Omsk hemorrhagic fever (OHF) is a rare disease that occurs sporadically or in small outbreaks, primarily in many regions of western Siberia in Russia. The annual incidence of OHF is estimated to be less than 1 per 100,000 population in these endemic areas. However, the exact number of cases is difficult to ascertain as many cases may go misdiagnosed or unreported, contributing to underestimating the disease burden.
According to data from the World Health Organization, 1,057 confirmed cases of OHF were reported in Russia between 1958 and 2019. Most of these cases occurred in the Omsk oblast, with 734 cases, followed by the Novosibirsk oblast, with 214 cases; Tyumen oblast, with 63 cases; Kurgan oblast, with 35 cases; and Tomsk oblast with 11 cases. While OHF is primarily endemic in western Siberia, a few imported cases have been reported from other countries, including Kazakhstan, Ukraine, Germany, and the United Kingdom.
OHFV is transmitted primarily through ticks or contact with infected rodents, particularly muskrats, which serve as the natural reservoirs and amplifying hosts of the virus. The primary transmission vector is the taiga tick (Ixodes persulcatus), which feeds on rodents and humans. The highest risk of exposure comes during the spring & summer months when tick activity is at its peak.
The case fatality rate (CFR) of OHF varies depending on the strain of OHFV, the severity of symptoms, and the availability of medical care. The overall CFR of OHF is estimated to be around 3%, but it can range from 0.5% to 20% in different outbreaks. In severe cases, hemorrhagic complications, respiratory distress syndrome & renal failure are the most common causes of death.
Kingdom: Virus
Phylum: Negarnaviricota
Class: Ellioviricetes
Order: Bunyavirales
Family: Nairoviridae
Genus:Orthonairovirus
Species:Omsk hemorrhagic fever virus
The Omsk hemorrhagic fever virus (OHFV) is a polygonal or spherical shaped virus enveloped by a host-cell-derived lipid bilayer.The size of the OHFV virion is approximately 40-50 nm in diameter, and it contains a nucleocapsid with a diameter of 25 nm.
The polyprotein generates structural proteins such as the capsid protein, which forms a protective shell around the viral genetic material, & two envelope proteins, which are required for viral attachment & penetration into host cells.
The OHFV genome comprises an open reading frame (ORF) flanked by 5′ & 3′ untranslated regions (UTR). The 5′ UTR is 123 nucleotides long and has a conserved section with a stem-loop structure and an extra stem loop at the 5′ ends. The ORF encodes a single polyprotein broken into three structural proteins & seven non-structural proteins by both viral & host proteases.
Omsk hemorrhagic fever virus (OHFV) exhibits genetic diversity, and two genotypes have been identified. The first genotype is characterized by prototypical strains OHFV/Kubrin and OHFV/Bogolubovska, which show a minimal genetic distance between them. These strains have only six nucleotide substitutions in the genome, encoding four amino acid changes.
The second genotype’s prototypical strain is OHFV/uve. Despite the genetic differences between the two genotypes, OHFV/uve still shares a close relationship with the first genotype, indicating their relatedness.
Interestingly, the two genotypes of OHFV display distinct geographic distributions. Genotype A is predominantly found in Novosibirsk and Omsk oblasts, while genotype B is more common in Kurgan and Tyumen oblasts. This geographical variation suggests localized evolution and virus adaptation in different regions.
The differences between the two genotypes also extend to their pathogenicity in humans. Genotype A has been associated with severe hemorrhagic fever in infected individuals. On the other hand, infections caused by genotype B tend to be mild or even asymptomatic. This variation in disease severity underscores the importance of understanding the genetic characteristics of OHFV and potential impact on human health.
One crucial element of the OHFV genome is the methyltransferase (MTase) domain. This domain plays a vital role in catalyzing the capping and methylation of viral RNA. These modifications are essential for the stability and translation of the viral RNA. The capping of the viral RNA protects it from degradation by host cellular enzymes. It facilitates the efficient translation of viral proteins, enabling the virus to replicate and spread effectively within the host.
The pathogenesis of the Omsk hemorrhagic fever virus (OHFV) involves a complex interplay between the virus and the host’s immune response. OHFV is primarily transmitted by ticks or contact with infected rodents, particularly muskrats, which serve as the natural reservoirs for the virus. The virus enters the host through the skin or mucous membranes and infects various types of cells, including endothelial cells, macrophages, dendritic cells, and hepatocytes.
