Questions and Answers
What is the primary form of fungi that consists of filamentous units?
Which of the following molds only exists in the mold form?
What term describes the ability of dimorphic molds to switch between two forms based on temperature?
What is often considered the gold standard for diagnosing fungal infections?
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Which of these fungi is considered endemic to the Southwest US?
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In diagnosing fungal infections, which of the following methods are known to suffer from sensitivity and specificity issues?
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Which type of parasite is Plasmodium classified as?
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Which of the following is NOT a category of parasites?
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What is the primary characteristic that distinguishes helminths from protozoan parasites?
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What is the common name for the disease caused by Coccidioides?
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What are pseudohyphae most commonly associated with?
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Which of the following correctly defines thermal dimorphism?
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What is generally regarded as a limitation of serology in diagnosing fungal infections?
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Which protozoan is primarily responsible for malaria?
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What is an example of a multicellular parasite?
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Which fungi are likely to cause disease when exposed to higher temperatures inside the human body?
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Which of the following correctly categorizes ectoparasites?
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What is a common symptom of the primary infection caused by Coccidioides?
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What is the primary issue with culturing fungal organisms?
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What is a key distinction between protozoan and helminth parasites?
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What type of clinical illness is primarily caused by Rotavirus in children?
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Which virus class is associated with both mosquito transmission and a variety of clinical syndromes?
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What significant risk was identified in the long-term studies of the Rotavirus vaccines?
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Which virus is known for its association with neonatal microcephaly?
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Which viral family includes Poliovirus and Hepatitis A virus?
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What type of virus is known for causing severe gastroenteritis outbreaks commonly referred to as 'cruise-ship' disease?
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Which of the following viruses is transmitted via mosquito and can lead to encephalitis?
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Which HSV variant is most commonly associated with causing cold sores?
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What severe condition can occur due to HSV 2 transmission during birth?
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Which virus reactivates to cause shingles?
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Which immune cells are primarily targeted by Epstein-Barr Virus during infection?
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What is a common outcome of congenital Cytomegalovirus infection in infants?
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What serological response occurs first during an Epstein-Barr Virus infection?
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What is the primary infectious unit of a virus referred to as?
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What type of toxins are secreted by bacteria and categorized based on their toxic effects?
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Which type of virus relies on hijacking the host cell machinery for replication?
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Which category of viral genomes includes both single-stranded and double-stranded forms?
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What is a key aspect of the immune response to viral infections?
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How can viruses contribute to mutation and evolution?
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What is the primary role of positive single-stranded RNA in viral replication?
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Which factor significantly contributes to viral pathogenesis during infection?
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What process allows viruses to evade immune responses by changing their antigenic appearance?
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What role does RNA polymerase play in the replication of negative single-stranded RNA viruses?
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What does the term 'viral quasispecies' refer to?
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What is the function of DNA-dependent RNA polymerase II in DNA viruses?
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Study Notes
Immune System Impacts
- Issues with the innate immune system can stem from impaired anatomical barriers or deficiencies in the adaptive immune system.
- Nutritional status influences immune function, primarily through protein deficiency, which affects T-cell function.
- Insufficient protein leads to increased susceptibility to infections including tuberculosis and disseminated Herpes infections.
- During pregnancy, risk for infections does not increase in the first trimester, but susceptibility rises as pregnancy progresses due to reduced T-cell, natural killer, and B-cell activity.
Co-morbidities and Infections
- Clinical infections often relate to situational factors such as diabetes or the use of immunosuppressive drugs (e.g., corticosteroids, chemotherapy).
- Conditions like surgical incisions or implanted foreign bodies also create infection risk.
Bacterial Characteristics
- Bacteria are classified by shape: spherical (coccus), rod-shaped (bacillus), or curved (spirillum/spirochete/vibrio).
- Bacterial cell walls consist of peptidoglycan, which influences Gram staining properties; Gram-positive bacteria appear purple, while Gram-negative bacteria appear red-pink.
- Bacteria can utilize oxygen, leading to the production of toxic molecules (H2O2, O2-); obligate aerobes need oxygen, whereas microaerophilic bacteria tolerate some oxygen.
Bacterial Pathogenesis and Toxins
- Bacteria produce enzymes (urease, catalase, coagulase) that enhance their pathogenicity.
