Risks of introduction and economic consequences associated with African swine fever, classical swine fever and foot-and-mouth disease: A review of the literature

Estimating waning immunity against classical swine fever virus among adult wild boar: A case study in Japan

Bait vaccination against classical swine fever virus (CSFV) among wild boar in Japan started in 2019 and has continued so far. While the proportion of immune individuals increased in the early phase of the CSFV epidemic, this proportion tended to decrease in some regions, even after the subsequent vaccination. Turnover of wild boar populations can reduce the proportion of immune individuals; however, the decrease was also observed among adult wild boar during the season when the influence of turnover was negligible. Waning immunity is hypothesized as an alternative mechanism. This study aimed to test the hypothesis of waning immunity and estimate the waning rate among wild boar. A mathematical model describing CSFV transmission dynamics, host population dynamics, effect of vaccination, and waning immunity was constructed. We also constructed a model without waning immunity. The two models were fitted to a time-series of the proportion of recovered/vaccinated animals (i.e., ELISA-positive and PCR-negative) among adult wild boar in Gifu, Japan, assuming that the influence of turnover was negligible from July to November. The hypothesis that immunity against CSFV can wane is accepted; the model with waning immunity showed a significantly better fit compared to another model. The time until ELISA test results became negative after recovery/vaccination was estimated to be 26.6 weeks. Our results imply that the acquired immunity against CSFV and bait vaccination wanes over time. The level of herd immunity after vaccination against CSFV should be evaluated taking the waning immunity into account.

Porvac® Subunit Vaccine Protects Against Three Field Isolates of Classical Swine Fever Virus

The control of classical swine fever (CSF) in endemic areas has been attempted with modified live vaccines. However, in some regions, the implementation of imperfect vaccination programs has led to a reduction in the genetic diversity of the circulating CSF virus (CSFV) strains and a change in their virulence. Porvac® subunit vaccine has been shown to provide a rapid onset of protection against the "Margarita" strain. The aim of this study was to evaluate whether the immune response induced by Porvac® is also effective against autochthonous CSFV isolates of low, medium or high virulence. All pigs vaccinated with Porvac® were protected against the disease after challenge. PR-11/10-3 isolate caused a very mild disease in controls, whilst Holguin_2009 isolate produced mild to moderate signs of CSF and one of the pigs died. Finally, controls inoculated with PR-2016 isolate developed moderate to severe signs of CSF and two of them died. Viral replication was detected in controls, but not in pigs immunized with Porvac®. Finally, anti-Erns antibodies were induced in five out of six control pigs but not in any of the vaccinated pigs. These results support the use of Porvac® for the control and elimination of CSF in Cuba and other endemic regions.

Habitat suitability mapping and landscape connectivity analysis to predict African swine fever spread in wild boar populations: A focus on Northern Italy

African swine fever (ASF) is a highly contagious disease affecting wild and domestic pigs, characterised by severe haemorrhagic symptoms and high mortality rates. Originally confined to Sub-Saharan Africa, ASF virus genotype II has spread to Europe since 2014, mainly affecting Eastern Europe, and progressing through wild boar migrations and human action. In January 2022, the first case of ASF, due to genotype II, was reported in North-western Italy, in a wild boar carcass. Thereafter, numerous positive wild boars were identified, indicating an expanding wild epidemic, severely threatening Italian pig farming and trade. This study focused on the mapping of the suitable habitats for wild boars and their potential dispersal corridors in Northern Italy, using species distribution models and landscape connectivity analysis. The resulting maps identified areas with higher likelihood of wild boar presence, highlighting their preferential pathways crossing Northern Italy. The distribution of ASF positive wild boars along the major corridors predicted by the model suggests the obtained maps as valuable support to decision-makers to improve ASF surveillance and carcass early detection, aiming for eradication. The applied framework can be easily replicated in other regions and countries.

Benefits and costs of measures to tackle the outbreak of African swine fever in Sweden

A common rule in many countries for mitigating the damage caused by African swine fever (ASF) is to eradicate the virus at the outbreak in order to prevent its dispersal and the associated social costs of depopulating infected domestic pigs. The economic performance of this practice, as measured by five different evaluation criteria (net present value, benefit-cost ratio, rate of return, internal rate of return, and payback time), depends on the type of control cost and the spatial and dynamic allocation of benefits, i.e. avoided losses from infected domestic pig farms. The present paper calculates the direct and indirect costs of immediate control measures during an ASF outbreak in wild boars in Mid Sweden. The direct costs include expenses incurred for surveillance, laboratory tests, depopulation of wild boar etc., while the indirect costs are borne by firms and people in the area in relation to movement restrictions. The calculations showed that the total cost of control measures amounted to 28 million euros, with indirect costs making up 40 % of this figure. The benefits were greatly dependent on the speed of ASF dispersal and assumptions about pig farmers' investment responses, which implied large variations in each of the five evaluation criteria.

Comparing efficiencies of population control methods for responding to introductions of transboundary animal diseases in wild pigs

Introductions of transboundary animal diseases (TADs) into free-ranging wildlife can be difficult to control and devastating for domestic livestock trade. Combating a new TAD introduction in wildlife with an emergency response requires quickly limiting spread of the disease by intensely removing wild animals within a contiguous area. In the case of African swine fever virus (ASFv) in wild pigs (Sus scrofa), which has been spreading in many regions of the world, there is little information on the time- and cost-efficiency of methods for intensively and consistently culling wild pigs and recovering carcasses in an emergency response scenario. We compared the efficiencies of aerial operations, trapping, experimental toxic baiting, and ground shooting in northcentral Texas, USA during two months in 2023. Culling and recovering carcasses of wild pigs averaged a rate of 0.15 wild pigs/person hour and cost an average of $233.04/wild pig ($USD 2023) across all four methods. Aerial operations required the greatest initial investment but subsequently was the most time- and cost-efficient, costing an average of $7266 to reduce the population by a standard measure of 10 %, including recovering carcasses. Aerial operations required a ground crew of ∼7 people/helicopter to recover carcasses. Costs for reducing the population of wild pigs using trapping were similar, although took 13.5 times longer to accomplish. In cases where carcass recovery and disposal are needed (e.g., response to ASFv), a benefit of trapping was immediate carcass recovery. Toxic baiting was less efficient because both culling and carcass recovery required substantial time. We culled very few wild pigs with ground shooting in this landscape. Our results provide insight on the efficiencies of each removal method. Strategically combining removal methods may increase overall efficiency. Overall, our findings inform the preparation of resources, personnel needs, and deployment readiness for TAD responses involving wild pigs.

