Trends in ELISA-Based Flavivirus IgG Serosurveys: A Systematic Review

Flaviviruses include virus species that are major public health threats worldwide. To determine the immunity landscape of these viruses, seroprevalence studies are often performed using IgG ELISA, which is a simple and rapid alternative to the virus neutralization test. In this review, we aim to describe the trends in flavivirus IgG ELISA-based serosurveys. A systematic literature review using six databases was performed to collate cohort and cross-sectional studies performed on the general population. A total of 204 studies were included in this review. The results show that most studies were performed on dengue virus (DENV), whereas Japanese Encephalitis Virus (JEV) was the least studied. For geographic distribution, serosurveys followed known disease prevalence. Temporally, the number of serosurveys increased after outbreaks and epidemics except for JEV, for which studies were performed to demonstrate the effectiveness of vaccination campaigns. Commercial kits were more commonly used than in-house assays for DENV, West Nile Virus (WNV), and Zika virus (ZIKV). Overall, most studies employed an indirect ELISA format, and the choice of antigens varied per virus. This review shows that flavivirus epidemiology is related to the regional and temporal distribution of serosurveys. It also highlights that endemicity, cross-reactivities, and kit availabilities affect assay choice in serosurveys.

Sero-positivity of Japanese Encephalitis Virus in Equine Population of India Using IgG ELISA: Unraveling the Need for Vaccination

Japanese encephalitis (JE) is a mosquito borne flaviviral zoonoses, causing fatal disease in equines and humans. JE is endemic in most of the states of India with occurrence of human cases every year. The horses are not vaccinated against JE in India and thus they are at more risk of acquiring the disease. Due to nonavailability of indigenously developed ELISA and high cost of imported kits, regular sero-surveillance is not being carried out to assess the true picture of JE virus in equine population of India. Therefore, a recombinant NS1 protein based indirect IgG ELISA was developed with the objective to assess the sero-positivity of JE virus in equine population of India. The diagnostic sensitivity and specificity of developed ELISA was 84.73% and 86.70%, respectively. The validation studies revealed good reproducibility of ELISA with kappa value ranging from 0.75 to 1 between the results of different laboratories. A total of 2,069 horse serum samples were screened using the developed ELISA and 401 samples were positive for IgG against JEV with an overall sero-positivity of 19.38% in equine population of India. A sero-positivity of 25.90% and 12.22% was recorded in Himachal Pradesh and Jammu-Kashmir, both hill states of North zone of India for the first time, revealing the spread of virus to the nonendemic parts of the country. The high sero-positivity of JE virus recorded in equine population warrants the need for initiation of vaccination of horses in India to prevent the morbidity and mortality.

Evaluation of a SARS-CoV-2 Capture IgM Antibody Assay in Convalescent Sera

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for a global pandemic with over 152 million cases and 3.19 million deaths reported by early May 2021. Understanding the serological response to SARS-CoV-2 is critical to determining the burden of infection and disease (coronavirus disease 2019 [COVID-19]) and transmission dynamics. We developed a capture IgM assay because it should have better sensitivity and specificity than the commonly used indirect assay. Here, we report the development and performance of a capture IgM enzyme-linked immunosorbent assay (ELISA) and a companion indirect IgG ELISA for the spike (S) and nucleocapsid (N) proteins and the receptor-binding domain (RBD) of S. We found that among the IgM ELISAs, the S ELISA was positive in 76% of 55 serum samples from SARS-CoV-2 PCR-positive patients, the RBD ELISA was positive in 55% of samples, and the N ELISA was positive in 15% of samples. The companion indirect IgG ELISAs were positive for S in 89% of the 55 serum samples, RBD in 78%, and N in 85%. While the specificities for IgM RBD, S, and N ELISAs and IgG S and RBD ELISAs were 97% to 100%, the specificity of the N IgG ELISA was lower (89%). RBD-specific IgM antibodies became undetectable by 3 to 6 months, and S IgM reached low levels at 6 months. The corresponding IgG S, RBD, and N antibodies persisted with some decreases in levels over this time period. These capture IgM ELISAs and the companion indirect IgG ELISAs should enhance serologic studies of SARS-CoV-2 infections. IMPORTANCE Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has inflicted tremendous loss of lives, overwhelmed health care systems, and disrupted all aspects of life worldwide since its emergence in Wuhan, China, in December 2019. Detecting current and past infection by PCR or serology is important to understanding and controlling SARS-CoV-2. With increasing prevalence of past infection or vaccination, IgG antibodies are less helpful in diagnosing a current infection. IgM antibodies indicate a more recent infection and can supplement PCR diagnosis. We report an alternative method, capture IgM, to detect serum IgM antibodies, which should be more sensitive and specific than most currently used methods. We describe this capture IgM assay and a companion indirect IgG assay for the SARS-CoV-2 spike (S), nucleocapsid (N), and receptor-binding domain (RBD) proteins. These assays can add value to diagnostic and serologic studies of coronavirus disease 2019 (COVID-19).

