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In 2007, African swine fever virus (ASFV) was introduced into the Transcaucasian countries and Russia. Since then, it has spread alarmingly and reached the European Union. ASFV strains are highly virulent and lead to almost 100 % mortality under experimental conditions. However, the possibility of dose-dependent disease courses has been discussed. For this reason, a study was undertaken to assess the risk of chronic disease and the establishment of carriers upon low-dose oronasal infection of domestic pigs and European wild boar. It was demonstrated that very low doses of ASFV are sufficient to infect especially weak or runted animals by the oronasal route. Some of these animals did not show clinical signs indicative of ASF, and they developed almost no fever. However, no changes were observed in individual animal regarding the onset, course and outcome of infection as assessed by diagnostic tests. After amplification of ASFV by these animals, pen- and stablemates became infected and developed acute lethal disease with similar characteristics in all animals. Thus, we found no indication of prolonged or chronic individual courses upon low-dose infection in either species. The scattered onset of clinical signs and pathogen detection within and among groups confirms moderate contagiosity that is strongly linked with blood contact. In conclusion, the prolonged course at the “herd level” together with the exceptionally low dose that proved to be sufficient to infect a runted wild boar could be important for disease dynamics in wild-boar populations and in backyard settings.

Classical swine fever (CSF) is a highly contagious disease affecting domestic pigs and wild boars, posing a serious threat to the global swine industry. In Japan, CSF re‐emerged on a pig farm in Gifu Prefecture in 2018, just 3 years after the country was declared CSF‐free. The CSF virus (CSFV) was soon detected in neighboring wild boars and subsequently spread to adjacent areas, leading to further farm outbreaks. Given that long‐distance transmission accelerates both spatial expansion and epidemic persistence, we aimed to identify such events during the current Japanese epidemic. Whole‐genome sequences were generated for 100 farm isolates and 585 wild boar isolates collected through national surveillance. Putative ancestral strains were inferred for each isolate by comparing single‐nucleotide variants (SNVs), and the great‐circle distance to the nearest ancestral strain was considered the transmission distance. Six routes exceeding the 99th percentile of the distance distribution (182.2 km) were classified as long‐distance transmission events: three involving farms and three involving wild boars. The sources of all these transmission events were identified as infected wild boars. The route to a farm in Okinawa Prefecture (January 2020) was linked to the illegal feeding of unheated food waste containing meat products. No specific sources were identified in the remaining two farm outbreaks. The three introductions into wild boar populations were most plausibly associated with anthropogenic activities, such as the movement of people or vehicles through infected habitats. To the best of our knowledge, this is the first study to comprehensively quantify long‐distance CSFV spread across the entire course of the Japanese epidemic (2018–2024). Our findings will inform targeted control measures to prevent farm infections and the inadvertent spread of contaminated material to remote areas.

Pre-emptive culling is becoming increasingly questioned as a means of controlling animal diseases, including classical swine fever (CSF). This has prompted discussions on the use of emergency vaccination to control future CSF outbreaks in domestic pigs. Despite a long history of safe use in endemic areas, there is a paucity of data on aspects important to emergency strategies, such as how rapidly CSFV vaccines would protect against transmission, and if this protection is equivalent for all viral genotypes, including highly divergent genotype 3 strains. To evaluate these questions, pigs were vaccinated with the Riemser® C-strain vaccine at 1, 3 and 5 days prior to challenge with genotype 2.1 and 3.3 challenge strains. The vaccine provided equivalent protection against clinical disease caused by for the two challenge strains and, as expected, protection was complete at 5 days post-vaccination. Substantial protection was achieved after 3 days, which was sufficient to prevent transmission of the 3.3 strain to animals in direct contact. Even by one day post-vaccination approximately half the animals were partially protected, and were able to control the infection, indicating that a reduction of the infectious potential is achieved very rapidly after vaccination. There was a close temporal correlation between T cell IFN-γ responses and protection. Interestingly, compared to responses of animals challenged 5 days after vaccination, challenge of animals 3 or 1 days post-vaccination resulted in impaired vaccine-induced T cell responses. This, together with the failure to detect a T cell IFN-γ response in unprotected and unvaccinated animals, indicates that virulent CSFV can inhibit the potent antiviral host defences primed by C-strain in the early period post vaccination.

