Neutralizing antibody response to booster vaccination with the 17d yellow fever vaccine.

A retrospective review was conducted of yellow fever vaccination among laboratory workers receiving annual serologic assessment to determine the initial and long-term response after boosting. Patients were divided into three groups based on pre-vaccination serology: Group 1, 1:10; Group 2, 1:20-1:40 and Group 3, >1:40. The percent with > or = four-fold increase in titers after booster vaccination were: 78% (646/829, Group 1), 65% (79/121, Group 2) and 10% (8/79, Group 3) (p<0.0001). The median times to titer failure (<1:40) were 798 days (Group 1), 3340 days (Group 2) and 7709 days (Group 3) (p<0.0001). Pre-vaccination serology influenced the initial and long-term response to yellow fever booster vaccination.

Isolation of viruses from mosquitoes (Diptera: Culicidae) collected in the Amazon Basin region of Peru.

As part of a comprehensive study on the ecology of arthropod-borne viruses in the Amazon Basin region of Peru, we assayed 539,694 mosquitoes captured in Loreto Department, Peru, for arboviruses. Mosquitoes were captured either by dry ice-baited miniature light traps or with aspirators while mosquitoes were landing on human collectors, identified to species, and later tested on Vero cells for virus. In total, 164 virus isolations were made and included members of the Alphavirus (eastern equine encephalomyelitis, Trocara, Una, Venezuelan equine encephalomyelitis, and western equine encephalomyelitis viruses), Flavivirus (Ilheus and St. Louis encephalitis), and Orthobunyavirus (Caraparu, Itaqui, Mirim, Murutucu, and Wyeomyia viruses) genera. In addition, several viruses distinct from the above-mentioned genera were identified to the serogroup level. Eastern equine encephalomyelitis virus was associated primarily with Culex pedroi Sirivanakarn & Belkin, whereas Venezuelan equine encephalomyelitis virus was associated primarily with Culex gnomatos Sallum, Huchings & Ferreira. Most isolations of Ilheus virus were made from Psorophora ferox (Von Humboldt). Although species of the Culex subgenus Melanoconion accounted for only 45% of the mosquitoes collected, 85% of the virus isolations were made from this subgenus. Knowledge of the viruses that are being transmitted in the Amazon Basin region of Peru will enable the development of more effective diagnostic assays, more efficient and rapid diagnoses of clinical illnesses caused by these pathogens, risk analysis for military/civilian operations, and development of potential disease control measures.

Atypical antibody responses in dengue vaccine recipients.

Eight of 69 (12%) healthy adult volunteers vaccinated with monovalent live-attenuated dengue virus (DENV) vaccine candidates had atypical antibody responses, with depressed IgM:IgG antibody ratios and induction of high-titer hemagglutination-inhibiting and neutralizing (NT) antibodies to all four DENV serotypes. These features suggested flavivirus exposure prior to DENV vaccination, yet no volunteer had a history of previous flavivirus infection, flavivirus vaccination, or antibody to flaviviruses evident before DENV vaccination. Moreover, production of antibody to DENV by atypical responders (AR) was not accelerated compared with antibody responses in the 61 flavivirus-naive responders (NR). Further evaluation revealed no differences in sex, age, race, DENV vaccine candidate received, or clinical signs and symptoms following vaccination between AR and NR. However, viremia was delayed at the onset in AR compared with NR. A comparative panel of all AR and five randomly selected NR found flavivirus cross-reactive antibody after vaccination only in AR. Unexpectedly, six of eight AR had NT antibodies to yellow fever virus (YFV) > 1:10 before vaccination while NR had none (P = 0.04). The AR also universally demonstrated YFV NT antibody titers > or = 1:160 after DENV vaccination, whereas four of five NR failed to seroconvert (P = 0.02). Yellow fever virus priming broadens the antibody response to monovalent DENV vaccination. The effect of flavivirus priming on the clinical and immunologic response to tetravalent DENV vaccine remains to be determined.

