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Graphical abstract During epidemics, such as the frequent and devastating Ebola virus outbreaks that have historically plagued regions of Africa, serological surveillance efforts are critical for viral containment and the development of effective antiviral therapeutics. Antibody serology can also be used retrospectively for population-level surveillance to provide a more complete estimate of total infections. Ebola surveillance efforts rely on enzyme-linked immunosorbent assays (ELISAs), which restrict testing to laboratories and are not adaptable for use in resource-limited settings. In this manuscript, we describe a paper-based immunoassay capable of detecting anti-Ebola IgG using Ebola virus envelope glycoprotein ectodomain (GP) as the affinity reagent. We evaluated seven monoclonal antibodies (mAbs) against GP—KZ52, 13C6, 4G7, 2G4, c6D8, 13F6, and 4F3—to elucidate the impact of binding affinity and binding epitope on assay performance and, ultimately, result interpretation. We used biolayer interferometry to characterize the binding of each antibody to GP before assessing their performance in our paper-based device. Binding affinity (KD) and on rate (kon) were major factors influencing the sensitivity of the paper-based immunoassay. mAbs with the best KD (3–25 nM) exhibited the lowest limits of detection (ca. μg mL−1), while mAbs with KD > 25 nM were undetectable in our device. Additionally, and most surprisingly, we determined that observed signals in paper devices were directly proportional to kon. These results highlight the importance of ensuring that the quality of recognition reagents is sufficient to support desired assay performance and suggest that the strength of an individual’s immune response can impact the interpretation of assay results. Supplementary Information The online version contains supplementary material available at 10.1007/s00216-021-03317-4.

Recent studies have evaluated alternatives to the use of live animals in colony health monitoring. Currently, an alternative method that is suitable for all rack types and that has been verified to detect the infectious agents most commonly excluded from mouse colonies is unavailable. We compared the use of filter paper placed on the inside floor of mouse cages to the traditional use of sentinel mice in the detection of several prevalent murine pathogens including mouse hepatitis virus (MHV), murine norovirus (MNV), minute virus of mice (MVM), mouse parvovirus (MPV), Theiler murine encephalomyelitis virus (TMEV), Helicobacter spp., Syphacia obvelata, and Aspiculuris tetraptera. Experimental groups comprised 7 cages containing either 2 pieces of filter paper on the cage floor or 2 ICR sentinel mice. Soiled bedding from pet-store mice was transferred to the experimental cages weekly for 8 wk. At 1 and 2 mo after bedding transfer, the filter papers were evaluated by PCR and sentinel mice were tested by serology and fecal PCR. Filter papers detected all pathogens as effectively (MHV, MNV, MPV, MVM, TMEV S. obvelata, and A. tetraptera) or more effectively (Helicobacter spp.) than sentinel mice at both time points. Filter papers more readily detected pathogens with a high copy number per RT-PCR analysis than a low copy number. Helicobacter spp. were not detected by sentinel mice at either time point. These results indicate that the use of filter paper placed on the interior floor of empty mouse cages and exposed to soiled bedding is efficient in detecting bacteria, endoparasites, and most of the common mouse viruses included in an animal health monitoring program.

We evaluated hemolyzed, bacterially contaminated, and Nobuto filter paper-derived serum, collected from 50 Rocky Mountain elk (Cervus elaphus nelson) in 2017 and 2019, divided into eight treatments to determine antibody retention. Serum was analyzed on Brucella abortus-specific fluorescence polarization assay utilizing plates and tubes. Reference titers and serostatus were compared to serum held at 22 C for 4, 8, 12, and 16 d; frozen clotted blood; blood with 2% and 10% elk rumen content (held for 8 d at 22 C); and serum eluted from Nobuto filter paper. Using Cohen's kappa test of agreement, plate assay serostatus agreement was substantial or outstanding in all treatments. Serostatus agreement was outstanding in all treatments utilizing tubes. The mean change in score (treatment minus reference) showed significant negative bias in serosuspect or seropositive animals in the frozen, 2% rumen, and 10% rumen treatments on the plate assay, and the day 16 and 10% rumen treatments on the tube assay, that could ultimately result in an animal being misclassified into a serosuspect or seronegative category. Serum eluted from Nobuto filter paper produced inconsistent results and is not recommended as an alternative to serum derived from blood. Although the potential for misclassification of animals with low titers exists, analyzing hemolyzed and bacterially contaminated serum from Brucella abortus nonendemic areas can increase sample size and the potential to detect seropositive animals.

