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 Microbiology

What Are Giant Viruses?

What are Filoviruses?

What is the Difference Between Bacteria and Viruses?

What are Viral Clades?

Virus Origins

Are Viruses a Lifeform?

Jamestown Canyon Virus: An Emerging Arboviral Threat in Temperate Climates

What is a Viral Mutation?

Antiviral Immunity and COVID-19

Human Diseases Caused by Viruses

See more featured articles »

Virus Uses in Virology

Virus Purification Methods

Virus History

What is Vertical Transmission?

Virus Eradication, Extinction, and Elimination Explained

Virus Classification

Virus Infection in Other Species

Latest Virus News and Research

Mammary glands of domesticated livestock and humans can harbor could harbor avian influenza

An ongoing outbreak of highly pathogenic avian influenza has affected more than 184 million domestic poultry since 2022 and, since making the leap to dairy cattle in spring 2024, more than 1,000 milking cow herds.

9 Dec 2025

Study explains why mpox cases can appear weeks after exposure

Mpox virus clade Ib shows a longer and more variable incubation period than previously characterized clades, with symptom onset extending well beyond 21 days in a substantial minority of cases. Incubation varies by transmission route, with shorter intervals after sexual exposure and longer periods following nonsexual community transmission, raising implications for surveillance and postexposure guidance.

9 Dec 2025

Online reference library provides a more accurate picture of drug exposure

Doctors and researchers try to understand what medications a person has taken by asking patients directly or by looking at medical records. But this information is often incomplete.

9 Dec 2025

Early RSV infection turns maternal allergy into a powerful driver of childhood asthma

Early-life RSV infection and parental allergy interact to substantially increase childhood asthma risk, supported by population data from more than 1.5 million children and mechanistic mouse experiments. The study shows that viral infection reprograms neonatal immune responses by altering how maternally transferred allergen-specific antibodies are handled, driving long-term allergic airway disease.

8 Dec 2025

Genome-edited immune cell therapy shows promise for treating aggressive blood cancer

A groundbreaking new treatment using genome-edited immune cells, developed by scientists at UCL (University College London) and Great Ormond Street Hospital (GOSH), has shown promising results in helping children and adults fight a rare and aggressive form of blood cancer called T-cell acute lymphoblastic leukemia (T-ALL).

8 Dec 2025

Older chemical libraries yield new leads for next-generation COVID-19 antivirals

SARS‑CoV‑2, the virus that causes COVID-19, continues to mutate, with some newer strains becoming less responsive to current antiviral treatments like Paxlovid.

8 Dec 2025

Poor dietary iron weakens lung memory T cells after flu infection

Dietary iron deficiency in mice alters lung T cell activation during influenza infection and leads to memory T cells that are present in normal or increased numbers but have impaired antiviral cytokine responses. These functional deficits are most pronounced in lung CD8-positive memory T cells and persist even under optimal recall conditions.

8 Dec 2025

Shingles vaccination is linked to fewer dementia diagnoses and deaths in older adults

A large quasi-experimental study in Wales shows that eligibility for shingles vaccination is linked to fewer new mild cognitive impairment diagnoses and lower dementia-related mortality. Benefits appear strongest in women and are observed at multiple stages of the dementia disease course.

7 Dec 2025

Study reveals how viral social interactions shape resistance to antivirals

Interactions among viruses can help them succeed inside their hosts or impart vulnerabilities that make them easier to treat. Scientists are learning the ways viruses mingle inside the cells they infect, as well as the consequences of their socializing.

5 Dec 2025

Brainwide circuitry mapping reveals how psilocybin drives therapeutic neural rewiring

An international collaboration led by Cornell University researchers used a combination of psilocybin and the rabies virus to map how – and where – the psychedelic compound rewires the connections in the brain.

5 Dec 2025

In RFK Jr.’s upside-down world of vaccines, panel votes to end hepatitis B shot at birth

Recent weeks have brought good news about vaccines, with studies indicating that flu vaccination reduces heart disease, shingles vaccines can prevent or slow dementia, and a single human papilloma virus shot protects a girl from cervical cancer for the rest of her life.

5 Dec 2025

Most Americans still back early hepatitis B vaccination despite policy debate

On December 5, 2025, the Trump administration's Advisory Committee on Immunization Practices (ACIP), whose members were handpicked by Health and Human Services (HHS) Secretary and vaccination critic Robert F. Kennedy Jr., is scheduled to determine whether it should recommend that the Centers for Disease Control and Prevention (CDC) change the recommendation in place since 1991 that newborns be vaccinated against hepatitis B.

5 Dec 2025

Engineered herpes virus activates potent immune responses against glioblastoma

Researchers at Mass General Brigham have modified a herpes simplex virus (HSV-1) that stimulates the immune system to attack glioblastoma cells.

4 Dec 2025

Long-acting HIV treatment could improve outcomes for breastfeeding women

Sujata Tewari, BA, previously of the Medical Practice Evaluation Center (MPEC) at Massachusetts General Hospital, and Andrea L. Ciaranello, MD, MPH, of the MPEC and Department of Medicine at Massachusetts General Hospital, are the lead and senior authors of a paper published in the Journal of Infectious Diseases, “Long-acting antiretroviral therapy for breastfeeding women with HIV experiencing barriers to adherence in Zimbabwe: Modeling clinical impact and cost-effectiveness.

4 Dec 2025

Researchers capture high-resolution footage of flu viruses entering human cells

For the first time, researchers have observed live and in high resolution how influenza viruses infect living cells. This was possible thanks to a new microscopy technique, which could now help to develop antiviral therapies in a more targeted manner.

4 Dec 2025

Common childhood virus linked to bladder cancer later in life

Tackling a common childhood virus could open the door to preventing bladder cancer, according to new research funded by Kidney Research UK and York Against Cancer.

4 Dec 2025

Single-dose dengue vaccine will benefit populations in hard-to-reach regions

A world-first single-dose vaccine against the dengue virus, manufactured and approved for use in Brazil, will especially benefit populations in hard-to-reach regions of the country such as the Amazon, say disease specialists.

4 Dec 2025

Wind-borne mosquitoes carry infectious pathogens for hundreds of miles

High-flying mosquitoes in West Africa are carriers of multiple pathogens, including West Nile virus, highlighting risks in vector-borne disease management.

4 Dec 2025

New rapid test distinguishes real HIV infections from vaccine-related false positives

Since the human immunodeficiency virus (HIV) was identified in 1983, roughly 91.4 million people around the world have contracted the virus and an additional 44.1 million have died from related causes.

3 Dec 2025

Americans trust AMA over CDC on vaccine safety

For decades, health-related statements by major professional health associations such as the American Medical Association (AMA) agreed with those of the Centers for Disease Control and Prevention (CDC) because both relied on the same body of scientific knowledge, much of it funded by the federal health sector.

3 Dec 2025