Transcript Guidelines for Preparing PowerPoint® Presentations

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