Regional perspectives on influenza surveillance in Africa.

Africa possesses little capacity for influenza surveillance-Senegal and South Africa being the only countries in the WHO African region who regularly pursue active surveillance and characterize influenza isolates. South Africa has three sites-in Cape Town, Durban and the largest in Johannesburg at the National Institute for Virology (NIV). The NIV antigenically and molecularly characterizes influenza viruses isolated from specimens provided by a sentinel network of approximately 50 clinical sites. This information, together with the isolates themselves are supplied to WHO International Influenza Centres in London and Melbourne. In addition, proxy markers of influenza severity such as school absenteeism and doctor/clinic visits are monitored to assess the severity of epidemics. Although, influenza exacts a heavier toll of the illness burden in developing countries already beset with underlying chronic medical conditions and also has a more severe impact on economies largely dependent on single income earners and subsistence farmers, influenza surveillance and vaccination awareness is woefully lacking on the African continent, and this urgently needs to be remedied.

Progress towards polio eradication: an African perspective.

Despite daunting competing health priorities, Africa has made significant progress in polio control. Northern and Southern Africa appear to be polio-free and may shortly be certified as such; however, polio still remains endemic in West and Central Africa and the Horn of Africa. Countries "in difficult circumstancess", wracked by major civil wars, have particularly low routine vaccine coverage, although NIDS have been carried out during negotiated days of tranquillity. AFP surveillance has also improved, although the quality of stool specimens is still far from ideal. There is, nevertheless, an extraordinary political commitment to the eradication campaign. Lessons from the history of polio in the continent need to be heeded in designing end-game strategies. Obstacles on the path to successful eradication are undoubtedly more formidable on the African continent--perhaps the most serious of all are the continuing wars. International political commitment and focussed and empowering developmental aid are urgently needed.

Impact of the introduction of A/Sydney/5/97 H3N2 influenza virus into South Africa.

In 1998 South Africa experienced a major influenza epidemic that was characterized by extensive illness and an unusually early season. The impact of the epidemic was charted by measuring proxy indexes of influenza activity such as school absenteeism and excess mortality in persons older than 65 years. Viruses isolated from patients of all age groups were analyzed both antigenically and at the molecular level to determine the characteristics of the influenza strain responsible for the outbreaks. The study revealed that influenza activity was detected as early as the middle of April and peaked toward the end of May and early June. School absenteeism correlated with a sharp rise in virus isolation during this period. Consumption of influenza-related pharmaceuticals, as well as mortality figures, also corresponded to the increased absenteeism and virus isolation. Characterization of the viruses isolated during 1997 and 1998 showed clearly that the epidemic was caused by the introduction of the A/Sydney/5/97-like H3N2 influenza strain into South Africa in 1998. With no prior exposure to this virus strain, which is antigenically distinct from the viruses that had been present in this country in 1997, the population was highly susceptible, resulting in an early, rapid spread of influenza. This epidemic has highlighted the importance of having an influenza vaccine specifically formulated for the Southern Hemisphere. If the 1998 vaccine had not contained the A/Sydney/5/97 strain, the widespread outbreaks in South Africa would have been far worse in terms of morbidity, mortality, and economic loss. This, in turn, emphasizes the need for increased influenza surveillance and international cooperation.

The molecular characterization of influenza virus strains isolated in South Africa during 1993 and 1994.

Influenza A (H3N2) and influenza B viruses isolated recently in South Africa were analysed by partial nucleotide sequencing of the haemagglutinin gene to examine antigenic drift of the isolates relative to the vaccine strains. The genomic analysis of the influenza B isolates revealed a number of differences in the amino acid residues compared with those of the B/Panama/45/90 vaccine strain, and these isolates were found to be antigenically more closely related to B/Quindao/102/91. In both the 1993 and 1994 influenza A (H3N2) isolates significant drift had taken place compared with the H3N2 vaccine strains for those years, emphasizing the need for an influenza vaccine formulated specifically for the southern hemisphere.

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.

The effect of neutralizing monoclonal antibodies on early events in Rift Valley fever virus infectivity.

Monoclonal antibodies (mAb) were used to examine possible stages at which antibody-mediated neutralization of Rift Valley fever virus occurs, and to assess whether binding of antibody is dependent on viral protein structure in order that antibody recognition take place. Analysis of the structural properties of the antigenic determinants revealed that the neutralizing sites are highly conformation-dependent. None of the mAb prevented virus binding, suggesting that the epitopes they define are spatially separate from the site(s) responsible for virus attachment to the cellular receptor. The finding that many of the mAb also did not inhibit virus entry into the cell demonstrated that neutralization of RVFV infectivity by immune antibodies is not dependent on blocking at the early stages in the viral life cycle.

