West Nile Antigen Research Articles

Indirect ELISA for serosurveillance of Japanese encephalitis in pigs

For monitoring the activity of Japanese encephalitis (JE) in pigs, no effective assay is available in Indian context. Being its endemicity in India and role of pigs as amplifiers, there was need to develop rapid and sensitive assay for serosurveillance of JE in pigs. An Indirect ELISA (I-ELISA) was standardized using ultracentrifuge sucrose density gradient purified JE antigen from standard virus strain. Cross reaction studies were done with West Nile antigen and comparative efficacy of I-ELISA assessed with Virus Neutralization Test (VNT). Optimum results recorded for detection of IgG and IgM, respectively, at 50 ng/well antigen and 1:200 and 1:300 serum dilutions. The positive - to - negative ratio of ³2 considered positive for JE antibodies. The overall prevalence of JE in pigs recorded to be 28.89 %. The concordance of the indirect ELISA (IgG) vis-a-vis VNT revealed good agreement (kappa = 0.66) and moderate agreement (kappa = 0.56) of standardized I- ELISA towards detection of IgG and IgM, respectively. The assay standardized in the present study could be useful for JE serosurveillance in pig population from endemic and non endemic areas in India.

Serological evidence of antibodies to certain arboviruses in desert rodent sera in Egypt

Introduction : Small rodents inhabiting the wadis close to St Katherine in the mountains of the Sinai Peninsula, Egypt, were trapped and antibodies to Sindbis (SIN) , West Nile (WN) and Quaranfil (QRF) viruses in their sera were studied. Materials and Methods One mouse had Haemagglutination–inhibition (HI) antibodies against SIN antigen in his serum, 3 mice had HI antibodies against WN antigen in their sera. The titers is low to be of any significance. Conclusion: It seems that natural cycle of transmission of SIN and WN viruses involving rodents does not exist. Seven mice had Complement-fixation (CF) antibodies in their sera against Quaranfil antigen. Conclusion, the CF test results suggest the existence of another mammal vector cycle.

Serological evidence of antibodies to certain arboviruses in desert rodent sera in Egypt

Introduction : Small rodents inhabiting the wadis close to St Katherine in the mountains of the Sinai Peninsula, Egypt, were trapped and antibodies to Sindbis (SIN) , West Nile (WN) and Quaranfil (QRF) viruses in their sera were studied. Materials and Methods One mouse had Haemagglutination–inhibition (HI) antibodies against SIN antigen in his serum, 3 mice had HI antibodies against WN antigen in their sera. The titers is low to be of any significance. Conclusion: It seems that natural cycle of transmission of SIN and WN viruses involving rodents does not exist. Seven mice had Complement-fixation (CF) antibodies in their sera against Quaranfil antigen. Conclusion, the CF test results suggest the existence of another mammal vector cycle.

Dengue virus infection among children with undifferentiated fever in Karachi.

Sera were collected from a total of 122 children, comprising 117 cases with undifferentiated fever and 5 cases with dengue hemorrhagic fever (DHF), during June to September 1994 in Karachi, Pakistan. Sera were tested by the IgM-capture ELISA using dengue type 1 (D1), dengue type 2 (D2), West Nile (WN), and Japanese encephalitis (JE) viral antigens. Among 92 single sera from undifferentiated fever cases, IgM antibodies were detected in 5 cases by D1, 8 cases by D2, and 5 cases by WN antigens, respectively. Corresponding number of positives among 25 paired sera from undifferentiated fever cases were 3 by D1, 6 by D2, and 1 by WN antigen. Four out of 5 DHF cases possessed anti-D1 as well as anti-D2 IgM antibodies. Only a single DHF case was positive for anti-WN IgM antibodies. Anti-JE IgM antibodies were not detected in any of the tested serum specimens. Clinical manifestations of undifferentiated fever patients were generally non specific, but the percentage of children with anemia, hepatomegaly and splenomegaly was higher in patients possessing anti-dengue IgM antibodies than those without. Among the groups with anti-dengue IgM antibodies, those possessing only anti-D2 but not anti-D1 IgM antibodies showed higher percentages with cough, edema, and splenomegaly. The results indicated that up to 26% of the undifferentiated fever cases were caused by dengue virus infection in Karachi, Pakistan.

Flavivirus-specific murine L3T4+ T cell clones: induction, characterization and cross-reactivity.

Murine T cell clones specific for the Kunjin (KUN), West Nile (WN) and Murray Valley encephalitis (MVE) flaviviruses were generated in vitro following priming in vivo. Clones were isolated by limiting dilution and maintained in culture with antigen stimulation and interleukin-2(IL-2). The cells were characterized as having the Thy 1+, L3T4+ and Lyt 2- phenotype by immunofluorescence. All clones proliferated strongly and secreted high levels of IL-2 and IL-3 in response to homologous antigen. Both KUN- and WN-specific clones showed extensive cross-reactivity to KUN and WN antigen, but recognized MVE to a lesser extent. In contrast, MVE-specific clones cross-reacted strongly with both KUN and WN. These data show that antigen-specific, major histocompatibility complex-restricted L3T4+ T cells are generated during flavivirus infection and are cross-reactive for viruses of the same subgroup.

Studies on arboviruses in Egypt. II. Contribution of arboviruses to the aetiology of undiagnosed fever among children.

