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Table of Contents:
Taxonomy Information
  1. Species:
    1. Crimean-Congo hemorrhagic fever virus (Website 2):
      1. Common Name: Crimean-Congo hemorrhagic fever virus
      2. GenBank Taxonomy No.: 11593
      3. Description: Crimean Congo hemorrhagic fever (CCHF), one of the most severe human viral diseases, has a death rate of up to 50%. CCHF is a public health problem in many regions of the world, including Africa, Middle East, southern and eastern Europe, and Western Asia. The causative agent, Crimean Congo hemorrhagic fever virus (CCHFV), is the type species of the genus Nairovirus in the Bunyaviridae family. The virus is transmitted to humans by the bite of Ixodid ticks (mostly of the Hyalomma genus) or by contact with blood or tissues from human patients or infected livestock (Papa et al., 2002).
      4. Variant(s):
Lifecycle Information
  1. CCHF Virus Information
    1. Stage Information:
      1. Virion(Website 17):
        • Size: Virions 100 (80-120) nm in diameter. Surface projections of envelope distinct; spikes (of about 10 nm). Nucleocapsids filamentous; 200-3000 nm long (depending on arrangement); 2-2.5 nm in diameter. Symmetry helical.
        • Shape: Virions enveloped; slightly pleomorphic; spherical. Virions contain 3 nucleocapsid(s) per envelope.
Genome Summary
  1. Genome of Crimean-Congo hemorrhagic fever virus
    1. Description: CCHFV, like all members of the genus, is a negative-stranded RNA virus with a tripartite genome consisting of a small (S), a medium (M), and a large (L) segment. The S RNA segment codes for the nucleocapsid (N) protein, and the M RNA segment codes for the glycoprotein precursor, resulting in the two envelope glycoproteins G1 and G2, while the L segment encodes the putative RNA-dependent polymerase. The first 8 to 13 nucleotide bases at the 3' ends of all three RNA segments have a sequence that is conserved in the viruses of this genus, with a complementary consensus sequence occurring at the 5' end; the ends of the segments are noncovalently linked so that the RNA occurs in a loosely bound circular configuration within the nucleocapsids. The M segment of nairoviruses is 30% to 50% larger than the M segments of members of other genera in the Bunyaviridae family(Papa et al., 2002).
    2. S Segment(Website 22)
      1. GenBank Accession Number: M86625 AJ010649 AJ010648
      2. Size: 1672 bp(Marriott and Nuttall, 1992).
      3. Gene Count: 1 gene. The S RNA segment codes for the nucleocapsid (N) protein(Papa et al., 2002).
      4. Description: The S RNA segments of the nairoviruses Crimean-Congo hemorrhagic fever (CCHF) virus (Chinese isolate) and Hazara (HAZ) virus were cloned and sequenced from PCR products. The RNAs comprise 1672 and 1677 nucleotides, respectively, and each encodes a protein in the viral complementary strand (54.0 and 54.2 kDa, respectively)(Marriott and Nuttall, 1992).
    3. M Segment(Website 20, Website 21)
      1. GenBank Accession Number: AF350448 AB069669 AF350449 AB069670 AB069671 AB069672 AB069673 AB069674 AB069675
      2. Size: 5,368 and 5,376 bp(Papa et al., 2002).
      3. Gene Count: 2 genes. The M RNA segment codes for the glycoprotein precursor, resulting in the two envelope glycoproteins G1 and G2 (Papa et al., 2002)(Papa et al., 2002).
      4. Description: Two CCHFV strains isolated in Xinjiang Province, a region endemic for CCHF in northwestern China, were studied. These strains, designated BA66019 and BA8402, were isolated in 1965 and 1984 from a CCHF patient and Hyalomma ticks, respectively. Viral RNA was extracted from suckling mouse brains infected with these two strains, amplified, and sequenced. The full-length M RNA, consisting of 5.3 kb, was determined for both strains. The coding nucleotide sequences of the two strains differed from each other by 17.5% and from the reference CCHFV strain IbAr10200 by a mean of 22%, suggesting that the genus Nairovirus comprises a group of genetically highly diverse strains(Papa et al., 2002).
