African swine fever (ASF) is a highly contagious disease that is caused by the ASF virus (ASFV) with a high fatality rate in domestic pigs resulting in a high socio-economic impact. The pig business in Vietnam was recently affected by ASF for the first time. This study thus aimed to develop a disease dynamic model to explain how ASFV spreads in Vietnamese pig populations and suggest a protective vaccine coverage level required to prevent future outbreaks. The outbreak data were collected from ten private small-scale farms within the first wave of ASF outbreaks in Vietnam. Three methods were used to estimate the basic reproduction number (R₀), including the exponential growth method, maximum likelihood method, and attack rate method. The average R₀ values were estimated at 1.49 (95%CI: 1.05–2.21), 1.58 (95%CI: 0.92–2.56), and 1.46 (95%CI: 1.38–1.57), respectively. Based on the worst-case scenario, all pigs in a herd would be infected and removed within 50 days. We suggest vaccinating at least 80% of pigs on each farm once a commercially approved ASF vaccine is available. However, an improvement in biosecurity levels in small-scale farms is still greatly encouraged to prevent the introduction of the virus.

Although intensive vaccination programs have been implemented, Newcastle disease (ND) outbreaks, accompanied by severe economic losses, are still reported in Egypt. The genetic characterization of ND virus (NDV) strains isolated from ND-vaccinated chicken flocks provides essential information for improving ND control strategies. Therefore, here, 38 NDV strains were isolated and identified from outbreaks among vaccinated flocks of broiler chickens located in the provinces of Qena, Luxor, and Aswan of Upper Egypt during 2011–2013. The investigated broiler chicken flocks (aged 28 to 40 days) had high mortality rates of up to 80%. All NDV isolates were genetically analyzed using next-generation DNA sequencing. From these isolates, 10 representative NDV strains were selected for further genetic analyses. Phylogenetic analysis of full-length coding genes revealed that the Egyptian NDV isolates belonged to a single sub-genotype, VII.1.1. These isolates were phylogenetically distant from the vaccine strains, including La Sota or Clone 30 (genotype II), which have been commonly used to vaccinate chicken flocks. Amino acid substitution K78R was observed in the neutralizing epitopes of the F proteins; whereas several mutations were found in the neutralizing epitopes of the hemagglutinin-neuraminidase proteins, notably, E347K. Overall, our results suggested that the occurrence of neutralizing epitope variants may be one of potential reasons for ND outbreaks. Further studies are needed to determine the protective effect of current vaccines against circulating virulent NDV strains.

A concurrent infection of chicken anemia virus (CAV) and infectious bronchitis virus (IBV) was detected in Japanese native chicks in 2017, in which a high mortality rate (97.6%) was recorded in a small flock of 130 chicks exhibiting poor growth. Histological examination revealed that the affected chicks exhibited two different pathological entities: one was severe hematopoietic and lymphocytic depletion with abnormally large cells containing intranuclear inclusion bodies of CAV, whereas the other was renal tubular necrosis due to IBV infection. Immunohistochemistry detected CAV antigens in the bone marrow, liver, and spleen as well as IBV antigens in the kidneys, trachea, and air sacs. CAV was isolated from the liver sample of the chicks, and the isolated strain was designated as CAV/Japan/HS1/17. A phylogenetic analysis of the CAV VP1 gene revealed that CAV/Japan/HS1/17 is genetically similar to Chinese strains collected from 2014 to 2016. An experimental infection was performed using CAV/Japan/HS/17 and specific-pathogen-free chicks to determine the pathogenicity of CAV/Japan/HS/17. The isolate caused 100% anemia and 70% mortality to chicks inoculated at one day old, 80% of chicks inoculated at seven days old also developed anemia, and 10% died from CAV infection. These results suggest that the unusually high mortality in Japanese native chicks can be attributed to dual infection with both CAV and IBV. The results of the experimental infection suggest that CAV/Japan/HS1/17 has a pathogenic potential to specific-pathogen-free chicks and a relatively higher pathogenicity than previous Japanese CAV strains.

African swine fever (ASF) is currently Vietnam’s most economically significant swine disease. The first ASF outbreak in Vietnam was reported in February 2019. In this study, VNUA/HY/ASF1 strain isolated from the first ASF outbreak was used to infect 10 eight-week-old pigs orally with 10³ HAD₅₀ per animal. The pigs were observed daily for clinical signs, and whole blood samples were collected from each animal for viremia detection. Dead pigs were subjected to full post-mortem analyses. All 10 pigs displayed acute or subacute clinical signs and succumbed to the infection between 10 to 27 (19.8 ± 4.66) days post-inoculation (dpi). The onset of clinical signs started around 4–14 dpi. Viremia was observed in pigs from 6–16 dpi (11.2 ± 3.55). Enlarged, hyperemic, and hemorrhagic lymph nodes, enlarged spleen, pneumonia, and hydropericardium were observed at post-mortem examinations.