Cartographical analysis of African swine fever outbreaks in the territory of the Russian Federation and computer modeling of the basic reproduction ratio

African swine fever (ASF), have been introduced into the Russian Federation from Transcaucasia countries, has spread widely across the territory of the southern region of Russia since 2008. In this work we present an analysis of the spatial and temporal spread of the disease, determine risk factors by means of GIS tools and model the dynamics of the epidemic process both within infected premises (farms) and at the between-farm level to estimate the basic reproduction ratio R(0). The analysis allowed us to make a conclusion about the anthropogenic nature of the risk factors for disease spread. The major significant risk factors identified were: density of the road network, density of domestic swine population and density of water bodies in the study area. The basic reproduction ratio was estimated to range from 2 to 3 at the between-farm level and from 8 to 11 within the infected farms. These initial studies of the ASF epidemic provide information on which to based control and prevention programs.     

The 1997-1998 classical swine fever epidemic in The Netherlands--a survival analysis

The aim of this analysis was to characterise the temporal pattern of infection during the 1997/98 classical swine fever (CSF) epidemic in The Netherlands and hence identify and quantify risk factors for infection in different enterprise types and areas. Survival analysis and Cox proportional hazards regression were used to describe the epidemic. Substantial differences in temporal survival patterns (herd breakdown rate) were found between areas where different control policies operated. Factors with a significant influence on the infection hazard of individual herds included: sow numbers as a percentage of total sows and fatteners (HR = 3.38 for mixed herds (0.1–60% sows) vs. fattening herds (0% sows) and HR = 2.74 for breeding herds (60–100% sows) vs. fattening herds), the number of ‘transport contacts per month’ (>0.3 vs. <0.3; HR = 4.11), pig density (pigs/km²) in the area (HR_{1000 pigs} 1.48) and herd size (HR_{100 pigs} = 1.01).

Pre-emptive slaughter in an area appeared to be associated with lower subsequent disease levels. Higher frequency of transport contacts for welfare slaughter during the epidemic, however, well regulated and controlled, was associated with a substantially higher risk of becoming infected. The positive association of a higher pig density with CSF indicates the potential importance of local spread as a factor in disease transmission and emphasizes that dilution of the pig population can contribute to reduction in CSF occurrence. This analysis suggests however, that if pre-emptive slaughter can promptly be applied effectively in an area after initial diagnosis, pig density is then not a significant factor. Mixed and breeding herds had a higher probability of becoming infected than fattening herds, possibly due to different types and frequencies of inter-herd contacts. These contacts continue to some extent during the epidemic, despite the standstill of animal movements.     

Developing stochastic epidemiological models to quantify the dynamics of infectious diseases in domestic livestock

A stochastic model describing disease transmission dynamics for a microparasitic infection in a structured domestic animal population is developed and applied to hypothetical epidemics on a pig farm. Rational decision making regarding appropriate control strategies for infectious diseases in domestic livestock requires an understanding of the disease dynamics and risk profiles for different groups of animals. This is best achieved by means of stochastic epidemic models. Methodologies are presented for 1) estimating the probability of an epidemic, given the presence of an infected animal, whether this epidemic is major (requires intervention) or minor (dies out without intervention), and how the location of the infected animal on the farm influences the epidemic probabilities; 2) estimating the basic reproductive ratio, R0 (i.e., the expected number of secondary cases on the introduction of a single infected animal) and the variability of the estimate of this parameter; and 3) estimating the total proportion of animals infected during an epidemic and the total proportion infected at any point in time. The model can be used for assessing impact of altering farm structure on disease dynamics, as well as disease control strategies, including altering farm structure, vaccination, culling, and genetic selection.     

