- 1What Is the Viral Structure, Genome, and Replicative Cycle?
- 2How Does the Oropouche Virus Get Replicated?
- 3What Are the Transmission Cycles Present in Viral Circulation?
- 4What Is the Incubation and Transmission Period?
- 5What Are the Clinical Aspects of the Oropouche Virus?
- 6What Is Molecular Epidemiology?
Introduction
Oropouche virus is a common arbovirus (transmitted by arthropod vectors) that affects the people of Brazil. This virus has affected over half a million people. The symptoms caused by this condition are very similar to those of other conditions such as Zika (mosquitoes cause this and can result in serious birth defects), dengue (a viral condition), Chikungunya (viral infection caused by mosquitoes), etc. This is why there is a need for proper diagnosis, which is why the estimated number of cases is less than the actual number of cases occurring among the population.
This condition is caused by the Oropouche virus, a segmented single-strand RNA (ribonucleic acid) virus that is a part of the genus Orthobunyavirus of the Peribunyaviridae family. Oropouche virus can be transmitted to humans through the bite of Culicoides paraensis midge. The symptoms related to the disease caused by this virus are similar to dengue. The infection starts between four to eight days after the infective bite. The symptoms caused are acute and include fever, pain, headache, joint stiffness, nausea, and vomiting. These symptoms can last up to five to seven days. Most of the cases recover within seven days, and some healing can take some more time. There is no proper or evident antiviral treatment or vaccine to manage this condition.
What Is the Viral Structure, Genome, and Replicative Cycle?
No ultrasound study based on the virus in human tissue has been published. It is known that this virus produces particles with similar morphological characteristics to another member of the Orthobunyavirus gene. Ultrastructural studies have shown that these viral particles are spherical and measure about 80 to 110 nanometers in diameter, and a lipid envelope surrounds them. The viral particles have three single strands of negative sense segments of RNA of various sizes. These are individually attached to the L protein.
Depending on their size, these segments are called small (SRNA), medium (MRNA), and large (LRNA). The LRNA has one open reading frame that helps to encode the L protein, an RNA-dependent RNA polymerase. This L protein is associated with the other three viral RNA segments. The MRNA has only one open reading frame that encodes a large polyprotein split during or after translation. This produces three viral proteins: two structural surface glycoproteins, Gn (glycoprotein N) and Gc (glycoprotein C), and one non-structural protein called NSm (non-structural protein M).
The SRNA (small ribonucleic acid) encodes a structural nucleocapsid protein and one non-structural NSs (non-structural small) protein in two overlapping open reading frames.
How Does the Oropouche Virus Get Replicated?
The details about the replication process of the Oropouche virus need to be clarified. The progeny production is seen ten hours after the inoculation of the virus in HeLe cells after 24 hours. The surface glycoproteins, such as Gn and Gc, monitor the interaction between the virus particle and the receptor cell. The virus enters the HeLa cells through endocytosis (a cellular procedure where substances are brought inside the cell), and the release of viral particles from the endosome depends on endosomal acidification. An important effect observed after Oropouche virus replication in the HeLa cell is the induction of apoptosis (programmed cell death) seen after 36 hours post-infection.
What Are the Transmission Cycles Present in Viral Circulation?
The viral circulation includes both epidemic and sylvatic cycles. In the sylvatic cycle, birds, sloths, and primates act as vertebrate hosts. A specific arthropod vector is not identified. In the epidemic cycle, humans act as an amplifying host, and the virus is primarily transmitted through the bite of Culicoides paraensis midge.
What Is the Incubation and Transmission Period?
Proper information needs to be provided regarding the incubation period of this virus. However, some studies done during epidemics show that the incubation period can vary from four to eight days. The patient’s blood during the acute phase of the illness is infectious in the initial three to four days after the symptoms. There is no evidence of direct transmission of this virus from one person to another.
What Are the Clinical Aspects of the Oropouche Virus?
The infection caused by the Oropouche virus in humans is an acute febrile illness. This condition occurs along with headaches, myalgia (soreness and pain in the muscle), arthralgia (discomfort caused when two bones meet to form a joint), anorexia (eating disorder), photophobia (sensitivity to light), dizziness, and chills. Some other people also experience nausea, vomiting, diarrhea, conjunctival congestion, orbital pain, etc. Some days after the initial febrile episode, the symptoms usually reoccur with reduced intensity. This is usually seen in about 60 percent of the affected cases. Some people exhibit a clinical presentation of meningitis (inflammation caused in the brain and spinal cord membrane). Recovery is complete without any sequel in some severe cases. There is no record of fatality associated with Oropouche fever. However, identification of the SRNA genomic segment of this virus in the cerebrospinal fluid seen in patients suggests that severe disease affecting the central nervous system occurred during the outbreak of this virus in Brazil.
What Is Molecular Epidemiology?
The first genetic study about the Oropouche virus was carried out in 2000 by Saeed and coworkers. They produced the basis for understanding the molecular epidemiology of this viral agent. This study shows at least three circulating genetic lineages: genotypes I, II, and III. Depending on the findings seen in the nucleotide sequence from the N gene of the 28 Oropouche virus strain, which is extracted from various hosts, locations, and times, it was seen that genotype I was present in Trinidad and Tobago, and genotype II was present in Peru. Genotype II was seen in Panama only. Genotypes I and II were seen in Brazil, and genotype I was also in the Eastern Amazon.
Conclusion
Oropouche virus is a common arbovirus. This is a segmented single-strand virus. This virus usually causes fever, which is a febrile arboviral illness. The symptoms caused by this virus are very similar to other conditions such as dengue, Chikungunya, Zika, etc. This condition is usually not diagnosed properly.
