Evaluation of the MUREX*ICE HIV-1.O.2 capture enzyme immunoassay for early identification of HIV-1 seroreverting infants in a developing country.

BACKGROUND: A simple, inexpensive serological assay is required for the early determination of HIV infection status among infants born to HIV-1-seropositive women in developing countries. OBJECTIVES: To evaluate the use of a commercially available capture enzyme immunoassay (EIA), the MUREX*ICE HIV-1.O.2, for the early identification of seroreverting, uninfected infants. STUDY DESIGN: Infants with a clearly defined HIV-1 infection status, as determined by polymerase chain reaction results and/or seroreactivity at 18 months, were tested for antibodies to HIV. The time to seroreversion using the capture EIA was compared with the results obtained using an indirect assay, the GENELAVIA MIXT EIA. RESULTS: Seroreverting infants were identified earlier with the capture than the indirect EIA; all of the uninfected infants were seronegative at 12 months with the capture EIA while 100% seroreversion was only seen at 18 months with the indirect EIA. CONCLUSIONS: In general, the capture EIA identified seroreverting infants 3-6 months earlier than the indirect EIA. However, caution must be exercised in interpreting seroreactivity in a breast-fed population where HIV infection may occur in a child who has previously seroreverted.

One year surveillance of HIV-1 infection in Johannesburg, South Africa.

A sero-epidemiological surveillance study to monitor the prevalence of HIV-1 infection in Johannesburg, South Africa, was commenced in February 1988. The population selected for study were attenders at clinics for sexually transmitted diseases (STD) and at family planning (FP) clinics. In the 12 months of the study 6631 sera were tested. Of the STD attenders, 15 of 1224 black females (1.2%) and 21 of 2482 black males (0.8%) were positive. Of the 449 white males tested 49 were homosexual, amongst whom 10 (20.4%) were positive; in the heterosexual white male group 4 of 400 (1.0%) were positive. Of the FP clinic attenders, 4 of 1459 black females (0.3%) were positive. 68 of the 6631 sera tested were indeterminate for infection. No attenders were positive for HIV-2 infection. These data confirmed the entry of HIV infection into the black population in South Africa.

Evaluation of a "dip-stick" methodology for detection of antibodies to HIV1.

An HIV1 antibody screening assay, the "ImmunoComb" HIV1 kit which uses a dip-stick methodology, was evaluated using a panel of selected sera. The ImmunoComb detected 144 of 147 (98%) Western-blot-confirmed positive sera. However, when the ImmunoComb was compared with a recombinant EIA capable of detecting early seroconversion, only 144 of 156 (92.3%) recombinant EIA or Western-blot-positive sera were ImmunoComb-positive. Thus, while the kit is suitable for serological surveys and prevalence studies, especially in areas where skilled laboratory staff and sophisticated equipment are unavailable, the low sensitivity precludes its use in blood banks and transfusion services.

Epidemiologic and clinical features of Crimean-Congo hemorrhagic fever in southern Africa.

Following the diagnosis in 1981 of the first case of Crimean-Congo hemorrhagic fever (CCHF) in South Africa, an antibody survey was undertaken on cattle sera to determine the distribution of the virus and specific diagnostic tests were routinely applied to specimens from suspected cases of hemorrhagic fever to establish the medical significance of its presence. Antibody to CCHF virus was demonstrated by reversed passive hemagglutination-inhibition technique in 2,460/8,667 (28%) cattle sera and in 140/180 herds tested in South Africa, as well as in 347/763 (45%) cattle sera and in 32/34 (94%) herds tested in Zimbabwe. The antibody was found in all major cattle farming areas, but was of low prevalence along the southern coast where 2 of the 3 species of Hyalomma tick which occur in South Africa are absent. From February 1981 to January 1986, inclusive, 29 indigenous cases of CCHF were diagnosed in 16 outbreaks which arose in various locations throughout South Africa. A further 2 imported cases of CCHF arose in Zaire and Tanzania. The clinical features of infection conformed to the classical descriptions of CCHF in the Soviet Union. The fatal outcome in 11/31 cases indicates that the African disease is no less severe than that which occurs in Eurasia. It is inferred that the virus is widespread in all countries in Africa and Eurasia which lie within the limits of world distribution of ticks of the genus Hyalomma.

