There are 46 scientifically recognized viruses that start with the letter “O,” spanning a wide range of hosts including humans, animals, plants, insects, and aquatic species. Many of these viruses are notable for their diverse transmission methods, such as vectors like mosquitoes, ticks, and aphids, or through direct contact and environmental exposure. This variety highlights the complexity of viral ecology and its global impact on health, agriculture, and ecosystems.
Explore the complete alphabetical list below to understand each virus’s classification, host range, symptoms, and transmission routes.
Virus Name This column lists the official name of each virus, providing clear identification.
Family and Genus (Classification) Here you find the taxonomic group the virus belongs to, which helps understand its biological relationships and common traits.
Primary Hosts (Affects humans?) This column specifies whether the virus infects humans, animals, plants, or other organisms, making it easier to assess relevance to public health or agriculture.
Associated Illness/Symptoms Describes typical symptoms or diseases caused by the virus to highlight its impact on hosts.
Transmission Method Details how the virus spreads from one host to another, such as through insect bites, direct contact, or environmental vectors.
Description Provides a brief summary of the virus, including notable features, history, and significance to human health, veterinary medicine, or crop production.
Viruses that start with O
| Viruses | Classification | Affects humans? | Symptoms | Transmission method |
|---|---|---|---|---|
| O‘nyong’nyong virus | Togaviridae, Alphavirus | Yes | Fever, joint pain, rash, swollen lymph nodes | Mosquito bite (Anopheles) |
| Obodhiang virus | Nairoviridae, Orthonairovirus | Unclear/Research Needed | Not well-documented in humans; isolated from ticks. | Tick-borne (Ornithodoros moubata) |
| Oat blue dwarf virus | Luteoviridae, Polerovirus | No (Plant virus) | Stunting, blue-green discoloration, sterility, reduced yield | Aphid vector |
| Oat chlorotic stunt virus | Tombusviridae, Alphacarmovirus | No (Plant virus) | Chlorotic spots, stunting, reduced growth | Soil-borne, possibly mechanically |
| Oat golden stripe virus | Potyviridae, Tritimovirus | No (Plant virus) | Yellow stripes, stunting, necrosis, reduced grain quality | Soil-borne (fungal vector Polymyxa graminis) |
| Oat mosaic virus | Potyviridae, Bymovirus | No (Plant virus) | Mosaic patterns, streaking, stunting, reduced yield | Soil-borne (fungal vector Polymyxa graminis) |
| Oat sterile dwarf virus | Reoviridae, Fijivirus | No (Plant virus) | Stunting, excessive tillering, dark green color, sterility, reduced yield | Planthopper vector |
| Odontoglossum ringspot virus | Tobamoviridae, Tobamovirus | No (Plant virus) | Ring spots, mosaic patterns, necrosis, flower deformation | Mechanical transmission, sap |
| Oita virus | Orthomyxoviridae, Thogotovirus | Unclear/Research Needed | Not well-documented in humans; isolated from ticks. | Tick-borne |
| Okra leaf curl virus | Geminiviridae, Begomovirus | No (Plant virus) | Leaf curling, stunting, yellowing, reduced fruit yield | Whitefly vector |
| Okra mosaic virus | Tymoviridae, Tymovirus | No (Plant virus) | Mosaic patterns, chlorosis, distortion, reduced fruit yield | Mechanical transmission, possibly beetle vectors |
| Olive latent virus 1 | Secoviridae, Nepovirus | No (Plant virus) | Often asymptomatic (latent); can contribute to decline | Mechanical transmission, possibly nematode vector |
| Olive leaf yellowing-associated virus | Closteroviridae, Ampelovirus | No (Plant virus) | Leaf yellowing, decline | Unknown, possibly insect vector |
| Oncorhynchus masou virus | Alloherpesviridae, Cyprinivirus | No (Fish virus) | Necrotic lesions, ascites, high mortality in salmonid fish | Waterborne, direct contact |
| Onion yellow dwarf virus | Potyviridae, Potyvirus | No (Plant virus) | Yellow streaks, curling, stunting, reduced bulb size | Aphid vector |
| Ophioviridae | Family | No (Plant viruses) | Causes mosaic patterns, ringspots, and stunting in plants. | Fungus vector (Olpidium brassicae), mechanical |
