The role of infectious aerosols in disease transmission in pigs

Distribution characteristics and potential risks of bioaerosols during scattered farming

In most economically underdeveloped areas, scattered farming and human‒livestock cohabitation are common. However, production of bioaerosols and their potential harm in these areas have not been previously researched. In this study, bioaerosol characteristics were analyzed in scattered farming areas in rural Northwest China. The highest bacteria, fungi, and Enterobacteria concentrations were 125609 ± 467 CFU/m³, 25175 ± 10305 CFU/m³, and 4167 ± 592 CFU/m³, respectively. Most bioaerosols had particle sizes >3.3 μm. A total of 71 bacterial genera and 16 fungal genera of potential pathogens were identified, including zoonotic potential pathogenic genera. Moreover, our findings showed that the scattered farming pattern of human‒animal cohabitation can affect the indoor air environment in the surrounding area, leading to chronic respiratory diseases in the occupants. Therefore, relevant government departments and farmers should enhance their awareness of bioaerosol risks and consider measures that may be taken to reduce them.

Airborne transmission of common swine viruses

The transmission of viral aerosols poses a vulnerable aspect in the biosecurity measures aimed at preventing and controlling swine virus in pig production. Consequently, comprehending and mitigating the spread of aerosols holds paramount significance for the overall well-being of pig populations. This paper offers a comprehensive review of transmission characteristics, influential factors and preventive strategies of common swine viral aerosols. Firstly, certain viruses such as foot-and-mouth disease virus (FMDV), porcine reproductive and respiratory syndrome virus (PRRSV), influenza A viruses (IAV), porcine epidemic diarrhea virus (PEDV) and pseudorabies virus (PRV) have the potential to be transmitted over long distances (exceeding 150 m) through aerosols, thereby posing a substantial risk primarily to inter-farm transmission. Additionally, other viruses like classical swine fever virus (CSFV) and African swine fever virus (ASFV) can be transmitted over short distances (ranging from 0 to 150 m) through aerosols, posing a threat primarily to intra-farm transmission. Secondly, various significant factors, including aerosol particle sizes, viral strains, the host sensitivity to viruses, weather conditions, geographical conditions, as well as environmental conditions, exert a considerable influence on the transmission of viral aerosols. Researches on these factors serve as a foundation for the development of strategies to combat viral aerosol transmission in pig farms. Finally, we propose several preventive and control strategies that can be implemented in pig farms, primarily encompassing the implementation of early warning models, viral aerosol detection, and air pretreatment. This comprehensive review aims to provide a valuable reference for the formulation of efficient measures targeted at mitigating the transmission of viral aerosols among swine populations.

What were the historical reasons for the resistance to recognizing airborne transmission during the COVID-19 pandemic?

The question of whether SARS-CoV-2 is mainly transmitted by droplets or aerosols has been highly controversial. We sought to explain this controversy through a historical analysis of transmission research in other diseases. For most of human history, the dominant paradigm was that many diseases were carried by the air, often over long distances and in a phantasmagorical way. This miasmatic paradigm was challenged in the mid to late 19th century with the rise of germ theory, and as diseases such as cholera, puerperal fever, and malaria were found to actually transmit in other ways. Motivated by his views on the importance of contact/droplet infection, and the resistance he encountered from the remaining influence of miasma theory, prominent public health official Charles Chapin in 1910 helped initiate a successful paradigm shift, deeming airborne transmission most unlikely. This new paradigm became dominant. However, the lack of understanding of aerosols led to systematic errors in the interpretation of research evidence on transmission pathways. For the next five decades, airborne transmission was considered of negligible or minor importance for all major respiratory diseases, until a demonstration of airborne transmission of tuberculosis (which had been mistakenly thought to be transmitted by droplets) in 1962. The contact/droplet paradigm remained dominant, and only a few diseases were widely accepted as airborne before COVID-19: those that were clearly transmitted to people not in the same room. The acceleration of interdisciplinary research inspired by the COVID-19 pandemic has shown that airborne transmission is a major mode of transmission for this disease, and is likely to be significant for many respiratory infectious diseases.

Environmental Risk Factors Influence the Frequency of Coughing and Sneezing Episodes in Finisher Pigs on a Farm Free of Respiratory Disease

This study aimed to assess baseline levels of coughing on a farm free of respiratory disease, and to identify relationships between environmental conditions and coughing frequency in finisher pigs. Six replicates were conducted (690 pigs in total). A cross-correlation analysis was performed and lags of the predictor variables were carried forward for multivariable regression analysis when significant and showing r > 0.25. Results show that coughing frequency was overall low. In the first replicate, coughing was best predicted by exposure to higher ammonia concentrations that occurred with a lag of 1, 7, and 15 days (p = 0.003, p = 0.001, and p < 0.001, respectively), while in the sixth replicate coughing frequency was best predicted by the exposure to lower relative humidity and higher ventilation rates with a lag of 7 and 15 days (p < 0.001 and p = 0.003, respectively). Ammonia concentrations varied according to ventilation rates recorded on the same day (r > −0.70). In conclusion, guidelines on coughing levels in healthy pigs and calibration of the alarm systems of tools that measure coughing frequency can be extrapolated from this study. Environmental risk factors are associated with the respiratory health of finisher pigs.

Non-respiratory particles emitted by guinea pigs in airborne disease transmission experiments

Animal models are often used to assess the airborne transmissibility of various pathogens, which are typically assumed to be carried by expiratory droplets emitted directly from the respiratory tract of the infected animal. We recently established that influenza virus is also transmissible via "aerosolized fomites," micron-scale dust particulates released from virus-contaminated surfaces (Asadi et al. in Nat Commun 11(1):4062, 2020). Here we expand on this observation, by counting and characterizing the particles emitted from guinea pig cages using an Aerodynamic Particle Sizer (APS) and an Interferometric Mie Imaging (IMI) system. Of over 9000 airborne particles emitted from guinea pig cages and directly imaged with IMI, none had an interference pattern indicative of a liquid droplet. Separate measurements of the particle count using the APS indicate that particle concentrations spike upwards immediately following animal motion, then decay exponentially with a time constant commensurate with the air exchange rate in the cage. Taken together, the results presented here raise the possibility that a non-negligible fraction of airborne influenza transmission events between guinea pigs occurs via aerosolized fomites rather than respiratory droplets, though the relative frequencies of these two routes have yet to be definitively determined.