Biosafety Information
  1. Biosafety information for Crimean-Congo hemorrhagic fever virus
    1. Level: 4. Virus isolation must only be attempted in Biosafety Level 4 facilities, such as are available at CDC (MMWR, 1988).
    2. Precautions: The patient should be isolated in a single room with an adjoining anteroom serving as its only entrance. The anteroom should contain supplies for routine patient care, as well as gloves, gowns, and masks for the staff. The Appendix lists suggested supplies for the anteroom. Hand-washing facilities should be available in the anteroom, as well as containers of decontaminating solutions. If possible, the patient's room should be at negative air pressure compared with the anteroom and the outside hall, and the air should not be recirculated. However, this is not absolutely required, and does not constitute a reason to transfer the patient. If a room such as described is not available, use adjacent rooms to provide safe and adequate space(MMWR, 1988). Strict barrier-nursing techniques should be enforced: all persons entering the patient's room should wear disposable gloves, gowns, masks, and shoe covers. Protective eye wear should be worn by persons dealing with disoriented or uncooperative patients or performing procedures that might involve the patient's vomiting or bleeding (for example, inserting a nasogastric tube or an intravenous or arterial line). Protective clothing should be donned and removed in the anteroom. Only essential medical and nursing personnel should enter the patient's room and anteroom. Isolation signs listing necessary precautions should be posted outside the anteroom(MMWR, 1988). Lipid-containing viruses, including the enveloped viruses, are among the most readily inactivated of all viral agents. Suitable disinfectant solutions include 0.5% sodium hypochlorite (10% aqueous solution of household bleach), as well as fresh, correctly prepared solutions of glutaraldehyde (2% or as recommended by the manufacturer) and phenolic disinfectants (0.5%-3%). Soaps and detergents can also inactivate these viruses and should be used liberally(MMWR, 1988). Laboratory personnel accidentally exposed to potentially-infected material (for example, through injections or cuts or abrasions on the hands) should immediately wash the infected part, apply a disinfectant solution such as hypochlorite solution, and notify the patient's physician. The person should then be considered as a high-risk contact and placed under surveillance. Accidental spills of potentially contaminated material should be liberally covered with disinfectant solution, left to soak for 30 minutes, and wiped up with absorbent material soaked in disinfectant(MMWR, 1988).
    3. Disposal: The patient should use a chemical toilet. All secretions, excretions, and other body fluids (other than laboratory specimens) should be treated with disinfectant solution. All material used for patients, such as disposable linen and pajamas, should be double-bagged in airtight bags. The outside bags should be sponged with disinfectant solution and later incinerated or autoclaved. Disposable items worn by staff, such as gowns, gloves, etc., should be similarly treated. Disposable items used in patient care (suction catheters, dressings, etc.) should be placed in a rigid plastic container of disinfectant solution. The outside of the container should be sponged with disinfectant, and the container should be autoclaved, incinerated, or otherwise safely discarded(MMWR, 1988). All unnecessary handling of the body, including embalming, should be avoided. Persons who dispose of the corpse must take the same precautions outlined for medical and laboratory staff. The corpse should be placed in an airtight bag and cremated or buried immediately(MMWR, 1988). Disposable items, such as pipette tips, specimen containers, swabs, etc., should be placed in a container filled with disinfectant solution and incinerated. Clothes and blankets that were used by the patient should be washed in a disinfectant, such as hypochlorite solution. Nondisposable items such as endoscopes used in patient care must be cleaned with decontaminating fluids (for example, gluteraldehyde or hypochlorite). Laboratory equipment must be treated similarly. All non-disposable materials that withstand autoclaving should be autoclaved, after they have been soaked in disinfectant solution. The patient's bed and other exposed surfaces in the hospital room, or in vehicles used to transport the patient, should be decontaminated with disinfectant solution(MMWR, 1988).