Simulating the spread of classical swine fever virus between a hypothetical wild-boar population and domestic pig herds in Denmark

Denmark has no free-range wild-boar population. However, Danish wildlife organizations have suggested that wild boar should be reintroduced into the wild to broaden national biodiversity. Danish pig farmers fear that this would lead to a higher risk of introduction of classical swine fever virus (CSFV), which could have enormous consequences in terms of loss of pork exports. We conducted a risk assessment to address the additional risk of introducing and spreading CSFV due to the reintroduction of wild boar. In this paper, we present the part of the risk assessment that deals with the spread of CSFV between the hypothetical wild-boar population and the domestic population. Furthermore, the economic impact is assessed taking the perspective of the Danish national budget and the Danish pig industry. We used InterSpreadPlus to model the differential classical swine fever (CSF) risk due to wild boar. Nine scenarios were run to elucidate the effect of: (a) presence of wild boar (yes/no), (b) locations for the index case (domestic pig herd/wild-boar group), (c) type of control strategy for wild boar (hunting/vaccination) and (d) presence of free-range domestic pigs. The presence of free-range wild boar was simulated in two large forests using data from wildlife studies and Danish habitat data. For each scenario, we estimated (1) the control costs borne by the veterinary authorities, (2) the control-related costs to farmers and (3) the loss of exports associated with an epidemic. Our simulations predict that CSFV will be transmitted from the domestic pig population to wild boar if the infected domestic pig herd is located close to an area with wild boar (<5 km). If an outbreak begins in the wild-boar population, the epidemic will last longer and will occasionally lead to several epidemics because of periodic transfer of virus from groups of infected wild boar to domestic pig herds. The size and duration of the epidemic will be reduced if there are no free-range domestic pig herds in the area with CSF-infected wild boar. The economic calculations showed that the total national costs for Denmark (i.e. the direct costs to the national budget and the costs to the pig industry) related to an outbreak of CSF in Denmark will be highly driven by the reactions of the export markets and in particular of the non-EU markets. Unfortunately, there is a substantial amount of uncertainty surrounding this issue. If hunting is used as a control measure, the average expenses related to a CSF outbreak will be 40% higher if wild boar are present compared with not present. However, a vaccination strategy for wild boar will double the total costs compared with a hunting strategy.     

Simulated effect of pig-population density on epidemic size and choice of control strategy for classical swine fever epidemics in The Netherlands

We examined the importance of pig-population density in the area of an outbreak of classical swine fever (CSF) for the spread of the infection and the choice of control measures. A spatial, stochastic, dynamic epidemiological simulation model linked to a sector-level market-and-trade model for The Netherlands were used. Outbreaks in sparsely and densely populated areas were compared under four different control strategies and with two alternative trade assumptions.The obligatory control strategy required by current EU legislation was predicted to be enough to eradicate an epidemic starting in an area with sparse pig population. By contrast, additional control measures would be necessary if the outbreak began in an area with high pig density. The economic consequences of using preventive slaughter rather than emergency vaccination as an additional control measure depended strongly on the reactions of trading partners. Reducing the number of animal movements significantly reduced the size and length of epidemics in areas with high pig density. The phenomenon of carrier piglets was included in the model with realistic probabilities of infection by this route, but it made a negligible contribution to the spread of the infection.     

Seroprevalence of Toxoplasma gondii among Nunavik Inuit (Canada)

As a result of their intimate contact with the land and their nutritional habits, the Inuit of Nunavik are considered to be at risk from zoonotic infections. To better understand the risk factors for Toxoplasma gondii infection, a serosurvey was conducted in Nunavik, Québec, in September 2004. A representative sample of the Inuit adult population of Nunavik participated in this cross-sectional study (n = 917). Antibodies (IgG) against T. gondii were detected by immunoassay. Information on sociodemographic characteristics, traditional activities, domestic environment and nutrition was gathered by questionnaire and explored as variables explanatory of seropositive results. Associations found to be statistically significant in univariate analyses were assessed by multivariable logistic regression to control for confounding factors. Almost two thirds (59.8%) of the Inuit of Nunavik were found to be seropositive for T. gondii. In multivariate analyses, risk factors for seropositivity were: increasing age, gender (women > men), lower level of education, consumption of potentially contaminated water (determined by an index of risk from waterborne infections), frequent cleaning of water reservoirs, and consumption of seal meat and feathered game. There was some variation in seroprevalence between the Ungava Bay coast (52.3%) and the Hudson Bay coast (65.6%), the two main regions of Nunavik, but this variation was not significant in the multivariable logistic regression model. This cross-sectional study demonstrated high T. gondii seroprevalence in the Inuit population and revealed that age, gender, schooling and community of residence all influence serostatus in this population. Variables related to drinking water and food choices may also influence the risk of infection. These results raise important questions about T. gondii transmission in Nunavik including possible links between terrestrial and marine cycles.     