Short report: absence of protective neutralizng antibodies to West Nile virus in subjects following vaccination with Japanese encephalitis or dengue vaccines.

Protection of individuals against West Nile (WN) encephalitis is an emerging concern in the United States and Europe. We investigated whether immunization with licensed inactivated Japanese encephalitis (JE) vaccine or experimental live attenuated dengue vaccines resulted in induction of cross-neutralizing antibodies against WN virus. Protective neutralizing antibody titers to WN virus were not detected in any volunteer despite successful immunization to related flaviviruses. Vaccination against JE or dengue is unlikely to prevent WN virus infection but may still protect against disease.

Detection of dengue virus neutralizing antibodies in bats from Costa Rica and Ecuador.

Neutralizing antibodies for dengue virus serotypes 1 and 2 and serotypes 2 and 3 were detected in 1998 in 12 of 53 (22.6%) and 3 of 10 (30.0%) bats sampled in Costa Rica and Ecuador, respectively. Dengue is a consistent health problem in the two Costa Rican communities in which bats were sampled. The high percentage of bats with neutralizing antibodies to dengue virus in these two Costa Rican communities suggests that bats may become infected with dengue virus. This appears to be the case in Costa Rica and Ecuador.

Anthrax vaccine: increasing intervals between the first two doses enhances antibody response in humans.

The influence of dosing interval on the human antibody response to anthrax vaccine adsorbed (AVA) was evaluated in two retrospective serological studies. In both studies, the interval between the first two doses was 2, 3 or 4 weeks. In the first study, banked sera were selected from 89 at-risk individuals at a mean time of 13 days after the second dose of vaccine. In the second study, banked sera were selected from 51 at-risk individuals at a mean time of 48 days following the first dose of AVA. In both studies, the geometric mean anti-protective antigen IgG antibody titer increased significantly as the interval between the two doses increased from 2 to 4 weeks (p=0.0005-0.029). In the first study, the seroconversion rate also increased as the interval between the first two doses increased (p=0. 0034). A prospective, randomized study has been completed and is being analyzed to confirm these findings.

Phase II safety and immunogenicity study of live chikungunya virus vaccine TSI-GSD-218.

We conducted a phase II, randomized, double-blind, placebo-controlled, safety and immunogenicity study of a serially passaged, plaque-purified live chikungunya (CHIK) vaccine in 73 healthy adult volunteers. Fifty-nine volunteers were immunized one time subcutaneously with the CHIK vaccine and 14 were immunized with placebo (tissue culture fluid). Vaccinees were clinically evaluated intensively for one month, and had repeated blood draws for serological assays (50% plaque-reduction neutralization test) for one year. Except for transient arthralgia in five CHIK vaccinees, the number and severity of local and systemic reactions and abnormal laboratory tests after immunization were similar in CHIK vaccinees and placebo recipients. Fifty-seven (98%) of 58 evaluable CHIK vaccinees developed CHIK neutralizing antibody by day 28, and 85% of vaccinees remained seropositive at one year after immunization. No placebo recipients seroconverted. This promising live vaccine was safe, produced well-tolerated side effects, and was highly immunogenic.

Immunogenicity of an inactivated Rift Valley fever vaccine in humans: a 12-year experience.

