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J S Peiris

Publications and source records attributed to J S Peiris.

At least 55 records · Page 3Linked to original sources
PubMed1990

Genetic complexity of Plasmodium vivax parasites in individual human infections analyzed with monoclonal antibodies against variant epitopes on a single parasite protein.

Monoclonal antibodies against variant epitopes of a highly polymorphic protein (PV200) in schizonts of Plasmodium vivax have been used to analyze the variety of genetically distinct populations of parasites present in the peripheral blood of individual P. vivax infections in Sri Lanka. In 9 out of 10 isolates of freshly drawn P. vivax infected blood from different individuals, parasites of only 1 PV200 serotype was found within each individual infection, even though parasites were serotypically distinct between individuals. In 1 isolate parasite population, 3 distinct PV200 serotypes were identified. Thus, most P. vivax infections appeared to consist of a single genetically homogeneous population of parasites within the detection limits of the technique. The prevalence of P. vivax infections in an area of malaria transmission in southern Sri Lanka and the densities of oocysts in mosquitoes fed on P. vivax infected individuals indicated that parasite populations would be transmitted many times before encountering parasites of other origins, and that individual populations would tend to reduce to genetic homogeneity during transmission. These expectations are consistent with the high proportion of genetically homogeneous P. vivax isolates observed.

Adult↗
PubMed1990

Microbiological agents associated with childhood diarrhoea in the dry zone of Sri Lanka.

Between March and July, 1987, faecal specimens from 371 diarrhoeal children reporting to four hospitals in the district of Kurunegala, Sri Lanka and from 121 controls with other diseases were investigated for enteric pathogens. All specimens were tested for Shigella spp, Salmonella spp and enteropathogenic Escherichia coli (EPEC). In addition, parasitic pathogens, heat labile enterotoxigenic Escherichia coli (ETEC LT), Campylobacter and rotavirus were sought among subsamples of the cases and controls. One or more pathogens were detected in the faecal specimens of 53.7% of the diarrhoeal children and 19.6% of the controls (P less than 0.001). Rotavirus was the most frequently identified pathogen. Cases (21.9%) were more likely to be positive for rotavirus than controls (6.5%) (p less than 0.05). Among children with diarrhoea the peak prevalence of rotavirus occurred in the 6-11 months age group. Shigella spp were the second most frequently isolated pathogens and the single most common cause of diarrhoea in children over two years of age. Again, cases (16.4%) were more likely to be infected than controls (1.7%) (p less than 0.001). Salmonella spp were isolated from 7.5% of diarrhoeal children and 3.3% of the controls (p greater than 0.10). Other pathogens had prevalence rates of less than 5%. Vomiting was associated with rotavirus diarrhoea (p less than 0.001), and fever with shigellosis (p = 0.02). In view of the different transmission routes and characteristics of the most important pathogens detected in this study it appears unlikely that a single environmental intervention can solve the public health problem posed by diarrhoeal diseases in Sri Lanka.

Acute Disease↗
PubMed1988

Type II heat-labile enterotoxin-producing Escherichia coli isolated from animals and humans.

Heat-labile enterotoxin (LT)-producing Escherichia coli strains, as identified by the Y1 adrenal cell assay, were examined with a DNA probe coding for type I and type II LTs. Of 236 LT-producing E. coli isolates, 60% hybridized with LT-I, 17% hybridized with LT-II, and 23% did not hybridize with either probe and no longer produced LT as determined by the Y1 adrenal cell assay. These isolates presumably lost plasmids coding for LT-I during storage. A total of 75% of LT-producing E. coli isolates (27 of 36) from cows, 64% of LT-producing E. coli isolates (7 of 11) from buffalo, 31% of LT-producing E. coli isolates (4 of 13) from beef obtained in markets, and 2% of LT-producing E. coli isolates (3 of 168) from humans contained genes coding for LT-II. Genes coding for LT-II were not found in 50 LT-I-producing and heat-stable enterotoxin-producing E. coli isolates from 11 children with diarrhea and 44 LT-nonproducing and heat-stable enterotoxin-producing E. coli isolates from 12 other children with diarrhea. A total of 9% of LT-II-producing E. coli isolates (3 of 34) from cows and buffalo hybridized with DNA probes for genes coding for verocytotoxin 2 (VT2), and 18% (6 of 34) hybridized with a DNA probe coding for enterohemorrhagic E. coli (EHEC) adhesin fimbriae. E. coli SA-53, the original isolate in which LT-II was found, contained genes coding for VT2 and EHEC adhesin fimbriae. Five VT-producing, LT-II-producing E. coli isolates that hybridized with the EHEC probe did not contain DNA sequences coding for VT1 or VT2. LT-II-producing E. coli strains were frequently isolated from cattle and buffalo but were rarely isolated from humans.

