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Topic 9The Eukaryotes(Fungi, Protozoa, & Helminths)Fungi: able to adapt to environments that are hostile to bacteria; grow better in acidic environments (i.e., pH=5); most are more resistant to osmotic pressure (can grow in high salt or sugar concentrations); can grow on substances with very low moisture content (i.e., bread). Includes mushrooms, yeasts, and molds.Mycology: the study of fungi.Mycosis: a disease caused by a fungus. The types are differentiated by their degree of tissue involvement and their mode of entry.Systemic: fungal infections that are deep within the body that affect many tissues and organs. Caused by inhalation of spores from soil fungi. Infections begin in the lungs and spread to other tissues and is not transmitted from person to person.Subcutaneous: fungal infections deep beneath the skin. Caused by spores/mycelial fragments from soil entering puncture wounds in the skin.Cutaneous: caused by dermatophytes. They affect keratin-containing tissues such as the epidermis, hair, and nails. They secrete keratinase and spread through contact (i.e., Ringworm [tineas], Athlete’s foot).Superficial: fungal infections limited to the outermost layers of the skin.Opportunistic: occur only under certain circumstances (i.e., Pneumocystic jirovecii causing Pneumonia, Aspergillus causing Aspergillosis, Candida albicans causing Candidiasis [yeast infection]). The following are predisposing factors for opportunistic infections:Chronic or debilitating disease (i.e., cancer, diabetes, TB, AIDS)Use of broad spectrum antibiotics or immunosupressantsLocal lesions that allow fungal access to deep tissueYeasts: also known as non-filamentous fungi. They are unicellular, spherical/oval, and have two types; budding and fission yeasts.Budding Yeasts: divide unevenly during reproduction.Fission Yeasts: divide evenly during reproduction.Dimorphic Fungi: some fungi, notably pathogens, exhibit dimorphism – they grow in two ways. At room temperature they grow like a mold, and at body temperature (37°C) they grow like yeasts (i.e., Histoplasma capsulatum).Molds: also known as filamentous fungi. They are multicellular.Hyphae: filaments of cells in molds. The type of hyphae present is useful for identification purposes.Septate: hyphae that contain cross-walls.Coenocytic: hyphae that lack cross-walls.Vegetative: hyphae that obtain nutrients.Aerial: hyphae involved in reproduction via spores.Mycelium: a mass of hyphae.Chitin: found in the cell walls of molds; strong, flexible polysaccharide that is also found in the exoskeleton of arthropods. *Mold cells walls do NOT contain peptidoglycan.Reproduction: molds reproduce by producing a vast number of spores (different than bacterial endospores which only produce one endospore per cell as a means of survival). Fungal spores are only meant for reproduction and are not resistant to environmental stress like endospores.Antifungal Drugs: difficult to find drugs that are selectively toxic to fungi; they work by targeting three different aspects of the fungus:Targeting Fungal Sterols: many anti-fungal drugs target sterols in fungal plasma membranes. The main fungal sterol is ergosterol and the main animal cell sterol is cholesterol. Inhibition of ergosterol biosynthesis is the basis of its selective toxicity, causing leakage of cellular components, killing the cell (i.e., Polyene Antibiotics (Amphotericin B))Targeting Fungal Cell Walls: targets β-glucan (a unique compound found in cell walls). Leads to incomplete formation of the cell wall, causing lysis.Echinocandins: new class of anti-fungal drugs that inhibit the biosynthesis of β-glucan.Targeting Fungal RNA Synthesis: target the production of RNA (transcription).Protozoa: unicellular microbes found in soil, water, and normal microbiota (in some animals). They move by cilia, flagella, or pseudopods.Trophozoite: feeding and growing stage (feed on bacteria and small particulate nutrients).Reproduction: Reproduce asexually by:Binary FissionBuddingSchizogonyConjugationCyst: a protective capsule produced by some protozoa that provides protection during adverse environmental conditions. Enables parasitic protozoa to survive outside hosts.Medically Important ProtozoaTrichomonas vaginalis: lack mitochondria; causes trichomoniasis in humans; does not have a cyst stage, therefore it must be transferred from host to host quickly; found in the vagina and the male urinary tract; transmitted sexually, or by toilet facilities/towels.Giardia lamblia: lack mitochondria; found in small intestines of humans and other mammals; causes water-borne giardiasis (beaver fever). Transmission: is excreted as a cyst, meaning is survives in the environment before being ingested by the next host Transmitted by contaminated water supplies. Stomach acid caused the release of the trophozoite from the cyst which then attaches to the intestinal wall using a ventral sucker. Symptoms: include diarrhea, malaise, nausea, flatulence, weakness, weight loss, and abdominal cramps.Treatment: Metronidazole, ORTDiagnosis: microscopic identification of cysts in feces.String Test: a gelatin capsule containing fine string is swallowed. One end of the string is taped to the cheek. The capsule dissolves; weighted rubber bag enter the upper bowel. String and bag are drawn up after a few hours.ELISA: detection of Giardia antigens.Prevention: filtering or boiling water (cysts resistant to chlorine)Entamoeba histolytica: moves by extending pseudopods and is found in the human intestine. Causes amoebic dysentery (water-borne, transmitted between people through ingestion of cysts in excreted feces).Plasmodium: causes malaria; the mature form is not motile; obligate intracellular parasite. There are 300-500 million new cases of malaria and 2-4 million deaths annually. The complex life cycle makes it difficult to develop a vaccine. Symptoms include fever, chills, headache, vomiting at 2-3 day intervals, and release of merozoites. Diagnosed by microscopic observation of blood smears for presence of Plasmodium. Bed nets