Comprehensive Virology and Mycology: Virus Structure, Infection, and Fungal Classification

Why are viruses not considered living organisms?

They are obligate intracellular parasites that cannot reproduce independently and are only active inside host cells.

Define a 'virion'.

A complete, infective form of a virus outside a host cell, consisting of a nucleic acid core (RNA or DNA) and a capsid.

What is the function of a viral capsid?

It is a protein matrix shell made of protomers that encloses and protects the viral nucleic acid.

What constitutes a 'nucleocapsid'?

The combination of the viral capsid and the enclosed nucleic acid.

What is the role of protein spikes on a virus?

They facilitate the attachment of the virus to the host cell.

List the four main methods of viral entry into a host cell.

Membrane translocation, genome insertion, membrane fusion, and endocytosis.

What is the primary difference between cytolytic and chronic viral infections?

Cytolytic infections cause host cell death (lysis), while chronic infections involve continuous virus production without cell lysis.

What characterizes a latent viral infection?

The virus remains dormant within cells until reactivated by signals like stress or immunosuppression, subsequently becoming cytolytic or chronic.

What is an 'immortalizing' viral infection?

A persistent infection by tumor viruses that promotes uncontrolled cell growth, contributing to the transformation of cells into cancer.

What are the three general approaches to diagnosing viral infections?

Direct detection of the virus (e.g., PCR, microscopy), virus isolation (e.g., cell culture), and serology (antibody detection).

What are interferons (INF) in the context of viral defense?

They are a natural part of the immediate protective host response elicited upon viral invasion.

What is the 'cytokine storm' associated with severe COVID-19?

An overflow of proinflammatory cytokines (TNF, IL-1beta, and IL-6) that causes fibrotic injury and multiorgan dysfunction.

What is the primary transmission route for Rhinovirus?

Aerosolized droplets and hand-to-upper respiratory tract contact.

What is the major complication associated with Poliovirus infection?

Irreversible paralysis in approximately 1 out of every 200 cases.

What is another name for the Rubella virus?

German measles or 3-day measles.

What is the clinical significance of Rubella during the first trimester of pregnancy?

It can lead to Congenital Rubella Syndrome.

Where does the Herpes Simplex Virus (HSV) establish latency?

In neurons.

How is the Epstein-Barr Virus (EBV) typically transmitted?

Through bodily fluids such as saliva, semen, or blood.

Which viral family does the Influenza virus belong to?

Orthomyxoviridae.

What is the structural classification of Adenovirus?

Naked, icosahedral, dsDNA virus.

What are the two main types of chemotherapeutic agents used against viruses?

Nucleoside analogs and protease inhibitors.

Why do nearly all naked viruses produce acute infections?

Because they cause host cell lysis during replication, leading to rapid transmission to adjacent cells.

What are the common symptoms of COVID-19?

Fever, cough, shortness of breath, fatigue, muscle aches, headache, and loss of taste or smell.

What is the difference between a protomer and a capsid?

A protomer is an individual structural protein unit, while a capsid is the complete shell formed by those protomers.

What is the primary site of infection for the Rhinovirus?

The epithelial cells of the nasal mucosa.

Rotavirus

Ds DNA, Reoviridae family

Norovirus

Ss RNA, caliciviridae family

Papillomaviruses/HPV

Small, nakes, ds DNA, papillomaviruses family

Retrovirus: HIV

Ss RNA, Retroviridae family

Mycology

A branch of microbiology that deals with the study of fungi

Fungus

A non- photosynthetic, eukaryotic organism that lacs chlorophyll and is classified in its own biological kingdom, distinct from both plants and animals

Penicillin

Produced by the sac fungus penicillium, which is used as an antibiotic to fight diseases

Ascomycota

A type of Yeast, which is filamentous; Sexual reproduction in ascus sac

Deuteromycota

No sexual spores

Oomycota

Asexual spore reproduction

Zygomycota

Sexual and asexual reproduction; no septate hyphae; sporangia

Basidiomycota

Sexual reproduction (forms spores) in basidium sac

Asexual reproduction (fungi)

Occurs via budding mainly and production of conidia (spores)

Sexual reproduction (fungi)

Consist of 3 phases: Plasmogamy, karyogamy and meiosis

Yeast

Unicellular, round, oval, elongated; remain yeast form at both room temp and body temp; reproduction: asexually (budding)

Pseudohyphae

Chains of elongated cells

Molds

Filamentous fungi, multicellular, hyphae - branching filaments, septate or aseptate

Mycelium

The hyphae branch out to form a tangled mass of growth

Dimorphic fungi

Multicellular, filamentous at 22C and yeast at 37 C

Mycotoxicosis

Due to toxic metabolites - aflatoxin and ergotoxine

Tinea versicolor

Also called Malassezia furfur; skin infection with hypopigmented or hyperpigmented macular lesions along the trunk of the body

Tinea Pedis

Fungal infection of the feet

Tinea unguium

Fungal infection of the fingernails and toenails and the nail bed

Sporotrichosis

Soil growing fungus; is the causative of lymphocutaneous sporotrichosis

What are the four main categories of pathogenic fungi based on tissue invasion?