The outbreak of infectious diseases in swine, such as classical swine fever (CSF), has become a significant concern in the pig‐farming industry. In Japan, after the re‐emergence of CSF in 2018, farms are now exposed to the risk of transmission from infected wild boar and CSF‐contaminated farms. This study aimed to identify biosecurity measures that were effective for the prevention of CSF introduction into farms during the period from the beginning of the CSF epidemic to the implementation of a vaccination campaign for domestic pigs at risk. The probability of virus introduction was assumed to be increased by the elevated risk from CSF‐infected wild boar and infected farms around the farm. The risk from infected wild boar was represented by the prevalence of CSF in wild boar or the occupancy of 1‐km grid cells with infected wild boar within 10‐km radii from a pig farm and the occurrence of CSF outbreaks on neighboring farms. Conversely, the probability of virus introduction was assumed to decrease in response to on‐farm biosecurity measures being implemented on each farm. The implementation of biosecurity measures on the farms and farm attributes were obtained through a questionnaire survey. Analyses were performed on each farm under the weekly situations where infected wild boar were both absent and present in the vicinity using a binomial generalized linear model. On farms where infected wild boar were not present around farms, daily washing and disinfecting of work clothing in pig houses was identified as the main measure to reduce the risk of CSF introduction into farms. On farms with infected wild boar in the vicinity, the absence of public roads on the farm and preventing wildlife intrusion into the areas where pig carcasses were stored were demonstrated to be effective in preventing CSF introduction. Based on the assumption that strict and comprehensive biosecurity measures are required to prevent CSF introduction, the implementation of these potentially effective measures is worth being prioritized.

Domestic livestock production is a major component of the agricultural sector, contributing to food security and human health and nutrition and serving as the economic livelihood for millions worldwide. The impact of disease on global systems and processes cannot be understated, as illustrated by the effects of the COVID-19 global pandemic through economic and social system shocks and food system disruptions. This study outlines a method to identify the most likely sites of introduction into the United States for three of the most concerning foreign animal diseases: African swine fever (ASF), classical swine fever (CSF), and foot-and-mouth disease (FMD). We first created an index measuring the amount of potentially contaminated meat products entering the regions of interest using the most recently available Agricultural Quarantine Inspection Monitoring (AQIM) air passenger inspection dataset, the AQIM USPS/foreign mail, and the targeted USPS/foreign mail interception datasets. The risk of introduction of a given virus was then estimated using this index, as well as the density of operations of the livestock species and the likelihood of infected material contaminating the local herds. Using the most recently available version of the datasets, the most likely places of introduction for ASF and CSF were identified to be in central Florida, while FMD was estimated to have been most likely introduced to swine in western California and to cattle in northeastern Texas. The method illustrated in this study is important as it may provide insights on risk and can be used to guide surveillance activities and optimize the use of limited resources to combat the establishment of these diseases in the U.S.

Classical swine fever (CSF) is the one of the most devastating contagious diseases in domestic swine and wild boar/pigs ( Sus scrofa ). Population genetics is often used to estimate animal dispersal and can also help evaluate host population connectivity, which is crucial for understanding pathogen dispersal. We surveyed genetic population structure of boars using MIG‐seq analysis to clarify the geographic barriers that influence boar dispersal in north‐central Japan and to demonstrate the relationship between the spread of CSF infection among boars and their population structure. We obtained 382 single‐nucleotide polymorphisms from 348 wild boar samples, and the results of STRUCTURE analysis indicated that the highest Δ K value was at K = 2, followed by K = 4. Based on these results, it is evident that the Abukuma river, a major river within north‐central Japan, does not act as a barrier to the gene flow of boars, but rather that human infrastructure hinders their dispersal. Further, according to the time series change in the capture site of CSF‐infected wild boar and the sum of the probability of belonging to each of the four clades in individual CSF‐infected wild boar, our results indicated that the genetic structure of boar populations was correlated with the outbreak pathway of CSF across our study region. Our study suggests that predictions of disease spread, especially for widely distributed host species, is challenging because of the risk of cryptic breaks and changes in wide range connectivity; however, understanding the genetic population structure of wild boar can be a useful tool for predicting the spread of CSF. We concluded that genetic analysis of host population structure may have the possibility to improve predictions of the future dynamics of disease spread.