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is emerging as a global pandemic outbreak. To date, approximately one million deaths and over 32 million cases have been reported. This ongoing pandemic urgently requires an accurate testing device that can be used in the field in a fast manner. Serological assays to detect antibodies have been proven to be a great complement to the standard method of reverse transcription-polymerase chain reaction (RT-PCR), particularly after the second week of infection. We have developed a specific and sensitive immunosensor for immunoglobulin detection produced against SARS-CoV-2. Unlike other lateral flow-based assays (LFAs) involving the utilization of multiple antibodies, we have reported a label-free paper-based electrochemical platform targeting SARS-CoV-2 antibodies without the specific requirement of an antibody. The presence of SARS-CoV-2 antibodies will interrupt the redox conversion of the redox indicator, resulting in a decreased current response. This electrochemical sensor was proven effective in real clinical sera from patients with satisfactory results. In addition, the proposed format was also extended to antigen detection (the spike protein of SARS-CoV-2), which presents new possibilities for diagnosing COVID-19., Highlights • Electrochemical sensor for COVID-19 diagnostic. • Serological assay for SARS-CoV-2 antibodies was demonstrated. • Sensitivity enhancement compared to the traditional LFA devices. • Applicable to real clinical sera with satisfactory results.

The incidence of flavivirus infections has increased dramatically in recent decades in tropical and sub-tropical areas worldwide, affecting hundreds of millions of people each year. Dengue viruses are typically transmitted by mosquitoes and can cause a wide range of symptoms from flu-like fever to organ impairment and death. Although conventional diagnostic tests can provide early diagnosis of acute dengue infections, access to these tests is often limited in developing countries. Consequently, there is an urgent need to develop affordable, simple, rapid, and robust diagnostic tools that can be used at 'Point of Care' settings. Early diagnosis is crucial to improve patient management and reduce the risk of complications. In the present study, a novel laser-cut device made of glass-fiber paper was designed and tested for the detection of the dengue Non Structural 1 (NS1) viral protein and specific IgM in blood and plasma. The device, called PAD, was able to detect around 25 ng/mL of NS1 protein in various sample types in 8 minutes, following a few simple steps. The PAD was also able to detect specific IgM in human plasmas in less than 10 minutes. The PAD appears to have all the potential to assist health workers in early diagnosis of dengue fever or other tropical fevers caused by flaviviruses.

International audience; The incidence of arbovirus infections has increased dramatically in recent decades, affecting hundreds of millions of people each year. The Togaviridae family includes the chikungunya virus (CHIKV), which is typically transmitted by Aedes mosquitoes and causes a wide range of symptoms from flu-like fever to severe arthralgia. Although conventional diagnostic tests can provide early diagnosis of CHIKV infections, access to these tests is often limited in developing countries. Consequently, there is an urgent need to develop efficient, affordable, simple, rapid, and robust diagnostic tools that can be used in point-of-care settings. Early diagnosis is crucial to improve patient management and to reduce the risk of complications. A glass-fiber laser-cut microfluidic device (paper-based analytical device [PAD]) was designed and evaluated in a proof of principle context, for the analysis of 30 µL of patient serum. Biological raw materials used for the functionalization of the PAD were first screened by MAC-ELISA (IgM capture enzyme-linked immunosorbent assay) for CHIKV Immunoglobulin M (IgM) capture and then evaluated on the PAD using various human samples. Compared with viral lysate traditionally used for chikungunya (CHIK) serology, CHIKV pseudo-particles (PPs) have proven to be powerful antigens for specific IgM capture. The PAD was able to detect CHIKV IgM in human sera in less than 10 minutes. Results obtained in patient sera showed a sensitivity of 70.6% and a specificity of around 98%. The PAD showed few cross-reactions with other tropical viral diseases. The PAD could help health workers in the early diagnosis of tropical diseases such as CHIK, which require specific management protocols in at-risk populations.

