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Scientists comment on cases of the Oropouche virus in South America and Europe.
Dr Philip Veal, Travel Health Consultant at UKHSA, said:
“The midge that carries Oropouche virus is not currently established in Europe. It is typically found in the Americas. There is no evidence that the virus can spread from person to person.
“When travelling to affected areas, you can avoid the infection, and others such as dengue, Zika and malaria, by preventing insect bites. Use insect repellent, cover exposed skin and sleep under a treated bed net. Plan ahead and visit the TravelHealthPro website to look up your destination and the latest health information and advice, particularly if you are pregnant.”
Background
Dr Benjamin Brennan, Senior Research Fellow, MRC-University of Glasgow Centre for Virus Research, said:
“The Oropouche virus is endemic in parts of South America and has been for some time. It is in the news now because there has been a large and sustained outbreak of Oropuche fever in several South American countries (approx. 8000 cases) associated with the emergence of a novel Oropouche virus that has arisen due to a reassortment event. What is unusual in this outbreak is the first reports of death following infection with this virus in South America and the observation that the virus may be being passed from mother to child in utero and result in miscarriage, abortion and/or developmental problems, and deformities of the foetus.
“The virus is transmitted to people through the bite of an infected Culicoides paraensis midge, which exists in South America (and not in Europe). Oropouche virus has not been demonstrated to be transmitted directly between humans.
“The virus causes a disease with typically mild symptoms, that people recover from after 1-2 weeks and is rarely fatal. In humans, Oropouche disease can manifest as an acute febrile illness with headache, nausea, vomiting, muscle and joint pains, and occasionally more severe symptoms (e.g. neurological symptoms and meningitis). The prognosis for recovery is good and fatal outcomes are extremely rare. However, there are recent reports in South America of Oropouche virus being transmitted from infected pregnant women to developing foetuses. The impact of Oropouche infection for pregnant women, foetuses and newborns may therefore be higher than that for the rest of the public. Pregnant women planning to travel to epidemic countries where transmission is ongoing (i.e. Cuba, Brazil) or has been reported should always seek pre-travel health advice to assess the risk of infection based on the local situation.
“Given the relatively high number of travellers between Europe and affected countries such as Brazil or Cuba, it is likely we will continue to see sporadic cases of Oropouche fever in returning travellers in Europe. Nineteen cases have been reported so far, in Spain, Italy and Germany. In these incidences most travellers had returned from Cuba. We may see cases in the UK in returning travellers that have visited or reside in an epidemic area.
“Currently there are no vaccines or specific medicines to treat Oropouche fever. Therefore, the best way to prevent an ongoing outbreak would be to follow any instructions given by local public health authorities in the affected country and to use personal protective measures to reduce midge and mosquito bites both when undertaking outdoor activities or inside houses that are not adequately screened. The midge species that transmits the virus in South America bites during the day and readily enters houses, with peaks in activity after sunrise and before sunset.”
Prof Stephen Graham, School of Biological Sciences Infection and Immunity Theme Leader and Professor of Virus:Host Interactions, University of Cambridge, said:
What is this virus, has it been around for a long time in South America?
“The virus was first discovered in Trinidad and Tobago in 1955, on the Oropouche river (hence the name). It has been circulating in Latin America and the Caribbean since then, with sporadic outbreaks in countries such as Brazil and Peru. Up until the Zika outbreak in 2016 it was the second most prevalent insect-transmitted virus in Brazil, after Dengue virus. This latest outbreak is notable because the virus has spread much further geographically than it has in previous outbreaks, as far north as Cuba and as far south as Sao Paulo state. There have also been cases imported by travellers into Spain, Italy and Florida.
“The virus has an RNA genome, like SARS-CoV-2, which means that it is capable or rapid mutation. It also has a genome with multiple segments, like influenza. This means that if you are unlucky enough to be infected with two different strains of the virus they can ‘reassort’ their genome segments, like shuffling two decks of cards together, and you might end up with a new virus strain that is more transmissible and/or more pathogenic. This is what appears to have happened recently in Brazil to launch the current outbreak. It’s important to note that individual humans or animals being infected by two different strains at the same time is a very rare event. In this case the most likely scenario is that the co-infection and reassortment occurred in a wild animal (sloth, monkey or other), probably some years ago, and was then subsequently transmitted to a human via a biting insect.
How is the virus transmitted?
“The virus is transmitted via biting insects – the main transmission vector is thought to be the midge Culicoides paraensis. It is possible that it can be transmitted by other types of midges and mosquitos – but for that to be a problem you’d also need to first have the virus present endemically in a country (which isn’t the case in Europe). The ECDC have said that there is no evidence that the insects we have in the UK or mainland Europe are capable of transmitting Oropouche virus, although we are working with somewhat sparse data on this. There are currently no known examples of ‘secondary transmission’ of the virus outside endemic areas so I concur with the ECDC that the risk of local transmission in Europe is low.
Is there anything unusual about the current outbreak in South America?
“As mentioned above, the above outbreak is unusual in its broad geographic spread. It’s also very unusual in the fact that we have observed the first recorded cases of mortality from Oropouche virus infection – two women in their 30s with no known co-infections or other serious disease. This marks quite a change in the virus as it has always made people very sick, with debilitating fever and muscle pain for about 1-2 weeks, and occasionally neuronal symptoms like meningitis, but it has never before killed people. Additionally, there have been anecdotal reports since the 1980s that Oropouche virus infection of women in the first trimester of pregnancy could cause foetal death. We have unfortunately now seen several cases of early-term abortions where the foetus was infected with Oropouche virus. This has potential public health implications so we need to maintain vigilance and monitor the situation carefully.
Is it normal for us to see some imported cases outside South America in returning travellers?