Risk factors for highly pathogenic H7N1 avian influenza virus infection in poultry during the 1999-2000 epidemic in Italy

In 1999-2000, Italian poultry production was disrupted by an H7N1 virus subtype epidemic of highly pathogenic avian influenza (HPAI). The objectives of the present study were to identify risk factors for infection on poultry farms located in regions that had the highest number of outbreaks (Veneto and Lombardia) and the impact of pre-emptive culling as a complementary measure for eradicating infection. A Cox regression model that included spatial factors, such as the G index, was used. The results confirmed the relationship between risk of infection and poultry species, production type and size of farms. The effectiveness of pre-emptive culling was confirmed. An increased risk of infection was observed for poultry farms located near an infected farm and those at altitudes less than 150m above sea level. The measures for the control and eradication of AI virus infection need to consider species differences in susceptibility, the types of production and the density of poultry farms in the affected areas.     

新发疫病猪圆环病毒3型研究概况及防控措施

猪病的传播和流行一直是制约我国生猪养殖业发展的主要因素,特别是近年来猪病流行情况的日益复杂,非洲猪瘟、猪圆环病毒3型（Porcine Circovirus Type 3, PCV3）等多种新发疫病的不断出现,严重制约了我国生猪产业的发展,对生猪产业造成严重打击,同时也加速了我国猪场转型升级的步伐,对现代化猪场的生物安全和饲养管理提出了更高的要求。PCV3在2016年国内猪场发生至今,已传播扩散至我国多省的不同地区,成为严重威胁我国养猪业的一种新发疫病,PCV3感染导致猪群健康受损的同时,也大大增加了其他病原微生物感染的风险,且目前暂无有效疫苗对PCV3进行防控,给猪场造成了严重经济损失。本文对PCV3病原学特征、流行病学特点、临床症状和防控措施等方面进行简单综述,以期为预防PCV3的流行传播和基础研究提供参考。     

Epidemic curve and hazard function for occurrence of clinical equine influenza in a closed population of horses at a 3-day event in southern Queensland, Australia, 2007

The risk of individuals becoming infected during an epidemic of infectious disease can vary as the disease progresses. Monitoring this risk may provide information about the dynamics of transmission. This study describes the epidemic curve for an epidemic of equine influenza (EI) in a closed population of horses predominantly immunologically na?ve to EI at a 3-day event at Morgan Park in southern Queensland, Australia. The hazard function suggested that a subset of horses were at reduced risk of becoming infected. This highlights the importance, when modelling infectious disease in populations, of considering possible differences in the risk of infection among subgroups in the population.     

The role of wild animal populations in the epidemiology of tuberculosis in domestic animals: how to assess the risk

Tuberculosis is present in wild animal populations in North America, Europe, Africa and New Zealand. Some wild animal populations are a source of infection for domestic livestock and humans. An understanding of the potential of each wild animal population as a reservoir of infection for domestic animals is reached by determining the nature of the disease in each wild animal species, the routes of infection for domestic species and the risk of domestic animals encountering an infectious dose. The mere presence of infection in a wild animal population does not of itself provide evidence of a significant wildlife reservoir. Although at times counterintuitive, wildlife populations with high disease prevalence may not necessarily have a role in the epidemiology of disease in domestic livestock. The key concepts used in deciding whether an infected wild animal population is involved in the epidemiology of tuberculosis in domestic livestock is illustrated by reference to six well-researched cases: the feral pig (Suis scrofa) and feral Asian water buffalo (Bubalus bubalis) in Australia, white tailed deer (Odocoileus virginianus) in Michigan, and the brushtail possum (Trichosurus vulpecula) and other species, such as the ferret (Mustela furo), in New Zealand. A detailed analysis of Mycobacterium bovis infection in the Eurasian badger (Meles meles) in Ireland and their role as a reservoir of infection for cattle is also presented.     

