Eukaryotic Microorganisms and Parasites

Important words and concepts from Chapter 11, Black, 1999 (3/28/2003):

by Stephen T. Abedon (abedon.1@osu.edu) for Micro 509 at the Ohio State University

Course-external links are in brackets

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(1) Chapter title: Eukaryotic Microorganisms and Parasites

(2) Parasite

(a) A parasite is an organism that lives in or on another organism (the host), which damages the host in some way plus fails to compensate for this damaging by also failing to help the host to an appreciable extent

(b) More narrowly, the term parasite is often used to describe parasitic protozoa, helminths (worms), and arthropods

(c) (in addition to parasites of animals, there exist numerous parasites of plants as well as parasites of members of the other various kingdoms)

(d) Some general external links: [Dave Gibson’s parasitological URLs] [A directory of academic links to Ectoparasites and Endoparasites, Medicine and Veterinary Science] [ASM’s parasite division page] [index]

(3) Pathogen

(a) A pathogen is a parasite that causes disease; yes, by and large pathogens are parasites (in the broader sense of the word) and parasites (ditto) are pathogens

(b) From here on out in this lecture I will be employing the term parasite is its narrower sense, limiting it to describing protozoa, helminths (worms), and arthropods

(4) Ectoparasite

(a) An ectoparasite is a parasite that lives on the surface of a host

(b) Ticks and lice (which are arthropods) are examples of ectoparasites

(c) [ectoparasite (Google Search)] [an ectoparasite is a parasite that attaches to skin and body openings of host organism (definition) (Agripedia)] [index]

(d) [Question: Are all ecoparasites arthropods? I don't think so. Yes, barnacles are indeed arthropods, but there must be mollusks that act as ectoparasites. Any additional phyla? Are there any worm ectoparasites? What about medusa?]

(5) Endoparasite

(a) An endoparasite is a parasite that lives within a host

(b) These include most parasitic protozoa and helminths

(c) [endoparasite (Google Search)] [diagnostics of veterinary endoparasitic infections (still very much under construction but still lots of cool stuff (University of Pennsylvania School of Veterinary Medicine)] [parasites and parasitological resources (a very cool site) images of parasites (ditto) (Peter W. Pappas)] [index]

(6) Vector (host)

(a) A vector is a living organism that carries a disease-causing organism to new hosts

(b) See arthropod vectors, below

(i) biological vectors

(ii) mechanical vectors

(d) Organisms that carry diseases include:

(i) definitive hosts

(ii) intermediate hosts

(iii) reservoir hosts

(e) (typically, from our perspective, these would be animals that carry human diseases, or humans themselves)

(f) These various hosts are either vectors themselves or what a vector carries a parasite/pathogen to from another host

(g) [parasite and vector (Google Search)] [index]

(7) Biological vector

(a) A biological vector is a vector in which or upon which a parasite goes through part of its life cycle (e.g., replicates)

(b) See also definitive host, intermediate host, and reservoir host, below

(8) Mechanical vector

(a) A mechanical vector is a vector in which or upon which a parasite is transported but otherwise the parasite does not go through significant aspects of its life cycle while in contact with this vector (e.g., does not replicate)

(b) [mechanical vector (Google Search)] [index]

(9) Definitive host

(a) Parasites that go through their sexual stage associated with a given host, that host is called the definitive host

(b) For example, the malaria parasite's definitive host is the mosquito; this mosquito additionally (simultaneously) serves as the biological vector for the malaria parasite

(10) Intermediate host

(a) The intermediate host is one that harbors the parasite but associated with which the parasite does not undergo sexual reproduction

(b) For example, the malaria parasite's intermediate host is humans (though for anthropocentric reasons we don’t typically consider humans to be vectors for the transmission of malaria to mosquitoes; besides, the malaria parasite does not make the mosquito sick)

(11) Reservoir hosts

(a) The reservoir host is the host that a parasite normally resides in

(b) Many parasites predominately infect animals rather than humans, but humans can become infected following contact with the animal reservoir (for example, Toxoplasma gondii)

(12) Host specificity

(a) Host specificity is a description of the range of hosts which can serve as biological vectors, e.g., within which the parasite can mature to produce infectious progeny

(b) [parasite host specificity (Google Search)] [index]

KINGDOM PROTISTA

(13) Protists

(a) Members of Kingdom Protista are always eukaryotic and mostly unicellular organisms

(b) Some protists are photoautotrophs (algae)