Biosecurity in pig farms: a review

The perception of the importance of animal health and its relationship with biosecurity has increased in recent years with the emergence and re-emergence of several diseases difficult to control. This is particularly evident in the case of pig farming as shown by the recent episodes of African swine fever or porcine epidemic diarrhoea. Moreover, a better biosecurity may help to improve productivity and may contribute to reducing the use of antibiotics. Biosecurity can be defined as the application of measures aimed to reduce the probability of the introduction (external biosecurity) and further spread of pathogens within the farm (internal biosecurity). Thus, the key idea is to avoid transmission, either between farms or within the farm. This implies knowledge of the epidemiology of the diseases to be avoided that is not always available, but since ways of transmission of pathogens are limited to a few, it is possible to implement effective actions even with some gaps in our knowledge on a given disease. For the effective design of a biosecurity program, veterinarians must know how diseases are transmitted, the risks and their importance, which mitigation measures are thought to be more effective and how to evaluate the biosecurity and its improvements. This review provides a source of information on external and internal biosecurity measures that reduce risks in swine production and the relationship between these measures and the epidemiology of the main diseases, as well as a description of some systems available for risk analysis and the assessment of biosecurity. Also, it reviews the factors affecting the successful application of a biosecurity plan in a pig farm.

Detection of naturally aerosolized Actinobacillus pleuropneumoniae on pig farms by cyclonic air sampling and qPCR

Respiratory infections caused by Actinobacillus pleuropneumoniae have a large impact on commercial pig farms globally. As current vaccines have limited efficacy, animal care and air hygiene are critical for disease control. Here we used a Coriolis μ cyclonic air sampler and an A. pleuropneumoniae-specific apxIV gene qPCR assay to detect the organism. Air samples were collected into a liquid medium by the Coriolis μ sampler for A. pleuropneumoniae detection by plate culture and qPCR assay. The method was validated by comparing the Coriolis μ sampler and a plate impactor (Millipore Air-T) in a specially designed aerosolization chamber. Two commercial farms, housing pigs between 3 and 21 weeks of age, were tested. On one farm, A. pleuropneumoniae was detected in low numbers (1000 organisms/m³ air) by qPCR, but not by culture, from sheds containing 8, 12, 16, and 18 weeks-old pigs. To our knowledge this is the first successful detection of naturally aerosolised A. pleuropneumoniae in commercial farms with the Coriolis μ air sampler, potentially allowing the identification of sub-clinically infected populations of pigs in the field.

Aerosol Detection and Transmission of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV): What Is the Evidence, and What Are the Knowledge Gaps?

In human and veterinary medicine, there have been multiple reports of pathogens being airborne under experimental and field conditions, highlighting the importance of this transmission route. These studies shed light on different aspects related to airborne transmission such as the capability of pathogens becoming airborne, the ability of pathogens to remain infectious while airborne, the role played by environmental conditions in pathogen dissemination, and pathogen strain as an interfering factor in airborne transmission. Data showing that airborne pathogens originating from an infectious individual or population can infect susceptible hosts are scarce, especially under field conditions. Furthermore, even though disease outbreak investigations have generated important information identifying potential ports of entry of pathogens into populations, these investigations do not necessarily yield clear answers on mechanisms by which pathogens have been introduced into populations. In swine, the aerosol transmission route gained popularity during the late 1990’s as suspicions of airborne transmission of porcine reproductive and respiratory syndrome virus (PRRSV) were growing. Several studies were conducted within the last 15 years contributing to the understanding of this transmission route; however, questions still remain. This paper reviews the current knowledge and identifies knowledge gaps related to PRRSV airborne transmission.

Use of trachea-bronchial swab qPCR testing to confirm Mycoplasma hyopneumoniae seropositivity in an SPF breeding herd

Background

A dedicated program to monitor for freedom of several economically important diseases is present within most of the breeding companies that currently deliver high health breeding animals to their customers. Serology is therefore the preferential approach in order to screen for most of these diseases, including Mycoplasma hyopneumoniae (M. hyopneumoniae). However, in case of positive serology, further decisions on farm health status and the related consequences should be based on additional confirmation tests.

Case presentation

The current case report demonstrates that tracheo-bronchial swab (TBS) sampling is a suitable alternative to confirm a suspect M. hyopneumoniae-seropositive situation. A Central-European SPF herd was shown positive (90% positive, 10% suspect; n = 10) for M. hyopneumoniae using the conventional ELISA serology (Idexx HerdChek Mhyo ELISA) and a second ELISA test (IDEIA™ Mycoplasma hyopneumoniae EIA kit) did not exclude potential M. hyopneumoniae infection (10% positive, 70% suspect; n = 10). Further follow-up remained inconclusive on both tests. Throughout the entire monitoring period of 6 months, no coughing, necropsy lesions or lesions at slaughter could be detected which could confirm the M. hyopneumoniae health status. TBS sampling was used to confirm the health status for M. hyopneumoniae. In total, 162 samples were collected at different ages (n = 18 per age category): piglets at 3-6-9-12 and 15 wks of age, rearing gilts at 18-21-24 and 27 weeks of age. Collected TBS samples were negative for M. hyopneumoniae until 15 wks of age, but rearing gilts were highly M. hyopneumoniae-positive from 18 wks onwards with 87-100% M. hyopneumoniae-positive animals and PCR Ct-values between 25 and 33.

Conclusions

This case report shows that collection of TBS samples to confirm the M. hyopneumoniae infection status of a breeding herd was able to provide additional information to serology in order to make crucial decisions concerning health management and eradication strategies within the breeding herd.