| Ophiovirus | Ophioviridae, Genus | No (Plant viruses) | Mosaic patterns, ringspots, stunting, necrosis in plants | Fungus vector (Olpidium brassicae), mechanical |
| Orbivirus | Reoviridae, Genus | Yes (some species) | Varies; fever, headache, muscle pain (humans); fever, hemorrhage, edema (animals) | Arthropod vector (midges, ticks, mosquitoes) |
| Orf virus | Poxviridae, Parapoxvirus | Yes (Zoonotic) | Painful, self-limiting skin lesions (nodules) | Direct contact with infected sheep/goats or contaminated materials |
| Orgyia pseudotsugata nudivirus | Nudiviridae, Alphapolyedrovirus | No (Insect virus) | Lethargy, swelling, liquefaction of internal organs, death | Oral ingestion (contaminates foliage) |
| Ornithodoros moubata tick virus | Nairoviridae, Orthonairovirus | Unclear/Research Needed | Not well-documented; isolated from ticks. | Tick-borne (Ornithodoros moubata) |
| Oropouche orthobunyavirus | Peribunyaviridae, Orthobunyavirus | Yes | Acute febrile illness, headache, muscle pain, joint pain; sometimes meningitis/encephalitis | Midge vector (Culicoides paraensis), also mosquitoes |
| Oryctes rhinoceros nudivirus | Nudiviridae, Alphabaculovirus | No (Insect virus) | Lethargy, loss of appetite, swelling, death in rhinoceros beetles | Oral ingestion, direct contact |
| Orthoavulavirus | Paramyxoviridae, Avulavirinae, Genus | No (Primarily avian, some mammals) | Respiratory, neurological, digestive issues in birds. Newcastle disease in poultry. | Direct contact, airborne, contaminated materials |
| Orthobornavirus | Bornaviridae, Bornavirinae, Genus | Yes (some species) | Neurological disorders, psychiatric symptoms, encephalitis | Unclear, possibly animal contact (e.g., shrews, birds) |
| Orthobunyavirus | Peribunyaviridae, Genus | Yes (many species) | Acute febrile illness, headache, muscle pain, rash, sometimes encephalitis | Mosquitoes or midges |
| Orthohepadnavirus | Hepadnaviridae, Genus | Yes (some species, e.g., Hepatitis B virus) | Hepatitis (inflammation of liver), jaundice, fatigue, abdominal pain; can lead to cirrhosis, liver cancer | Blood, sexual contact, mother-to-child |
| Orthohepeviridae | Hepeviridae, Family | Yes (some species, e.g., Hepatitis E virus) | Hepatitis, jaundice, fatigue, nausea; often self-limiting, but can be severe in pregnant women | Fecal-oral route (contaminated water/food); zoonotic for some types |
| Orthohepevirus | Hepeviridae, Orthohepeviridae, Genus | Yes (some species, e.g., Hepatitis E virus) | Hepatitis, jaundice, fatigue, nausea; often self-limiting, but can be severe in pregnant women | Fecal-oral route (contaminated water/food); zoonotic for some types |
| Orthojongvirus | Rhabdoviridae, Genus | Unclear/Research Needed (Isolated from bats) | Not well-documented in humans; associated with bats. | Likely bat-associated, possibly zoonotic |
| Orthokaryovirus | Bornaviridae, Bornavirinae, Genus (newly proposed) | Unclear/Research Needed | Not well-documented. | Unclear |
| Orthomarburgvirus | Filoviridae, Marburgvirinae, Genus | Yes | Severe viral hemorrhagic fever, sudden onset of fever, severe headache, muscle pain, vomiting, diarrhea, rash, hemorrhage | Direct contact with infected bodily fluids or contaminated objects; zoonotic (bats) |
| Orthomyxoviridae | Family | Yes (e.g., Influenza viruses) | Respiratory illness, fever, cough, sore throat, muscle aches | Airborne (droplets), direct contact |
| Orthoparamyxovirus | Paramyxoviridae, Orthoparamyxovirinae, Genus | Yes (some species, e.g., Mumps virus) | Varies. For humans: fever, headache, malaise, swelling of salivary glands (mumps). Respiratory illness in animals. | Airborne (droplets), direct contact |
| Orthopneumovirus | Pneumoviridae, Genus | Yes (e.g., Respiratory Syncytial Virus – RSV) | Respiratory illness, cough, wheezing, shortness of breath. Especially severe in infants and elderly. | Direct contact, airborne (droplets) |
| Orthopoxvirus | Poxviridae, Chordopoxvirinae, Genus | Yes (e.g., Variola virus – smallpox, Vaccinia virus, Monkeypox virus) | Rash progressing to papules, vesicles, pustules, scabs; fever, headache, body aches | Direct contact with lesions/body fluids, respiratory droplets |