Rift Valley fever (RVF) virus causes serious and fatal disease in animals and man. To protect personnel who work with RVF virus in the laboratory, or troops who may be exposed to this virus, the US Army successfully developed an improved version of inactivated RVF vaccine, TSI-GSD-200. From early 1986 to late 1997, 598 at-risk workers at the US Army Medical Research Institute of Infectious Diseases (USAMRIID) were vaccinated as part of an occupational safety and health program. The subjects of this study received three subcutaneous doses (0, 7 and 28 days) of 0.5 ml of TSI-GSD-200. A total of 540 vaccinees (90.3%) initially responded (group A) with an 80% plaque-reduction neutralization antibody titer (PRNT80) of > or =1:40; whereas 58 subjects (9.7%) were initial nonresponders (group B) failing to achieve this titer. Volunteers who either failed to respond or who achieved a titer of > or =1:40 but whose titer waned below 1:40 were boosted 1-4 times with the same vaccine. Among 247 group A subjects who received the first recall injection, 242 (98%) were successfully boosted, achieving a PRNT80 > or =1:40. Thirty-three of 44 (75%) initial nonresponders were converted to responder status after the first booster, which is a lower rate than that of group A (P < 0.001). After the primary series and the first booster, Kaplan-Meier analysis showed 50% probability of group A members maintaining a titer of > or =1:40 for approximately eight years; whereas group B had a 50% probability of maintaining a titer for only 204 days. Group A immune response rates to boosts 1-4 ranged from 87 to 100% with geometric mean titers (GMTs) ranging from 80 to 916. Boosts 1-4 immune response rates of group B volunteers ranged from 67 to 79% with GMTs ranging from 90 to 177. Minor side effects to TSI-GSD-200 were noted in 2.7% of all vaccinees after primaries and 3.5% of all vaccinees who had primaries and up to four boosters. We conclude that the use of TSI-GSD-200 is safe and provides good long-term immunity in humans when the primary series and one boost are administered.

Immunologic interference from sequential administration of live attenuated alphavirus vaccines.

Two different human vaccine trials examined interference arising from sequential administration of vaccines against heterologous alphaviruses. The first trial indicated that persons previously vaccinated against Venezuelan equine encephalitis virus (VEEV) exhibited poor neutralizing antibody responses to a live attenuated chikungunya virus (CHIKV) vaccine (46% response rate). The second trial prospectively examined neutralizing antibody responses to live attenuated VEEV vaccine in persons previously inoculated with either CHIKV vaccine or placebo. Following seroconversion to CHIKV, CHIKV vaccine recipients' geometric mean titers (GMTs) to VEEV by 80% plaque-reduction neutralization titration never exceeded 10, compared with a peak GMT of 95 after VEEV vaccination for alphavirus-naive volunteers who initially received placebo (P < .003). ELISA antibody responses demonstrated cross-reactive IgG to VEEV after primary CHIKV immunization and then an anamnestic response upon subsequent VEEV vaccination. These data indicate that preexisting alphavirus immunity in humans interferes with subsequent neutralizing antibody response to a live attenuated, heterologous vaccine.

Long-term duration of detectable neutralizing antibodies after administration of live-attenuated VEE vaccine and following booster vaccination with inactivated VEE vaccine.

The US Army successfully developed a live-attenuated Venezuelan Equine Encephalitis (VEE) vaccine, TC-83, in 1961, and subsequently developed a formalin-inactivated vaccine, C-84, in 1974. Initial evaluation of both vaccines was promising, but no long-term safety and immunogenicity data have been reported. This study is the first analysis of the long-term safety and immunogenicity of TC-83 and C-84. From January 1976 to December 1990, 821 laboratory workers at the USAMRIID were vaccinated with a single 0.5 ml subcutaneous (s.c.) dose of TC-83; 128 were boosted with a single 0.5 ml s.c. dose of C-84. Eighty-two per cent of vaccinees responded to TC-83 with an 80% plaque reduction neutralization titer (PRNT80) of > or = 1:20. Minor side-effects were noted in 23% of vaccinees. No long-term sequelae were recorded. Kaplan-Meier analysis showed a 60% probability of vaccinees maintaining a PRNT80 of > or = 1:20 for 5.5-8 years. C-84 was given to two groups: 76 initial nonresponders to TC-83, Group A, and 52 initial responders to TC-83 whose PRNT80 became < 1:20 over time, Group B. C-84 successfully boosted 76% of Group A and 100% of Group B to a PRNT80 > or = 1:20 Kaplan-Meier analysis showed 100% probability of Group B members maintaining a titer of > or = 1:20 for the duration of follow-up, which, in some cases, exceeded 10 years; while Group A had only a 60% probability of maintaining a titer for 1-2 years. Only minor local reactions to C-84 were noted in 6.3% of vaccinees. We conclude that, although TC-83 is reactogenic, when administered as the primary vaccine and C-84 is administered as a boost, these vaccines provide good long-term immunity and are safe in humans. However, a single dose vaccine that is more immunogenic and less reactogenic is needed.

