Prospective, double-blind, concurrent, placebo-controlled clinical trial of intravenous ribavirin therapy of hemorrhagic fever with renal syndrome.

A prospective, randomized, double-blind, concurrent, placebo-controlled clinical trial of intravenous ribavirin (loading dose of 33 mg/kg, 16 mg/kg every 6 h for 4 days, and 8 mg/kg every 8 h for 3 days) was conducted in 242 patients with serologically confirmed hemorrhagic fever with renal syndrome (HFRS) in the People's Republic of China. Mortality was significantly reduced (sevenfold decrease in risk) among ribavirin-treated patients, when comparisons were adjusted for baseline risk estimators of mortality (P = .01; two-tailed). HFRS typically consists of five consecutive but frequently overlapping clinical phases. Only occurrence of oliguric phase and hemorrhage was associated with severity of clinical disease in the placebo group. Ribavirin therapy also resulted in a significant reduction in the risk of entering the oliguric phase and experiencing hemorrhage. The only ribavirin-related side effect was a well-recognized, fully reversible anemia after completion of therapy.

Double-stranded ribonuclease coinduced with interferon.

Double-stranded (ds) RNA and many viruses are inducers of interferon (IFN), the latter presumably because they contain, or can form, dsRNA. Concomitant with the induction of IFN in chicken embryo cells was the induction of a novel double-stranded ribonuclease (dsRNase), which was released into the medium and continued to accumulate long after IFN production ceased. Only avian cells (chicken, quail, turkey, or duck) expressed high levels of this dsRNase; mammalian, turtle, or fish cells did not. Production of the nuclease was inducer dose-dependent. Optimum pH and cation requirements distinguished it from other dsRNase activities. Degradation of dsRNA was endonucleolytic. Activity resided in a molecule of an Mr of approximately 34,500. Low levels of a single-stranded (ss) RNase activity were inseparable from the dsRNase. The role for a dsRNA-inducible dsRNase released from cells is unknown.

Rift Valley fever infection of rhesus monkeys: implications for rapid diagnosis of human disease.

Rhesus monkeys inoculated with Rift Valley fever (RVF) virus provide a model in which serial observations of serum viral antigen and antibodies can be made. In 9 non-fatal and 3 fatal infections, either antigen or IgM enzyme-linked immunosorbent assay (ELISA) antibodies were detected in every serum sample during the acute phase. Furthermore, viral nucleic acid could be detected by filter hybridization in most samples taken on days 1 to 3. Circulation of significant quantities of viral RNA provides an additional approach to the diagnosis and study of RVF.

Assessment of an rDNA probe filter hybridization assay for the detection of Rift Valley fever virus RNA in human serum samples from the Mauritanian epidemic.

The Rift Valley fever virus (RVFV) epidemic that occurred in southern Mauritania during the 1987 rainy season provided a unique opportunity to test and evaluate a recently developed, M-segment-specific, nucleic acid filter hybridization assay on a large collection of infected human serum samples. It afforded the opportunity to compare the procedure with two other methods for detecting virus: virus isolation and antigen detection by ELISA. The filter hybridization procedure employed a polyethylene-glycol-precipitation and proteinase-K-digestion sample treatment step developed specifically for preparing serum samples for hybridization. The procedure was less sensitive for detecting RVFV in the Mauritanian human viremic samples than in sera from experimentally infected monkeys used to evaluate this procedure. It was also less sensitive than an antigen detection procedure used to test the Mauritanian samples. However, we were able to detect virus RNA in a significant proportion of the virus-isolation-positive samples. Advances in sample preparation, labelling and detection procedures, and hybridization methods will improve the sensitivity, precision and ease of use of this assay and increase its value as a diagnostic tool.

Rift Valley fever among domestic animals in the recent West African outbreak.

