Development of a Filament Extruder Using Flow Theory with the Newtonian Fluid Assumption

This article presents an investigation of the flow characteristics of the polymer melt in a single-screw extruder and the design of a filament extruder to verify the above theory. The flow characteristics of the polymer melt in a single-screw extruder are likable to that of a viscous liquid between two infinitely parallel sheets, one moving and the other stationary. An integrated flow equation was then found for a case when the viscosity of a liquid remains constant in an isothermal extrusion. These flow behavior theories were then verified via the design and fabrication of a filament extruder for 3D printers

Development of a Filament Extruder Using Flow Theory with the Newtonian Fluid Assumption

This article presents an investigation of the flow characteristics of the polymer melt in a single-screw extruder and the design of a filament extruder to verify the above theory. The flow characteristics of the polymer melt in a single-screw extruder are likable to that of a viscous liquid between two infinitely parallel sheets, one moving and the other stationary. An integrated flow equation was then found for a case when the viscosity of a liquid remains constant in an isothermal extrusion. These flow behavior theories were then verified via the design and fabrication of a filament extruder for 3D printers

Development of a nutritional model to define the energy and protein requirements of cobia, Rachycentron canadum

This study assessed the protein and energy requirements of Cobia (Rachycentron canadum) using a bio-energetic factorial approach. Using a series of inter-related studies, several parameters were defined to enable the construction of a bio-energetic factorial model for this species. The studies included two controlled laboratory experiments and also extensive field-data collection from commercial and research farms in Vietnam. The devised model includes parameters for both maintenance and protein demands; the effect of fish live-weight on maintenance protein (LW0.697), lipid (LW0.972), and energy demands (LW0.815); the efficiencies of protein, lipid and energy utilisation at various protein, lipid and energy intake levels; and the variability in whole body composition with varying live-weight. The protein utilisation efficiencies (0.456·[protein intake]−0.445), lipid utilisation efficiencies (1.292·[lipid intake]−1.120) and energy utilisation efficiencies (0.651·[energy intake]−48.41) were similar to other carnivorous fish species. However, the maintenance requirements for both energy (74.3kJ/kgBW0.8/d−at 28°C) and protein (0.99g/kgBW0.7/d at 27.9°C) were about double to other species. Using this modelling approach it was possible to iteratively derive optimal dietary protein and energy specifications for this species

Unexpected cases in field diagnosis of African swine fever virus in Vietnam: The needs consideration when performing molecular diagnostic tests

Background: The first confirmed case of African swine fever (ASF) in Vietnam was reported officially in February 2019. To date, ASF virus (ASFV) have been detected in 63/63 provinces in Vietnam. Currently, real-time polymerase chain reaction (PCR) is considered to be a powerful tool for viral detection in field samples, including ASFV. However, some recent reports have suggested that mismatches in primer and probe binding regions may directly affect real-time PCR qualification, leading a false-negative result.Aim: This study aims to further examine a conflicting result obtained from two OIE recommended methods, conventional PCR and real-time PCR, for ASFV detection.Methods: Two ASF suspected pigs from different provinces in the north of Vietnam were selected for this study based on clinical signs and postmortem lesions. The different results obtained by OIE-recommended conventional PCR and real-time PCR were further analyzed by the Sanger sequencing method and virus isolation in combination with hemadsorption (HAD) test using porcine alveolar macrophages cells.Results: The results showed that when the primer sequence matched perfectly with the sequences of field isolates, a mutation in probe binding region was found, indicating that a single mismatch in the probe binding site may cause a false-negative result by real-time PCR in detecting ASFV in clinical samples in Vietnam. An agreement between conventional PCR, using PPA1/PPA2 primers and two golden standard methods, virus isolation in combination with HAD assay, and sequencing method was observed in this study.Conclusion: A single mismatch in the probe binding site caused a failse-negative result by realtime PCR method in field diagnosis of ASFV. The needs consideration when selecting the appropriate molecular diagnostic methods is based on the current databases of ASFV sequences,  particularly for epidemiological surveillance of ASF. Keywords: African swine fever, PCR, Pigs, Real-time PCR, Vietna

