Crimean-Congo Hemorrhagic Fever
Crimean-Congo Hemorrhagic Fever
Crimean-Congo hemorrhagic fever (CCHF) is a viral disease caused by infection with a tick-borne virus. The virus that causes CCHF is contained within Nairovirus, a member of related pathogenic (disease-causing) viruses within the Bunyaviridae family.
All Nairovirus viruses are transmitted by the bite of argasid (soft) or isodid (hard) ticks. However, only a few of these ticks have shown to cause human infections. According to the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), the tick of the Hyalomma genus is most capable of serving as the vector for the disease, especially in small vertebrates on which immature ticks feed.
CCHF is an infectious disease that is capable of being transmitted by ticks between domesticated and wild animals; from animals to humans; and from humans to animals. Common animals infected are cattle, sheep, goats, and hares. Humans are infected through contact with infected animal blood or ticks.
CCHF was documented in Russia in the twelfth century. However, the first accurate description came from the Crimea region of the former U.S.S.R. in 1944–1945. At that time, it was called Crimean hemorrhagic fever. In 1969, it was realized that the pathogen causing CCHF was also an illness identified in 1956 in Stanleyville (now Kisangani), Congo. Because of this, it was renamed Crimean-Congo hemorrhagic fever.
Small vertebrates on which the immature ticks feed seem to serve as the primary method that the virus spreads. Infected female ticks pass the disease into their eggs, which develop into infected immature ticks. Mature ticks carry the virus to larger animals, such as large vertebrates, who can become intermediate hosts. CCHF transmission to humans occurs when people butcher or eat infected livestock, and when health workers became exposed to infected blood.
After a tick bite, the incubation period is about one to three days, but up to nine days. After contact with infected blood or tissue, the incubation period is usually five to six days, with a maximum of 13 days. Influenza-like symptoms occur suddenly. In most cases, they last for about one week. However, signs of bleeding appear 75% of the time in cases lasting longer than one week. Death occurs in 30–60% of cases.
Symptoms include high fever, aching muscles, dizziness, neck pain, backache, stomach pain, headache, sore eyes, and light sensitivity. Later, nosebleeds, red eyes, flushed face, red throat, bruising, bloody urine, vomiting, black stools, skin rash, and diarrhea occur. Still later, abdominal pain occurs, along with mental confusion and mood swings.
Unlike humans, most infected mammals do not show noticeable symptoms. Most cases occur in domesticated animals and wild animals. CCHF occurs less frequently in humans.
WORDS TO KNOW
ARTHROPOD: A member of the largest single animal phylum, consisting of organisms with segmented bodies, jointed legs or wings, and exoskeletons. Includes insects and spiders.
HEMORRHAGIC FEVER: A hemorrhagic fever is caused by viral infection and features a high fever and a high volume of (copious) bleeding. The bleeding is caused by the formation of tiny blood clots throughout the bloodstream. These blood clots—also called microthrombi—deplete platelets and fibrinogen in the bloodstream. When bleeding begins, the factors needed for the clotting of the blood are scarce. Thus, uncontrolled bleeding (hemorrhage) ensues.
INTERMEDIATE HOST: An organism infected by a parasite while the parasite is in a developmental form, not sexually mature.
VECTOR: Any agent, living or otherwise, that carries and transmits parasites and diseases. Also, an organism or chemical used to transport a gene into a new host cell.
IN CONTEXT: TRENDS AND STATISTICS
According to World Health Organization and the European Center for Disease Prevention and Control (ECDE), recent cases of Crimean hemorrhagic fever were reported in Albania (2001, 8 cases), Iran (1999–2004, 155 cases), Kosovo (2001, 18 cases), Mauritania (2003, 38 cases), Pakistan (2002, 3 cases), and Turkey (2001–2003, 83 cases). In Bulgaria and South Africa, between five and 25 cases are reported annually in each country. In July 2005, a major outbreak occurred in Turkey's Yozgat Province (one death out of 42 cases). Between January 1–4, 2006, 242 confirmed cases (20 deaths) were reported in Turkey.
SOURCE: World Health Organization
The disease is found in over thirty countries around the world. It is reported in central Asia, northwestern China, the Middle East, eastern and southern Europe, the Indian subcontinent, across central and southern Africa (especially eastern and western parts) and Madagascar.
Small mammals carry the disease, especially the Middle-African hedgehog, multi mammaterat, and European hare. Domestic animals, such as sheep, goats, and cattle, also carry the tick. Most birds do not become infected, except ostriches.