The infection & destruction of endothelial cells, which line the blood arteries, increase vascular permeability, edema, bleeding, and shock. OHFV also infects and damages other organs, such as the liver, kidneys, lungs, and brain, causing inflammation, necrosis, and dysfunction. The severity of OHFV infection can vary depending on the virus strain, the infection dose, and the host’s genetic factors.
The host immune response plays a dual role in the pathogenesis of OHFV. Also, it helps to control the viral infection by producing antibodies and cytokines that can neutralize or inhibit the virus. On the other hand, it can also contribute to tissue damage and disease severity by causing excessive inflammation, immune activation, and coagulation disorders. The balance between the protective & harmful effects of the immune response triggers the outcome of OHFV infection.
OHFV replication occurs in the cytoplasm of infected cells, and viral particles are released from the cells by budding or lysis, spreading to other tissues and organs via the bloodstream or lymphatic system. The virus can also propagate via contact with infected rodents’ blood, feces, or urine, and in rare cases, through milk from infected goats or sheep.
Like other severe viral illnesses, OHFV infection may lead to a hyperimmune response known as a “cytokine storm,” where a massive release of pro-inflammatory cytokines such as IL-1, IL-6, IL-8, and TNF-α. Excessive cytokine release can result in vasodilation, multiple organ failure, and shock. Additionally, OHFV has evolved mechanisms to evade the host’s interferon response, delaying interferon production and inhibiting interferon regulatory factor-3 (IRF3) activation.
Host defenses against Omsk hemorrhagic fever virus (OHFV) involve various components of the immune system that work together to combat the viral infection. In a study analyzing the effect of OHFV and RSSEV on the cell population of the spleen, it was observed that the total number of splenocytes was not significantly affected following RSSEV infection in mice. However, both OHFV and RSSEV infections led to changes in the proportions of specific immune cell populations in the spleen.
During the early stages of infection, OHFV infections significantly increased the fraction of CD8+ T cells in BALB/c mice. Later, point, this rise was more evident in OHFV-infected mice than in RSSEV-infected animals. Furthermore, compared to RSSEV, OHFV infection resulted in more immense proportions of NK cells, granulocytes, and plasmacytoid dendritic cells (pDCs) at 3 days post-infection (dpi). In both BALB/c & C57BL/6 mice, the proportion of CD4+ T lymphocytes in the spleen was unaffected by OHFV infection.
In the spleens of OHFV-infected mice, they observed an early increase in pro-inflammatory mediators such as IL-1 and TNF-α and chemokines such as MCP-1, MIP-1β, MIP-1α, & RANTES. Compared to RSSEV or mock-infected animals, these chemokines and cytokines were enhanced at 3 dpi and positively linked with viral titer. The fact that these pro-inflammatory mediators are released in the spleen before they are detected in the serum and brain shows that the immune response to OHFV is created peripherally.
Although the immune response is critical for viral infection control, pro-inflammatory cytokines such as IL-1 & TNF-α may trigger endothelial dysfunction and shock during viral hemorrhagic fevers. Infection with other hemorrhagic fever viruses, like Ebola, has been linked to NK, CD4+ T cells, & CD8+ T cell depletion, possibly contributing to illness development.
Surprisingly, no splenic subset loss was found in OHFV-infected mice in this investigation, indicating that the quantity of splenocyte subsets may not closely correspond with the pathophysiology of OHFV infection. However, further research is needed into the activation status of immune cells and their impact on cytokine & chemokine production and modulation.
Omsk hemorrhagic fever virus (OHFV) is the causative agent of Omsk hemorrhagic fever (OHF), a rare and severe disease that affects both humans and some animals. The clinical manifestations of OHF can vary in severity, ranging from mild to severe and life-threatening. Common symptoms include a sudden high fever (39-40°C) and chills.
The fever can last for 1-2 weeks and may show a biphasic pattern, where it briefly improves before recurring.One of the most characteristic and prominent symptoms of OHF is a severe headache, which may be associated with dizziness, confusion, or altered consciousness. Patients often experience intense muscle pain, particularly in the back and legs, which can significantly limit their mobility.
