Diagnostic Performance of Dengue NS1 and Antibodies by Serum Concentration Technique.

Dengue infection has been a public health problem worldwide, especially in tropical areas. A lack of sensitive diagnostic methods in the early phase of the illness is one of the challenging problems in clinical practices. We, herein, analyzed 86 sera of acute febrile patients, from both dengue and non-dengue febrile illness, to study the diagnostic performance of dengue diagnostics. When compared with detection by Polymerase Chain Reaction (PCR), dengue NS1 detection by enzyme-linked immunosorbent assay (ELISA) had the highest sensitivity of 82.4% (with 94.3% specificity), while NS1 by rapid diagnostic test (RDT) had 76.5% sensitivity. IgM detection by ELISA and RDT showed only 27.5% and 17.9% sensitivity, respectively. The combination of NS1 and IgM in RDT yielded a sensitivity of 78.4%, with 97.1% specificity. One of the essential steps in making a diagnosis from patient samples is the preparation process. At present, a variety of techniques have been used to increase the number of analytes in clinical samples. In this study, we focused on the sample concentration method. The sera were concentrated three times with the ultrafiltration method using a 10 kDa molecular weight cut-off membrane. The results showed an increase in the sensitivity of RDT-NS1 detection at 80.4%, with 100% specificity. When combining NS1 and IgM detection, the concentration method granted RDT an 82.4% sensitivity, with 100% specificity. In conclusion, serum concentration by the ultrafiltration method is a simple and applicable technique. It could increase the diagnostic performance of point-of-care dengue diagnostics.

Evidence of transmission of influenza A and influenza B co-infection in healthcare workers.

INTRODUCTION: Co-infection of influenza A and B has been reported, especially in outbreak situations, but epidemiological and clinical information is limited. We aimed to investigate an outbreak of influenza among health care workers in which the index case suffered from influenza A and B co-infection. METHODOLOGY: We investigated the outbreak setting through the utilization of structural questionnaires, molecular methods, and serological tests. RESULTS: Among 13 persons, one index case and five confirmed secondary cases were confirmed. The overall influenza infection rate was 46.2% (6/13), with infection rates for influenza A and B at 38.5% (5/13) and 23.1% (3/13), respectively. Interestingly, one of the secondary cases had influenza A and B co-infection identical to the index case. There was no significant association between vaccination status and influenza infection. CONCLUSIONS: This study unveils the demonstration of human-to-human influenza A and B co-infection transmission for the first time. Surveillance systems, combined with epidemiological case investigation comprising molecular diagnosis, should be strengthened for future influenza outbreak preparedness.

False Positivity of Anti-SARS-CoV-2 Antibodies in Patients with Acute Tropical Diseases in Thailand.

Serology remains a useful indirect method of diagnosing tropical diseases, especially in dengue infection. However, the current literature regarding cross-reactivity between SARS-CoV-2 and dengue serology is limited and revealed conflicting results. As a means to uncover relevant serological insight involving antibody classes against SARS-CoV-2 and cross-reactivity, anti-SARS-CoV-2 IgA, IgM, and IgG ELISA, based on spike and nucleocapsid proteins, were selected for a fever-presenting tropical disease patient investigation. The study was conducted at the Faculty of Tropical Medicine during March to December 2021. The study data source comprised (i) 170 non-COVID-19 sera from 140 adults and children presenting with acute undifferentiated febrile illness and 30 healthy volunteers, and (ii) 31 COVID-19 sera from 17 RT-PCR-confirmed COVID-19 patients. Among 170 non-COVID-19 samples, 27 were false positives (15.9%), of which IgA, IgM, and IgG cross-reactive antibody classes were detected in 18 (10.6%), 9 (5.3%), and 3 (1.8%) cases, respectively. Interestingly, one case exhibited both IgA and IgM false positivity, while two cases exhibited both IgA and IgG false positivity. The false positivity rate in anti-SARS-CoV-2 IgA and IgM was reported in adults with dengue infection (11.3% and 5%) and adults with other tropical diseases (16.7% and 13.3%). The urea dissociation method applied to mitigate false positivity resulted in significantly decreased ELISA-based false and true positives. In conclusion, the analysis of antibody against SARS-CoV-2 in sera of patients with different tropical diseases showed that high IgA and IgM false positivity thus potentially limits serological assay utility in fever-presenting patients in tropical areas.

Survey of hepatitis E virus in pork products and pig stools in Nakhon Pathom Province, Thailand.

