What Is Oropouche Virus

Introduction

The Oropouche virus (OROV) is a virus which causes Oropouche fever. It is a common cause of arbovirus illness, meaning it is transmitted to a person by a bite from a certain group of insects known as arthropods.¹ Symptoms include fever, headache, nausea, joint and muscle pain. It is estimated to have affected more than half a million people since it was first discovered in Trinidad and Tobago in 1955 and has had a considerable social and economic impact. OROV has been implicated in over 30 epidemics since the early 1960s. ORO fever affects all age groups, although, in some outbreaks, children and young adults appear to be more affected. Transmission of OROV occurs through two different life cycles, however, transmission to humans is mainly through biting midges called Culicoides paraensis.³ It is difficult to distinguish OROV from other arboviral illnesses with similar symptoms, such as dengue, zika and, therefore, cases are underreported.¹

Oropouche virus

OROV is a single-stranded RNA virus and a member of the Simbu group of viruses. One of the main characteristics of the Simbu group of viruses is their genetic diversity, which is due to their wide geographical distribution.

Transmission of OROV generally occurs during the daytime, especially at sunrise and sunset, from Culicoides paraensis midges. There is no evidence for direct human-to-human transmission. Transmission of OROV occurs via two life cycles, an urban one and a sylvatic one, meaning it can spread to both people and animals. The sylvatic life cycle (the one in which an animal gets infected) is not well understood, but it is believed to involve wild mammals (mainly sloths and monkeys), and both wild and domestic birds. The exact insect carrying the virus in this lifecycle is unknown, but it is believed to be different types of mosquitoes and midges. Humans are believed to be the link between the two transmission cycles; if an individual from an urban area visits a forest, gets infected there and then returns to the urban area while carrying the virus, it can then spread to the urban area.³

Geographical distribution

Until now, the only reported cases of ORO fever have occurred in Brazil, Panama, Peru, and Trinidad and Tobago. Most cases occur in Brazil, with a disease prevalence of 20% in both urban and rural human populations of the affected regions. It is the second most common arbovirus in Brazil after dengue fever. Cases will likely continue to occur as it is very densely populated (the fifth most populated in the world), with inhabitants living mostly in large, densely populated cities infested by various species of midges and mosquitoes.³

It is expected that cases of OROV will continue to increase and spread further in the region due to climate and environmental change, as well as animal and human relocations. With extensive animal and human population migration globally, it will not be surprising if OROV spreads outside South America.

Symptoms

The incubation period (time between exposure to the virus (a.k.a the midge bite) and symptoms occurring) for ORO fever is believed to be between 4 and 8 days.

ORO fever is characterised by the following:¹

• Sudden onset of high fever
• Headache
• Myalgia (muscle pain)
• Arthralgia (joint pain)
• Anorexia
• Dizziness
• Chills
• Photophobia (light sensitivity)

Some patients may also exhibit a rash. 

Nausea, vomiting, diarrhoea, conjunctivitis, epigastric and retro-ocular pain (pain behind the eyes), are also common.

A recurrence of symptoms is usually observed several days after the initial fever but with milder symptoms.

In severe cases, the central nervous system is affected, with the virus being detected in the cerebrospinal fluid (fluid around the brain and the spine). This is usually only the case in immunocompromised individuals and children.³

No fatalities have been recorded, but some patients develop aseptic meningitis.²

Management and treatment

Treatment for ORO fever is supportive and usually includes painkillers.

There is currently no vaccine available to prevent OROV infection. The prevention of infection is based on personal protection methods, such as the use of repellents and the eradication and control of the transmitting biting midges.²

Diagnosis

OROV is difficult to diagnose as the symptoms are similar to other febrile illnesses (those with the symptom of a fever). Often, a differential diagnosis has to be made in regard to other febrile illnesses, particularly dengue fever, chikungunya fever, and malaria.

It can be diagnosed by using blood samples collected during the acute phase of the illness (up to 5 days after the onset of symptoms). The most common molecular detection method is RT-PCR (reverse transcription polymerase chain reaction). This is a method used for detecting specific genetic materials, such as that from a virus, within a sample.²

Tests using different antigens to detect specific antibodies have also been used to diagnose OROV.³

Prevention and control

Prevention strategies for OROV infection are based on control or eradication measures for the Culicoides biting midges and personal protection measures.

Control measures depend on reducing midge populations through the ending of mating sites. This can be done by reducing the number of natural and artificial water-filled habitats, as these act as breeding grounds for midges. 

Personal protection measures rely on preventing midge bites by using mosquito nets, insect-repellent devices and mosquito repellent.

Chemical insecticides such as deltamethrin and DEET have been efficient at eliminating the Culicoides species, however, the ecological consequences of insecticide usage on a large scale are of particular concern.³

FAQs

What is the Oropouche virus?

The Oropouche virus is a member of the Simbu group of Orthobunyaviruses and a major cause of disease in the Amazon region of Brazil and Peru. It is transmitted by the Culicoides paraensis midges and some mosquito species.¹

What are the symptoms of the Oropouche virus?

Symptoms of the Oropouche virus occur 4-8 days after exposure. Symptoms include the sudden onset of high fever, headache, myalgia, joint pain, nausea and rash. The illness typically lasts 3-6 days. In 60% of cases, symptoms reoccur in a milder form after the initial fever.¹

How do you treat the Oropouche virus?

There is currently no cure or vaccine for Oropouche fever. Painkillers are commonly used to relieve the symptoms.

Summary

The Oropouche virus (OROV) is one of the most prevalent arboviruses in South America, and the cause of Oropouche (ORO) fever. More than 30 epidemics have been reported in Central and South America since the 1960s, with an estimated occurrence of 500,000 cases.

Symptoms of Oropouche fever are similar to dengue, zika, and chikungunya fever, making it difficult to diagnose and leading to an underreporting of cases. Symptoms of Oropouche fever include fever, headache, nausea, joint and muscle pain.  Patients usually recover within a week, and the illness is mainly mild, although cases of aseptic meningitis have been reported in immunocompromised individuals and children.

There is currently no cure or vaccine for OROV, and treatment involves pain relief medication used for symptom management. Prevention of infection consists mainly of personal control measures such as preventing midge bites by using mosquito nets and repellents and control measures such as eradicating midge breeding sites. It is expected that due to environmental and climate change and global migration, OROV cases will continue to increase and spread further into other countries, including those outside of Central and South America.