Omsk hemorrhagic fever

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Omsk hemorrhagic fever
Synonyms	N/A
Pronounce	N/A
Specialty	N/A
Symptoms	Fever, headache, myalgia, nausea, vomiting, rash, hemorrhage
Complications	Encephalitis, bleeding disorders
Onset	Sudden
Duration	1 to 2 weeks
Types	N/A
Causes	Omsk hemorrhagic fever virus
Risks	Tick bites, contact with infected animals
Diagnosis	Serology, PCR
Differential diagnosis	Dengue fever, Crimean-Congo hemorrhagic fever, Yellow fever
Prevention	Avoiding tick bites, protective clothing, vaccination
Treatment	Supportive care, fluid replacement
Medication	N/A
Prognosis	Generally good with supportive care
Frequency	Rare
Deaths	Low mortality rate

Omsk hemorrhagic fever is a viral hemorrhagic fever caused by a Flavivirus. It is found in Siberia.

Cause

Omsk hemorrhagic fever (OHF) is caused by Omsk hemorrhagic fever virus (OHFV), a member of the virus family Flaviviridae.

History

OHF was described between 1945 and 1947 in Omsk, Russia from patients with hemorrhagic fever.

Primary host

Rodents serve as the primary host for OHFV, which is transmitted to rodents from the bite of an infected tick.

Vectors

• Common tick vectors include Dermacentor reticulatus, Dermacentor marginatus, Ixodes persulcatus and common rodents infected with OHFV include the muskrat (Ondatra zibethica), water vole (Arvicola terrestris), and narrow-skulled voles (Microtus gregalis).
• Muskrats are not native to the Omsk region but were introduced to the area and are now a common target for hunters and trappers.
• When infected with the virus, muskrats can become ill and die.
• OHF occurs in the western Siberia regions of Omsk, Novosibirsk, Kurgan and Tyumen.

Transmission

• Humans can become infected through tick bites or through contact with the blood, feces, or urine of an infected, sick, or dead animal – most commonly, rodents. Occupational and recreational activities such as hunting or trapping may increase human risk of infection.
• Transmission may also occur with no direct tick or rodent exposure as OHFV appears to be extremely stable in different environments.
• It has been isolated from aquatic animals and water and there is even evidence that OHFV can be transmitted through the milk of infected goats or sheep to humans.
• No human-to-human transmission of OHFV has been documented but infections due to lab contamination have been described.

Signs and symptoms

There are a number of symptoms of the virus. In the first 1–8 days the first phase begins. The symptoms in this phase are:

• chills
• headache
• pain in the lower and upper extremities and severe prostration
• a rash on the soft palate
• swollen glands in the neck
• appearance of blood in the eyes (conjunctival suffusion)
• dehydration
• hypotension
• gastrointestinal symptoms (symptoms relating to the stomach and intestines)
• patients may also experience effects on the central nervous system

Neglected tropical disease

As of 2017, the World Health Organization categorizes the following communicable diseases as neglected tropical diseases (NTDs):

Mortality

The case fatality rate of OHF is low (0.5% to 3%).

Risk of Exposure

• In areas where rodent reservoirs and tick species are prevalent, people with recreational or occupational exposure to rural or outdoor settings (e.g., hunters, campers, forest workers, farmers) are potentially at increased risk for OHF by contact with infected ticks and animals.
• Furthermore, those in Siberia who hunt and trap muskrats specifically are at higher risk for OHF.
• Exposure may also occur in the laboratory environment.

Diagnosis

• OHF virus may be detected in blood samples by virus isolation in cell culture or using molecular techniques such as PCR.
• Blood samples can also be tested for antibody presence using enzyme-linked immunosorbent seologic assay (ELISA).

Treatment

There is no specific treatment for OHF, but supportive therapy is important. Supportive therapy includes the maintenance of hydration and the usual precautions for patients with bleeding disorders. Though rare, OHF can cause hearing loss, hair loss, and behavioral or psychological difficulties associated with neurological conditions and long term supportive case may be needed.

Prevention

There is no vaccine currently available for OHF, but vaccines for tick-borne encephalitis disease (TBE) have been shown to confer some immunity and may be used for high-risk groups. Additionally, utilizing insect repellents and wearing protective clothing in areas where ticks are endemic is recommended.

• CDC Omsk hemorrhagic fever