Impact of different supply air and recirculating air filtration systems on stable climate, animal health, and performance of fattening pigs in a commercial pig farm

Biosecurity is defined as the implementation of measures that reduce the risk of disease agents being introduced and/or spread. For pig production, several of these measures are routinely implemented (e.g. cleaning, disinfection, segregation). However, air as a potential vector of pathogens has long been disregarded. Filters for incoming and recirculating air were installed into an already existing ventilation plant at a fattening piggery (3,840 pigs at maximum) in Saxony, Germany. Over a period of three consecutive fattening periods, we evaluated various parameters including air quality indices, environmental and operating parameters, and pig performance. Animal data regarding respiratory diseases, presence of antibodies against influenza A viruses, PRRSV, and Actinobacillus pleuropneumoniae and lung health score at slaughter were recorded, additionally. There were no significant differences (p = 0.824) in total bacterial counts between barns with and without air filtration. Recirculating air filtration resulted in the lowest total dust concentration (0.12 mg/m³) and lung health was best in animals from the barn equipped with recirculating air filtration modules. However, there was no difference in animal performance. Antibodies against all above mentioned pathogens were detected but mostly animals were already antibody-positive at re-stocking. We demonstrated that supply air filtration as well as recirculating air filtration technique can easily be implemented in an already existing ventilation system and that recirculating air filtration resulted in enhanced lung health compared to supply air-filtered and non-filtered barns. A more prominent effect might have been obtained in a breeding facility because of the longer life span of sows and a higher biosecurity level with air filtration as an add-on measure.

Aerosol Transmission of Filoviruses

Filoviruses have become a worldwide public health concern because of their potential for introductions into non-endemic countries through international travel and the international transport of infected animals or animal products. Since it was first identified in 1976, in the Democratic Republic of Congo (formerly Zaire) and Sudan, the 2013–2015 western African Ebola virus disease (EVD) outbreak is the largest, both by number of cases and geographical extension, and deadliest, recorded so far in medical history. The source of ebolaviruses for human index case(s) in most outbreaks is presumptively associated with handling of bush meat or contact with fruit bats. Transmission among humans occurs easily when a person comes in contact with contaminated body fluids of patients, but our understanding of other transmission routes is still fragmentary. This review deals with the controversial issue of aerosol transmission of filoviruses.

Induction of mycoplasmal pneumonia in experimentally infected pigs by means of different inoculation routes

The purpose of this study was to assess the effect of three different inoculation routes into mycoplasmal pneumonia (MP) in pigs challenged with Mycoplasma hyopneumoniae (M. hyopneumoniae). Thirty six-week-old M. hyopneumoniae seronegative piglets were randomly assigned to four groups: three challenged groups with experimentally inoculated pigs by either the endotracheal (ET; n = 8), intranasal (IN; n = 8) or aerosol (AE; n = 8) routes and one uninfected group (Control; n = 6). Blood samples were collected 1 day before challenge and at necropsy, 28 days post-inoculation (dpi), to assess seroconversion. Laryngeal swabs were collected at −1, 7, 14, 21 and 28 dpi in order to evaluate colonization. At necropsy, lung lesions were scored and lung tissue was collected for histopathological studies and M. hyopneumoniae DNA detection. Broncho-alveolar lavage fluid (BALF) was also obtained to detect M. hyopneumoniae DNA, specific IgA antibodies and cytokines. MP was observed in all inoculated groups, but the ET group displayed a significantly higher number of animals affected by MP as well as a higher mean lung lesion score. These results were paralleled with an earlier seroconversion and upper respiratory tract colonization of M. hyopneumoniae. Additionally, in the ET group, higher levels of pro-inflammatory cytokines and specific IgA antibodies in BALF were found. Under the conditions of the present study, MP was reproduced by the three evaluated inoculation routes. Obtained results suggest that the ET route is the most effective in order to induce MP in pigs experimentally challenged with M. hyopneumoniae.

Quantitative effects of a declaration of a state of emergency on foot-and-mouth disease

OBJECTIVES

The law in Japan requires the declaration of a state of emergency and implementation of countermeasures for an epidemic of a new infectious disease. However, because a state of emergency has never been declared in Japan, its effects remain unknown. The required countermeasures are similar to those implemented in the foot-and-mouth disease epidemic in Miyazaki in 2010. This study aimed to quantitatively estimate the effect of the declaration in 2010 and investigate the nature of the epidemic based on the day on which the declaration took effect.

METHODS

Only publicly available data were used. Data for farms in the most affected town were analyzed. A modified susceptible-infected-recovered model was used to estimate the effect and for the simulation. Another model was used to estimate the effective reproduction number.

RESULTS

After the declaration, the intra-bovine transmission rate decreased by 18.1 %, and there were few days when the effective reproduction number was >1.0. A few weeks delay in the declaration significantly increased the possibility of epidemic, number of farms at peak, and final infection scale.

CONCLUSIONS

Based on the substantial decrease in the transmission rate after the declaration of a state of emergency in 2010, a future declaration will have a similar effect for a new infectious disease even though a direct extrapolation is not valid. Although a declaration should be carefully considered owing to the potential socioeconomic effects, it is essential to prepare for the implementation given that a delay of only a few weeks should be acceptable.

Atmospheric dispersion modelling of bioaerosols that are pathogenic to humans and livestock - A review to inform risk assessment studies

In this review we discuss studies that applied atmospheric dispersion models (ADM) to bioaerosols that are pathogenic to humans and livestock in the context of risk assessment studies. Traditionally, ADMs have been developed to describe the atmospheric transport of chemical pollutants, radioactive matter, dust, and particulate matter. However, they have also enabled researchers to simulate bioaerosol dispersion. To inform risk assessment, the aims of this review were fourfold, namely (1) to describe the most important physical processes related to ADMs and pathogen transport, (2) to discuss studies that focused on the application of ADMs to pathogenic bioaerosols, (3) to discuss emission and inactivation rate parameterisations, and (4) to discuss methods for conversion of concentrations to infection probabilities (concerning quantitative microbial risk assessment). The studies included human, livestock, and industrial sources. Important factors for dispersion included wind speed, atmospheric stability, topographic effects, and deposition. Inactivation was mainly governed by humidity, temperature, and ultraviolet radiation. A majority of the reviewed studies, however, lacked quantitative analyses and application of full quantitative microbial risk assessments (QMRA). Qualitative conclusions based on geographical dispersion maps and threshold doses were encountered frequently. Thus, to improve risk assessment for future outbreaks and releases, we recommended determining well-quantified emission and inactivation rates and applying dosimetry and dose-response models to estimate infection probabilities in the population at risk.

