Measuring impact of vaccination among wildlife: The case of bait vaccine campaigns for classical swine fever epidemic among wild boar in Japan.

Understanding the impact of vaccination in a host population is essential to control infectious diseases. However, the impact of bait vaccination against wildlife diseases is difficult to evaluate. The vaccination history of host animals is generally not observable in wildlife, and it is difficult to distinguish immunity by vaccination from that caused by disease infection. For these reasons, the impact of bait vaccination against classical swine fever (CSF) in wild boar inhabiting Japan has not been evaluated accurately. In this study, we aimed to estimate the impact of the bait vaccination campaign by modelling the dynamics of CSF and the vaccination process among a Japanese wild boar population. The model was designed to estimate the impact of bait vaccination despite lack of data regarding the demography and movement of wild boar. Using our model, we solved the theoretical relationship between the impact of vaccination, the time-series change in the proportion of infected wild boar, and that of immunised wild boar. Using this derived relationship, the increase in antibody prevalence against CSF because of vaccine campaigns in 2019 was estimated to be 12.1 percentage points (95% confidence interval: 7.8-16.5). Referring to previous reports on the basic reproduction number (R0) of CSF in wild boar living outside Japan, the amount of vaccine distribution required for CSF elimination by reducing the effective reproduction number under unity was also estimated. An approximate 1.6 (when R0 = 1.5, target vaccination coverage is 33.3% of total population) to 2.9 (when R0 = 2.5, target vaccination coverage is 60.0% of total population) times larger amount of vaccine distribution would be required than the total amount of vaccine distribution in four vaccination campaigns in 2019.

Additive Bayesian network analysis of the relationship between bovine respiratory disease and management practices in dairy heifer calves at pre-weaning stage.

BACKGROUND: Nursery farms that accept nursing and growing pre-weaned heifer calves from private dairy farms must work to prevent bovine respiratory disease (BRD). Knowledge of the BRD-associated risk factors related to calf management and calves' condition will help to develop appropriate neonatal management practices at original farms and to identify calves at higher risk for BRD at nursery farms. In this study, the relationship between BRD and calf management practices (colostrum feeding, dam parity, serum total protein concentration at introduction (TP), body weight at introduction, introduction season, and daily average growth) was investigated using observational data from pre-weaned dairy calves introduced into a nursery farm in Hokkaido, Japan between 2014 and 2018 (n = 3185). Using additive Bayesian network (ABN) analysis, which is a multivariate statistical modelling approach, the direct and indirect associations between these factors were assessed. RESULTS: Colostrum feeding contributed to an increase in TP (correlation 1.02 [95 % CI, 0.94;1.10]), which was negatively associated with BRD directly (log odds ratio - 0.38 [- 0.46;-0.31]) and indirectly through increasing daily growth (correlation 0.12 [0.09;0.16]). Calves of multiparous dams had higher body weight at introduction (correlation 0.82 [0.74;0.89]), which indirectly reduced BRD risk through the increasing daily growth (correlation 0.17 [0.14;0.21]). Calves introduced during winter had the highest risk for BRD (log odds ratio 0.29 [0.15;0.44]), while those introduced in summer had the lowest risk (log odds ratio - 0.91 [- 1.06;-0.75]). The introduction season was also associated with BRD indirectly through dam parity, body weight at introduction, and daily growth. CONCLUSIONS: The following calf management practices are recommended for preventing BRD in pre-weaned calves at nursery farms: (1) encouraging colostrum feeding to neonatal calves at their original farms; and (2) identifying calves with higher BRD risk, i.e., those without feeding colostrum, born to primiparous cattle, with low body weight at introduction, and/or introduced in winter, and paying intensive attention to the calves for rapid detection of BRD. ABN analysis applied enabled us to understand the complex inter-relationships between BRD incidence and the risk factors, which will help to reduce BRD incidence and to rear healthy calves at nursery farms.

Region-wise analysis of dairy cow movements in Japan.