The synergistic neutralization of Rift Valley fever virus by monoclonal antibodies to the envelope glycoproteins.

A panel of monoclonal antibodies (MAbs) mapping to different antigenic sites on the RVFV G1 and G2 proteins were used to examine the mechanisms involved in neutralization of the virus. Three types of synergistic neutralization of RVFV were observed on mixing various pairs of MAbs. Firstly, enhanced neutralization occurred for two MAb pairs that showed augmented binding for G2. These comprised a combination of a neutralizing MAb with a non-neutralizing antibody, as well as two antibodies which were non-neutralizing individually. In the second category, synergistic neutralization was observed between combinations of MAbs for which increased binding had not been detected. Lastly, mixtures of G1 and G2-specific MAbs were also capable of enhancing neutralization. Post-adsorption neutralization assays revealed that some MAbs neutralized cell-attached virus efficiently, indicating that they can neutralize by inhibiting the infection process after virus attachment. MAbs mapping to G1 IIe, G2I b and G2I c were unable to neutralize adsorbed virus and thus probably neutralize by preventing virus attachment to cells. Several G1-reactive MAbs displayed low level post-adsorption activity, suggesting they may be capable of inhibiting RVFV infectivity at different stages of the replication cycle.

Antigenic analysis of Rift Valley fever virus isolates: monoclonal antibodies distinguish between wild-type and neurotropic virus strains.

Rift Valley fever virus (RVFV) isolates from southern Africa were analysed for possible strain variation using monoclonal antibodies prepared against the South African prototype RVF 1830 strain. By the indirect immunofluorescence antibody assay and neutralization tests, the wild type southern African isolates were found to be antigenically similar to RVFV strains from other parts of Africa. In contrast, differences in several biologically important neutralizing and haemagglutination epitopes on both the G1 and G2 glycoproteins of the attenuated Onderstepoort veterinary vaccine and the Smithburn neurotropic strain were identified.

A study of the effect of chemical inactivants on the epitopes of Rift Valley fever virus glycoproteins using monoclonal antibodies.

A panel of 23 monoclonal antibodies (mAbs) was used to study the effect of formalin, beta propriolactone (BPL) and binary ethylenimine (BEI) on the epitopes of the Rift Valley fever virus glycoproteins. After the initial inactivation period BEI had very little adverse affect on the epitopes whereas BPL significantly altered seven and formalin partially changed the conformation or accessibility of most of the epitopes. The epitopes of all of the inactivated antigens showed a reduced activity against the specific mAbs over a six month storage period.

Differentiation of primary cytomegalovirus infection from reactivation using the urea denaturation test for measuring antibody avidity.

Cytomegalovirus (CMV) is probably the most common agent of prenatal infection of the newborn, and one of 20 congenitally infected newborns shows serious symptoms. It was therefore considered important to be able to differentiate primary CMV from reactivation in pregnant females. A urea denaturation test was used to distinguish primary from secondary rubella infection in which the urea is included in the wash step of the standard IgG ELISA. This resulted in the removal of low-avidity antibodies, which are the antibodies produced early in infection. A group of CMV IgM-negative and -positive sera were tested, and all but one showed moderate to high avidity, with an avidity index reading of more than 30%. Among a group of babies 3-12 months of age, who were CMV IgM positive, 55% (16 of 29) showed low-avidity CMV antibodies. A small group of renal transplant patients and patients with clinically and laboratory-confirmed CMV gave more or less predicted avidity index results. It appears that, with the method used at this laboratory, the urea denaturation test can be applied to CMV to determine primary infection or reactivation in the majority of cases.

Topological mapping of antigenic sites on the Rift Valley fever virus envelope glycoproteins using monoclonal antibodies.

A panel of 17 monoclonal antibodies (MAbs) to the G1 and G2 envelope glycoproteins of Rift Valley fever (RVF) virus were used to analyze the topography and functional properties of the viral antigenic sites. Four heterogeneous antigenic regions which may be interlinked were identified on the G1 protein and four distinct domains on the G2 protein by competitive binding assays. Comparison of the biological activities and epitope specificities of the MAbs against G1 showed that the antigenic domains I, II, and IV were involved in virus neutralization and haemagglutination at different potencies. For both the G1 and G2 proteins, determinants mapping to domain G1 Ia and G2 Ia were associated with very strong neutralization independent of complement (C'), suggesting that they represent biologically important areas. Domain G2 II was involved in haemagglutination and weak C' dependent neutralization while the other two G2 regions had no haemagglutination function and neutralized to a low level only in the presence of C'. Epitopes Ia and IIb on G1 and Ia and IIa on G2 were also associated with protection of mice against virulent RVFV infection, indicating that both envelope glycoproteins play an important role in RVF viral infection and pathogenesis.

