Disease Outbreak News, Oropouche virus disease – Region of the Americas

Oropouche virus disease is a febrile disease caused by the Oropouche virus (OROV), spread primarily through the bite of an insect known as a midge (Culicoides paraensis). In 2024, the number of reported Oropouche virus disease has increased in the WHO Region of the Americas, including in areas with no previously recognized history of Oropouche virus disease. Additionally, some countries have identified fatal infections and potential vertical transmission. As of 20 July 2024, a total of 8078 confirmed Oropouche cases, including two deaths, have been reported in the Region of the Americas, across five countries: Bolivia, Brazil, Colombia, Cuba, and Peru. Brazil has also reported one fetal death and one miscarriage in the state of Pernambuco, as well as four cases of newborns with microcephaly possibly related to OROV infection. Since Oropouche virus disease is an emerging and poorly identified arbovirus in the Americas, the detection of a positive sample and confirmation of a case requires the use of Annex 2 of the International Health Regulations (IHR) and its consequent notification through the established channels of the IHR. OROV has been historically transmitted in the Amazon region. However, possible reasons for the spread beyond its historical range include climate change, deforestation and unplanned urbanization which have facilitated its spread to non-Amazonian states in Brazil and to countries where, until now, there have been no reported cases, including Bolivia and Cuba. Based on available information, WHO assesses the overall public health risk posed by this virus to be high at the regional level and low at the global level.

 

Between 1 January and 20 July 2024, there were 8078 confirmed Oropouche cases reported in the Region of the Americas, including two deaths. The cases are reported among five countries in the region: the Plurinational State of Bolivia (356 cases), Brazil¹ (7284 cases, including two deaths), Peru (290 cases), Colombia (74 cases), and Cuba (74 cases).

Brazil has reported one fetal death and one miscarriage in the state of Pernambuco, as well as four cases of newborns with microcephaly, identified through retrospective studies in the states of Acre and Pará indicating possible cases of vertical transmission of OROV infection and their consequences.² Three additional possible cases of vertical transmission are being investigated in the state of Pernambuco. Despite the evidence of vertical transmission of OROV (polymerase chain reaction [PCR] positivity on tissues from pregnancy loss reported), it cannot be concluded that OROV is the cause of the fetal deaths, and investigations are still ongoing.

As of 30 July 2024, five cases of possible vertical transmission have been identified in Brazil: four cases of stillbirth and one case of spontaneous abortion in the state of Pernambuco, as well as four cases of newborns with microcephaly in the states of Acre and Pará. The investigations are ongoing(1).

Figure 1. Number of confirmed Oropouche cases in 2024 by country and epidemiological week of symptom onset, Region of the Americas*

*Note: Data by epidemiological week of onset are not available for Cuba. Source: Adapted and reproduced by PAHO/WHO from the data reported by the respective countries.

The following is a summary of the situation in the countries that have reported confirmed Oropouche cases in the Americas during 2024.

The Plurinational State of Bolivia: Between 1 January and 20 July 2024, there were 356 Oropouche cases confirmed using reverse transcription polymerase chain reaction (RT-PCR). Transmission has been recorded in three departments: La Paz, with 75.3% of the cases (268 cases); Beni, with 21.3% of the cases (76 cases); and Pando, with 3.4% of the cases (12 cases). The cases are reported among 16 municipalities that are considered endemic for this disease, with the highest proportion of cases reported in the municipalities of Irupana, La Paz, with 33% of the cases, followed by La Asunta, La Paz, with 13% of the cases, and Chulumani, La Paz, and Guayaramerin, Beni, with 12% each.

Half of the cases are female (179 cases) and the age group with the highest number of cases in the 30-39 years age group, with 20% of cases (70 cases). No deaths have been recorded that could be associated with OROV infection. Additionally, between 16 March and 13 April 2024, five cases of Oropouche virus disease co-infection with dengue were reported in patients from three municipalities in the department of La Paz, who presented with positive RT-PCR results for DENV-1 serotype (one case) and DENV-2 (four cases) (2).

Brazil: Between 1 January and 27 July 2024, 7284 Oropouche cases were confirmed by RT-PCR. The Amazon region, considered endemic for Oropouche virus disease, accounted for 75.7% of the cases recorded in the country, with six states reporting cases: Amazonas (3224 cases), Rondônia (1709 cases), Acre (265 cases), Roraima (239 cases), Pará (74 cases), and Tocantins (two cases) (3). Additionally, autochthonous transmission has been documented in ten non-Amazonian states, some of which had not previously reported cases: Bahía (831 cases), Espírito Santo (420 cases), Santa Catarina (165 cases), Pernambuco (92 cases), Minas Gerais (83 cases), Rio de Janeiro (64 cases), Ceará (39 cases), Piauí (28 cases), Maranhão (19 cases), and Mato Grosso (17 cases). In addition, the probable place of infection is being investigated for several cases registered in the states of Amapá (seven cases), Paraná (three cases), Sergipe (two cases), and Paraíba (one case).