Development of Human Toxo IgG ELISA Kit, and False-Positivity of Latex Agglutination Test for the Diagnosis of Toxoplasmosis

Toxoplasma gondii is an intracellular zoonotic parasite that causes infection in a wide range of warm-blooded animals and humans. The main aim of this study was to assess the diagnostic value of the recombinant SAG1 antigen (rSAG1) for T. gondii-IgG screening through the Human Toxo IgG ELISA Kit (K). The rSAG1 was expressed in E. coli (DE3), and it was purified through metal-affinity chromatography. The rSAG1 was confirmed by immunoblotting, and it had a band on 35 kDa. Total of 400 human sera were tested by LAT and K. One hundred and twenty-two (30.5%) sera were found positive by LAT and eighty-nine (22.25%) sera were found positive by K. Out of 400 samples, 80 were selected to evaluate the performance of K through commercial Toxoplasma gondii IgG ELISA Kit (C). Out of 80 human sera, 55 (68.75%) were found positive, 25 (31.25%) were found negative by K and C, respectively. The cut-off value for K was 0.398 and it was calculated through the receiver operator characteristic curve. The ELISA plates were coated at optimized concentration of rSAG1 = 0.125 µg/mL, and the test was performed by diluting the sera at 1:50. The sensitivity and specificity of K were observed to be 98.5% and 100%, respectively. The six sera (K⁻L⁺) were found positive through LAT and these human sera were later evaluated by Western blot analysis. These sera did not produce a band equivalent to 35 kDa on WB analysis thus, LAT produced false-positive results.

Detection of Nipah virus in Pteropus medius in 2019 outbreak from Ernakulam district, Kerala, India

Background

In June 2019, Nipah virus (NiV) infection was detected in a 21-year-old male (index case) of Ernakulum, Kerala, India. This study was undertaken to determine if NiV was in circulation in Pteropus species (spp) in those areas where the index case had visit history in 1 month.

Methods

Specialized techniques were used to trap the Pteropus medius bats (random sampling) in the vicinity of the index case area. Throat and rectal swabs samples of 141 bats along with visceral organs of 92 bats were collected to detect the presence of NiV by real-time reverse transcriptase-polymerase chain reaction (qRTPCR). Serum samples of 52 bats were tested for anti-NiV Immunoglobulin (Ig) G antibodies by Enzyme-Linked Immunosorbent Assay (ELISA). The complete genome of NiV was sequenced by next-generation sequencing (NGS) from the tissues and swab samples of bats.

Results

One rectal swab sample and three bats visceral organs were found positive for the NiV. Interestingly, 20.68% (12/58) of Pteropus were positive for anti-NiV IgG antibodies. NiV sequences of 18,172; 17,200 and 15,100 nucleotide bps could be retrieved from three Pteropus bats.

Conclusion

A distinct cluster of NiV sequences, with significant net-evolutionary nucleotide divergence, was obtained, suggesting the circulation of new genotype (I-India) in South India. NiV Positivity in Pteropus spp. of bats revealed that NiV is circulating in many districts of Kerala state, and active surveillance of NiV should be immediately set up to know the hotspot area for NiV infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-05865-7.

National Seroprevalence and Risk Factors for Eastern Equine Encephalitis and Venezuelan Equine Encephalitis in Costa Rica

Eastern equine encephalitis and Venezuelan equine encephalitis are endemic neglected tropical diseases in the Americas, causing encephalitis in both horses and humans. In 2013, a cross-sectional study was performed in 243 horses located in the highlands and lowlands throughout Costa Rica. Serum samples were analyzed with an IgG ELISA and confirmed by the plaque-reduction neutralization test (PRNT80). Venezuelan equine encephalitis virus (VEEV) and Eastern equine encephalitis virus (EEEV) overall seroprevalences by the PRNT80 were 36% (95% confidence interval [CI]: 29.9-42.5; 78/217 horses) and 3% (95% CI: 1.3-5.9; 6/217 horses), respectively. Both the viruses occurred in the lowlands and highlands. Rainfall and altitude were associated with VEEV seropositivity in the univariate analysis, but only altitude <100 meters above sea level was considered a risk factor in the multivariate analysis. No risk factors could be identified for the EEEV in the multivariate analysis. This is the first study that estimates the seroprevalence of the EEEV and VEEV in Costa Rican horses. The VEEV is widely distributed, whereas the EEEV occurs at a much lower frequency and only in specific areas. Clinical cases and occasional outbreaks of both viruses are to be expected.

