---start---- dr farrell parasit 10/17 introduction to protozoa handout we're going to discuss these suckers in general terms, go over classification and what they are, and look at a couple of examples. yes, we will discuss the life cycle. protozoans are single celled organisms. produce disease more like bacterial disease than helminth type disease, but protozoa are true cells - surrounded by lipid bilayer membrane, have nuclei enclosed in membrane, adn have typical mammalian type cell structures like mitochondria, golgi etc. they often have microtubules or microfibrils beneath the cell membrane, adding structure to the membrane. so the whole outer surface including tubules is called a "pellicle" sometimes they secrete or have bound to them a membranous component outside the membrane, made of either glycolipid or glycosugars, which we often call a glycocalyx. this has a protective function. some protozoa, passed outside the host, have stages called 'cysts' which have a protective coating not too unlike the eggshells of platyhelminths in function. the cyst wall is secreted by the protozoan, and is made generally of chitin (an insoluble complex polysaccharide). there are other structural components as well we will discuss later. Classification of protozoa: see handout 4 subphylums subphylum: sarcomastigophora - have flagella, pseudopods, or both class: sarcodina: pseudopods. ameoba types. sp: entamoeba histolytica the only real pathogen class: mastigophora: flagellated. reproduce by binary fission. spp: trichomonas - venereal in cattle, man; giardia - very common. about 4-5% of fecals here are positive. leishmania - common elsewhere, not in us. trypanosomes - most important parasite worldwide in vet med. infect a lot of cattle in parts of the world. subphylum Ciliophora - ciliated at some point, and two types of nuclei class: ciliata spp balantidium coli is the only real pathogen subphylum: apicomplexa - all intracellular organisms at some point. use a special organelle called the apical complex to get into the cell - complex in structure,will discuss later. sexual or asexual repro class: coccidia - some/all intracellular. eimeria (cattle), isospora (dog/cat), sarcocystis (other carnivores), cryptosporidium (humans w/HIV, some animals), toxoplasma (widespread - cats shed infectious stage in feces) class: piroplasmidia: no oocyst, shed by ticks spp: babesia (dogs, cows), theileria (east coast fever in africa), cytauxzoon (can be fatal to cats) class: hemosporidia: very important in people. blood borne spp: plasmodia falciparum (malaria) et al - humans, rodents, birds, reptiles, major problem!, haemoproteus, leukocytozoon - these two also parasitize birds many important protozoa are arthropod borne and not seen a lot in US. the sarcomastigophora are typically ameboid, and may have flagellae. trypanosomes: have flagellae which are usually on the anterior end of the organism. have nucleus. have mitochondria. has an undulating membrane with an attached marginal flagellum - in many cases. slide: trypanosomes in blood - about 25 microns, 3x size of rbc. can see nucleus. little purple snakes is what they look like. wiggly. giardia trophozooite- piriform body. double nuclei. upside down teardrop shape with 8 flagella hanging down, nuclei in upper rounded area. has some kind of support structure i couldn't get the name of. when passed in feces,secretes a chitinous wall to form a cyst, which is oval and which is infective, and which contains smaller nuclei. trophozooite means "feeding animal" so this stage is always the organism which is actively feeding and growing and so forth. slide: giardia lamblia: multiple flagellae, which arise from structures called kinetosomes. flagellae are just packets of microtubules 2 central, 9 around it. there are two nuclei and an axostyle, centrally located, a hardened median strip, if you will, made of microtubules, runs anterior to posterior and provides structural support. it's visible when you look at the parasite. personally, i always just look for swimming little things that look like they have faces on them in fresh fecal smears. he says cyst stage is diagnostic stage ciliates: cilia are present in larger numbers than flagellae. membrane bound microfibrils attached to microtubule complex beneath membrane, allowing cilia to beat in coordinated manner. ciliates have a large macronucleus and a small micronucleus not seen well under microscope. can reproduce via conjugation and exchanging of micronuclei. apicomplexa have the apical complex - toxoplasma gondii, at anterior tip, has a structure called a conoid - it's a helical structure. running back from the tip are a bunch of structures called "rhoptry" (dense staining vesicles -long strips hanging down) and a number of small things called micronemes (round spots near the rhoptry. these together are primary structures of the apical complex. when this organism contacts a cell, the conoid is projected out, the rhoptry vesicles empty out (secrete something, probably), and parasite actively enters into the cell. may have different specificities depending on species. eg, malaria organism might enter only RBC, whereas t.gondii can enter almost all nucleated cells. all use this apical complex to invade