Brza serotipizacija virusa afričke kuge svinja zasnovana na analizi kratkih fragmenata EP402R gena koji kodira CD2-like protein

The first confirmed case of African swine fever (ASF) in Vietnam was officially reported in February 2019. To date, the ASF virus (ASFV) has been detected in all 63 cities/provinces in Vietnam. In order to get a better understanding of the potential role of the EP402R gene in a grouping of ASFV serotypes, thirty ASFV sequences of EP402R genes (accession numbers: MN711757-86) from North Central Coast of Vietnam and 68 well-known references of serotype groups from previous studies were further analyzed. Interestingly, we found that a short fragment of 90 nucleotides was very typical for 8 serological groups of ASFVs. A primer set was designed to amplicon the short fragment of 90 nucleotides using the Primer3 program to establish a simplified method for the serotyping of ASFV. Our results indicated that phylogenetic analysis of the short fragment (90 nucleotides) of the EP402R gene is a very specific and useful method for ASFV serotyping when compared to the previous method using a long fragment (816 nucleotides) of this gene and well-known serotype references based on haemadsorption inhibition (HAI) assay.Prvi potvrđen slučaj afričke kuge svinja (ASF) u Vijetnamu bio je zvanično prijavljen u februaru 2019. godine. Do danas, ASF virus (ASFV) je detektovan u 63 provincije Vijetnama. Radi boljeg razumevanja potencijalne uloge EP402R gena u grupisanju ASFV serotipova, analizirano je trideset ASFV sekvenci EP402R gena (pristupni brojevi: MN711757-86) poreklom iz Centralne severne obale Vijetnama i 68 referentnih uzoraka serotip grupa koji su dobro poznati iz prethodnih studija. Interesantan je bio nalaz da je kratak fragment od 90 nukleotida bio tipičan za 8 seroloških grupa ASF virusa. Dizajniran je set prajmera sa ciljem amplifi kacije kratkih fragmenata (90 nukleotida), korišćenjem Primer3 programa, a za uspostavljanje jednostavne metode serotipiziranja ASFV. Rezultati ukazuju da je fi logenetska analiza kratkih fragmenata (90 nukleotida) EP402R gena je veoma specifična i predstavlja korisnu metodu serotipizacije ASFV u poređenju sa prethodno opisanim metodama koje su koristile duge fragmente (816 nukleotida) ovog gena kao i dobro poznate referentne serotipove dobijene metodom inhibicije hemadsorbcije

Reduction in Plasmodium falciparum Pfk13 and pfg377 allele diversity through time in southern Vietnam

Background: Plasmodium falciparum has acquired resistance to artemisinin in Southeast Asia, with mutations in the P. falciparum Kelch-13 (Pfk13) gene associated with the resistance phenotype. The widespread use of Artemisinin-based combination therapy (ACT)s in Southeast Asia has led to the selection and spread of parasites carrying mutations in Pfk13. We characterised the allele diversity of Pfk13 and pfg377, an artemisinin-resistance neutral polymorphic gene, in parasite DNA extracted human blood from in southern Vietnam in 2003, 2012, 2015 and 2018.Method: This study was conducted in Bu Gia Map commune, Binh Phuoc province, Vietnam, from May 2018 to January 2019. Twenty-four samples from 2018 to 2019, 30 from 2003, 24 from 2012 and 32 from 2015 were analysed. Malaria-infected human blood was collected by finger-prick and used for molecular analysis. A nested-PCR targeting the small subunit ribosomal RNA gene was used for Plasmodium species identification, followed by amplification and nucleotide sequencing of Pfk13 and region 3 of pfg377. Archived blood samples collected in the same region in 2012 and 2015 were also analysed as above for comparison.Results: The genetic diversity of Pfk13 and pfg377 was lower in 2018–2019 compared to 2012 and 2015. The number of distinct Pfk13 mutants decreased from three in 2012 and 2015, P553L, V568G and C580Y, to one, C580Y in 2018–2019. In 2018–2019, the frequency of C580Y mutant strains was 71% (17/24 isolates). All samples were wild type in 2003. In 2012 and 2015, there were single-strain infections as well as co-infections with two mutant strains or with mutant and wild strains, whereas there were no co-infections in 2018. pfg377 allele diversity decreased from five alleles in 2012 to two alleles in 2018–2019.Conclusion: The genetic diversity of P. falciparum was reduced at the two genetic loci surveyed in this study, Pfk13 and pfg377. In the case of the former gene, we observed an increase in the prevalence of parasites carrying the C580Y gene, known to confer reduced susceptibility to ACTs. The reduction in the diversity of pfg377 may be linked to the clonal expansion of parasite strains carrying the C580Y mutation, leading to an overall reduction in parasite genetic diversity across the population