are used preventatively.Life Cycle: has a complex life cycle; the definitive host (anopheles mosquito) harbours the sexually-reproducing stage and the intermediate host (human) harbours the asexually reproducing stage.Toxoplasma gondii: life cycle involves domestic cats; tophozoites (tachyzoite) reproduce sexually in intestinal tract of infected cats. Ooxysts (containing 8 sporozoites) are excreted in feces and are transmitted via ingestion by humans. Causes toxoplasmosis (mild symptoms in health people. Dangerous in pregnant women (infect the fetus, cause stillbirth, brain damage, vision problems) and in the immunocompromised (confusion, seizures, vision changes, coma, death).30-50% of the population in the US and UK are infected with T- gondii. France may be as high as 80%.It causes rats and mice to become strongly attracted to cats (Fatal Feline Attraction)Infected men tend to have a lower IQ, are more risk-taking, exhibit jealously, and break rules more often.Infected women tend to have a higher a higher IQ, are more friendly, sociable, and promiscuous.Because infected individuals have a tendency to have slower reaction times, toxoplasmosis may have a significant role in car accidients.Trypanosoma cruzi: moves by flagella; causes Chaga’s Disease; transmitted by the kissing bug which bites the face (often near the lips). Can cause congestive heart failure.Where does Charga’s occur?Phases (stages) of the disease?Symptoms at each stage?Trypanosoma brucei gambiense: causes African Sleeping Sickness; transmitted by the testes fly; can invade the CNS, cause fever, headaches, coma, and death. Fatal if left untreated.Anti-Protozoan DrugsChloroquine: treats malaria; inhibits DNA synthesis (red blood cell stage only). Can be used prophylactically as well.Mefloquine (Larium): treats malaria; used in areas where resistance to chloroquine has developed. Can be used prophylactically as well.Metronidazole (Flagyl): widely used; unique in that it acts against both parasitic protozoa and obligately anaerobic bacteria (i.e., Clostridium difficile). Interferes with anaerobic metabolism. Active against Trichomonas vaginalis, Giardia lamblia, and Entamoeba histolytica.Helminths: multicellular, eukaryotic animals; some are free living while others are parasites. Their anatomy and life style are modified for parasitism.Characteristics: parasitic helminths:May lack a digestive system: absorb nutrients from host’s food, body fluids, and tissues.Have a reduced nervous system: do not have to search for food or respond to the environment.Their means of locomotion may be reduced or lacking: do not need to search for a suitable habitat.May have a complex reproductive system: ensures transmission to new hosts.Life Cycle: the adult stage is found in the definitive host, and each larval stage requires an intermediate host.Monecious: both male and female organs are present in the same organisms.Dioecious: separate male and female organisms.Phyla: plathelminthes and nematoda.Platyhelminthes: dorsoventrally flattened animals.Trematodes: flukes; flat, leaf-shaped worms with incomplete digestive systems that absorb nutrient through their outer covering (cuticle). Oral and ventral suckers attach to the host.Schistomiasis: debilitating disease caused by a small fluke (Schistosoma). Results from the release of eggs in a human host; defence reactions in the host lead to local tissue damage (granulomas). Damage to many different organs can occur. Estimated over 250 million people affected worldwide.Cestodes: tapeworms; intestinal parasites. No mouth and no digestive system; absorb nutrients through cuticle.Scolex: head; has suckers and hooks for attachment.Proglottids: body segments, produced by the neck region. Each mature proglottid has male and female reproductive organs. Proglottids furthest from the head contain eggs and shed in the feces. Ingested by grazers, larvae hatch in the intestine, and encyst in the muscle tissue as cysticerci which can be ingested by humans. The scolex attaches to small intestines and start producing proglottids.Taenia saginata: can be 6m long, human is the definitive host and cattle are the intermediate host (transmitted to humans in raw or undercooked beef). Diagnosis based on presence of mature proglottids and eggs in feces. Beef is visibly inspected for presence of cysticerci. Avoid use of untreated human sewage as fertilizer in grazing pastures.Nematoda: round worms; cylindrical, tapered at each end; have a complex digestive system; dioecious. Larvae and/or eggs can be infective.Enterobius vernicularis: eggs are infective; most common helminths infection in North America and Western Europe. Lives in large intestine in humans. Females migrate to the anus to deposit eggs. Eggs can be ingested by another human exposed through contaminated bedding or clothing.Dirofilaria immitis: larvae are infective; heartworm. Larvae spread from host to host by the bite of Aedes mosquito. Primarily affects dogs and cats (definitive host), very rarely in humans. Adult stage found in the heart, can cause death by congestive heart failure.Angiostrongylus vasorum: French Heartworm; dogs in Newfoundland a susceptible. Dogs consume slugs or snails infected with larvae; larvae molt, adult worms end up in the heart. Cannot be passed onto humans.Anti-Helminthic DrugsPraziquantel: broad-spectrum anti-helminthic, good for treating infections caused by flukes and tapeworms.Mebendazole: broad-spectrum, drug of choice for treating helminthic infections, very few side effectsIvermectins: effective for nematodes, mites, ticks, insects; causes paralysis of the worms (mechanisms unknown).Arthropod Vectors: characterized by segmented bodies, hard external skeletons, and jointed legs; some suck blood and transmit microbial diseases (i.e., mosquitoes). Arthropods that carry pathogenic microbes are called vectors. Important arthropod vectors include sucking lice, fleas, true flies, mosquitoes, ticks, mites. Sometimes, vector eradication is used for disease control. ................
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