Assessment of Effectiveness of Control Strategies Against Simulated Outbreaks of Highly Pathogenic Avian Influenza in Ontario, Canada.

The North American Animal Disease Spread Model (NAADSM) is a stochastic model framework developed to simulate the spread of highly contagious diseases of livestock and poultry, such as foot-and-mouth disease and highly pathogenic avian influenza (HPAI). The objective of this study was to make recommendations on the most effective HPAI control policy for Canada, specifically, on the effect of different speeds of detection, effectiveness of movement restrictions and stamping-out and ring-culling strategies on the magnitude of an HPAI outbreak. In addition, the effect of introduction of infection in a range of multiple farms simultaneously was also evaluated. A total of 21 060 scenarios, defined as different combinations of parameters for various epidemiological conditions and control measures, were created to simulate the number of poultry flocks that would become infected as a result of an incursion of HPAI. Each scenario was parameterized in NAADSM and replicated 1000 times, generating the median number of flocks infected at the end of the simulated outbreak for each scenario. Negative binomial regression analysis was used to model significant explanatory variables of the median number of flocks infected at the end of each simulated outbreak for each of the 21 060 scenarios. The final model included the following explanatory variables: number and type initially infected flock(s), density of flocks within the county where the initially infected flock(s) was located, probability of transmission through indirect contact, subclinical spread of the infection, speed of detection and a two-way interaction between intensity of bird destruction strategy and movement restriction effectiveness to reduce transmission through direct and indirect contacts. The modelling results suggested that stamping out of the detected infected flocks, without ring culling, in combination with effective movement restrictions on direct and indirect contacts, would be the most appropriate policy for Ontario.

One-Health Simulation Modelling: Assessment of Control Strategies Against the Spread of Influenza between Swine and Human Populations Using NAADSM.

Simulation models implemented using a range of parameters offer a useful approach to identifying effective disease intervention strategies. The objective of this study was to investigate the effects of key control strategies to mitigate the simultaneous spread of influenza among and between swine and human populations. We used the pandemic H1N1 2009 virus as a case study. The study population included swine herds (488 herds) and households-of-people (29,707 households) within a county in Ontario, Canada. Households were categorized as: (i) rural households with swine workers, (ii) rural households without swine workers and (iii) urban households without swine workers. Seventy-two scenarios were investigated based on a combination of the parameters of speed of detection and control strategies, such as quarantine strategy, effectiveness of movement restriction and ring vaccination strategy, all assessed at three levels of transmissibility of the virus at the swine-human interface. Results showed that the speed of detection of the infected units combined with the quarantine strategy had the largest impact on the duration and size of outbreaks. A combination of fast to moderate speed of the detection (where infected units were detected within 5-10 days since first infection) and quarantine of the detected units alone contained the outbreak within the swine population in most of the simulated outbreaks. Ring vaccination had no added beneficial effect. In conclusion, our study suggests that the early detection (and therefore effective surveillance) and effective quarantine had the largest impact in the control of the influenza spread, consistent with earlier studies. To our knowledge, no study had previously assessed the impact of the combination of different intervention strategies involving the simultaneous spread of influenza between swine and human populations.

One-Health Simulation Modelling: A Case Study of Influenza Spread between Human and Swine Populations using NAADSM.

The circulation of zoonotic influenza A viruses including pH1N1 2009 and H5N1 continue to present a constant threat to animal and human populations. Recently, an H3N2 variant spread from pigs to humans and between humans in limited numbers. Accordingly, this research investigated a range of scenarios of the transmission dynamics of pH1N1 2009 virus at the swine-human interface while accounting for different percentages of swine workers initially immune. Furthermore, the feasibility of using NAADSM (North American Animal Disease Spread Model) applied as a one-health simulation model was assessed. The study population included 488 swine herds and 29, 707 households of people within a county in Ontario, Canada. Households were categorized as follows: (i) rural households with swine workers, (ii) rural households without swine workers, and (iii) urban households without swine workers. Forty-eight scenarios were investigated, based on the combination of six scenarios around the transmissibility of the virus at the interface and four vaccination coverage levels of swine workers (0-60%), all under two settings of either swine or human origin of the virus. Outcomes were assessed in terms of stochastic 'die-out' fraction, size and time to peak epidemic day, overall size and duration of the outbreaks. The modelled outcomes indicated that minimizing influenza transmissibility at the interface and targeted vaccination of swine workers had significant beneficial effects. Our results indicate that NAADSM can be used as a framework to model the spread and control of contagious zoonotic diseases among animal and human populations, under certain simplifying assumptions. Further evaluation of the model is required. In addition to these specific findings, this study serves as a benchmark that can provide useful input to a future one-health influenza modelling studies. Some pertinent information gaps were also identified. Enhanced surveillance and the collection of high-quality information for more accurate parameterization of such models are encouraged.

