Search PubMed⌕ Search

Biomedical subjects

David W Vaughn

Publications and source records attributed to David W Vaughn.

At least 19 recordsLinked to original sources
PubMed2006

Cellular immune activation in children with acute dengue virus infections is modulated by apoptosis.

Apoptosis is an important modulator of cellular immune responses during systemic viral infections. Peripheral-blood mononuclear cell (PBMC) apoptosis and plasma soluble levels of CD95, a mediator of apoptosis, were determined in sequential samples from children participating in a prospective study of dengue virus (DV) infections. During the period of defervescence, levels of PBMC apoptosis were higher in children developing dengue hemorrhagic fever (DHF), the most severe form of illness, than in those with dengue fever (DF) and other, nondengue, febrile illnesses. CD8(+) T lymphocytes made up approximately half of the peak circulating apoptotic PBMCs in DHF and DF. Maximum plasma levels of soluble CD95 were also higher in children with DHF than in those with DF. The level of PBMC apoptosis correlated with dengue disease severity. Apoptosis appears to be involved in modulation of the innate and adaptive immune responses to DV infection and is likely involved in the evolution of immune responses in other viral hemorrhagic fevers.

Adolescent↗
PubMed2006

Role of US military research programs in the development of US Food and Drug Administration--approved antimalarial drugs.

US military physicians and researchers helped identify the optimum treatment dose of the naturally occurring compound quinine and collaborated with the pharmaceutical industry in the development and eventual US Food and Drug Administration approval of the synthetic antimalarial drugs chloroquine, primaquine, chloroquine-primaquine, sulfadoxine-pyrimethamine, mefloquine, doxycycline, halofantrine, and atovaquone-proguanil. Because malaria parasites develop drug resistance, the US military must continue to support the creation and testing of new drugs to prevent and treat malaria until an effective malaria vaccine is developed. New antimalarial drugs also benefit civilians residing in and traveling to malarious areas.

Antimalarials↗
PubMed2006

Protection of Rhesus monkeys against dengue virus challenge after tetravalent live attenuated dengue virus vaccination.

Rhesus monkeys develop viremia after dengue virus (DENV) inoculation and have been used as an animal model to study DENV infection and DENV vaccine candidates. We evaluated, in this model, the protective efficacy of a live attenuated tetravalent DENV vaccine (TDV) candidate against parenteral challenge with parental near-wild-type DENV strains. Twenty monkeys were vaccinated with TDV at 0 and 1 month, and 20 unvaccinated monkeys served as controls. Vaccinated animals and their controls were inoculated with 10(3)-10(4) pfu of challenge virus 4.5 months after the second vaccination. Primary vaccination resulted in 95%, 100%, 70%, and 15% seroconversion to DENV serotypes 1, 2, 3, and 4 (DENV-1, -2, -3, and -4), respectively. After the second vaccination, the seropositivity rates were 100%, 100%, 90%, and 70%, respectively. Vaccination with TDV resulted in complete protection against viremia from DENV-2 challenge and in 80%, 80%, and 50% protection against challenge with DENV-1, -3, and -4, respectively. Our results suggest that the TDV can elicit protective immunity against all 4 DENV serotypes. Interference among the 4 vaccine viruses may have resulted in decreased antibody responses to DENV-3 and -4, which would require reformulation or dose optimization to minimize this interference during testing of the vaccine in humans.

Animals↗
PubMed2006

Hepatitis E antibody kinetics in Nepalese patients.

A cohort of 62 Nepalese adults with acute hepatitis E was identified and total Ig as well as IgM levels to hepatitis E virus (HEV) capsid protein were determined using the Walter Reed Army Institute of Research (WRAIR) immunoassay. An antibody profile was constructed from serial serum specimens collected up to 14 months following the onset of illness. The decline in total Ig was rapid for the first 3 months. There followed a slow, sustained decline, but antibodies remained above the seropositive level of 20 WRAIR units. The decline of IgM was steeper than total Ig for the first 3 months, but IgM remained detectable after 14 months in 25% of cases. Study data contribute to an understanding of the pathophysiology of human hepatitis E and set an antibody response pattern to be targeted as a part of HEV vaccine development.