(d) Kingdom Protista represents an extremely diverse taxon including members that are described as

(i) Flagellates

(ii) Ciliates

(iii) Amoebas (many of which have shells)

(iv) Sporozoans

(e) Kingdom Protista also includes a number of parasitic members

(f) [protozoa (Google Search)] [the origins of eukaryotic diversity (MicroDude)] [protist images (lots and lots) (Protist Information Server)] [protist image data (Molecular Evolution & Organelle Genomics)] [index]

(14) Parasitic protists (parasites)

(a) A few examples of many (and, yes, please learn these):

(b) Trichomonas vaginalis

(i) sexually transmitted disease

(ii) [graphic images of Trichomonas vaginalis (Parasites and Parasitological Resources)] [Trichomonas vaginalis (Google Search)]

(c) Giardiasis

(i) Giardia lamblia

(ii) Infections obtained upon drinking cyst-contaminated water

(iii) The reservoir host (probably) includes numerous mammals

(iv) (infections are also known as, for example, “beaver fever” and may be avoided by chemically treating drinking water obtained from otherwise unknown sources, by filtering the water, or by boiling the water)

(v) [graphic images of Giardia lamblia (Parasites and Parasitological Resources)] [Giardia lamblia (Google Search)]

(d) Toxoplasmosis

(i) Toxoplasma spp.

(ii) The definitive host = cats = reservoir host

(iii) Obtained upon inhaling or ingesting eggs associated with cat litter, or by consuming not-fully cooked meat that contains infectious cells (called bradiozoites)

(iv) Typically not highly pathogenic in humans but

· Can seriously harm fetuses when mother is infected during pregnancy

· Can lead to significant disease in immunocompromised individuals

(v) [graphic images of Toxoplasma gondii (Parasites and Parasitological Resources)] [Toxoplasma gondii (Google Search)]

(e) Malaria

(i) Plasmodium spp.

(ii) vector = mosquitoes = definitive host

(iii) “Each year, 300-500 million people become ill with malaria and several million die… Most who die are children under five.”

(iv) (“There’s no preventive vaccine for malaria, which kills about 2 million people a year, and in the past 2 decades the organism has become resistant to other key antimalarial drugs in addition to chloroquine.” Elizabeth Pennisi, 1999, Malarial genome comes into view, Science, 286:1263-1265)

(v) [graphic images of Plasmodium spp. (Parasites and Parasitological Resources)]

(vi) [Plasmodium (Google Search)]

(vii) [Malaria Foundation International]

(f) See Figure 11.4, The life cycle of the malaria parasite Plasmodium

(g) [parasite life cyles] [parasitic protists (Joe Camp)] [index]

KINGDOM FUNGI

(15) Fungi

(a) Fungi are eukaryotic organisms that are heterotrophic

(b) Fungi have cell walls, and those cell walls are composed of chitin (insect exoskeletons are also composed of chitin)

(d) Typically fungi reside within the food they are consuming

(e) Often that food is plant material, but their food can be animal in origin as well

(f) Most fungi are multicellular and many are macroscopic

(g) [fungi (Google Search)] [fungi (MicroDude)] [index]

(16) Saprophyte

(a) Saprophytes are organisms that consume and digest dead organic matter and organic waste

(b) Most fungi are saprophytes

(17) Mycology

(a) The study of fungi is called mycology

(b) [mycology (Google Search)] [index]

(18) Fungal anatomy (chitin, hyphae, mycelia, thallus)

(a) The "body" of a fungi is its thallus

(b) The thallus of most multicellular fungi consists of mycelia, which are branched mycelia

(d) Fungi live by growing mycelia into (or onto) substrate (e.g., a dead plant), secreting exoenzymes from these cells, and then absorbing digested nutrient into the mycelia

(e) Mycelia often are tangled masses of hyphae; this is an image of fungal mycelia à

(f) [thallus fungus or fungi, thalli fungus or fungi (Google Search)] [chitin, hyphae, mycelium (MicroDude)] [index]

(19) Septa

(a) Hyphae may be divided up into individual cells by crosswalls called septa

(b) These septa are typically incomplete barriers between cells

(c) In many cases, the septa are absent altogether, resulting in hyphae consisting of long chains of multinucleated, unpartitioned cytoplasm

(d) Movement of nutrients, cytoplasm, and organelles (including the nucleus) along hyphae, i.e., through septa, allows fungi to divert resources to new food supplies; fungi can grow extremely rapidly at the growing ends of hyphae due to this movement of cytoplasm along hyphae