Culturing Information
  1. Vero Cell Culture :
    1. Description: Stock cultures of CER cells and the E6 clone of Vero cells were grown in Eagle minimum essential amino acid medium with Hank's sal solutions (HMEM) supplemented with 10% fetal bovine serum and antibiotics(Shepherd et al., 1986).
    2. Medium: Eagle minimum essential amino acid medium with Hank's sal solutions (HMEM) supplemented with 10% fetal bovine serum and antibiotics(Shepherd et al., 1986).
    3. Note: Plaques were formed in CER cells by all four of the CCHF virus strains used. The plaques were usually visible by microscopy after 3 days of incubation and could be read and enumerated by the naked eye 24 h later, after application of the staining overlay(Shepherd et al., 1986, Website 7). We failed to obtain reproducible results with E6 cells. When present, plaques in these cells were small and indistinct, requiring incubation periods of 6 to 7 days. However, E6 cells were of approximately equal sensitivity to CER cells when virus was titrated in fluorescence focus assays(Shepherd et al., 1986). For specimens from 26 Crimean-Congo hemorrhagic fever patients in South Africa, virus was isolated from 20 by mouse inoculation and from only 11 by cell culturing. Although cell cultures were less sensitive for the isolation of virus from clinical specimens, they produced diagnostic results much more rapidly(Shepherd et al., 1986, Website 7). Diagnosis by viral cultivation and identification for the VHF-causing agents requires 3 to 10 days for most (longer for the hantaviruses); and, with the exception of dengue, specialized microbiologic containment is required for safe handling of these viruses(Website 7).
  2. Continuous Culturing in Vero-E6 cells :
    1. Description: Adaptation of the Crimean-Congo hemorrhagic fever (CCHF) virus to continuous culturing in Vero-E6 cells was studied by coculturing of infected and intact cells. Adapted strain Hoja-A exerted a complete cytocidal effect and was characterized by a high level of virus accumulation in the early period of the infection. The resultant strain survived through more than 80 passages and retained the newly acquired properties; lyophilized, it can be stored for a long time. Availability of such a strain opens new vistas in studies of the CCHF agent(Smirnova et al., 1997).
    2. Note: Diagnosis by viral cultivation and identification for the VHF-causing agents requires 3 to 10 days for most (longer for the hantaviruses); and, with the exception of dengue, specialized microbiologic containment is required for safe handling of these viruses(Website 7).
Epidemiology Information:
  1. Outbreak Locations:
    1. The geographic range of CCHF virus is the most extensive among the tickborne viruses associated with human disease, and with the exception of dengue virus, the most widespread of all the medically important arboviruses. Sporadically distributed enzootic foci originally described throughout southern Eurasia have since been recognized in western China and other countries in Southern Europe. A similar focal distribution pattern extends southward and spans a vast portion of the Middle East region, possibly including India and a large portion of Africa extending into the Southern Hemisphere. Evidence of CCHF virus enzootic foci for most countries is based on virus isolations from either humans or ticks, and or/antibody detection in humans and domestic animals(Watts et al., 1988).
  2. Transmission Information:
    1. From: Human(Papa et al., 2002). , To: Human(Papa et al., 2002). , With Destination:Human(Papa et al., 2002). (Papa et al., 2002)
      Mechanism: The virus is transmitted to humans by the bite of Ixodid ticks (mostly of the Hyalomma genus) or by contact with blood or tissues from human patients or infected livestock(Papa et al., 2002).