Groups most likely to become infected are slaughterhouse workers, veterinarians, surgeons and medical workers, animal herders, and agricultural workers. Wide-spread infections in medical facilities have occurred due to improperly sterilization of equipment, reuse of injection needles, and supply contamination. Travelers are at risk in countries where CCHF is present.
Diagnosis includes the following: serological test (to find antibodies in serum); immunohistochemical staining (to find viral antigen in tissue); microscopic examination (to find viral RNA [ribonucleic acid] sequence in blood or tissue); polymerase chain reaction (PCR) technique (to detect viral genome); and enzyme linked immunosorbent assay (ELISA) technique (to detect immunoglobulin-G and immunoglobulin-M antibodies in serum).
Oral and intravenous treatment involves the antiviral drug ribavirin (Copegus®, Ribasphere®, Virazole®). Ribavirin has been shown to be effective during actual outbreaks, although scientific studies have not supported that conclusion.
Treatment is generally supportive and based on the symptom's type and degree of severity. Fluid balance, electrolyte levels, and secondary infections are carefully monitored. Fatality rates in hospitalized patients range widely from 9% to 50%, depending on infection severity, care quality, and other variables.
CCHF is commonly prevented by governments that require de-ticking of farm animals. Insect repellents (containing DEET, N,N-diethy-m-toluamide), appropriate clothing (gloves and clothing treated with permethrin), and body inspections help prevent the disease. Persons are advised to avoid contact with blood and fluids of infected livestock and humans.
Crimean-Congo hemorrhagic fever is one of the world's most severe arthropod-borne diseases. It has a mortality rate of up to 60%. CCHF remains a public health problem in many parts of the world, including Africa, the Middle East, southern and eastern Europe, and western Asia.
IN CONTEXT: REAL-WORLD RISKS
As of May 2007, the World Health Organization states that “although an inactivated, mouse brain-derived vaccine against CCHF has been developed and used on a small scale in Eastern Europe, there is no safe and effective vaccine widely available for human use.”
WHO also states that:
- The tick vectors are numerous and widespread and tick control with acaricides (chemicals intended to kill ticks) is only a realistic option for well-managed livestock production facilities. Persons living in endemic areas should use personal protective measures that include avoidance of areas where tick vectors are abundant and when they are active (spring to fall); regular examination of clothing and skin for ticks, and their removal; and use of repellents.
- Persons who work with livestock or other animals in the endemic areas can take practical measures to protect themselves. These include the use of repellents on the skin (e.g., DEET) and clothing (e.g., permethrin) and wearing gloves or other protective clothing to prevent skin contact with infected tissue or blood.
SOURCE: World Health Organization
Because of this, the CDC identifies the need for increased knowledge about CCHF. Currently, the prevalence of CCHF is not measured accurately. The CDC recommends: measurements to be performed on both animals and humans so accurate statistics are available; further CCHF research to be performed; effectiveness of treatments recorded; and a widespread, safe, and effective vaccine for CCHF developed. Currently, only a local vaccine developed in Eastern Europe, made from the brains of mice, is available.
Crimean-Congo hemorrhagic fever's causative agent, the Nairovirus, is classified as a biosafety level four (BSL4) pathogen by the CDC. Scientists study biosafety level four pathogens, which are mostly viruses, in specialized facilities designed to contain them. All biosafety level four pathogens have the capacity to cause life-threatening diseases, and no effective vaccine is readily available to prevent them. Currently, there are eleven BSL4 facilities in the United States, and several more are planned or under construction. Access to BSL4 labs is usually restricted to essential personnel. Among the extensive safety measures used by scientists when conducting research with BSL4 pathogens are multi-containment areas, one-piece positive pressure personnel suits with separate ventilation systems, negative air pressure rooms, and a safe working area called a biological safety cabinet. Other viral hemorrhagic fevers such as Ebola, Lassa, and Marburg, are also considered BSL4 pathogens.
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National Guideline Clearinghouse. “Hemorrhagic Fever Viruses as Biological Weapons: Medical and Public Health Management.” March 5, 2007 <http://www.guideline.gov/summary/summary.aspx?ss=15doc_id=3224&nbr=2450> (accessed March 11, 2007).
World Health Organization. “Crimean-Congo Hemorrhagic Fever.” <http://who.int/mediacentre/factsheets/fs208/en/> (accessed March 8, 2007).