(e) [septa (MicroDude)] [index]

(20) Fungal ecology

(a) Fungi tend to be able to do the same kinds of things bacteria do, especially gram-positive bacteria, (that is, they are exoenzyme-employing absorbers) but do so in dryer, more acidic, more highly osmotic environments than most bacteria prefer

(b) Some fungi are parasitic, but most fungi are decomposers, especially of plant material

(c) "Fungi are never obligate parasites because all fungi can obtain nutrients from dead organisms. Even when fungi parasitize living organisms, they kill cells and obtain nutrients as saprophytes."

(d) Many fungi produce antibiotics that they use to inhibit bacterial growth and thus reduce competition for resources

(e) "Saprophytic fungi are beneficial as decomposers and as producers of antibiotics. The digestive activities of such fungi provide nutrients not only for the fungi themselves but for other organisms, too. The carbon and nitrogen compounds they release from dead organisms contribute significantly to the recycling of substances."

(f) See Figure 11.7, One method of sexual reproduction in fungi

(g) [fungal ecology, fungi ecology, fungus ecology (Google Search)] [index]

(21) Fungal disease (mycoses)

(a) A fungi-caused disease is called a mycosis

(b) Fungal diseases can be superficial (on the skin), subcutaneous (under the skin), or systemic (throughout various organs of the body)

(c) Fungal diseases tend to progress slowly but can be especially difficult to treat (the latter is a consequence of the close similarities between human and fungal metabolisms)

(d) Examples of mycoses include:

(i) Disease-causing fungi include Candida albicans (yeast infections, etc.)

(ii) Histoplasmosis is a fungal disease, one that resembles tuberculosis in symptoms

(iii) Athletes foot and ringworm are fungal skin diseases

(iv) Certain atypical pneumonia are caused by fungi (i.e., pneumocystis pneumonia)

(e) Fungal diseases are especially a problem among individuals with depressed immunity (chemotherapy and AIDS patients)

(f) [fungal diseases, fungus diseases, mycoses (Google Search)] [Candida albicans information] [index]

(22) Superficial mycoses

(a) A superficial mycosis is one that fails to appreciably penetrate the body, instead affecting only the keratinized tissues including the outer layer of skin, the hair, and the nails

(b) Superficial mycoses are the least damaging mycoses

(d) [superficial mycoses (Google Search)] [index]

(23) Subcutaneous mycoses

(a) Subcutaneous mycoses invade below the skin and can also affect the lymphatic system

(b) [subcutaneous mycoses (Google Search)] [index]

(24) Systemic mycoses

(a) Systemic mycoses can invade throughout the body

(b) Systemic mycoses are the most damaging of mycoses

(25) Fungal classification

(a) Fungi are typically grouped into taxonomic categories based on similarities in sexual structures (in fact, fungi lacking such structures are termed "imperfect"); here we will ignore these distinctions

(b) Fungal classification can be difficult: "Fungi are classified according to the nature of the sexual stage in their life cycles. Such classification is complicated by two problems: (1) No sexual cycle has been observed for some fungi, and (2) it is often difficult to match the sexual and asexual stages of some fungi. For instance, one researcher may work out an asexual phase and give the fungus a name; another researcher may work out a sexual phase and give the same fungus a different name. Because the relationship between the sexual and asexual phases is not always apparent, a particular species of fungi may have two names until someone discovers that the two phases occur in the same organism. Another problem is that many fungi look quite different when growing in tissues (yeastlike) and when growing in their natural habitat (filamentous)."

(d) [fungal classification (Google Search)] [index]

(26) Yeasts

(a) Yeasts are single-celled fungi; budding yeast are shown to the right à

(b) Note that many fungal taxa possess single-celled forms (i.e., yeasts tend to be more closely related to molds than to other yeasts)

(27) Molds

(a) Molds are multi-celled microfungi

(b) [mold and fungus (Google Search)] [index]

(28) Macrofungi

(a) Macrofungi are such things as large, clonal masses of mycelia that produce large fruiting bodies such as mushrooms

(b) See Figure 11.12, The life cycle of an ascomycete

(c) [macrofungi (Google Search)] [Ralph’s finest fungi fancier file] [fungi images on the net] [index]

(29) Dimorphism

(a) Dimorphism is the ability of many fungi to take on different forms (e.g., yeast-like versus mold-like) depending on growth conditions