Animals↗
PubMed1988

Monoclonal and polyclonal antibodies both block and enhance transmission of human Plasmodium vivax malaria.

Antibodies against gametes of the malarial parasite inhibit the development of the parasite in the mosquito and curtail the transmission of malaria. We now report that a monoclonal antibody against gametes of the human malaria pathogen Plasmodium vivax and antibodies induced during natural infections of P. vivax in humans which suppress infectivity of the parasites to the vector at high concentrations can, at lower concentrations, have the opposite effect and enhance the level of malaria infection in the mosquitoes. Infectivity enhancing effects of up to 12-fold were demonstrated when a transmission blocking monoclonal antibody and immune human sera were diluted, in some undiluted immune human sera, and in the sera of vivax malaria patients during convalescence after drug cure.

Animals↗
PubMed1988

Immunoelectron microscopy of Schüffner's dots in Plasmodium vivax-infected human erythrocytes.

Plasmodium vivax induces morphologic alterations in infected host erythrocytes that are visible by light microscopy in Romanovsky-stained blood smears as multiple brick-red dots. These morphologic changes, referred to as Schüffner's dots, are important in the identification of this species of malarial parasite and have been associated by electron microscopy with caveolavesicle complexes along the erythrocyte plasmalemma. We have produced a monoclonal antibody (MAb A 20) that identifies an antigen in Plasmodium vivax-infected erythrocytes that is associated with the caveola-vesicle complexes of the parasitized host cell. This monoclonal antibody reacts with air-dried P vivax-infected erythrocytes to produce a pattern by the indirect immunofluorescence test (IFT) that is evocative of Schüffner's dots. Immunoelectron microscopy of P vivax-infected human erythrocytes using MAb A 20 confirmed the location of this antigen within vesicles of caveola-vesicle complexes. On Western blots MAb A 20 recognized four polypeptides of 54, 64, 72, and 86 kd. MAb A 20 reacted by IFT with 90% of Sri Lankan isolates and with a Brazilian P vivax isolate, which indicates that the epitope identified by this monoclonal is conserved.

Animals↗
PubMed1987

Demonstration of antigenic polymorphism in Plasmodium vivax malaria with a panel of 30 monoclonal antibodies.

A panel of 30 monoclonal antibodies was established against asexual erythrocytic stages of Plasmodium vivax and used to investigate the antigenic composition of the parasite. At least 38 different antigenic polypeptides of P. vivax were characterized by the Western blot technique. The possible location of these antigens, as well as their stage and species specificity, was determined on the basis of the staining patterns produced by these antibodies on air-dried parasites in the indirect immunofluorescence test. Immunofluorescence performed with 30 different monoclonal antibodies on 50 different isolates of P. vivax obtained from patients showed that a high level of antigenic polymorphism prevailed in P. vivax. Only six monoclonal antibodies reacted with epitopes that were represented in more than 80% of parasite isolates, and therefore, appeared to be relatively conserved among different isolates. The other 24 monoclonal antibodies reacted with only 20 to 70% of parasite isolates.

Animals↗
PubMed1985

Detection of rotavirus by a latex agglutination test, Rotalex: comparison with electron microscopy, immunofluorescence, polyacrylamide gel electrophoresis, and enzyme linked immunosorbent assay.

A commercially available latex agglutination test, Rotalex (Orion Diagnostics, Finland), for detecting rotaviruses was evaluated in comparison with four other tests (electron microscopy, immunofluorescence, polyacrylamide gel electrophoresis, and enzyme linked immunosorbent assay) routinely used in our laboratories. Although Rotalex was the least complex method, it showed lack of specificity and sensitivity when carried out according to the manufacturer's instructions. Four basic modifications of Rotalex are described. These include the use of Hank's balanced salt solution, increasing the incubation time to 20 min, reading the agglutination result by an experienced observer, and the use of 50 mm square glass plates. The modified procedure gave results which were comparable with those obtained by electron microscopy, immunofluorescence, polyacrylamide gel electrophoresis, and enzyme linked immunosorbent assay. The latter techniques, when used to detect rotavirus, all gave similar results.

Electrophoresis, Polyacrylamide Gel↗
PubMed1984

Enzyme-linked immunosorbent assays based on polyclonal and monoclonal antibodies for rotavirus detection.