Severe haemorrhagic disease among the human population of the Senegal River Basin brought the Rift Valley fever virus (RVFV) outbreak of 1987 to the attention of science. As in previous RVFV outbreaks, local herdsmen reported a high incidence of abortion and disease in their livestock. Serum samples were obtained from domestic animal populations from areas near Rosso, the best studied focus of human infection, as well as other areas distant from known human disease. Among animals from the area of high incidence of human disease, antibody prevalence was as high as 85%, with approximately 80% of the sera positive for both RVFV IgG- and viral-specific IgM antibodies. In contrast, human populations in the same area had lower RVFV antibody prevalences, 40% or less, with 90% also being IgM-positive. Sera from livestock in coastal areas 280 km south of the epidemic area were negative for RVFV antibodies. Thus, the detection of RVFV specific IgG and IgM antibodies provided evidence of recent disease activity without the requirement to establish pre-disease antibody levels in populations or individuals and without viral isolation. Subsequently, detection of modest levels of IgG and IgM in the Ferlo region, 130 km south of the Senegal River flood plain, established that RVFV transmission also occurred in another area of the basin. Similar serological testing of domestic ungulates in The Gambia, 340 km south of Rosso, demonstrated antibody prevalence consistent with a lower level of recent transmission of RVFV, i.e., 24% IgG-positive with 6% of the positive sera also having RVFV-specific IgM.

Experimental infection of Phlebotomus papatasi with sand fly fever Sicilian virus.

Experimental studies were conducted to evaluate humans as hosts infecting the sand fly Phlebotomus papatasi with sand fly fever Sicilian (SFS) virus. Viral antigen and infectious virus circulated in the blood of infected volunteers on days 4 and 5 after intravenous inoculation with SFS virus. Viremia levels during the latter period were high enough to infect feeding sand flies, but only 13% (9/69) of the flies became infected. One out of every 3 infected sand flies that survived to feed a second time transmitted SFS to a hamster. These results confirm a vertebrate-sand fly-vertebrate transmission cycle for SFS virus, and demonstrate that horizontal transmission may contribute to the maintenance of this virus in nature.

Enzyme-linked immunosorbent assay for detection of antibodies to Rift Valley fever virus in ovine and bovine sera.

An enzyme-linked immunosorbent assay (ELISA) was developed for the rapid detection of antibodies to Rift Valley fever virus (RVFV) in ovine and bovine sera. Conditions to reduce nonspecific reactions were optimized. The ELISA results correlated with those of a plaque-reduction neutralization test, revealing 100% specificity and 90.7% sensitivity. In sera from sheep and cattle inoculated against RVFV, the hemagglutination-inhibition test in combination with the ELISA provided a better indication of response to killed RVFV vaccine than did either test alone.

Comparison of an indirect fluorescent-antibody test with an enzyme-linked immunosorbent assay for serological studies of Lyme disease.

An enzyme-linked immunosorbent assay was compared with an indirect fluorescent antibody test for its ability to detect antibodies to the Lyme disease spirochete in sera of naturally infected humans, dogs, and white-footed mice and experimentally infected Swiss mice. Ninety-five percent of the total 123 sera analyzed reacted similarly in both tests. For 36 human sera, the correlation coefficient (r = 0.47) for logarithmic transformations of indirect fluorescent antibody and enzyme-linked immunosorbent assay titers was significant at P less than 0.01. Within each mammalian species, mean titers for indirect fluorescent antibody and enzyme-linked immunosorbent assay antibodies were within three-fold. Comparisons of different naturally infected mammals revealed relatively higher average titration endpoints in both tests for patients with Lyme disease. Human sera also had the widest range of titers. Both methods proved satisfactory for serological confirmation of prior spirochetal infections.

Use of enzyme immunoassays and the latex agglutination test to measure the temporal appearance of immunoglobulin G and M antibodies after natural infection or immunization with rubella virus.

The time course of appearance of antibodies after infection with rubella virus was determined with an immunoglobulin G (IgG) detection enzyme-linked immunosorbent assay, a latex agglutination test, and an IgM detection enzyme-linked immunosorbent assay. In six naturally infected rubella patients and 26 vaccinees, antibodies measured by either the IgG enzyme-linked immunosorbent assay or the latex agglutination test generally appeared in parallel with those detected by the hemagglutination inhibition test. By 28 days after inoculation of live virus vaccine and by 2 days postonset of clinical rubella symptoms caused by natural infection, antibodies were found by the two tests for all individuals. A commercially available enzyme-linked immunosorbent assay kit was used to detect rubella-specific IgM. After natural infection, IgM appeared earlier than IgG, and although IgM titers decreased rapidly postinfection, in four of five patients antibodies were still detectable 40 to 43 days after the onset of clinical symptoms. After vaccine-induced infection, rubella-specific IgM was lower in titer than after natural infection and was detected in only three of seven vaccinees 70 days post-immunization.

