Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Venezuelan equine encephalitis



Venezuelan equine encephalitis


  • Last modified
  • 03 September 2020
  • Datasheet Type(s)
  • Animal Disease
  • Preferred Scientific Name
  • Venezuelan equine encephalitis
  • Overview
  • Venezuelan equine encephalitis virus (VEEV) is a mosquito-borne alphavirus capable of causing large outbreaks of encephalitis in humans and equids. VEEV has caused periodic outbreaks of febrile and neurological disease, primarily in Latin America...

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Preferred Scientific Name

  • Venezuelan equine encephalitis

International Common Names

  • English: Venezuelan equine encephalomyelitis


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Venezuelan equine encephalitis virus (VEEV) is a mosquito-borne alphavirus capable of causing large outbreaks of encephalitis in humans and equids. VEEV has caused periodic outbreaks of febrile and neurological disease, primarily in Latin America since the 1930s. Many outbreaks have involved tens to hundreds of thousands of equine and human cases, have spread over large geographical regions, and have lasted up to several years (Weaver et al., 2004). VEEV is also a highly developed biological weapon amenable to use in warfare or terrorism (Hawley and Eitzen, 2001; Reichert et al., 2009).

Venezuelan equine encephalitis (or encephalomyelitis) is on the list of diseases notifiable to the World Organisation for Animal Health (OIE).

Host Animals

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Animal nameContextLife stageSystem
EquusDomesticated host; Wild host
Equus asinus (donkeys)
Equus caballus (horses)Domesticated host
Homo sapiens

Hosts/Species Affected

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VEEV causes disease in horses, donkeys, mules and man.


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VEE complex viruses are endemic to South and Central America, Mexico, and Florida (Weaver et al., 2004). Epizootics in North America have been limited (OIE, 2020). For the most recent, detailed information on the occurrence of this disease worldwide, see the OIE World Animal Health Information Database (WAHID) interface.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Last updated: 14 Dec 2021
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes


AlgeriaAbsent, No presence record(s)Jul-Dec-2019
AngolaAbsent, No presence record(s)Jul-Dec-2018
BeninAbsent, No presence record(s)
BotswanaAbsent, No presence record(s)Jul-Dec-2018
Burkina FasoAbsent, No presence record(s)Jul-Dec-2019
BurundiAbsent, No presence record(s)Jul-Dec-2018
Cabo VerdeAbsent, No presence record(s)Jul-Dec-2019
CameroonAbsent, No presence record(s)
Central African RepublicAbsent, No presence record(s)Jul-Dec-2019
ChadAbsent, No presence record(s)Jul-Dec-2019
Congo, Democratic Republic of theAbsent, No presence record(s)
Congo, Republic of theAbsent, No presence record(s)Jan-Jun-2019
Côte d'IvoireAbsent, No presence record(s)Jul-Dec-2019
DjiboutiAbsent, No presence record(s)Jul-Dec-2019
EgyptAbsent, No presence record(s)Jul-Dec-2019
EswatiniAbsent, No presence record(s)Jul-Dec-2019
EthiopiaAbsent, No presence record(s)Jul-Dec-2018
GhanaAbsent, No presence record(s)Jan-Jun-2019
GuineaAbsent, No presence record(s)Jan-Jun-2019
KenyaAbsent, No presence record(s)Jul-Dec-2019
LesothoAbsent, No presence record(s)Jan-Jun-2020
LibyaAbsent, No presence record(s)
MadagascarAbsent, No presence record(s)Jan-Jun-2019
MalawiAbsent, No presence record(s)Jul-Dec-2018
MaliAbsent, No presence record(s)Jul-Dec-2019
MauritaniaAbsent, No presence record(s)Jul-Dec-2018
MauritiusAbsent, No presence record(s)Jul-Dec-2019
MayotteAbsent, No presence record(s)Jul-Dec-2019
MoroccoAbsent, No presence record(s)Jul-Dec-2019
NamibiaAbsent, No presence record(s)Jul-Dec-2019
NigerAbsent, No presence record(s)Jul-Dec-2019
NigeriaAbsent, No presence record(s)Jul-Dec-2019
RéunionAbsent, No presence record(s)Jul-Dec-2019
RwandaAbsent, No presence record(s)Jul-Dec-2018
Saint HelenaAbsent, No presence record(s)Jan-Jun-2019
São Tomé and PríncipeAbsent, No presence record(s)Jul-Dec-2019
SenegalAbsent, No presence record(s)Jul-Dec-2019
SeychellesAbsent, No presence record(s)Jul-Dec-2018
Sierra LeoneAbsent, No presence record(s)Jan-Jun-2018
South AfricaAbsent, No presence record(s)Jul-Dec-2019
SudanAbsent, No presence record(s)Jul-Dec-2019
TanzaniaAbsent, No presence record(s)Jul-Dec-2019
TogoAbsent, No presence record(s)Jul-Dec-2019
TunisiaAbsent, No presence record(s)Jul-Dec-2019
UgandaAbsent, No presence record(s)Jul-Dec-2019
ZambiaAbsent, No presence record(s)Jul-Dec-2018
ZimbabweAbsent, No presence record(s)Jul-Dec-2019


