The Parasites January 19 th, 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 Cyst Trophozoite

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 Cyst Trophozoite

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

Nematodes AscarisNecatorTrichinella

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)