Use of Chemical Tracers in Sus scrofa Population Studies-A Scoping Review

A highly invasive species, free-ranging Sus scrofa often negatively impact the ecosystem and are capable of spreading a number of impactful pathogens to domestic livestock. Measures taken to ameliorate these impacts and/or control population size are based on the delivery of oral baits containing bioactive chemicals or vaccines, e.g., classical swine fever vaccine. The efficacy of these methods depends on the rate at which inoculated baits are consumed by the pigs. Rhodamine B, tetracycline, and iophenoxic acid are commonly used to quantitate bait uptake in free-ranging pig population studies. All three are effective in this application but differ in fundamental characteristics. When used as a tracer, the effective dose of rhodamine B was established at 15 mg/kg to ensure a 12-week window of detection based on evaluation of hair samples using fluorescent microscopy. Tetracyclines are likewise effective tracers in free-ranging pigs, but the process of detection is highly invasive, i.e., requires euthanasia, and extraction of bone or teeth, followed by examination by fluorescence microscopy. Iophenoxic acid and its derivatives also highly suitable tracers and may be detected in serum for ≥9 months after exposure. Notably tracers used in free-ranging pigs are not suitable for behavioral studies in farm-raised pigs either because the detection method is highly invasive (tetracyclines) or because they are unapproved for use in meat destined for human consumption.

Phylogenetic analyses and antigenic characterization of foot-and-mouth disease virus PanAsia lineage circulating in China between 1999 and 2023

Foot-and-mouth disease (FMD) is one of the most important transboundary animal diseases caused by foot-and-mouth disease virus (FMDV), leading to significant economic losses worldwide. The first report of PanAsia lineage of FMDV in China was in 1999. Since 2011, 18 outbreaks attributed to PanAsia lineage viruses have been reported across 7 provinces or municipality in China. Phylogenetic analysis indicated that these PanAsia strains were clustered into three distinct clades (clade 1, clade 2, and clade 3), with nucleotide homology ranging from 91.4% to 100%. The outbreaks of FMD caused by clade 1 strains occurred around 1999 when this lineage was prevalent globally. Clade 2 strains dominated from 2011 to 2013, while clade 3 strains were prevalent during 2018-2019, sharing only 93% homology with clade 2 strains and 91% with clade 1 strains. Tracing analysis showed that these outbreaks represented 3 distinct introductions of PanAsia viruses into China. Virus neutralization tests (VNT) have demonstrated that current commercial vaccines are effective to protect susceptible animals against these strains (r1 ​> ​0.3). However, the growing demand for livestock has promoted animal movement and encouraged the exchange of products, services, and materials between countries, thereby heightening the risk of exotic strain incursions. Therefore, it is imperative to reinforce border controls and limit animal movements among various Asian countries continually to reduce the risk of new transboundary diseases, such as FMD incursion. Additionally, PanAsia-2 strains need to be taken seriously to prevent its incursions, and the relevant vaccines against PanAsia-2 strains need to be stockpiled in preparation for any possible incursion.

Boar semen cryopreservation: State of the art, and international trade vision

Biosecurity is a major concern in the global pig production. The separation in time of semen collection, processing and insemination in the pig farm is a few days for chilled semen but it can be indefinite when using cryopreserved semen. Field fertility results of boar cryopreserved semen are close to chilled semen, which makes it a valuable resource for the establishment of semen genebanks, long-distance semen trade, and the implementation of other technologies such as the sex-sorted semen. But cryopreserved semen is far from being routine in pig farms. The most recent research efforts to facilitate its implementation include the use of additives before freezing, or in the thawing extender. Long-term preserved semen trade is a biosecurity challenge. To harmonize international trade of germplasm, the World Organization of Animal Health (WOAH) established a regulatory framework for all member countries. The present paper aims to review the latest advances of boar semen cryopreservation with special focus on the benefits of its inclusion as a routine tool in the pig industry. We also review recently reported field fertility results of cryopreserved semen, its international trade compared to chilled semen, and the regulatory framework involved. Boar cryopreserved semen is a valuable tool to control biosecurity risk, implement other technologies, and facilitate international trade. Research already demonstrated good field fertility results, but it still represents less than 0.1 % of the international trade. As boar cryopreserved semen gets closer to implementation, the correspondent authorities are reviewing the trade rules.

Analysis of the swine movement network in Mexico: A perspective for disease prevention and control

Pig farming in Mexico is critical to the economy and food supply. Mexico has achieved advancements in swine health and established an electronic database that records swine movements (Sistema Nacional de Avisos de Movilización, SNAM). In this study, we characterized swine movement patterns in México between 2017 and 2019 to identify specific areas and periods that require concentrated efforts for effective epidemiological surveillance and disease control. We employed a Social Network Analysis (SNA) methodology to comprehensively describe and analyze the intricate patterns of pig movement. In addition, we sought to integrate swine population density into the analysis. We used metrics to characterize the network structure and identify the most critical nodes in the movement network. Cohesion metrics were used to identify commercial communities characterized by a high level of interconnectivity in swine movements between groups of nodes. Of a cumulative count of 662,255 pig shipments, 95.9% were attributed to slaughterhouse shipments. We observed that 54% of all Mexican municipalities were part of the network; however, the density of the movement network was less than 0.14%. We identified four Swine Production Centers in Mexico with high interconnectivity in the movement network. We detected moderate positive correlations (ρ ≥0.4 and <0.6, p < 0.001) between node metrics and swine population indicators, whereas the number of commercial swine facilities showed weak correlations with the node metrics. We identified six large, geographically clustered commercial communities that aligned with the Swine Production Centers. This study provides a comprehensive overview of swine movement patterns in Mexico and their close association with swine production centers, which play a dual role as producers and traders within the swine industry of Mexico. Our research offers valuable insights for policymakers in developing disease prevention and control strategies.

Agricultural and Ecological Resources Safeguarded by the Prevention of Wild Pig Population Expansion

Wild pigs (Sus scrofa) are one of the most destructive invasive species in the US, known for causing extensive damage to agricultural commodities, natural resources, and property, and for transmitting diseases to livestock. Following the establishment of the National Feral Swine Damage Management Program (NFSDMP) in 2014, the expansion of wild pig populations has been successfully slowed. This paper combines two modeling approaches across eight separate models to characterize the expansion of wild pig populations in the absence of intervention by the NFSDMP and forecasts the value of a subset of resources safeguarded from the threat of wild pigs. The results indicate that if wild pigs had continued spreading at pre-program levels, they would have spread extensively across the US, with significant geographic variation across modeling scenarios. Further, by averting the threat of wild pigs, a substantial amount of crops, land, property, and livestock was safeguarded by the NFSDMP. Cumulatively, between 2014 and 2021, wild pig populations were prevented from spreading to an average of 724 counties and an average of USD 40.2 billion in field crops, pasture, grasses, and hay was safeguarded. The results demonstrate that intervention by the NFSDMP has delivered significant ecological and economic benefits that were not previously known.

Economics of reducing response time to foreign-animal disease in the United States with point-of-care diagnostic tests

BACKGROUND

As low probability events, United States producers, value chain actors, and veterinary services (VS) have limited experience with identifying foreign animal disease (FAD), which can allow FADs to spread undetected. Point-of-care (POC) diagnostic testing may help reduce the time from detecting an initial suspect case to implementing actionable interventions compared to the current approach of only using laboratory diagnostic testing for disease diagnosis and confirmation. To evaluate the value of the reduced response time, we compare the associated costs between the two diagnostic approaches while accounting for the uncertainty surrounding the size of a FAD event.