(b) As you might expect, dimorphism additionally complicates fungi taxonomy

(30) Spores

(a) Many fungi produce spores; this is a mushroom spore print à

(b) These spores typically represent the dispersal stage

(d) Depending on the fungi as well as the stage of the life cycle, spores may be produced sexually (meiosis) or asexually (mitosis)

(e) [fungus spores (Google Search)] [index]

(31) Saccharomyces cerevisiae

(a) This is the yeast used to make breads, beers, and wines

(b) [saccharomyces cerevisiae (Google Search)] [index]

HELMINTHS (KINGDOM ANIMALIA)

(PHYLUM PLATYHELMINTHES OR NEMOTODA)

(32) Helminths

(a) Helminths are worms

(b) Worms are relevant to microbiology because they are small (can be studied using microbiological techniques) and they can cause disease

(c) The two types of worms that parasitize humans are flatworms and roundworms (segmented worms, like our friend the earthworm, are not parasitic)

(i) Flatworms = free-living flatworms, flukes, and tapeworms

(ii) Roundworms = free-living roundworms (nematodes), pinworms, and hookworms

(d) Helminths can have complex life cycles involving more than one host or host species

(e) [How does the human immune system fight animal endoparasites? Humans fall victim to many different internal animal parasites. In the developing world, many of these have been reduced or eliminated by developing anti-parasitic drugs or learning about the life cycles of these organisms and modifying our behavior to avoid infection. In developing nations and throughout pre-industrial history, animal endoparasites were by far the most common and troublesome of human pathogens, causing immense suffering and death. Behaviors that help prevent infection by parasites have become ritualized in some cultures. For example, the widespread avoidance of pork, which is notorious for passing on parasites because of the undiscerning tastes of pigs. It is safe to assume that during our evolution, most or all humans were perpetually infected by multiple species of parasites, just as most other wild mammals are today. Defending the body against animal parasites is difficult because many of them are more heavily armed and armored than bacterial pathogens. They may have chewing mouthparts, well-developed muscles and thick, resistant outer layers that enable them to penetrate and survive inside their host. Clearly, animal parasites are formidable adversaries that call for aggressive counter-measures. One of the five classes of human antibodies, known as IGE, seems to be exclusively dedicated to the destruction of multicellular parasites. It is usually found attached to special cells called mast cells where it acts as receptor for any substance that may have been produced by or is attached to a multicellular parasite. If the IGE molecules signal the presence of a parasite, the mast cell responds by immediately releasing compounds such as histamine. These compounds are presumably toxic to the parasite and initiate a powerful inflammatory response in the infected tissue, causing swelling, irritation, dilation of blood vessels, the release of proteolytic enzymes and the immigration of white blood cells. Although intended to fight parasites, this immune response is the basis for the most common allergies. Note that most allergies are caused by substances that come from multicellular organisms (cat hair, pollen, fungi, flea saliva, etc.). Allergies are really just the body’s reaction to a perceived invasion by a parasite. The unpleasant side effects may seem excessive but not when we consider the serious consequences of infection. Allergic reactions are often medically countered by administering an anti-histamine to reduce the inflammatory response.]

(f) [helminths (Google Search)] [worms (including a wonderful on-line, graphical quiz)] [index]

(33) Flatworms

(a) Flatworms are, well, flat

(b) This lack of significant depth to their body allows nutrient, etc., circulation within flatworms without flatworms needing to possess a very sophisticated circulatory system (mostly things move around by diffusion)

(d) Parasitic flatworms include the flukes and the tapeworms

(e) Free-living flatworms (planarians) as viewed from above:

(f) [flatworms (Google Search)] [index]

(34) Tapeworms (scolex, proglottid, cysticercus, hydatid cyst[THESE ARE NOT LINK TARGETS])

(a) Tapeworms are flatworms that lack a digestive tract and acquire nutrients from their host’s digestate

(b) "Tapeworms consist of a scolex (sko'lex), or head end, with suckers that attach to the intestinal wall, and a long chain of hermaphroditic proglottids (pro-glot'tidz), body components that contain mainly reproductive organs of both sexes."