Evaluation of an electrostatic particle ionization technology for decreasing airborne pathogens in pigs

Influenza A virus (IAV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV) and Staphylococcus aureus are important swine pathogens capable of being transmitted via aerosols. The electrostatic particle ionization system (EPI) consists of a conductive line that emits negative ions that charge particles electrically resulting in the settling of airborne particles onto surfaces and potentially decreasing the risk of pathogen dissemination. The objectives of this study were to determine the effect of the EPI system on the quantity and viability of IAV, PRRSV, PEDV and S. aureus in experimentally generated aerosols and in aerosols generated by infected animals. Efficiency at removing airborne particles was evaluated as a function of particle size (ranging from 0.4 to 10 µm), distance from the source of ions (1, 2 and 3 m) and relative air humidity (RH 30 vs. 70 %). Aerosols were sampled with the EPI system "off" and "on." Removal efficiency was significantly greater for all pathogens when the EPI line was the closest to the source of aerosols. There was a greater reduction for larger particles ranging between 3.3 and 9 µm, which varied by pathogen. Overall airborne pathogen reduction ranged between 0.5 and 1.9 logs. Viable pathogens were detected with the EPI system "on," but there was a trend to reducing the quantity of viable PRRSV and IAV. There was not a significant effect on the pathogens removal efficiency based on the RH conditions tested. In summary, distance to the source of ions, type of pathogen and particle size influenced the removal efficiency of the EPI system. The reduction in infectious agents in the air by the EPI technology could potentially decrease the microbial exposure for pigs and people in confinement livestock facilities.

Increased Mycoplasma hyopneumoniae Disease Prevalence in Domestic Hybrids Among Free-Living Wild Boar

Wildlife immune genes are subject to natural selection exerted by pathogens. In contrast, domestic immune genes are largely protected from pathogen selection by veterinary care. Introgression of domestic alleles into the wild could lead to increased disease susceptibility, but observations are scarce due to low introgression rates, low disease prevalence and reduced survival of domestic hybrids. Here we report the first observation of a deleterious effect of domestic introgression on disease prevalence in a free-living large mammal. A fraction of 462 randomly sampled free-living European wild boar (Sus scrofa) was genetically identified as recent wild boar-domestic pig hybrids based on 351 SNP data. Analysis of antibody prevalence against the bacterial pathogen Mycoplasma hyopneumoniae (Mhyo) showed an increased Mhyo prevalence in wild-domestic hybrids. We argue that the most likely mechanism explaining the observed association between domestic hybrid status and Mhyo antibody prevalence would be introgression of deleterious domestic alleles. We hypothesise that large-scale use of antibiotics in the swine breeding sector may have played a role in shaping the relatively deleterious properties of domestic swine immune genes and that domestic introgression may also lead to increased wildlife disease susceptibility in the case of other species.

Impact of particulate matter and ammonia on average daily weight gain, mortality and lung lesions in pigs

The present study investigated the simultaneous influence of particulate matter (PM10) and ammonia (NH3) on performance, lung lesions and the presence of Mycoplasma hyopneumoniae (M. hyopneumoniae) in finishing pigs. A pig herd experiencing clinical problems of M. hyopneumoniae infections was selected. In total, 1095 finishing pigs of two replicates in eight compartments each were investigated during the entire finishing period (FP). Indoor PM10 and NH3 were measured at regular intervals during the FP with two Grimm spectrometers and two Graywolf Particle Counters (PM10) and an Innova photoacoustic gas monitor (NH3). Average daily weight gain (ADG) and mortality were calculated and associated with PM10 and NH3 during the FP. Nasal swabs (10 pigs/compartment) were collected one week prior to slaughter to detect DNA of M. hyopneumoniae with nested PCR (nPCR). The prevalence and extent of pneumonia lesions, and prevalence of fissures and pleurisy were examined at slaughter (29 weeks). The results from the nasal swabs and lung lesions were associated with PM10 and NH3 during the FP and the second half of the FP. In the univariable model, increasing PM10 concentrations resulted in a higher odds of pneumonia lesions (second half of the FP: OR=8.72; P=0.015), more severe pneumonia lesions (FP: P=0.04, second half of the FP: P=0.009), a higher odds of pleurisy lesions (FP: OR=20.91; P<0.001 and second half of the FP: OR=40.85; P<0.001) and a higher number of nPCR positive nasal samples (FP: OR=328.00; P=0.01 and second half of the FP: OR=185.49; P=0.02). Increasing NH3 concentrations in the univariable model resulted in a higher odds of pleurisy lesions (FP: OR=21.54; P=0.003) and a higher number of nPCR positive nasal samples (FP: OR=70.39; P=0.049; second half of the FP: OR=8275.05; P=0.01). In the multivariable model, an increasing PM10 concentration resulted in a higher odds of pleurisy lesions (FP: OR=8.85; P=0.049). These findings indicate that the respiratory health of finishing pigs was significantly affected by PM10.