AfghanistanAbsent, No presence record(s)Jul-Dec-2019
ArmeniaAbsent, No presence record(s)Jul-Dec-2019
AzerbaijanAbsent, No presence record(s)Jul-Dec-2019
BahrainAbsent, No presence record(s)Jul-Dec-2020
BangladeshAbsent, No presence record(s)Jan-Jun-2020
BhutanAbsent, No presence record(s)Jan-Jun-2020
BruneiAbsent, No presence record(s)Jul-Dec-2019
CambodiaAbsent, No presence record(s)Jul-Dec-2019
ChinaAbsent, No presence record(s)Jul-Dec-2018
GeorgiaAbsent, No presence record(s)Jul-Dec-2019
Hong KongAbsent, No presence record(s)Jul-Dec-2019
IndiaAbsent, No presence record(s)Jan-Jun-2019
IndonesiaAbsent, No presence record(s)Jul-Dec-2019
IranAbsent, No presence record(s)Jan-Jun-2019
IsraelAbsent, No presence record(s)Jul-Dec-2020
JapanAbsent, No presence record(s)Jan-Jun-2020
JordanAbsent, No presence record(s)Jul-Dec-2018
KazakhstanAbsent, No presence record(s)Jul-Dec-2019
KuwaitAbsent, No presence record(s)Jan-Jun-2019
KyrgyzstanAbsent, No presence record(s)Jan-Jun-2019
LaosAbsent, No presence record(s)Jan-Jun-2019
LebanonAbsent, No presence record(s)Jul-Dec-2019
MalaysiaAbsent, No presence record(s)Jan-Jun-2019
-Peninsular MalaysiaAbsent, No presence record(s)
-SabahAbsent, No presence record(s)
MaldivesAbsent, No presence record(s)Jan-Jun-2019
MongoliaAbsent, No presence record(s)Jan-Jun-2019
MyanmarAbsent, No presence record(s)Jul-Dec-2019
NepalAbsent, No presence record(s)Jul-Dec-2019
North KoreaAbsent, No presence record(s)
PakistanAbsent, No presence record(s)Jan-Jun-2020
PhilippinesAbsent, No presence record(s)Jul-Dec-2019
QatarAbsent, No presence record(s)Jul-Dec-2019
Saudi ArabiaAbsent, No presence record(s)Jan-Jun-2020
SingaporeAbsent, No presence record(s)Jul-Dec-2019
South KoreaAbsent, No presence record(s)Jul-Dec-2019
Sri LankaAbsent, No presence record(s)Jul-Dec-2018
SyriaAbsent, No presence record(s)Jul-Dec-2019
TaiwanAbsent, No presence record(s)Jul-Dec-2019
TurkeyAbsent, No presence record(s)Jul-Dec-2019
United Arab EmiratesAbsent, No presence record(s)Jul-Dec-2020
UzbekistanAbsent, No presence record(s)Jul-Dec-2019
VietnamAbsent, No presence record(s)Jul-Dec-2019
YemenAbsent, No presence record(s)Jan-Jun-2020