- Endotoxins are structural components of the bacterial cell wall; lipopolysaccharide (LPS) triggers inflammatory responses.
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Exotoxins are secreted proteins classified as:
- Protein synthesis inhibitors
- Neurotoxins
- Super-antigens
- cAMP inducers
- Cytolysins
Viruses
- Viruses are the smallest (20-300 nm) infectious agents, consisting of nucleic acid (DNA or RNA) encased in a protein shell, sometimes with a lipid envelope.
- Viruses hijack host cell machinery for replication; the infectious unit is termed a virion.
- Viral classification is based on nucleic acid type, capsid symmetry, and presence of an envelope.
Notable Viral Infections
- Measles: Characterized by cough, coryza, conjunctivitis, and a rash; complications include severe CNS disease and SSPE.
- Mumps: Resurgent mainly on college campuses; similar vaccination concerns as measles.
- Ebola and Marburg: Cause hemorrhagic syndromes with high fatality rates and pose risks especially to healthcare workers.
Fungal Infections
- Fungi are eukaryotic with cell walls of polysaccharides and ergosterol; significant targets for antifungal therapies.
- Pathogenic fungi are divided into yeasts (single-celled), dimorphic molds (change morphology based on environment), and monomorphic molds (fixed form).
- Coccidioidomycosis, endemic in the Southwestern US, usually presents as asymptomatic pneumonia; culture and serological tests are essential for diagnosis.
Parasitology
- Parasites, eukaryotic organisms that derive nutrients from hosts, are categorized into protozoan (unicellular), helminths (multicellular), and ectoparasites (arthropods).
- Key differences exist between protozoan and helminthic parasites, reflecting their biological and pathogenic complexities.
Viral Structure and Replication
- DNA can be single-stranded, linear double-stranded, or circular double-stranded.
- Viral replication involves producing structural proteins/enzyme and replicating the viral genome.
- The primary objective of viruses is to synthesize mRNA, with positive single-stranded RNA acting as infectious mRNA, directly translated into proteins.
- Negative single-stranded RNA and double-stranded RNA viruses require viral RNA polymerase for mRNA transcription, while DNA viruses use host DNA-dependent RNA polymerase II.
Pathogenic Factors and Viral Evolution
- Viruses attach to host cells to inject nucleic acids for replication, leading to multiple copies and potential immune responses.
- Immune responses during and after infection are key contributors to viral pathogenesis.
- Antigenic drifting and shifting allow viruses to evade immune responses, due to rapid evolution and high mutation rates during replication.
- Viral quasispecies emerge from variant genomes forming population structures, influenced by mutations, recombination, and reassortment.
DNA Viruses Overview
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Herpes Viruses:
- HSV-1: Causes cold sores and can lead to severe CNS infections like HSV encephalitis.
- HSV-2: Primarily causes genital disease; can lead to severe neonatal infections.
- Varicella-zoster virus: Causes chickenpox and shingles (dermatomal distribution).
- Epstein-Barr Virus: Responsible for infectious mononucleosis, targeting B-lymphocytes; follows a specific serological response pattern.
- Cytomegalovirus: Another cause of mononucleosis, significant congenital infections and hearing loss.
Commonly Relevant Viruses
- Coronaviruses: Known for mild respiratory illnesses and severe diseases like SARS and COVID-19, which emerged in late 2019.
- Influenza Viruses: Types A and B cause severe illness, subject to antigenic drift and shift, leading to annual epidemics.
- Parainfluenza Viruses: Associated with croup; notable for causing severe airway obstruction.
- Respiratory Syncytial Virus (RSV): Major cause of bronchiolitis in infants; monoclonal antibody therapy available.
- Measles Virus: Notable for classic symptoms (cough, coryza, conjunctivitis) and risks of complications like SSPE.
- Mumps Virus: Similar resurgence patterns as measles; vaccine may be ineffective due to waning immunity.
- Ebola and Marburg Viruses: Cause hemorrhagic syndromes with high fatality rates, transmissibility through body fluids.
Fungi Characteristics
- Fungi are eukaryotic, characterized by cell walls containing polysaccharides and ergosterol.
- Pathogenic fungi categorized into yeasts, dimorphic molds, and monomorphic molds.
- Yeasts are unicellular; some can form pseudohyphae (e.g., Candida albicans).