    2. From: Ixodidae(Papa et al., 2002). Argasidae(Watts et al., 1988). , To: Human(Papa et al., 2002). , With Destination:Human(Papa et al., 2002). (Papa et al., 2002)
      Mechanism: The virus is transmitted to humans by the bite of Ixodid ticks (mostly of the Hyalomma genus) or by contact with blood or tissues from human patients or infected livestock(Papa et al., 2002). Among invertebrates, CCHF viral infection has been demonstrated only in ticks, including viral isolations from numerous species/subspecies of seven genera of the family Ixodidae, and two species of the family Argasidae(Watts et al., 1988).
    3. From: Cattle(Watts et al., 1988, Swanepoel et al., 1985). Sheep(Watts et al., 1988, Fisher-Hoch et al., 1992). , To: Human(Watts et al., 1988, Swanepoel et al., 1985). , With Destination:Human(Watts et al., 1988, Swanepoel et al., 1985). (Watts et al., 1988)
      Mechanism: Forty-six cows were purchased from the western Cape Province in January 1984; 2 died from the tick-borne disease anaplasmosis in March and a laborer who helped butcher the carcasses became ill a few days later. Another cow died at the end of April and within 9 days 4 people who had come into contact with its blood became ill. Antibodies to CCHF virus were found in the sera of the 5 patients but not in other residents of the farm(Swanepoel et al., 1985). Human infection with CCHF virus was uncommon (point prevalence 12.6/1,000). Antibody prevalence in humans on farms increased with age (P less than 0.001), and was correlated with handling lambs(Fisher-Hoch et al., 1992).
  3. Environmental Reservoir:
    1. Ticks:
      1. Description: While only a few species of ticks have been incriminated as vectors of CCHF virus, an enormous number of species/subspecies have been implicated primarily by viral isolations. In 1973, only 6 years after the first isolations of CCHF virus, a total of 10 species/subspecies had yielded isolates of this virus. A remarkable and especially important epidemiological feature that emerged was not only the large number of implicated vector tick species, but the association of CCHF virus with ticks in a variety of different ecological biotypes in the Palearctic, Oriental, and Ethiopian faunal regions(Watts et al., 1988). Among the total 29 species/subspecies of ticks associated with CCHF virus, most are either two- or three-host ticks of the family Ixodidae(Watts et al., 1988). An especially important biological feature of ticks in general as potential vector/reservoirs of arboviruses is their ability to transmit arboviruses transovarially. Evidence of this phenomenon for CCHF virus in nature is based mainly on limited isolations from eggs of H. marginatum and Dermacentor marginatus(Watts et al., 1988). Most of the ticks collected (618 of 912) from all species of sampled livestock were Hyalomma anatolicum anatolicum, a competent vector and reservoir of CCHF virus(Williams et al., 2000).
      2. Survival: Only a few controlled experimental studies have been conducted in an attempt to demonstrate the vector and reservoir potential of selected tick species for CCHF virus. However, none has been designed to address the possibility that CCHF viral infection may have a detrimental effect on this arthropod's potential role in the ecology and epidemiology of CCHF virus(Watts et al., 1988).
  4. Intentional Releases:
    1. Intentional Release Information:
      1. Emergency Contact: If clinicians feel that VHF is a likely diagnosis, they should take two immediate steps: 1) isolate the patient, and 2) notify local and state health departments and CDC (MMWR 1998). Report incidents to state health departments and the CDC (telephone {404} 639-1511; from 4:30 p.m. to 8 a.m., telephone {404} 639-2888). Information on investigating and managing patients with suspected viral hemorrhagic fever, collecting and shipping diagnostic specimens, and instituting control measures is available on request from the following persons at Centers for Disease Control (CDC) in Atlanta, Georgia; for all telephone numbers, dial 404-639 + extension: Epidemic Intelligence Service (EIS) Officer, Special Pathogens Branch, Division of Viral Diseases, Center for Infectious Diseases (ext. 1344); Chief, Special Pathogens Branch, Division of Viral Diseases, Center for Infectious Diseases: Joseph B. McCormick, M.D. (ext. 3308); Senior Medical Officer, Special Pathogens Branch, Division of Viral Diseases, Center for Infectious Diseases: Susan P. Fisher-Hoch, M.D. (ext. 3308); Director, Division of Viral Diseases, Center for Infectious Diseases (ext. 3574). After regular office hours and on weekends, the persons named above may be contacted through the CDC duty officer (ext. 2888) (MMWR 1998)(MMWR, 1988).
