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CHAPTER 3 More Medical Microbiology Specialties 3-2 Introduction • Subspecialties of medical microbiology ─Virology ─Mycology ─Parasitology 3-3 Virology • Study of viruses ─Most common infectious agent in humans ─Contains core of genetic material surrounded by a capsid; no organelles ─Obligate parasite; most are destroyed by immune system ─Requires host cell ─Protein coat covering strands of DNA or RNA 3-4 Virus • RNA viruses – For example, influenza, polio, AIDS, rabies • DNA viruses – For example, common cold, cold sores, warts • Transmission – Direct – Indirect (Continues) 3-5 Virus • Signs and symptoms of viral infection ─Low-grade fever, muscle aches, general fatigue ─(or) Asymptomatic • Treatment ─Rest ─Fluids ─Palliative treatment • Prevention ─Vaccines 3-6 Viral Infections • Classified by – Severity and length of time present – Body organs/sites affected • Identification – Cell culture – Direct detection – Multipathogen detection systems – Serodiagnosis 3-7 Antiviral Therapy • • • • Not curative Lessens severity Keeps infection under control Treats viruses, such as – Respiratory syncytial virus (RSV) – Acquired immunodeficiency syndrome (AIDS) – Hepatitis C (HCV) – Severe acute respiratory syndrome (SARS) 3-8 Respiratory Syncytial Virus (RSV) • Causes bronchiolitis and pneumonia • Major cause of acute respiratory disease in children • Treatment – Ribavirin (inhibits essential nucleic acid formation) 3-9 Acquired Immunodeficiency Syndrome (AIDS) • Caused by retrovirus HIV • Diagnosis – CD4 T cell count less than 200 cells/mm³ – Presentation of AIDS-defining diseases • Cannot be cured • Treatment – Three antiretrovirals 3-10 Hepatitis C (HCV) • Usually asymptomatic during acute stage • Usually progresses to chronic Hepatitis C (also may be asymptomatic, and may progress to liver cirrhosis or liver cancer) • Has six genetically distinct types (Genotypes 1–6) • Genotypes 1 and 4 are most difficult to treat 3-11 Severe Acute Respiratory Syndrome (SARS) • Signs and symptoms – Fever – Headache – Body aches – Dry cough • Spread by respiratory droplets • Fatal for 30% of those infected 3-12 Ebola • Signs and symptoms – Fever, sore throat, muscle pain, headache (within 2–21 days after contracting the virus) – Followed by severe vomiting, diarrhea, rash – May exhibit internal and external bleeding (Continues) 3-13 Ebola • High mortality rate due to – Dehydration – Electrolyte imbalance – Kidney or liver failure – Hypotension • Supportive treatment includes – Oral rehydration – IV fluids 3-14 Parasitology • Study of parasites – Unicellular or multicellular – Live in host at host’s expense – Exist in many body areas (e.g., blood, skin) • Three main classes – Protozoa – Helminths – Ectoparasites 3-15 Parasites • Identified by – Name – Specific state of development • • • • • Trophozoite (feeding and growing) Cyst (dormant) Ova (eggs) Larvae (immature) Adult (mature) 3-16 Protozoa • Microscopic • Most favorable host: humans • Infestation may be caused by – Ingestion of contaminated water – Penetration through skin – Insect bites • Symptoms vary according to type 3-17 Giardia • Common parasite in GI tract • Transmission from people, food, or water • Signs and symptoms – Watery, foul-smelling diarrhea – Nausea, vomiting, abdominal gas, cramps – (or) Asymptomatic • Treatment – Fluids, electrolytes, antimicrobials 3-18 Malaria • Caused by mosquito bite (Plasmodium) • Signs and symptoms – Mimic flu: fever, chills – Death if untreated • Diagnosis – Microscopic exam of blood of infected patient • Treatment varies with species and geographical area where acquired 3-19 Helminths • Viewed upon gross examination • Survive in nature or in humans • Three main groups – Tapeworms – Flukes – Roundworms (hookworms and pinworms) 3-20 Tapeworm • Acquired from ingesting improperly cooked beef or pork • Signs and symptoms – Abdominal pain – Nausea – Loss of appetite – Some types cause blindness or seizures – (or) Asymptomatic • Treatment: praziquantel or niclosamide 3-21 Hookworm • Acquired by walking barefoot in fecally contaminated soil • Reside in host’s GI tract • Signs and symptoms: nausea, vomiting, diarrhea, abdominal pain, possibly nutritional deficiencies, anemia • Treatment: albendazole or mebendazole 3-22 Pinworms • Small, round worms • Most often in children and institutionalized individuals • Signs and symptoms: anal itching more intense at night • Diagnosed by “tape test” • Treatment: albendazole, mebendazole, (require prescriptions), pyrantel pamoate, (available OTC) 3-23 Ectoparasites • External parasites with hard, segmented bodies • Feed on blood from humans/animals • Transmission of disease occurs with – Fleas, ticks, mosquitoes • No transmission of disease – Bed bugs (present economic and public health consequences) 3-24 Mycology • Study of fungi – Reproduced by spores (used in identification) – No chlorophyll – For example, mushrooms, yeast, molds – Have ergosterol instead of cholesterol as in human cells – Destruction of body’s natural flora through use of antibiotics and steroids may lead to opportunistic fungal infection 3-25 Fungi • Most susceptible: immunocompromised patient • Identification: microscopic observation or biochemical reaction testing • Transmission: inhalation or ingestion of spores, or through non-intact skin • Most are opportunistic in occurrence • Signs and symptoms vary according to location on host 3-26 Yeasts • • • • Single-celled microorganisms Cannot manufacture own nutrients Thrive on organic matter in living host Candida: most common in humans – May cause local mucous membrane infection (or) life-threatening septicemia (or) multisystem organ infection 3-27 Prions • • • • Lack nucleic acid Resistant to routine sterilization technique Infect nervous system Five related diseases in humans – Creutzfeldt-Jakob Disease, Variant Creutzfeldt-Jakob Disease, GerstmannStraussler-Scheinker Syndrome, Fatal Familial Insomnia, Kuru 3-28 Creutzfeldt-Jakob Disease (CJD) • Worldwide disease; usually fatal within one year of diagnosis • Signs and symptoms – Dementia – Difficult walking/balance – Myoclonus • Diagnosis – Based on signs and symptoms; definitive diagnosis made from examination of brain tissue sample 3-29 Summary • Viral species and parasites require host • Virology: study of viruses – Virus: infectious particles containing genetic material surrounded by a capsid • Examples: RSV, AIDS, SARS • Parasitology: study of parasites – Parasite: unicellular or multicellular organism living in/on host at host’s expense • Examples: protozoa, malaria, pinworms (Continues) 3-30 Summary • Mycology: study of fungi – Fungi: reproduced by spores, have a rigid cell wall and no chlorophyll • Examples: yeasts, prions, CJD – Fungal infection likely to develop in immunocompromised patient 3-31