Acute blood samples from 120 children, attending the fever hospital in Alexandria and complaining of fever, were collected and examined for haemagglutination-inhibiting (HAI) and complement-fixing (CF) antibodies against the following arbovirus antigens; Sindbis, West Nile (WN), yellow fever, dengue 1, sandfly fever, Quaranfil, Chenuda and Nyamanini. Positive reactions in the acute sera were only detected against Sindbis (4.3%) and WN (4.3%) antigens. The convalescent sera obtained from 48 of these children showed a pronounced HAI titre against WN antigen in 14.6% of them. The same sera showed a lower titre against yellow fever antigen (Asibi strain) which is due to cross-reaction between the two viruses. None of the acute or the convalescent sera showed CF antibodies against Quaranfil, Chenuda or Nyamanini antigens. The convalescent sera were not tested against dengue type 1 antigen. It is suggested that of the known arboviruses in Egypt, WN is the most important from the public health point of view.

Survey for antibodies to arboviruses in the serum of various animals in Israel during 1965-1966.

Abstract Serum from 2,294 wild birds, 128 mammals, 22 reptiles, and 96 amphibians caught from May 1965 to June 1966 in Israel were examined for antibodies against Eastern equine encephalomyelitis. Semliki Forest, Sindbis, Langat, Israel turkey meningoencephalitis, and West Nile (WN) viruses by hemagglutination-inhibition (HI) tests. The incidence of positive serum was 14.4% for wild birds, 5% for mammals, and 9% for reptiles. No antibodies were detected in the amphibian serum; 73% of the positive avian serum had antibodies against group B viruses. The rest of the positive serum was divided among that positive for group A and that positive for both group A and group B viruses. Serologic conversions in sentinel chickens confirmed the activity of WN virus in the Hadera region during the period studied. Use of acetone extraction followed by kaolin treatment of serum minimized the number of falsely positive results obtained in the HI tests. Good correlation was found between results obtained in HI tests and indirect fluorescent-antibody staining of WN antigen among serum samples from 116 Columbidae examined by these two methods.

Use of goose cells in haemagglutination tests with arthropod-borne viruses.

HAEMAGGLUTINATION studies with arthropod-borne viruses are normally carried out using red blood cells from one-day-old chicks, although cells from mature pigeons have been used in the case of Murray Valley encephalitis virus1. An observation made in the West African Council for Medical Research Laboratories in Lagos that cells from mature ducks were agglutinated by a yellow fever antigen led to a study of readily available domestic birds. Cells from Muscovy ducks (Cairina maschatai), from a local (Badagri) variety of the domestic duck (Anas boscas) and from Chinese geese (Cygnopsis cygnoides) were compared with cells from one-day-old chicks against yellow fever, Uganda S, Zika and West Nile antigens. Goose cells gave titres which were at least as high as those obtained with chick cells, and usually higher, and the settling patterns were consistently sharp and easy to read. Duck cells, although agglutinated, gave lower titres and showed a tendency to spontaneous agglutination in controls. Goose cells were thereafter used as a routine in the Lagos laboratory, and experience over more than a year has shown them to be highly satisfactory in haemagglutination and haemagglutination-inhibition tests with the antigens already mentioned, and in addition with antigens prepared against Semliki forest, Ilheus and the Trinidad 1751 strain of dengue virus. Details of this work will be published elsewhere.

IMMUNOLOGICAL RELATIONSHIPS AMONG CENTRAL NERVOUS SYSTEM VIRUSES

From observations carried out with the viruses of Russian spring-summer encephalitis, louping ill, W.E.E., and the Japanese B, St. Louis, and West Nile types of encephalitis, the following facts and inferences have been derived. 1. Russian encephalitis and louping ill viruses showed a close relationship by complement fixation, neutralization, and intraperitoneal cross-resistance tests. Intracerebral cross-resistance tests, on the other hand, failed to reveal any connection between them. Neither Russian nor louping ill virus appeared to be related to the remaining viruses tested. 2. Japanese B, St. Louis, and West Nile types of encephalitis, as a group, showed a certain degree of group relationship, but it was not so close as that between the Russian and louping ill viruses. In complement fixation tests, besides homologous reactions, Japanese serum brought about reactions with both St. Louis and West Nile antigens; St. Louis serum reacted with Japanese antigen, and West Nile serum with Japanese antigen. In neutralization tests with mouse sera, no relationship was found amongst these three viruses, while in similar tests with either hamster or guinea pig serum,-which gave higher homologous titers,-it was found that Japanese serum protected against West Nile and St. Louis viruses, St. Louis serum protected against West Nile virus, and West Nile serum against Japanese virus. In intracerebral and intraperitoneal cross-resistance tests, no relationship was found to exist between these three viruses. Moreover, the Japanese B, St. Louis, and West Nile viruses appeared to be unrelated to any one of the three other viruses tested. 3. W.E.E. virus stood apart in all tests as unrelated to any of the other viruses studied. 4. The homologous titers of complement-fixing antibodies in mouse sera showed a gradual decline with the passing of time after vaccination, and this loss of homologous titer was paralleled by a similar drop in the titer of the heterologous reactions. In the case of the Japanese B, St. Louis, and West Nile viruses, with which at the start the amount of crossing was not high, a point was reached beyond which heterologous reactions could no longer be detected. 5. A comparison of the specific levels of complement-fixing and neutralizing antibodies for the viruses in mouse hyperimmune sera showed their rate of persistence to differ. Complement-fixing antibodies which had highest titers on the 10th day, diminished gradually until, when tested on the 50th day, all titers had reached levels from one-fourth to one-eighth of their values on the 10th day. On the other hand, the levels of neutralizing antibodies for the same samples of serum were, on the 50th day, as high as or higher than those found on either the 25th or 10th days, save in the case of the Japanese B virus. 6. The state of immunity of animals following vaccination with the viruses discussed was found to be different at a given time, depending on the method employed to determine it. Thus, mice vaccinated with St. Louis virus had positive complement-fixing antibodies on the 10th day and no neutralizing antibodies. The state of immunity changed in the course of time. For this reason it is felt that in order to detect whether two viruses are related or not, multiple observations are necessary, over a considerable time and employing all available methods of immune comparison.