The little-known Oropouche virus is causing concern among healthcare workers and researchers and scientists in South America. This arthropod-borne virus, OROV, primarily transmitted by midge flies and occasionally by mosquitoes, has been rapidly spreading in the region. Brazil has reported over 5,000 cases this year, a significant increase from over 800 in 2023.
Countries like Bolivia, Colombia, and Peru are also experiencing a spike in the number of cases. Traditionally found in the Amazon basin, the virus is now affecting people far beyond the rainforest.
In May 2024, the first case of OROV was reported in Cuba. While the present outbreaks are restricted to less populated regions in the Amazon, the fear of the virus moving to larger and more populous cities in Latin America is giving sleepless nights to public health experts and policymakers.
Rapid speed, high attack rate
OROV has a long history of over seven decades but was relatively unknown and neglected until very recently. First identified in mosquitoes in Trinidad and Tobago in 1955, this pathogen rose to prominence during its first major outbreak in 1960 in Belém, northern Brazil. This outbreak affected thousands of individuals and brought attention to the virus. Since then, Brazil has experienced numerous outbreaks, with some estimates suggesting that over half a million cases may have occurred. The Brazilian Amazon has been particularly vulnerable due to the favourable conditions, characterised by vast river systems and a tropical climate ideal for the breeding of the primary vector—the midge Culicoides paraensis.
Most OROV infections are mild, with symptoms such as high fever, headache, muscle and joint pains, and sometimes a rash, with the illness typically lasting about a week. While the fever is generally non-lethal, its impact on communities can be substantial, causing significant morbidity and economic disruption. The overlap of clinical symptoms with other diseases like dengue or Zika, which are also endemic in the region, means many cases are not fully diagnosed and often mislabelled. Additionally, the confirmation of the infection typically involves molecular methods such as polymerase chain reaction (PCR) or detection of antibodies in the body.
Consequently, because the virus is not routinely tested for or part of any active surveillance, there is a firm belief that many severe cases and deaths may have been undercounted.
Peru has also seen significant OROV activity, particularly in its Amazonian regions. The virus was first detected in the country in the early 1990s and has caused several outbreaks since then. Large-scale outbreaks in Iquitos, a major city in the Peruvian Amazon, underscore the virus’ capacity to affect urban populations. These outbreaks have been notable for their rapid spread and high attack rates, emphasising the virus’ potential for swift transmission in susceptible populations.
The Oropouche virus has an RNA genome, which is segmented into three parts unlike many viruses. Like influenza viruses, the segmented nature of its genome allows for the swapping of genetic material during co-infections with multiple strains—a process known as reassortment. This can lead to the emergence of new lineages. Reassortments of Oropouche virus genomes have happened in the past, and the current outbreak is largely driven by a new lineage that emerged around 2015 from the reassortment of genomes between lineages prevalent in Peru and Colombia.
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Public health challenge
The spread of the Oropouche virus is closely linked to environmental and socio-economic factors. Deforestation, urbanisation, and climate change contribute to the changing epidemiology of the vector and consequently the virus. Deforestation, which has accelerated in the Amazon region over the last decade, has disrupted many natural ecosystems and brought humans closer to vector species. Urbanisation has created densely populated areas with poor sanitation, facilitating vector breeding and increasing human exposure. And climate change is also believed to alter the distribution and abundance of vectors, potentially expanding the geographical range of the virus.
Despite its public health significance, the Oropouche virus remains severely under-researched. The lack of resources to test and track the virus through comprehensive surveillance systems severely hampers efforts to accurately monitor and respond to outbreaks. Diagnostic facilities are often limited, especially since the outbreaks have largely occurred in remote areas, leading to misdiagnosis and potential underreporting of cases. This issue is compounded by the prevalence of other endemic diseases in the region.
Efforts to control the spread of the Oropouche virus have primarily focused on vector control measures. These include the use of insecticides to reduce midge populations and public health campaigns to educate communities about reducing exposure to vectors. Personal protective measures, such as using insect repellent and installing screens on windows and doors, are also recommended to minimise bites from infected vectors.
Research into vaccines and antiviral treatments for the virus is still in its early stages. While the development of effective vaccines could significantly reduce the burden of the disease, challenges in creating vaccines for arboviruses and the limited financial incentives for pharmaceutical companies to invest in diseases that primarily affect low-income countries have slowed progress in this area.
The Oropouche virus has the potential to create a significant public health challenge in South America, particularly in the Amazon basin. Its capacity to cause large outbreaks with high morbidity highlights the need for enhanced surveillance, improved diagnostic capabilities, and effective vector control strategies. Addressing the socio-economic and environmental factors that facilitate the spread of the virus is also crucial. Greater investment in research and development of vaccines and treatments is necessary to mitigate the impact of Oropouche fever and protect vulnerable populations in affected regions.
Dr Bani Jolly is a senior scientist at Karkinos Healthcare. She tweets @bani_jolly. Dr Vinod Scaria is a Senior Consultant at Vishwanath Cancer Care Foundation and Adjunct Professor at IIT Kanpur and DY Patil Vidyapeeth. He tweets @vinodscaria. Views are personal.
(Edited by Ratan Priya)