Adult↗
PubMed2006

The comparative accuracy of 8 commercial rapid immunochromatographic assays for the diagnosis of acute dengue virus infection.

BACKGROUND: The serological diagnosis of acute dengue virus infection relies on the detection of dengue-specific immunoglobulin M (IgM) antibodies. Immunochromatographic tests are rapid diagnostic tests (RDTs) that can be performed at the bedside, but they have not been fully validated for diagnosis of dengue infection. METHODS: More than 20 RDTs for diagnosis of acute dengue infection are commercially available. Of these, 8 were selected for evaluation of performance by use of characterized dengue and nondengue serum specimens, and results were compared with those of a previously published dengue IgM/IgG enzyme-linked immunosorbent assay in conjunction with dengue virus serotyping by reverse-transcriptase polymerase chain reaction. RESULTS: Assay sensitivities were low, ranging from 6.4% (95% confidence interval [CI], 4.0%-9.7%) to 65.3% (95% CI, 59.9%-70.5%), and specificities ranged from 69.1% (95% CI, 61.4%-76.0%) to 100% (95% CI, 97.8%-100%). Of the 8 tests, only 2 had sensitivities of >50%, the level considered to be clinically useful, and, of these, 1 had relatively low specificity (69.1%). Samples collected early in the infection were less likely to test positive than those collected later. A thermal stability study demonstrated a loss in performance of some RDTs when they were stored at a high ambient temperature for 3 months. CONCLUSIONS: Users of RDTs for dengue should be aware that many of these tests have a diagnostic accuracy that falls well below the manufacturers' claims. If an acute specimen yields a negative result, a convalescent serum sample should be tested to confirm the result. No RDT adequately differentiated primary and secondary dengue infections, and the tests should not be used for this purpose.

Acute Disease↗
PubMed2006

Structure and age of genetic diversity of dengue virus type 2 in Thailand.

Dengue virus type 2 (DENV-2) is a common viral infection and an important health concern in South-East Asia. To determine the molecular evolution of DENV-2 in Thailand, 105 isolates of the E (envelope) gene and 10 complete genomes sampled over a 27 year period were sequenced. Phylogenetic analysis of these data revealed that three genotypes of DENV-2 have circulated in Thailand, although, since 1991, only viruses assigned to Asian genotype I have been sampled from the population. A broader analysis of 35 complete genomes of DENV-2 revealed that most amino acids are subject to strong selective constraints, indicative of widespread purifying selection against deleterious mutations. This was further supported by an analysis of genome-wide substitution rates, which indicated that DENV-2 fixes approximately 10 mutations per genome per year, far lower than expected from its mutational dynamics. Finally, estimates of the age of DENV-2 were remarkably consistent among genes, indicating that the current genetic diversity in this virus probably arose within the last 120 years, concordant with the first determination of the aetiology of dengue disease.

Adolescent↗
PubMed2006

Comparative analysis reveals no consistent association between the secondary structure of the 3'-untranslated region of dengue viruses and disease syndrome.

A comparative analysis was performed of the 3'-untranslated region (UTR) of Dengue virus (DENV) sampled from Bangkok, Thailand, over a 30 year period and representing all four serotypes. Considerable genetic variation was observed both within and among serotypes. Notably, a full-length version of the critical 3'-long stable hairpin structure was absent from some isolates, suggesting the occurrence of complex structural interactions within the 3'-UTR, including the influence of upstream mutations. The Thai sequences were then combined with 61 globally sampled isolates of DENV taken from patients with either dengue fever or severe dengue disease. No consistent association was found between 3'-UTR secondary structure and the clinical outcome of DENV infection, although some evidence for a trend in this direction was observed in DENV-2. It was concluded that the 3'-UTR is not the sole determinant of DENV virulence in nature, although variation in secondary structure may greatly influence viral fitness.