      2. Delivery Mechanism: The VHF agents are all highly infectious via the aerosol route, and most are quite stable as respirable aerosols. This means that they satisfy at least one criterion for being weaponized, and some clearly have the potential to be biological warfare threats. Most of these agents replicate in cell culture to concentrations sufficiently high to produce a small terrorist weapon, one suitable for introducing lethal doses of virus into the air intake of an airplane or office building. Some replicate to even higher concentrations, with obvious potential ramifications. Since the VHF agents cause serious diseases with high morbidity and mortality, their existence as endemic disease threats and as potential biological warfare weapons suggests a formidable potential impact on unit readiness. Further, returning troops may well be carrying exotic viral diseases to which the civilian population is not immune, a major public health concern(Website 7).
      3. Containment: Patients with VHF syndrome generally have significant quantities of virus in their blood, and perhaps in other secretions as well (with the exceptions of dengue and classic hantaviral disease). Well-documented secondary infections among contacts and medical personnel not parenterally exposed have occurred. Thus, caution should be exercised in evaluating and treating patients with suspected VHF syndrome. Over-reaction on the part of medical personnel is inappropriate and detrimental to both patient and staff, but it is prudent to provide isolation measures as rigorous as feasible. At a minimum, these should include the following: stringent barrier nursing; mask, gown, glove, and needle precautions; hazard-labeling of specimens submitted to the clinical laboratory; restricted access to the patient; and autoclaving or liberal disinfection of contaminated materials, using hypochlorite or phenolic disinfectants. For more intensive care, however, increased precautions are advisable. Members of the patient care team should be limited to a small number of selected, trained individuals, and special care should be directed toward eliminating all parenteral exposures. Use of endoscopy, respirators, arterial catheters, routine blood sampling, and extensive laboratory analysis increase opportunities for aerosol dissemination of infectious blood and body fluids. For medical personnel, the wearing of flexible plastic hoods equipped with battery-powered blowers provides excellent protection of the mucous membranes and airways(Website 7).
Diagnostic Tests Information
  1. Organism Detection Test:
    1. Electrom Microscopy :
      1. Description: When the identity of a VHF agent is totally unknown, isolation in cell culture and direct visualization by electron microscopy, followed by immunological identification by immunohistochemical techniques is often successful(Website 7).
    2. Indirect Immunofluorescence Assay Technique :
      1. Description: The recombinant nucleoprotein-based Crimean-Congo hemorrhagic fever virus antibody detection systems for sheep sera were developed by enzyme-linked immunosorbent assay (ELISA) and an indirect immunofluorescence assay techniques. The samples used for evaluation were 80 sera collected from sheep in a Crimean-Congo hemorrhagic fever-endemic area (western part of the Xinjiang Uygur Autonomous Region) and 39 sera collected from sheep in a disease-free region (Shandong province, eastern China). The ELISA and indirect immunofluorescence assay using recombinant nucleoprotein of the virus proved to have high sensitivity and specificity for detecting the immunoglobulin G antibodies to the virus in sheep sera (Qing et al., 2003). The sensitivity and specificity of the recombinant nucleoprotein-based indirect immunofluorescence assay were calculated as 94 and 97%, respectively(Qing et al., 2003).