Network analysis of swine shipments in Ontario, Canada, to support disease spread modelling and risk-based disease management.

Understanding contact networks are important for modelling and managing the spread and control of communicable diseases in populations. This study characterizes the swine shipment network of a multi-site production system in southwestern Ontario, Canada. Data were extracted from a company's database listing swine shipments among 251 swine farms, including 20 sow, 69 nursery and 162 finishing farms, for the 2-year period of 2006 to 2007. Several network metrics were generated. The number of shipments per week between pairs of farms ranged from 1 to 6. The medians (and ranges) of out-degree were: sow 6 (1-21), nursery 8 (0-25), and finishing 0 (0-4), over the entire 2-year study period. Corresponding estimates for in-degree of nursery and finishing farms were 3 (0-9) and 3 (0-12) respectively. Outgoing and incoming infection chains (OIC and IIC), were also measured. The medians (ranges) of the monthly OIC and IIC were 0 (0-8) and 0 (0-6), respectively, with very similar measures observed for 2-week intervals. Nursery farms exhibited high measures of centrality. This indicates that they pose greater risks of disease spread in the network. Therefore, they should be given a high priority for disease prevention and control measures affecting all age groups alike. The network demonstrated scale-free and small-world topologies as observed in other livestock shipment studies. This heterogeneity in contacts among farm types and network topologies should be incorporated in simulation models to improve their validity. In conclusion, this study provided useful epidemiological information and parameters for the control and modelling of disease spread among swine farms, for the first time from Ontario, Canada.

A review of simulation modelling approaches used for the spread of zoonotic influenza viruses in animal and human populations.

Increasing incidences of emerging and re-emerging diseases that are mostly zoonotic (e.g. severe acute respiratory syndrome, avian influenza H5N1, pandemic influenza) has led to the need for a multidisciplinary approach to tackling these threats to public and animal health. Accordingly, a global movement of 'One-Health/One-Medicine' has been launched to foster collaborative efforts amongst animal and human health officials and researchers to address these problems. Historical evidence points to the fact that pandemics caused by influenza A viruses remain a major zoonotic threat to mankind. Recently, a range of mathematical and computer simulation modelling methods and tools have increasingly been applied to improve our understanding of disease transmission dynamics, contingency planning and to support policy decisions on disease outbreak management. This review provides an overview of methods, approaches and software used for modelling the spread of zoonotic influenza viruses in animals and humans, particularly those related to the animal-human interface. Modelling parameters used in these studies are summarized to provide references for future work. This review highlights the limited application of modelling research to influenza in animals and at the animal-human interface, in marked contrast to the large volume of its research in human populations. Although swine are widely recognized as a potential host for generating novel influenza viruses, and that some of these viruses, including pandemic influenza A/H1N1 2009, have been shown to be readily transmissible between humans and swine, only one study was found related to the modelling of influenza spread at the swine-human interface. Significant gaps in the knowledge of frequency of novel viral strains evolution in pigs, farm-level natural history of influenza infection, incidences of influenza transmission between farms and between swine and humans are clearly evident. Therefore, there is a need to direct additional research to the study of influenza transmission dynamics in animals and at the animal-human interface.

Assessment of occupational exposure to leptospirosis in a sheep-only abattoir.

This study estimated the frequency of exposure of meat workers to carcasses infected with Leptospira serovars Hardjobovis or Pomona in a sheep-only abattoir in New Zealand. A stochastic spreadsheet model was developed to assess the daily risk of exposure of eviscerators, meat inspectors and offal handlers to live leptospires in sheep carcasses from May to November 2004 (high-risk period), and from December 2004 to June 2005 (low-risk period). The average sheep processed per day were 225 for an eviscerator, 374 for a meat inspector, and 1123 for an offal handler. The median daily exposures during high- and low-risk periods were 11 [95% distribution interval (DI) 5-19] and three (95% DI 1-8) infected carcasses/day for eviscerators, 18 (95% DI 9-29) and six (95% DI 2-12) for meat inspectors, and 54 (95% DI 32-83) and 18 (95% DI 8-31) for offal handlers, respectively. Stochastic risk modelling provided evidence that processing of sheep carcasses exposed meat workers regularly to live leptospires with substantial seasonal variation.

Are white-spot lesions in kidneys in sheep associated with leptospirosis?