Serodiagnostic methods for diagnosing larval toxocariasis

Toxocariasis is a human infection primarily caused by larvae of Toxocara canis from dogs, and also by T. cati from cats. Children have a more significant risk of acquiring the infection due to their closer contact with pets, and greater chances of ingesting soil. Diagnosis of toxocariasis is based on clinical, epidemiological, and serological data. Indirect IgG ELISA is a widely used serodiagnostic method for toxocariasis, with native T. canis TES most commonly used as the antigen. Western blots, using the same antigen, can be used to confirm positive ELISA findings to reduce false-positive results. Improvements in Toxocara serodiagnosis include the use of recombinant TES antigens, simpler and more rapid assay formats, and IgG4 subclass detection. Also, incorporation of recombinant T. cati TES protein increases the diagnostic sensitivity. Development of antigen detection tests using polyclonal and monoclonal antibodies, nanobodies, or aptamers can complement the antibody detection assays, and enhance the effectiveness of the serodiagnosis.

Decreased humoral immunity to mumps in young adults immunized with MMR vaccine in childhood

In the past decade, multiple mumps outbreaks have occurred in the United States, primarily in close-contact, high-density settings such as colleges, with a high attack rate among young adults, many of whom had the recommended 2 doses of mumps-measles-rubella (MMR) vaccine. Waning humoral immunity and the circulation of divergent wild-type mumps strains have been proposed as contributing factors to mumps resurgence. Blood samples from 71 healthy 18- to 23-year-old college students living in a non-outbreak area were assayed for antibodies and memory B cells (MBCs) to mumps, measles, and rubella. Seroprevalence rates of mumps, measles, and rubella determined by IgG enzyme-linked immunosorbent assay (ELISA) were 93, 93, and 100%, respectively. The index standard ratio indicated that the concentration of IgG was significantly lower for mumps than rubella. High IgG avidity to mumps Enders strain was detected in sera of 59/71 participants who had sufficient IgG levels. The frequency of circulating mumps-specific MBCs was 5 to 10 times lower than measles and rubella, and 10% of the participants had no detectable MBCs to mumps. Geometric mean neutralizing antibody titers (GMTs) by plaque reduction neutralization to the predominant circulating wild-type mumps strain (genotype G) were 6-fold lower than the GMTs against the Jeryl Lynn vaccine strain (genotype A). The majority of the participants (80%) received their second MMR vaccine ≥10 years prior to study participation. Additional efforts are needed to fully characterize B and T cell immune responses to mumps vaccine and to develop strategies to improve the quality and durability of vaccine-induced immunity.

Investigation of three outbreaks of Porcine Epidemic Diarrhea in Germany in 2016 demonstrates age dependent differences in the development of humoral immune response

Porcine epidemic diarrhea (PED) has reemerged in Europe since 2014. Characterized by a rapid onset of diarrhea in pigs of all ages, morbidity can reach up to 100% whereas mortality is variable. The virus strains involved in the recent European outbreaks all cluster together with US strains (S INDEL) that lead to less severe clinical signs. In this study, fattening pigs and suckling piglets (n = 105) on farms with no prior PED history were monitored after an acute outbreak of the disease, caused by an S INDEL strain of PED virus (PEDV). For diagnostic investigations in the affected farms, real time RT-PCR was performed to detect PEDV RNA in individually taken fecal samples, and two commercial ELISA kits, both based on the N protein of PEDV, were used to detect IgG in serum samples of pigs experiencing acute signs of the disease. PEDV RNA could be detected in fecal samples up to 14 days after initial sampling. Comparing both ELISAs by Cohens Kappa showed substantial agreement (κ = 0,771). Antibodies were detectable in all fattening pigs (100%) within 10 days after the occurrence of first clinical signs and remained detectable for about two months at least in 20.6% (farm 1) and 45.7% (farm 2) of the animals, respectively. In contrast, only 18 of 34 (52.9%) suckling piglets seroconverted. Although, PEDV RNA was found in fecal samples of all piglets, 13 piglets did not demonstrate antibodies at any sampling day. PCR to detect PEDV RNA in fecal samples seems to be a reliable diagnostic tool during and after the acute outbreak. In the present study, IgG ELISA kits proved to be a feasible diagnostic tool, but age dependent differences in detection rate and persistence of antibodies need to be considered.