- Dimorphic molds change form based on temperature (environmental vs. human body).
- Coccidioidomycosis (“Valley Fever”) is endemic in the Southwest U.S., often asymptomatic.
Diagnosing Fungal Infections
- Diagnoses rely on culture, smear, histology from biopsies, and serological tests.
- Fungal cultures require specific media, with variable sensitivity and specificity for serology and antigen tests.
Parasitology Basics
- Parasitology studies eukaryotic pathogens distinct from fungi, involving organisms living off hosts.
- Parasites classified into:
- Protozoa (unicellular, e.g., Plasmodium)
- Helminths (multicellular, e.g., flatworms, roundworms)
- Ectoparasites (arthropods, e.g., ticks, lice, fleas)
- Understanding differences between protozoan and helminth parasites is crucial.
Viral Structure and Replication
- DNA can exist in multiple forms: single-stranded, linear double-stranded, or circular double-stranded.
- Viruses replicate through two main processes: production of structural proteins and enzymes, and replication of the viral genome.
- The primary goal of viruses is to generate mRNA for protein synthesis during their replication cycle.
- Positive single-stranded RNA is directly infectious and translated to proteins, while negative single-stranded RNA requires a viral RNA polymerase for transcription.
- DNA viruses use host-cell enzymes (DNA-dependent RNA polymerase II) to produce mRNA.
Viral Pathogenesis
- Viruses attach to host cells, inserting nucleic acids, which can trigger an immune response leading to pathogenesis.
- Antigenic drift and shift allow viruses to evade immune detection by altering their antigenic structure.
- High mutation rates during replication contribute to the formation of viral quasispecies.
- Viral evolution can occur through mutations, recombination, and reassortment.
Bacterial Enzymes and Toxins
- Bacteria produce various enzymes (e.g., urease, catalase, coagulase) that contribute to their pathogenicity.
- Endotoxins are structural components (e.g., lipopolysaccharides) that induce inflammatory responses, potentially leading to shock.
- Exotoxins are secreted by bacteria and classified into categories based on their effects, including:
- Protein synthesis inhibitors
- Neurotoxins
- Super-antigens
- cAMP inducers
- Cytolysins
Characteristics of Viruses
- Viruses are the smallest infectious agents (20-300 nm) and contain either DNA or RNA encased in a protein shell (capsid), which may be surrounded by a lipid envelope.
- Viruses lack the machinery for independent replication and depend entirely on host cells for propagation.
- The basic classification of viruses includes their nucleic acid type (DNA or RNA), capsid symmetry, presence of an envelope, and virion dimensions.
Overview of DNA Viruses
-
Herpes Viruses:
- HSV 1: Commonly causes oral diseases (cold sores) and can lead to encephalitis.
- HSV 2: Primarily causes genital disease and can result in severe neonatal infections.
- Varicella-zoster virus: Causes chickenpox and shingles, with lesions noted in a dermatomal distribution upon reactivation.
- Epstein-Barr Virus: Associated with infectious mononucleosis, targeting B-lymphocytes, with distinct serological responses.
- Cytomegalovirus: Causes infectious mononucleosis and is a leading cause of congenital infections and childhood hearing loss.
Overview of Positive-Strand RNA Viruses
- Rotavirus: Known for severe gastroenteritis in children, associated with vaccines that increased intussusception risk.
- Caliciviruses (noroviruses): Cause gastroenteritis outbreaks, notoriously linked to cruise ships.
- Picornaviruses: Include Poliovirus, Human Rhinovirus (common cold), Hepatitis A (fecal-oral transmission), and Enteroviruses with milder illness profiles.
- Flaviviruses: Include Hepatitis C, Yellow Fever, Dengue, St. Louis Encephalitis, West Nile, and Zika, with many transmitted by mosquitoes and causing various syndromes.
- Togaviruses: Includes Rubella (German Measles), Eastern and Western Equine Encephalitis, and Chikungunya, with several transmitted by mosquitoes, linked to distinct clinical manifestations.
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Description
Explore the intricate relationship between the immune system and various infections in this quiz. Understand how nutritional status, co-morbidities, and bacterial characteristics influence immune function and susceptibility to infections. Delve into the details of innate and adaptive immune responses and their clinical implications.