Background Beak and feather disease virus (BFDV) is a circovirus that infects captive and wild psittacine birds, and is of conservation concern. The haemagglutination inhibition (HI) assay is used to determine antibody titres against BFDV, and the use of dried blood spots (DBS) on filter paper stored at room temperature has been suggested to be an equally valid technique to the use of frozen serum. However, research on other pathogens has found variable results when investigating the longevity of antibodies stored on DBS at room temperature. Consequently, we aimed to test the temporal stability of antibodies to BFDV in DBS samples stored long-term at room temperature. A further goal was to add to the current knowledge of antibody response to naturally acquired BFDV infection in crimson rosellas (Platycercus elegans). Methods Blood was collected from wild P. elegans in Victoria, Australia, that had been live-trapped (n = 9) or necropsied (n = 11). BFDV virus load data were obtained from blood stored in ethanol by real-time quantitative PCR (qPCR); antibody titres were obtained by HI assay from either DBS or serum samples, which had been collected concurrently. All HI assays were performed commercially by the Veterinary Diagnostic Laboratory (VDL) in Charles Sturt University, Australia, who were blind to BFDV blood status. Results HI titres from DBS stored at room temperature declined significantly over time (~80 weeks). By contrast, frozen serum samples assayed after 80 weeks in storage all had high HI titres, only varying up to one dilution step from the initial HI titres obtained from DBS at 3–6 weeks after sampling. Weak HI titres from DBS samples all came back negative when the test was repeated only nine weeks later. Novel high HI titres were reported in P. elegans, and while most birds with high antibody titres had corresponding negative qPCR results, a single subadult presented with high HI titres and virus load simultaneously. Conclusion Detection of antibodies on filter paper stored at room temperature decreases over time, increasing the chances of false negatives in these samples, and in repeated testing of samples with weak HI titres. Consequently, serum should be the preferred sample type to use for seroepidemiological studies on BFDV in parrots and other bird species. When not possible, it may help to store DBS on filter paper at −20 °C or lower. However, prompt testing of DBS samples (e.g., P. elegans, especially adults, can produce high antibody titres against BFDV, which may help them resist infection.

Peste des petits ruminants (PPR) is a highly contagious disease caused by peste-des-petits-ruminants virus. Following the successful eradication of the related rinderpest virus, a program to control and eradicate PPR was launched by the FAO and OIE. PPR is today present in many tropical countries where maintaining the cold chain for sample transportation is one of the major barriers for timely processing. Transport of samples on filter paper is a simple and cost-effective method, however validation and optimization is required to fully adapt this approach. The objective of this study was to evaluate and validate the use of filter paper in serological diagnosis of PPR. Blood samples (serum and filter paper) were collected from sheep and goats in both Tanzania and Pakistan and analysed using a PPRV-specific cELISA. The positive proportion was 10.7% in Tanzania and 80% in Pakistan when performing the analysis on serum. These results were then considered as reference and compared to the results from the filter papers analysed by the same cELISA. According to the statistical analysis the cut-off for a positive results for samples stored on filter paper was adjusted from < 50 % competition percentage to < 84% in Tanzania and to < 69% in Pakistan.These results demonstrate that filter papers are an acceptable and cost-effective transport method of whole blood samples for later use in serological analysis.