Investigating the role of free-ranging wild boar (Sus scrofa) in the re-emergence of enzootic pneumonia in domestic pig herds: a pathological, prevalence and risk-factor study

Enzootic pneumonia (EP) caused by Mycoplasma hyopneumoniae has a significant economic impact on domestic pig production. A control program carried out from 1999 to 2003 successfully reduced disease occurrence in domestic pigs in Switzerland, but recurrent outbreaks suggested a potential role of free-ranging wild boar (Sus scrofa) as a source of re-infection. Since little is known on the epidemiology of EP in wild boar populations, our aims were: (1) to estimate the prevalence of M. hyopneumoniae infections in wild boar in Switzerland; (2) to identify risk factors for infection in wild boar; and (3) to assess whether infection in wild boar is associated with the same gross and microscopic lesions typical of EP in domestic pigs. Nasal swabs, bronchial swabs and lung samples were collected from 978 wild boar from five study areas in Switzerland between October 2011 and May 2013. Swabs were analyzed by qualitative real time PCR and a histopathological study was conducted on lung tissues. Risk factor analysis was performed using multivariable logistic regression modeling. Overall prevalence in nasal swabs was 26.2% (95% CI 23.3–29.3%) but significant geographical differences were observed. Wild boar density, occurrence of EP outbreaks in domestic pigs and young age were identified as risk factors for infection. There was a significant association between infection and lesions consistent with EP in domestic pigs. We have concluded that M. hyopneumoniae is widespread in the Swiss wild boar population, that the same risk factors for infection of domestic pigs also act as risk factors for infection of wild boar, and that infected wild boar develop lesions similar to those found in domestic pigs. However, based on our data and the outbreak pattern in domestic pigs, we propose that spillover from domestic pigs to wild boar is more likely than transmission from wild boar to pigs.

Airborne Microorganisms From Livestock Production Systems and Their Relation to Dust

Large amounts of airborne microorganisms are emitted from livestock production. These emitted microorganisms may associate with dust, and are suspected to pose a risk of airborne infection to humans in vicinity and to animals on other farms. However, the extent to which airborne transmission may play a role in the epidemic, and how dust acts as a carrier of microorganisms in the transmission processes is unknown. The authors present the current knowledge of the entire process of airborne transmission of microorganisms-from suspension and transportation until deposition and infection-and their relation to dust. The sampling and the mitigation techniques of airborne microorganisms and dust in livestock production systems are introduced as well.

Using Bayesian networks to explore the role of weather as a potential determinant of disease in pigs

Many pathogens are sensitive to climatic variables and this is reflected in their seasonality of occurrence and transmission. The identification of environmental conditions that influence disease occurrence can be subtle, particularly considering their complex interdependencies in addition to those relationships between climate and disease. Statistical treatment of environmental variables is often dependent on their correlations and thus descriptions of climate are often restricted to means rather than accounting for the more precise aspects (including mean, maximum, minimum, variability). Here we utilize a novel multivariate statistical modelling approach, additive Bayesian network (ABN) analyses, to identify the inter-linkages of different weather variables to better capture short-term environmental conditions that are important drivers of disease. We present a case study that explores weather as a driver of disease in livestock systems. We utilize quality assurance health scheme data on ten major diseases of pigs from 875 finishing pig herds distributed across the United Kingdom over 7 years (2005-2011). We examine the relationship between the occurrence of these pathologies and contemporary weather conditions measured by local meteorological stations. All ten pathologies were associated with at least 2 other pathologies (maximum 6). Three pathologies were associated directly with temperature variables: papular dermatitis, enzootic pneumonia and milk spots. Latitude was strongly associated with multiple pathologies, though associations with longitude were eliminated when clustering for repeated observations of farms was assessed. The identification of relationships between climatic factors and different (potentially related) diseases offers a more comprehensive insight into the complex role of seasonal drivers and herd health status than traditional analytical methods.

Quantification of airborne African swine fever virus after experimental infection

Knowledge on African Swine Fever (ASF) transmission routes can be useful when designing control measures against the spread of ASF virus (ASFV). Few studies have focused on the airborne transmission route, and until now no data has been available on quantities of ASF virus (ASFV) in the air. Our aim was to validate an air sampling technique for ASF virus (ASFV) that could be used to detect and quantify virus excreted in the air after experimental infection of pigs. In an animal experiment with the Brazil'78, the Malta'78 and Netherlands'86 isolates, air samples were collected at several time points. For validation of the air sampling technique, ASFV was aerosolised in an isolator, and air samples were obtained using the MD8 air scan device, which was shown to be suitable to detect ASFV. The half-life of ASFV in the air was on average 19 min when analysed by PCR, and on average 14 min when analysed by virus titration. In rooms with infected pigs, viral DNA with titres up to 10(3.2) median tissue culture infective dose equivalents (TCID50eq.)/m(3) could be detected in air samples from day 4 post-inoculation (dpi 4) until the end of the experiments, at dpi 70. In conclusion, this study shows that pigs infected with ASFV will excrete virus in the air, particularly during acute disease. This study provides the first available parameters to model airborne transmission of ASFV.

Exploratory study on the influence of climatological parameters on Mycoplasma hyopneumoniae infection dynamics

The objective of the present work was to elucidate the potential relationship between Mycoplasma hyopneumoniae infection and seroconversion dynamics and climatological conditions in four groups of pigs from the same farm born in different seasons of the year. Nasal swabs and blood samples were taken from 184 pigs at 1, 3, 6, 9, 12, 15, 18, 22 and 25 (slaughter age) weeks of age. Outside climatologic parameters, including temperature (°C), relative humidity (%), precipitation (l/m(2)) and wind speed (m/s) were recorded weekly from January 2003 to June 2004. Percentage of nPCR detection of M. hyopneumoniae in nasal swabs was associated significantly with the weekly precipitation rate [P = 0.0018, OR = 1.31 (IC = 1.11-1.55)]; the higher the precipitation rate, the higher the probability of being M. hyopneumoniae nPCR-positive. On the other hand, the percentage of seropositive pigs had a significant association with mean weekly temperature rate [P = 0.0012, OR = 0.89 [IC = 0.84-0.95]); the lower the temperature, the higher the probability of being M. hyopneumoniae seropositive. Animals born in autumn (when higher precipitations rates were recorded), entering finishing units in winter (when lower temperatures were recorded), and reaching slaughter in spring, had the highest probability of being infected by M. hyopneumoniae and the highest probability of being M. hyopneumoniae seropositive.

