Oropouche fever

Oropouche fever is characterized as an acute febrile illness, meaning that it begins with a sudden onset of a fever followed by other clinical symptoms. It typically takes four to eight days (the incubation period) from the bite of the infected mosquito or midge to the first signs of infection. As in dengue, a skin rash resembling rubella, conjunctival injection, and pain behind the eyes may occur. Fetal deaths were observed possibly associated with vertical transmission, i.e. from mother to child. == Cause ==

The oropouche virus is an emerging infectious agent, which causes the illness oropouche fever. OROV was first described in Trinidad in 1955 when the prototype strain was isolated from the blood of a febrile human and from Coquillettidia venezuelensis mosquitoes. In Brazil, OROV was first described in 1960 when it was isolated from a three-toed sloth (Bradypus tridactylus) and Ochlerotatus serratus mosquitoes captured nearby during the construction of the Belém–Brasília Highway. ==Epidemiology==

Large epidemics are common and very swift, one of the earliest and largest having occurred in 1961 at the city of Belém, in the Brazilian Amazon state of Pará, with 11,000 recorded cases. In the Brazilian Amazon, oropouche is the second most frequent viral disease, after dengue fever. Several epidemics have generated more than 263,000 cases, of which half occurred in the period from 1978 to 1980. It is estimated that more than half a million cases have occurred since in Brazil alone, with most having gone undiagnosed or misdiagnosed due to limited availability of laboratory methods for diagnosis, the clinical similarity of Oropouche fever to other more prevalent arboviral illnesses, and the fact that in many cases there may be co-infection with other similar mosquito-borne viruses. By August 2024, over 8,000 laboratory-confirmed cases were reported in Bolivia, Brazil, Colombia, Cuba, and Peru, large outbreaks that resulted in travel-associated cases, including 19 Oropouche virus disease cases in European travelers returning from Cuba (n = 18) and Brazil (one) during June–July 2024, and 21 cases in U.S. residents returning from travel to Cuba (20 in Florida, one in New York). While most cases were characterized by mild self-limited febrile illness, two deaths were reported, both in non-pregnant women who were otherwise healthy. ORO fever occurs mainly during the rainy seasons, because there is an increase in breeding sites in the vector populations. There has also been reports of the oropouche epidemics during the dry season but this is most likely due to the high population density of mosquitoes from the past rainy season. == Mechanism ==

Oropouche fever is caused by the oropouche virus (OROV). Pathogenesis There is not a significant amount of information regarding the natural pathogenesis of OROV infections. Within two to four days from the initial onset of systematic symptoms in humans, the virus is detected in the blood. In some cases the virus has also been recovered from the cerebrospinal fluid, but the route of invasion to the central nervous system (CNS) remains unclear. Animal models To further elucidate the pathogenesis of OROV, experiments using murine models have been performed. BALB/c neonate mice were infected subcutaneously and presented clinical symptoms five days after inoculation. The mice revealed a high concentration of the replicating virus in the brain along with inflammation of the meninges and apoptosis of neurons without encephalitis, which is inflammation of the brain due to an infection. These findings confirmed the neurotropism of this virus, which means that this virus is capable of infecting nerve cells. Immunohistochemistry was used to reveal how this virus had access to the central nervous system. As the infection progresses, the virus crosses the blood-brain barrier and spreads to the brain parenchyma leading to severe manifestations of encephalitis. OROV infection starts from the posterior parts of the brain and progresses toward the forebrain.The oropouche virus spreads through the neural routes during early stages of the infection, reaching the spinal cord and traveling upward to the brain through brainstem with little inflammation. == Diagnosis ==

Laboratory diagnosis of the oropouche infection is done through classic and molecular virology techniques. (obtained from recovered patients rich in anti- ORO antibodies) • Reverse transcription polymerase chain reaction (RT-PCR) and real time RT-PCR for genome detection in acute samples (sera, blood, and viscera of infected animals) Clinical diagnosis of oropouche fever is challenging due to the nonspecific nature of the disease; in many cases, it can be confused with dengue fever or other arboviral illnesses. == Prevention ==

Oropouche fever occurs in outbreaks, so the chance contracting it even after being exposed to areas with midges or mosquitoes is small. Prevention strategies include reducing the breeding of midges through source reduction by removal and modification of breeding sites and reducing contact between midges and people. This can be accomplished by reducing the number of natural and artificial water-filled habitats in which the midge larvae grow. There is no vaccine. == Treatment ==

There is no cure or specific therapy for Oropouche fever; only symptomatic treatment (such as analgesics for pain relief and fluids to prevent and treat dehydration) is recommended. Aspirin and other non-steroidal anti-inflammatory drugs are not recommended for treatment. Ribavirin is ineffective and is not recommended. ==Prognosis==

The infection is usually self-limited and complications are rare. Illness usually lasts for about a week, although in extreme cases can be prolonged == See also ==