We compared Nobuto filter paper (FP) whole-blood samples to serum for detecting antibodies to seven pathogens in reindeer (Rangifer tarandus tarandus). Serum and FP samples were collected from captive reindeer in 2008-2009. Sample pairs (serum and FP eluates) were assayed in duplicate at diagnostic laboratories with the use of competitive enzyme-linked immunosorbent assays (cELISAs) for Neospora caninum and West Nile virus (WNV); indirect ELISA (iELISAs) for bovine herpesvirus type 1 (BHV-1), parainfluenza virus type 3 (PI-3), and bovine respiratory syncytial virus (BRSV); and virus neutralization (VN) for bovine viral diarrhea virus (BVDV) types I and II. Assay thresholds were evidence-based values employed by each laboratory. Comparable performance to serum was defined as FP sensitivity and specificity ≥ 80%. Filter-paper specificity estimates ranged from 92% in the cELISAs for N. caninum and WNV to 98% in the iELISAs for PI-3 and BRSV. Sensitivity was85% for five tests (most ≥ 95%) but was insufficient (71-82%) for the PI-3 and BRSV iELISAs. Lowering the threshold for FP samples in these two ELISAs raised sensitivity to ≥ 87% and reduced specificity slightly (≥ 90% in three of the four test runs). Sample size limited the precision of some performance estimates. Based on the criteria of sensitivity and specificity ≥ 80%, and using adjusted FP thresholds for PI-3 and BRSV, FP sensitivity and specificity were comparable to serum in all seven assays. A potential limitation of FP is reduced sensitivity in tests that require undiluted serum (i.e., N. caninum cELISA and BVDV VNs). Possible toxicity to the assay cell layer in VN requires investigation. Results suggested that cELISA is superior to iELISA for detecting antibodies in FP samples from reindeer and other Rangifer tarandus subspecies. Our findings expand the potential utility of FP sampling from wildlife.

Chagas disease (CD) caused by the parasite Trypanosoma cruzi, belongs to the so-called neglected diseases group. In Argentina about 1,500 children are born with congenital Chagas disease per year. The diagnosis of CD in the newborn relies on the ability to detect parasites in the blood by microscopic observation, as the serological tests are ruled out because of the presence of maternal antibodies. CD treatment is more effective during the acute phase of infection. Early diagnosis and treatment of the disease is thus very important. The Argentinian National Program for early detection of metabolic diseases uses Whatman903 filter paper for blood sampling. This type of sample collection presents many advantages as the use of low blood volumes, minimal biological risk, and easy storage and transportation. The objective of the study was to evaluate the conservation efficiency of blood samples on filter paper in order to access good sensitivity on qPCR results for the detection of T. cruzi. To standardize the procedure, negative samples of blood were infected artificially with serial dilutions of trypomastigotes forms of T. cruzi from the TcVI strain obtained by cell culture in Vero cells. Concentrations between 50000 and 5 parasites/mL were prepared and loaded in filter paper for analysis. DNA extraction was conducted by the QIAamp DNA Mini Kit from QIAGEN. For qPCR, a method based on TaqMan technology was used, with a multiplex reaction for quantification of T. cruzi satellite DNA and an internal amplification control (IAC). The detection limit found from our results was 400 parasites/mL, demonstrating that this method could be a reliable option for the diagnosis of congenital CD by the detection of T. cruzi in blood collected in filter paper.

Demonstration of successful elimination of lymphatic filariasis (LF) in endemic countries requires sensitive diagnostics for accurate definitions of endpoints and future surveillance. There has been interest in complementing available diagnostics with antibody serology testing in children, since negative serology would correspond with cessation of LF transmission. The Filariasis CELISA detects antifilarial IgG4 and has favourable results with serum samples but field application requires an easier sampling method. Ninety-four paired plasma and filter paper samples were assayed with promising results. The filter paper method resulted in a sensitivity of 92% and a specificity of 77% when compared to the paired plasma. One hundred and one filter paper samples were assessed for storage effects. Following 10-month storage at −20°C there was a significant reduction in reactivity (P

The ring-infected erythrocyte surface antigen (RESA), is one of the falciparum malaria vaccine candidates rarely studied in Brazil. Fieldwork logistics to conduct serology studies is simplified when eluates from whole blood dried on filter paper can be used. Therefore, this study aimed to assess the inter-test reliability for the anti-RESA ELISA-based indices using eluates from filter paper and from serum samples. The study population consisted of 210 individuals (Brazil) from whom matched samples were collected. Anti-RESA ELISA-based index means (±S.D.) were 15.29% (±28.13%) for filter paper and 11.79% (±23.67%) for serum samples. The intra-class correlation coefficient was estimated to be 82.38%, indicating high test reliability. However, there was a significant tendency for filter paper test results to have higher values than serum sample test results (P