A maculopapular rash, consisting of small red bumps or spots, may appear on the soft palate, the roof of the mouth, as well as on the face, neck, chest, and limbs. The rash can sometimes be petechial, characterized by tiny red dots resulting in bleeding under the skin.OHF is characterized by irritation and swelling of the neck, face, and mucous membranes of the throat and mouth, which can cause trouble breathing or swallowing.
Conjunctival suffusion, or the flow of blood into the eye’s white area, can cause red and watery eyes.Bleeding problems are significant complications of OHF and can manifest as nosebleeds, gum bleeding, blood in the urine or stool, or internal bleeding in the organs. In severe cases, bleeding can be seen in the brain, leading to stroke-like symptoms such as weakness, numbness, or paralysis.
In addition to the main symptoms, patients with OHF may experience other manifestations such as nausea, vomiting, diarrhea, abdominal pain, cough, sore throat, or chest pain. Approximately one-third of patients may develop pneumonia, kidney damage, meningitis (brain inflammation), or a combination of these conditions. These complications can be life-threatening and often require intensive medical care and management.
Diagnosing Omsk hemorrhagic fever virus (OHFV) involves various laboratory tests and clinical evaluation. Two main approaches for diagnosing OHFV are virus isolation in cell culture and molecular techniques such as polymerase chain reaction & serologic testing using enzyme-linked immunosorbent serological assay (ELISA).
In the early stages of infection, OHFV may be detected in blood samples through virus isolation in cell culture. This method involves culturing the virus from the patient’s blood sample in specialized cells in the laboratory. Alternatively, molecular techniques like PCR can be employed to directly detect the presence of OHFV genetic material in the blood. PCR is particularly useful in the early phase of the disease when the viral load may be higher.
Serologic testing plays a crucial role in OHFV diagnosis. Blood samples can be tested for antibodies specific to OHFV using ELISA. The essence of specific antibodies confirms exposure to the virus. In some cases, a paired sera approach is used, where blood samples taken during the acute and convalescent phases of the disease are compared. A significant increase in antibody titer between the two samples confirms the diagnosis of Omsk hemorrhagic fever.
Diagnosis of OHFV also involves considering the patient’s characteristic clinical data and epidemiological history. Clinical manifestations, such as high fever, headache, muscle pain, bleeding problems, and characteristic rash, are considered. Additionally, laboratory tests are performed, including general blood and urine analysis. OHFV infection often leads to leukopenia (low white blood cell count), thrombocytopenia (low platelet count), and other abnormal blood and urine parameters.
In complicated cases, further diagnostic investigations may include electrocardiography (ECG) to detect myocardial changes and chest radiography to assess for signs of interstitial pneumonia.
People residing or working in natural foci of OHFV infection should regularly examine their clothing and bodies to detect and remove ticks promptly. Early detection and removal of ticks can reduce the risk of transmission.
Individuals at risk, such as those engaged in camping, farming, forestry, and hunting (particularly Siberian muskrat hunting), should take personal protective measures. It involves wearing protective clothing that covers the body and using insect repellents to prevent tick bites.
Omsk hemorrhagic fever (OHF) is a rare disease that occurs sporadically or in small outbreaks, primarily in many regions of western Siberia in Russia. The annual incidence of OHF is estimated to be less than 1 per 100,000 population in these endemic areas. However, the exact number of cases is difficult to ascertain as many cases may go misdiagnosed or unreported, contributing to underestimating the disease burden.
According to data from the World Health Organization, 1,057 confirmed cases of OHF were reported in Russia between 1958 and 2019. Most of these cases occurred in the Omsk oblast, with 734 cases, followed by the Novosibirsk oblast, with 214 cases; Tyumen oblast, with 63 cases; Kurgan oblast, with 35 cases; and Tomsk oblast with 11 cases. While OHF is primarily endemic in western Siberia, a few imported cases have been reported from other countries, including Kazakhstan, Ukraine, Germany, and the United Kingdom.
OHFV is transmitted primarily through ticks or contact with infected rodents, particularly muskrats, which serve as the natural reservoirs and amplifying hosts of the virus. The primary transmission vector is the taiga tick (Ixodes persulcatus), which feeds on rodents and humans. The highest risk of exposure comes during the spring & summer months when tick activity is at its peak.
The case fatality rate (CFR) of OHF varies depending on the strain of OHFV, the severity of symptoms, and the availability of medical care. The overall CFR of OHF is estimated to be around 3%, but it can range from 0.5% to 20% in different outbreaks. In severe cases, hemorrhagic complications, respiratory distress syndrome & renal failure are the most common causes of death.
