SARS-CoV-2 infections among asymptomatic individuals contributed to COVID-19 cases: A cross-sectional study among prospective air travelers from Ghana

BackgroundThe spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by asymptomatic individuals has been reported since the early stages of the coronavirus disease 2019 (COVID-19) outbreak in various parts of the world. However, there are limited data regarding SARS-CoV-2 among asymptomatic individuals in Ghana. The aim of the study was to use test data of prospective travelers from Ghana as a proxy to estimate the contribution of asymptomatic cases to the spread of COVID-19.MethodsThe study analyzed the SARS-CoV-2 PCR test data of clients whose purpose for testing was classified as “Travel” at the COVID-19 walk-in test center of the Noguchi Memorial Institute for Medical Research (NMIMR) from July 2020 to July 2021. These individuals requesting tests for travel generally had no clinical symptoms of COVID-19 at the time of testing. Data were processed and analyzed using Microsoft Excel office 16 and STATA version 16. Descriptive statistics were used to summarize data on test and demographic characteristics.ResultsOut of 42,997 samples tested at the center within that period, 28,384 (66.0%) were classified as “Travel” tests. Of these, 1,900 (6.7%) tested positive for SARS-CoV-2. The majority (64.8%) of the “Travel” tests were requested by men. The men recorded a SARS-CoV-2 positivity of 6.9% compared to the 6.4% observed among women. Test requests for SARS-CoV-2 were received from all regions of Ghana, with a majority (83.3%) received from the Greater Accra Region. Although the Eastern region recorded the highest SARS-CoV-2 positivity rate of 8.35%, the Greater Accra region contributed 81% to the total number of SARS-CoV-2 positive cases detected within the period of study.ConclusionOur study found substantial SARS-CoV-2 positivity among asymptomatic individuals who, without the requirement for a negative SARS-CoV-2 result for travel, would have no reason to test. These asymptomatic SARS-CoV-2-infected individuals could have traveled to other countries and unintentionally spread the virus. Our findings call for enhanced tracing and testing of asymptomatic contacts of individuals who tested positive for SARS-CoV-2

Human vaccination against RH5 induces neutralizing antimalarial antibodies that inhibit RH5 invasion complex interactions.

The development of a highly effective vaccine remains a key strategic goal to aid the control and eventual eradication of Plasmodium falciparum malaria. In recent years, the reticulocyte-binding protein homolog 5 (RH5) has emerged as the most promising blood-stage P. falciparum candidate antigen to date, capable of conferring protection against stringent challenge in Aotus monkeys. We report on the first clinical trial to our knowledge to assess the RH5 antigen - a dose-escalation phase Ia study in 24 healthy, malaria-naive adult volunteers. We utilized established viral vectors, the replication-deficient chimpanzee adenovirus serotype 63 (ChAd63), and the attenuated orthopoxvirus modified vaccinia virus Ankara (MVA), encoding RH5 from the 3D7 clone of P. falciparum. Vaccines were administered i.m. in a heterologous prime-boost regimen using an 8-week interval and were well tolerated. Vaccine-induced anti-RH5 serum antibodies exhibited cross-strain functional growth inhibition activity (GIA) in vitro, targeted linear and conformational epitopes within RH5, and inhibited key interactions within the RH5 invasion complex. This is the first time to our knowledge that substantial RH5-specific responses have been induced by immunization in humans, with levels greatly exceeding the serum antibody responses observed in African adults following years of natural malaria exposure. These data support the progression of RH5-based vaccines to human efficacy testing

Acquisition and decay of IgM and IgG responses to merozoite antigens after <i>Plasmodium falciparum</i> malaria in Ghanaian children

Developing a vaccine against Plasmodium falciparum malaria has been challenging, primarily due to high levels of antigen polymorphism and a complex parasite lifecycle. Immunization with the P. falciparum merozoite antigens PfMSRP5, PfSERA9, PfRAMA, PfCyRPA and PfRH5 has been shown to give rise to growth inhibitory and synergistic antisera. Therefore, these five merozoite proteins are considered to be promising candidates for a second-generation multivalent malaria vaccine. Nevertheless, little is known about IgG and IgM responses to these antigens in populations that are naturally exposed to P. falciparum. In this study, serum samples from clinically immune adults and malaria exposed children from Ghana were studied to compare levels of IgG and IgM specific for PfMSRP5, PfSERA9, PfRAMA, PfCyRPA and PfRH5. All five antigens were found to be specifically recognized by both IgM and IgG in serum from clinically immune adults and from children with malaria. Longitudinal analysis of the latter group showed an early, transient IgM response that was followed by IgG, which peaked 14 days after the initial diagnosis. IgG levels and parasitemia did not correlate, whereas parasitemia was weakly positively correlated with IgM levels. These findings show that IgG and IgM specific for merozoite antigens PfMSRP5, PfSERA9, PfRAMA, PfCyRPA and PfRH5 are high in children during P. falciparum malaria, but that the IgM induction and decline occurs earlier in infection than that of IgG

Kinetics of antibody responses to PfRH5-complex antigens in Ghanaian children with Plasmodium falciparum malaria.