We describe two enzyme-linked immunosorbent assays for rotavirus antigen in feces, which were designed to be as sensitive and specific as possible, and easy to use anywhere. Both are indirect methods, using the antibody capture method, but the second assay utilizes a rotavirus group-specific monoclonal "detecting" antibody instead of the hyperimmune polyvalent guinea pig antisera used in the first assay. Both tests were found to be more sensitive than electron microscopy for detecting virus. To develop these tests, solid phase, antiserum production methods, treatment of the test antigen with EDTA, substrate, stability of reagents, and the need for confirmatory "blocking" tests were all examined. The first assay described is that used at present by the World Health Organization for their worldwide diarrheal disease control program.

Animals↗
PubMed1983

Comparison of P388D1 mouse macrophage cell line and human monocytes for assay of dengue-2 infection-enhancing antibodies.

Tissue culture-adapted dengue 2 virus (DEN 2), strain 16681, exhibits antibody-dependent enhancement of infection (ADE) in P388D1 cells, a mouse macrophage-like cell line. ADE is dependent upon maintaining DEN 2 multiplicity of infection at between 0.1 and 0.001, and can be simply measured in multi-well plastic plates. The assay uses either trypsinized or non-trypsinized P388D1 cells at 5 x 10(5) cells per ml, an appropriate dilution of DEN 2 virus, and a source of antibody, and is most conveniently performed without further washing of stationary cultures, which are incubated in 5% CO2. Trypsinization of P388D1 cells prior to the addition of virus-serum mixtures reduced infection in control cultures thus increasing ADE. When cells were washed after incubation of virus-serum mixtures for 1 hour, a paradoxical increase of infection in cultures exposed to virus plus normal serum was noted, which reduced the sensitivity of the ADE assay. Using human cord blood sera, ADE titers measured in human monocytes and P388D1 cells were closely similar. This convenient and economical assay will facilitate large scale biological and epidemiological studies of dengue virus enhancing antibodies.

Animals↗
PubMed1982

Monoclonal antibodies against the flavivirus West Nile.

Monoclonal antibodies having three different specificities have been prepared against the Egypt 101 strain of West Nile virus (WNV). All were reactive against the envelope glycoprotein in radioimmune precipitation tests, and all enhanced WNV replication in the mouse macrophage line P388D1. One antibody, which is of IgG2a subclass, had strong neutralizing activity against the homologous virus, although it failed to neutralize a different WNV strain. The other two antibodies, both of IgG1 subclass, had little neutralizing activity, but one had strong reactivity with the haemagglutinin of the inducing virus and other flavivirus haemagglutinins.

Antibodies, Monoclonal↗
PubMed1982

Antibody-dependent plaque enhancement: its antigenic specificity in relation to Togaviridae.

The antigenic specificity of antibody-dependent plaque enhancement (ADPE) on the macrophage cell line P388D1 has been investigated using viruses in the flavivirus and alphavirus genera. Whereas ADPE detected group-specific antigenic determinants in the flaviviruses, narrower specificity (type and subgroup) was seen with alphaviruses. ADPE titres correlated well with haemagglutination inhibition titres.

Alphavirus↗
PubMed1981

Monoclonal anti-Fc receptor IgG blocks antibody enhancement of viral replication in macrophages.

Flaviviruses, when complexed with antibody at subneutralizing concentrations, show enhanced replication in human and simian peripheral blood leukocytes (ref. 1, and J.S.M.P. and J.S.P., unpublished observations) and in P388 D1 and other macrophage cell lines. A comparable phenomenon has been demonstrated with alphaviruses and Bunyaviruses in P388 D1 cells, (J.S.M.P. and J.S.P., unpublished observations) but cells lacking macrophage characteristics fail to show antibody-dependent enhancement (ADE) of viral replication. It has been suggested that the macrophage Fc receptor (FcR) provides an efficient route of entry of virus through the attachment of non-neutralized virus-antibody complexes and that for those viruses that escape destruction by the phagocyte, antibody results in a paradoxical increase in virus replication. West Nile virus (WNV) replication in the P388 D1 macrophage cell line provides a reproducible model system for studying ADE of viral replication. Mouse macrophages have two FcRs-FcRI, which is trypsin-sensitive and binds IgG2a, and FcRII, which is trypsin-resistant and binds IgG2b and IgG1 complexes. The FcR has been purified using rat anti-mouse FcR monoclonal antibody which blocks FcRII. We show here that anti-FcRIgG and its Fab fragment block ADE of virus replication by anti-WNV monoclonal antibodies.

Animals↗
PubMed1981

Antibody-dependent enhancement of plaque formation on cell lines of macrophage origin - a sensitive assay for antiviral antibody.