Over half of the cases (51.9%; 3779) are male and the age group with the highest number of cases is 30-39 years, with 21.2 % of cases (1541 cases) (3).

On 23 July 2024, Brazil’s IHR National Focal Point (NFP) reported two fatal cases of OROV infection detected retrospectively in the state of Bahia. Both cases were in females, aged 21 and 24 years old. These two deaths would be the first fatal cases due to acute OROV infection in Brazil and in the Region of the Americas, occurring amid an active outbreak on the southern coast of Bahia. Both cases, without a history of chronic diseases, tested RT-PCR positive for OROV and serology and negative for other arboviruses. The cases showed a rapid evolution from the onset of symptoms (fever, myalgia, headache, retro-orbital pain, pain in the lower extremities, asthenia, and joint pain) to death, with severe coagulopathy and liver involvement identified as probable causes of death. Additionally, the Brazilian Ministry of Health is investigating two other fatal cases associated with OROV, in Paraná and Maranhão (4).

Colombia: Between 1 January and 20 July 2024, 74 confirmed Oropouche cases have been reported in three departments of the country: Amazonas (70 cases), Caquetá (one case), and Meta (one case); additionally, two cases were identified in travelers from from Tabatinga, Brazil. The cases were identified through a retrospective laboratory case-finding strategy implemented in 2024 by the National Institute of Health of Colombia based on dengue surveillance (38 cases) and through investigation of febrile syndrome cases (36 cases). Over half of the cases (51.4%; 38) were female and the age group with the highest number of cases was 10-19 years, with 36.5% of the cases (27 cases). No deaths have been recorded that could be associated with OROV infection.

Cuba: On 27 May 2024, the Ministry of Public Health of Cuba reported the country’s first outbreak of Oropouche virus disease. A total of 74 confirmed cases were reported from the Santiago de Cuba Province (54 cases) and Cienfuegos Province (20 cases). Half of the cases (50%; 38) were female and the age group with the highest number of cases was 15-19 years, with 16% of the cases (12 cases). No deaths have been recorded that could be associated with OROV infection (5).

Peru: Between 1 January and 20 July 2024, 290 confirmed Oropouche cases have been reported in five departments, the highest number of cases reported to date in this country. The departments are: Loreto (193 cases), Madre de Dios (47 cases), Ucayali (41 cases), Huánuco (eight cases), and Tumbes (one case). Over half of the cases (52%; 150) were male, and the age group with the highest number of cases was 30-39 years, with 40% of the cases (115 cases) (6).

 

 

Oropouche virus disease is an arboviral disease caused by the Oropouche virus (OROV), a segmented single-stranded RNA virus that is part of the genus Orthobunyavirus of the Peribunyaviridae family. The virus has been found to circulate in Central and South America and the Caribbean. OROV can be transmitted to humans primarily through the bite of the Culicoides paraensis midge, found in forested areas and around water bodies, or certain Culex quinquefasciatus mosquitoes. It is suspected that viral circulation includes both urban epidemic and sylvatic cycles. In the sylvatic cycle, primates, sloths, and perhaps birds are vertebrate hosts, but a definitive arthropod vector has not been identified. In the urban epidemic cycle, humans are the amplifying host and OROV is transmitted primarily through the bite of the Culicoides paraensis midge. Vertical transmission has recently been documented and is being investigated further. To date, there is no evidence of other modes of human-to-human OROV transmission.

The disease symptoms are similar to dengue and start four to eight days (range between three to 12 days) after the infective bite. The onset is sudden, usually with fever, intense headache, joint stiffness, pain, chills, and sometimes persistent nausea and vomiting, for up to seven days. Up to 60% of cases have a relapse of symptoms after the fever stops. Most cases recover within seven days, however, in some patients, convalescence can take weeks. Severe clinical presentation is rare, but it may result in aseptic meningitis during the second week of the disease.

There is no specific antiviral treatment or vaccine for Oropouche virus disease.