Indirect immunofluorescence for serological diagnosis of dengue virus infections in Swedish patients.

BACKGROUND: An increasing number of travellers to dengue endemic areas has emphasized the need for an easy and reliable serological test for diagnosis of dengue virus infections. OBJECTIVES: Indirect immunofluorescence (IF) and hemagglutination inhibition (HI) tests were compared for serological diagnosis of dengue fever (DF). STUDY DESIGN: Sera from patients with clinical symptoms compatible with DF and a travel history comprising dengue endemic areas were included in the study. Paired serum samples from 24 patients and single convalescent sera from five patients were investigated by HI and IF. Paired sera from ten patients were investigated by plaque reduction neutralization test (PRNT) in order to confirm the HI/IF results. RESULTS: In twelve of the patients with paired sera a sero-conversion or a significant (4-fold) antibody titer rise was seen with HI as well as with IF. Four patients with stationary HI-titers had significant titer rises when investigated by IF. Stationary or declining HI- and IF-titers were found in the remaining eight patients. The five single sera were antibody-positive by both methods. Investigation by PRNT of paired sera from ten patients confirmed the IF results. A total of 298 serum samples (paired sera or early convalescent samples) were investigated for dengue antibodies by IF. A sero-conversion, significant titer-rise or an IF-titer of 320 was generally seen 7-13 days post onset of disease. During the years 1991-1993 altogether 161 cases of dengue were diagnosed by IF in Swedish patients, a majority of which had travelled to Southeast Asia. CONCLUSION: Antibody detection by indirect IF proved to be at least as reliable as HI for diagnosis of dengue infections in Swedish patients. The specificity of the IF was ensured by testing the sera of ten patients for serotype specific neutralizing dengue antibodies.

Enzyme-linked immunosorbent assay using a recombinant baculovirus-expressed Bacillus anthracis protective antigen (PA): measurement of human anti-PA antibodies.

We developed an antigen capture enzyme-linked immunosorbent assay (ELISA) which does not require purified protective antigen (PA) for detection of human antibodies to Bacillus anthracis PA. Lysates of Spodoptera frugiperda (Sf-9) cells infected with recombinant baculovirus containing the PA gene were used as the source of PA to develop the ELISA. Recombinant PA from crude Sf-9 cell lysates or PA purified from B. anthracis Sterne strain was captured by an anti-PA monoclonal antibody coated onto microtiter plates. We demonstrated that human serum antibody titers to PA were identical in the ELISA whether we used crude Sf-9 cell lysates containing recombinant baculovirus-expressed PA or purified Sterne PA. Finally, false-positive results observed in a direct ELISA were eliminated with this antigen capture ELISA. Thus, the antigen capture ELISA with crude preparations of baculovirus-expressed PA is reliable, safe, and inexpensive for determining anti-PA antibody levels in human sera.

Venezuelan equine encephalitis-specific immunoglobulin responses: live attenuated TC-83 versus inactivated C-84 vaccine.