Within-farm transmission of bovine paratuberculosis: recent developments

Mycobacterium avium subspecies paratuberculosis is the causative agent of paratuberculosis in cattle which causes a chronic infection of the small intestine. Since the transmission is only partly understood current control programs have been able to only decrease prevalence but not to eradicate disease from a herd. Unknown and therefore uncontrolled routes of transmission were suggested and infective bioaerosols were hypothesized as a potential candidate. This review gives an overview concerning disease transmission and focuses on consequences of bioaerosols on the within-herd transmission of paratuberculosis.

Aerial dissemination of Clostridium difficile on a pig farm and its environment

Clostridium difficile is increasingly recognized as an important enteropathogen in both humans and animals. The finding of C. difficile in air samples in hospitals suggests a role for aerial dissemination in the transmission of human C. difficile infection. The present study was designed to investigate the occurrence of airborne C. difficile in, and nearby a pig farm with a high prevalence of C. difficile. Airborne colony counts in the farrowing pens peaked on the moments shortly after or during personnel activity in the pens (P=0.043 (farrowing pens 1, 2), P=0.034 (farrowing pen 2)). A decrease in airborne C. difficile colony counts was observed parallel to aging of the piglets. Airborne C. difficile was detected up to 20 m distant from the farm. This study showed widespread aerial dissemination of C. difficile on a pig farm that was positively associated with personnel activity.

Airborne transmission of a highly pathogenic avian influenza virus strain H5N1 between groups of chickens quantified in an experimental setting

Highly pathogenic avian influenza (HPAI) is a devastating viral disease of poultry and quick control of outbreaks is vital. Airborne transmission has often been suggested as a route of transmission between flocks, but knowledge of the rate of transmission via this route is sparse. In the current study, we quantified the rate of airborne transmission of an HPAI H5N1 virus strain between chickens under experimental conditions. In addition, we quantified viral load in air and dust samples. Sixteen trials were done, comprising a total of 160 chickens housed in cages, with three treatment groups. The first group was inoculated with strain A/turkey/Turkey/1/2005 H5N1, the second and third group were not inoculated, but housed at 0.2 and 1.1m distance of the first group, respectively. Tracheal and cloacal swabs were collected daily of each chicken to monitor virus transmission. Air and dust samples were taken daily to quantify virus load in the immediate surroundings of the birds. Samples were tested by quantitative RRT-PCR and virus isolation. In 4 out of 16 trials virus was transmitted from the experimentally inoculated chickens to the non-inoculated chickens. The transmission rate was 0.13 and 0.10 new infections per infectious bird at 0.2m and 1.1m, respectively. The difference between these estimates was, however, not significant. Two air samples tested positive in virus isolation, but none of these samples originated from the trials with successful transmission. Five dust samples were confirmed positive in virus isolation. The results of this study demonstrate that the rate of airborne transmission between chickens over short distances is low, suggesting that airborne transmission over a long distance is an unlikely route of spread. Whether or not this also applies to the field situation needs to be examined.

Optofluidic device monitoring and fluid dynamics simulation for the spread of viral pathogens in a livestock environment

Rapid monitoring of the spreads of porcine reproductive and respiratory syndrome virus (PRRSV) was attempted using samples collected from nasal swabs of pigs and air samplers within an experimental swine building. An optofluidic device containing liquid-core waveguides was used to detect forward Mie light scattering caused by the agglutination of anti-PRRSV-conjugated submicron particles, with enhanced sensitivity, signal reproducibility, and reusability (reusable up to 75 assays). These results were compared with reverse transcription polymerase chain reaction (RT-PCR) assays (35 cycles) and showed excellent agreements to them. Each assay took less than 10 min including all necessary sample pre-processing, while the RT-PCR assays took up to 4 h including sample pre-processing and gel imaging for PCR products. A 3-D computational fluid dynamics (CFD) simulation was utilized to track the transport and distribution of PRRSV (from the mouths of pigs to the exhaust fans) within a swine building, and compared with the readings from an optofluidic device. Simulation results corresponded well with the experimental data, validating our 3-D CFD model for the spread of viral pathogens in a livestock environment. The developed optofluidic device and 3-D CFD model can serve as a good model for monitoring the spread of influenza A (swine and avian) within animal and human environments.

An epidemiological analysis of the foot-and-mouth disease epidemic in Miyazaki, Japan, 2010

An epidemic of foot-and-mouth disease occurred in Miyazaki, Japan, beginning in late March 2010. Here, we document the descriptive epidemiological features and investigate the between-farm transmission dynamics. As of 10 July 2010, a total of 292 infected premises have been confirmed with a cumulative incidence for cattle and pig herds of 8.5% and 36.4%, respectively, for the whole of Miyazaki prefecture. Pig herds were more likely to be infected than cattle herds (odds ratio = 4.3 [95% confidence interval (CI): 3.2, 5.7]). Modelling analysis suggested that the relative susceptibility of a cattle herd is 4.2 times greater than a typical pig herd (95% CI: 3.9, 4.5), while the relative infectiousness of a pig herd is estimated to be 8.0 times higher than a cattle herd (95% CI: 5.0, 13.6). The epidemic peak occurred around mid-May, after which the incidence started to decline and the effective reproduction numbers from late May were mostly less than unity, although a vaccination programme in late May could have masked symptoms in infected animals. The infected premises were geographically confined to limited areas in Miyazaki, but sporadic long-distance transmissions were seen within the prefecture. Given that multiple outbreaks in Far East Asian countries have occurred since early 2010, continued monitoring and surveillance is deemed essential.