METHODS

We apply a state-contingent approach (SCA) to model the uncertainty surrounding a FAD through alternative events, where the event defines the scale of outbreak size and its duration. We apply this approach within a cost-benefit framework (CBA) to determine the economic value from the two testing investment strategies to help explain the policymaker's response (and costs) to alternative FAD events while also considering the cost impacts on the producers from each event.

RESULTS

Compared to the current laboratory strategy, a POC strategy that reduces response time by 0.5-days (swine, cattle scenarios) and 1.5-days (poultry scenario) may provide cost-saving to both producers and public response efforts. The benefit-cost analysis further suggests that despite the higher fixed costs to adopt the POC strategy, the swine and cattle sectors may benefit while the benefits may not be as pronounced in the poultry sector.

DISCUSSION

POC testing that can reduce the time between detection and response during a FAD event may be a sound strategy for public expenditure and provide cost-savings for producers, especially when minimal fixed costs are incurred. However, to fully determine the value of POC testing, the consequences (costs) associated with potential actions if something goes wrong, (e.g. false positive results), should be considered in future studies.

Assessment of the Safety Profile of Chimeric Marker Vaccine against Classical Swine Fever: Reversion to Virulence Study

Chimeric marker vaccine candidates, vGPE-/PAPeV Erns and vGPE-/PhoPeV Erns, have been generated and their efficacy and capability to differentiate infected from vaccinated animals were confirmed in previous studies. The safety profile of the two chimeric marker vaccine candidates, particularly in the potential reversion to virulence, was evaluated. Each virus was administered to pigs with a dose equivalent to the vaccination dose, and pooled tonsil homogenates were subsequently inoculated into further pigs. Chimeric virus vGPE-/PAPeV Erns displayed the most substantial attenuation, achieving this within only two passages, whereas vGPE-/PhoPeV Erns was detectable until the third passage and disappeared entirely by the fourth passage. The vGPE- strain, assessed alongside, consistently exhibited stable virus recovery across each passage without any signs of increased virulence in pigs. In vitro assays revealed that the type I interferon-inducing capacity of vGPE-/PAPeV Erns was significantly higher than that of vGPE-/PhoPeV Erns and vGPE-. In conclusion, the safety profile of the two chimeric marker vaccine candidates was affirmed. Further research is essential to ensure the stability of their attenuation and safety in diverse pig populations.

Assessing and comparing disease prevention knowledge, attitudes, and practices among veterinarians in Illinois, United States of America

Veterinarians play an essential role in safeguarding and promoting animal and human health by timely reporting of notifiable diseases to animal and public health agencies and by educating animal owners on effective disease prevention measures. Moreover, clinical veterinarians can prevent the transmission and spread of zoonotic diseases by adopting effective biosecurity practices in their clinics. An online questionnaire was administered between October and November 2021 to veterinarians registered with the Illinois State Veterinary Medical Association. Veterinarians were surveyed on their disease risk perception, biosecurity practices, and disease reporting knowledge. In total, 104 veterinarians (64 % females and 46 % males) completed the questionnaire, of whom 88 % were veterinarians working in clinical practice (88 % companion animals and 12 % bovine or swine), while 12 % were employed in non-clinical settings. The disease-reporting knowledge score was higher for veterinarians with biosecurity training (IRR: 1.35; 95 % CI: 1.47-1.75). Compared to large animal veterinarians, companion animal veterinarians had lower odds of having biosecurity training (OR=0.68; 95 % CI=0.02-0.28) and were less familiar with current biosecurity guidelines (OR=0.12; 95 % CI = 0.03-0.51). Veterinarians familiar with biosecurity guidelines had a higher probability (OR=4.4; 95 % CI: 1.21-16.28) of perceiving biosecurity practices as practical while working with animals. Conversely, veterinarians who perceived that they could transmit diseases to animals had lower odds (OR: 0.42; 95 % CI: 0.20-0.91) of wearing protective clothing while dealing with confirmed cases of zoonotic diseases. Based on our study results, a gap in disease-reporting knowledge was identified among companion animal veterinarians. Biosecurity training improved the disease-reporting knowledge of veterinarians, suggesting that providing continuing education for veterinarians would be beneficial to disease reporting. A disconnect between disease risk perception and biosecurity practices was identified and further studies are needed to understand this discrepancy to design effective education programs.

Deciphering the epidemiological dynamics: Toxoplasma gondii seroprevalence in mainland China's food animals, 2010-2023

Background

Toxoplasma gondii (T. gondii) is a significant protozoan pathogen among food animals. Despite the threat to public health by T. gondii infections, there's limited understanding of its seroprevalence and trends in food animals across mainland China. This study aimed to estimate the seroprevalence of T. gondii infections among swine, sheep, goats, chickens, and cattle in mainland China from 2010 to 2023.

Methods

We searched cross-sectional studies published between 2010 and 2023 that reported the prevalence of T. gondii in food animals from databases including PubMed, Embase, Web of Science, China Biology Medicine Disc (CBM), China National Knowledge Infrastructure (CNKI), Wanfang data, and the China Science and Technology Journal Database (CQVIP). We performed subgroup analyses to explore the impact of different factors on the seroprevalence of T. gondii. Pooled estimates of T. gondii seroprevalence were calculated with a random-effects model.

Results

An analysis of 184 studies involving 211985 animals revealed a T. gondii overall seroprevalence of 15.3% (95% CI: 13.1-17.8). Although the seroprevalence of food animals across mainland China was relatively stable from 2010 to 2023, notable variations were observed across different animal types and regions (P < 0.01), along with changes in geographical distribution. Sample type, detection method, animal age, and history of abortion were identified as key risk factors for T. gondii seroprevalence.

Conclusion

The study conducted a meta-analysis on the seroprevalence of T. gondii in mainland China's Food Animals from 2010 to 2023, and identified key risk factors. These findings advance our understanding of T. gondii infection dynamics, offering critical insights for developing control strategies and guiding public health policies.

Inactivation of highly transmissible livestock and avian viruses including influenza A and Newcastle disease virus for molecular diagnostics

There is a critical need for an inactivation method that completely inactivates pathogens at the time of sample collection while maintaining the nucleic acid quality required for diagnostic PCR testing. This inactivation method is required to alleviate concerns about transmission potential, minimize shipping complications and cost, and enable testing in lower containment laboratories, thereby enhancing disease diagnostics through improved turn-around time. This study evaluated a panel of 10 surrogate viruses that represent highly pathogenic animal diseases. These results showed that a commercial PrimeStore® molecular transport media (PSMTM) completely inactivated all viruses tested by >99.99%, as determined by infectivity and serial passage assays. However, the detection of viral nucleic acid by qRT-PCR was comparable in PSMTM and control-treated conditions. These results were consistent when viruses were evaluated in the presence of biological material such as sera and cloacal swabs to mimic diagnostic sample conditions for non-avian and avian viruses, respectively. The results of this study may be utilized by diagnostic testing laboratories for highly pathogenic agents affecting animal and human populations. These results may be used to revise guidance for select agent diagnostic testing and the shipment of infectious substances.