3' Untranslated Regions↗
PubMed2006

Characterization of antibody responses to combinations of a dengue virus type 2 DNA vaccine and two dengue virus type 2 protein vaccines in rhesus macaques.

We evaluated three nonreplicating dengue virus type 2 (DENV-2) vaccines: (i) a DNA vaccine containing the prM-E gene region (D), (ii) a recombinant subunit protein vaccine containing the B domain (i.e., domain III) of the E protein as a fusion with the Escherichia coli maltose-binding protein (R), and (iii) a purified inactivated virus vaccine (P). Groups of four rhesus macaques each were primed once and boosted twice using seven different vaccination regimens. After primary vaccination, enzyme-linked immunosorbent assay (ELISA) antibody levels increased most rapidly for groups inoculated with the P and DP combination, and by 1 month after the second boost, ELISA titers were similar for all groups. The highest plaque reduction neutralization test (PRNT) titers were seen in those groups that received the DR/DR/DR combination (geometric mean titer [GMT], 510), the P/P/P vaccine (GMT, 345), the DP/DP/DP combination (GMT, 287), and the R/R/R vaccine (GMT, 200). The next highest titers were seen in animals that received the D/R/R vaccine (GMT, 186) and the D/P/P vaccine (GMT, 163). Animals that received the D/D/D vaccine had the lowest neutralizing antibody titer (GMT, 49). Both ELISA and PRNT titers declined at variable rates. The only significant protection from viremia was observed in the P-vaccinated animals (mean of 0.5 days), which also showed the highest antibody concentration, including antibodies to NS1, and highest antibody avidity at the time of challenge.

Animals↗
PubMed2005

An evaluation of dengue type-2 inactivated, recombinant subunit, and live-attenuated vaccine candidates in the rhesus macaque model.

The safety, immunogenicity, and protective efficacy of two non-replicating antigen-based vaccines and one live-attenuated virus (LAV) vaccine for dengue type-2 (dengue-2) virus were evaluated in the rhesus macaque model. The non-replicating vaccines consisted of whole, purified inactivated virus (PIV) and a recombinant subunit protein containing the amino-(N)-terminal 80% of envelope protein (r80E), each formulated with one of five different adjuvants. Each formulation was administered to three animals on a 0, 3-month schedule. Following the primary immunizations, 37 of 39 animals demonstrated dengue-2 virus neutralizing antibodies. After the booster immunizations all animals had dengue neutralizing antibodies with peak titers ranging from 1:100 to 1:9700. The highest neutralizing antibody titers were observed in the groups that received r80E antigen formulated with AS04, AS05, or AS08 adjuvant, and PIV formulated with AS05 or AS08 adjuvant. These newer adjuvants are based on alum, fraction QS-21 of saponin, and monophosphoryl lipid A (MPL). Protection was evaluated by dengue-2 virus challenge 2 months after the booster by the measurement of circulating virus (viremia) and post-challenge immune responses. Several groups exhibited nearly complete protection against viremia by bioassay, although there was evidence for challenge virus replication by Taqmantrade mark and immunological assays. None of the vaccines conferred sterile immunity.

Animals↗
PubMed2005

Dengue Virus (DV) enhancing antibody activity in preillness plasma does not predict subsequent disease severity or viremia in secondary DV infection.

BACKGROUND: Dengue hemorrhagic fever, the most severe form of dengue illness, is associated with secondary dengue virus (DV) infection. Preexisting nonneutralizing antibodies to DV that enhance the infection of Fc gamma receptor-bearing cells have been implicated in DV pathogenesis. METHODS: We conducted a prospective cohort study in Thai schoolchildren. Enhancing activity (EA) was measured as the percentage of DV-infected K562 cells, and viral titer (infected K562 cell supernatants) was measured in preillness plasma samples from children who subsequently had secondary DV2 or DV3 infection. RESULTS: Plaque-reduction neutralizing titers to the child's own DV2 or DV3 isolate were detected in 23 of 32 and 8 of 27 of the preillness plasma samples, and EA was detected to a low-passage Thai DV2 or DV3 in 31 of 32 and 26 of 27, respectively, of the samples. EA in undiluted preillness plasma did not correlate with subsequent disease severity or peak viremia levels in either secondary DV2 or DV3 infections. CONCLUSIONS: Preillness plasma enhances DV infection of K562 cells even in the presence of detectable neutralizing antibodies in LLC-MK2 cells. However, levels of preillness plasma EA of DV infection in K562 cells did not correlate with the clinical severity or viral burden of secondary DV infection.