AndorraAbsent, No presence record(s)Jul-Dec-2019
AustriaAbsent, No presence record(s)Jul-Dec-2019
BelarusAbsent, No presence record(s)Jul-Dec-2019
BelgiumAbsent, No presence record(s)Jul-Dec-2019
Bosnia and HerzegovinaAbsent, No presence record(s)Jul-Dec-2019
BulgariaAbsent, No presence record(s)Jan-Jun-2019
CroatiaAbsent, No presence record(s)Jul-Dec-2019
CyprusAbsent, No presence record(s)Jul-Dec-2019
CzechiaAbsent, No presence record(s)Jul-Dec-2019
DenmarkAbsent, No presence record(s)Jan-Jun-2019
EstoniaAbsent, No presence record(s)Jul-Dec-2019
Faroe IslandsAbsent, No presence record(s)Jul-Dec-2018
FinlandAbsent, No presence record(s)Jul-Dec-2019
FranceAbsent, No presence record(s)Jul-Dec-2019
GermanyAbsent, No presence record(s)Jul-Dec-2019
GreeceAbsent, No presence record(s)Jan-Jun-2018
HungaryAbsent, No presence record(s)Jul-Dec-2019
IcelandAbsent, No presence record(s)Jul-Dec-2019
IrelandAbsent, No presence record(s)Jul-Dec-2019
Isle of ManAbsent, No presence record(s)
ItalyAbsent, No presence record(s)Jul-Dec-2020
JerseyAbsent, No presence record(s)
LatviaAbsent, No presence record(s)Jul-Dec-2020
LiechtensteinAbsent, No presence record(s)Jul-Dec-2019
LithuaniaAbsent, No presence record(s)Jul-Dec-2019
LuxembourgAbsent, No presence record(s)
MaltaAbsent, No presence record(s)Jan-Jun-2019
MoldovaAbsent, No presence record(s)Jan-Jun-2020
MontenegroAbsent, No presence record(s)Jul-Dec-2019
NetherlandsAbsent, No presence record(s)Jul-Dec-2019
North MacedoniaAbsent, No presence record(s)Jul-Dec-2019
NorwayAbsent, No presence record(s)Jul-Dec-2019
PolandAbsent, No presence record(s)Jan-Jun-2019
PortugalAbsent, No presence record(s)Jul-Dec-2019
RomaniaAbsent, No presence record(s)Jul-Dec-2018
RussiaAbsent, No presence record(s)Jan-Jun-2020
San MarinoAbsent, No presence record(s)Jan-Jun-2019
SerbiaAbsent, No presence record(s)Jul-Dec-2019
Serbia and MontenegroAbsent, No presence record(s)
SlovakiaAbsent, No presence record(s)Jul-Dec-2020
SloveniaAbsent, No presence record(s)Jul-Dec-2018
SpainAbsent, No presence record(s)Jul-Dec-2020
SwedenAbsent, No presence record(s)Jul-Dec-2020
SwitzerlandAbsent, No presence record(s)Jul-Dec-2020
UkraineAbsent, No presence record(s)Jul-Dec-2020
United KingdomAbsent, No presence record(s)Jul-Dec-2019
-Northern IrelandAbsent, No presence record(s)

North America

BahamasAbsent, No presence record(s)Jul-Dec-2018
BarbadosAbsent, No presence record(s)Jul-Dec-2020
BermudaAbsent, No presence record(s)
British Virgin IslandsAbsent, No presence record(s)
CanadaAbsent, No presence record(s)Jul-Dec-2019
Cayman IslandsAbsentJan-Jun-2019
Costa RicaPresentJul-Dec-2020
CubaAbsent, No presence record(s)Jan-Jun-2019
DominicaAbsent, No presence record(s)
Dominican RepublicAbsent, No presence record(s)Jan-Jun-2019
El SalvadorAbsent, No presence record(s)
GreenlandAbsent, No presence record(s)Jul-Dec-2018
HaitiAbsent, No presence record(s)Jul-Dec-2019
JamaicaAbsent, No presence record(s)Jul-Dec-2018
MartiniqueAbsent, No presence record(s)Jul-Dec-2019
Saint Kitts and NevisAbsent, No presence record(s)
Saint LuciaAbsent, No presence record(s)Jul-Dec-2018
Saint Vincent and the GrenadinesAbsent, No presence record(s)Jan-Jun-2019
Trinidad and TobagoAbsentJan-Jun-2018
United StatesAbsentJul-Dec-2019