AIM: To determine the association between white-spot lesions in kidneys and serological and cultural prevalence of leptospirosis in sheep, and to evaluate the diagnostic value of these lesions in individual sheep and lines of sheep at slaughter as indicators of past or current episodes of leptospirosis. METHODS: Lines of lambs were randomly selected, and within lines individual lambs were randomly selected at slaughter. Blood samples and entire kidneys were collected. Serum was tested using the microscopic agglutination test (MAT) for antibody against Leptospira borgpetersenii serovar Hardjobovis or Leptospira interrogans serovar Pomona. Kidneys were cultured for the presence of Leptospira spp. The association between grossly visible white-spotted kidneys (WSK) and the serological status, and between WSK and culture status was evaluated at both line and individual levels. A fixed-effect multivariable logistic regression model was fitted to the line-level data, and included within-line prevalence of carcasses with WSK and line size. A random-effect multivariable logistic regression model was fitted to the individual-level data. This model included WSK lesion score and a random line effect. RESULTS: White-spot lesions in kidneys were significantly associated with the serological status for Leptospira spp. in individual sheep. A strong positive dose-response relationship between sero-status and the number of white spots on kidneys was observed. However, the sensitivity of WSK to detect seropositive carcasses was low (51 (95% CI=43-59)%), and specificity was moderately low (86 (95% CI=84-87)%). Due to a low observed seroprevalence of 5.2 (95% CI=3.9-7.1)% to serovar Hardjo or Pomona, the positive predictive value (PPV) of WSK for serology was only 18 (95% CI=14-22)%, and the negative predictive value (NPV) was 96 (95% CI=96-97)%. Carcasses with high WSK lesion scores (more than five white spots or white mottling on one or both kidneys) were 6.1 (95% CI=4.3-8.3) times more likely to be seropositive to either serovar than were carcasses with low scores (one to five white spots on one or both kidneys). However, the test sensitivity and PPV for these criteria were regarded unacceptably low (27 (95% CI=20-34)% and 27 (95% CI=21-35)%, respectively). Consideration of lesion status of lines rather than individual animals resulted in a high sensitivity of 98 (95% CI=87-100)%, but very low specificity of 15 (95% CI=8-27)% and a PPV of 48 (95% CI=37-59)%. Due to the low sensitivity of WSK and low prevalence of culture- positive carcasses, the PPV for WSK was as low as 4 (95% CI=2-12)%. CONCLUSIONS: Whereas highly significant associations, including a strong dose-response effect, were observed between WSK and MAT serology, WSK was a poor predictor for the antibody and pathogen status of sheep carcasses with respect to leptospirosis.

Prevalence of pathogenic Leptospira spp. in sheep in a sheep-only abattoir in New Zealand.

AIM: To determine the prevalence of the two most commonly diagnosed pathogenic Leptospira spp. serovars, Hardjobovis and Pomona, in sheep in a sheep-only abattoir in New Zealand, and to determine the prevalence of kidneys which were leptospire culture-positive collected from sheep seropositive or seronegative to the microscopic agglutination test (MAT). METHODS: A repeated cross-sectional observational study was conducted of serological and kidney culture prevalences of Leptospira borgpetersenii serovar Hardjobovis and Leptospira interrogans serovar Pomona. Lines of sheep and individual sheep were systematically randomly selected at a sheep-only abattoir during 18 May 2004 to November 2004 and 06 December 2004 to 14 June 2005. Additionally, a cross-sectional study examined prevalences in a purposively selected line of sheep from a flock with clinical evidence of an outbreak of leptospirosis. RESULTS: In the study population of 15,855 sheep of which 2,758 were sampled, 5.7 (95% CI=4.9-6.7)% were seropositive to one or both serovars; 44.2 (95% CI=34.6-54.2)% of 95 lines of sheep and 44.9 (95% CI=35.0-55.3)% of 89 farms showed serological evidence of infection. The serological prevalence of serovar Hardjobovis was significantly higher than that of serovar Pomona both at line (33% and 4%, respectively) and individual (5% and 1%, respectively) levels. A low but persistent seroprevalence of Hardjobovis throughout both years suggested low-level endemicity to this serovar, whereas Pomona infections appeared to be sporadic. Leptospires were isolated from kidneys of 8/37 (22%) Hardjobovis- and 1/6 (17%) Pomona-seropositive, and 5/499 (1%) seronegative animals. Of the animals purposively sampled from a farm with a clinical outbreak of leptospirosis, all kidneys from the 13 seropositive animals were culture-positive, indicating a high risk of exposure of meat workers in outbreak situations. Kidneys of MAT-seropositive sheep were 21.7 (95% CI=7.6-61.9) times more likely to test culture-positive than kidneys from animals with negative MAT titres. In general, the results indicated that 13/1,000 sheep slaughtered were potentially shedding leptospires. CONCLUSIONS: The study demonstrated the presence of a definite risk of occupational exposure of meat workers in a sheep-only slaughterhouse to the two most commonly diagnosed pathogenic Leptospira spp. serovars in New Zealand.