In this study we investigated if whole blood could substitute for serum in the direct card agglutination test (CATT/ Trypansosoma evansi ) and the indirect card agglutination test (LATEX/ T. evansi ) for the sero-diagnosis of T. evansi in buffaloes. Likewise blood spots on filter paper were compared with sera for use in the indirect enzyme-linked immunosorbent assay/ T. evansi (ELISA) and immunotrypanolysis test (T.L./ T. evansi ). Samples were collected weekly from experimentally T. evansi infected- and non-infected water buffaloes. To estimate test agreement between serum and respectively whole fresh blood and dried blood spots on filterpaper of the tests, κ values with 95% confidence intervals were calculated, 0.75±0.11 for the CATT/ T. evansi ; 0.80±0.11 for the ELISA/ T. evansi ; 0.84±0.11 for the LATEX/ T. evansi and 0.93±0.11 for the T.L./ T. evansi . In addition κ values with 95% confidence intervals were computed to assess agreement between results obtained in the reference T.L./ T. evansi test and those obtained in the other assays; 0.70±0.10 for the CATT-Serum; 0.75±0.11 for the LATEX-Blood; 0.77±0.11 for the LATEX-Serum; 0.81±0.10 for the CATT-Blood; 0.81±0.11 for the ELISA-Serum and 0.84±0.11 for the ELISA-Confetti. Based on the high κ values as calculated, we conclude that serum can be replaced by fresh whole blood for the agglutination assays or blood on filter paper for the ELISA/ T. evansi and T.L./ T. evansi .

As measles control and elimination campaigns progress, laboratory confirmation of clinically diagnosed measles cases becomes increasingly important. However, in many tropical countries collection and storage of clinical specimens for this purpose are logistically complicated. In this study it is shown that blood samples spotted on filter paper are suitable for the laboratory diagnosis of measles using a combination of reverse transcriptase PCR (RT-PCR) analysis and immunoglobulin M (IgM) detection. First, it was shown that in vitro measles virus (MV)-infected cells diluted in human blood and spotted on filter paper can be detected by RT-PCR. Small amounts of infected cells remained detectable after 25 weeks of storage of the filter paper at room temperature, 4 weeks at 37°C, or 2 weeks at 45°C. Subsequently, this RT-PCR was applied to filter paper blood samples collected from 117 clinically diagnosed measles patients in Sudan in 1997 and 1998. Prior laboratory diagnosis had confirmed 90 cases as acute MV infections, while 27 proved to be nonmeasles rash disease cases. Positive RT-PCR signals were detected in filter paper blood samples of 43 of the 90 confirmed cases (48%) but in none of the 27 nonmeasles cases. In addition, MV-specific IgM levels measured in reconstituted filter paper samples correlated well with those measured in plasma samples. Measles diagnosis based on the combination of filter paper RT-PCR and IgM detection had a sensitivity and specificity of 99 and 96%, respectively. An advantage of this diagnostic approach is that sequencing of RT-PCR products allows phylogenetic analysis of the MV strain involved.

The use of filter paper is an inexpensive and convenient method for collecting, storing, and transporting blood samples for serological studies. In addition, samples occupy little space and can be readily transported without refrigeration. Rickettsial diseases often evolve according to an epidemic mode and are now considered reemerging diseases, especially in developing countries, under conditions where fieldwork could be difficult. The suitability of collecting whole-blood specimens on filter paper discs for rickettsial antibody assay was evaluated. Dried blood specimens from 64 individuals with antibodies to Coxiella burnetii , Bartonella quintana , or Rickettsia conorii were tested for rickettsial antibodies by microimmunofluorescence. Although occasional titers were 1 or 2 dilutions lower than those of tested serum samples, no statistically significant differences were observed. Among patients with negative serology, no false positives were found. This study demonstrated that the recovery of antibodies from finger-stick blood dried on filter paper after elution produces results comparable to those obtained by recovering antibodies from serum. Storing paper samples for 1 month at room temperature or at 4°C did not significantly affect the level of antibodies recovered. This report shows the utility of this sample collection method in developing countries where refrigeration is not possible and venipuncture is problematic.