AustraliaAbsent, No presence record(s)Jul-Dec-2019
Cook IslandsAbsent, No presence record(s)Jan-Jun-2019
Federated States of MicronesiaAbsent, No presence record(s)Jan-Jun-2019
FijiAbsent, No presence record(s)Jan-Jun-2019
French PolynesiaAbsentJan-Jun-2019
KiribatiAbsent, No presence record(s)Jan-Jun-2018
Marshall IslandsAbsent, No presence record(s)Jan-Jun-2019
New CaledoniaAbsent, No presence record(s)Jul-Dec-2019
New ZealandAbsent, No presence record(s)Jul-Dec-2019
PalauAbsent, No presence record(s)Jul-Dec-2020
SamoaAbsent, No presence record(s)Jan-Jun-2019
Timor-LesteAbsent, No presence record(s)Jul-Dec-2018
VanuatuAbsent, No presence record(s)Jan-Jun-2019

South America

ArgentinaAbsent, No presence record(s)Jul-Dec-2019
BoliviaAbsent, No presence record(s)Jan-Jun-2019
BrazilAbsent, No presence record(s)Jul-Dec-2019
ChileAbsent, No presence record(s)Jan-Jun-2019
Falkland IslandsAbsent, No presence record(s)Jul-Dec-2019
French GuianaAbsentJul-Dec-2019
ParaguayAbsent, No presence record(s)Jul-Dec-2019
SurinameAbsent, No presence record(s)Jan-Jun-2019
UruguayAbsent, No presence record(s)Jul-Dec-2019


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Gross lesions of the central nervous system in horses associated with VEE are generally nonspecific, varying from no lesions to extensive necrosis with haemorrhages. Histopathologically, the predominant lesions are related to a diffuse necrotising meningoencephalitis; varying from some perivascular mixed cellular reaction to marked vascular necrosis with associated haemorrhages, gliosis, and clear neuronal necrosis (OIE, 2020).


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A confirmatory diagnosis of VEE is based on the isolation and identification of the virus or on the demonstration of seroconversion. For detailed information regarding laboratory diagnostic methodologies, refer to the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals.

Disease Course

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In horses, infections with epidemic VEE viruses may be asymptomatic, mild, severe or fatal. In symptomatic horses, a febrile prodrome with depression, tachycardia, and inappetence is sometimes followed by neurological signs indicative of encephalitis. Some animals also have diarrhoea and colic. Death can occur within hours after the onset of neurological signs; after a protracted illness accompanied by dehydration and extreme weight loss; or in animals without signs of encephalitis. Sudden death has also been reported (Spickler, 2017). Enzootic VEE viruses tend not to (but can sometimes) cause overt signs of disease in equids, but they can cause clinical disease in humans (OIE, 2020).


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Haematophagous insects play a central role in the transmission of VEE viruses. Epizootic strains have been isolated from the genera: Aedes, Anopheles, Culex, Deinocerites, Mansonia and Psorophora. Mechanical transmission of epizootic VEE has been demonstrated for blackflies (Simulium spp.). Enzootic VEE variants and subtypes cycle in tropical ecosystems among rodents, and possibly birds, by the feeding of mosquitoes. In the epizootic/epidemic cycle, horses are the main amplifying host (high, prolonged viraemia) and infect a wide range of mosquitoes. Non-vector spread of disease via direct contact or aerosols has been suggested (OIE, 2020).

Zoonoses and Food Safety

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In humans, VEE is usually an acute, often mild, systemic illness. The symptoms caused by endemic and epidemic strains are similar. The initial signs may include fever, chills, generalized malaise, headache, photophobia and myalgia. Coughing, sore throat, nausea, vomiting, diarrhoea and a rash may also be seen. Mild to severe neurological signs can be seen in a small percentage of affected children, and to a lesser extent in adults over the age of 50 years, but in few healthy adults (e.g., less than 1% of symptomatic young adults). VEE usually resolves within 1 to 2 weeks, with acute symptoms subsiding after 4 to 6 days, and deaths are rare. In pregnant women, VEE can affect the fetus (Spickler, 2017).

