Preparation and use of monoclonal antibodies for identifying Crimean-Congo hemorrhagic fever virus

Mammarenaviruses of Rodents, South Africa and Zimbabwe

We conducted a survey for group-specific indirect immunofluorescence antibody to mammarenaviruses by using Lassa fever and Mopeia virus antigens on serum specimens of 5,363 rodents of 33 species collected in South Africa and Zimbabwe during 1964-1994. Rodents were collected for unrelated purposes or for this study and stored at -70°C. We found antibody to be widely distributed in the 2 countries; antibody was detected in serum specimens of 1.2%-31.8% of 14 species of myomorph rodents, whereas 19 mammarenavirus isolates were obtained from serum specimens and viscera of 4 seropositive species. Phylogenetic analysis on the basis of partial nucleoprotein sequences indicates that 14 isolates from Mastomys natalensis, the Natal multimammate mouse, were Mopeia virus, whereas Merino Walk virus was characterized as a novel virus in a separate study. The remaining 4 isolates from 3 rodent species potentially constitute novel viruses pending full characterization.

Crimean-Congo haemorrhagic fever virus: Past, present and future insights for animal modelling and medical countermeasures

Crimean–Congo haemorrhagic fever (CCHF) is a widespread tick‐borne viral zoonosis with a case‐fatality rate ranging from 9% to 50% in humans. Although a licensed vaccine to prevent infection by the CCHF virus (CCHFV) exists, its ability to induce neutralizing antibodies is limited and its efficacy against CCHFV remains undetermined. In addition, controlling CCHF infections by eradication of the tick reservoir has been ineffective, both economically and logistically, and the treatment options for CCHF remain limited. In this review, we first critically discuss the existing animal models to evaluate therapeutics for CCHF. We then review the therapeutic options for CCHF that have been investigated in human cases, followed by investigational drugs that have been evaluated in pre‐clinical studies. We highlight the importance of understanding human prognostic factors in developing an animal model for CCHF that recapitulates hallmarks of human disease and its implication for selecting therapeutic candidates.

A Crimean-Congo hemorrhagic fever (CCHF) viral vaccine expressing nucleoprotein is immunogenic but fails to confer protection against lethal disease

Crimean-Congo Hemorrhagic Fever (CCHF) is a severe tick-borne disease, endemic in many countries in Africa, the Middle East, Eastern Europe and Asia. Between 15–70% of reported cases are fatal with no approved vaccine available. In the present study, the attenuated poxvirus vector, Modified Vaccinia virus Ankara, was used to develop a recombinant candidate vaccine expressing the CCHF virus nucleoprotein. Cellular and humoral immunogenicity was confirmed in 2 mouse strains, including type I interferon receptor knockout mice, which are susceptible to CCHF disease. Despite the immune responses generated post-immunisation, the vaccine failed to protect animals from lethal disease in a challenge model.

Possible future monoclonal antibody (mAb)-based therapy against arbovirus infections

More than 150 arboviruses belonging to different families are known to infect humans, causing endemic infections as well as epidemic outbreaks. Effective vaccines to limit the occurrence of some of these infections have been licensed, while for the others several new immunogens are under development mostly for their improvements concerning safety and effectiveness profiles. On the other hand, specific and effective antiviral drugs are not yet available, posing an urgent medical need in particular for emergency cases. Neutralizing monoclonal antibodies (mAbs) have been demonstrated to be effective in the treatment of several infectious diseases as well as in preliminary in vitro and in vivo models of arbovirus-related infections. Given their specific antiviral activity as well-tolerated molecules with limited side effects, mAbs could represent a new therapeutic approach for the development of an effective treatment, as well as useful tools in the study of the host-virus interplay and in the development of more effective immunogens. However, before their use as candidate therapeutics, possible hurdles (e.g., Ab-dependent enhancement of infection, occurrence of viral escape variants) must be carefully evaluated. In this review are described the main arboviruses infecting humans and candidate mAbs to be possibly used in a future passive immunotherapy.

Presence of broadly reactive and group-specific neutralizing epitopes on newly described isolates of Crimean-Congo hemorrhagic fever virus

Crimean-Congo hemorrhagic fever virus (CCHFV), a member of the genus Nairovirus of the family Bunyaviridae, causes severe disease in humans with high rates of mortality. The virus has a tripartite genome composed of a small (S), a medium (M) and a large (L) RNA segment; the M segment encodes the two viral glycoproteins, G(N) and G(C). Whilst relatively few full-length M segment sequences are available, it is apparent that both G(N) and G(C) may exhibit significant sequence diversity. It is unknown whether considerable antigenic differences exist between divergent CCHFV strains, or whether there are conserved neutralizing epitopes. The M segments derived from viral isolates of a human case of CCHF in South Africa (SPU 41/84), an infected tick (Hyalomma marginatum) in South Africa (SPU 128/81), a human case in Congo (UG 3010), an infected individual in Uzbekistan (U2-2-002) and an infected tick (Hyalomma asiaticum) in China (Hy13) were sequenced fully, and the glycoproteins were expressed. These novel sequences showed high variability in the N-terminal region of G(N) and more modest differences in the remainder of G(N) and in G(C). Phylogenetic analyses placed these newly identified strains in three of the four previously described M segment groups. Studies with a panel of mAbs specific to G(N) and G(C) indicated that there were significant antigenic differences between the M segment groups, although several neutralizing epitopes in both G(N) and G(C) were conserved among all strains examined. Thus, the genetic diversity exhibited by CCHFV strains results in significant antigenic differences that will need to be taken into consideration for vaccine development.