Kingdom: Virus
Phylum: Negarnaviricota
Class: Ellioviricetes
Order: Bunyavirales
Family: Nairoviridae
Genus:Orthonairovirus
Species:Omsk hemorrhagic fever virus
The Omsk hemorrhagic fever virus (OHFV) is a polygonal or spherical shaped virus enveloped by a host-cell-derived lipid bilayer.The size of the OHFV virion is approximately 40-50 nm in diameter, and it contains a nucleocapsid with a diameter of 25 nm.
The polyprotein generates structural proteins such as the capsid protein, which forms a protective shell around the viral genetic material, & two envelope proteins, which are required for viral attachment & penetration into host cells.
The OHFV genome comprises an open reading frame (ORF) flanked by 5′ & 3′ untranslated regions (UTR). The 5′ UTR is 123 nucleotides long and has a conserved section with a stem-loop structure and an extra stem loop at the 5′ ends. The ORF encodes a single polyprotein broken into three structural proteins & seven non-structural proteins by both viral & host proteases.
Omsk hemorrhagic fever virus (OHFV) exhibits genetic diversity, and two genotypes have been identified. The first genotype is characterized by prototypical strains OHFV/Kubrin and OHFV/Bogolubovska, which show a minimal genetic distance between them. These strains have only six nucleotide substitutions in the genome, encoding four amino acid changes.
The second genotype’s prototypical strain is OHFV/uve. Despite the genetic differences between the two genotypes, OHFV/uve still shares a close relationship with the first genotype, indicating their relatedness.
Interestingly, the two genotypes of OHFV display distinct geographic distributions. Genotype A is predominantly found in Novosibirsk and Omsk oblasts, while genotype B is more common in Kurgan and Tyumen oblasts. This geographical variation suggests localized evolution and virus adaptation in different regions.
The differences between the two genotypes also extend to their pathogenicity in humans. Genotype A has been associated with severe hemorrhagic fever in infected individuals. On the other hand, infections caused by genotype B tend to be mild or even asymptomatic. This variation in disease severity underscores the importance of understanding the genetic characteristics of OHFV and potential impact on human health.
One crucial element of the OHFV genome is the methyltransferase (MTase) domain. This domain plays a vital role in catalyzing the capping and methylation of viral RNA. These modifications are essential for the stability and translation of the viral RNA. The capping of the viral RNA protects it from degradation by host cellular enzymes. It facilitates the efficient translation of viral proteins, enabling the virus to replicate and spread effectively within the host.
The pathogenesis of the Omsk hemorrhagic fever virus (OHFV) involves a complex interplay between the virus and the host’s immune response. OHFV is primarily transmitted by ticks or contact with infected rodents, particularly muskrats, which serve as the natural reservoirs for the virus. The virus enters the host through the skin or mucous membranes and infects various types of cells, including endothelial cells, macrophages, dendritic cells, and hepatocytes.
The infection & destruction of endothelial cells, which line the blood arteries, increase vascular permeability, edema, bleeding, and shock. OHFV also infects and damages other organs, such as the liver, kidneys, lungs, and brain, causing inflammation, necrosis, and dysfunction. The severity of OHFV infection can vary depending on the virus strain, the infection dose, and the host’s genetic factors.
The host immune response plays a dual role in the pathogenesis of OHFV. Also, it helps to control the viral infection by producing antibodies and cytokines that can neutralize or inhibit the virus. On the other hand, it can also contribute to tissue damage and disease severity by causing excessive inflammation, immune activation, and coagulation disorders. The balance between the protective & harmful effects of the immune response triggers the outcome of OHFV infection.
OHFV replication occurs in the cytoplasm of infected cells, and viral particles are released from the cells by budding or lysis, spreading to other tissues and organs via the bloodstream or lymphatic system. The virus can also propagate via contact with infected rodents’ blood, feces, or urine, and in rare cases, through milk from infected goats or sheep.
Like other severe viral illnesses, OHFV infection may lead to a hyperimmune response known as a “cytokine storm,” where a massive release of pro-inflammatory cytokines such as IL-1, IL-6, IL-8, and TNF-α. Excessive cytokine release can result in vasodilation, multiple organ failure, and shock. Additionally, OHFV has evolved mechanisms to evade the host’s interferon response, delaying interferon production and inhibiting interferon regulatory factor-3 (IRF3) activation.