Seroprevalence of toxoplasmosis in voluntary blood donors of Puducherry and surrounding districts of Tamil Nadu

Our objective is to study the seroprevalence of toxoplasmosis in the voluntary blood donors of Puducherry and surrounding districts of Tamil Nadu. A total of 275 healthy blood donors were screened for the presence of IgM and IgG antibodies to Toxoplasma gondii by ELISA test. Donor samples positive for IgM and/or IgG antibodies to T. gondii were subjected to IgG avidity ELISA. While, 54 out of 275 donors had IgG antibodies (19.66%), only one donor had IgM (0.36%) along with IgG. Among 54 IgG positive donors, only two had low avidity (3.7%), indicating recent exposure to the protozoa. Feasibility and cost effectiveness studies should be conducted throughout India to decide regarding screening of blood donors for toxoplasmosis.

Evaluation of a diagnostic algorithm for Heparin-Induced Thrombocytopenia

INTRODUCTION

Heparin-Induced Thrombocytopenia (HIT) is a rare but serious immune-mediated complication of heparin treatment. HIT is characterized by an acute, transient prothrombotic state combined with thrombocytopenia and is caused by platelet-activating IgG antibodies that bind to complexes of heparin and platelet factor 4. The diagnosis of HIT relies on clinical presentation and the demonstration of HIT antibodies. One approach to improve the efficacy of laboratory analysis is to use a diagnostic algorithm.

AIM

To evaluate one diagnostic algorithm for HIT where the 4 T's clinical risk score is combined with immunochemical and/or functional assays.

MATERIALS AND METHODS

The quality of the diagnostic algorithm was retrospectively evaluated in 101 patients with suspected HIT. Laboratory results obtained from the diagnostic algorithm were compared to Heparin-Induced Platelet Aggregation (HIPA) and clinico-pathological evaluation of patients' medical records.

RESULTS

We found that the algorithm had a diagnostic efficacy of 94%, with specificity of 94% and sensitivity 94%. Positive likelihood ratio (LR+) was 16.0, and the negative likelihood ratio (LR-) 15.5. The efficacy of PaGIA (n=95) was 0.46, and IgG-specific HPF4-abELISA (n=54) was 0.87.

CONCLUSIONS

The diagnostic algorithm for HIT is sufficiently accurate and leads to in overall faster results and decreased cost of analysis. The weakest link of the algorithm is the risk of miscalculated 4T's scores, which is inevitably exacerbated by the insufficient experience most clinicians have with HIT. This highlights the importance of clear instructions from the laboratory and coagulation clinic.

Isolation and characterization of Oya virus a member of Simbu serogroup, family Bunyaviridae, isolated from Karnataka, India

During a study on Japanese encephalitis (JE) from Kolar district of Karnataka state, India in 1986; two virus isolates were obtained in infant Swiss albino mouse from a pig and a human serum sample. For characterization of these virus isolates, they were propagated in Vero CCL-81 cells. These virus isolates were screened for flaviviruses (Japanese encephalitis, West Nile, Dengue, Kyasanur forest disease) and Alphavirus (Chikungunya) by RT-PCR and found to be negative. Further these they were screened for bunyaviruses using genus-specific primers. A virus isolate from a human sample was sequenced using next generation sequencing; which identified it as Oya virus, Simbu group of the genus Orthobunyavirus of the family Bunyaviridae. Phylogenetic analysis of L, M, S (N and NSs) revealed its close association with Chinese strain of Oya virus in Simbu serogroup with the distance of 6.5>4.2>3.2% for nucleotides and 2.4>0.8>0.0% for the amino acid of L>M>S segments respectively. Based on the PCR results; an isolate from pig sample was also confirmed as Oya virus. This study was strengthened by findings of IgG antibody positivity against Oya virus in retrospective serum samples of suspected febrile illness cases from this area by an indigenously developed ELISA. Oya virus positivity was also recorded in human samples collected from Karnataka using nested RT-PCR. This is the first report of the presence of Oya virus in human samples. Further studies are needed to determine disease-causing potential in humans.