This study evaluates whether blood collected on filter paper kept at 4 degrees C and tested at different intervals of time (1, 7, 15, 30 and 60 days after collection) would present similar results when compared to the serum samples and whether the type of filter paper influences the results. Eluates from filter paper samples were tested for Trypanosoma cruzi antibodies using indirect immunofluorescence antibody test (IFAT), indirect haemagglutination (IHA) and enzyme-linked immunosorbent assay (ELISA) as reference, the antibody titer in sera. Analysis of data showed that results obtained with IFAT, IHA (cut off point = 1:40) and ELISA in sera had similar sensitivity and good concordance among reactions. The use of a multiple linear regression model indicated that titer fall in eluates occurs up to the 7th day after the collection, and it is more marked for samples with lower antibodies titers. However, no significant differences were observed by IFAT, IHA (cut off point = 1:20) and ELISA in the proportion of positive reactions between sera and eluates. The results also showed that Melitta, Klabin or Whatman (reference) filter papers could be indicated for surveys, since they have shown similar capacity of maintenance of anti-T. cruzi immunoglobulins.

The aim of this study was to investigate the microagglutination test (MAT) results in serum samples dried on filter paper and stored at different temperatures during 1 day, 7 days, 30 days and 1 year to determine the stability of sera antibody against leptospires. Serum samples collected onto filter paper for the detection of leptospires antibody was compared with MAT in a study of 300 serum samples from patients with suspected leptospirosis. Among 300 fresh serum samples analyzed by MAT 156 (52%) were positive and 144 (48%) negative. All the negative fresh serum samples were negative when dried on filter paper (specificity 100%). The sensitivity of MAT performed on dried serum samples was 100%. Storage on filter paper at room temperature and at 4 °C for 1 and 7 days did not affect the MAT titers. For up to 7 days, 98.72% of dried serum samples had titers identical to those of the corresponding serum samples, and 1.18% of dried serum samples showed 1 dilution of difference. After a storage period of one month a prozone phenomenon was observed. After a storage period of one year all serum samples were negative. Serum samples collected onto filter paper are a convenient source of antibodies for serological diagnosis and epidemiological surveys.

Control of human African trypanosomiasis (HAT) in the Democratic Republic of Congo is based on mass population screening by mobile teams; a costly and labor-intensive approach. We hypothesized that blood samples collected on filter paper by village health workers and processed in a central laboratory might be a cost-effective alternative. We estimated sensitivity and specificity of micro-card agglutination test for trypanosomiasis (micro-CATT) and enzyme-linked immunosorbent assay (ELISA)/T.b. gambiense on filter paper samples compared with parasitology-based case classification and used the results in a Monte Carlo simulation of a lot quality assurance sampling (LQAS) approach. Micro-CATT and ELISA/T.b. gambiense showed acceptable sensitivity (92.7% [95% CI 87.4-98.0%] and 82.2% [95% CI 75.3-90.4%]) and very high specificity (99.4% [95% CI 99.0-99.9%] and 99.8% [95% CI 99.5-100%]), respectively. Conditional on high sample size per lot (> or = 60%), both tests could reliably distinguish a 2% from a zero prevalence at village level. Alternatively, these tests could be used to identify individual HAT suspects for subsequent confirmation.

Serological diagnosis of filariasis is generally known to be more reliable than detection of microfilariae. The recently developed Og4C3 enzyme-linked immunosorbent assay (ELISA) for detecting Wuchereria bancrofti circulating antigen has been shown to be very sensitive in diagnosing filiariasis using serum samples. The commercially available form of this ELISA, using whole blood collected on filter paper, has not been validated independently. We evaluated the sensitivity of this new method against standard 20 microL night blood films in 1808 paired samples from 18 communities in different endemic areas of Ghana. The diagnostic performance of the method was consistently low in all but 2 communities (sensitivity = 50.3%). This method of diagnosing filariasis is not suitable for field use in its present form.