BACKGROUND: Animal movement is considered the most significant factor in the transmission of infectious diseases in livestock. A better understanding of its effects would help provide a more reliable estimation of the disease spread and help develop effective control measures. If the movement pattern is heterogeneous, its characteristics should be considered in epidemiological analyses, such as when using simulation models to obtain reliable outputs. In Japan, following the bovine spongiform encephalopathy epidemic, a traceability system for cattle was established in 2003, and the registration of all cattle movements in the national database began. This study is the first to analyze cattle movements in Japan. We examined regional and seasonal heterogeneity in dairy cow movements, which accounted for most Japanese breeding cattle. RESULTS: In the 14 years from April 2005 to March 2018, 4,577,709 between-farm movements of dairy cows were recorded, and the number of movements was counted by month and age for both inter- and intra-regional movements. As a result, two characteristic round-trip movements were observed: one was non-seasonal and inter-regional movements related to cattle-breeding ranches in Hokkaido (the northern region of Japan), which consists of the movement of cows around ages 6 to 8 and 21 to 23 months old. In addition, the seasonal movement of heifers for summer grazing within Hokkaido occurred in May and October at the peak ages of 13 to 14 and 19 to 20 months old, respectively. The observed heterogeneity seemed to reflect the suitability of raising the Holstein breed in Hokkaido and the shortage of supply of replacement heifers and available farming areas outside Hokkaido. CONCLUSIONS: Understanding the patterns of dairy cow movements will help develop reliable infectious disease models and be beneficial for developing effective control measures against these diseases.

Epidemiological analysis of classical swine fever in wild boars in Japan.

BACKGROUND: Classical swine fever (CSF) is a contagious disease of pigs and wild boars that is transmitted through direct/indirect contact between animals or CSF virus-contaminated fomites. When the disease re-emerged in 2018 in Japan, a CSF-infected wild boar was reported shortly after the initial pig farm outbreak; subsequently, the disease spread widely. To control the disease spread among wild boars, intensive capturing, fencing, and oral bait vaccination were implemented with concomitant virological and serological surveillance. This study aimed to describe the disease spread in the wild boar population in Japan from September 2018, when the first case was reported, to March 2020, based on the surveillance data. We conducted statistical analyses using a generalized linear mixed model to identify factors associated with CSF infection among wild boars. Moreover, we descriptively assessed the effect of oral bait vaccination, which started in March 2019 in some municipalities in the affected areas. RESULTS: We observed a faster CSF infection spread in the wild boar population in Japan compared with the CSF epidemics in European countries. The infection probability was significantly higher in dead and adult animals. The influence of the multiple rounds of oral bait vaccination was not elucidated by the statistical modeling analyses. There was a decrease and increase in the proportion of infected and immune animals, respectively; however, the immunization in piglets remained insufficient after vaccination for 1 year. CONCLUSIONS: Conditions regarding the wild boar habitat, including forest continuity, higher wild boar population density, and a larger proportion of susceptible piglets, were addressed to increase the infection risk in the wild boar population. These findings could improve the national control strategy against the CSF epidemic among wild boars.

Alkaline phosphatase in pediatric patients with genu varum caused by vitamin D-deficient rickets.

An elevated serum alkaline phosphatase (ALP) level is one of the markers for the presence of rickets in children, but it is also associated with bone formation. However, its role in diagnosing genu varum in pediatric patients with vitamin D-deficient rickets is still unknown. To clarify the role of the serum ALP level in assessing the severity of genu varum, we retrospectively investigated this issue statistically using data on rickets such as serum intact parathyroid hormone (iPTH), 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, ALP, the level of creatinine as the percentage of the median according to age (%Cr), and the metaphyseal diaphyseal angle (MDA) in the lower extremities as an index of the severity of genu varum. A multiple regression analysis revealed that log ALP and %Cr values were negatively associated with MDA values. The former association was also confirmed by a linear mixed model, while iPTH was positively associated with MDA by path model analysis. To elucidate the association of ALP with MDA in the presence of iPTH, we investigated three-dimensional figures by neural network analysis. This indicated the presence of a biphasic association of ALP with MDA: the first phase increases while the second decreases MDA. The latter phenomenon is considered to be associated with the increase in bone formation due to the mechanical stress loaded on the lower extremities. These findings are important and informative for pediatricians to understand the significance of the serum ALP level in pediatric patients with genu varum caused by vitamin D deficiency.