Host defenses against Omsk hemorrhagic fever virus (OHFV) involve various components of the immune system that work together to combat the viral infection. In a study analyzing the effect of OHFV and RSSEV on the cell population of the spleen, it was observed that the total number of splenocytes was not significantly affected following RSSEV infection in mice. However, both OHFV and RSSEV infections led to changes in the proportions of specific immune cell populations in the spleen.
During the early stages of infection, OHFV infections significantly increased the fraction of CD8+ T cells in BALB/c mice. Later, point, this rise was more evident in OHFV-infected mice than in RSSEV-infected animals. Furthermore, compared to RSSEV, OHFV infection resulted in more immense proportions of NK cells, granulocytes, and plasmacytoid dendritic cells (pDCs) at 3 days post-infection (dpi). In both BALB/c & C57BL/6 mice, the proportion of CD4+ T lymphocytes in the spleen was unaffected by OHFV infection.
In the spleens of OHFV-infected mice, they observed an early increase in pro-inflammatory mediators such as IL-1 and TNF-α and chemokines such as MCP-1, MIP-1β, MIP-1α, & RANTES. Compared to RSSEV or mock-infected animals, these chemokines and cytokines were enhanced at 3 dpi and positively linked with viral titer. The fact that these pro-inflammatory mediators are released in the spleen before they are detected in the serum and brain shows that the immune response to OHFV is created peripherally.
Although the immune response is critical for viral infection control, pro-inflammatory cytokines such as IL-1 & TNF-α may trigger endothelial dysfunction and shock during viral hemorrhagic fevers. Infection with other hemorrhagic fever viruses, like Ebola, has been linked to NK, CD4+ T cells, & CD8+ T cell depletion, possibly contributing to illness development.
Surprisingly, no splenic subset loss was found in OHFV-infected mice in this investigation, indicating that the quantity of splenocyte subsets may not closely correspond with the pathophysiology of OHFV infection. However, further research is needed into the activation status of immune cells and their impact on cytokine & chemokine production and modulation.
Omsk hemorrhagic fever virus (OHFV) is the causative agent of Omsk hemorrhagic fever (OHF), a rare and severe disease that affects both humans and some animals. The clinical manifestations of OHF can vary in severity, ranging from mild to severe and life-threatening. Common symptoms include a sudden high fever (39-40°C) and chills.
The fever can last for 1-2 weeks and may show a biphasic pattern, where it briefly improves before recurring.One of the most characteristic and prominent symptoms of OHF is a severe headache, which may be associated with dizziness, confusion, or altered consciousness. Patients often experience intense muscle pain, particularly in the back and legs, which can significantly limit their mobility.
A maculopapular rash, consisting of small red bumps or spots, may appear on the soft palate, the roof of the mouth, as well as on the face, neck, chest, and limbs. The rash can sometimes be petechial, characterized by tiny red dots resulting in bleeding under the skin.OHF is characterized by irritation and swelling of the neck, face, and mucous membranes of the throat and mouth, which can cause trouble breathing or swallowing.
Conjunctival suffusion, or the flow of blood into the eye’s white area, can cause red and watery eyes.Bleeding problems are significant complications of OHF and can manifest as nosebleeds, gum bleeding, blood in the urine or stool, or internal bleeding in the organs. In severe cases, bleeding can be seen in the brain, leading to stroke-like symptoms such as weakness, numbness, or paralysis.
In addition to the main symptoms, patients with OHF may experience other manifestations such as nausea, vomiting, diarrhea, abdominal pain, cough, sore throat, or chest pain. Approximately one-third of patients may develop pneumonia, kidney damage, meningitis (brain inflammation), or a combination of these conditions. These complications can be life-threatening and often require intensive medical care and management.
Diagnosing Omsk hemorrhagic fever virus (OHFV) involves various laboratory tests and clinical evaluation. Two main approaches for diagnosing OHFV are virus isolation in cell culture and molecular techniques such as polymerase chain reaction & serologic testing using enzyme-linked immunosorbent serological assay (ELISA).
In the early stages of infection, OHFV may be detected in blood samples through virus isolation in cell culture. This method involves culturing the virus from the patient’s blood sample in specialized cells in the laboratory. Alternatively, molecular techniques like PCR can be employed to directly detect the presence of OHFV genetic material in the blood. PCR is particularly useful in the early phase of the disease when the viral load may be higher.