Plasmodium falciparum PfRH5 protein binds Ripr, CyRPA and Pf113 to form a complex that is essential for merozoite invasion of erythrocytes. The inter-genomic conservation of the PfRH5 complex proteins makes them attractive blood stage vaccine candidates. However, little is known about how antibodies to PfRH5, CyRPA and Pf113 are acquired and maintained in naturally exposed populations, and the role of PfRH5 complex proteins in naturally acquired immunity. To provide such data, we studied 206 Ghanaian children between the ages of 1-12 years, who were symptomatic, asymptomatic or aparasitemic and healthy. Plasma levels of antigen-specific IgG and IgG subclasses were measured by ELISA at several time points during acute disease and convalescence. On the day of admission with acute P. falciparum malaria, the prevalence of antibodies to PfRH5-complex proteins was low compared to other merozoite antigens (EBA175, GLURP-R0 and GLURP-R2). At convalescence, the levels of RH5-complex-specific IgG were reduced, with the decay of PfRH5-specific IgG being slower than the decay of IgG specific for CyRPA and Pf113. No correlation between IgG levels and protection against P. falciparum malaria was observed for any of the PfRH5 complex proteins. From this we conclude that specific IgG was induced against proteins from the PfRH5-complex during acute P. falciparum malaria, but the prevalence was low and the IgG levels decayed rapidly after treatment. These data indicate that the levels of IgG specific for PfRH5-complex proteins in natural infections in Ghanaian children were markers of recent exposure only

Correction: Kinetics of antibody responses to PfRH5-complex antigens in Ghanaian children with Plasmodium falciparum malaria.

[This corrects the article DOI: 10.1371/journal.pone.0198371.]

Clinical characteristics of study participants.

<p>Clinical characteristics of study participants.</p

Kinetics of merozoite-specific IgG levels following episodes of <i>P</i>. <i>falciparum</i> malaria.

<p>Plasma levels of IgG specific for PfRH5 (A, D), CyRPA (B, E), and Pf113 (C, F) in children with P. falciparum malaria (Day 0), and in the same children two weeks (Day 14) and six weeks (Day 42) later. Temporal changes in levels of IgG in individual children (A-C) and in the cohort mean IgG level (D-F). Data from individual children are connected by lines (A-C). Cohort running means (heavy lines) and their 95% confidence intervals (thin lines), calculated as described previously [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198371#pone.0198371.ref034" target="_blank">34</a>], as well as calculated catabolic decay from Day 14 (dashed lines) are shown (D-F). Negative cut-offs (shaded areas) are shown (all panels). The presented data is from one experiment.</p

Correlations (Spearman’s ρ [associated P-values] of IgG responses.

<p>Correlations (Spearman’s ρ [associated P-values] of IgG responses.</p

Merozoite-specific IgG according to clinical category.

<p>Levels (AU) of IgG specific for PfRH5 (A), CyRPA (B), Pf113 (C), EBA175 (D), GLURP-R0 (E) and GLURP-R2 (F) in plasma of individual children according to clinical category: SM (severe P. falciparum malaria), UM (uncomplicated P. falciparum malaria), FC (non-parasitemic febrile controls), AC (asymptomatic controls), HC (non-parasitemic healthy controls). Please refer to Materials and Methods for category definitions. The number of individuals with IgG above cut-off and the total number of individuals in each clinical category are given along the top of each panel. Horizontal lines along the top of the panels indicate statistically significant (P<0.05) differences between groups. Data presentation otherwise as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198371#pone.0198371.g001" target="_blank">Fig 1B</a>. The presented data is from one experiment.</p

Merozoite-specific IgG in acutely ill <i>P</i>. <i>falciparum</i> malaria patients.

<p>A: Prevalences (proportions of donors with specific IgG levels above the negative cut-off) and their 95% confidence intervals (error bars) of merozoite-specific IgG in plasma of individual children with acute P. falciparum malaria. B: Levels of merozoite antigen-specific IgG in plasma, expressed as fold arbitrary units (AU) of the negative cut-off AU value for each antigen (indicated by the shaded area). Medians (center lines), central 50% (boxes), central 80% (bars), and outliers (dots) are indicated. C: Proportion of IgG-positive donors with detectable IgG subclass response to PfRH5 (left), CyRPA (center), and Pf113 (right). Proportions and corresponding 95% confidence intervals of IgG1 (white), IgG2 (black), IgG3 (gray), and IgG4 (dark gray) are shown. The presented data is from one experiment.</p