Antibodies, Viral↗
PubMed2005

Characterization of dengue-2 virus binding to surfaces of mammalian and insect cells.

The binding of dengue type 2 (DEN-2) virus to mammalian (LLC-MK(2) and Vero) and mosquito (C6/36 and AP61) cell surfaces was investigated by a virus-binding assay using purified (3)H-labeled DEN-2 virus. The DEN-2 virus binding to all four cell types was specific and saturable, indicating the presence of a single class of receptors (ranging from 3.7 x 10(3) to 3.5 x 10(4) receptors/cell) with a high affinity for DEN-2 virus (K(d) ranging from 98 to 171 pM). Treatment of cell surfaces with certain glycosidases significantly reduced virus binding to mammalian cell lines, but not to the insect cell lines examined. Furthermore, heparin was found to compete with mammalian cell receptors for binding to DEN-2 virus and to inhibit viral infection of mammalian cells, but heparin had no effect on viral binding to or infection of insect cells. These results confirm previous reports suggesting that DEN-2 virus receptors on mammalian cell lines are different from those on insect cell lines.

Animals↗
PubMed2004

Development and evaluation of an efficient 3'-noncoding region based SARS coronavirus (SARS-CoV) RT-PCR assay for detection of SARS-CoV infections.

The severe acute respiratory syndrome (SARS) epidemic originating from China in 2002 was caused by a previously uncharacterized coronavirus that could be identified by specific RT-PCR amplification. Efforts to control future SARS outbreaks depend on the accurate and early identification of SARS-CoV infected patients. A real-time fluorogenic RT-PCR assay based on the 3'-noncoding region (3'-NCR) of SARS-CoV genome was developed as a quantitative SARS diagnostic tool. The ideal amplification efficiency of a sensitive SARS-CoV RT-PCR assay should yield an E value (PCR product concentration increase per amplification cycle) equal to 2.0. It was demonstrated that the 3'-NCR SARS-CoV based RT-PCR reactions could be formulated to reach excellent E values of 1.81, or 91% amplification efficacy. The SARS-CoV cDNA preparations derived from viral RNA extract and the cloned recombinant plasmid both exhibit the identical amplification characteristics, i.e. amplification efficacy using the same PCR formulation developed in this study. The viral genomic copy (or genomic equivalences, GE) per infectious unit (GE/pfu) of SARS-CoV used in this study was also established to be approximate 1200-1600:1. The assay's detection sensitivity could reach 0.005 pfu or 6-8 GE per assay. It was preliminarily demonstrated that the assay could efficiently detect SARS-CoV from clinical specimens of SARS probable and suspected patients identified in Taiwan. The 3'-NCR based SARS-CoV assay demonstrated 100% diagnostic specificity testing samples of patients with acute respiratory disease from a non-SARS epidemic region.

3' Untranslated Regions↗
PubMed2004

Relationship of preexisting dengue virus (DV) neutralizing antibody levels to viremia and severity of disease in a prospective cohort study of DV infection in Thailand.