BACKGROUND: Hepatitis E virus (HEV) is an important public health threat resulting in more than 3 million symptomatic cases and 70,000 deaths annually. HEV is classified into at least eight genotypes, and five are associated with human infection. Genotypes 1 and 2 primarily affect humans, whereas genotypes 3 and 4 circulate in both humans and swine and are considered zoonotic viruses. Previous studies in Central Thailand have reported human HEV isolates with high similarity to swine strains and high seroprevalence in pigs, suggesting the potential for pig-to-human transmission. OBJECTIVES: This study aimed to detect and analyse HEV in pork products and pig stools collected from local markets and pig farms in Nakhon Pathom Province in Central Thailand. METHODS: A total of 177 pig stool and 214 pork product samples were detected for HEV by using RT-PCR amplification. Next, nucleotide sequencing and phylogenetic analysis were performed. RESULTS: We found one sample of pork products (1/214, 0.5%), which was a pig liver sample (1/51, 2.0%), and 49 HEV-positive samples in pig stools (49/177, 27.7%). Phylogenetic analysis showed that all these HEV sequences belonged to genotype 3, with a high correlation between our samples and HEV from humans and swine was previously reported in Thailand. CONCLUSIONS: This study suggested that the consumption of poorly sanitized or uncooked animal meat or food and frequent exposure to pig stools may be risk factors for HEV infections in humans.

Mass spectrometry-based identification and whole-genome characterisation of the first pteropine orthoreovirus isolated from monkey faeces in Thailand.

BACKGROUND: The pteropine orthoreovirus (PRV) was isolated from monkey (Macaca fascicularis) faecal samples collected from human-inhabited areas in Lopburi Province, Thailand. These samples were initially obtained to survey for the presence of hepatitis E virus (HEV). RESULTS: Two virus isolates were retrieved by virus culture of 55 monkey faecal samples. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was successfully used to identify the viruses as the segmented dsRNA orthoreovirus. Phylogenetic analysis of the Lopburi orthoreovirus whole-genomes revealed relationships with the well-characterised PRVs Pulau (segment L1), Cangyuan (segments L2, M3 and S3), Melaka (segments L3 and M2), Kampar (segments M1 and S2) and Sikamat (segments S1 and S4) of Southeast Asia and China with nucleotide sequence identities of 93.5-98.9%. RT-PCR showed that PRV was detected in 10.9% (6/55) and HEV was detected in 25.5% (14/55) of the monkey faecal samples. CONCLUSIONS: PRV was isolated from monkey faeces for the first time in Thailand via viral culture and LC-MS/MS. The genetic diversity of the virus genome segments suggested a re-assortment within the PRV species group. The overall findings emphasise that monkey faeces can be sources of zoonotic viruses, including PRV and HEV, and suggest the need for active virus surveillance in areas of human and monkey co-habitation to prevent and control emerging zoonotic diseases in the future.

Genetic variations in regions of bovine and bovine-like enteroviral 5'UTR from cattle, Indian bison and goat feces.

BACKGROUND: Bovine enteroviruses (BEV) are members of the genus Enterovirus in the family Picornaviridae. They are predominantly isolated from cattle feces, but also are detected in feces of other animals, including goats and deer. These viruses are found in apparently healthy animals, as well as in animals with clinical signs and several studies reported recently suggest a potential role of BEV in causing disease in animals. In this study, we surveyed the presence of BEV in domestic and wild animals in Thailand, and assessed their genetic variability. METHODS: Viral RNA was extracted from fecal samples of cattle, domestic goats, Indian bison (gaurs), and deer. The 5' untranslated region (5'UTR) was amplified by nested reverse transcription-polymerase chain reaction (RT-PCR) with primers specific to BEV 5'UTR. PCR products were sequenced and analyzed phylogenetically using the neighbor-joining algorithm to observe genetic variations in regions of the bovine and bovine-like enteroviral 5'UTR found in this study. RESULTS: BEV and BEV-like sequences were detected in the fecal samples of cattle (40/60, 67 %), gaurs (3/30, 10 %), and goats (11/46, 24 %). Phylogenetic analyses of the partial 5'UTR sequences indicated that different BEV variants (both EV-E and EV-F species) co-circulated in the domestic cattle, whereas the sequences from gaurs and goats clustered according to the animal species, suggesting that these viruses are host species-specific. CONCLUSIONS: Varieties of BEV and BEV-like 5'UTR sequences were detected in fecal samples from both domestic and wild animals. To our knowledge, this is the first report of the genetic variability of BEV in Thailand.

Detection and characterization of enteric viruses in flood water from the 2011 thai flood.

Severe flooding, which is associated with numerous outbreaks of a wide range of infectious diseases, particularly those caused by enteric viruses, occurred in all areas of Thailand in 2011. To determine the prevalence of five human enteric viruses, namely enterovirus, rotavirus (RV), norovirus (NV), hepatitis A virus (HAV), and hepatitis E virus, in the flood water, 100 water samples were collected from flood-damaged areas in central Thailand. Viral RNA was extracted from concentrated samples and analyzed by RT-PCR and sequencing. NV was the most commonly detected pathogen in the tested samples (14%). RV and HAV were detected in 9% and 7% of samples, respectively. This study is the first to detect enteric viral genes in flood water in Thailand. Furthermore, it is the first to detect an NV gene in any type of environmental water in Thailand. These results provide useful information for estimating the risk of flood waterborne viral infection.