“In short yes, this is a virus that infects people and people travel. If you visit an area where there is an epidemic and are bitten by an insect carrying Oropouche you might not develop symptoms for 2-3 days, and by that time you might have flown home to Europe or the USA. However, we have no evidence that the virus can spread directly from person to person – you need an insect to bite you and then bite someone else to transmit the disease – and there’s no evidence that the insects we have in the UK or on mainland Europe are able to transmit Oropouche virus infection. We also don’t have any evidence that the virus can infect other animals in the UK, whereas in Brazil it is thought to circulate in the local sloth and monkey populations. The good news is that cases in the Amazon region are starting to drop. However, there is a lot we don’t know about this virus still so we can’t completely rule out that the virus will continue to spread more widely in Brazil or Latin America during the current outbreak, especially given the continuing climate and land use changes in areas where the virus circulates like the Amazon. As the climate warms the insects that spread the virus will change their geographical distribution, potentially introducing new human and animal populations to the infection – and as more people live in close proximity to the Amazon you have more potential for spread from wild animals to human hosts. Again, the good news here is that most people recover completely from Oropouche virus infection within a few weeks, so this virus won’t cause a SARS-CoV-2 like global pandemic.”
Prof Jonathan Ball, Deputy Director of Liverpool School of Tropical Medicine and Professor of Molecular Virology, Liverpool School of Tropical Medicine (LSTM), said:
“There is no evidence of direct human-to-human infection, the infection is acquired from an insect bite in an area where the virus is endemic, often from a tick, but sometimes a mosquito that lives in South America.
“The symptoms are akin to those seen with Dengue fever, varying from relatively mild, often asymptomatic to much more painful aching and fever. There have been reported possible cases of serious disease in newborn children in South America presumably arising from infection in the womb, and possibly still-births, but this isn’t proven to be associated with Oropouche infection.
“There are no vaccines or specific treatments, so the only way to reduce outbreaks is limit exposure to insects in infected areas (i.e. South America) and also use insect controls. Eventually, as people become naturally immune following infection then the size of the susceptible population declines so the outbreak declines.
“For anyone travelling from an area where the virus isn’t normally found (so-called non-endemic areas) to an area where the virus is circulating – in this case South America – there is the risk of them becoming infected. This risk increases as the number of active cases increases, so during an outbreak, as we are seeing in Brazil, then there is a greater chance of becoming infected, but the absolute risk is still low, especially if the traveller protects themselves from insect bites, and especially tick bites. The fact that CDC have travel to the Americas as level 1 risk – ‘Practice usual precautions’ – highlights this relatively low risk. We could see isolated cases in the UK, but these would be in travellers returning from an outbreak area. The risk of subsequent onward transmission within the UK is very unlikely.”
Dr Enny Paixao, Associate Professor, London School of Hygiene & Tropical Medicine, said:
Commenting on the Oropouche outbreak across South America:
“There is much we still do not know about the Oropouche virus but one of the main concerns arising from the current outbreak in South America is its potential harmful effects on unborn foetuses.
“In July 2024, the Pan American Health Organization (PAHO) issued an alert regarding the potential transmission of the Oropouche virus from mother to child in Brazil. Some very limited studies have suggested that antibodies against the virus have been found in children born with microencephaly and that there may be a link between infection, miscarriage, and foetal deaths in Brazil, but further research is needed to investigate a potential causal link.
“While the current Oropouche outbreak in South America does not yet show the same level of abnormalities in newborns as the Zika epidemic, the risks to foetal development remain uncertain and require closer scrutiny.
“Several factors may explain the recent outbreak, including enhanced surveillance, climate and environmental changes, and potential changes to the virus.
“Similarly to other vector-borne diseases such as dengue, climate change may also be impacting Oropouche virus expansion. Changes to temperature and precipitation can affect transmission, for example, rising temperatures can enhance the rate of development of Culicoides midges, one of the virus’ main transmission vectors in South America alongside mosquitos.
“Previous studies have linked OROV outbreaks to increased agricultural activities, highway and road development and bridge construction in South America. These activities disrupt ecosystems by causing population migration, vegetation loss (such as deforestation and illegal mining) and changes in agricultural practices. These changes can alter the distribution of wild animal reservoirs and vectors.
“A recent study also indicates that the main Oropouche virus circulating in South America in 2023-2024 exhibits significantly higher replication in mammalian cells compared to older strains. While it remains unclear if this increased replication leads to greater transmissibility by its vectors, it could help explain the recent rise in cases.
“Surveillance for Oropouche infection is challenging, as there is overlap of symptoms with other co-circulating arboviruses like dengue, Zika and chikungunya. It’s also important to note that the reported figures are based on laboratory-confirmed cases and taking into account that some individuals will not experience symptoms or seek health care, it’s likely that the true number of infections is higher.
“Therefore, it is plausible that the increased number of cases and enhanced surveillance are bringing rare events, including deaths, to light. The same principle applies to the potential harmful effects on unborn children.
“Although Oropouche virus is not new to Brazil, the factors driving the recent sharp increase—including reported deaths and potential foetal harm—highlight the need for further investigation. Until advancements are made in vaccine development or mosquito and midge control, or until natural immunity within the population in Brazil increases, the challenge posed by this neglected tropical disease will persist.”
Declared interests
Dr Benjamin Brennan: “I have no conflicts of interest to declare.”
Prof Stephen Graham: “I hold an International Collaboration Award research grant from the Royal Society to study Oropouche virus, together with my colleague Eurico Arruda at the University of Sao Paulo. We are working to develop rapid testing (lateral flow devices) to diagnose Oropouche virus infection at community points of care in the Amazon.”
For all other experts, no reply to our request for DOIs was received.