Effects of housing on the incidence of visna/maedi virus infection in sheep flocks

The incidence of seroconversion to visna/maedi virus (VMV) infection and its relationship with management and sheep building structure was investigated in 15 dairy sheep flocks in Spain during 3-7years. Incidence rates were 0.09 per sheep-year at risk in semi-intensive Latxa flocks and 0.44 per sheep-year at risk in intensive Assaf flocks and was greatest for the one year old Assaf replacement flock. Separate multivariable models developed for replacement and adult flocks indicated that in both cases seroconversion was strongly associated to direct contact exposure to infected sheep and to being born to a seropositive dam. The latter effect was independent of the mode of rearing preweaning and the risk of seroconversion was similar for sheep fed colostrum and milk from a seropositive or a seronegative dam. These results are further evidence of the efficiency of horizontal VMV transmission by close contact between sheep and also suggest a inheritable component of susceptibility and resistance to infection. In contrast, indirect aerogenous contact with seropositive sheep was not associated with seroconversion as evidenced in replacement sheep housed in separate pens in the same building as adult infected sheep for one year. Consequently, VMV may not be efficiently airborne over short distances and this is important for control of infection. Moreover, there was no relationship between seroconversion and shed open areas. The latter could be related to having examined few flocks in which high infection prevalence dominated the transmission process while ventilation, may depend on a variety of unrecorded factors whose relationship to infection needs to be further investigated.

Distribution characteristics of airborne bacteria and fungi in the feedstuff-manufacturing factories

The objective of the study is to investigate the distribution patterns of airborne bacteria and fungi in three feedstuff-manufacturing factories in Korea. The geometric mean (+/-GSD) levels of airborne bacteria and fungi in the feedstuff-manufacturing factory were 113(+/-18)cfu/m(3) and 89(+/-5)cfu/m(3) for pelleting process and 198(+/-5)cfu/m(3) and 124(+/-12)cfu/m(3) for powdering process, respectively. The percentage of respirable (0.65-4.7 microm) and total (>4.7 microm) concentration of airborne bacteria and fungi in the feedstuff-manufacturing factory ranged from 60% to 90% and were higher in pelleting process than powdering process. The ratio of indoor concentration and concentration in ventilation air from outside for airborne bacteria and fungi exceeded 1.0 regardless of types of feedstuff manufacture process. The predominant airborne microorganisms in the feedstuff-manufacturing factory were Staphylococcus spp., Micrococcus spp., Corynebacterium spp. and Bacillus spp. for airborne bacteria and Cladosporium spp., Penicillium spp. and Aspergillus spp. for airborne fungi, respectively. Based on the result of the study, there would be an association between relative humidity among environmental factors and airborne microorganism's bioactivity.

Current perspectives on the diagnosis and epidemiology of Mycoplasma hyopneumoniae infection

Mycoplasma hyopneumoniae is the principal aetiological agent of enzootic pneumonia (EP), a chronic respiratory disease that affects mainly finishing pigs. Although major efforts to control M. hyopneumoniae infection and its detrimental effects have been made, significant economic losses in pig production worldwide due to EP continue. M. hyopneumoniae is typically introduced into pig herds by the purchase of subclinically infected animals or, less frequently, through airborne transmission over short distances. Once in the herd, M. hyopneumoniae may be transmitted by direct contact from infected sows to their offspring or between pen mates.

The ‘gold standard’ technique used to diagnose M. hyopneumoniae infection, bacteriological culture, is laborious and is seldom used routinely. Enzyme-linked immunosorbent assay and polymerase chain reaction detection methods, in addition to post-mortem inspection in the form of abattoir surveillance or field necropsy, are the techniques most frequently used to investigate the potential involvement of M. hyopneumoniae in porcine respiratory disease. Such techniques have been used to monitor the incidence of M. hyopneumoniae infection in herds both clinically and subclinically affected by EP, in vaccinated and non-vaccinated herds and under different production and management conditions. Differences in the clinical course of EP at farm level and in the efficacy of M. hyopneumoniae vaccination suggest that the transmission and virulence characteristics of different field isolates of M. hyopneumoniae may vary. This paper reviews the current state of knowledge of the epidemiology of M. hyopneumoniae infection including its transmission, infection and seroconversion dynamics and also compares the various epidemiological tools used to monitor EP.

Indirect transmission of Escherichia coli O157:H7 occurs readily among swine but not among sheep

Transmission of Escherichia coli O157:H7 among reservoir animals is generally thought to occur either by direct contact between a naïve animal and an infected animal or by consumption of food or water containing the organism. Although ruminants are considered the major reservoir, there are two reports of human infections caused by E. coli O157:H7 linked to the consumption of pork products or to the contamination of fresh produce by swine manure. The objective of this study was to determine whether E. coli O157:H7 could be transmitted to naïve animals, both sheep and swine, that did not have any direct contact with an infected donor animal. We recovered E. coli O157:H7 from 10/10 pigs with nose-to-nose contact with the infected donor or animals adjacent to the donor and from 5/6 naïve pigs that were penned in the same room as the donor pig but 10 to 20 ft away. In contrast, when the experiment was repeated with sheep, E. coli O157:H7 was recovered from 4/6 animals that had nose-to-nose contact with the infected donor or adjacent animals and from 0/6 naïve animals penned 10 to 20 ft away from the donor. These results suggest that E. coli O157:H7 is readily transmitted among swine and that transmission can occur by the creation of contaminated aerosols.

Detection and quantification of classical swine fever virus in air samples originating from infected pigs and experimentally produced aerosols

During epidemics of classical swine fever (CSF), neighbourhood infections occurred where none of the 'traditional' routes of transmission like direct animal contact, swill feeding, transport contact or transmission by people could be identified. A hypothesized route of virus introduction for these herds was airborne transmission. In order to better understand this possible transmission route, we developed a method to detect and quantify classical swine fever virus (CSFV) in air samples using gelatine filters. The air samples were collected from CSFV-infected pigs after experimental aerosolization of the virus. Furthermore, we studied the viability of the virus with time in aerosolized state. Three strains of CSFV were aerosolized in an empty isolator and air samples were taken at different time intervals. The virus remained infective in aerosolized state for at least 30 min with half-life time values ranging from 4.5 to 15 min. During animal experiments, concentrations of 10(0.3)-10(1.6)TCID(50)/m(3) CSFV were detected in air samples originating from the air of the pig cages and 10(0.4)-10(4.0)TCID(50)/m(3) from the expired air of infected animals. This is the first study describing the isolation and quantification of CSFV from air samples originating from infected pigs and their cages, supporting previous findings that airborne transmission of CSF is feasible.