An assay for antiviral antibody based on antibody-dependent plaque enhancement (ADPE) in the macrophage cell line P388D1 is described which is as sensitive as, or more sensitive than a radioimmune assay. The method is applicable to a range of Togaviridae and Bunyaviridae although not to Picornaviridae and Herpesviridae. The variables affecting the assay are investigated.

Animals↗
PubMed1979

Antibody-mediated enhancement of Flavivirus replication in macrophage-like cell lines.

Interactions between animal viruses and antiviral antisera may exceptionally result in an apparent increase in viral infectivity. Halstead and coworkers demonstrated enhanced replication of dengue virus (a Flavivirus, family Togaviridae) in human or simian peripheral blood leucocytes carrying Fc receptors at subneutralising concentrations of antidengue antibody. We have used three continuous cell lines which express macrophage markers to explore the mechanism of this phenomenon. Dengue virus failed to replicate in these cells, but West Nile virus, another Flavivirus, replicated in all three, and we were able to demonstrate reproducibly 50--100-fold enhancement of virus yields in the presence of Flavivirus antisera, the effect also being directly demonstrable in P388D1 cells by increased numbers of virus-induced plaques. The phenomenon of antibody-dependent enhancement of viral replication is not unique to dengue virus, and may have far wider relevance in other viral infections.

Animals↗
PubMedDate not supplied

Antibodies to Plasmodium falciparum sporozoites following a malarial outbreak in a non-endemic area of Sri Lanka.

An enzyme-linked immunosorbent assay (ELISA) based on the synthetic peptide (NANP)40 was used to characterize the sporozoite antibodies in an unusual Plasmodium falciparum outbreak in a non-malarious area in Sri Lanka. A positive antibody response was seen in 62% of patients with their first P. falciparum illness. There was no correlation between sporozoite antibodies and the antibody against blood stages, determined by immunofluorescence assay. The majority (91%) of the patients lost the antibodies to circumsporozoite (CS) protein within one year (in the absence of re-exposure). Three patients had high levels of CS antibodies even after one year, and this persistence was related to the level of the initial antibody response. In the area of the outbreak 10% of schoolchildren had antibodies to the (NANP)40 peptide. 21% of the 42 children with present or past overt malaria were antibody positive. Of the children with no such background, 8% were antibody positive. The corresponding seropositivity rates for asexual blood stages were 31% and 1% for the 2 groups respectively. It is concluded that (NANP)40 ELISA is potentially a valuable tool in sero-epidemiology, particularly in situations of seasonal transmission and recurrences due to drug resistance.

Animals↗
PubMedDate not supplied

Japanese encephalitis in Sri Lanka--the study of an epidemic: vector incrimination, porcine infection and human disease.

A prospective study of mosquito vectors, porcine infection and human disease was carried out during a Japanese encephalitis (JE) epidemic in the North Central province of Sri Lanka (November-December 1987) and a subsequent non-epidemic year (1988). The epidemic involved 361 cases of human encephalitis, virologically confirmed by immunoglobulin M enzyme-linked immunosorbent assay (ELISA), and was preceded 2-3 weeks earlier by sentinel porcine seroconversion. Virus isolation and viral antigen detection (ELISA) in field-caught mosquitoes incriminated Culex tritaeniorhynchus (Giles) and Cx gelidus Theobald as the major vectors of virus transmission during the porcine amplification and human 'spill-over' phases of the epidemic. Virus was also demonstrated in Cx fuscocephala Theobald, Cx whitmorei (Giles) and Mansonia uniformis (Theobald) during the epidemic. The major difference between the epidemic (1987) and non-epidemic (1988) years was a lower vector biomass and lower rates of virus carriage in the mosquito population.

Animals↗
PubMedDate not supplied

Japanese encephalitis in Sri Lanka: comparison of vector and virus ecology in different agro-climatic areas.

The ecology of Japanese encephalitis (JE) in different agro-climatological areas of Sri Lanka was studied in relation to the abundance of mosquito vectors, infection in domestic livestock, and human infection and disease. There was an inverse correlation between altitude and the abundance of potential JE vectors, as well as JE seroprevalence in domestic livestock and in man. Little or no JE infection was documented above 1200 m elevation. JE seroprevalences in cattle and goats were better predictors of human infection risk than was porcine seroprevalence. In areas with asynchronous porcine infection occurring over many months, high overall JE seroprevalence in pigs was found with little evidence of human infection. Porcine JE infection occurring in synchronous bursts associated with monsoonalrains was correlated with significant bovine, ovine and human seroprevalence in 2 low elevation study areas, Anuradhapura (dry zone) and Ragama (wet zone), with epidemic human JE in the former area and endemic disease in the latter.

Adolescent↗