Epidemiology, Infectious Diseases, Viruses

Omsk Hemorrhagic Fever (OHF): A Rare Viral Disease

Author Chandana Balasubramanian , 29-May-2023

Omsk hemorrhagic fever (OHF) is a rare and severe virus first discovered in Siberia, Russia. It is caused by the Omsk hemorrhagic fever virus or OHFV, which belongs to the Flavivirus family of viruses. Other well-known viruses from this family are dengue, yellow fever, and the West Nile virus. You may wonder, if a disease is rare, why learn about it?


Well, the main issue is that viruses mutate, and learning from early outbreaks can help healthcare professionals and public health officials prepare better and prevent larger outbreaks or epidemics. Also, as we will see, the story of OHF is a cautionary tale about the impact of human-mediated disturbances on the ecology of an area. Recent research also shows that the effects of climate change may be spreading this tick-borne disease beyond Russia’s borders. Lastly, viral hemorrhagic fevers have been listed as potential bioterrorism agents, so it is important to stay vigilant.


This article is an OHF 101. We will explore the history of Omsk hemorrhagic fever (OHF), followed by a discussion on its epidemiology. Next, we dive into the symptoms, diagnostic methods, treatment, and preventive measures associated with OHF.



Omsk hemorrhagic fever (OHF) was first identified in the Omsk region of Russia in the 1940s. The virus responsible for OHF, known as Omsk hemorrhagic fever virus (OHFV), belongs to the Flavivirus genus, which also includes other viruses such as dengue, yellow fever, and West Nile virus. Sporadic outbreaks have occurred primarily in Siberia and Kazakhstan.

Gagarina et al. (1959) first noted that a disease found in muskrats was caused by a virus. This was later confirmed by Melentyeva and Fedorova. Konstantinov and Chudinov (1963) reported on Omsk outbreaks among hunters who came in touch with muskrats.

The transmission cycle involves two main hosts: ticks (Dermacentor reticulatus and Ixodes persulcatus) and muskrats (Ondatra zibethicus). Humans can contract OHF through tick bites or contact with infected animals’ blood or tissues.



Omsk hemorrhagic fever (OHF) is a rare viral disease primarily found in Western Siberia, Russia. The virus responsible for OHF belongs to the tick-borne flavivirus group and is transmitted through the bite of infected ticks (Dermacentor reticulatus and Ixodes persulcatus) or contact with sick muskrats. Although human cases are sporadic, notable outbreaks have occurred in 1945, 1953-54, and 1968.

From 1945 to 1951, 1,000 residents who were in contact with Ixodes ticks fell ill. This was the highest recorded incidence of OHF.

The incidence of OHF varies seasonally due to tick activity; most cases occur between April and November. Additionally, people who work outdoors or engage in recreational activities near rivers or forests are at a higher risk for infection. The epidemiology of Omsk Hemorrhagic Fever is still being examined, yet the existing evidence implies it has a seasonal pattern and mostly affects rural locales.

The CDC notes that the case fatality rate of OHF is quite low, at 0.5% to 3%. Recent studies suggest that climate change may influence the distribution of tick vectors and potentially expand the geographic range of OHF into new areas.


How is it spread?

Although humans have been infected by the OHFV virus, there is no evidence of human-to-human transmission. The virus is spread through tick bites or contact with infected muskrats. Muskrats are big rodents and are a part of the same family as rats, moles, and hamsters. They are usually found next to water bodies like rivers, lakes, or ponds.

Muskrats are native to North America, but because they were in much demand for their fur, they were introduced to Europe in the early 20th century. Unfortunately, they spread through Europe and even Asia and are now considered a pest. Now, they are also responsible for carrying and spreading the Omsk Hemorrhagic fever virus to humans, a human-mediated ecological disturbance because there had never been an issue until human intervention in Russia.

Recent research indicates that the disease may be spreading beyond Russian borders due to climate change making non-endemic regions favorable for ticks.

The OHFV virus is a single-stranded RNA virus.



OHF is a severe viral illness characterized by a sudden onset and a range of symptoms. According to the CDC, the incubation period is 3-8 days. The initial phase, known as the febrile stage, typically lasts for 3-7 days and includes high fever, chills, headache, muscle pain, fatigue, and bleeding.

Patients can also experience low blood pressure and low blood cell counts during this phase. During this time, patients may also experience gastrointestinal issues such as nausea, vomiting, diarrhea, or abdominal pain.