      2. False Positive: Both the positive and negative predictive values were calculated as 96%(Qing et al., 2003).
      3. False Negative: Both the positive and negative predictive values were calculated as 96%(Qing et al., 2003).
    3. Indirect immunofluorescence assay (Papa et al., 2002):
      1. Description: Indirect immunofluorescent assay was used for the detection of specific CCHF antibodies. Sera were tested in twofold dilutions (initial dilution 1:8) with fluorescein-labeled goat IgG and IgM anti-human immunoglobulin on spot slides containing Vero E6 cells (ATCC CRL 1586), with approximately 50% of the cells infected with the 10200 IbAr strain of the prototype CCHF virus. Titers were recorded as the greatest dilution of serum at which characteristic cytoplasmic immunofluorescence was detected(Papa et al., 2002).
      2. False Negative: Specific IgG and IgM antibodies to CCHF virus were detected in all patients except patient 3. Although no specific antibodies were detectable in this patient (the 9-year-old boy), the diagnosis was established on the basis of the clinically compatible syndrome and the fact that CCHF was confirmed by serological and/or molecular methods in members of his family (cases 4 and 5) who were taking care of him and came in close contact with him(Papa et al., 2002).
  2. Immunoassay Test:
    1. Reversed Passive Hemagglutination :
      1. Description: Enzyme-linked immunosorbent assay (ELISA) and a reversed passive hemagglutination (RPHA) test were evaluated for rapid detection of Crimean-Congo hemorrhagic fever (CCHF) virus antigens. Both RPHA and ELISA detected CCHF antigen in the brains of infant mice 2 to 3 days after infection, several days before the animals sickened and died. Antigen was also detected after 1 to 2 days in infected cell culture extracts and after 2 to 4 days in culture supernatant fluids. Both tests detected CCHF antigen at threshold values of approximately 2.5 log10 tissue culture infective doses per ml and were more sensitive than complement fixation, immunodiffusion, or immunofluorescence. In a comparative study on specimens from CCHF patients, virus was isolated from 38 of 49 sera and 23 of 28 patients. Antigen was detected in 20 of 49 sera (15 of 28 patients) by RPHA and in 29 of 49 sera (18 of 28 patients) by ELISA. Antigenemia was detected more frequently in fatal cases (9 of 11) than in nonfatal cases (9 of 17). Although the antigen detection assays offered a more rapid approach than infectivity assays for diagnosing CCHF, the latter test was more sensitive. The results suggest that RPHA and ELISA may be of use in rapid diagnosis of CCHF infection, particularly in severe cases, in which the danger of nosocomial spread is greatest(Shepherd et al., 1988).
      2. False Negative: Antigen was detected in 20 of 49 sera (15 of 28 patients) by RPHA and in 29 of 49 sera (18 of 28 patients) by ELISA(Shepherd et al., 1988).
    2. Enzyme-linked Immunosorbent Assay :
      1. Description: IgG and IgM antibodies became demonstrable by indirect immunofluorescence on days 7 to 9 of illness in 35 survivors of Crimean-Congo hemorrhagic fever. Maximum titers of antibody were usually attained in the second to third week of illness. Titers of IgM declined gradually thereafter and were low or negative by the fourth month. In some patients titers of IgG increased markedly between 2 and 4 months after onset of illness and remained readily demonstrable by indirect immunofluorescence 3 years after infection. Endogenous antibody response was demonstrated in only two of 15 patients who died of infection. Techniques for demonstrating antibody were (in order of decreasing sensitivity) enzyme-linked immunosorbent assay, reversed passive hemagglutination-inhibition, indirect immunofluorescence, fluorescent-focus reduction, complement-fixation, and immunodiffusion. Most patients developed relatively low levels of neutralizing antibodies (range, 1:8 to 1:32 by fluorescent-focus reduction tests), but some developed titers of 1:256 to 1:512(Shepherd et al., 1989).