BACKGROUND: Infection with any 1 of the 4 dengue viruses (DVs) can produce several illnesses, ranging from a mild febrile illness to classic dengue fever (DF) to dengue hemorrhagic fever (DHF), a potentially life-threatening disease. Most DHF cases occur after sequential heterotypic DV infections. The role of preexisting humoral immunity in modifying severity of dengue disease is not well understood. METHODS: We conducted a prospective cohort study of children in a region where dengue disease is hyperendemic and examined the role of preexisting neutralizing anti-DV antibodies (Abs) in modifying secondary dengue-3 virus (D3V), dengue-2 virus (D2V), and dengue-1 virus (D1V) infections. RESULTS: In secondary D3V infection, higher levels of preexisting neutralizing Ab directed against D3V (reference virus strain and patient's virus isolate) were associated with lower viremia levels and milder disease. Preexisting neutralizing Ab levels against D2V were not associated with severity of secondary D2V infection. The levels of preexisting neutralizing Ab against the infecting virus isolates were not associated with viremia levels in secondary D2V or D1V infections. CONCLUSIONS: Cross-reactive memory humoral immune responses appear to be beneficial in symptomatic secondary D3V infection, but not in secondary D2V or D1V infection. These results may have important implications for the development of live attenuated tetravalent dengue vaccines.

Adolescent↗
PubMed2004

Evaluation of a rapid quantitative diagnostic test for adenovirus type 4.

Acute respiratory disease (ARD) due to adenoviruses is a reemerging disease in military recruits. It is a challenge for clinicians to accurately diagnose this disease and to appropriately treat affected individuals. This study investigated the utility of a quantitative, rapid-cycle, real-time fluorogenic polymerase chain reaction (PCR) technique for detecting adenovirus type 4 (Ad4) in a clinical setting. Throat swab specimens and clinical data were collected from US Army basic trainees hospitalized with ARD at Fort Jackson, South Carolina. A total of 140 throat swab specimens were collected from 83 subjects. Rapid PCR results (obtained in <2 h) had a sensitivity of 100% and a specificity of 100%, compared with viral culture. There was no difference, qualitative or quantitative, between frozen and fresh samples for PCR detection of Ad4. Individuals with test results positive for Ad4 were hospitalized longer than were individuals with negative test results. Higher virus loads at hospital admission corresponded to longer lengths of stay for Ad4-positive subjects.

Adenovirus Infections, Human↗
PubMed2003

Interferon alfa-2a in Japanese encephalitis: a randomised double-blind placebo-controlled trial.

BACKGROUND: Japanese encephalitis virus (JEV), although confined to Asia, causes about 35000-50000 cases and 10000 deaths every year, and is the most important cause of encephalitis worldwide. There is no known antiviral treatment for any flavivirus. Results from in-vitro studies and work in animals have shown inteferon alfa has antiviral activity on Japanese encephalitis and other flaviviruses; therefore, we aimed to assess the efficacy of inteferon alfa-2a in Japanese encephalitis. METHODS: We did a randomised double-blind placebo-controlled trial of interferon alfa-2a (10 million units/m2, daily for 7 days) in 112 Vietnamese children with suspected Japanese encephalitis, 87 of whom had serologically confirmed infections. Our primary endpoints were hospital death or severe sequelae at discharge. Analysis was by intention to treat. FINDINGS: Overall, 21 children (19%) died, and 17 (15%) had severe sequelae. Outcome at discharge and 3 months did not differ between the two treatment groups; 20 children in the interferon group had a poor outcome (death or severe sequelae), compared with 18 in the placebo group (p=0.85, difference 0.1%, 95% CI -17.5 to 17.6%), there were no long-term side effects of interferon. INTERPRETATION: The doses of interferon alfa-2a given in this regimen did not improve the outcome of patients with Japanese encephalitis.

Adolescent↗
PubMed2003

Modification of dengue virus strains by passage in primary dog kidney cells: preparation of candidate vaccines and immunization of monkeys.

Dengue (DENV) virus strains for each of the four DENV serotypes were modified by passage in primary dog kidney (PDK) cell cultures with final manufacture of vaccine lots in fetal rhesus monkey diploid cell cultures. "Strain sets" consisting of serially-passaged DENV were inoculated in rhesus monkeys along with unmodified parent viruses for each strain. Vaccine candidates were compared with unmodified parent viruses by measuring viremia and immune responses. All except one DENV-1 strain demonstrated reduced infection in monkeys after PDK cell passage. A DENV-3 strain lost all monkey infectivity after PDK cell passage. Twelve vaccine candidates were selected for Phase 1 human trials through this selection process.

Animals↗