The disease is biphasic. In the second phase of OHF, people who are infected can have a fever and brain inflammation (encephalitis). Patients may also experience weakness, hearing loss, hair loss, and mental health issues. In rare cases, infected individuals can also experience neurological functions.


Omsk hemorrhagic fever is diagnosed through a combination of clinical symptoms, epidemiological data, and laboratory testing. The CDC suggests utilizing ELISA tests to detect antibodies in the patient’s blood or RT-PCR to recognize viral RNA as diagnostic methods for Omsk hemorrhagic fever.

Healthcare professionals should also consider other factors such as travel history, exposure to ticks or muskrats, and the presence of similar cases in the area. Collecting patient travel history when they present can help clinicians perform more accurate differential diagnosis at the point of care. Early diagnosis is crucial for effective treatment and management of this potentially fatal disease.



Currently, there is no specific antiviral treatment or cure for Omsk hemorrhagic fever (OHF). The primary focus lies in providing supportive care to patients. This includes hydration, pain relief, and management of complications that may arise due to the infection.

Intravenous fluids are administered to maintain hydration levels, while medications like acetaminophen can help alleviate pain and reduce fever. In severe cases, blood transfusions or platelet infusions might be necessary if bleeding occurs.

Research on potential treatments for OHF is ongoing; however, none have been approved yet. Investigations have been conducted to get a grasp on the molecular activities of the Omsk hemorrhagic fever virus (OHFV) and create potential cures. One significant development is the identification of a key protein interaction that plays a role in OHFV replication, which could serve as a target for antiviral drugs.

Healthcare professionals should closely monitor patients with suspected or confirmed OHF infections and provide appropriate supportive care as needed. Tackling Omsk Hemorrhagic Fever is imperative to controlling the spread and severity of this potentially fatal illness.


Preventing OHF mainly involves reducing exposure to ticks and rodents, which are the primary vectors and reservoirs of the virus. Here are some effective prevention strategies:

  • Avoid tick-infested areas: Be cautious when venturing into wooded or grassy regions where ticks may be present, especially during spring and summer months.
  • Use insect repellent: Apply an EPA-registered insect repellent containing DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanoate on exposed skin and clothing to repel ticks.
  • Rodent control measures: Implement proper sanitation practices such as sealing holes in buildings and eliminating food sources to reduce rodent populations around residential areas.


In addition to these personal protective measures, ongoing surveillance programs can help monitor OHF cases and identify potential outbreaks early. It is important for healthcare professionals to be aware of the most effective prevention strategies for OHF in order to minimize its spread. Next, let’s examine the latest updates about this affliction.



What is Omsk Hemorrhagic Fever (OHF)?

OHF is a viral disease that primarily affects humans and rodents and is transmitted through tick bites or contact with infected animals. The illness typically presents with high fever, headache, muscle pain, and bleeding disorders.

What Causes OHF?

Omsk hemorrhagic fever is caused by the Omsk hemorrhagic fever virus (OHFV), which belongs to the Flavivirus genus. Transmission occurs mainly through bites from infected ticks (Dermacentor reticulatus and Ixodes persulcatus) or direct contact with tissues or fluids from infected animals such as muskrats.

What are the clinical features of OHF?

Clinical features of OHF include a sudden onset of high-grade fever, chills, severe headache, myalgia (muscle pain), fatigue, vomiting, and diarrhea. Hemorrhages may occur in various organs like skin petechiae (small red spots), nosebleeds (epistaxis), gums bleeding, and hematuria (blood in urine). Severe cases can lead to shock or multi-organ failure.

What family of viruses does OHFV belong to? 

OHFV belongs to the Flavivirus genus, which is part of the Flaviviridae family. This group of viruses also includes other significant human pathogens such as dengue, yellow fever, West Nile, and Zika viruses.

Is OHF contagious?

There is no evidence so far that OHF can be transmitted from person to person.



Omsk hemorrhagic fever is a rare but serious disease that can cause severe symptoms and potentially fatal outcomes. Healthcare professionals should be knowledgeable about the epidemiology, indications, diagnosis methods, management plans, and preventive strategies of Omsk hemorrhagic fever to ensure appropriate care is given and its spread contained.


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Learn more about Omsk hemorrhagic fever on the GIDEON platform.


Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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