Venezuelan equine encephalitis (VEE)-specific immunoglobulin responses to the two vaccines, TC-83 (a live attenuated vaccine) and C-84 (a formalin inactivated vaccine derived from the TC-83 strain of virus) were evaluated using an antigen and isotype-specific enzyme-linked immunoadsorbent assay (ELISA). The VEE-specific ELISA for IgG, IgG subclasses, IgA and IgM were developed and standardized using sera from vaccine-exposed and unexposed human subjects. Paired human sera (before and 28 days after immunization) were tested from laboratory workers vaccinated with either TC-83 (Group A: 20 paired sera from subjects receiving a single TC-83 vaccine and with no prior history of vaccination) or C-84 in varying schedules (Group B: 19 paired sera from subjects who had a distant vaccination history to TC-83 but no evidence of neutralizing antibody; Group C: 19 paired sera from subjects receiving their first C-84 vaccination and no prior documented history of vaccination; Group D: 15 paired sera from subjects receiving a C-84 booster vaccination with prior history of C-84 but no TC-83 exposure). Sera were all tested for viral neutralization in vitro using a Vero cell monolayer for culturing virus and establishing 80% plaque reduction for each serum tested. All pre-sera tested demonstrated no plaque reduction neutralization at a level of 80% for a dilution of 1:10. ELISA antibody titers for all pre-sera with no prior VEE exposure through vaccination or possible environmental factors were negative at a titer of 1:160 for IgM, 1:80 for IgG, IgA, and G subclasses.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of a Rift Valley fever virus vaccine against an aerosol infection in rats.

The formalin-inactivated Rift Valley fever virus (RVFV) vaccine, TSI-GSD-200, was administered subcutaneously to highly susceptible adult Wistar-Furth rats (LD50-1 p.f.u., ZH501 strain). Vaccine was administered on days 0, 7 and 28, the same time course used for at-risk personnel. Six months postimmunization, when the serum plaque-reduction neutralization titre (PRNT)80 had declined to low or undetectable levels, rats were challenged with 4.4 log10 p.f.u. of the virulent ZH501 strain in a nose-only dynamic aerosol apparatus. Ninety-seven per cent (33/34) of the non-vaccinated control rats died. In contrast, only 32% (33/105) of the vaccinated animals died. In vaccinated rats that succumbed, there was a doubling of the mean time to death and the cause of death shifted from hepatitis to encephalitis. Rats with a PRNT80 of greater than or equal to 1:40 were protected from clinical disease and histological evidence of hepatic or encephalitic lesions. While the precise mechanisms of immunity against aerosol challenge remain unresolved, here the serum PRNT titre correlated with protection.

Isolation of a newly recognized Bunyamwera serogroup virus from a febrile human in Panama.

A virus, strain 86MSP18, was isolated from the acute phase serum of a U.S. soldier with a febrile illness. He was stationed at Fort Sherman in the Republic of Panama when the onset of his illness occurred. A rise in neutralizing antibody to the viral isolate was observed between the patient's acute and convalescent-phase serum samples. Virus strain 86MSP18 has been shown by plaque reduction neutralization to be closely related to but distinct from Cache Valley virus and known subtypes. It appears to be a newly recognized subtype of Cache Valley virus and is believed to be the second isolation of a Cache Valley virus subtype from a human with a febrile illness. The name "Fort Sherman" virus for strain 86MSP18 is proposed.

Rapid and sensitive method for quantitation of Legionella pneumophila serogroup 1 antigen from human urine.

A reversed passive hemagglutination test was developed to assay relative concentrations of soluble antigen of Legionnaires disease (Legionella pneumophila serogroup 1) in human urine samples. The test is highly sensitive, being able to detect as little as 0.0002 microgram of total antigen. Preliminary results with this test on serial urine and serum samples from a patient with legionellosis show that measurable amounts of antigen are present in urine during the course of the illness. However, no antigen could be detected in the serum of the patient.

Swine influenza virus vaccine: potentiation of antibody responses in rhesus monkeys.

Polyriboinosinic-polyribocytidylic acid stabilized with poly-L-lysine and carboxymethylcellulose [poly(ICLC)] enhances the antibody response in rhesus monkeys immunized with swine influenza virus subunit vaccine. Monkeys given the vaccine-adjuvant combination had earlier and significantly (P less than .05) higher titers by 14 days compared to those that received vaccine alone. The potentiation of the antibody response of young monkeys given a split-virus vaccine in combination with poly(ICLC) suggests that this vaccine-adjuvant combination may similarly provide a potentially useful alternative approach to the immunization of pediatric and young adult age groups against swine influenza.