Most people are infected by exposure to VEEV-infected arthropods, but cases have been documented after laboratory accidents or exposure to aerosolized debris from the cages of infected laboratory rodents (Spickler, 2017). Horse-to-human and human-to-human transmission has not been recorded (OIE, 2020). VEEV is highly infectious in aerosol form and is a known biowarfare agent. Several candidate vaccines against VEEV are at various stages of development (Sharma and Knollmann-Ritschel, 2019).

Disease Treatment

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There is no effective treatment for VEE. Supportive care may include administration of fluids to horse unable to drink and therapy with antiinflammatory agents and anticonvulsants (OIE, 2020).

Prevention and Control

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Epizootics of VEE are most effectively controlled by quarantine and movement controls of all Equidae and vaccination of animals. Vector control measures include elimination of mosquito breeding locations (i.e. pooled or stagnant water), stabling equids in screened housing and use of repellents and fans (OIE, 2020).


Approved vaccines for equids include attenuated and inactivated vaccines (made with strain TC-83). For details, see the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals.


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Hawley RJ, Eitzen EM Jr, 2001. Biological weapons - a primer for microbiologists. Annual Review of Microbiology, 55:235-253

OIE Handistatus, 2002. World Animal Health Publication and Handistatus II (dataset for 2001). Paris, France: Office International des Epizooties

OIE Handistatus, 2003. World Animal Health Publication and Handistatus II (dataset for 2002). Paris, France: Office International des Epizooties

OIE Handistatus, 2004. World Animal Health Publication and Handistatus II (data set for 2003). Paris, France: Office International des Epizooties

OIE Handistatus, 2005. World Animal Health Publication and Handistatus II (data set for 2004). Paris, France: Office International des Epizooties

OIE, 2009. World Animal Health Information Database - Version: 1.4. World Animal Health Information Database. Paris, France: World Organisation for Animal Health.

OIE, 2020. Venezuelan equine encephalitis (updated January 2020). In: OIE Technical disease cards Paris, France: World Organisation for Animal Health.

Reichert E, Clase A, Bacetty A, Larsen J, 2009. Alphavirus antiviral drug development: scientific gap analysis and prospective research areas. Biosecurity and Bioterrorism: Biodefense Strategy, Practice and Science, 7(4):413-427.

Sharma, A., Knollmann-Ritschel, B., 2019. Current understanding of the molecular basis of Venezuelan equine encephalitis virus pathogenesis and vaccine development. Viruses, 11(2), 164. doi: 10.3390/v11020164

Spickler, A. R., 2017. Eastern, Western and Venezuelan equine encephalomyelitis (updated January 2015). Iowa, USA: Center for Food Security and Public Health (CFSPH), Iowa State University.

Weaver SC, Ferro C, Barrera R, Boshell J, Navarro JC, 2004. Venezuelan equine encephalitis. Annual Review of Entomology, 49:141-174

Distribution References

OIE Handistatus, 2005. World Animal Health Publication and Handistatus II (dataset for 2004)., Paris, France: Office International des Epizooties.

OIE, 2009. World Animal Health Information Database - Version: 1.4., Paris, France: World Organisation for Animal Health.

OIE, 2018. World Animal Health Information System (WAHIS): Jul-Dec. In: OIE-WAHIS Platform, Paris, France: OIE (World Organisation for Animal Health). unpaginated.

OIE, 2018a. World Animal Health Information System (WAHIS): Jan-Jun. In: OIE-WAHIS Platform, Paris, France: OIE (World Organisation for Animal Health). unpaginated.

OIE, 2019. World Animal Health Information System (WAHIS): Jul-Dec. In: OIE-WAHIS Platform, Paris, France: OIE (World Organisation for Animal Health). unpaginated.

OIE, 2019a. World Animal Health Information System (WAHIS): Jan-Jun. In: OIE-WAHIS Platform, Paris, France: OIE (World Organisation for Animal Health). unpaginated.

OIE, 2020. World Animal Health Information System (WAHIS): Jul-Dec. In: OIE-WAHIS Platform, Paris, France: OIE (World Organisation for Animal Health). unpaginated.

OIE, 2020a. World Animal Health Information System (WAHIS). Jan-Jun. In: OIE-WAHIS Platform, Paris, France: OIE (World Organisation for Animal Health). unpaginated.

Distribution Maps

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