First nationwide survey of the seroprevalence of Toxoplasma gondii in wild boars in Japan.

The increase in some wildlife species is of global concern. The utilization of wildlife meat as food and feed represents a potential source of food-borne pathogens; this is particularly a potential concern for the use of wild board as a food source in Japan. Regarding food safety and an animal infectious disease control, however, little is known about the infection level of zoonotic pathogens including Toxoplasma gondii (T. gondii) in wild boar populations in their natural habitats in Japan. A total of 1279 blood samples from 41 prefectures were collected from apparently healthy wild boars during the three hunting periods (September to February) of 2014-2015, 2015-2016, and 2017-2018. Out of these sera, 461 samples tested positive by a commercial indirect ELISA for T. gondii, and the total apparent and adjusted true seroprevalence were estimated to 36.0% (95% confidence interval [CI], 33.4-38.7) and 31.3% (95% CI, 33.1-38.9), respectively. The seroprevalence was significantly higher in yearlings and adults than in piglets (P < 0.05); however, no significant difference according to gender was noted. These results indicate the importance of adequate heating of wild boar meat before consumption to prevent transmission of T. gondii to humans. Furthermore, freezing meat for several days before cooking is recommended to reduce the risk of infection. In addition, although the incidence of toxoplasmosis in pig farms is relatively low in Japan, biosecurity measures against the felids and the varied intermediate hosts should be strengthened, especially, at the farms located in the wild boar habitats to prevent livestock infection.

Fat distribution in short-stature children born small for gestational age.

BACKGROUND: Children born small for gestational age (SGA) with catch-up growth are at high risk for developing obesity; however, the characteristics of body composition, especially fat distribution, before and after growth hormone (GH) treatment in SGA children without catch-up growth remains largely unknown. METHODS: Anthropometric characteristics, body composition by dual-energy X-ray absorption, and fat distribution by computed tomography at the umbilical level were examined in 27 prepubertal short-stature children born SGA before and 1 year after GH treatment. RESULTS: Before GH treatment, short-stature SGA children had lean phenotypes, and both visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) were significantly lower than the age- and sex-matched Japanese reference values. Growth hormone treatment significantly increased height standard deviation scores (SDS), without affecting body mass index SDS. Percentage fat mass decreased with GH treatment; however, fat mass was not altered. Both VAT and SAT were significantly lower than the reference values after GH treatment. The ratio of VAT over SAT significantly increased by GH treatment. CONCLUSIONS: Both VAT and SAT were within or below the age- and sex-matched Japanese reference values in short-stature children born SGA before and after GH treatment, indicating that GH treatment may not have unfavorable effects on adiposity in short-stature children born SGA, although it may alter fat distribution.

Evaluation of Hemodialysis Arteriovenous Bruit by Deep Learning.

Physical findings of auscultation cannot be quantified at the arteriovenous fistula examination site during daily dialysis treatment. Consequently, minute changes over time cannot be recorded based only on subjective observations. In this study, we sought to supplement the daily arteriovenous fistula consultation for hemodialysis patients by recording the sounds made by the arteriovenous fistula and evaluating the sounds using deep learning methods to provide an objective index. We sampled arteriovenous fistula auscultation sounds (192 kHz, 24 bits) recorded over 1 min from 20 patients. We also extracted arteriovenous fistula sounds for each heartbeat without environmental sound by using a convolutional neural network (CNN) model, which was made by comparing these sound patterns with 5000 environmental sounds. The extracted single-heartbeat arteriovenous fistula sounds were sent to a spectrogram and scored using a CNN learning model with bidirectional long short-term memory, in which the degree of arteriovenous fistula stenosis was assigned to one of five sound types (i.e., normal, hard, high, intermittent, and whistling). After 100 training epochs, the method exhibited an accuracy rate of 70-93%. According to the receiver operating characteristic (ROC) curve, the area under the ROC curves (AUC) was 0.75-0.92. The analysis of arteriovenous fistula sound using deep learning has the potential to be used as an objective index in daily medical care.