Genetic and morphometric characterization of a local Vietnamese Swamp Buffalo population

The water buffalo plays a key role in the socio-economy of South-East Asia as it is the main draught power for paddy rice cultivation. While in the Indian subcontinent the water buffalo is the riverine type, in South-East Asia the majority of buffaloes are of the swamp type. In the poor remote northern province of Ha Giang in Vietnam, improvement of the swamp buffalo breed may be one of the best ways to increase sustainability of farming systems. Therefore, analysis of the genetic structure of the province buffalo population is a prerequisite to any conservation or improvement project. A total of 1122 animals were described for 11 body and horn measurements for morphometric characterization. From this sample set, 744 animals were genotyped for 17 microsatellite markers. Also 17 animals from southern provinces of Vietnam were genotyped as a comparative sample. The results showed that genetic diversity as well as inbreeding value in the Ha Giang was high. The F _ST values within the province and across Vietnam were low indicating that most of the population variation is explained by individual variability. Bayesian clustering analysis did not highlight the presence of subdivided populations. These results are useful for the implementation of a conservation and improvement strategy of the swamp buffalo in order to guarantee the householders' needs for sustainability of the farming system in the Ha Giang province.     

饲粮精氨酸与丙氨酸对环江香猪肉质、氨基酸组成及抗氧化功能的影响

本试验旨在研究饲粮精氨酸与丙氨酸对环江香猪肉质、氨基酸组成及抗氧化功能的影响,选用体重为 ２８～３３ｋｇ的环江香猪 １６头（公母各占 １／２）,按体重相近原则随机分为 ２组,每组 ４个重复,每个重复 ２头猪。丙氨酸组在基础饲粮中外源添加 １．７１％的 Ｌ－丙氨酸（等氮对照）,精氨酸组在基础饲粮中外源添加 ０．８３％的 Ｌ－精氨酸和 ０．８８％的米糠。试验期为 ４５ｄ。结果表明：与丙氨酸组相比,精氨酸组瘦肉率显著提高（Ｐ＜０．０５）,脂肪率和背最长肌中粗脂肪含量显著降低（Ｐ＜０．０５）;肝脏丝氨酸、缬氨酸、亮氨酸和异亮氨酸含量显著提高（Ｐ＜０．０５）;血浆过氧化氢酶活性显著提高（Ｐ＜０．０５）,丙二醛含量显著降低（Ｐ＜０．０５）。上述结果提示,饲粮中适宜水平的精氨酸可提高环江香猪瘦肉率,降低脂肪率,增强机体抗氧化功能,从而改善部分肉品质指标。     

Development of a control strategy for Leptospira hardjo infection in a closed beef herd.

Serological evidence of infection with a leptospire belonging to the Sejroe serogroup was identified in a closed population of Luing cattle in the west of Scotland, and the geographical isolation of the population presented an opportunity to control and possibly eradicate the infection in a large beef herd farmed under extensive conditions. Serological and bacteriological studies revealed that infection was present at a high level throughout the herd, and that the infecting serovar was hardjo. Unlike endemic hardjo infection in dairy herds, new infections were still occurring in older age-groups. Investigations of other domestic and free-living species sharing the habitat demonstrated that the maintenance of an endemic focus of hardjo was restricted to the cattle. Changes in management to prevent the transmission of infection to successive cohorts of young animals were impractical and risky, and antibiotic treatment followed by removal to clean pasture failed to prevent new cases. Thus vaccination offered the only means of control and possible eradication, and the epidemiological characteristics of the infection dictated that the programme be applied to the whole herd.     

