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Congo fever, also known as Crimean-Congo hemorrhagic fever (CCHF), is caused by the Nairovirus infection. CCHF is a communicable disease that spreads through tick bites, as well as contact with infected people and livestock. Animal hosts usually remain subclinical - that is, without any apparent symptoms.

Niarovirus belongs to the family Bunyaviridae. It usually spreads through the bite of Hyalomma ticks - these ticks act as a reservoir (they provide a favourable home to the virus) and vector (they transmit the infection from one person or animal to another) for Congo fever. Other than ticks, cattle also play a key role in the spread of the disease among humans.

Congo fever causes severe hemorrhagic fever. Due to easy transmission, lack of definitive treatment or vaccines and high mortality rate (10-40%), the World Health Organization (WHO) has classified CCHF virus a high-priority pathogen.

  1. Prevalence of Crimean-Congo Haemorrhagic Fever
  2. Symptoms of Crimean-Congo Haemorrhagic Fever
  3. Causes of Crimean-Congo Haemorrhagic Fever
  4. Diagnosis of Crimean-Congo Haemorrhagic Fever
  5. Treatment of Crimean-Congo Haemorrhagic Fever
  6. Prevention of Crimean-Congo Haemorrhagic Fever

Prevalence of Crimean-Congo Haemorrhagic Fever

The first case of this tick-borne viral fever was reported in Crimea in Eastern Europe, in 1944. The same viral fever was also widely reported in Congo, on the African continent, in 1969. Hence, the name Crimean-Congo Hemorrhagic Fever.

Congo fever is endemic to several parts of the world where these ticks live - the list includes the former Soviet Union nations, the Mediterranean region, north-west China, Central Asia, Africa, the Middle-East and India.

Healthcare workers and people working in the livestock industry are at higher risk of getting Congo fever.

Symptoms of Crimean-Congo Haemorrhagic Fever

A person infected with the Congo fever virus manifests a range of signs and symptoms after the incubation period - if a person gets the infection after being bitten by a tick, the incubation period is shorter - usually one to three days. If a person gets Nairovirus infection through contaminated blood and body fluids, the incubation period becomes slightly longer - usually five to six days, but symptoms can take up to 13 days to show.

The most commonly reported symptoms of Congo fever are:

Causes of Crimean-Congo Haemorrhagic Fever

Ixodid or hard ticks act as a reservoir for the Congo fever virus - Niarovirus. Animals that have been bitten by infected ticks, including domesticated animals like goat, sheep, camels and hare, act as amplifying hosts - they help in the spread of the disease among humans.

When an animal is bitten by an infected tick, the virus enters their bloodstream and causes infection. Unfortunately, signs of the disease remain hidden in animals.

Transmission of the disease occurs in several ways:

  • If the infected tick bites a human being
  • If an infected animal is bitten by a non-vector tick - causing tick-animal-tick cycle, now, this newly infected tick will carry the infection for their lifetime
  • If a human comes in contact with the blood of an infected animal, say, while slaughtering the animal or in a veterinary set-up where they have to handle the blood and tissues of infected animals
  • If you come in contact with the blood or bodily fluid of an infected person
  • Through contaminated medical equipment (hospital-acquired infections)

Diagnosis of Crimean-Congo Haemorrhagic Fever

Congo fever can be elicited from the presence of Nairovirus or Nairovirus antibodies in the blood - our immune cells produce antibodies to fight infection caused by pathogen like viruses.

Some laboratory tests that can help in diagnosing Congo fever are:

  • Enzyme-linked immunosorbent assay (ELISA)
  • Antigen detection
  • Serum neutralization
  • Reverse transcriptase-polymerase chain reaction (RT-PCR) assay
  • Virus isolation by cell culture

Healthcare professionals are at high risk for infection - it can be transmitted through direct contact with the blood and tissue of a patient. Therefore, they are strictly advised to run the tests under maximum biological containment conditions. Another way is to counter the enhanced risk to healthcare professionals who have to test samples, is by using virucides, gamma rays, formaldehyde or heat to create what is known as a "biosafety environment".

Treatment of Crimean-Congo Haemorrhagic Fever

The mainstay treatment for Congo fever is supportive in nature - it is crucial to maintain fluid and electrolyte balance, adequate oxygen supply, normal heart and breathing rate, and to manage any internal bleeding to avoid complications.

Patients usually respond to the antiviral drug ribavirin

For now, there is no vaccine for CCHF. However, research is on to develop a vaccine for the potentially fatal disease.

Prevention of Crimean-Congo Haemorrhagic Fever

People residing in endemic regions, like India, are at risk for the disease. But we can always take preventive measures to avoid getting the infection. Try these tips:

  • Use insect repellant on exposed skin as well as your clothing if you go into a field or anywhere you are likely to come in contact with animals. Repellants containing DEET (N, N-diethyl-m-toluamide) are said to be most effective for killing ticks
  • Wear clothes that cover your whole body. Don't forget to wear gloves if you work with animals
  • If you are a medical professional or a lab technician, take adequate precautions while handling the blood samples and tissue of patients who are suspected to have Congo fever


  1. Center for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services; Crimean-Congo Hemorrhagic Fever (CCHF)
  2. World Health Organization [Internet]. Geneva (SUI): World Health Organization; Crimean-Congo haemorrhagic fever.
  3. Laura T Mazzola, Cassandra Kelly-Cirino. Diagnostic tests for Crimean-Congo haemorrhagic fever: a widespread tickborne disease . BMJ journals, Volume 4, Issue Suppl 2
  4. David W. Hawman, Heinz Feldmann Recent advances in understanding Crimean–Congo hemorrhagic fever virus . Version 1. F1000Res. 2018; 7: F1000 Faculty Rev-1715. PMID: 30416710
  5. Ali Ahmed et al. Knowledge, perception and attitude about Crimean Congo Hemorrhagic Fever (CCHF) among medical and pharmacy students of Pakistan . BMC Public Health. 2018; 18: 1333. PMID: 30509226
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