Viruses

Viruses

Noncellular agents that cannot live or reproduce on their own; typically smaller than 200 nanometers.

Capsid

The protein shell of a virus that can be naked (no outer membrane) or enveloped (with a membrane derived from the host cell).

Icosahedral

A virus shape characterized by 20 triangular faces, as seen in adenoviruses.

Helical

A rod-shaped virus morphology with a spiral protein coat, exemplified by the tobacco mosaic virus.

Bacteriophage

Viruses that infect bacteria, attaching to receptors and injecting genetic material.

Baltimore Classification

A system used to classify viruses based on their type of genetic material, including groups like double-stranded DNA and positive-sense single-stranded RNA.

Viroids

Small, naked RNA strands that cause diseases in plants.

Prions

Misfolded proteins that lead to brain diseases such as Mad Cow and Kuru.

Zika Virus

A virus spread by Aedes mosquitoes, associated with symptoms like fever and rash, and significant birth defects.

COVID-19 (SARS-CoV-2)

An infectious disease caused by a coronavirus, with symptoms including fever and cough, and spread primarily through respiratory droplets.

Emerging Diseases

New or rapidly spreading diseases, such as AIDS and Ebola.

Re-emerging Diseases

Diseases that were previously controlled but are now coming back, like tuberculosis and malaria.

Treatment for Viral Infections

Cannot be treated with antibiotics; prevention relies on vaccines and antiviral drugs.

Influenza Symptoms

Common symptoms of the flu include fever, cough, muscle aches, and a runny nose.

Viral Entry Points

Common points of entry for viruses include skin, respiratory tract, digestive tract, and sexual contact.

Infectiousness ($R_0$)

A measure of how contagious a disease is; for example, COVID-19 has an $R_0$ of approximately 2

–5.7.

Complex Viruses

Viruses with intricate structures that do not fit into helical or icosahedral categories, often having a head-tail morphology like some bacteriophages.

Antiviral Drugs

Medications that target specific steps in the viral life cycle to inhibit replication, often by interfering with viral enzymes or entry/exit mechanisms.

Nucleic Acid Core

The genetic material of a virus, consisting of either DNA or RNA, which can be single or double-stranded, and linear or circular.

Spherical Viruses

Viruses that appear round due to the presence of an outer membrane (envelope), as seen in the influenza virus.

Viral Metabolism

Viruses lack their own metabolism and cannot respond to stimuli, relying entirely on host cells for survival and reproduction.

Viral Evolution

Viruses evolve rapidly through mutations and natural selection, leading to new strains and drug resistance.

HIV Transmission Methods

HIV is primarily transmitted through sexual contact, blood transfusion, shared needles, and from mother to child.

Influenza Types

The four types of influenza viruses are A, B (seasonal), C, and D.

Influenza Surface Proteins

The key surface proteins on influenza viruses are Hemagglutinin (H) and Neuraminidase (N), which are critical for infection.

COVID-19 Origin

COVID-19, caused by SARS-CoV-2, likely originated from bats and was first identified in Wuhan, China, in 2019.

Naked Viral Capsid

A viral protein shell that does not have an outer lipid membrane.

Enveloped Viral Capsid

A viral protein shell surrounded by an outer lipid membrane derived from the host cell during budding.

Baltimore Classification Group I

Viruses with a double-stranded DNA genome.

Baltimore Classification Group II

Viruses with a single-stranded DNA genome.

Baltimore Classification Group III

Viruses with a double-stranded RNA genome.

Baltimore Classification Group IV

Viruses with a positive-sense single-stranded RNA genome, which can be directly translated into protein.

Baltimore Classification Group V

Viruses with a negative-sense single-stranded RNA genome, which must be converted to positive-sense RNA before translation.

Baltimore Classification Group VI

Viruses with a single-stranded RNA genome that use reverse transcriptase to synthesize DNA from their RNA template.

Baltimore Classification Group VII

Viruses with a double-stranded DNA genome that replicate through an RNA intermediate using reverse transcriptase.

Obligate Intracellular Parasitism

The characteristic of viruses that they can only replicate inside living host cells, as they lack the cellular machinery for self-reproduction.

Bacteriophage Attachment

The initial step where bacteriophages bind specifically to receptors on the surface of bacterial cells.

Viral Evasion of Immune Detection

Mechanisms by which viruses, including bacteriophages, avoid being recognized and eliminated by the host's immune system.

Viral Vaccines

Biological preparations that provide active acquired immunity to a particular viral disease by stimulating the immune system to produce antibodies.

HIV/AIDS Global Impact

As of 2023, approximately 39 million people globally were living with HIV, with 1.2 million in the U.S. and 65% of new cases in Sub-Saharan Africa.

Common Cold (Viral Illness)

A common respiratory tract infection primarily caused by rhinoviruses, leading to symptoms like runny nose, sneezing, and sore throat.

Genital Herpes

A sexually transmitted infection caused by the herpes simplex virus (HSV), characterized by painful blisters and ulcers on the genitals.

Viral Warts

Small, rough skin growths caused by the human papillomavirus (HPV).

Shingles

A painful skin rash with blisters, caused by the reactivation of the varicella-zoster virus (the same virus that causes chickenpox).

Viral Gastroenteritis

An inflammation of the stomach and intestines caused by various viruses, leading to symptoms such as diarrhea, vomiting, and abdominal cramps.

Rabies

A deadly viral disease that infects the central nervous system, typically transmitted to humans through animal bites.

Polio

A highly infectious viral disease that can cause paralysis, primarily affecting young children, but has been largely eradicated through vaccination efforts.

Measles

A highly contagious viral disease characterized by fever, cough, runny nose, red eyes, and a widespread rash.

Mumps

A viral disease characterized by painful swelling of the salivary glands, particularly the parotid glands.

Chickenpox

A highly contagious viral infection causing an itchy, blister-like rash all over the body.

Hepatitis (Viral)

An inflammation of the liver caused by various hepatitis viruses (e.g., A, B, C, D, E).

Viral-Induced Cancers

Cancers caused or promoted by certain viruses, such as human papillomavirus (HPV) leading to cervical cancer, or hepatitis viruses leading to liver cancer.

Mononucleosis

An infectious disease typically caused by the Epstein-Barr virus (EBV), characterized by fever, sore throat, and swollen lymph glands.

SARS (Severe Acute Respiratory Syndrome)

An emerging viral respiratory illness caused by the SARS-CoV coronavirus, which first appeared in 2002.

Ebola Virus Disease

A severe, often fatal, emerging viral hemorrhagic fever in humans and other primates, caused by ebolaviruses.

Hantavirus Pulmonary Syndrome

A severe and sometimes fatal respiratory disease in humans caused by hantaviruses, typically transmitted through rodent droppings.

Chikungunya Fever

An emerging viral disease transmitted by Aedes mosquitoes, causing fever and severe joint pain, often debilitating.

Dengue Fever

A re-emerging mosquito-borne viral infection causing severe flu-like illness, and sometimes a potentially lethal complication called severe dengue.

Influenza-Associated Cardiac Risk

The statistically higher chance of experiencing a heart attack or other cardiac events following an influenza infection.

COVID-19 Vaccination Recommendation

As of the 2024–25 season, COVID-19 vaccination is recommended for everyone 6 months and older.