The Parasites January 19 th, 2010. Parasite biology Eukaryotic cells –Complex cell structure...
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Transcript of The Parasites January 19 th, 2010. Parasite biology Eukaryotic cells –Complex cell structure...
The Parasites
January 19th, 2010
Parasite biology
• Eukaryotic cells– Complex cell structure– Nucleus– Organelles– Mitochondria or similar structures
• Can be single celled or multicellular• Feed on bacteria and small nutrients
Parasite biology
• Complex life cycles• Distinct life stages that undergo structural
changes• Some stages are reproductive• Only certain stages are infectious• Different stages take place in different
places– Environment– Tissues of host– Tissues of vector (insect)
Example: Malaria life cycle
Example: Cryptosporidium life cycle
Parasite Classification
• The protozoa (protists)– Single celled
eukaryotes
• The helminths– Multicellular
eukaryotes
The Protozoa: Characteristics
• Single celled organisms• Environmental stages inhabit water or
soil• Most are aerobic• Consume food in several ways
– Transport across membrane– Taking food into cellular openings– Engulfing food– Digest food using specialized structures
inside cells (food vacuoles)
The Protozoa: Structure
Protozoa: life cycles
• Different from organism to organism, but some common elements
• Environmentally resistant life stages– The cyst
• Reproductive stages– Sexual and asexual
Protozoa: the cyst
• Environmentally resistant life stage
• Protective capsule forms around the cell
• Allows survival outside a living host– transmission from host to host
• Resistance to environmental stressors– Low moisture
– Lack of nutrients
– Lack of oxygen
– Unsuitable temperatures
Protozoa: Reproduction• Some have sexual reproductive
stages– gametocytes
• Asexual reproduction is common– Fission (like bacteria)– Budding– Schizogony
Protozoan taxonomy
• Protozoa are quite diverse• Divided into phyla• Currently done using ribosomal RNA
sequencing• As with bacteria, this is changing as
techniques advance and more organisms are sequenced
Protozoan taxonomy: the phyla
• Archaezoa• Microspora• Amoebozoa• Apicomplexa• Ciliophora• Euglenozoa
Archaezoa• Unique feature: lack mitochondria• Many live in intestinal tracts of animals• Flagellated• Species of public health importance:
Giardia lamblia
Microspora• Unique feature: lack mitochondria• Intracellular parasites (live inside host
cells)• Species of public health importance:
Enterocytozoon bieneusi
E. bieneusi cysts inside a eukaryotic cell E. bieneusi in stool smear
Amoebozoa
• The amoebas• Unique feature: use pseudopods for
motility and to get food• Intestinal parasites• Species of public health importance:
Entamoeba histolytica
CystTrophozoite
Apicomplexa• Unique feature: have organelles that
release enzymes to aid in penetration of host tissues
• Intracellular parasites (live inside host cells)
• Complex life cycles with multiple hosts• Genus of public health importance:
Plasmodium
Ciliophora
• Unique feature: cilia– Small “hairs” on the cell that propel the cell
and move food toward it
• Intestinal parasite• Genus of public health importance:
Balantidium coli
CystTrophozoite
Euglenozoa
• Unique feature: the hemoflagellates travel in the circulatory system of an infected host
• Long, slender cells move by undulation• Genus of public health importance:
Trypanosoma
The Helminths
The Helminths: Characteristics
• The parasitic worms• Multicellular organisms• Digestive, circulatory, nervous,
excretory, and reproductive systems• Spend part or all of their lives in
humans• Invade and live in tissues
The Helminths: life cycles
• Complex life cycles• May have multiple hosts• Larval stages: developmental
– Include eggs
• Adult stages– Worms
• Sexual reproduction
The Helminths: life cycles
Helminth taxonomy
Two phyla:• Platyhelminthes (the flatworms)
– Trematodes– Cestodes
• Nematoda (the roundworms)
Trematodes
• Also known as flukes• Flat shaped body• Attach to tissues via suckers• Genus of public health importance:
Schistosoma
Cestodes• Also known as the tapeworms• Intestinal parasites
– Lack a digestive system; absorb nutrients from their host
– Attach to tissues via suckers
• Genus of public health importance: Ehinococcus and Taenia
Nematodes• Also known as the roundworms• Two types
– Egg is infective– Larva is infective
• Genus of public health importance– Ascaris– Necator (hookworm)– Trichinella
NematodesAscaris Necator
Trichinella
Key Concepts
• Eukaryotic cells• Can be single celled or multicellular• Feed on bacteria and small nutrients• Complex life cycles
– Distinct life stages that undergo structural changes
– Some stages are reproductive– Different stages take place in different
places
Key Concepts
• The protozoa (protists)– Single celled eukaryotes– Environmental stages inhabit water or soil– Most are aerobic– Consume food in several ways
• The helminths– Multicellular eukaryotes– The parasitic worms– Multicellular organisms– Digestive, circulatory, nervous, excretory, and
reproductive systems– Spend part or all of their lives in humans– Invade and live in tissues
Key Concepts
The protozoa:• Archaezoa• Microspora• Amoebozoa• Apicomplexa• Ciliophora• Euglenozoa
The helminths:• Platyhelminthes
(the flatworms)– Trematodes– Cestodes
• Nematoda (the roundworms)