Comparison of the latex agglutination test with the hemagglutination inhibition test, enzyme-linked immunosorbent assay, and neutralization test for detection of antibodies to rubella virus.

The ability of a rapid, latex agglutination test to diagnose rubella infection and to measure immune status was evaluated by comparison with the hemagglutination-inhibition (HAI) test, enzyme-linked immunosorbent assay (ELISA), and the neutralization (NT) test. The latex agglutination test accurately detected serological conversions in 74 pairs of sera representing 21 natural infections and 53 immunizations. The antibody levels of 276 sera from the general population were determined by latex agglutination, HAI, and ELISA. The correlation coefficients between the titers obtained by HAI and latex agglutination and by ELISA and latex agglutination were statistically significant. Results on 12 sera did not agree when measured by the three tests. These sera were included among the 196 specimens tested by NT. The correlation coefficient between NT and latex agglutination titers was statistically significant. There was one serum positive by latex agglutination but negative by NT, and five sera were negative by latex agglutination but had titers of 4 to 8 in the NT. The relative sensitivity of detecting antibody was greater by latex agglutination than by HAI. An additional 49 sera containing residual nonspecific hemagglutinin inhibitors were evaluated by latex agglutination and NT. The untreated sera showed no false positive reactions, and 36 of 39 NT positive sera were positive in the latex agglutination test.

Detection of La Crosse arbovirus antigen in mosquito pools: application of chromogenic and fluorogenic enzyme immunoassay systems.

An enzyme immunoassay producing either a chromogenic or fluorogenic end product was developed and evaluated for detecting La Crosse viral antigen within mosquito pools. The enzyme immunoassay was found to be sensitive, detecting one infected mosquito within a pool of 100 mosquitoes, and specific, distinguishing between closely related California group viruses. Assays were completed within 5 h after the addition of test samples. La Crosse viral antigen could be readily detected in mosquito pools after seven freeze-thaw cycles.

Experimental transmission and field isolation studies implicating Culex pipiens as a vector of Rift Valley fever virus in Egypt.

Attempts were made to isolate virus from wild caught mosquitoes during the 1977 and 1978 Rift Valley fever (RVF) epizootics in Egypt. Over 95% of the 55,126 mosquitoes collected from epizootic areas in the Nile Delta and Valley were Culex pipiens. Two strains of RVF virus were isolated from unengorged female C. pipiens taken in 1978. Laboratory-reared C. pipiens originating from a population sample from the Nile Delta epizootic area transmitted RVF virus. The infection rate of mosquitoes that fed on viremic hamsters was 86.7%; the transmission rate was 40.0% (46.2% based only on infected mosquitoes). From these results, it is suggested that C. pipiens was a vector of RVF virus during the 1977-1978 epizootics in Egypt.

Rift Valley fever ocular manifestations: observations during the 1977 epidemic in Egypt.

Ocular manifestations resulting from Rift Valley fever (RVF) virus infection were studied during an extensive RVF epidemic in Egypt during 1977. Colour photography and fluorescein angiography of 7 serologically diagnosed patients showed the commonest manifestations to be macular, paramacular, and/or extramacular retinal lesions, often occurring bilaterally. Haemorrhage and oedema were frequently associated with the lesions, and vasculitis, retinitis, and vascular occlusion were also observed. Patients were monitored during a 6-month convalescence, and, though resorption of the lesions occurred, approximately half the patients experienced permanent loss of visual acuity. Ocular disease was one form of the clinical spectrum of RVF; acute febrile, encephalitic, and fatal haemorrhagic RVF illnesses were also observed during the epidemic.

Ocular disease resulting from infection with Rift Valley fever virus.

The demonstration of serological conversion to Rift Valley fever (RVF) virus in paired acute and convalescent sera established RVF as the cause of two cases of retinitis seen during the 1977 RVF epidemic in Egypt. Colour photography of the retina revealed macular, paramacular and extramacular exudate-like lesions with associated haemorrage and oedema. One patient has not recovered central vision during a six-month convalescence. An ongoing study of a larger group of RVF patients with ocular disease revealed that the findings presented for these two cases represented the types of lesions most frequently encountered during the epidemic.