Development of scoliosis in young children with osteogenesis imperfecta undergoing intravenous bisphosphonate therapy.

The purpose of this study was to clarify the prevalence of scoliosis and determine risk factors for the development of scoliosis in young children with osteogenesis imperfecta (OI) who underwent intravenous pamidronate (PAM) therapy. Thirty-four young children with OI who had no scoliosis at the first PAM administration underwent cyclic PAM therapy alone. The medical records and radiographs of these patients were retrospectively reviewed. We examined the relationship between scoliosis (Cobb angle ≥ 10) and type of OI (Sillence classification: types I, III, and IV), physical mobility, Z-scores of bone mineral density in L2-4 of the lumbar spine (L2-4 BMD Z-scores), age of patients at first treatment with PAM, pelvic frontal tilt and leg-length discrepancy. The prevalence of scoliosis was 23.5% in 34 young children with OI who underwent PAM therapy for a mean of 4.2 years. Lower L2-4 BMD Z-scores, the presence of coronal and sagittal vertebral deformities and higher percentage of corrective osteotomy in the lower extremities were significant risk factors for the development of scoliosis. In patients with type III or IV OI, L2-4 BMD Z-scores were significantly lower (p = 0.02) and the percentage of patients who started PAM therapy in early childhood was significantly lower in scoliosis group than in the non-scoliosis group (p = 0.01). Development of scoliosis depends on the severity of OI and has a strong relationship with bone fragility even under PAM therapy. Starting intravenous PAM therapy in infancy or early childhood has a potential to prevent the occurrence and progression of scoliosis associated with bone fragility in young children with severe type III or IV OI.

Wild boars: A potential source of Erysipelothrix rhusiopathiae infection in Japan.

The potential role of wild boars as a source of erysipelas infection was investigated. An ELISA test of wild boar serum samples from 41 prefectures in Japan revealed that proportions of the Erysipelothrix rhusiopathiae-positive samples were very high in all the prefectures, and the mean positive rate was 95.6% (1312/1372). Serovars of E. rhusiopathiae isolates from wild boars were similar to those of previously reported swine isolates, and all serovar isolates tested were found to be pathogenic to mice. These results suggest that wild boars in Japan constitute a reservoir of E. rhusiopathiae and may pose risks to other animals.

Simultaneous evaluation of diagnostic marker utility for enzootic bovine leukosis.

BACKGROUND: Enzootic bovine leukosis (EBL) is a disease of cattle caused by bovine leukemia virus (BLV). More than 60% of BLV-infected cattle remain subclinical and are thus referred to as aleukemic (AL) cattle. Approximately 30% of infected cattle show a relatively stable increase in the number of B lymphocytes; these cattle are termed persistent lymphocytosis (PL) cattle. A small percentage of infected cattle develop BLV-induced B cell lymphoma (EBL) and are called EBL cattle. Due to the increase in the number of BLV-infected cattle, the number of EBL cattle has featured a corresponding increase over recent years in Japan. Several diagnostic criteria for EBL (e.g., enlarged superficial lymph nodes, protrusion of the eye, increased peripheral blood lymphocyte, etc.) are used for on-farm diagnosis and antemortem tests at slaughterhouses. Since the slaughter of EBL cattle for human consumption is not allowed, on-farm detection of EBL cattle is important for reducing the economic loss incurred by farms. Therefore, establishing new diagnostic markers to improve the efficiency and accuracy of the antemortem detection of EBL cattle is a critical, unmet need. To simultaneously evaluate the utility of candidate markers, this study measured the values of each marker using the blood samples of 687 cattle with various clinical statuses of BLV infection (EBL, PL, AL and non-infected cattle). RESULTS: Sensitivity (Se) and specificity (Sp) were highest for the serum thymidine kinase (TK) followed by the serum lactate dehydrogenase (LDH) isozyme 2. The number of peripheral blood lymphocytes and proviral load in peripheral blood had the lowest Se and Sp. The values of all markers other than TK were influenced by the sex of the tested cattle. CONCLUSIONS: Although tLDH and its isozymes (LDHs) may be influenced by the sex of the tested cattle, the high accuracy of TK and LDH2 as well as accessibility and simplicity of the protocol used to measure these enzymes recommend the utility of TK and LDHs for EBL cattle detection. Using these markers for screening followed by the application of existing diagnostic criteria may improve the efficiency and accuracy of EBL cattle detection on farms, thereby contributing to the reduction of economic losses in farms.

The effectiveness of colostral antibodies for preventing bovine leukemia virus (BLV) infection in vitro.

BACKGROUND: Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL). The incidence of EBL in Japan is increasing annually; and the cases of EBL in cattle younger than 2 years old has been reported. Therefore, it is vital to find a method to control BLV infection, especially in young calves. In this study, to evaluate the protective ability of colostral antibodies against BLV infection, as well as the potential for BLV infection mediated by colostrum/milk, we investigated temporal fluctuations in the anti-BLV antibody titer and BLV proviral load (PVL) in colostrum/milk and peripheral blood of six infected dams during lactation. The association between PVL and antibody titer in colostrum and peripheral blood was then investigated using samples from a further twenty-seven cattle. Antibody concentrations were measured with a Syncytium-induction Inhibition Assay using colostral/milk whey and serum. PVL in peripheral blood and colostrum was measured by real-time PCR. RESULTS: Colostral antibodies showed high inhibitory activity until day 3 of lactation. The antibody titer and PVL in peripheral blood showed lesser changes than those in colostrum/milk throughout lactation. The colostral antibody titer was significantly higher than the serum antibody titer in all samples, whereas the colostrum PVL was significantly lower than the blood PVL. The blood PVL showed a significant correlation with serum antibody titer, colostrum PVL, and colostral antibody titer. However, there were no major correlations between the serum and colostral antibody titers. CONCLUSIONS: This is the first report investigating the temporal changes in colostral antibody titer in terms of inhibiting BLV infection in vitro. The results of antibody detection by Syncytium-induction Inhibition Assay suggested that the protective activity of the colostral antibodies against BLV infection would be conferred by anti-BLV gp51 antibody. The high antibody titer of colostral whey suggests that colostral whey could be a potential source of antibodies with a low risk of infection in neonatal calves.

Meteorological factors affecting seroconversion of Akabane disease in sentinel calves in the subtropical Okinawa Islands of Japan.

Akabane virus, the pathogen-causing Akabane disease, is an arthropod-borne virus (arbovirus) transmitted by the Culicoides biting midge. A nationwide serological surveillance program for bovine arboviral diseases, including Akabane disease, has been established in Japan to monitor the circulation of arboviruses by targeting sentinel calves. Okinawa, which is located in the southwestern-most region of Japan, is a high-risk area for incursion of arboviruses. The aim of the present study was to identify the meteorological factors related to farm-level seroconversion of Akabane virus by analyzing the serological surveillance data for sentinel calves collected in Okinawa between 2007 and 2015. Rainfall in winter, spring, and autumn was positively associated with seroconversion. Adequate rainfall seems to keep the soil in a suitably moist state for growth and survival of biting midges. Maximum temperature in winter was also positively associated with seroconversion in sentinel calves. The warmer temperatures in winter may provide conditions suitable for shortening the larval development cycle and increase production of adult midges. Our findings indicate that meteorological factors such as temperature and rainfall may be important factors that produce circumstances conducive to effective transmission of the virus between vectors and the host. The results of this study provide a better understanding of the circulation of arboviruses and offer suggestions for developing better surveillance and measures to prevent arboviral disease.

Pig epidemic diarrhoea virus S gene variant with a large deletion non-lethal to colostrum-deprived newborn piglets.