Antibody to Crimean-Congo hemorrhagic fever virus in wild mammals from southern Africa.

Crimean-Congo hemorrhagic fever (CCHF) virus is becoming increasingly recognized as an important human pathogen in southern Africa. In order to determine the role of wild mammals in the natural ecology of the virus, sera from 3,772 wild mammals of 87 species and from 1,978 domestic dogs collected in South Africa and Zimbabwe between 1964 and 1985 were tested for antibody to CCHF virus by reversed passive hemagglutination inhibition (RPHI) and by indirect immunofluorescence (IF). Antibody was found to be highly prevalent in large mammals in the Orders Artiodactyla and Perissodactyla such as giraffe, Giraffa camelopardalis (3/3 positive), rhinoceros, Ceratotherium simium and Diceros bicornis (7/13), eland, Taurotragus oryx (59/127), buffalo, Syncerus caffer (56/287), kudu, Tragelaphus strepsiceros (17/78), and zebra, Equus burchelli (16/93). In small mammals antibody was found in the sera of 40/293 hares, 22/1,305 rodents, and 1/74 wild carnivores, but not in 522 primates, 176 insectivores, or 19 hyrax. Antibody was also found in the sera of 118/1,978 domestic dogs. The species of wild mammal in which antibody was distributed (with highest antibody prevalence in hares and large herbivores) reflects the feeding preference of immature and adult ticks of the genus Hyalomma, suggesting that Hyalomma sp. are the principal CCHF vectors in the wild.

Comparison of techniques for demonstrating antibodies to Rift Valley fever virus.

Nine serological techniques were compared by monitoring the response to infection with Rift Valley fever (RVF) virus in three sheep. Antibodies were monitored daily for the first 14 days after infection, then weekly and later fortnightly up to week 24. The earliest antibody response was detected in one sheep on day 3 by a plaque reduction neutralization test, and by day 6 antibodies were demonstrable in all three sheep by haemagglutination-inhibition, reversed passive haemagglutination-inhibition, immunodiffusion, indirect immunofluorescence (IF), enzyme-linked immunosorbent assay and neutralization of cytopathic effect in cell cultures. Antibodies were demonstrable by complement fixation on day 8 at the earliest. IF and the two neutralization techniques produced the highest titres, but all tests could be used satisfactorily for the serological diagnosis of RVF. Inactivated antigen could be used for all except the neutralization tests. A radioimmunoassay technique using 125I-labelled staphylococcal protein A detected antibodies on day 8 at the earliest and produced lower mean titres than some of the other techniques. This was probably because sheep immunoglobulins bind protein A poorly.

Comparative pathogenicity and antigenic cross-reactivity of Rift Valley fever and other African phleboviruses in sheep.

Homologous and heterologous haemagglutination-inhibition (HAI), complement-fixation (CF), immunodiffusion (ID) and mouse neutralization tests were performed with the Lunyo (LUN) and a Zimbabwean strain of Rift Valley fever (RVF) virus, the prototype and a South African strain of Arumowot (AMT) virus and prototype strains of Gordil (GOR), Saint-Floris (SAF) and Gabek Forest (GF) viruses, using immune mouse ascitic fluids prepared against these viruses. Reactions of identity occurred in all tests between LUN and the Zimbabwean strains of RVF and between the two strains of AMT virus. Otherwise, cross-reactions occurred between all the phleboviruses in HAI tests, while reactions in CF, ID and neutralization tests were monospecific for virus serotypes, except that weak cross-reaction occurred between GOR and SAF viruses in CF and ID tests. Four sheep infected subcutaneously with the Zimbabwean strain of RVF virus developed transient fever, viraemia, leucopaenia, relative thrombocytopaenia, haemoconcentration and raised serum enzyme levels, which indicated that the sheep had developed necrotic hepatitis. Disseminated focal necrotic hepatitis was confirmed in a sheep killed for examination on day 4 post-infection. The other three sheep recovered uneventfully after only mild depression and anorexia. Groups of three sheep infected with SAF, GOR, AMT and GF viruses had no demonstrable viraemia or other sign of infection or illness, except that the sheep infected with AMT developed mild fever lasting less than 24 h. Antibody responses were monitored at intervals over a period of 24 weeks in all sheep by homologous and heterologous HAI, CF and cell culture neutralization (CPENT) tests. Homologous antibody responses were marked in the RVF-infected sheep and their sera cross-reacted strongly in HAI tests with antigens of the other viruses. The sera of the RVF-infected sheep cross-reacted less markedly in CF and CPENT tests. Homologous antibody responses were poor in all the sheep infected with phleboviruses other than RVF, and the cross-reactivity of their sera for RVF antigen or virus was negligible. All sheep were challenged with RVF virus 48 weeks after their initial infection. The sheep which had originally been infected with RVF virus were immune and developed neither fever nor viraemia. All other sheep developed fever, viraemia and antibodies to RVF virus. It was concluded that the African phleboviruses, other than RVF, are unlikely to cause disease in livestock or to induce antibodies which could cause confusion in the diagnosis of RVF.