[Use of monoclonal antibodies for the antigenic analysis of West Nile viral strains isolated in Madagascar. Contribution to the understanding of the epidemiological cycle]. / Utilisation des anticorps monoclonaux pour l'analyse antigénique des souches de virus West Nile isolées à Madagascar. Apport pour la compréhension du cycle épidémiologique.

The antigenic relationship of 53 MADAGASCAR West Nile isolates to each other and to the two prototype viruses (Eg 101 and G 2266) was assessed using monoclonal antibodies. In MADAGASCAR exist 5 antigenic groups: 4 which are much closer to the Egyptian strain Eg 101 than to the Indian, and antigenically distinct from South african H 442 strain. One other is closely related to Indian strain G 2266. Antigenic variations are observed in every periods of transmission cycle. Some differences between strains isolated in a same region are also observed. MADAGASCAR is an exchange place for West Nile virus through the instrumentality of migratory birds.

Comparison of an antibody-capture IgM enzyme-linked immunosorbent assay with IgM-indirect immunofluorescence for the diagnosis of acute Sindbis and West Nile infections.

The development and evaluation of an antibody-capture ELISA for the detection of IgM antibodies to Sindbis (SIN) and West Nile (WN) viruses are described. Comparison of the ELISA results with those obtained by indirect immunofluorescence (IIF) antibody tests using both fluorescein and biotinylated anti-human IgM conjugates, showed that the former technique was both more sensitive and specific than the IIF methods. There were no false positives by the ELISA whereas with the IgM-IIF assays a high percentage of false positives were obtained. These were due to rheumatoid factor and also to an interfering factor which was not detected by the RF latex agglutination test. Absorption of the sera with anti-IgG was necessary to eliminate this interference in the IgM-IIF tests.

Antigenic analysis of West Nile virus strains using monoclonal antibodies.

Seventeen monoclonal antibodies (MAbs) were prepared against the flavivirus West Nile strain H442. While the majority of these were specific for the major envelope protein, MAbs directed against the NS1 and ns4a nonstructural proteins were also identified. The MAbs were tested by indirect immunofluorescence against 16 southern African West Nile (WN) isolates, representative strains from the two main WN antigenic groups and several viruses from other flavivirus complexes. The MAb reactivities ranged from WN strain-specific to broadly flavivirus-group reactive. Comparison of the local isolates revealed the presence of several different strains, all of which were antigenically distinct from the representative strains of the two WN antigenic groups.

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

Seven monoclonal antibodies were prepared against a South African strain of Crimean-Congo hemorrhagic fever (CCHF) virus and were found to be directed against viral nucleocapsid protein. Five of the monoclonal antibodies reacted to high titer in indirect immunofluorescence (IF) tests and enzyme-linked immunosorbent assays (ELISA) with 22 strains of CCHF virus and failed to cross-react with the closest antigenic relative of CCHF, Hazara virus, or with 4 other nairoviruses which need to be distinguished from CCHF virus in Africa. These antibodies, used in the IF technique, readily detected antigens induced by all strains of CCHF virus included in the study in cell culture monolayers and mouse brain tissue, which represent the systems commonly used for isolation of CCHF virus. The IF technique with monoclonal antibodies constitutes a rapid and specific means of identifying newly isolated strains of CCHF virus.

Characterization of rotaviruses and subgroup F adenoviruses from acute summer gastroenteritis in South Africa.

Six hundred and sixteen specimens were collected from black children hospitalised with acute gastroenteritis during the summer and autumn of 1982-1983 (October to May). Eighty-five children (13.8%) shed rotavirus and at least 40 (6.5%) shed adenovirus (Ad) type 40 or 41 belonging to subgroup F. The highest monthly prevalence of shedding subgroup F adenoviruses (10.1%) coincided with a peak in admissions in midsummer, whereas the highest monthly prevalence of shedding rotaviruses (41.9%) coincided with a peak in admissions in autumn. There were at least five genome types of rotavirus, at least three genome types of Ad40, and at least five genome types of Ad41 circulating in the Johannesburg-Soweto area during the study period. The high rate of rotavirus shedding in autumn could not be attributed to an upsurge in infections by any particular rotavirus strain.

Atypical rotavirus from South African neonates. Brief report.

Rotaviruses displaying an RNA profile different from other human rotaviruses were detected in stools from six healthy neonates. These viruses shared the common group A antigen, unlike most other atypical human rotavirus electropherotypes described to date.