Classical swine fever (CSF) is a globally significant disease of swine caused by classical swine fever virus. The virus affects the wild boars and pigs of all age groups, leading to acute, chronic, late-onset or in-apparent course of the disease. The disease causes great economic loss to the piggery industry due to mortality, stunted growth, poor reproductive performance, and by impeding the international trade of pig and pig products. In India, CSF outbreaks are reported from most of the states wherever pig rearing is practiced and more frequently from northeast states. In spite of the highly devastating nature and frequent outbreaks, CSF remained underestimated and neglected for decades in India. The country requires rapid and sensitive diagnostic tests for an early detection of infection to limit the spread of the disease. Also, effective prophylactics are required to help in control and eradication of the disease for the development of the piggery industry. This review looks into the economic impact; epidemiology of CSF highlighting the temporal and spatial occurrence of outbreaks in the last two decades, circulation, and emergence of the virus genotypes in and around the country; and the constraints in the disease control, with the aim to update the knowledge of current status of the disease in India. The article also emphasizes the importance of the disease and the need to develop rapid specific diagnostics and effective measures to eradicate the disease.

As the size of livestock farms in The Netherlands is on the increase for economic reasons, an important question is how disease introduction risks and risks of onward transmission scale with farm size (i.e. with the number of animals on the farm). Here we use the epidemic data of the 1997-1998 epidemic of Classical Swine Fever (CSF) Virus in The Netherlands to address this question for CSF risks. This dataset is one of the most powerful ones statistically as in this epidemic a total of 428 pig farms where infected, with the majority of farm sizes ranging between 27 and 1750 pigs, including piglets. We have extended the earlier models for the transmission risk as a function of between-farm distance, by adding two factors. These factors describe the effect of farm size on the susceptibility of a 'receiving' farm and on the infectivity of a 'sending' farm (or 'source' farm), respectively. Using the best-fitting model, we show that the size of a farm has a significant influence on both farm-level susceptibility and infectivity for CSF. Although larger farms are both more susceptible to CSF and, when infected, more infectious to other farms than smaller farms, the increase is less than linear. The higher the farm size, the smaller the effect of increments of farm size on the susceptibility and infectivity of a farm. Because of changes in the Dutch pig farming characteristics, a straightforward extrapolation of the observed farm size dependencies from 1997/1998 to present times would not be justified. However, based on our results one may expect that also for the current pig farming characteristics in The Netherlands, farm susceptibility and infectivity depend non-linearly on farm size, with some saturation effect for relatively large farm sizes.

The control of emergence and spread of infectious diseases depends critically on the details of the genetic makeup of pathogens and hosts, their immunological, behavioral and ecological traits, and the pattern of temporal and spatial contacts among the age/stage-classes of susceptible and infectious host individuals. We show that failing to acknowledge the existence of heterogeneities in the transmission rate among age/stage-classes can make traditional eradication and control strategies ineffective, and in some cases, policies aimed at controlling pathogen emergence can even increase disease incidence in the host. When control strategies target for reduction in numbers those subsets of the population that effectively limit the production of new susceptible individuals, then control can produce a flush of new susceptibles entering the population. The availability of a new cohort of susceptibles may actually increase disease incidence. We illustrate these general points using Classical Swine Fever as a reference disease. Negative effects of culling are robust to alternative formulations of epidemiological processes and underline the importance of better assessing transmission structure in the design of wildlife disease control strategies.