A survey of knowledge, attitudes, and practices of veterinary professionals regarding ticks and tick-borne diseases: Insights from Ohio, USA

Globally, ticks are becoming more problematic as agricultural pests and vectors of tick-borne diseases (TBDs), many of which are shared between animals and people. Veterinary professionals, including veterinarians and non-veterinarians, are considered a vulnerable group through occupational exposure. To inform educational interventions at the intrapersonal level, a common approach is to first assess knowledge, attitudes, and practices (KAP) of target populations. Thus, our objective was to assess KAP of veterinary professionals in Ohio, a state faced with expanding and invading ticks of medical and veterinary concern. Using a convenience sample, we surveyed 178 veterinary professionals across Ohio with an electronic questionnaire that covered knowledge, attitudes, practices, exposures, demography, education, and surveillance regarding ticks and TBDs. We found that veterinary professionals had cautionary attitudes towards ticks and TBDs and practiced prevention for themselves and their patients, even when tick exposures were infrequently reported. However, veterinary professionals significantly lacked in knowledge regarding tick biology and local TBD epidemiology. Furthermore, we found that knowledge regarding tick biology and attitudes towards ticks and TBDs did not associate with practices. Instead, we found that veterinarian status and routine tick checks of patients were associated with frequent discussions of tick prevention with clients. Our findings emphasize that most tick exposures of veterinary professionals are occupational, and thus prevention should start at the workplace. Cultivating knowledge of veterinary professionals regarding tick biology and local TBD epidemiology may lead to greater motivation and confidence with identifying ticks and testing for TBDs, which may also increase the diagnostic capacity of veterinary professionals for tick and TBD surveillance. Because veterinary professionals typically interact with both animals and their owners, improving their KAP regarding ticks and TBDs, can in turn promote animal, human, and environmental health within a "One Health" context.

Describing the experience of livestock producers from Ohio, USA with ticks and associated diseases

BACKGROUND

As tick ranges expand across North America, the risk of tick bites and tick-borne diseases (TBDs, i.e. diseases or syndromes associated with ticks) rises for humans and animals, making prevention critical. Several U.S. studies have examined knowledge, attitudes, and practices regarding ticks and TBDs for various cohorts of people. However, among occupational groups with high exposure risk from ticks and TBDs are livestock producers, of which we know little about. To help address this gap, an electronic questionnaire was distributed to livestock producers in Ohio, U.S, a state with a robust agricultural sector.

METHODS

We generated descriptive statistics and conducted a multiple correspondence analysis followed by hierarchical clustering on principal components to identify producers with similar response profiles.

RESULTS

Responses from 57 producers showed that most (52.6%) think the American dog tick (Dermacentor variabilis) is found in Ohio but are unsure about other species. Although several TBDs are present in Ohio, most (> 50%) producers were unsure or unaware of their presence. Interestingly, most (54.4%) thought ticks pose major health risks for their livestock but fewer (49.1%) thought the same for humans. Regardless, most producers did employ at least one prevention method for themselves (96.5%) and their animals (82.5%). Cluster analysis (n = 48) identified three groups: the largest (n = 21) was considered "aware and cautious" consisting primarily of farm owners. The others generally practiced less prevention and consisted primarily of farm employees.

CONCLUSIONS

Our findings indicate that producers in Ohio practice prevention for themselves and their livestock, but demonstrate gaps in knowledge (e.g., TBD occurrence) and attitudes (e.g., health risks) that could be addressed via educational formats we found producers preferred (e.g., extension materials), to encourage informed prevention. This is especially important for farm employees that may practice less prevention because of lower awareness. Our study can guide others in regions faced with similar tick and TBD risks to protect occupational and livestock health.

Emergent Molecular Techniques Applied to the Detection of Porcine Viruses

Molecular diagnostic tests have evolved very rapidly in the field of human health, especially with the arrival of the recent pandemic caused by the SARS-CoV-2 virus. However, the animal sector is constantly neglected, even though accurate detection by molecular tools could represent economic advantages by preventing the spread of viruses. In this regard, the swine industry is of great interest. The main viruses that affect the swine industry are described in this review, including African swine fever virus (ASFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), and porcine circovirus (PCV), which have been effectively detected by different molecular tools in recent times. Here, we describe the rationale of molecular techniques such as multiplex PCR, isothermal methods (LAMP, NASBA, RPA, and PSR) and novel methods such as CRISPR-Cas and microfluidics platforms. Successful molecular diagnostic developments are presented by highlighting their most important findings. Finally, we describe the barriers that hinder the large-scale development of affordable, accessible, rapid, and easy-to-use molecular diagnostic tests. The evolution of diagnostic techniques is critical to prevent the spread of viruses and the development of viral reservoirs in the swine industry that impact the possible development of future pandemics and the world economy.

Livestock health and disease economics: a scoping review of selected literature

Animal diseases in production and subsistence environments have the potential to negatively affect consumers, producers, and economies as a whole. A growing global demand for animal sourced food requires safe and efficient production systems. Understanding the burden of animal disease and the distribution of burden throughout a value chain informs policy that promotes safe consumption and efficient markets, as well as providing more effective pathways for investment. This paper surveys existing knowledge on the burden of animal disease across economic categories of production, prevention and treatment, animal welfare, and trade and regulation. Our scoping review covers 192 papers across peer-reviewed journals and reports published by organizations. We find there exists a gap in knowledge in evaluating what the global burdens of animal diseases are and how these burdens are distributed in value chains. We also point to a need for creating an analytical framework based on established methods that guides future evaluation of animal disease burden, which will provide improved access to information on animal health impacts.