Serologic testing plays a crucial role in OHFV diagnosis. Blood samples can be tested for antibodies specific to OHFV using ELISA. The essence of specific antibodies confirms exposure to the virus. In some cases, a paired sera approach is used, where blood samples taken during the acute and convalescent phases of the disease are compared. A significant increase in antibody titer between the two samples confirms the diagnosis of Omsk hemorrhagic fever.
Diagnosis of OHFV also involves considering the patient’s characteristic clinical data and epidemiological history. Clinical manifestations, such as high fever, headache, muscle pain, bleeding problems, and characteristic rash, are considered. Additionally, laboratory tests are performed, including general blood and urine analysis. OHFV infection often leads to leukopenia (low white blood cell count), thrombocytopenia (low platelet count), and other abnormal blood and urine parameters.
In complicated cases, further diagnostic investigations may include electrocardiography (ECG) to detect myocardial changes and chest radiography to assess for signs of interstitial pneumonia.
People residing or working in natural foci of OHFV infection should regularly examine their clothing and bodies to detect and remove ticks promptly. Early detection and removal of ticks can reduce the risk of transmission.
Individuals at risk, such as those engaged in camping, farming, forestry, and hunting (particularly Siberian muskrat hunting), should take personal protective measures. It involves wearing protective clothing that covers the body and using insect repellents to prevent tick bites.
Omsk hemorrhagic fever (OHF) is a rare disease that occurs sporadically or in small outbreaks, primarily in many regions of western Siberia in Russia. The annual incidence of OHF is estimated to be less than 1 per 100,000 population in these endemic areas. However, the exact number of cases is difficult to ascertain as many cases may go misdiagnosed or unreported, contributing to underestimating the disease burden.
According to data from the World Health Organization, 1,057 confirmed cases of OHF were reported in Russia between 1958 and 2019. Most of these cases occurred in the Omsk oblast, with 734 cases, followed by the Novosibirsk oblast, with 214 cases; Tyumen oblast, with 63 cases; Kurgan oblast, with 35 cases; and Tomsk oblast with 11 cases. While OHF is primarily endemic in western Siberia, a few imported cases have been reported from other countries, including Kazakhstan, Ukraine, Germany, and the United Kingdom.
OHFV is transmitted primarily through ticks or contact with infected rodents, particularly muskrats, which serve as the natural reservoirs and amplifying hosts of the virus. The primary transmission vector is the taiga tick (Ixodes persulcatus), which feeds on rodents and humans. The highest risk of exposure comes during the spring & summer months when tick activity is at its peak.
The case fatality rate (CFR) of OHF varies depending on the strain of OHFV, the severity of symptoms, and the availability of medical care. The overall CFR of OHF is estimated to be around 3%, but it can range from 0.5% to 20% in different outbreaks. In severe cases, hemorrhagic complications, respiratory distress syndrome & renal failure are the most common causes of death.
Kingdom: Virus
Phylum: Negarnaviricota
Class: Ellioviricetes
Order: Bunyavirales
Family: Nairoviridae
Genus:Orthonairovirus
Species:Omsk hemorrhagic fever virus
The Omsk hemorrhagic fever virus (OHFV) is a polygonal or spherical shaped virus enveloped by a host-cell-derived lipid bilayer.The size of the OHFV virion is approximately 40-50 nm in diameter, and it contains a nucleocapsid with a diameter of 25 nm.
The polyprotein generates structural proteins such as the capsid protein, which forms a protective shell around the viral genetic material, & two envelope proteins, which are required for viral attachment & penetration into host cells.
The OHFV genome comprises an open reading frame (ORF) flanked by 5′ & 3′ untranslated regions (UTR). The 5′ UTR is 123 nucleotides long and has a conserved section with a stem-loop structure and an extra stem loop at the 5′ ends. The ORF encodes a single polyprotein broken into three structural proteins & seven non-structural proteins by both viral & host proteases.
Omsk hemorrhagic fever virus (OHFV) exhibits genetic diversity, and two genotypes have been identified. The first genotype is characterized by prototypical strains OHFV/Kubrin and OHFV/Bogolubovska, which show a minimal genetic distance between them. These strains have only six nucleotide substitutions in the genome, encoding four amino acid changes.