Superficial/cutaneous, subcutaneous, systemic, and opportunistic mycoses.

What is mycotoxicosis?

A condition caused by toxic fungal metabolites, such as aflatoxin and ergotoxin.

What type of immune response is primarily associated with fungal infections?

Cell-mediated immunity, specifically delayed-type hypersensitivity and granulomatous responses.

What is the causative agent of Tinea versicolor?

Malassezia furfur.

What are the clinical characteristics of Tinea versicolor?

Hypopigmented or hyperpigmented macular lesions on the trunk, often associated with dandruff and seborrheic dermatitis.

Which fungus causes Tinea nigra?

Hortaea werneckii or Exophiala werneckii.

What is the common name for dermatophytosis?

Ringworm.

Define Tinea pedis.

A fungal infection of the feet, commonly known as athlete's foot.

What is Tinea unguium?

A fungal infection of the fingernails, toenails, and the nail bed.

What is the primary cause of subcutaneous mycoses?

Fungal infection following trauma, such as a thorn prick.

What is the most common form of subcutaneous nodular fungal disease?

Lymphocutaneous sporotrichosis, caused by Sporothrix schenckii.

What are the clinical signs of sporotrichosis?

Erythematous, nodular ascending lesions along the lymphatics, often starting from a thorn prick.

What characterizes chromomycosis?

Infection by dematiaceous (black-brown) fungi resulting in subcutaneous lesions along lymphatics and the presence of giant cells.

What is mycetoma?

A deep tissue fungal infection characterized by swelling and the drainage of pus through sinus tracts.

Which fungi are known to cause eumycotic mycetoma?

Pseudallescheria boydii and Madurella grisea.

Why is Aspergillus considered an opportunistic pathogen?

It typically does not affect individuals with healthy immune systems but can cause invasive disease in immunocompromised populations.

How is Cryptococcus infection typically diagnosed in the lab?

Detection from cerebral spinal fluid using India ink stains.

What is the primary environmental source of Histoplasma?

Soil containing large amounts of bird or bat droppings.

What is a unique morphological characteristic of Blastomyces?

It is a mold in the environment that appears as a yeast when it enters host cells.

What severe complication can arise from Mucor infections?

Necrosis of infected tissue resulting from vascular invasion.

What is the primary predisposing factor for Pneumocystis jiroveci infection?

A weakened immune system, specifically T-cell counts below 200/mm3.

What are the common clinical findings of Pneumocystis pneumonia?

Cysts and bilateral infiltrates in the lungs.

List four major classes or examples of antifungal agents.

Amphotericin B, Azoles, Echinocandins, and Flucytosine.

What is an example of a nutraceutical used as a natural remedy for fungal issues?

Oregano oil.

Decomposers

are fungi that use enzymes to break down and absorb nutrients from nonliving, organic matter such as fallen trees and fruits.

Penicillium digitatum

this decomposes citrus fruits to gain nutrients.

Mutualists

are fungi that form beneficial relationships with other organisms.

Specialized hyphae of mutualists

Many mutualists have specialized hyphae that will tangle together with the roots of a plant for both organisms' benefit.

Mycorrhizae

have hyphae that intertwine with the plant roots.

Function of Mycorrhizae

This fungus helps the plant absorb nutrients by breaking down the nutrients more efficiently than the plant roots can.

Plant benefit from Mycorrhizae

In return, the fungus can stretch its hyphae into the plant root tissues to withdraw energy rich sugars.

Leucoagaricus gongylophorus

Leucoagaricus gongylophorus uses chemical signals to recruit leaf cutter ants.

Leaf cutter ants and Leucoagaricus gongylophorus relationship

These ants will form a supply chain to quickly deliver thousands of leaf fragments to the fungus for food.

Fungus benefit from leaf cutter ants

In return, the fungus produces little baby sized mushrooms to feed the ants.

Predators

are fungi that actively capture prey with their hyphae.

Arthrobotrys

use modified hoops on their filaments to capture nematodes and absorb their tissues.

Parasites

are fungi that feed on other living organisms while keeping them alive temporarily.