Assessing mammal fence crossing and local fence management in relation to classical swine fever spread in Japan

Infectious diseases at the wildlife-livestock-human interface have become a crucial issue, and evidence-based measures are growing increasingly important. One countermeasure against animal diseases in wildlife is using fencing to contain and reduce disease spread and transmission rates between wild populations; however, quantitative assessments on fencing are rare. Moreover, existing research on fencing has highlighted knowledge gaps on the social and ecological aspects relevant to the use and design of fences. To control the spread of classical swine fever, fences were installed from the east to west in Gifu Prefecture, Japan, by March 2019, with the aim of restricting wild boar movement. To clarify the process of installation and maintenance of the fences, we conducted semi-structured interviews with prefectural government officers in Gifu Prefecture. Additionally, we installed infrared-triggered cameras at fence locations with and without gaps to evaluate the fence permeability of mammals. We used a generalized linear mixed model to evaluate the relationship between the presence of gaps and the relative abundance and permeability of each mammal. Our findings showed that the occurrence of gaps was inevitable during the installation and management of wide-area perimeter fence in Japan, partly because of social factors. For example, fences could not be installed on roads that were frequently used by residents and were not adequately maintained owing to budgetary reasons in some cases. Analysis of footage from the infrared-triggered cameras revealed that several mammal species crossed the fence at gaps and even had the ability to cross the gapless parts of the fences. Wild boars crossed through the gaps regularly. It is possible that Sika deer, Japanese serows, raccoons, Japanese badgers, raccoon dogs, Japanese macaques, and feral cats crossed through fence gaps because their relative abundance was high at gap locations. In contrast, Japanese hares slipped through the fence mesh rather than crossing through the gaps. In conclusion, we suggest that coordination and collaboration among related parties, a sufficient supply of fence materials, and securing a budget for fence maintenance are important for fence installation and maintenance. Furthermore, as fence gaps are inevitable, technical development of countermeasures for these gaps could be effective.

Assessing and improving on-farm biosecurity knowledge and practices among swine producers and veterinarians through online surveys and an educational website in Illinois, United States

There is a growing risk to the health and productivity of the Illinois and United States swine population from foreign and endemic infectious diseases. Effective on-farm biosecurity practices play a pivotal role in preventing these high-consequence pathogens from affecting swine farms. Veterinarians are essential in providing disease prevention advice to swine producers that can help them implement effective biosecurity practices on their farms. Our descriptive study objectives were to assess Illinois swine producers' and veterinarians' biosecurity perception, knowledge, and practices to identify knowledge gaps and address these by developing an online educational website. We developed two independent online questionnaires using Qualtrics^XM software. Swine producer members of the Illinois Pork Producers Association and veterinarians registered with the Illinois State Veterinary Medical Association were contacted via e-mail through their associations and asked to complete an online survey. In total, 13 swine producers across 9 Illinois counties operating 82 farms (8 managed single farms and 5 managed multiple farms) responded to the swine producer survey. Despite some biosecurity awareness among swine producers, the need for a biosecurity-related outreach program was evident. Among the 7 swine veterinarian responders, 5 predominantly treated swine (oversaw an average of 21.6 farms), and 2 were mixed animal practitioners. The swine veterinarian survey showed a disconnect between their biosecurity perception and practices. We developed a biosecurity educational website and used Google Analytics to collect website traffic and user data. The 4 months of data showed good coverage that included the highest proportion of users from the Midwest and North Carolina, the largest swine-production regions in the US, and China and Canada, the leading producers of swine worldwide. The most accessed webpage was the resources page, and the swine diseases page had the highest engagement time. Our study highlights the effectiveness of combining online surveys with an educational website to assess and improve the biosecurity knowledge of swine producers and veterinarians that can be applied to assess and improve the biosecurity knowledge and practices of other livestock farmers.

Efficient detection of African Swine Fever Virus using minimal equipment through a LAMP PCR method

African swine fever virus (ASFV) currently represents the biggest threat to the porcine industry worldwide, with high economic impact and severe animal health and welfare concerns. Outbreaks have occurred in Europe and Asia since ASFV was reintroduced into the continent in 2007 and, in 2021, ASFV was detected in the Caribbean, raising alarm about the reemergence of the virus in the Americas. Given the lack of vaccines against ASFV, control of the virus relies on molecular surveillance, which can be delayed due to the need for sample shipment to specialized laboratories. Isothermal PCR techniques, such as LAMP, have become increasingly attractive as point-of-care diagnostic tools given the minimal material expense, equipment, and training required. The present study aimed to develop a LAMP assay for the detection of ASFV. Four LAMP primer sets were designed, based on a consensus sequence for the ASFV p72 gene, and were tested using a synthetic plasmid containing the cloned ASFV p72 target gene as a positive control. Two primer sets, were selected for further validation, given their very short time for amplification. Both primer sets showed thermal stability, amplifying the ASFV DNA at temperatures between 60-70°C and proved to have an analytical limit of detection as low as one ASFV-plasmid DNA copy/µL, using both fluorometric and colorimetric methods. The selected primers did not yield false positive or cross reactive results with other common swine pathogens, showing high specificity. Testing of DNA-spiked samples showed that LAMP amplification was not affected by the nature of the matrices, including oral fluids, tonsils, blood, or rectal swabs. The primer sets were able to detect the two more prevalent ASFV genotypes in the field. Taken together, the results show that ASFV-LAMP-BG2 and ASFV-LAMP-BG3 would be a useful tool for rapid, highly sensitive on-site diagnostic testing.

Advances in the differential molecular diagnosis of vesicular disease pathogens in swine

Foot-and-mouth disease virus (FMDV), Senecavirus A (SVA) and swine vesicular disease virus (SVDV) are members of the family Picornaviridae, which can cause similar symptoms - vesicular lesions in the tissues of the mouth, nose, feet, skin and mucous membrane of animals. Rapid and accurate diagnosis of these viruses allows for control measures to prevent the spread of these diseases. Reverse transcription-polymerase chain reaction (RT-PCR) and real-time RT-PCR are traditional and reliable methods for pathogen detection, while their amplification reaction requires a thermocycler. Isothermal amplification methods including loop-mediated isothermal amplification and recombinase polymerase amplification developed in recent years are simple, rapid and do not require specialized equipment, allowing for point of care diagnostics. Luminex technology allows for simultaneous detection of multiple pathogens. CRISPR-Cas diagnostic systems also emerging nucleic acid detection technologies which are very sensitivity and specificity. In this paper, various nucleic acid detection methods aimed at vesicular disease pathogens in swine (including FMDV, SVA and SVDV) are summarized.

Development and Validation of a Bioinformatic Workflow for the Rapid Detection of Viruses in Biosecurity

The field of biosecurity has greatly benefited from the widespread adoption of high-throughput sequencing technologies, for its ability to deeply query plant and animal samples for pathogens for which no tests exist. However, the bioinformatics analysis tools designed for rapid analysis of these sequencing datasets are not developed with this application in mind, limiting the ability of diagnosticians to standardise their workflows using published tool kits. We sought to assess previously published bioinformatic tools for their ability to identify plant- and animal-infecting viruses while distinguishing from the host genetic material. We discovered that many of the current generation of virus-detection pipelines are not adequate for this task, being outperformed by more generic classification tools. We created synthetic MinION and HiSeq libraries simulating plant and animal infections of economically important viruses and assessed a series of tools for their suitability for rapid and accurate detection of infection, and further tested the top performing tools against the VIROMOCK Challenge dataset to ensure that our findings were reproducible when compared with international standards. Our work demonstrated that several methods provide sensitive and specific detection of agriculturally important viruses in a timely manner and provides a key piece of ground truthing for method development in this space.