| Orthoreovirus | Reoviridae, Orthoreovirinae, Genus | Yes (some species) | Mild respiratory or gastrointestinal illness in humans; various symptoms in animals. | Fecal-oral, respiratory droplets, possibly contact |
| Ossa virus | Peribunyaviridae, Orthobunyavirus | Unclear/Research Needed (Isolated from bats) | Not well-documented in humans. | Bat-associated; potentially insect-borne |
| Ostreid herpesvirus 1 | Malacoherpesviridae, Ostreavirus | No (Mollusk virus) | High mortality in oysters, especially larvae and juveniles. | Waterborne, direct contact |
| Ourmiavirus | Botourmiaviridae, Ourmiavirinae, Genus | No (Plant virus) | Mosaic, yellowing, stunting in some plant hosts (e.g., melons). | Unknown, possibly fungal vector |
| Ovine adenovirus A | Adenoviridae, Mastadenovirus | No (Sheep virus) | Respiratory and gastrointestinal disease in sheep; lambs more susceptible. | Fecal-oral, respiratory droplets |
| Ovine adenovirus B | Adenoviridae, Mastadenovirus | No (Sheep virus) | Respiratory and gastrointestinal disease in sheep; lambs more susceptible. | Fecal-oral, respiratory droplets |
| Ovine adenovirus D | Adenoviridae, Mastadenovirus | No (Sheep virus) | Respiratory and gastrointestinal disease in sheep; lambs more susceptible. | Fecal-oral, respiratory droplets |
| Ovine astrovirus | Astroviridae, Mamastrovirus | No (Sheep virus) | Diarrhea in lambs; subclinical infections are common. | Fecal-oral route |
| Ovine gammaherpesvirus 2 | Herpesviridae, Macavirus | No (Sheep virus, causes disease in cattle) | In cattle: Malignant Catarrhal Fever (fever, ocular discharge, corneal opacity, erosions of mucous membranes, high mortality). Subclinical in sheep. | Direct contact (shed by sheep, infects cattle) |
| Ovine lentivirus | Retroviridae, Lentivirus | No (Sheep virus) | Chronic progressive diseases in sheep: respiratory (Ovine Pulmonary Adenomatosis), neurological (visna), arthritis, mastitis. | Direct contact, body fluids (e.g., colostrum, milk) |
Descriptions
O‘nyong’nyong virus
This arbovirus, related to Chikungunya, causes fever, severe joint pain, and rash in humans. It was first identified during epidemics in Uganda and Sudan in the 1950s. Spread by Anopheles mosquitoes, it’s an important public health concern in parts of Africa.
Obodhiang virus
Isolated from ticks in Sudan, Obodhiang virus is a less-understood nairovirus. Its potential impact on human health is not clearly established, but it’s part of the broader research on tick-borne pathogens.
Oat blue dwarf virus
This plant virus causes significant damage to oat crops and other cereals, leading to stunting and yield loss. It is transmitted by aphids, which act as vectors, spreading the disease from infected plants to healthy ones in agricultural fields.
Oat chlorotic stunt virus
A plant virus affecting oats, causing chlorotic (yellowing) spots and stunted growth. It is primarily soil-borne, meaning it persists in the soil and can infect plants through their roots, impacting crop health and yield.
Oat golden stripe virus
This plant virus causes distinct yellow stripes on oat leaves, leading to stunted growth and reduced grain quality. It is transmitted through the soil by a fungal vector, impacting cereal crops globally and affecting agricultural productivity.
Oat mosaic virus
Affecting oat crops, this virus causes mosaic patterns and streaking on leaves, leading to stunted growth and reduced yields. It is transmitted by a soil-dwelling fungus, making it a persistent challenge for oat cultivation.
Oat sterile dwarf virus
This plant virus causes severe stunting and sterility in oats, leading to significant yield losses. It is transmitted by planthoppers, which feed on the sap of infected plants and then spread the virus to healthy ones.
Odontoglossum ringspot virus
A common and widespread virus affecting orchids, causing characteristic ringspots, mosaic patterns, and flower deformation. It is highly contagious and easily transmitted mechanically, often through contaminated tools or hands during orchid cultivation.