New recombinant chimeric antigens, P35-MAG1, MIC1-ROP1, and MAG1-ROP1, for the serodiagnosis of human toxoplasmosis

The aim of the study was to evaluate the usefulness of 3 chimeric Toxoplasma gondii antigens, P35-MAG1, MIC1-ROP1 and MAG1-ROP1, in the serodiagnosis of an acute toxoplasmosis in humans. Proteins were produced as fusion proteins containing His tags ends and then further purified by metal affinity chromatography. Their application for the diagnosis of recently acquired T. gondii infection was tested in IgG and IgM enzyme-linked immunosorbent assays (ELISAs). At 100%, 77.3%, and 86.4%, respectively, the reactivity of the IgG ELISA using P35-MAG1, MIC1-ROP1, and MAG1-ROP1 for sera from patients where acute toxoplasmosis was suspected was significantly higher than for the samples from people with a chronic infection, at 26.2%, 36.1%, and 32.8%, respectively. Moreover, P35-MAG1, MIC1-ROP1, and MAG1-ROP1 detected IgM antibodies with a reactivity at 81.8%, 72.7%, and 59.1%, respectively. The results presented in the article show that, particularly, P35-MAG1 may be useful in the preliminary detection of recent T. gondii infection.

Serological Profile of HSV-2 in STD Patients: Evaluation of Diagnostic Utility of HSV-2 IgM and IgG Detection

BACKGROUND AND OBJECTIVES

The present study was undertaken to determine Herpes Simplex Virus-2 seroprevalence in sexually active adults aged 20-49 and to investigate the correlation with sociodemographic characteristics and to find its association with other sexually transmitted diseases especially HIV and also to assess the proportion of primary and reactivated HSV-2 cases.

MATERIALS AND METHODS

This prospective study was carried out for a period of six months in a tertiary care hospital. Serum samples were taken from 91 patients attending the out Patient clinic of the Department of Venereology. The serological testing for HSV-2 was performed on all the specimens by using Euroimmun anti-HSV2 (gG2) IgM ELISA and IgG ELISA.

RESULTS

Out of the 91 STD patients in the study group, 18 males (34.62%) and 14 females (36.84%) tested positive for HSV-2 antibodies. Seropositivity rate is 35.16%. More number of HSV-2 positive cases were seen among males, older age, rural residence, low socioeconomic status, single marital status, irregular condom usage during the sexual intercourses with new partners and with higher number of sexual partners during lifetime. HSV-2 IgM alone was positive in three cases, HSV-2 IgG alone was positive in 26 cases and three had a positive HSV-2 IgM and IgG result. Addition of IgM testing increased rate of detecting seroconversion, 31.87%, when only IgG ELISA was used, to 35.16 % patients when IgM test was added. In the study group four cases tested positive for VDRL, and one of them was a known positive case. Among the 55 HIV positive cases in the study group, HSV 2 was positive in 17 cases and among the 36 HIV negative cases HSV 2 was positive in 15 cases. (30.91% and 47.22%).Though the number of HIV cases were high, HSV 2 positivity among them was statistically not significant.

CONCLUSION

The purpose of screening for HSV-2 is not only to identify seropositivity, but to help seropositive people identify symptoms and protect themselves from acquiring HIV and to protect their partners and seronegative people from acquiring HSV-2 and/or HIV.

Frequency of Toxoplasma gondii in HIV Positive Patients from West of Iran by ELISA and PCR

BACKGROUND

Toxoplasma gondii, the obligate intracellular parasite is life threatening in AIDS patients. Diagnosis of toxoplasmosis is based on serological methods especially increasing of IgM and IgG titers, but finding of parasite or its components (antigenemia) may be beneficial method in order to detection of acute toxoplasmosis in immunocompromised patients.

METHODS

Ninety-four serum samples from HIV positive patients were collected from Sanandaj, Kordistan west of Iran. These patients were lived in Sanandaj of whom 26 were prisoners infected with HIV virus in prison. Toxoplasma gondii antibodies were determined by IgG ELISA. T. gondii antigen was identified by capture-ELISA. PCR was performed on samples with T. gondii antigenemia. CD4+ T cells counts had been determined by flowcytometry and were obtained from records of each patient.

RESULTS

Among the examined HIV seropositive individuals, 19.1% (18/94) and 5.3% (5/94) were positive for Toxoplasma-IgG and antigenemia, respectively. Besides, one of the samples was positively detected by PCR method. Mean age of participants was 37.9 ± 9.5 year. Prevalence of IgG antibody and antgenemia was higher in age group of 40-50 years old. The Mean of CD4+ T cells counts of participants (total of HIV+ patients, IgG positive patients and patients with antigenemia) was 699.2 ± 345.2, 655.1 ± 237.9 and 620.2 ± 215.1 respectively.

CONCLUSION

Capture-ELISA and PCR could confirm the T. gondii acute infection in HIV positive patients. For precise diagnosis of acute toxoplasmosis in HIV positive patient, performance of more studies based on more sensitive types of PCR is suggested.