Limitations of enzyme immunoassay tests for detection of HTLV-III/LAV antibodies.

A commercial enzyme immunoassay (EIA) kit was compared with an immunofluorescence test for the detection of antibodies directed against human T-cell lymphotropic virus type III (HTLV-III). The EIA kit is recommended for the screening of blood and plasma products only and is not suitable for diagnostic purposes because of the problem of nonspecific reactions. It is also recommended that the EIA kit not be used for screening immunoglobulin preparations for anti-HTLV-III antibodies because of the problem of false-positive reactions.

Sero-epidemiology of HTLV-III antibody in southern Africa.

A preliminary survey has demonstrated that antibodies directed against human T-cell leukaemia virus type III (HTLV-III), the virus implicated as the agent causing the acquired immunodeficiency syndrome, are not present in the low-risk population groups studied. The survey, in which an indirect immunofluorescence assay was used, has indicated that HTLV-III is not endemic in southern Africa (as opposed to central Africa, where it has been suggested that the virus is endemic). Anti-HTLV-III antibodies were, however, found in sera from male homosexuals, the one high-risk population group studied.

Crimean-congo hemorrhagic fever in South Africa.

Crimean-Congo hemorrhagic fever virus was isolated for the first time in South Africa in February 1981, from the blood of a 13-year-old boy who died in Johannesburg after attending a camp in a nature reserve in the western Transvaal. Virus was isolated from 21/120 pools of questing ticks from the nature reserve, the infected species being Hyalomma marginatum rufipes and H. truncatum. Virus was also isolated from 4/38 pools of partially engorged ticks and other ectoparasites collected off hosts, the infected species being H.m. rufipes, H. truncatum and Rhipicephalus evertsi. Antibodies were found in the sera of 5/74 humans, 8/26 wild vertebrates, 74/270 sheep, and 109/170 cattle from the reserve and surrounding farms. Antibodies were also found in 28/200 hares from various locations in the country. It was concluded that the virus is widely prevalent in South Africa, but the full medical and veterinary significance of its presence has yet to be determined.

Reversed passive hemagglutination and inhibition with Rift Valley fever and Crimean-Congo hemorrhagic fever viruses.

Reversed passive hemagglutination (RPHA) tests were performed by coating glutaraldehyde-fixed and tannic acid-treated sheep erthrocytes with antibodies to Rift Valley fever (RVF) and Crimean-Congo hemorrhagic fever (CCHF) viruses. Cells coated with crude antibody, in the form of mouse immune ascitic fluid, reacted with high specificity and sensitivity in RPHA tests with live or inactivated virus antigens. In inhibition (RPHI) tests, RVF antibody titers in human and sheep sera were similar to those determined by hemagglutination inhibition test. RVF virus antigen could be detected in viremic sheep sera by the RPHA technique. RPHI antibody titers to CCHF virus in human and hare sera were similar to indirect immunofluorescence (IF) titers, but sheep and cattle sera with RPHI titers of 1:32 or less were negative in IF tests.