Oita virus
Oita virus is a tick-borne thogotovirus, initially identified in Japan. Its potential impact on human or animal health is currently not well-characterized, requiring further research to understand its epidemiology and pathogenicity.
Okra leaf curl virus
This plant virus severely impacts okra crops, causing characteristic leaf curling, stunting, and yellowing. Transmitted by whiteflies, it can lead to significant reductions in fruit yield, posing a major challenge for okra cultivation in affected regions.
Okra mosaic virus
Okra mosaic virus causes mosaic patterns and chlorosis on okra leaves, leading to distorted growth and reduced fruit yield. It can be mechanically transmitted and is also potentially spread by beetle vectors, affecting okra production.
Olive latent virus 1
As its name suggests, this virus is often latent, meaning it causes no obvious symptoms in olive trees. However, it can contribute to tree decline, especially when present with other pathogens. Mechanical transmission is a primary mode of spread.
Olive leaf yellowing-associated virus
This virus is associated with yellowing symptoms and general decline in olive trees. While its specific transmission method is still under investigation, it is believed to be spread by an insect vector, contributing to olive grove health issues.
Oncorhynchus masou virus
A highly pathogenic virus affecting salmonid fish, particularly masu salmon, causing severe disease with necrotic lesions and high mortality rates. It spreads through water and direct contact, impacting aquaculture and wild fish populations.
Onion yellow dwarf virus
This plant virus causes significant damage to onion crops, characterized by yellow streaks, leaf curling, and stunted growth, leading to reduced bulb size and yield. It is efficiently transmitted by aphids, making it a widespread problem for onion growers.
Ophioviridae
Ophioviridae is a family of plant viruses known for their filamentous, circular RNA genomes. Members cause diseases in a variety of crops, often transmitted by soil-borne fungi, impacting agricultural productivity worldwide.
Ophiovirus
Ophiovirus is a genus within the Ophioviridae family, comprising several plant viruses. They typically cause distinct foliar symptoms like ringspots and mosaic patterns, often spread through the soil by a fungal vector or mechanical means.
Orbivirus
Orbivirus is a diverse genus of viruses transmitted by arthropods. While many primarily affect animals, causing diseases like Bluetongue, some can cause febrile illness in humans. They are characterized by their segmented, double-stranded RNA genomes.
Orf virus
Orf virus causes a contagious skin disease in sheep and goats, and can be transmitted to humans as a zoonosis. It manifests as a painful, self-limiting nodular lesion, typically on the hands or arms of those in contact with infected animals.
Orgyia pseudotsugata nudivirus
This virus specifically infects the Douglas-fir tussock moth, an insect pest. It causes a fatal disease, leading to lethargy and eventual death of the larvae. It’s often used as a natural biological control agent against these forest pests.
Ornithodoros moubata tick virus
A virus identified in the soft tick Ornithodoros moubata, known to transmit various pathogens. Its pathogenicity and potential impact on human or animal health are still under investigation, highlighting the role of ticks in pathogen circulation.
Oropouche orthobunyavirus
This arbovirus causes Oropouche fever, an acute febrile illness with headache and body aches, primarily in South America. It can lead to large epidemics, transmitted mainly by midges. Cases of meningitis or encephalitis are rare but possible.
Oryctes rhinoceros nudivirus
This virus is a highly effective biological control agent against the coconut rhinoceros beetle, a destructive pest. It causes a fatal disease in the beetle, leading to lethargy and death, helping to protect palm crops globally.
Orthoavulavirus
Orthoavulavirus is a genus of viruses primarily known for infecting birds, notably causing Newcastle disease in poultry, a highly contagious and devastating avian illness. While not typically affecting humans, some strains can cause mild conjunctivitis.
Orthobornavirus
This genus includes bornaviruses that can cause severe neurological and psychiatric disorders in animals and, in rare cases, humans. They are known for infecting the nervous system and are associated with a range of symptoms including encephalitis.
Orthobunyavirus
Orthobunyavirus is a large genus with many species that are significant human pathogens, causing diseases ranging from mild fevers to severe encephalitis. They are primarily transmitted by mosquitoes or midges and are found globally.
Orthohepadnavirus
This genus includes the Human Hepatitis B Virus (HBV), a major global health concern. HBV causes acute and chronic liver infections, which can lead to severe conditions like cirrhosis and liver cancer. It is transmitted through blood and body fluids.
