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 Uses in Virology

Are Viruses a Lifeform?

Virus Microbiology

Virus History

What are Viral Clades?

What Are Giant Viruses?

Virus Eradication, Extinction, and Elimination Explained

Virus Infection in Other Species

What is Vertical Transmission?

What is the Difference Between Bacteria and Viruses?

Jamestown Canyon Virus: An Emerging Arboviral Threat in Temperate Climates

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Virus Origins

Antiviral Immunity and COVID-19

Human Diseases Caused by Viruses

What are Filoviruses?

Virus Purification Methods

What is a Viral Mutation?

Virus Classification

Latest Virus News and Research

Azithromycin fails to improve severe wheezing in preschool children

A study led by researchers at the University of Arizona College of Medicine – Tucson showed that giving the antibiotic azithromycin did not help preschool children seen in the hospital emergency room with bouts of severe wheezing.

18 May 2026

DNA-guided CRISPR system targets RNA and expands Cas12 beyond gene editing

Researchers developed ΨDNA, a DNA-based CRISPR guide that allows Cas12 enzymes to target RNA with high specificity while retaining compatibility with DNA-editing workflows. The platform detected HCV RNA in clinical samples and enabled programmable RNA knockdown, multiplex targeting, and RNA modification in human cells.

18 May 2026

Bundibugyo virus outbreak triggers international public health emergency declaration

Pursuant to paragraph 2 of Article 12 - Determination of a public health emergency of international concern, including a pandemic emergency of the International Health Regulations (2005) (IHR), the Director-General of the World Health Organization (WHO), after having consulted the States Parties where the event is known to be currently occurring, is hereby determining that the Ebola disease caused by Bundibugyo virus in the Democratic Republic of the Congo and Uganda constitutes a public health emergency of international concern (PHEIC), but does not meet the criteria of pandemic emergency, as defined in the IHR.

18 May 2026

Health experts outline symptoms and risks of shipboard hantavirus

It's one of the cruisegoer's biggest fears: a contagious disease outbreak at sea.

18 May 2026

Scientists call for innovative strategies to combat tuberculosis superspreaders

Superspreading became a familiar concept to many during the COVID-19 pandemic. Prior studies examining infectious disease epidemics, including those on COVID-19, have found that some individuals are much more likely to transmit infections to other people. Superspreading, when one person with an infection passes it to an unusually large number of other people, is a key feature of tuberculosis (TB) epidemiology.

15 May 2026

Genetic mapping in wastewater sets a new standard for pathogen surveillance

Tracking the genetic diversity of SARS-CoV-2 in wastewater, rather than just viral abundance, dramatically improves the ability to monitor and predict COVID-19 outbreaks, researchers report. Their study suggests that the new approach to wastewater pathogen surveillance could serve as a powerful predictive tool for public health, providing earlier and more accurate insight into emerging waves of infection.

15 May 2026

Asymptomatic transmission plays a prominent role in mpox infection patterns

A Kaiser Permanente study of nearly 8,000 men shows that in mid- to late 2024, mpox was far more common among men who have sex with men than previously thought. Individuals without symptoms accounted for most infections and likely played a prominent role in transmission, contrary to prior assumptions that people had to be symptomatic to spread the disease.

15 May 2026

How Andes virus super-spreaders reveal the risk behind the MV Hondius hantavirus cluster

A 2020 NEJM study of the 2018 to 2019 Epuyén outbreak showed that Andes virus spread from one zoonotic introduction into four generations of human infection, causing 34 cases and 11 deaths. The findings are newly relevant after WHO reported an ANDV cluster linked to the MV Hondius cruise ship, where close indoor exposure may have enabled onboard human-to-human transmission.

14 May 2026

Scientists develop a dual action strategy to destabilize the COVID virus

An unprecedented study led by researchers at the University of Malaga proposes a new antiviral strategy against SARS-CoV-2 -the virus responsible for causing COVID-19 disease- based on a treatment that combines two complementary approaches, capable of attacking the virus simultaneously, forcing its instability and hindering its ability to adapt.

14 May 2026

New imaging technique maps 38000 liver cells to solve fibrosis

The liver is often called a "silent organ," as it can sustain significant damage without obvious symptoms. But when injury is prolonged, whether from alcohol, poor diet, or chronic hepatitis virus infection, it triggers fibrosis: a progressive hardening and scarring of liver tissue.

14 May 2026

Turning the flu virus into a powerful tool to fight cancer

A recent Views & Comments article published in Engineering highlights advances in repurposing influenza viruses as flexible therapeutic platforms for infectious diseases and cancer, driven by progress in reverse genetics and viral vector engineering.

14 May 2026

Experts urge WHO to strengthen airborne virus precautionary measures

With three people dead and 11 cases from the recent hantavirus outbreak on a cruise ship, UMD's internationally renowned expert on airborne viruses, Dr. Don Milton, joins public health colleagues in an opinion piece in the British Medical Journal (BMJ) calling on the World Health Organization (WHO) to shift its default response to emerging respiratory viruses.

13 May 2026

Immune cell discovery reveals new pathway for hepatitis B treatment

Fifteen years ago, doctors in Europe noticed a remarkable thing happening in people with chronic hepatitis B infections. When patients went off their medications, the virus started to come back - and then some of the patients were cured.

13 May 2026

Wastewater monitoring may predict influenza outbreaks one week earlier

Seasonal influenza can spread rapidly, and timely information on rising cases is essential for public health decisions and healthcare resource planning.

13 May 2026

Study reveals hidden airborne infection pathways in multi-family buildings

Airborne diseases like measles, influenza and COVID-19 can easily spread between units in multi-family buildings via a type of bathroom ventilation system commonly used around the world, new research suggests.

13 May 2026

Why is the US falling behind other high-income nations on survival?

A JAMA Network Open study found that the US recorded 12.7 million excess deaths compared with 17 peer high-income countries between 1999 and 2022. Circulatory and metabolic diseases drove much of the burden, while drug poisonings, alcohol-related deaths, and suicide sharply widened the gap among younger Americans.

12 May 2026