Foot-and-mouth disease - quantification and size distribution of airborne particles emitted by healthy and infected pigs

There is strong evidence to suggest that foot-and-mouth disease (FMD) can be transmitted by airborne virus up to many kilometres from a virus source. Atmospheric dispersion models are often used to predict where this disease might spread. This study investigated whether FMD virus (FMDV) aerosol has specific characteristics which need to be taken into consideration in these models. The characteristics and infectiousness of particles emitted by 12 pigs have been studied pre- and post-infection with O UKG 2001 FMDV. Aerosol generated by individual pigs was found log normally distributed in the range 0.015-20.0microm with concentrations between 1000 and 10000cm(-3) at the smallest size and <1cm(-3) above 10microm. No differences in either the total number of particles produced or their size distribution were detected between uninfected and infected pigs. However, a correlation between aerosol concentration and animal activity was found with a more active pig producing significantly greater concentrations than those that were less active. Viable virus was found up to a maximum of 6.3 log TCID(50)/24h/animal. The virus was distributed almost equally across the three size ranges; <3, 3-6 and >6microm. No correlation could be established between the production of virus and animal activity. In general the production of airborne virus closely followed the detection of viraemia in the blood and the presence of clinical symptoms. However, in one instance a pig excreted as much airborne virus as the other animals in the study, but with less virus detected in its blood. The results suggest that there is little merit in including a sophisticated virus release pattern based on physical activity periods or FMDV aerosol size spectrum, together with the appropriate dry deposition calculations, in models used to predict airborne spread of FMD. An estimate of the total daily virus production based on the clinical assessment of disease and virus strain is sufficient as input.

Experimental airborne transmission of Salmonella Agona and Salmonella Typhimurium in weaned pigs

This study tested the hypothesis of airborne transmission of Salmonella Agona (Trial I) and Salmonella Typhimurium (Trial II) in weaned pigs. The trials were performed using stainless-steel/glass isolation cabinets connected by air ducts to permit an unidirectional airflow from cabinet 1 (two control pigs) to cabinet 3 (two sentinel pigs), passing through cabinet 2 (two inoculated pigs). Air samples, pooled faecal samples from the floor and rectal swabs were collected daily and assessed by culture and PCR. A fumigation chamber and rubber gloves coupled to the cabinets allowed sampling without opening the system. Trials I and II lasted 15 and 19 days respectively. The recovery of S. Agona and S. Typhimurium and detection of seroconversion in sentinel pigs indicate that airborne Salmonella transmission in weaned pigs over short distances is possible. Further studies on the role of aerosols in the epidemiology of Salmonella in intensive pig production should be performed.

A review of approaches to quality assurance of veterinary systems for health-status certification

Regarding national and international trade of animals and animal products, certificates are required to document specific health levels. The credibility of such certificates depends on the quality of the data used to establish the status. Credibility also depends on the quality of the design and protocols used in the data-gathering process (i.e. on the quality of the surveillance-and-monitoring systems (SMS) and on the quality of the veterinary administrative systems (VAdminS)). The major requirements for the assessment of the SMS and VAdminS are: objectivity, accuracy, transparency, practicality, quantitative in nature. To assess the quality of SMS and VAdminS, systems analysis might provide a suitable framework. Systems analysis requires the identification and description of all components of the system-how they interact with each other and with other systems. Graphical methods (e.g. fault trees) are available to support this procedure. To assess the quality of SMS, scoring systems have been suggested. Their main weakness is the inherent subjectiveness. Alternatively, performance indicators (PI) could be used. For the assessment of VAdminS, questionnaires have been developed and applied. Their main limitations are that they focus on the input rather than on the output and that they are purely descriptive in nature. Thus, comparisons between countries are almost impossible. Semi-quantitative questionnaires using scores now are being developed and tested, although their limitations will be similar to those mentioned above. Another approach is the use of risk assessment including standardised data files assembled by countries volunteering to be assessed. This was applied successfully by the European Union (EU) in the geographic risk assessment for bovine spongiform encephalopathy (BSE). In general, the publication and documentation of veterinary systems needs to be encouraged to make them accessible to peer review.

Biosecurity and bovine respiratory disease

Although biosecurity practices play a role in minimizing respiratory disease in cattle, they must be used in combination with other management strategies that address the many other risk factors. Because the pathogens involved in bovine respiratory disease are enzootic in the general cattle population, biosecurity practices aimed at the complete elimination of exposure are currently impractical. Several animal husbandry and production management practices can be used to minimize pathogen shedding, exposure, and transmission within a given population, however. Various combinations of these control measures can be applied to individual farms to help decrease the morbidity and mortality attributed to respiratory disease.

Epidemiology: Risk factors for introduction of BHV1 into BHV1‐free Dutch dairy farms: A case‐control study

In May 1998, a compulsory eradication programme for BHV1 started in the Netherlands. In December 1999 approximately 24% of Dutch dairy farms were certified BHV1-free (Animal Health Service (AHS)). Ninety-three certified BHV1-free dairy farms participated in a cohort study that investigated the probability of introduction of infectious diseases. The probability of introduction of BHV1 was determined from March 1997 until April 1999. Ninety of these farms remained BHV1-free and could be used as control farms. From January 1997 until March 1998, BHV1 was introduced into 41 BHV1-free dairy farms in the Netherlands (case farms). Management data were collected for both cases and controls and were complete for 37 case farms and 82 control farms. For small data sets and for data in which both low and high frequencies were expected in the contingency tables, the asymptotic methods were unreliable. Our data set clearly resembled such a data set; the risk factors were rare events because the BHV1-free farms were closed farms on which few direct animal contacts occurred. Therefore, an exact stratified modelling approach was most suitable for the data. The study showed that dairy farms should prevent cattle from escaping or mingling with other cattle and that professional visitors should always wear protective farm clothing.