Developing and validating a modified enzyme linked immunosorbent assay method for detecting HEV IgG antibody from dried blood spot (DBS) samples in endemic settings

Hepatitis E virus in the Kathmandu Valley: Insights from a representative longitudinal serosurvey

BACKGROUND

Hepatitis-E virus (HEV), an etiologic agent of acute inflammatory liver disease, is a significant cause of morbidity and mortality in South Asia. HEV is considered endemic in Nepal; but data on population-level infection transmission is sparse.

METHODS

We conducted a longitudinal serosurvey in central Nepal to assess HEV exposure. At each visit, capillary blood samples were collected and analyzed for the presence of anti-HEV IgG antibodies. The study took place between February 2019 and April 2021, with up to 4 visits per participant approximately 6 months apart.

RESULTS

We collected 2513 samples from 923 participants aged 0-25 years, finding a seroprevalence of 4.8% and a seroincidence rate of 10.9 per 1000 person-years. Young adults and individuals consuming surface water faced the highest incidence of infection. Geospatial analysis identified potential HEV clusters, suggesting a need for targeted interventions.

SIGNIFICANCE

Our findings demonstrate that HEV is endemic in Nepal and that the risk of infection increases with age.

A Pilot Study of Biliary Atresia Newborn Screening Using Dried Blood Spot Matrix Metalloproteinase-7

OBJECTIVES

Timely diagnosis is a critical challenge and is associated with improved survival of biliary atresia (BA) patients. We aimed to measure matrix metalloproteinase-7 (MMP-7) levels in BA patients within 3 days of birth using the dried blood spot (DBS) method and evaluate its potential as a screening tool.

METHODS

The study enrolled 132 patients, including 25 patients diagnosed with BA and 107 non-BA patients with other congenital or perinatal conditions from the National Taiwan University Children Hospital. The stored DBS samples collected from 48 to 72 hours of life were retrieved from newborn screening centers. MMP-7 on the DBS was quantified using a sensitive sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS

The MMP-7 levels of BA patients on the DBS were significantly higher than those of non-BA patients (19.2 ± 10.4 vs 5.6 ± 2.7 ng/mL, P value < 0.0001). MMP-7 levels in non-BA patients, including 5 patients with hepatobiliary structural anomaly, 9 patients with intrahepatic cholestasis, and 93 patients with other perinatal diseases, were 11.6 ± 4.2 ng/mL, 6.9 ± 3.0 ng/mL, and 5.2 ± 2.1 ng/mL, respectively. The DBS MMP-7 level showed good accuracy for identifying BA, with an area under the curve of 93.7% [95% confidence interval (CI): 87.7%-99.7%]. The MMP-7 cutoff at 8.0 ng/mL showed a sensitivity of 92.0% (95% CI: 75.0%-98.6%) and specificity of 92.5% (95% CI: 85.9%-96.1%) for detecting BA from other congenital or perinatal diseases.

CONCLUSIONS

MMP-7 DBS analysis can be used to distinguish BA from other conditions as early as 3 days of age.

Effect of the Hematocrit and Storage Temperature of Dried Blood Samples in the Serological Study of Mumps, Measles and Rubella

Dried blood spots (DBSs) are an economical and convenient alternative to serum/plasma, which allow for the serological and molecular study of different pathogens. Sixty-four blood samples were collected by venipuncture and spotted onto Whatman™ 903 cards to evaluate the utility of DBSs and the effect of the storage temperature for 120 days after sample collection to carry out serological diagnosis. Mumps, measles and rubella IgG were investigated from DBSs and plasma using an automated chemiluminescent immunoassay. Using a calculated optimal cut-off value, the serological evaluation of mumps, measles and rubella using DBSs achieved high sensitivity (100%, 100% and 82.5%, respectively) and specificity (100%, 87.5% and 100%, respectively). The correlation observed between the plasma and the DBSs processed after sample collection was high (0.914-0.953) for all antibodies studied, both considering hematocrit before sample elution or not. For the different storage conditions, the correlation with plasma was high at 4 °C (0.889-0.925) and at -20 °C (0.878-0.951) but lower at room temperature (0.762-0.872). Measles IgG results were more affected than other markers when DBSs were stored at any temperature for 120 days. To summarize, hematocrit does not affect the processing of DBSs in the study of serological markers of mumps, measles and rubella. DBS stability for serological diagnosis of mumps and rubella is adequate when samples are stored at -20 °C or 4 °C, but not at room temperature, for a period of 4 months.

Stability and Feasibility of Dried Blood Spots for Hepatitis E Virus Serology in a Rural Setting

Hepatitis E virus (HEV) is the most common cause of acute viral hepatitis worldwide. In many low-income countries it causes large outbreaks and disproportionally affects pregnant women and their offspring. Surveillance studies to find effective preventive interventions are needed but are hampered by the lack of funding and infrastructure. Dried blood spots (DBS) offer an easier and more robust way to collect, transport, and store blood samples compared to plasma/serum samples, and could ease some of the barriers for such studies. In this study we optimize an HEV IgG ELISA for DBS samples and validate it on 300 paired DBS and plasma samples collected in rural areas of Bangladesh from participants in a HEV vaccine study. We demonstrate that HEV IgG in blood stored as DBS is stable for two months at up to 40 °C, and for five freeze-thaw cycles. The specificity was 97% and the overall sensitivity of the DBS assay was 81%. The sensitivity was higher in samples from vaccinated participants (100%) compared to previously infected participants (59%), reflecting a positive correlation between IgG titer and sensitivity. We found a strong correlation between DBS and plasma samples with an r2 of 0.90, but with a higher degree of difference between individual paired samples. Our study shows that DBS offers a stable alternative to plasma/serum for HEV IgG measurements and can facilitate serological studies, particularly in resource limited areas.

Ecoimmunology in the field: Measuring multiple dimensions of immune function with minimally invasive, field-adapted techniques

OBJECTIVE

Immune function is multifaceted and characterizations based on single biomarkers may be uninformative or misleading, particularly when considered across ecological contexts. However, measuring the many facets of immunity in the field can be challenging, since many measures cannot be obtained on-site, necessitating sample preservation and transport. Here we assess state-of-the-art methods for measuring immunity, focusing on measures that require a minimal blood sample obtained from a finger prick, which can be: (1) dried on filter paper, (2) frozen in liquid nitrogen, or (3) stabilized with chemical reagents.

RESULTS

We review immune measures that can be obtained from point-of-care devices or from immunoassays of dried blood spots (DBSs), field methods for flow cytometry, the use of RNA or DNA sequencing and quantification, and the application of immune activation assays under field conditions.

CONCLUSIONS

Stable protein products, such as immunoglobulins and C-reactive protein are reliably measured in DBSs. Because less stable proteins, such as cytokines, may be problematic to measure even in fresh blood, mRNA from stabilized blood may provide a cleaner measure of cytokine and broader immune-related gene expression. Gene methylation assays or mRNA sequencing also allow for the quantification of many other parameters, including the inference of leukocyte subsets, though with less accuracy than with flow cytometry. Combining these techniques provides an improvement over single-marker studies, allowing for a more nuanced understanding of how social and ecological variables are linked to immune measures and disease risk in diverse populations and settings.