The second genotype’s prototypical strain is OHFV/uve. Despite the genetic differences between the two genotypes, OHFV/uve still shares a close relationship with the first genotype, indicating their relatedness.
Interestingly, the two genotypes of OHFV display distinct geographic distributions. Genotype A is predominantly found in Novosibirsk and Omsk oblasts, while genotype B is more common in Kurgan and Tyumen oblasts. This geographical variation suggests localized evolution and virus adaptation in different regions.
The differences between the two genotypes also extend to their pathogenicity in humans. Genotype A has been associated with severe hemorrhagic fever in infected individuals. On the other hand, infections caused by genotype B tend to be mild or even asymptomatic. This variation in disease severity underscores the importance of understanding the genetic characteristics of OHFV and potential impact on human health.
One crucial element of the OHFV genome is the methyltransferase (MTase) domain. This domain plays a vital role in catalyzing the capping and methylation of viral RNA. These modifications are essential for the stability and translation of the viral RNA. The capping of the viral RNA protects it from degradation by host cellular enzymes. It facilitates the efficient translation of viral proteins, enabling the virus to replicate and spread effectively within the host.
The pathogenesis of the Omsk hemorrhagic fever virus (OHFV) involves a complex interplay between the virus and the host’s immune response. OHFV is primarily transmitted by ticks or contact with infected rodents, particularly muskrats, which serve as the natural reservoirs for the virus. The virus enters the host through the skin or mucous membranes and infects various types of cells, including endothelial cells, macrophages, dendritic cells, and hepatocytes.
The infection & destruction of endothelial cells, which line the blood arteries, increase vascular permeability, edema, bleeding, and shock. OHFV also infects and damages other organs, such as the liver, kidneys, lungs, and brain, causing inflammation, necrosis, and dysfunction. The severity of OHFV infection can vary depending on the virus strain, the infection dose, and the host’s genetic factors.
The host immune response plays a dual role in the pathogenesis of OHFV. Also, it helps to control the viral infection by producing antibodies and cytokines that can neutralize or inhibit the virus. On the other hand, it can also contribute to tissue damage and disease severity by causing excessive inflammation, immune activation, and coagulation disorders. The balance between the protective & harmful effects of the immune response triggers the outcome of OHFV infection.
OHFV replication occurs in the cytoplasm of infected cells, and viral particles are released from the cells by budding or lysis, spreading to other tissues and organs via the bloodstream or lymphatic system. The virus can also propagate via contact with infected rodents’ blood, feces, or urine, and in rare cases, through milk from infected goats or sheep.
Like other severe viral illnesses, OHFV infection may lead to a hyperimmune response known as a “cytokine storm,” where a massive release of pro-inflammatory cytokines such as IL-1, IL-6, IL-8, and TNF-α. Excessive cytokine release can result in vasodilation, multiple organ failure, and shock. Additionally, OHFV has evolved mechanisms to evade the host’s interferon response, delaying interferon production and inhibiting interferon regulatory factor-3 (IRF3) activation.
Host defenses against Omsk hemorrhagic fever virus (OHFV) involve various components of the immune system that work together to combat the viral infection. In a study analyzing the effect of OHFV and RSSEV on the cell population of the spleen, it was observed that the total number of splenocytes was not significantly affected following RSSEV infection in mice. However, both OHFV and RSSEV infections led to changes in the proportions of specific immune cell populations in the spleen.
During the early stages of infection, OHFV infections significantly increased the fraction of CD8+ T cells in BALB/c mice. Later, point, this rise was more evident in OHFV-infected mice than in RSSEV-infected animals. Furthermore, compared to RSSEV, OHFV infection resulted in more immense proportions of NK cells, granulocytes, and plasmacytoid dendritic cells (pDCs) at 3 days post-infection (dpi). In both BALB/c & C57BL/6 mice, the proportion of CD4+ T lymphocytes in the spleen was unaffected by OHFV infection.
In the spleens of OHFV-infected mice, they observed an early increase in pro-inflammatory mediators such as IL-1 and TNF-α and chemokines such as MCP-1, MIP-1β, MIP-1α, & RANTES. Compared to RSSEV or mock-infected animals, these chemokines and cytokines were enhanced at 3 dpi and positively linked with viral titer. The fact that these pro-inflammatory mediators are released in the spleen before they are detected in the serum and brain shows that the immune response to OHFV is created peripherally.