• Regional level: Epidemiological alerts and updates have been issued to alert Member States and recommend actions to be implemented. Information has also been disseminated through regional and national webinars for health personnel.
• Algorithms for laboratory testing have been developed and disseminated. Training on molecular testing (RT-PCR) and characterization (whole genome sequencing) has been provided through workshops or remote assistance, and critical reagents have been distributed. As a result of regional and national efforts, molecular testing capacity is available in 23 of the 33 countries in Latin America and the Caribbean. The Pan American Health Organization (PAHO; the WHO Regional Office for the Americas) is working to expand these capacities as necessary.
• The available clinical information has been reviewed to recommend interim case definitions (suspected, probable, and confirmed, vertical transmission).
• A virtual collaboration space has been created at the regional level to develop epidemiological analytics of the disease.
• Generic research protocols for the characterization of pregnancy outcomes in infants from OROV-exposed pregnant individuals have been drafted and shared.
• PAHO/WHO experts are providing support in countries that are experiencing outbreaks.

Brazilian local and national health authorities have implemented the following public health measures:

• Entomo-epidemiological actions have been developed to identify the main vector species and the landscape where they are breeding, to cut the chains of transmission and achieve control of the disease in the shortest time possible.
• Surveillance is being maintained in all Federative Units of the country. The Ministry of Health monitors cases and possible deaths from Oropouche through the National Arbovirus Room, in constant dialogue with Federative Units.
• Monitoring has also been carried out through technical visits, on-site research, active search and research of vectors, supporting the local response of states and municipalities.
• Three research groups are working on OROV fever. One is focused on laboratory information, such as the lineage of the virus and genomic characteristics. Another is monitoring the clinical manifestations of patients, and the third is investigating the disease cycle in the mosquitoes that transmit it.

In the Region of the Americas, outbreaks of Oropouche virus disease have occurred mainly in the Amazon region during the last ten years. With geographical limitations, OROV causing persistent endemicity and periodic outbreaks are reported in in both rural and urban communities in Brazil, the Plurinational State of Bolivia, Cuba, Colombia, Ecuador, French Guiana, Panama, Peru, and Trinidad and Tobago (7).

The ongoing outbreak highlights the need to strengthen epidemiological and entomological surveillance and to reinforce preventive measures in the population. This is crucial due to the potential expansion of the virus’s transmission area and the growing understanding of the disease spectrum, including possible new transmission routes, and possible new vectors that could affect both the general population and vulnerable groups, such as pregnant women, their fetuses, and newborns.

Based on available information, WHO assesses the overall public health risk posed by this virus to be high at the regional level and low at the global level.

The proximity of midge vector breeding sites to human habitations is a significant risk factor for OROV infection. Prevention strategies are based on control measures against the arthropod vectors and on personal protection measures. Vector control measures rely on reducing midge populations through the control of breeding sites, achieved by reducing the number of natural and artificial water-filled habitats that support midge larvae, thereby reducing the adult midge populations around at-risk communities. Personal protection measures rely on the prevention of midge bites using mechanical barriers (mosquito nets), insect repellant devices, repellent-treated clothing and mosquito repellents. Chemical insecticides such as deltamethrin and N,N-Diethyl-meta-toluamide (DEET) have been demonstrated to be effective in providing protection against bites from Culicoides and Culex species.

Given its clinical presentation and considering that this is the ongoing season for dengue in Central America and the Caribbean and for other vector-borne diseases in the Region of the Americas, laboratory diagnosis is essential to confirm cases, characterize the outbreak, and monitor disease trends.

Since it is an emerging and poorly identified arbovirus in the Americas, the detection of a positive sample and confirmation of a case requires the use of Annex 2 of the IHR and its consequent notification through the established channels of the IHR.

WHO advises against applying any travel or trade restrictions based on the current information available on this event.

 