Risk Factors of Streptococcus suis Infection in Vietnam. A Case-Control Study

Background: Streptococcus suis infection, an emerging zoonosis, is an increasing public health problem across South East Asia and the most common cause of acute bacterial meningitis in adults in Vietnam. Little is known of the risk factors underlying the disease. Methods and Findings: A case-control study with appropriate hospital and matched community controls for each patient was conducted between May 2006 and June 2009. Potential risk factors were assessed using a standardized questionnaire and investigation of throat and rectal S. suis carriage in cases, controls and their pigs, using real-time PCR and culture of swab samples. We recruited 101 cases of S. suis meningitis, 303 hospital controls and 300 community controls. By multivariate analysis, risk factors identified for S. suis infection as compared to either control group included eating "high risk" dishes, including such dishes as undercooked pig blood and pig intestine (OR1 = 2.22; 95% CI = [1.15-4.28] and OR2 = 4.44; 95% CI = [2.15-9.15]), occupations related to pigs (OR1 = 3.84; 95% CI = [1.32-11.11] and OR2 = 5.52; 95% CI = [1.49-20.39]), and exposures to pigs or pork in the presence of skin injuries (OR1 = 7.48; 95% CI = [1.97-28.44] and OR2 = 15.96; 95% CI = [2.97-85.72]). S. suis specific DNA was detected in rectal and throat swabs of 6 patients and was cultured from 2 rectal samples, but was not detected in such samples of 1522 healthy individuals or patients without S. suis infection. Conclusions: This case control study, the largest prospective epidemiological assessment of this disease, has identified the most important risk factors associated with S. suis bacterial meningitis to be eating 'high risk' dishes popular in parts of Asia, occupational exposure to pigs and pig products, and preparation of pork in the presence of skin lesions. These risk factors can be addressed in public health campaigns aimed at preventing S. suis infectio

An Outbreak of Severe Infections with Community-Acquired MRSA Carrying the Panton-Valentine Leukocidin Following Vaccination

Background: Infections with community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) are emerging worldwide. We investigated an outbreak of severe CA-MRSA infections in children following out-patient vaccination. Methods and Findings: We carried out a field investigation after adverse events following immunization (AEFI) were reported. We reviewed the clinical data from all cases. S. aureus recovered from skin infections and from nasal and throat swabs were analyzed by pulse-field gel electrophoresis, multi locus sequence typing, PCR and microarray. In May 2006, nine children presented with AEFI, ranging from fatal toxic shock syndrome, necrotizing soft tissue infection, purulent abscesses, to fever with rash. All had received a vaccination injection in different health centres in one District of Ho Chi Minh City. Eight children had been vaccinated by the same health care worker (HCW). Deficiencies in vaccine quality, storage practices, or preparation and delivery were not found. Infection control practices were insufficient. CA-MRSA was cultured in four children and from nasal and throat swabs from the HCW. Strains from children and HCW were indistinguishable. All carried the Panton-Valentine leukocidine (PVL), the staphylococcal enterotoxin B gene, the gene complex for staphylococcal-cassette-chromosome mec type V, and were sequence type 59. Strain HCM3A is epidemiologically unrelated to a strain of ST59 prevalent in the USA, althoughthey belong to the same lineage. Conclusions. We describe an outbreak of infections with CA-MRSA in children, transmitted by an asymptomatic colonized HCW during immunization injection. Consistent adherence to injection practice guidelines is needed to prevent CA-MRSA transmission in both in- and outpatient settings