Modelling and assessing additional transmission routes for porcine reproductive and respiratory syndrome virus: Vehicle movements and feed ingredients

Accounting for multiple modes of livestock disease dissemination in epidemiological models remains a challenge. We developed and calibrated a mathematical model for transmission of porcine reproductive and respiratory syndrome virus (PRRSV), tailored to fit nine modes of between-farm transmission pathways including: farm-to-farm proximity (local transmission), contact network of batches of pigs transferred between farms (pig movements), re-break probabilities for farms with previous PRRSV outbreaks, with the addition of four different contact networks of transportation vehicles (vehicles to transport pigs to farms, pigs to markets, feed and crew) and the amount of animal by-products within feed ingredients (e.g., animal fat or meat and bone meal). The model was calibrated on weekly PRRSV outbreaks data. We assessed the role of each transmission pathway considering the dynamics of specific types of production (i.e., sow, nursery). Although our results estimated that the networks formed by transportation vehicles were more densely connected than the network of pigs transported between farms, pig movements and farm proximity were the main PRRSV transmission routes regardless of farm types. Among the four vehicle networks, vehicles transporting pigs to farms explained a large proportion of infections, sow = 20.9%; nursery = 15%; and finisher = 20.6%. The animal by-products showed a limited association with PRRSV outbreaks through descriptive analysis, and our model results showed that the contribution of animal fat contributed only 2.5% and meat and bone meal only .03% of the infected sow farms. Our work demonstrated the contribution of multiple routes of PRRSV dissemination, which has not been deeply explored before. It also provides strong evidence to support the need for cautious, measured PRRSV control strategies for transportation vehicles and further research for feed by-products modelling. Finally, this study provides valuable information and opportunities for the swine industry to focus effort on the most relevant modes of PRRSV between-farm transmission.

Adaptive risk-based targeted surveillance for foreign animal diseases at the wildlife-livestock interface

Animal disease surveillance is an important component of the national veterinary infrastructure to protect animal agriculture and facilitates identification of foreign animal disease (FAD) introduction. Once introduced, pathogens shared among domestic and wild animals are especially challenging to manage due to the complex ecology of spillover and spillback. Thus, early identification of FAD in wildlife is critical to minimize outbreak severity and potential impacts on animal agriculture as well as potential impacts on wildlife and biodiversity. As a result, national surveillance and monitoring programs that include wildlife are becoming increasingly common. Designing surveillance systems in wildlife or, more importantly, at the interface of wildlife and domestic animals, is especially challenging because of the frequent lack of ecological and epidemiological data for wildlife species and technical challenges associated with a lack of non-invasive methodologies. To meet the increasing need for targeted FAD surveillance and to address gaps in existing wildlife surveillance systems, we developed an adaptive risk-based targeted surveillance approach that accounts for risks in source and recipient host populations. The approach is flexible, accounts for changing disease risks through time, can be scaled from local to national extents and permits the inclusion of quantitative data or when information is limited to expert opinion. We apply this adaptive risk-based surveillance framework to prioritize areas for surveillance in wild pigs in the United States with the objective of early detection of three diseases: classical swine fever, African swine fever and foot-and-mouth disease. We discuss our surveillance framework, its application to wild pigs and discuss the utility of this framework for surveillance of other host species and diseases.

Evaluation of the economic impact of classical and African swine fever epidemics using OutCosT, a new spreadsheet-based tool

African swine fever (ASF) and classical swine fever (CSF) are two major transboundary animal diseases of swine with important socioeconomic consequences at farm, subnational and national level. The objective of this study was to evaluate the direct cost of outbreaks and their control at country/regional level in four countries: namely CSF in Colombia in 2015-2016, the retrospective cost of ASF in the Philippines in 2019 and in a province of Vietnam in 2020 and a hypothetical ASF scenario in one region in North Macedonia, using the newly developed Outbreak Costing Tool (OutCosT). The tool calculates the costs of 106 different items, broken down by up to four types of farms, and by who assumes the cost (whether veterinary services, farmers or other stakeholders). The total cost of CSF in Colombia was US$ 3.8 million, of which 88% represented the cost of the vaccination campaign. For ASF, there were wide differences between countries: US$ 8,26,911 in Lao Cai (Vietnam), US$ 33,19,666 in North Macedonia and over US$ 58 million in the Philippines. While in the Philippines and Vietnam, 96-98% of the cost occurred in the affected farms, the highest expenditure in North Macedonia scenario was the movement control of the neighbouring and at-risk farms (77%). These important differences between countries depend on the spread of the disease, but also on the production systems affected and the measures applied. Apart from the financial cost, these diseases have other negative impacts, especially in the livelihoods of smallholder farms. The OutCosT tool also allows users to evaluate qualitatively other important aspects related to the epidemics, such as the impact on human health, the environment, animal welfare, socioeconomic vulnerability, trading and political response. OutCosT, which is a FAO corporate tool (available online at: https://www.fao.org/fileadmin/user_upload/faoweb/animal-health/OutCosT_PIG.xlsx), can be an important tool to support country authorities to rapidly respond to a swine disease outbreak by estimating the associated costs and for advocacy purposes to mobilize resources at national or international levels.

Reliability of water-based medium-expansion foam as a depopulation method for nursery pigs and cull sows

Animal disease preparedness plans including depopulation guidelines are paramount to prevent the spread of emerging infectious diseases but difficult to implement for swine under field conditions. However, water-based foam (WBF) is currently an approved and successfully deployed depopulation methodology in poultry. Therefore, the reliability of WBF as a depopulation method and the effectiveness and irreversibility of consciousness and consequential mortality in pigs of different ages was assessed across two trials. Trial 1 investigated the time to loss of consciousness and cessation of cardiac activity in nursery pigs (n = 72) at six different foam immersion time points (2.5, 5, 7.5, 10, 12.5 and 15 min) when placed in a 1.47 m³ (1.2 × 1.2 × 1.02 m, length × width × height) plastic bulk container. One pig per replicate was implanted with an ECG bio-logger. Irreversible loss of consciousness was observed after a 5-min immersion. The average (SD) time to development of a fatal arrhythmia from the initiation of the foam application was 7.3 min (1.82 s). Trial 2 aimed to validate the findings from Trial 1 in 75 larger cull sows across three replicates (n = 25). Sows were loaded into a 41-m³ sealed trailer (12.2 × 1.5 × 2.24 m), immersed in WBF and left undisturbed for 5 min post foam-filling completion. Six pigs in each replicate were implanted with an ECG bio-logger. A 5-min dwell time resulted in irreversible loss of consciousness and subsequent mortality in all cull sows. The average time (SD) to cessation of movement and fatal arrhythmia post foam-filling completion was 2.2 min (34.8 s) and 8.7 min (138.0 s), respectively. While a 5-min immersion in WBF induced irreversible loss of consciousness and death in both trials, a 7.5-min dwell time followed by observation for confirmation of death post WBF removal would be advisable for pigs of all sizes.

Optimizing response to an introduction of African swine fever in wild pigs

African swine fever virus (ASFv) is a virulent pathogen that threatens domestic swine industries globally and persists in wild boar populations in some countries. Persistence in wild boar can challenge elimination and prevent disease-free status, making it necessary to address wild swine in proactive response plans. In the U.S., invasive wild pigs are abundant and found across a wide range of ecological conditions that could drive different epidemiological dynamics among populations. Information on size of control areas required to rapidly eliminate ASFv in wild pigs and how this area should change with management constraints and local ecology are needed to optimize response planning. We developed a spatially-explicit disease transmission model contrasting wild pig movement and contact ecology in two ecosystems in southeastern U.S. We simulated ASFv spread and determined optimal response area (reported as radius of a circle) for eliminating ASFv rapidly over a range of detection times (when ASFv is detected relative to true date of introduction), culling capacities (proportion of wild pigs in the culling zone removed weekly), and wild pig densities. Large radii for response areas (14 km) were needed under most conditions but could be shortened with early detection (≤ 8 weeks) and high culling capacities (≥ 15% weekly). Under most conditions ASFv was eliminated in less than 22 weeks using optimal control radii, although ecological conditions with high rates of wild pig movement required higher culling capacities (≥ 10% weekly) for elimination within one year. Results highlight the importance of adjusting response plans based on local ecology and show wild pig movement is a better predictor of optimal response area than numbers of ASFv cases early in the outbreak trajectory. Our framework provides a tool for determining optimal control plans in different areas, guiding expectations of response impacts, and planning resources needed for rapid elimination. This article is protected by copyright. All rights reserved.

Analysis of Epidemiological and Economic Impact of Foot-and-Mouth Disease Outbreaks in Four District Areas in Thailand

Foot and mouth disease (FMD) is one of the most important infectious animal diseases impacting livestock production in Thailand. Despite a national vaccination program, FMD outbreaks are reported every year. We studied the epidemiological impacts of FMD outbreaks in four districts of Thailand between 2015 and 2016. Epidemiological data were collected from 193 FMD-affected dairy farms, 55 FMD-affected beef farms, and 25 FMD-affected pig farms. A significant difference in morbidity rates were observed between the dairy farms in the different areas, which could be explained by the differences in FMD outbreak management in each area. The morbidity rates in dairy and beef cattle also significantly differed between each animal age category, with the lowest morbidity rate observed in calves. Remarkably, vaccination was not significantly associated with the morbidity rate. In addition, the economic impact of FMD was calculated for 60 dairy farms in Muak Lek district. The economic losses were determined as the sum of milk production loss, mortality loss, additional labor costs, and veterinary service and medical costs, which averaged 56 USD per animal on the farm (ranging from 2 to 377 USD). Milk loss had the largest economic impact, although it varied substantially between farms. The farm size and outbreak duration were significantly associated with the total economic losses per farm. These results affirm the substantial epidemiological and economic impact of FMD on farms in Thailand, emphasizing the importance of FMD control.

Models to assess the risk of introduction of selected animal viral diseases through the importation of live animals as a key part of risk analysis

Introduction of an animal viral disease, especially a notifiable disease, into an importing country or region free from the disease may lead to serious epidemiological consequences and economic losses. Trade in live animals is historically considered one of the most important risk pathways. To estimate the magnitude of such risk, the likelihood of a virus’ entry into a country and the consequences of this event should be jointly evaluated. Depending on data availability, the urgency of the problem and the detail level of the objectives, a risk assessment may be conducted in a qualitative, semi-quantitative or quantitative way. The purpose of this review was firstly to provide a brief description of each step of the risk analysis process, with particular emphasis on the risk assessment component, and subsequently to supply examples of different approaches to the assessment of the risk of the introduction of selected animal viral diseases. Based on the reviewed models, the overall likelihood of introduction of particular diseases was generally estimated as low. The output risk value was strongly dependent on the duration of the silent phase of the epidemic in the country of origin. Other parameters with some bearing upon the risk derived from the epidemiological situation in the country of origin and the biosecurity or mitigation measures implemented in the country of destination. The investigated models are universal tools for conducting assessment of the risk of introduction of various animal diseases to any country. Their application may lead to timely implementation of appropriate measures for the prevention of the spread of a disease to another country or region.

Assessment of foot-and-mouth disease risk areas in mainland China based spatial multi-criteria decision analysis

Background

Foot-and-mouth disease (FMD) is a highly contagious viral disease of cloven-hoofed animals. As a transboundary animal disease, the prevention and control of FMD are important. This study was based on spatial multi-criteria decision analysis (MCDA) to assess FMD risk areas in mainland China. Ten risk factors were identified for constructing risk maps by scoring, and the analytic hierarchy process (AHP) was used to calculate the criteria weights of all factors. Different risk factors had different units and attributes, and fuzzy membership was used to standardize the risk factors. The weighted linear combination (WLC) and one-at-a-time (OAT) were used to obtain risk and uncertainty maps as well as to perform sensitivity analysis.

Results

Four major risk areas were identified in mainland China, including western (parts of Xinjiang and Tibet), southern (parts of Yunnan, Guizhou, Guangxi, Sichuan and Guangdong), northern (parts of Gansu, Ningxia and Inner Mongolia), and eastern (parts of Hebei, Henan, Anhui, Jiangsu and Shandong). Spring is the main season for FMD outbreaks. Risk areas were associated with the distance to previous outbreak points, grazing areas and cattle density. Receiver operating characteristic (ROC) analysis indicated that the risk map had good predictive power (AUC=0.8634).

Conclusions

These results can be used to delineate FMD risk areas in mainland China, and veterinary services can adopt the targeted preventive measures and control strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03084-5.

Unraveling the Contact Network Patterns between Commercial Turkey Operation in North Carolina and the Distribution of Salmonella Species

Salmonellosis originating from poultry poses a significant threat to human health. Surveillance within production is thus needed to minimize risk. The objectives of this work were to investigate the distribution of Salmonella spp. from a commercial turkey operation and describe the animal movement patterns to investigate the association between contact network structure and Salmonella infection status. Four years of routine growout farm samples along with data on facility location, time since barns were built, production style, and bird movement data were utilized. From all of the surveillance samples collected, Salmonella serotyping was performed on positive samples and results showed that the most represented groups were C1 (28.67%), B (24.37%) and C2 (17.13%). The serovar Infantis (26.44%) was the most highly represented, followed by Senftenberg (12.76%) and Albany (10.93%). Results illustrated the seasonality of Salmonella presence with a higher number of positive samples being collected in the second half of each calendar year. We also demonstrated that Salmonella was more likely to occur in samples from older farms compared to farms built more recently. The contact network connectivity was low, although a few highly connected farms were identified. Results of the contact network showed that the farms which tested positive for Salmonella were not clustered within the network, suggesting that even though Salmonella dissemination occurs via transferring infected birds, for this study case it is unlikely the most important route of transmission. In conclusion, this study identified seasonality of Salmonella with significantly more cases in the second half of each year and also uncovered the role of between-farm movement of birds as not a major mode of Salmonella transmission.