Antigenic diversity of Akabane virus detected by monoclonal antibodies

The antigenic properties of 21 Japanese field isolates and two Australian strains of Akabane (AKA) virus (Simbu serogroup, bunyavirus) isolated from 1959 to 1990 were compared by enzyme-linked immunosorbent assay (ELISA), plaque-reduction neutralization (PRNT) and hemagglutination inhibition (HI) tests using monoclonal antibodies (Mabs) to the OBE-1 strain of AKA virus. Sixteen Mabs were established by fusing P3X63Ag8U1 mouse myeloma cells and spleen cells from BALB/c mice immunized with the OBE-1 strain. Of the 16 clones, 13 produced immunoglobulin (Ig) which precipitated glycoprotein G1 and three produced Ig which precipitated nucleoprotein (N). Twelve out of 13 Mabs had both NT and HI activities to not only the homologous OBE-1 strain but also the other isolates. By the competitive binding assay, at least five antigenic regions for G1, and two for N were defined. Some of the anti-G1 Mabs which reacted to the same antigenic region had unique reactivity while anti-N Mabs recognizing the same epitope reacted with almost the same degree to all of the isolates. Finally, nine epitopes of the G1 protein in five different antigenic regions have been identified. There was no striking correlation between isolation date and place of the isolates and their reactivity to Mabs. A most interesting result is that three isolates collected in the same place over a three week period had different reactivity patterns detected by ELISA, showing great antigenic variation of the virus. AKA virus may be a single gene pool consisting of different genotypes in the field.

Antigenic relationship between chikungunya virus strains and o'nyong nyong virus using monoclonal antibodies

Chikungunya (CHIK) strains from Africa and Asia were shown to be antigenically closely related using a panel of monoclonal antibodies (mAb) prepared against strains H817 from Africa and PhH15483 from Asia. The one-way antigenic relationship between CHIK and o'nyong nyong (ONN) viruses was demonstrated at the epitope level using the immunofluorescence and haemagglutination inhibition techniques. Results of tests with mAb against ONN virus suggest that, while ONN virus has retained most of the CHIK antigenic sites, many of the ONN epitopes have undergone sufficient conformational change such that mAbs prepared against them do not recognize sites on CHIK virus.

Serodiagnosis of Crimean-Congo haemorrhagic fever

Several methods for demonstrating antibody to Crimean-Congo haemorrhagic fever virus were compared on serum samples taken from 101 patients during the acute stage of illness and at intervals for up to 59 months thereafter, with emphasis on early detection of the immune response. The deaths of 23 patients on days 5-14 of illness were ascribed to the effects of the disease; two patients died later from other causes. Very few of the patients who died from the acute illness mounted an antibody response detectable by the methods tested. Four patients who died and 18 who recovered were treated with immune plasma collected from recovered patients. Treated patients acquired IgG antibody from the plasma, but it was possible to discern the onset of an endogenous IgM response in those individuals who survived the disease by all of the methods tested. Indirect immunofluorescence (IF) tests detected IgM and/or IgG antibodies at the earliest on day 4 of illness in about 10% of patients who survived the disease, and by day 9 all survivors had antibodies demonstrable by IF. A biotin-streptavidin IF technique offered no advantage over the standard IF test for the early detection of IgG antibody, but demonstrated higher antibody titres and detected IgM antibody earlier in about a quarter of the patients tested. An IgM-capture enzyme-linked immunoassay (ELISA) and an IgG sandwich ELISA demonstrated higher antibody titres than did IF tests, and detected antibody responses at an earlier stage of infection than did IF tests in about one-fifth of patients, but the reverse was true in a similar proportion of instances. A competition ELISA, which detected total antibody activity, produced lower titres than did the IgM and IgG ELISAs, but yielded results which were in close agreement with the findings in IF tests. It was concluded that the IF tests were most convenient for use in making a rapid serodiagnosis of the disease.

Enzyme-linked immunosorbent assays for the detection of antibody to Crimean-Congo haemorrhagic fever virus in the sera of livestock and wild vertebrates

IgM antibody response to Crimean-Congo haemorrhagic fever (CCHF) virus was monitored in experimentally infected sheep and cattle by an IgM capture enzyme-linked immunoassay (ELISA). Specific binding of antigen was detected by a rabbit anti-CCHF horseradish peroxidase conjugate or a sandwich technique with hyperimmune mouse anti-CCHF ascitic fluid and commercially available anti-mouse immunoglobulin peroxidase conjugate. The persistence of IgM antibody activity was found to be of shorter duration than in humans, and this may be a function of the relative lack of susceptibility of these animals to infection with CCHF virus. IgG antibody responses in the sheep could be monitored by sandwich ELISA using commercially available anti-sheep immunoglobulin peroxidase conjugates. Total antibody activity in the sera of experimentally infected sheep, cattle and small mammals could be monitored in a competitive ELISA (CELISA) using rabbit anti-CCHF peroxidase conjugate. The CELISA was applied to the sera of 960 wild vertebrates from a nature reserve in South Africa, and the prevalence of antibody was found to be greatest in large mammals such as rhinoceros, giraffe and buffalo, which are known to be the preferred hosts of the adult tick (Hyalomma) vectors of the virus.