Using expert opinion to identify risk factors important to infectious salmon-anemia (ISA) outbreaks on salmon farms in Maine, USA and New Brunswick, Canada

Thirty industry or regulatory professionals, with extensive experience in the local infectious salmon-anemia (ISA) epidemic, were queried on their opinions regarding the spread and impact of ISA in Maine, USA and New Brunswick, Canada. Subjective probability-estimation techniques were used to elicit likelihood ratios (LR) for risk factors of potential relevance to the epidemic. Experts were asked to answer questions based on their direct and local experience with ISA, rather than through knowledge gained from scientific references or experience in other regions. The results found the strongest independent predictors of ISA infection to include (1) a site's proximity to other farms with clinically infected fish, (2) a previous history of ISA on the site, (3) whether a site fallows for a month or more between year classes and (4) whether the site employs harvest vessels practicing full containment of blood and stun water. The strongest predictors of ISA severity included (1) stocking density, (2) the length of time between infection and removal of infected fish, (3) whether fish are moved between pens (after infection) and (4) a farm's sea-lice (Lepeophtheirus salmonis) status. Experts believed that transmission of ISA virus during the local epidemic was influenced by proximity (spatial and temporal) to activities resulting in large-scale shedding of virus into a shared water column, and that severity of infection corresponded more to infected-fish removal practices and certain husbandry decisions. Personnel and equipment biosecurity measures were not seen as strong predictors of either infection or severity in this analysis, though their perceived level of importance was greater among government than industry experts.     

Risk factors and characteristics of H5N1 Highly Pathogenic Avian Influenza (HPAI) post-vaccination outbreaks

Highly pathogenic avian influenza (HPAI) virus H5N1 is now endemic in South-East Asia but HPAI control methods differ between countries. A widespread HPAI vaccination campaign that started at the end of 2005 in Viet Nam resulted in the cessation of poultry and human cases, but in 2006/2007 severe HPAI outbreaks re-emerged. In this study we investigated the pattern of this first post-vaccination epidemic in southern Viet Nam identifying a spatio-temporal cluster of outbreak occurrence and estimating spatially smoothed incidence rates of HPAI. Spatial risk factors associated with HPAI occurrence were identified. Medium-level poultry density resulted in an increased outbreak risk (Odds ratio (OR) = 5.4, 95% confidence interval (CI): 1.6–18.9) but also climate-vegetation factors played an important role: medium-level normalised difference vegetation indices during the rainy season from May to October were associated with higher risk of HPAI outbreaks (OR = 3.7, 95% CI: 1.7–8.1), probably because temporal flooding might have provided suitable conditions for the re-emergence of HPAI by expanding the virus distribution in the environment and by enlarging areas of possible contacts between domestic waterfowl and wild birds. On the other hand, several agricultural production factors, such as sweet potatoes yield, increased buffalo density, as well as increased electricity supply were associated with decreased risk of HPAI outbreaks. This illustrates that preventive control measures for HPAI should include a promotion of low-risk agricultural management practices as well as improvement of the infrastructure in village households. Improved HPAI vaccination efforts and coverage should focus on medium poultry density areas and on the pre-monsoon time period.     

Herd factors associated with the seroprevalences of four major respiratory pathogens in slaughter pigs from farrow-to-finish pig herds

The objective of this study was to investigate sero-epidemiological aspects of Mycoplasma hyopneumoniae (Mh), influenza H1N1 and H3N2 viruses and Aujeszky disease virus (ADV) in fattening pigs from 150 randomly selected farrow-to-finish pig herds. Different herd factors were examined as potential risk indicators for the percentage of pigs with antibodies against the 4 pathogens. The median within-herd seroprevalences of the pathogens were: Mh 76%, H1N1 100%, H3N2 40% and ADV 53%. There was a positive association between the seroprevalences of both influenza viruses, and a negative association between the seroprevalences of ADV and H1N1. The percentage of pigs seropositive for Mh increased with the purchase of gilts and with the season (slaughter date in March-April). The within-herd seroprevalences of both influenza viruses were higher in the case of a higher density of pig herds in the municipality. A higher number of fattening pigs per pen additionally increased the risk of being seropositive for H3N2. The percentage of pigs with anti-gE-antibodies against the wild type ADV increased with higher airspace stocking density in the finishing unit, increasing herd size, increasing number of pig herds in the municipality and slaughter date in March-April. Increased seroprevalences for these 4 respiratory pathogens were mostly associated with pig density in the herd and its vicinity, the winter period, and with the purchase of gilts. Purchase of gilts, number of fattening pigs per pen and airspace stocking density are risk factors that can be managed directly by farmers striving to attain a high respiratory health status of pigs.     