Although the immune response is critical for viral infection control, pro-inflammatory cytokines such as IL-1 & TNF-α may trigger endothelial dysfunction and shock during viral hemorrhagic fevers. Infection with other hemorrhagic fever viruses, like Ebola, has been linked to NK, CD4+ T cells, & CD8+ T cell depletion, possibly contributing to illness development.
Surprisingly, no splenic subset loss was found in OHFV-infected mice in this investigation, indicating that the quantity of splenocyte subsets may not closely correspond with the pathophysiology of OHFV infection. However, further research is needed into the activation status of immune cells and their impact on cytokine & chemokine production and modulation.
Omsk hemorrhagic fever virus (OHFV) is the causative agent of Omsk hemorrhagic fever (OHF), a rare and severe disease that affects both humans and some animals. The clinical manifestations of OHF can vary in severity, ranging from mild to severe and life-threatening. Common symptoms include a sudden high fever (39-40°C) and chills.
The fever can last for 1-2 weeks and may show a biphasic pattern, where it briefly improves before recurring.One of the most characteristic and prominent symptoms of OHF is a severe headache, which may be associated with dizziness, confusion, or altered consciousness. Patients often experience intense muscle pain, particularly in the back and legs, which can significantly limit their mobility.
A maculopapular rash, consisting of small red bumps or spots, may appear on the soft palate, the roof of the mouth, as well as on the face, neck, chest, and limbs. The rash can sometimes be petechial, characterized by tiny red dots resulting in bleeding under the skin.OHF is characterized by irritation and swelling of the neck, face, and mucous membranes of the throat and mouth, which can cause trouble breathing or swallowing.
Conjunctival suffusion, or the flow of blood into the eye’s white area, can cause red and watery eyes.Bleeding problems are significant complications of OHF and can manifest as nosebleeds, gum bleeding, blood in the urine or stool, or internal bleeding in the organs. In severe cases, bleeding can be seen in the brain, leading to stroke-like symptoms such as weakness, numbness, or paralysis.
In addition to the main symptoms, patients with OHF may experience other manifestations such as nausea, vomiting, diarrhea, abdominal pain, cough, sore throat, or chest pain. Approximately one-third of patients may develop pneumonia, kidney damage, meningitis (brain inflammation), or a combination of these conditions. These complications can be life-threatening and often require intensive medical care and management.
Diagnosing Omsk hemorrhagic fever virus (OHFV) involves various laboratory tests and clinical evaluation. Two main approaches for diagnosing OHFV are virus isolation in cell culture and molecular techniques such as polymerase chain reaction & serologic testing using enzyme-linked immunosorbent serological assay (ELISA).
In the early stages of infection, OHFV may be detected in blood samples through virus isolation in cell culture. This method involves culturing the virus from the patient’s blood sample in specialized cells in the laboratory. Alternatively, molecular techniques like PCR can be employed to directly detect the presence of OHFV genetic material in the blood. PCR is particularly useful in the early phase of the disease when the viral load may be higher.
Serologic testing plays a crucial role in OHFV diagnosis. Blood samples can be tested for antibodies specific to OHFV using ELISA. The essence of specific antibodies confirms exposure to the virus. In some cases, a paired sera approach is used, where blood samples taken during the acute and convalescent phases of the disease are compared. A significant increase in antibody titer between the two samples confirms the diagnosis of Omsk hemorrhagic fever.
Diagnosis of OHFV also involves considering the patient’s characteristic clinical data and epidemiological history. Clinical manifestations, such as high fever, headache, muscle pain, bleeding problems, and characteristic rash, are considered. Additionally, laboratory tests are performed, including general blood and urine analysis. OHFV infection often leads to leukopenia (low white blood cell count), thrombocytopenia (low platelet count), and other abnormal blood and urine parameters.
In complicated cases, further diagnostic investigations may include electrocardiography (ECG) to detect myocardial changes and chest radiography to assess for signs of interstitial pneumonia.
People residing or working in natural foci of OHFV infection should regularly examine their clothing and bodies to detect and remove ticks promptly. Early detection and removal of ticks can reduce the risk of transmission.
Individuals at risk, such as those engaged in camping, farming, forestry, and hunting (particularly Siberian muskrat hunting), should take personal protective measures. It involves wearing protective clothing that covers the body and using insect repellents to prevent tick bites.
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