This list includes 9 Viruses that start with O, from “O’nyong-nyong virus” to “Ovine herpesvirus 2”. These viruses range from human pathogens like O’nyong-nyong to veterinary agents affecting livestock. They are important for diagnosis, public health surveillance, and vaccine research.

Viruses that start with O are virus species and strains whose common names begin with the letter O. One notable example, O’nyong-nyong virus, caused large outbreaks in East Africa and remains important in arbovirus studies.

Below you’ll find the table with Name, Classification, Affects humans?, Symptoms, and Transmission.

Name: The standard virus name used in literature; use it to quickly find the pathogen you need.

Classification: Family and genus information so you can see related viruses and basic taxonomic context.

Affects humans?: A simple Yes or No with a short qualifier (for example, “zoonotic”) to show human relevance.

Symptoms: Common or typical clinical presentations in five to ten words, helping you recognize disease patterns.

Transmission: A concise summary of how the virus spreads, so you can assess risk and common exposure routes.

Viruses that start with O

NameClassificationAffects humans?Transmission
O‘nyong-nyong virusTogaviridae / Alphavirus / O’nyong-nyong virusYes (human-adapted)Mosquito-borne
Oropouche virusPeribunyaviridae / Orthobunyavirus / Oropouche virusYes (zoonotic)Biting midges (Culicoides)
Orf virusPoxviridae / Parapoxvirus / Orf virusYes (zoonotic)Direct contact with animals
Omsk hemorrhagic fever virusFlaviviridae / Flavivirus / Omsk hemorrhagic fever virusYes (zoonotic)Tick-borne; contact exposure
Orungo virusReoviridae / Orbivirus / Orungo virusYes (zoonotic)Mosquito-borne
Orsay virusNodaviridae / Alphanodavirus / Orsay virusNoFecal–oral among nematodes
Ovine herpesvirus 2Herpesviridae / Macavirus / Ovine herpesvirus 2NoRespiratory secretions (sheep to cattle)
Ostreid herpesvirus 1Malacoherpesviridae / Ostreavirus / Ostreid herpesvirus 1NoWaterborne; contact among shellfish
Oryctes rhinoceros nudivirusNudiviridae / Alphanudivirus / Oryctes rhinoceros nudivirusNoBeetle-to-beetle contact

Descriptions

O‘nyong-nyong virus
Alphavirus causing O’nyong-nyong fever: sudden fever, rash, severe joint pain, malaise; humans are main hosts in African outbreaks, transmitted by Anopheles mosquitoes. (ICTV 2023)
Oropouche virus
Causes urban febrile outbreaks in South America; symptoms: fever, headache, myalgia, rash, malaise; reservoirs likely sloths and primates; transmitted by Culicoides midges. (WHO 2022)
Orf virus
Parapoxvirus of sheep and goats causing human localized skin lesions; symptoms: painful pustules, swelling, sometimes fever; zoonotic from handling infected animals and usually self-limited. (CDC 2023)
Omsk hemorrhagic fever virus
Flavivirus causing severe hemorrhagic fever in Western Siberia; symptoms: fever, hemorrhage, headache, neurological symptoms; rodents and ticks are reservoirs; notable morbidity. (WHO 2021)
Orungo virus
African orbivirus associated with human seropositivity and occasional febrile illness; symptoms: fever, headache, myalgia, malaise, rash; transmitted by mosquitoes and infects livestock. (PubMed 2019)
Orsay virus
Naturally infects Caenorhabditis elegans and is a model for RNA virus–host studies; no known human disease; discovered in the wild and characterized in labs. (PubMed 2011)
Ovine herpesvirus 2
Sheep reservoir virus that causes malignant catarrhal fever in cattle—severe mucosal, ocular and systemic disease in susceptible ruminants; not a human pathogen. (ICTV 2023)
Ostreid herpesvirus 1
Major pathogen of Pacific oysters causing mass mortalities in hatcheries and wild stocks; significant economic impact on aquaculture; no human health risk. (ICTV 2022)
Oryctes rhinoceros nudivirus
Nudivirus infecting the coconut rhinoceros beetle, used as a biocontrol agent against this pest; not known to infect humans. (ICTV 2020)
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