The suitability of blood collected on filter papers in comparison with corresponding conventional serum samples in the diagnosis of bovine anaplasmosis was studied using the complement fixation test, DOT-ELISA, Western immunoblot and rapid card agglutination test. Dried blood on Whatman filter paper no. 1 was eluted in PBS 0.05% Tween 20 giving an initial dilution of 1:10. The reactivity of the eluted samples in both DOT-ELISA and Western immunoblotting were similar to those obtained with the corresponding straight serum sample dilutions. Filter paper samples gave lower reactivity in the remaining tests when compared with corresponding serum samples. There was no significant difference in the reactivity between the eluates from filter papers stored at temperatures ranging between 15.5 and 24 degrees C and those kept refrigerated. Storage at 15.5 to 24 degrees C did not significantly affect reactivity for up to six months. Eluates from filter papers stored for six months at 15.5 to 24 degrees C continued to give similar reactivity as those from freshly prepared filter papers in both DOT-ELISA and Western blot, and in the rapid card agglutination test. It is concluded that collecting blood on filter papers is a suitable technique for large scale seroepidemiological studies on anaplasmosis and offers many advantages in developing countries where transport and cold chain facilities are a major constraint.

We compared detection of rubella virus hemagglutination inhibition (HI) antibody and rubella virus-specific immunoglobulin M (IgM) in dried whole blood spotted onto Whatman filter paper and serum samples, both of which were obtained from the same subject by venipuncture. Of 1,000 paired serum samples obtained to study HI antibodies, 807 dried blood samples had HI titers identical to those of the corresponding serum samples, and 193 dried blood samples showed 1 dilution difference. Storage of dried blood at room temperature for 28 days did not affect the HI antibodies. In a study of specific IgM by a solid-phase immunosorbent HI test done with blood from healthy subjects and patients with rubella, the result of the presence, positive or negative, of specific IgM from both blood sample sources corresponded when the dried blood samples were stored at room temperature from 5 h to 38 days. This study demonstrated that the use of Whatman filter paper as a transport medium for blood samples for the determination of rubella virus immunity and the diagnosis of rubella virus infection is possible.

International audience; During a dengue-3 outbreak in Paraguay at the beginning of 2007, capillary blood samples absorbed onto filter papers were collected from 44 suspected cases. These samples were subjected to three molecular and serologic tests, and 31 of the 44 samples gave a positive result by at least one of the techniques used. Molecular analyses detected the dengue-3 serotype in 22 patients and additionally the dengue-2 serotype in two patients. Therefore two different serotypes were co-circulating during this outbreak. Overall, this study validates the use of dried-blood samples for field screening investigations. Indeed, all types of laboratory studies of dengue were possible with samples consisting of a few drops of dried blood from finger pricks.

Diluted dried blood drops on filter paper were compared with serum samples as a specimen source for qualitative anti-HAV antibody determination by ELISA. A total of 298 serum samples and dried blood drops were collected from a population of healthy adolescents (15·3±1·2 years old). The prevalence of anti-HAV antibody obtained by testing serum samples was 7·7% (95% CI: 4·8–10·1). Compared with serum sampling the sensitivity and specificity of diluted dried blood drops were 91·3 and 99·3%. The positive and negative predictive values were 91·3 and 99·3%, respectively, and the likelihood ratios of positive and negative results were 91 and 0·09. It is proposed that this test represents a reliable procedure for anti-HAV antibody testing.

The utility of using Nobuto paper strips for the detection of avian influenza antibodies was examined in mallards (Anas platyrhynchos) experimentally infected with low pathogenic avian influenza viruses. Blood was collected 2 wk after infection and was preserved either as serum or whole blood absorbed onto Nobuto strips. Analysis of samples using a commercially available blocking enzyme-linked immunosorbent assay revealed comparable results (or = 96% sensitivity for all methods) between sera stored at -30 C and the Nobuto strip preservation method even when the Nobuto strips were stored up to 3 mo at room temperature (RT). Significant differences were detected in the ratio of sample absorbance to negative control absorbance for Nobuto strips stored at RT compared with sera stored at -30 C, although these differences did not affect the ability of the test to reliably detect positive and negative samples. Nobuto strips are a convenient and sensitive alternative to the collection of serum samples when maintaining appropriate storage temperatures is difficult.

