisms
• Parasites provide unique examples of biological phenomena not found in free-living organisms.
* Medical Importance
* Veterinary Importance
* Economic Importance


______ are hosts to many species of parasites

Humans are hosts to many species of parasites


Medical Importance of Parasites

• Humans are hosts to many species of parasites.
• Many of these parasites are causative agents of major public health problems of the world.


Examples of Medical Importance in the World

• The life expectancy of an Egyptian is in the mid-40's due to Schistosomes.
• 15 million children in the world will die this year from a combination of malnutrition and parasites.
• Over 1 million African children will die this year from the effects of malaria.
• Many cases of plague, transmitted by fleas, still occur throughout the world.
• We in the comfort of the U.S. are not immune from parasites.


Common parasitic diseases in the U.S. include

1) Pinworms
2) Giardiasis
3) Dog roundworms
4) Ticks


Importation of Parasites from Tropics to the U.S.

Movement of persons from all areas of the world have introduced parasitic diseases into the U.S
– Numerous cases of malaria are brought back by vacationers from the tropics.
– Service personnel are often employed in areas endemic with many parasites.
– Many immigrants have brought their parasites with them.


Veterinary Importance of Parasites

• In Africa, cattle cannot be raised in an area equal to that of the U.S. due to trypanosomes.
• A poultry farmer can be wiped out by coccidia.
• Cattle, pigs, and sheep infected with parasites fail to gain weight and may not reproduce.
• Dogs may become infected with heartworm and die if untreated.
• Cats are infected by many species of protozoans and helminths.


Parasites are primarily divided in 2 major groups

– Protozoa
– Helmints


Protozoa are? (specific types)

– Sarcodina (Amoeba)
– Sporozoa (Sporozoans)
– Mastigophora (flagellates)
– Cilliata (Ciliates)


Helmints are (specific types)

– Platyhelmints (flatworms)
• Cestoda (Tapeworms)
• Trematoda (Flukes)
– Nemathelmints (Roundworms)



– Trophozoite: Motile, feeding and reproducing
– Cyst: Non motile, non metabolizing and non reproducing form surrounded by thick wall.


Helmints are

– Egg
– Larva
– Adult


Definitive Host is?

One in which the sexual cycle takes place or the adults are present.


Intermediate Host is?

Asexual cycle takes place or the larva is present.


Protozoa features

– Microscopic unicellular organisms
– Lack photosynthetic capability
– Usually motile
– Reproduce by asexual fission


Protozoan habitats

– Majority are free-living
• Found in marine, fresh water and terrestrial habitats
– Essential decomposers
– Require large amounts of moisture
– Important part of food chain
• Protozoa eat bacteria and serve as food for larger species
• Help maintain ecological balance in soil
• Important in sewage disposal
– Results in decrease of sewage solids


Structure of protozoa

– Cell wall: Lack cell wall
– Shape determined by material beneath plasma
– Cell structures:
• Have membrane bound nucleus and organelles
• lack photosynthetic chloroplasts
• Have specialized structures for movement– Cilia, flagella or pseudopodia
• Protozoa grouped by mode of locomotion