    3. Complement Fixation :
      1. Description: IgG and IgM antibodies became demonstrable by indirect immunofluorescence on days 7 to 9 of illness in 35 survivors of Crimean-Congo hemorrhagic fever. Maximum titers of antibody were usually attained in the second to third week of illness. Titers of IgM declined gradually thereafter and were low or negative by the fourth month. In some patients titers of IgG increased markedly between 2 and 4 months after onset of illness and remained readily demonstrable by indirect immunofluorescence 3 years after infection. Endogenous antibody response was demonstrated in only two of 15 patients who died of infection. Techniques for demonstrating antibody were (in order of decreasing sensitivity) enzyme-linked immunosorbent assay, reversed passive hemagglutination-inhibition, indirect immunofluorescence, fluorescent-focus reduction, complement-fixation, and immunodiffusion. Most patients developed relatively low levels of neutralizing antibodies (range, 1:8 to 1:32 by fluorescent-focus reduction tests), but some developed titers of 1:256 to 1:512. Plasma intended for therapeutic use should be selected on the basis of its neutralizing ability(Shepherd et al., 1989).
    4. ELISA :
      1. Description: Enzyme-linked immunosorbent assay (ELISA) and a reversed passive hemagglutination (RPHA) test were evaluated for rapid detection of Crimean-Congo hemorrhagic fever (CCHF) virus antigens. Both RPHA and ELISA detected CCHF antigen in the brains of infant mice 2 to 3 days after infection, several days before the animals sickened and died. Antigen was also detected after 1 to 2 days in infected cell culture extracts and after 2 to 4 days in culture supernatant fluids. Both tests detected CCHF antigen at threshold values of approximately 2.5 log10 tissue culture infective doses per ml and were more sensitive than complement fixation, immunodiffusion, or immunofluorescence. In a comparative study on specimens from CCHF patients, virus was isolated from 38 of 49 sera and 23 of 28 patients. Antigen was detected in 20 of 49 sera (15 of 28 patients) by RPHA and in 29 of 49 sera (18 of 28 patients) by ELISA. Antigenemia was detected more frequently in fatal cases (9 of 11) than in nonfatal cases (9 of 17). Although the antigen detection assays offered a more rapid approach than infectivity assays for diagnosing CCHF, the latter test was more sensitive. The results suggest that RPHA and ELISA may be of use in rapid diagnosis of CCHF infection, particularly in severe cases, in which the danger of nosocomial spread is greatest(Shepherd et al., 1988).
      2. False Negative: Antigen was detected in 20 of 49 sera (15 of 28 patients) by RPHA and in 29 of 49 sera (18 of 28 patients) by ELISA(Shepherd et al., 1988).
    5. Recombinant Nucleoprotein-Based Enzyme-Linked Immunosorbent Assay :
      1. Description: The full-length nucleoprotein of Crimean-Congo hemorrhagic fever virus (CCHFV; 482 amino acid residues) was expressed as a His-tagged recombinant protein (His-CCHFV rNP) in the baculovirus system. The His-CCHFV rNP was efficiently expressed in insect cells and purified by Ni2+ column chromatography. Using this substrate, an immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) was developed. We evaluated the sensitivity and specificity of the IgG ELISA, using serum samples previously determined to be antibody positive or negative by immunofluorescence tests on CCHFV-infected Vero E6 cells. We found very good correlation between the two tests: 87% for the positive sera (13 of 15) and 99% for the negative sera (107 of 108). These results indicate that the new IgG ELISA using His-CCHFV rNP has high sensitivity and specificity for detecting CCHFV antibodies. The CCHF patients' sera with high titers reacted only with the NP fragment containing amino acid residues between 201 and 306 in Western blotting. It is known that amino acid homologies are high in this region among various isolates. Thus, it is expected that this ELISA can detect antibodies not only for Chinese strains of CCHFV but also for other strains circulating in the world. These results suggest that the IgG ELISA system developed with the recombinant CCHFV NP is a valuable tool for diagnosis and epidemiological investigations of CCHFV infections(Saijo et al., 2002).
  3. Nucleic Acid Detection Test: