Biology subjects

Machado, G.

Publications and source records attributed to Machado, G..

At least 19 recordsLinked to original sources

bioRxiv2025

Evaluation of porcine epidemic diarrhea virus RNA contamination on swine industry transportation vehicles

Porcine epidemic diarrhea virus (PEDV) is one of the most devastating pathogens of global swine health and welfare. It is well known that contaminated fomites and vehicle movements play an important role in farm-to-farm PEDV spread, but the efficacy of cleaning and disinfection (C&D) protocols on the reduction in dissemination risk via vehicles and trailers remains unclear. This study used swine industry data to determine how frequently vehicles and trailers were contaminated with PEDV RNA before and after C&D. Environmental RNA samples were collected at three eastern North Carolina C&D sites from four different vehicle types: crew trucks, feed trucks, pigs-to-farm trucks and trailers, and pigs-to-market trucks and trailers. A total of 2,004 samples were collected from truck cabins, trailers, and tires before and after C&D with two commercial disinfectants at two different concentrations. An in-house RT-qPCR assay was used to detect the presence of PEDV RNA only (not infectivity status). Results suggest that pigs-to-market trucks hauling live pigs were the most likely to be contaminated with PEDV (82.06% of trucks tested positive before C&D and 89.55% tested positive after C&D), while feed trucks were the least likely contaminated (11.73% of trucks testing positive before C&D and 11.25% testing positive after C&D). Based on PEDV RNA detection, we demonstrated that quaternary ammonium and glutaraldehyde is a more effective disinfectant compared to advanced hydrogen peroxide in eliminating detectable PEDV RNA. Results also show that truck cabins are just as contaminated as the exterior of their vehicles. Based on these results, vehicle biosecurity measures should be evaluated and modified to prevent the spread of PEDV.

ecology↗

bioRxiv2025

Identifying control strategies to eliminate African swine fever from the United States swine industry in under 12 months

With the rising risk of African swine fever (ASF) introduction into the U.S., there is substantial emphasis on preparation for an epidemic to mitigate the economic and societal impacts. Mathematical models represent a vital tool for simulating future epidemics and examining the effectiveness of response strategies. This study expands on our spatially explicit stochastic compartmental farm-level transmission model, PigSpread-ASF, to identify the control strategies necessary to eliminate ASF from domestic swine populations in three, six, nine, and twelve months. We achieved this by incrementally increasing the intensity of the control actions detailed in the USDAs national response plan, which consists of i) quarantine and depopulation of detected farms; ii) a 72-hour movement standstill; iii) contact tracing with subsequent diagnostic testing; and iv) the implementation of control areas (infected and buffer zone) and surveillance zones (including routine diagnostic testing, pre-permit testing and movement restrictions). For this model, ASF was deemed eliminated after three consecutive months of no new ASF cases following each time period, as determined by WOAH. Our results indicate that the current national response plan would need to i) increase radii and duration of control areas and surveillance zones, ii) extend the traceback and quarantine for contact farms; iii) extend the movement standstill; iv) prohibit repopulation of depopulated farms; and v) quicker baseline detection of ASF, at varying intensities, to eliminate ASF within three, six, nine and twelve months. The elimination of ASF in 12-months required extension of the buffer zone radius to 5 km and maintenance of the control areas and surveillance zones for 60 days, a traceback and quarantine of 60 and 30 days for the contact tracing, and a standstill of 30 days. In contrast, the three-month scenario required extension of the infected zone, buffer zone and surveillance zone radii to 20 km each and maintenance of the control area and surveillance zones for 90 days, a traceback and quarantine of 90 days for contact tracing, and a standstill of 90 days. By intensifying the current national response plan, ASF would likely be eliminated within 12-months of its introduction. However, it is pertinent to consider the limitations posed by resource capacities and the impact that intensifying control may have on business continuity. Nevertheless, our study provides beneficial guidance to aid preparation for a future ASF introduction and estimates the infrastructure and personnel required to bring an epidemic under control promptly.

ecology↗

bioRxiv2024

Estimating sampling and laboratory capacity for a simulated African swine fever outbreak in the United States

The introduction of African swine fever virus (ASFV) into uninfected countries can impact economic and animal welfare. Rapid detection and control of the outbreak contribute to successful eradication and promote business continuity. We developed a model to determine the number of samples, sample collectors, laboratory capacity, and processing times following an ASFV introduction into the U.S. We simulated the spread of ASFV in one densely populated swine region, generating a median of 27 (range = 1-68) outbreaks in 150 days, resulting 616 (range = 1-15,011) sampling events with a total of 3,068 barns (range = 7-69,118) sampled. We calculated the total sample collectors needed, considering daily working hours, sampling and driving time, and laboratory capabilities with and without blood sample pooling. Samples included 31 blood samples and five oral fluid samples per barn, which equal 84,830 (range = 52-2,066,831) and 14,195 (range = 10-345,590) blood and oral fluid samples, respectively. The median number of sample collectors needed to prevent sampling delay varied from 136 to 367 and, in the worst epidemic scenarios, from 833 to 3,115. Notably, excluding downtime-which prevented the sampler from visiting additional farms for 24 or 72 hours-reduced the number of sample collectors needed between 28% and 75%, while switching from blood to oral fluid samples reduced this number between 47% and 75%. At a laboratory processing daily capacity of 1,000 samples, the median days for sample processing without pooling were 92 days, with a maximum of 5.7 years. We demonstrated a need to redistribute 10,062 (range = 2-67,940) unprocessed samples daily to other laboratories to prevent processing delays. Our study addresses the challenge of efficiently organizing resources for managing a potential ASFV outbreak, providing information about the number of sample collectors and laboratory capacity needed for one densely populated swine region in the U.S.

ecology↗

bioRxiv2024

Parasitic and Commensal interactions among Mimiviruses, Sputnik-like virophages, and Transpovirons: A theoretical and dynamical systems approach.

Giant viruses have been in the scope of virologists since 2003 when they were isolated from Acanthamoeba spp. Giant viruses, in turn, get infected by another virus named virophage and a third biological entity that corresponds to a transpoviron which can be found in the capsids of giant and virophage viruses. So far, transpovirons seem to behave as commensal entities while some virophages exhibit commensal behavior under laboratory conditions. To study the systems behavior, we used a theoretical approximation and developed an ordinary differential equation model. The dynamical analysis showed that the system exhibits an oscillatory robust behavior leading to a hyperparasitic Lotka-Volterra dynamic. But the biological mechanism that underlines the transpoviron persistence over time remains unclear and its status as a commensal entity needs further assessment. Also, the ecological interaction that leads to the overall coexistence of the three viral entities needs to be further studied.

systems biology↗

bioRxiv2024

The evolution of male weapons is associated with the type of breeding site in a clade of Neotropical frogs

Male weaponry evolution is often linked to resource or female defense polygyny. This pattern emerges from highly studied taxa, such as arthropods and mammals. However, whether factors such as breeding site type influence weaponry evolution remains an open question. We explore this question using frogs of the subfamily Leptodactylinae, where males of species spawning in exposed sites (water bodies) fight to hold oviposition sites or dislodge rivals during amplexus. Conversely, males of species spawning in concealed sites (ground nests and crevices) rarely engage in intense physical contests. We hypothesize that male weaponry evolution would be associated with reproduction in exposed sites. Using two complementary phylogenetic comparative methods, we first found a macroevolutionary correlation between male weapons and breeding site type. The presence of weapons is consistently associated with exposed sites, while their absence is linked to concealed sites. We explore how this macroevolutionary pattern can also be influenced by female mate choice. Second, we found that both gains and losses of weapons occurred more frequently in species spawning in exposed sites. This unexpected finding suggests that the dynamics of weapon evolution are more intricate than anticipated. We propose some explanations aspiring to stimulate further investigations with other external fertilizer species.

evolutionary biology↗

bioRxiv2024

Modeling the effects of vaccination against multiple strains of porcine reproductive and respiratory syndrome at the barn level

Porcine reproductive and respiratory syndrome (PRRSV) remains costly for the swine industry. Measures intended to irradicate or reduce the prevalence of PRRSV have limited effectiveness. Vaccination, the primary control strategy for PRRSV, has yet to be thoroughly investigated to ensure an optimal strategy is being implemented. Due to insufficient cross-immunity between strains, it is prudent to administer the most influential vaccine for the most dominant or threatening PRRSV strain in circulation at a given time. With this in mind, we demonstrated the benefits of targeted vaccination using metapopulation-based modeling. By using up-to-date data describing real farms to simulate the effects of variable vaccine efficacy in both a single and a double strain system, we showed that tailoring vaccines to prevalent PRRSV strains reduces infections, but using multiple vaccines may be more effective if strains vary in vaccine response. Therefore, the impact of the strain-specific effectiveness of market vaccines, paired with computational methods that allow tracking the effects on PRRVS dissemination at individual barns.

ecology↗

bioRxiv2024

Modeling the transmission dynamics of African swine fever virus within commercial swine barns: Quantifying the contribution of multiple transmission pathways

Transmission of the African swine fever virus (ASFV) within commercial swine barns occurs through direct and indirect pathways. Identifying and quantifying the roles of ASFV dissemination within barns is crucial for the development of effective disease control strategies. We developed a stochastic transmission model to examine the ASFV dissemination dynamics through eight transmission routes within commercial swine barns. We consider seven transmission routes at three disease dynamics levels: within-pens, between-pens, and within-room transmission, along with the transfer of pigs between pens within the same room. We simulated ASFV spread within barns of various sizes and layouts from rooms with a median of 32 pens (IQR:28-40), where each pen housing a median of 34 pigs (IQR: 29-36). Our model enables the tracking of the viral load in each pen and the monitoring of the disease status at the pen level. Simulation results show that between-pen transmission pathways exhibited the highest contribution to ASFV spread, accounting for 71.4%, where within-pen and within-room pathways account for 20.1% and 8.5%, respectively. Among the direct transmission pathways, nose-to-nose contact between pens was the primary route of dissemination, comprising an average of 49%, while the fecal transmission between pens contributed 21%. On the other hand, aerosol transmission within pens had the lowest contribution, accounting for less than 1%. Furthermore, we show that the daily transfer of pigs between pens did not impact the spread of ASFV. The combination of passive surveillance of daily detection and active surveillance focused on mortality allowed the detection of ASFV within three Days, with peak detection occurring when mortality rates peaked. The model also allows us to pinpoint where the majority of infections and viral load are concentrated during the ASFV spread. This work significantly deepens our understanding of ASFV spread within commercial swine production farms in the U.S. and highlights the main transmission pathways that should be prioritized when implementing ASFV countermeasure actions at the room level.

ecology↗

bioRxiv2024

Modeling the impact of optimized airflow and sick pen management on the spread of infectious diseases in swine barns

The airborne spread of infectious livestock diseases plays a crucial role in the propagation of epidemics, particularly in populations confined to densely populated facilities, such as commercial swine barns. Therefore, quantitative assessments for the performance of barn ventilation systems may serve as an alternative biocontainment control strategy to reduce the spread of infectious pathogens. In this study, we present a framework to simulate airborne disease dissemination within swine barns and facilitate the strategic design of control actions, including optimization of ventilation and placement of sick animals (sick pen). This framework is based on a susceptible-infected-recovered (SIR) model that accounts for the between-pen disease spread within swine barns. A pen-to-pen contact network is used to construct a transmission matrix according to the transport of airborne respiratory pathogens across pens in the barns, via our Reynolds-averaged Navier-Stokes computational fluid dynamics (CFD) solver. By employing this CFD-augmented SIR model, we demonstrated that the location of the sick pen and the barn ventilation configuration played crucial roles in modifying disease dissemination dynamics at the barn level. In addition, we examined the effect of natural ventilation through different curtain adjustments. We observed that curtain adjustments either suppress the disease spread by an average of 56.5% or exacerbate the outbreak potential by an average of 5.7%, compared to the scenario where side curtains are not raised. Furthermore, we optimize the ventilation configuration via the selection and placement of ventilation fans through the integration of the CFD-augmented framework with the genetic algorithm to minimize the dissemination of swine disease within barns. Compared to regular barn ventilation settings, our optimized ventilation system significantly reduced disease spread by an average of 43.2%. Our study emphasizes the role of airborne transmission and a strategy for sick pen management in controlling the spread of within-barn disease.

bioengineering↗

bioRxiv2024

Analyzing the intrastate and interstate swine movement network in the United States

Disease prevention and control tactics rely on identifying and restricting animal movement to attenuate the between-premises spread of disease in livestock systems. Therefore, it is essential to uncover between-premises movement dynamics, including shipment distances and network-based control strategies. Here, we analyzed three years of between-premises pig movements, which include 197,022 unique animal shipments, 3,973 premises, and 391,625,374 pigs shipped across 20 U.S. states. We constructed unweighted, directed, temporal networks at 180-day intervals to calculate premises-to-premises movement distances, the size of connected components, network loyalty, and degree distributions, and, based on the out-going contact chains, identified network-based control actions. Our results show that the median distance between premises pig movements was 74.37 km, with median intrastate and interstate movements of 52.71 km and 328.76 km, respectively. On average, 2,842 premises were connected via 6,705 edges, resulting in a weak giant connected component that included 91% of the premises. The premises-level network exhibited loyalty, with a median of 0.65 (IQR: 0.45 - 0.77). Results highlight the effectiveness of node targeting and disease spread; we demonstrated that targeting 25% of farms with the highest degree or betweenness limited spread to 1.23% and 1.7% of premises, respectively. While there is no complete shipment data for the entire U.S., our multi-state movement analysis demonstrated the value and the needs of such data for enhancing the design and implementation of proactive-disease control tactics.

ecology↗

bioRxiv2022

Estimating the effectiveness of control and eradication actions on African swine fever transmission in commercial swine populations in the United States

Given the proximity of African swine fever (ASF) to the U.S., there is an urgent need to better understand the possible dissemination pathways of the virus within the U.S. swine industry and to evaluate mitigation strategies. Here, we extended PigSpread, a farm-level spatially-explicit stochastic compartmental transmission model incorporating six transmission routes including between-farm swine movements, vehicle movements, and local spread, to model the dissemination of ASF. We then examined the effectiveness of control actions similar to the ASF national response plan. The average number of secondary infections during the first 60 days of the outbreak was 49 finisher farms, 17 nursery farms, 5 sow farms, and less than one farm in other production types. The between-farm movements of swine were the predominant route of ASF transmission with an average contribution of 71.1%, while local spread and movement of vehicles were less critical with average contributions of 14.6% and 14.4%. We demonstrated that the combination of quarantine, depopulation, movement restrictions, contact tracing, and enhanced surveillance, was the most effective mitigation strategy, resulting in an average reduction of 79.0% of secondary cases by day 140 of the outbreak. Implementing these control actions led to a median of 495,619 depopulated animals, 357,789 diagnostic tests, and 54,522 movement permits. Our results suggest that the successful elimination of an ASF outbreak is likely to require the deployment of all control actions listed in the ASF national response plan for more than 140 days, as well as estimating the resources needed for depopulation, testing, and movement permits under these controls.

ecology↗

bioRxiv2022

Modeling foot-and-mouth disease dissemination in Brazil and evaluating the effectiveness of control measures

Foot-and-mouth disease (FMD) is known to infect multiple food-animal species and to spread among ungulate populations. We introduce a multiscale compartmental stochastic model that incorporates population dynamics, births, deaths, and species-specific transmission dynamics. The model integrates disease dynamics at both the between-farm and the within-farm levels. We developed four scenarios to evaluate the effectiveness of countermeasures, including movement standstill, vaccination, and depopulation. The base scenario involved vaccinating the animals on 20 farms and depopulating four infected farms. The three alternative control scenarios included increasing vaccination and depopulation capacities and no vaccination. Our findings indicate that bovines were the most frequently infected species, followed by swine and small ruminants. After ten days of initial spread, the number of infected farms ranged from 1 to 123, with most simulations (90.12%) predicting fewer than 50 infected farms. Most of the secondary spread occurred within a range of 25 km. Early response to initiating the control action reduces the number of days spent working on control actions while intensifying daily depopulation and vaccination capacity; this may be worth considering in decision-making processes for future control of FMD. Emergency vaccination proved to be efficient in reducing the magnitude and duration of outbreaks, whereas increasing depopulation without the use of vaccination also proved to be effective in eliminating the outbreaks.

ecology↗

bioRxiv2022

A discrete-time survival model for porcine epidemic diarrhea virus

Since the arrival of porcine epidemic diarrhea virus (PEDV) in the United States in 2013, elimination and control programs have had partial success. The dynamics of its spread are hard to quantify, though previous work has shown that local transmission and the transfer of pigs within production systems are most associated with the spread of PEDV. Our work relies on the history of PEDV infections in a region of the southeastern United States. This infection data is complemented by farm-level features and extensive industry data on the movement of both pigs and vehicles. We implement a discrete-time survival model and evaluate different approaches to modeling the local-transmission and network effects. We find strong evidence in that the local-transmission and pig-movement effects are associated with the spread of PEDV, even while controlling for seasonality, farm-level features, and the possible spread of disease by vehicles. Our fully Bayesian model permits full uncertainty quantification of these effects. Our farm-level out-of-sample predictions have a receiver-operating characteristic area under the curve (AUC) of 0.779 and a precision-recall AUC of 0.097. The quantification of these effects in a comprehensive model allows stakeholders to make more informed decisions about disease prevention efforts.

ecology↗

bioRxiv2022

Assessing epidemiological parameters and dissemination characteristics of the 2000 and 2001 foot-and-mouth disease outbreaks in Rio Grande do Sul, Brazil

Since 1998 the state of Rio Grande do Sul, Brazil, has been free of foot-and-mouth disease (FMD) with yearly mandatory vaccination, until the 2000 and 2001 reintroductions. This study gathers data from both outbreaks including official veterinary state service archives and field investigation reports to quantify epidemiological parameters such as epidemic duration, number of secondary infected farms and animals, and estimate the epidemic rate of growth. We apply a Bayesian latent variable approach to estimate the time-varying reproduction number and calculate new confirmed cases by infection date. Additionally, we utilized between-farm animal movements to reconstruct possible FMD transmission and characteristics of spread over the current at-risk population, by incorporating bovine movement data from 2018 to 2020 as standard to benchmark infected network parameters. The results were consistent with the reports generated by the official investigation of the outbreaks and the models and results presented in this study may be useful for assessing the transmission dynamics and support control measures in the future.

ecology↗

bioRxiv2021

Modelling porcine reproductive and respiratory syndrome virus dynamics to quantify the contribution of multiple modes of transmission: between-farm animal and vehicle movements, farm-to-farm proximity, feed ingredients, and re-break

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 0.03% 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 modeling. 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.

ecology↗

bioRxiv2021

Modeling 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 movement restrictions. Here we developed a nested multiscale model for the transmission of ASF, combining spatially explicit network model of animal movements with a deterministic compartmental model for the dynamics of two ASF strains within-pixels of 3 km x 3 km, amongst the pig population 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 modeling 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.

ecology↗

bioRxiv2020

Transmission and control strategies for porcine reproductive and respiratory syndrome virus

Many aspects of the porcine reproductive and respiratory syndrome virus (PRRSV) between-farm transmission dynamics have been investigated, but uncertainty remains about the significance of farm type and different transmission routes on PRRSV spread. We developed a stochastic epidemiological model calibrated on weekly PRRSV outbreaks accounting for the population dynamics in different pig production phases, breeding herds, gilt development units, nurseries, and finisher farms, of three hog producer companies. Our model accounted for indirect contacts by the close distance between farms (local transmission), between-farm animal movements (pig flow), and reinfection of sow farms (re-break). The fitted model was used to examine the effectiveness of vaccination strategies and complementary interventions such as enhanced PRRSV detection and vaccination delays and forecast the spatial distribution of PRRSV outbreak. The results of our analysis indicated that for sow farms, 59% of the simulated infections were related to local transmission (e.g. airborne, feed deliveries, shared equipment) whereas 36% and 5% were related to animal movements and re-break, respectively. For nursery farms, 80% of infections were related to animal movements and 20% to local transmission; while at finisher farms it was split between local transmission and animal movements. Assuming that the current vaccines are 1% effective in mitigating between-farm PRRSV transmission, weaned pigs vaccination would reduce the incidence of PRRSV outbreaks by 2%, indeed under any scenario vaccination alone was insufficient for completely controlling PRRSV spread. Our results also showed that intensifying PRRSV detection and/or vaccination pigs at placement increased the effectiveness of all simulated vaccination strategies. Our model reproduced the incidence and PRRSV spatial distribution; therefore, this model could also be used to map current and future farms at-risk. Finally, this model could be a useful tool for veterinarians, allowing them to identify the effect of transmission routes and different vaccination interventions to control PRRSV spread.

ecology↗

bioRxiv2020

Nairobi Sheep Disease Virus: a historical and epidemiological perspective

Nairobi Sheep Disease virus (NSDv) is a zoonotic and tick-borne disease that can cause over 90% mortality in small ruminants. NSDv has historically circulated in East Africa and has recently emerged in the Asian continent. Despite efforts to control the disease, some regions, mostly in warmer climates, persistently report disease outbreaks. Consequently, it is necessary to understand how environmental tolerances and factors that influence transmission may shed light on its possible emergence in other regions. In this study, we quantified the available literature of NSDv from which occurrence data was extracted. In total, 308 locations from Uganda, Kenya, Tanzania, Somalia, India, Sri Lanka and China were coupled with landscape conditions to reconstruct the ecological conditions for NSDv circulation and identify areas of potential disease transmission risk. Our results identified areas suitable for NSDv in Ethiopia, Malawi, Zimbabwe, Southeastern China, Taiwan, and Vietnam. Unsuitable areas included Democratic Republic of Congo, Zambia, and Southern Somalia. In summary, soil moisture, livestock density, and precipitation predispose certain areas to NSDv circulation. It is critical to investigate the epidemiology of NSDv in order to promote better allocation of resources to control its spread in regions that are more at risk. This will help reduce disease impact worldwide as climate change will favor emergence of such vector-borne diseases in areas with dense small ruminant populations.

ecology↗

bioRxiv2020

On reproductive and respiratory syndrome virus dissemination across pig production systems in the United States

Porcine reproductive and respiratory syndrome virus (PRRSV) remains widespread in the North American pig population. Despite improvements in virus characterization, it is unclear whether PRRSV infections are a product of viral circulation within a farm, within production systems (local) or across production systems (external). Here we examined the dissemination dynamics of PRRSV and the processes facilitating its spread within and among pig farms in three production systems. Overall, PRRSV genetic diversity declined since 2018, while phylodynamic results support frequent transmission across-production systems. We found that PRRSV dissemination occurred mostly through transmission between farms of different production companies, which were predominant for several months, especially from November until May when PRRSV tends to peak in the studied region. Within production systems, dissemination occurred mainly through regular pig flow (from sow to nursery and then to finisher farms); nevertheless, an important flux of PRRSV dissemination from finisher to sow and nursery farms highlighted the importance of downstream farms as sources of the virus. Farms at areas with pig density from 500 to 1000 pig/km2 and farms located at a range within 0.5 km and 0.7 km from major roads were more likely to infect by PRRSV, whereas farms at elevation between 41 and 61 meters and denser vegetation acted as dissemination barriers. Although remains a challenge, there is a need to disentangle the route of PRRSV transmission, results evidenced that dissemination among commercially unrelated pig production systems was intense, reinforcing the importance of farm proximity on PRRSV spread. Thus, consideration of farm location and their geographic characteristics may help to forecast dissemination. The understanding of PRRSV transmission routes has the potential to inform targeted strategies for its prevention and control. Further studies are needed to quantify the relative contribution of PRRSV transmission routes.

evolutionary biology↗