cells. reproduction: most only asexual. usually by binary fission. so basically mitotic asexual repro. we have an organism, say a trypanosome, with a nucleus. binary fission means the nucleus divides in half to form two new ones, and there is cytokinesis, the whole thing splits in half and you end up with two new trypanosomes. there are other forms of asexual repro - mostly in the apicomplexa. basically these are forms of internal budding. all apicomplexans live w/in host cells. they do not undergo binary fission. instead, the first thing that happens is the nucleus divides , and then there is arrangement of cytoplasm around each nucleus, to form two new daughter cells. this all occurs within the membrane of the original mother cell, though. instead of the whole cell splitting, you haev two new ones within the original membrane. if this occurs we call it endodyogeny. also you can see a similar process in which the nucleus divides into many nuclei and you get many daughter cells within the original mother cell. then the mother cell membrane is lysed and you have release of multiple daughter cells. this is called schizogony or multiple fission. in many intestinal coccidia, instead of binary fission, which very slowly amplifies numbers, you see that over 24-48 hrs one organism can produce 1000-10000 progeny all within one cell, so increase is exponential. invasion of one host cell may give rise to huge numbers of new parasites. and each daughter cell can go invade other cells and be similarly amplified. example: intestinal parasite eg eimeria, isospora. start with one infected host cell. you have a cell infected by single organism. this single organism undergoes schizogeny and forms multiple daughter cells and releases them to infect other cells. in some parasites this process is limited in terms of number of cycles, in others it can go on until host dies or mounts immune response. additional terminology used in this process: product of schizogeny is called "merozoites" and the merozoites can infect other cells ad repeat the process. now, all apicomplexans also have a sexual cycle. so the organism cacn pass into cell, become male or female gametocyte, fuse, form gamete, which can then fuse, form zygote- wait, that doens't make sense. well, whatever. see handout. i thik he said somethign wrong. malarian parasite - life cycle can be very complex. division in mosquito, multiple cell types, amplification by schizogeny, sexual repro in mosquito. trichomonas - important in cows and, apparently, people, per this slide with people kissing. simple structure. single nucleus, multiple flagellae, no cyst produced. transmitted sexually. so it doens't really need a cyst stage. so it only has the trophozooite stage. another extreme is toxoplasma gondii. cat is definitive host. passes sporogonya in feces, makes oocysts which are eaten by mouse, human, or dog. they release parasite and invade multiple body tissues including brain. makes mice easier to catch..cat eats them... also passed from infected mouse mom to neonate, and causes disease. multiple transmission mechanisms. can infect almost any nucleated cell in any host. but rarely causes severe dz. entamoeba histolytica - occurs in large intestine. trophozooite stage...moves around with psueopods. undergoes binary fission only. these parasites live mainly in the lumen of the LI. but they have capacity to bind to intestinal wall by receptor mediated mechanism, using a number of enzymes and proteases, and can invade tissue, get down to lamina propria, and continue to divide, and cause disease. generally in humans with amebiasis you see severe watery diarrhea or dysentery (blood in diarrhea) which occurs if organisms have invaded deeply into intestine. these organisms then can travel through the portal circulation to the liver and set up shop there making necrotic abscesses which can be severely debilitating/fatal. can go to heart, lung, brain, skin. can be ugly. back to GI tract...as it passes down LI it secretes chitin and is passed as cyst stage. these are very common in many parts of the world. occurs in US. many people in mexico city or other parts of mexico with worse hygeine have this protozoan. africa, se asia, etc. this can also infect dogs, horses, other animals, but in order to get it there there must be a primate host, because it only forms cysts in primates. in other animals there is no cyst formation. so you can give it to your dog but you can't get it from your dog. most infected animals with e.histolytica do not show signs of disease. these organisms eat phagocytes, lyse all surrounding cells. very pathogenic. but only when they invade tissue. only important ciliate: balantidium coli. mainly in pigs. 80-90% of pigs infected with it as a commensal. trophozooite lives in lumen of LI. divides by binary fission. but can sometimes act like ameba and invade, causing ulcerated lesions of lg int. not nearly as pathogenic as e.histolytica. most often no signs of disease seen in pigs. we only see this in the US if humans and animals have close association with pigs, pig is primary reservoir. cyst can infect any other animal, if that occurs, generally no disease occurs except in minority of cases where it invades GI tract. ---end----