Assessment of progesterone-induced acrosome reaction by biotinylated monoclonal antibody probes.

PROBLEM: To develop an immunohistochemical assay for determination of acrosome-reacted human sperm and to study the effects of progesterone and cholesterol treatment on human sperm acrosome reaction. METHOD OF STUDY: Three distinct anti-sperm monoclonal antibodies were biotinylated and used as probes for assessment of acrosome reaction in a 30-min immunohistochemical assay. Progesterone and/or cholesterol were added to sperm preparation to influence the acrosome reaction in different experimental conditions. RESULTS: Percentages of acrosome-intact sperm decreased significantly during the 18-hr incubation. Acrosome reaction could be induced by progesterone as early as 2 hr after sperm incubation in human tubal fluid. The degree of progesterone-induced acrosome reaction was time dependent and the optimal effect was reached by adding 10 micrograms/ml progesterone for 30 min incubation. Progesterone-induced acrosome reaction was shown to be hormone-concentration dependent with 50% stimulation at 1 microgram/ml. Cholesterol (1 microgram/ml) was found to inhibit progesterone-induced acrosome reaction either by co-incubation with human sperm during capacitation, or by simultaneous incubation with progesterone during acrosome reaction induction. CONCLUSIONS: Assessment of human sperm acrosomal status by avidin-biotin immunohistochemical assay can be a routine in clinical laboratories for male infertility services. Cholesterol can inhibit progesterone-induced acrosome reaction, possibly by its modifications of sperm plasma membrane and/or interference of progesterone binding to its surface receptors.

Monoclonal antibodies as direct probes for human sperm acrosome reaction.

PROBLEM: To develop simple and rapid assay procedures for determining human sperm acrosome reaction under various experimental conditions. METHODS: Specific monoclonal antibodies against human sperm acrosome were generated and utilized as probes for acrosome reaction assays by direct labelling of antibodies with fluorescein-isothiocyanate (FITC). RESULTS: Among the generated monoclonal antibodies, HS-63 was shown to react with antigens in the acrosome content of permeabilized acrosome-intact human sperm, but not with those of the live ones. HSA-10 was found to recognize antigens on the surface of sperm inner acrosome and to react with acrosome-reacted human sperm in suspension. Following a swim-up procedure, highly motile sperm were recovered and incubated in BWW medium at 37 degrees C for 18 h. The percentages of acrosome-reacted sperm were determined at various incubation times by using FITC-labeled HS-63 or HSA-10 as the indicators in 10 min direct immunofluorescent assay. With the FITC-labeled HS-63 probe, the percentage of positively stained human sperm fixed in methanol decreased significantly after 18 h of incubation from > 90 to 70-80%. In contrast, positively stained live human sperm by HSA-10 increased significantly from < 1% to 15-30%. A high correlation was obtained between the use of monoclonal antibodies and PSA (Pissum sativum agglutinin) for direct assessment of human sperm acrosome reaction. CONCLUSION: In view of the simplicity in assay procedures and evaluations, these FITC-labeled monoclonal antibodies are reliable probes for direct assessment of acrosomal status of human sperm.

Molecular characterizations of an intraacrosomal antigen defined by HS-33 monoclonal antibody.

Among the numerous anti-sperm monoclonal antibodies generated in our laboratory, HS-33 was shown to react with a conserved antigen on the acrosome of spermatozoa from human and mouse. By using indirect immunofluorescent assay, it was demonstrated that HS-33 did not bind to live human sperm. However, this antibody was found to react with the methanol-fixed acrosome-intact, but not with acrosome-reacted sperm. The human sperm antigen recognized by this antibody was purified from human sperm extract by immunoaffinity chromatography. The purified cognate human sperm antigen designated as HSAg-33 was found to be a protein with a molecular weight of approximately 72 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions. The tissue-specificity and the developmental expression of this sperm antigen were examined using frozen sections of various human and mouse tissues. The antigen was shown to be expressed specifically in the testicular sperm at the postmeiotic stages of spermatogenesis but not in any other somatic tissues. "Spontaneous" acrosome reaction was determined following 18 hours of incubation in Biggers, Whitten, and Whittingham (BWW) medium by using HS-33 monoclonal antibody and Pisum sativum agglutinin (PSA) as probes. The number of sperm stained positively with this antibody decreased significantly following overnight incubation, indicating the occurrence of an acrosome reaction. The results of this study suggest that HSAg-33 is a potentially useful sperm-specific acrosome marker for studies of sperm capacitation and acrosome reaction.