Orthohepeviridae
Orthohepeviridae is a family of viruses, notably including the Hepatitis E virus (HEV), a significant cause of acute viral hepatitis. HEV is mainly transmitted via the fecal-oral route through contaminated water or undercooked meat, causing liver inflammation.
Orthohepevirus
As a genus within the Hepeviridae family, Orthohepevirus includes the Hepatitis E virus (HEV). HEV causes acute hepatitis, primarily through contaminated food and water, posing a risk to public health, especially in developing regions and for vulnerable groups.
Orthojongvirus
Orthojongvirus is a recently identified genus of rhabdoviruses, with members isolated from bats. Its potential to infect humans or other animals is still under investigation, contributing to the growing list of bat-borne viruses being studied.
Orthokaryovirus
Orthokaryovirus is a newly proposed genus of bornaviruses, with limited information available. Research is ongoing to understand its hosts, pathogenicity, and potential impact, adding to the diversity of known bornaviruses.
Orthomarburgvirus
This genus includes Marburg virus, a highly pathogenic agent causing severe viral hemorrhagic fever in humans. It is characterized by high mortality rates and is transmitted through direct contact with bodily fluids, posing a serious public health threat.
Orthomyxoviridae
Orthomyxoviridae is a family of RNA viruses, most famously including influenza viruses (Flu A, B, C). They cause respiratory illness in humans and animals, characterized by seasonal epidemics and occasional pandemics, spread via respiratory droplets.
Orthoparamyxovirus
This genus includes various viruses that cause diseases in humans and animals. Notable members include the Mumps virus, causing swelling of salivary glands in children, and other viruses responsible for respiratory or neurological symptoms.
Orthopneumovirus
Orthopneumovirus includes significant human pathogens like Respiratory Syncytial Virus (RSV), a leading cause of severe lower respiratory tract infections in infants and young children, also affecting older adults and immunocompromised individuals.
Orthopoxvirus
This genus contains several important human pathogens, most notably Variola virus (smallpox), now eradicated, and Monkeypox virus, which causes a rash, fever, and flu-like symptoms. They are known for causing characteristic skin lesions.
Orthoreovirus
Orthoreovirus is a genus of viruses that can infect a wide range of hosts, including humans and various animals. While human infections are often mild, causing respiratory or gastrointestinal symptoms, they are widespread and continue to be studied.
Ossa virus
Ossa virus is an orthobunyavirus identified in bats. Its role in human or animal disease is currently not well-understood, but its presence in bats suggests a potential for zoonotic transmission, warranting further epidemiological study.
Ostreid herpesvirus 1
This herpesvirus is a major pathogen for oysters, causing devastating outbreaks and high mortality rates, particularly in young oysters. It poses a significant threat to aquaculture and the oyster industry worldwide.
Ourmiavirus
Ourmiavirus is a genus of plant viruses, with its most known member affecting melons. It causes symptoms like mosaic patterns and yellowing, impacting crop health. Its transmission mechanism is still under investigation.
Ovine adenovirus A
This adenovirus infects sheep, particularly lambs, causing respiratory and gastrointestinal issues. While it doesn’t affect humans, it is an important pathogen in veterinary medicine, impacting sheep health and productivity.
Ovine adenovirus B
Similar to Ovine adenovirus A, this type also affects sheep, causing respiratory and gastrointestinal diseases. It’s a common pathogen in sheep flocks, especially affecting young animals, but poses no threat to human health.
Ovine adenovirus D
Another variant of adenovirus affecting sheep, Ovine adenovirus D contributes to respiratory and gastrointestinal illnesses in livestock. It is not transmissible to humans and is mainly a concern for sheep farmers.
Ovine astrovirus
Ovine astrovirus is a cause of diarrhea in lambs, particularly young ones, leading to potential economic losses for livestock farmers. It primarily spreads via the fecal-oral route and does not pose a threat to human health.
Ovine gammaherpesvirus 2
This virus is carried latently by sheep without causing disease, but can cause highly fatal Malignant Catarrhal Fever in cattle. It is an important pathogen in mixed-species grazing systems, not affecting humans.
Ovine lentivirus
Ovine lentiviruses cause chronic, progressive diseases in sheep, including forms of pneumonia, neurological disease, and arthritis. These infections are persistent and widespread in sheep flocks, leading to significant economic losses, but do not affect humans.