• Pan American Health Organization / World Health Organization. Guidelines for the Detection and Surveillance of Emerging Arboviruses in the Context of the Circulation of Other Arboviruses. 4 May 2024. Washington, D.C.: PAHO/WHO; 2024. Available from: https://www.paho.org/en/documents/guidelines-detection-and-surveillance-emerging-arboviruses-context-circulation-other(link is external)
• Pan American Health Organization / World Health Organization. Tool for the diagnosis and care of patients with suspected arboviral diseases. Washington, D.C.: PAHO; 2017. Available at: https://iris.paho.org/handle/10665.2/33895 (link is external)
• Pan American Health Organization / World Health Organization. Epidemiological Alert: Outbreak of Oropouche fever. 22 June 2010. Washington, D.C.: PAHO/WHO; 2010. Available in Spanish from: https://www.paho.org/es/documentos/alertaepidemiologica-brote-fiebre-oropouche-22-junio-2010(link is external).
• Romero-Alvarez D, Escobar LE. Oropouche fever, an emergent disease from the Americas. Microbes and Infection. March 2018; 20(3):135-46.
• Sakkas H, Bozidis P, Franks A, Papadopoulou C. Oropouche Fever: A Review. Viruses. 2018; 10(4):175. Available from: https://www.mdpi.com/1999-4915/10/4/175(link is external)
• Health Surveillance Foundation of Amazonas “Dr. Rosemary Costa Pinto” (FVSRCP). Epidemiological Alert No. 1/2024. Manaos; 2024. Available in Portuguese from: https://www.fvs.am.gov.br/media/publicacao/ALERTA_EPIDEMIOLOGICO_N%C2%BA_01.2024_-_CIRCULACAO_DO_VIRUS_OROPOUCHE_NO_AMAZONAS.pdf(link is external)
• Karl A. Ciuoderis, Michael G. Berg, Lester J. Perez, Abbas Hadji, Laura S. PerezRestrepo, Leidi Carvajal Aristizabal, Kenn Forberg, Julie Yamaguchi, Andres Cardona, Sonja Weiss, Xiaoxing Qiu, Juan Pablo Hernandez-Ortiz, Francisco Averhoff, Gavin A. Cloherty & Jorge E. Osorio (2022). Oropouche virus as an emerging cause of acute febrile illness in Colombia, Emerging Microbes & Infections, 11:1, 2645-2657. 2022. DOI: 10.1080/22221751.2022.2136536
• World Health Organization. Event information site, Brazil, Oropouche Vertical Transmission, 21 July 2024. Geneva, WHO, 2024. Available from: https://extranet.who.int/ihr/eventinformation/event/2024-e000303

References:

1. PAHO/WHO Epidemiological Alert on Oropouche in the Region of the Americas: vertical transmission event under investigation in Brazil, 17 July 2024. Washington, D.C.: PAHO/WHO; 2024. Available from: Epidemiological Alert Oropouche in the Region of the Americas: vertical transmission event under investigation in Brazil – 17 July 2024 – PAHO/WHO | Pan American Health Organization
2. Plurinational State of Bolivia International Health Regulations National Focal Point (IHR NFP). Communication received on 30 July 2024 via e-mail. La Paz; 2024. Unpublished.
3. Ministério da Saúde do Brasil, Centro de Operação de Emergências. Informe Semanal nº 21 – Centro de Operações de Emergências – SE 26 – 3 July 2024. Brasilia; EOC; 2024. Available in Portuguese from: https://www.gov.br/saude/pt-br/assuntos/saude-de-a-a
4.  Bandeira, A, Barbosa, A, Souza, M, Saavedra, R, Pereira F, Santos S, et al. Clinical profile of Oropouche Fever in Bahia, Brazil: unexpected fatal cases. SciELO Preprints. 2024-07-16 (version 1);2024. Available from: https://doi.org/10.1590/SciELOPreprints.9342
5. World Health Organization. Disease Outbreak News, Oropouche virus disease in Cuba, 11 June 2024. Geneva: WHO; 2024. Available from: https://www.who.int/emergencies/disease-outbreak-news/item/2024-DON521
6. Peru Centro Nacional de Epidemiología, Prevención y Control de Enfermedades. Indicadores de Riesgo Epidémico Sala virtual de situación de salud. Lima: CDC Peru; 2024. [cited 26 July 2024]. Available in Spanish from: https://www.dge.gob.pe/salasituacional/sala/index/salasit_dash/143
7. Pan American Health Organization / World Health Organization. Epidemiological alert Outbreaks – Oropouche in the Region of the Americas, May 9, 2024. Washington, D.C.: PAHO/WHO; 2024. Available in:https://www.paho.org/en/documents/epidemiological-alert-oropouche-region-americas-9-may-2024

¹ Cases in Brazil are reported up to epidemiological week 30 of 2024. 

² The detailed Information concerning these cases was published in the PAHO/WHO Epidemiological Alert on Oropouche in the Region of the Americas: vertical transmission event under investigation in Brazil, 17 July 2024. Washington, D.C.: PAHO/WHO; 2024. Available from: https://www.paho.org/en/documents/recommendations-detection-and-surveillance-oropouche-possible-cases-vertical-infection

Citable reference: World Health Organization (23 August 2024). Disease Outbreak News; Oropouche virus disease in the Region of the Americas. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2024-DON530