(d)

(e) "The life cycle of tapeworms usually include the following stages: Embryos develop inside eggs and are released from proglottids; the proglottids and eggs leave the host's body with the feces. When another animal ingests vegetation or water contaminated with eggs, the eggs hatch into larvae, which invade the intestinal wall and can migrate to other tissues. A larva can develop into cysticercus (sis-ti-ser'kus), or bladder worm, or it can form a cyst. A cysticercus can remain in the intestinal wall or migrate through blood vessels to other organs. A cyst can enlarge and develop many tapeworm heads within it, becoming a hydatid (hi-da'tid) cyst. If an animal eats flesh containing such a cyst, each scolex can develop into a new tapeworm." [Cysticercus bovis (image)] [graphic images of parasites (cysticercus)] [graphic images of tape worm scolex and proglottids] [index]

(f) See Figure 11.16, The life cycle of the beef tapeworm Taenia saginata

(g) [tapeworms (Google Search)] [graphic images of Taena spp. (Parasites and Parasitological Resources)] [graphic images of Trichinella spiralis (Parasites and Parasitological Resources)] [tapeworms in dogs] [phylum Platyhelminthes] [Wormman’s intestinal parasites page (funny, informative, disgusting, and cool pictures)] [index]

(35) Flukes

(a) Flukes are flatworms that tend to live in tissues other than the lumen of your digestive tract

(b) See Figure 11.15, The life cycle of a blood fluke, Schistosoma japonicum

(d)

(e) [flukes and worm, flukes and worms (Google Search)] [index]

(36) Roundworms (hookworms, pinworms)

(a) Roundworms are more sophisticated than flatworms, possessing not just a separate mouth and anus, but a circulatory system as well

(b) Round worms are small but important (and extremely numerous) components of most ecosystems

(d) Parasitic round worms include the hook worms and the pin worms

(e) Trichinosis is an example of a disease caused by a parasitic roundworm [graphic images of Trichinella spiralis]

(f) Sushi (raw fish) can harbor parasitic roundworms [graphic images (well, description) of Anisakis spp.]

(g) See Figure 11.17, The life cycle of the roundworm Trichinella spiralis

(h) See Figure 11.18, The life cycle of the roundworm Wuchereria bancrofti

(i) See Figure on page 311 (lower right-hand corner)

(j) [roundworms (Google Search)] [hookworms (Google Search)] [pinworms (Google Search)] [graphic images of Wuchereria bancrofti (Parasites and Parasitological Resources)] [a round worm has been fully sequenced and more sequences are on the way] [index]

ATHROPODS (KINGDOM ANIMALIA)

(PHYLUM ATHROPODA)

(37) Arthropod vectors

(a) Arthropods are insects and insect-like animals

(b) Arthropod vectors are responsible for the transmission of a variety of diseases, though often each vector (i.e., arthropod species) can transmit only a limited number of pathogens, and each pathogen may be transmitted by only a limited number of arthropod vectors

(i) mosquitoes

(ii) ticks

(iii) lice

(iv) fleas

(v) flies

(d) [arthropod vectors (Google Search)] [bugs that bug your pet] [index]

(38) Mosquito-borne diseases

(a) Examples of important mosquito-borne diseases include:

(i) Malaria (protozoa) [graphic images of Plasmodium spp.]

(ii) Yellow fever (virus)

(iii) Various roundworms [graphic images of Wuchereria bancrofti]

(b) [mosquito-borne diseases (Google Search)] [graphic images of mosquitos] [index]

(39) Tick-borne diseases

(a) Examples of important tick-borne diseases include

(i) Lyme disease (bacteria: Borrelia burgdorferi)

(ii) Rocky Mountain spotted fever (bacteria: Rickettsia rickettsii)

(b) [tick-borne diseases (Google Search)] [Rocky Mountain spotted fever FAQs] [bugs that bug your pet - ticks] [index]

(40) Louse-borne diseases

(a) “Epidemics of louseborne diseases usually occur under crowded, unsanitary conditions. All louseborne disease agents enter the body when louse feces are scratched into bite wounds.”

(b) Examples of important louse-borne diseases include:

(i) Epidemic typhus (bacteria: Rickettsia prowazekii)

(41) Flea-borne diseases

(a) Examples of important flea-borne diseases include:

(i) Plague (bacteria: Yersinia pestis)

(b) [flea-borne diseases (Google Search)] [bugs that bug your pet - fleas] [index]

(42) Fly-borne diseases

(a) Flies carry pathogens from feces to food

(b) Flies tend to be mechanical vectors rather than biological vectors since the role they play in disease transmission is to carry the pathogen rather than to serve as a host for the replication of the pathogen