Virus

A virus is a microscopic infectious agent that can reproduce only inside a host cell. Viruses infect all types of organisms: from animals and plants, to bacteria and archaea. Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898, more than 5,000 types of virus have been described in detail, although most types of virus remain undiscovered. Viruses are ubiquitous, as they are found in almost every ecosystem on Earth, and are the most abundant type of biological entity on the planet. The study of viruses is known as virology, and is a branch of microbiology.

What is a Virus?

A virus is a small infectious agent that can only replicate inside the cells of another organism.

Virus Infection in Other Species

What are Viral Clades?

Virus Eradication, Extinction, and Elimination Explained

Virus Uses in Virology

Virus Classification

What are Filoviruses?

Antiviral Immunity and COVID-19

Are Viruses a Lifeform?

What Are Giant Viruses?

Virus Microbiology

Virus History

See more featured articles »

What is Vertical Transmission?

Jamestown Canyon Virus: An Emerging Arboviral Threat in Temperate Climates

Virus Purification Methods

Human Diseases Caused by Viruses

Virus Origins

What is the Difference Between Bacteria and Viruses?

What is a Viral Mutation?

Latest Virus News and Research

Hepatitis C infection associated with reduced portal insulin levels

Insulin resistance is a common extrahepatic manifestation of hepatitis C virus (HCV) infection (HCVi), but its mechanism is poorly understood.

28 Apr 2026

Modeling the synergy of maternal screening and newborn HBV vaccination

Hepatitis B virus (HBV) infection acquired at birth or during early infancy can lead to lifelong health complications, including chronic liver disease. Despite longstanding recommendations for prenatal screening, an estimated 12% to 16% of pregnant individuals in the US are not screened for hepatitis B. This gap leaves a portion of newborns at risk for undetected exposure.

28 Apr 2026

WHO simulation tests global response to fictional bacterial pandemic

The World Health Organization (WHO) wrapped up Exercise Polaris II, a 2-day high-level simulation exercise, based around an outbreak of a fictional new bacterium spreading across the world.

27 Apr 2026

Delaying hepatitis B birth vaccines increases infant infection risks

Delaying hepatitis B vaccination after birth increases infections among newborns and decreases their survival rates and quality of life, according to a new Cornell University study.

27 Apr 2026

Did life-saving HIV drugs unintentionally fuel a syphilis comeback?

The introduction of HAART for HIV has coincided with a syphilis resurgence, suggesting unintended public health trade-offs from this medical breakthrough.

27 Apr 2026

Scientists map 239 human-infective RNA viruses to track future outbreak risks

Researchers updated the global catalogue of human-infective RNA viruses to 239 ICTV-recognised species, incorporating taxonomy, discovery dates, locations, genome links, host range, transmissibility, and transmission routes. The dataset shows that most known human-infective RNA viruses remain strictly zoonotic, while only a minority are endemic in humans or capable of epidemic spread.

26 Apr 2026

Engineered cells boost production of gene editing delivery vehicles

Gene editing has emerged as a powerful approach for targeting the genetic causes of disease, but getting the editing machinery into the right cells efficiently, safely, and at the scale needed for therapies remains one of the biggest set of challenges in the field.

25 Apr 2026

Long-term study supports tenofovir alafenamide for chronic hepatitis B

Tenofovir alafenamide (TAF) has demonstrated comparable efficacy to tenofovir disoproxil fumarate (TDF), with improved renal and bone safety, in Chinese participants with chronic hepatitis B enrolled in two Phase 3 trials.

24 Apr 2026

Influenza D shows strong potential to spill over to humans

The influenza D virus that researchers say has been flying under the radar since its detection in animals in 2011 can vigorously make copies of itself in human cells and lung tissue samples, a new study shows.

24 Apr 2026

Nasal memory cells help slow influenza virus at entry

Memory cells in the nose slow the influenza virus as soon as it enters the body. They reduce viral levels and may help protect against more severe illness.

23 Apr 2026

Washington’s hepatitis C elimination initiative improves treatment access, reduces costs

It took less than 22 years after the discovery of the hepatitis C virus (HCV) for a fast-acting, highly effective treatment to become available.

23 Apr 2026

New approach identified for treating infections with Hepatitis E virus

Instead of directly attacking the virus, the compound acts on the host cell and prevents infection.

23 Apr 2026

Astrocytes form complex networks across the mouse brain

Cells long thought to play a secondary role in brain function build their own far-reaching connections, a new study in mice showed. These pathways appear to connect distant regions in ways that have not been mapped before.

23 Apr 2026

Bioengineered chewing gum reduces cancer-linked oral microbes

Researchers led by Henry Daniell of the School of Dental Medicine have shown that extracts from bioengineered chewing gum reduce the levels of three microbes known to be associated with head and neck squamous cell cancer (HNSCC), paving the way for more effective and affordable therapies.

23 Apr 2026

New gene therapy improves hearing in patients with rare genetic deafness

A new international study co-led by investigators from Mass General Brigham and the Eye & ENT Hospital of Fudan University shows that a gene therapy for a rare form of genetic deafness successfully restored hearing in most participants, with results lasting up to 2.5 years.

23 Apr 2026

COVID-19 virus not retained in placenta after maternal recovery

A new Yale study published in JAMA Network Open finds that the virus that causes COVID-19 does not linger in placental tissue weeks to months after a pregnant woman recovers from infection - offering important reassurance for clinicians and patients alike.

22 Apr 2026

Rising rotavirus cases highlight importance of childhood vaccination

With a rising number of rotavirus cases being reported across the country and in New Jersey this spring, experts from Hackensack Meridian Children's Health are urging parents to ensure their children are vaccinated against this common and potentially severe illness.

21 Apr 2026