Comparison of Gaseous and Water-Based Medium-Expansion Foam Depopulation Methods in Cull Sows

Simple Summary

In the face of a swine health crisis, emerging zoonotic diseases or environmental catastrophe, the mass depopulation of swine may be required to prevent the additional spread of disease and to minimize animal pain or suffering. Due to the increasing risk of global disease outbreaks, the U.S. swine industry needs feasible guidelines in place in preparation for such events. Current American Veterinary Medical Association (AVMA) approved swine depopulation methods can be difficult to implement under field conditions. Emergency depopulation using inhalants such as carbon dioxide (CO₂) and nitrogen gas (N₂) or the use of aspirated foam agents have been approved and conducted in poultry in the US, but are not approved for use in other livestock. Our findings, using cull sows, demonstrate that although CO₂, N₂ and aspirated foam combinations successfully killed all the animals, CO₂ and aspirated foam did so in the shortest timeframe. In addition, the use of aspirated foam was as effective as CO₂ for sow depopulation while having potential operational advantages, such as no use of lethal gases and reduced risk of associated equipment failure.

Abstract

The U.S. swine industry is currently inadequately prepared to counteract the increasing threat of high-consequence diseases. Although approved and preferred depopulation guidelines exist, ventilation shutdown (VSD+) is currently the only method being deployed during a state of emergency to depopulate large swine populations. However, the permitted use of VSD+ during constrained circumstances has been criticized due to raised swine welfare concerns. The objective of this study was to investigate the effectiveness of carbon dioxide gas (CO₂), nitrogen gas (N₂), compressed air foam (CAF), compressed nitrogen foam (CAF-N₂) and aspirated foam (AF) during a 15-min dwell time on adult swine in an emergency depopulation situation. A small-scale trial using 12 sows per depopulation method showed the highest efficiency to induce cessation of movement for AF and CO₂ (186.0 ± 48 vs. 202.0 ± 41, s ± SD). The ease of implementation and safety favored AF for further investigation. A large-scale field study using AF to depopulate 134 sows in modified rendering trailers showed a mean fill time of 103.8 s (SD: 5.0 s) and cessation of movement of 128.0 s (SD: 18.6 s) post filling. All sows were confirmed dead post-treatment for both trials. The implementation of AF in modified rendering trailers may allow for a safe and reliable method that allows for the expedient and mobile depopulation of both small and large numbers of sows during an emergency.

Modelling the role of mortality-based response triggers on the effectiveness of African swine fever control strategies

African swine fever (ASF) is considered the most impactful transboundary swine disease. In the absence of effective vaccines, control strategies are heavily dependent on mass depopulation and shipment restrictions. Here, we developed a nested multiscale model for the transmission of ASF, combining a spatially explicit network model of animal shipments with a deterministic compartmental model for the dynamics of two ASF strains within 3 km × 3 km pixels in one Brazilian state. The model outcomes are epidemic duration, number of secondary infected farms and pigs, and distance of ASF spread. The model also shows the spatial distribution of ASF epidemics. We analyzed quarantine-based control interventions in the context of mortality trigger thresholds for the deployment of control strategies. The mean epidemic duration of a moderately virulent strain was 11.2 days, assuming the first infection is detected (best-case scenario), and 15.9 days when detection is triggered at 10% mortality. For a highly virulent strain, the epidemic duration was 6.5 days and 13.1 days, respectively. The distance from the source to infected locations and the spatial distribution was not dependent on strain virulence. Under the best-case scenario, we projected an average number of infected farms of 23.77 farms and 18.8 farms for the moderate and highly virulent strains, respectively. At 10% mortality-trigger, the predicted number of infected farms was on average 46.27 farms and 42.96 farms, respectively. We also demonstrated that the establishment of ring quarantine zones regardless of size (i.e. 5 km, 15 km) was outperformed by backward animal movement tracking. The proposed modelling framework provides an evaluation of ASF epidemic potential, providing a ranking of quarantine-based control strategies that could assist animal health authorities in planning the national preparedness and response plan.

African swine fever vaccine: Turning a dream into reality

African swine fever (ASF) is currently threatening the swine industry at a global level. The disease originated in Africa has spread to Europe, Asia and Oceania, since 2007, reaching a pandemic dimension. Currently, the spread of ASF is unstoppable and that the development of a safe and effective vaccine is urgently required. The objective of this paper is to review the vaccine candidates tested during the 20th and 21st centuries, to identify the strengths and weaknesses of these studies and to highlight what we should learn. Several strategies have been explored to date, some of which have shown positive and negative results. Inactivated preparations and subunit vaccines are not a viable option. The most promising strategy would appear to be live attenuated vaccines, because these vaccine candidates are able to induce variable percentages of protection against certain homologous and heterologous virus isolates. The number of studies on live attenuated vaccine candidates has steadily increased in the 21st century thanks to advances in molecular biology and an in-depth knowledge of ASF virus, which have allowed the development of vaccines based on deletion mutants. The deletion of virulence-related genes has proved to be a useful tool for attenuation, although attenuation does not always mean protection and even less, cross protection. Therefore, ASF vaccine development has proved to be one of the top priorities in ASF research. Efforts are still being made to fill the gaps in the knowledge regarding immune response, safety and cross protection, and these efforts will hopefully help to find a safe and effective vaccine that could be commercialised soon, thus making it possible to turn a dream into reality.

CRISPR/Cas12a-Based Versatile Method for Checking Quantitative Polymerase Chain Reaction Samples with Cycles of Threshold Values in the Gray Zone

Quantitative polymerase chain reaction (qPCR) is widely applied in foodborne pathogen detection and diagnosis. According to the cycles of threshold (Ct) values of qPCR testing, samples are judged as positive or negative. However, samples with Ct values in the gray zone are classified as "possibly positive" and required to be tested again. Repetitive qPCR may not eliminate the uncertain results but increase the workload of detection. CRISPR/Cas12a can specifically recognize the nucleic acid of the nM level and then indiscriminately slash the single-strand DNA with multiple turnovers. In this way, the detection signals can be greatly amplified. Here, we propose a CRISPR-based checking method to solve gray zone problems. After qPCR testing, the screening gray zone samples can be successfully checked by the CRISPR/Cas12a method. Furthermore, to conduct CRISPR reaction assay more conveniently and prevent possible aerosol contamination in the operational process, a gray zone checking cassette is designed. African swine fever virus (ASFV) is selected as an example to demonstrate the feasibility of the CRISPR-based checking method. Of 28 real swine blood samples, 6 ASFV qPCR gray zone samples are successfully checked. The CRISPR-based checking method provides a novel solution to eliminate gray zone sample problems with no additional effects on the PCR, which is operable and applicable in practical detection. The entire process can be completed within 10-15 min. This method will be a good supplementary and assistance for qPCR-based detection, especially in the diagnosis of diseases such as COVID-19.