Epidemiological investigations of the 2001 foot-and-mouth disease outbreak in Argentina

A total of 2126 herds, an attack rate of 0.82 per cent, were affected during an epidemic of foot-and-mouth disease in Argentina in 2001. The spatial and temporal distribution of the epidemic was investigated using nearest-neighbour and spatial scan tests and by estimating the frequency distributions of the times to intervention, and distances and times between outbreaks. The outbreaks were clustered and associated significantly (P<0.01) with herd density; 94 per cent were located in the Pampeana region, where the cattle population is concentrated, which had an attack rate of 1.4 per cent. The clustering results suggested that the virus had spread locally between outbreaks. Most of the outbreaks were separated by one day and the maximum distance between outbreaks was almost 2000 km, indicating that the infection spread rapidly over large distances. The index outbreak was detected more than 15 days after the primary outbreak, and restrictions on the movement of cattle were probably not enforced until about one month after infection occurred. As in other major epidemics, the period between the first outbreaks and the effective application of control strategies was probably crucial in determining the progress of the epidemic.     

Modeling the spread and control of foot-and-mouth disease in Pennsylvania following its discovery and options for control

In this paper, we simulate outbreaks of foot-and-mouth disease in the Commonwealth of Pennsylvania, USA - after the introduction of a state-wide movement ban - as they might unfold in the presence of mitigation strategies. We have adapted a model previously used to investigate FMD control policies in the UK to examine the potential for disease spread given an infection seeded in each county in Pennsylvania. The results are highly dependent upon the county of introduction and the spatial scale of transmission. Should the transmission kernel be identical to that for the UK, the epidemic impact is limited to fewer than 20 premises, regardless of the county of introduction. However, for wider kernels where infection can spread further, outbreaks seeded in or near the county with highest density of premises and animals result in large epidemics (>150 premises). Ring culling and vaccination reduce epidemic size, with the optimal radius of the rings being dependent upon the county of introduction. Should the kernel width exceed a given county-dependent threshold, ring culling is unable to control the epidemic. We find that a vaccinate-to-live policy is generally preferred to ring culling (in terms of reducing the overall number of premises culled), indicating that well-targeted control can dramatically reduce the risk of large scale outbreaks of foot-and-mouth disease occurring in Pennsylvania.     

Analysis of the 1999-2000 highly pathogenic avian influenza (H7N1) epidemic in the main poultry-production area in northern Italy

We evaluated the effects of risk factors and control policies following the highly pathogenic avian influenza (HPAI) epidemic that struck northern Italy's poultry industry in the winter of 1999–2000. The epidemic was caused by a type-A influenza virus of the H7N1 subtype, that originated from a low-pathogenic AI virus which spread among poultry farms in northeastern Italy in 1999 and eventually became virulent by mutation. Most infected premises (IP) were located in the regions of Lombardy and Veneto (382 out of 413, 92.5%), and the eradication measures provided for in the European legislation were enforced. In Veneto, where flock density was highest, infection-control was also accomplished by means of depopulation of susceptible flocks through a ban on restocking and pre-emptive slaughter of flocks that were in the vicinities of or that had dangerous contacts with IPs. In Lombardy, such control measures were applied to a lesser extent. Infection incidence rate (IR) was 2.6 cases per 1000 flocks per day in Lombardy and 1.1 in Veneto. After the implementation of infection-control measures, the at-risk population, the percentage of flocks ≤1.5 km from IPs, and the HPAI-IR underwent a greater reduction in Veneto than in Lombardy. Although the proximity (≤1.5 km) to IPs in the temporal risk window (TRW) was a major risk factor for HPAI at the individual flock level, its effect at the population level (population-attributable fraction) did not exceed 31.3%. Viral transmission therefore also occurred among relatively distant flocks. Turkey flocks were characterised by grerater IR of HPAI compared with other bird species such as layer hens, broilers, gamebirds, and waterfowl, even when located at distances >1.5 km from IPs. In Lombardy, IR for species other than turkeys was also relatively high.