Rapid Spread and Genetic Characterisation of a Recently Emerged Recombinant Lumpy Skin Disease Virus in Thailand.

The emergence of the lumpy skin disease virus (LSDV) was first detected in north-eastern Thailand in March 2021. Since then, the abrupt increase of LSD cases was observed throughout the country as outbreaks have spread rapidly to 64 out of a total of 77 provinces within four months. Blood, milk, and nodular skin samples collected from affected animals have been diagnosed by real-time PCR targeting the p32 gene. LSDV was isolated by primary lamb testis (PLT) cells, followed by Madin-Darby bovine kidney (MDBK) cells, and confirmed by immunoperoxidase monolayer assay (IPMA). Histopathology and immunohistochemistry (IHC) of a skin lesion showed inclusion bodies in keratinocytes and skin epithelial cells. Phylogenetic analyses of RPO30 and GPCR genes, and the whole genome revealed that Thai viruses were closely related to the vaccine-derived recombinant LSDV strains found previously in China and Vietnam. Recombination analysis confirmed that the Thai LSDV possesses a mosaic hybrid genome containing the vaccine virus DNA as the backbone and a field strain DNA as the minor donor. This is an inclusive report on the disease distributions, complete diagnoses, and genetic characterisation of LSDV during the first wave of LSD outbreaks in Thailand.

Thermal inactivation of African swine fever virus in feed ingredients.

African swine fever virus (ASFV) causes a fatal infectious disease affecting domestic pigs and wild boars. ASFV is highly stable and easily transmitted by consumption of contaminated swine feed and pork products. Heat treatment of feed ingredients is a means to minimize the risk of contamination through swine feed consumption. The objectives of this study were to determine the thermal inactivation of ASFV in non-animal and animal origin feed ingredients. The rate of thermal inactivation is represented by decimal reduction time (DT) or time required to reduce ASFV per 1 log at temperature T. The mean D60, D70, D80 and D85 of meat and bone meal (MBM), soybean meal (SBM), and maize grain (MZ) are in the ranges 5.11-6.78, 2.19-3.01, 0.99-2.02, and 0.16-0.99 min, respectively. DT is used to compare the heat resistance of ASFV in the feed ingredient matrices. The mean DT of ASFV in MBM, SBM and MZ was not statistically significant, and the heat resistance of ASFV in MBM, SBM, and MZ was not different at 60, 70, 80, or 85 °C. The multiple DT was used to develop a DT model to predict DT at various inactivation temperatures. The DT models for MBM, SBM, and MZ are log DT = - [Formula: see text] + 2.69, log DT = - [Formula: see text] + 2.55, and log DT = - [Formula: see text] + 4.01. To expand and ease the field applications, a spreadsheet predicting the DT and the inactivation time (with 95% confidence interval) from these DT models is available to download.

Persistence of African swine fever virus on porous and non-porous fomites at environmental temperatures.

BACKGROUND: African swine fever (ASF) is a lethal contagious disease affecting both domestic pigs and wild boars. Even though it is a non-zoonotic disease, ASF causes economic loss in swine industries across continents. ASF control and eradication are almost impossible since effective vaccines and direct antiviral treatment are not available. The persistence of ASFV on fomites plays an important role in the indirect transmission of ASFV to pigs encountering ASFV-contaminated fomites. ASFV persistence on porous and non-porous fomites (glass, metal, rubber, and cellulose paper) at different environmental temperatures was determined. The persistence of ASFV of fomites was determined by the rate of ASFV inactivation in terms of DT, or the time required to reduce ASFV per 1 log at each selected environmental temperature (T). DT is used to compare the persistence of ASFV on the fomites. RESULTS: The mean D25, D33, and D42, of dried infectious ASFV on glass, metal, rubber, and paper were in the ranges 1.42-2.42, 0.72-1.94, and 0.07-0.23 days, respectively. The multiple DT were used to develop a DT model to predict the DT for some other environmental temperatures. The DT models to predict the persistence of dried infectious ASFV on glass, metal, rubber, and paper are log DT = (- T/21.51) + 1.34, log DT = (- T/20.42) + 1.47, log DT = (- T/14.91) + 2.03, and log DT = (- T/10.91) + 2.84, respectively. A spreadsheet as a quick and handy tool predicting the persistence time of dried infectious ASFV on fomites at various environmental temperatures based on these DT models is available for public to download. CONCLUSION: Persistence of dried infectious ASFV on paper are significantly the longest at lower environmental temperatures whereas that of dried infectious ASFV on paper is significantly the shortest at higher environmental temperature.