INTRODUCTION: Human papillomavirus (HPV) is one of the most common causes of sexually transmitted diseases (STD). The incidence of condyloma acuminata (CA) has increased in recent years. AIM: To determine demographical features and serological test results of STD in patients with CA. MATERIAL AND METHODS: A cross-sectional survey was conducted on 94 patients presenting to a dermatology clinic in Ankara, Middle Anatolia, Turkey. Dermatological examinations were made and the patients completed a questionnaire which consisted of questions about their marital status, partners and condom use. In all cases, VDRL/RPR, anti-HIV, HBsAg, anti-HCV and in 57 cases - HSV type 1-2 IgM and IgG were studied. If the value of VDRL or RPR was positive, TPHA was conducted. RESULTS: In our study, 83 men and 11 women had CA. We could not analyze whether our cases had multiple partners and a habit of condom use as some of the patients did not answer questions about their sexual life. We observed VDRL and TPHA positivity in 3 (3.1%) cases, none of those cases had clinical findings of syphilis and they denied using any therapy for syphilis. HBsAg positivity was found in 3 cases. No anti-HIV and anti-HCV antibody positivity was detected. CONCLUSIONS: The seroprevalence of HBsAg in our study was similar to that of the general population of Turkey. But as we found positive syphilis serology in 3 patients, we suggest that syphilis serology should be investigated in patients with CA.

Conventional diagnosis of infection with Giardia duodenalis is by faecal examination but the sensitivity of a single examination is low. Serological tests, although not always positive, are more acceptable to patients and are useful in determining the prevalence of giardiasis in large populations. We show here that blood collected on filter paper and dried provides an excellent source of material for enzyme-linked immunosorbent assays; using samples from a group of 88 stool-negative and 45 positive patients, the optimum results were obtained by taking the control mean optical density plus one standard deviation as the negative/positive cut-off value. The sensitivity was 91% ( 2 45 false negatives), and the specificity 95% ( 4 88 false positives). This method should be particularly useful for large-scale surveys in developing countries or wherever serological testing is done in central laboratories.

Filter-paper (FP) blood sampling can facilitate wildlife research and expand disease surveillance. Previous work indicated that Nobuto FP samples from caribou and reindeer (Rangifer tarandus subspecies) had comparable sensitivity and specificity to serum samples (≥ 80% for both) in competitive enzyme-linked immunosorbent assays (cELISAs) for Brucella spp., Neospora caninum, and West Nile virus. The same sensitivity and specificity criteria were met in indirect ELISAs for Brucella spp., bovine herpesvirus type 1 (BHV-1), parainfluenza virus type 3 (PI-3), and bovine respiratory syncytial virus (BRSV), with adjusted FP thresholds used for PI-3 and BRSV. Comparable sensitivity and specificity values to serum were also observed for FP in virus neutralization (VN) assays for bovine viral diarrhea virus types I and II; however, reduced sensitivity is a potential limitation of FP samples in protocols that require undiluted serum (i.e., VN and N. caninum cELISA). We evaluated the performance of FP samples from reindeer and caribou in these nine assays after simulating potential challenges of high-latitude field collections: 1) different durations of storage and 2) different processing/storage regimes involving freezing or drying. Sample pairs (serum and FP) were collected from reindeer and caribou populations in 2007-10 and were tested in duplicate. Comparable performance to serum was defined as sensitivity and specificity ≥ 80%. In the storage experiments, FP performance was determined after 2 mo of storage dry at room temperature, and after two longer periods (variable depending on assay; up to 2 yr). After 1 yr, compared to frozen serum stored for the same period, sensitivity was ≥ 88% for all but two assays (68% BHV-1; 75% PI-3), and specificity remained90%. A limited trial evaluated the effect of freezing FP samples as opposed to drying them for storage. There were no observed detrimental effects of freezing on FP sample performance, but rigorous investigation is warranted.