Thermal Inactivation of African Swine Fever Virus in Swill.

The indirect transmission of the African swine fever virus (ASFV) is through contaminated fomite, feed ingredients, pork- and pig-derived products, including swill, as ASFV is highly stable within suitable organic material. Some previous studies have indicated that ASFV outbreaks were associated with swill feeding, particularly in smallholder pig farms. These outbreaks emphasize the significance of the appropriate heat treatment of swill to eliminate ASFV residual titer. The World Organization for Animal Health (OIE) recommended the heat treatment of swill at a temperature of at least 90°C for at least 60 min, with continuous stirring, while the Food and Agriculture Organization (FAO) recommended heat treatment at 70°C for 30 min. The lack of scientific evidence regarding ASFV inactivation by heat treatment of swill leads to such inconsistent recommendations. Therefore, the objectives of this study were to assess the thermal inactivation of ASFV in three swill formulae and to develop a D T model to predict D T at some other inactivation temperatures. The significant reduction of ASFV in swill occurred at temperatures as low as 60°C. D T or decimal reduction time (DRT) is defined as the time required to reduce the virus titer by 1 log, and this was also used as a comparative index of heat resistance. The mean D 60, D 70, D 75, and D 80 of ASFV in three swill formulae were in the ranges 23.21-33.47, 5.83-10.91, 2.15-2.22, and 1.36-1.47 min, respectively. These D T could be widely used for any nutritive composition of swill other than the three swill formulae in this study since there was no statistical difference of all D T of ASFV across three swill formulae. Based on D 70 and the predicted D 90 from the D T model in this study, including the highest ASFV titer in pork products, the calculated inactivation times at 70 and 90°C were 119 and 4 min, respectively.

Genetic and antigenic dynamics of influenza A viruses of swine on pig farms in Thailand.

Surveillance studies of influenza A virus of swine (IAV-S) have accumulated information regarding IAVs-S circulating in Thailand, but how IAVs-S evolve within a farm remains unclear. In the present study, we isolated 82 A(H1N1)pdm09 and 87 H3N2 viruses from four farms from 2011 through 2017. We then phylogenetically and antigenically analyzed the isolates to elucidate their evolution within each farm. Phylogenetic analysis demonstrated multiple introductions of A(H1N1)pdm09 viruses that resembled epidemic A(H1N1)pdm09 strains in humans in Thailand, and they reassorted with H3N2 viruses as well as other A(H1N1)pdm09 viruses. Antigenic analysis revealed that the viruses had acquired antigenic diversity either by accumulating substitutions in the hemagglutinin protein or through the introduction of IAV-S strains with different antigenicity. Our results, obtained through continuous longitudinal surveillance, revealed that IAV-S can be maintained on a pig farm over several years through the generation of antigenic diversity due to the accumulation of mutations, introduction of new strains, and reassortment events.

Co-infection of influenza A viruses of swine contributes to effective shuffling of gene segments in a naturally reared pig.

Following the 2009 H1N1 pandemic, surveillance activities have been accelerated globally to monitor the emergence of novel reassortant viruses. However, the mechanism by which influenza A viruses of swine (IAV-S) acquire novel gene constellations through reassortment events in natural settings remains poorly understood. To explore the mechanism, we collected 785 nasal swabs from pigs in a farm in Thailand from 2011 to 2014. H3N2, H3N1, H1N1 and H1N2 IAVs-S were isolated from a single co-infected sample by plaque purification and showed a high degree of diversity of the genome. In particular, the H1N1 isolates, possessing a novel gene constellation previously unreported in Thailand, exhibited greater variation in internal genes than H3N2 IAVs-S. A pair of isolates, designated H3N2-B and H1N1-D, was determined to have been initially introduced to the farm. These results demonstrate that numerous IAVs-S with various gene constellations can be created in a single co-infected pig via reassortment.