We previously identified a third porcine epidemic diarrhoea virus (PEDV) S variant with a large deletion of 582 nucleotides in the 5' terminal region of the S gene, in addition to the North American type and the S INDELs type. To investigate the pathogenicity of this variant, TTR-2/JPN/2014, we performed experimental infection using colostrum-deprived piglets and compared the results with those from the North American type PEDV, OKN-1/JPN/2013. Fifteen newborn piglets were divided into two groups of 7-8 piglets each and inoculated orally with one of PEDV isolates maintained at the eighth passage in Vero cell culture. Although all PEDV-inoculated piglets showed acute watery diarrhoea, lethality clearly differed between both PEDV-inoculated groups. Moreover, there were differences in virus distribution and lesions on the intestines between the two PEDV-inoculated groups. Therefore, our data suggest that the OKN-1/JPN/2013 PEDV isolate is virulent, whereas the TTR-2/JPN/2014 PEDV isolate is avirulent.

Epidemiological analysis of bovine ephemeral fever in 2012-2013 in the subtropical islands of Japan.

BACKGROUND: Bovine ephemeral fever (BEF) is a febrile disease of cattle that is transmitted by arthropod vectors such as mosquitoes and Culicoides biting midges. An outbreak of BEF recently occurred in Ishigaki Island and surrounding islands that are located southwest of Japan. In this study, an epidemiological analysis was conducted to understand the temporal and spatial characteristics of the outbreak. Factors associated with the disease spread within Ishigaki Island were investigated by hierarchical Bayesian models. The possibility of between-island transmission by windborne vectors and transmission by long-distance migration of infected vectors were examined using atmospheric dispersion models. RESULTS: In September 2012, the first case of the disease was detected in the western part of Ishigaki Island. In 1 month, it had rapidly spread to the southern part of the island and to surrounding islands, and led to 225 suspected cases of BEF during the outbreak. The dispersion model demonstrated the high possibility of between-island transmission by wind. Spatial analysis showed that paddy fields, farmlands, and slope gradients had a significant impact on the 1-km cell-level incidence risk. These factors may have influenced the habitats and movements of the vectors with regard to the spread of BEF. A plausible incursion event of infected vectors from Southeast Asia to Ishigaki Island was estimated to have occurred at the end of August. CONCLUSION: This study revealed that the condition of a terrain and land use significantly influenced disease transmission. These factors are important in assessing favorable environments for related vectors. The results of the dispersion model indicated the likely transmission of the infected vectors by wind on the local scale and on the long-distance scale. These findings would be helpful for developing a surveillance program and developing preventive measures against BEF.

Spatial epidemiological analysis of bovine encephalomyelitis outbreaks caused by Akabane virus infection in western Japan in 2011.

Akabane disease, which is distributed in temperate and tropical regions in the world, is a vector-borne disease of ruminants caused by the Akabane virus, transmitted by Culicoides biting midges. In 2011, outbreaks of Akabane viral encephalomyelitis occurred in the Shimane Prefecture in western Japan. In this study, a spatial epidemiological analysis was conducted to understand environmental factors associated with the spread of Akabane disease. By applying a conditional autoregressive model, the relationship between infection and environmental variables was explored. The results showed that the dominance of farmlands and the presence of infected farms within a 3-km radius had a significant effect on infection. This result implies that land use, which would relate with the vector habitat, and the presence of neighboring infected farms as a source of infection may have influenced the spread of the disease in this region. These findings provide basic insights into the spread of Akabane disease and useful suggestions for developing a surveillance program and preventive measures against the disease.

Impact of wastewater from different sources on the prevalence of antimicrobial-resistant Escherichia coli in sewage treatment plants in South India.

The sewage treatment plant (STP) is one of the most important interfaces between the human population and the aquatic environment, leading to contamination of the latter by antimicrobial-resistant bacteria. To identify factors affecting the prevalence of antimicrobial-resistant bacteria, water samples were collected from three different STPs in South India. STP1 exclusively treats sewage generated by a domestic population. STP2 predominantly treats sewage generated by a domestic population with a mix of hospital effluent. STP3 treats effluents generated exclusively by a hospital. The water samples were collected between three intermediate treatment steps including equalization, aeration, and clarification, in addition to the outlet to assess the removal rates of bacteria as the effluent passed through the treatment plant. The samples were collected in three different seasons to study the effect of seasonal variation. Escherichia coli isolated from the water samples were tested for susceptibility to 12 antimicrobials. The results of logistic regression analysis suggest that the hospital wastewater inflow significantly increased the prevalence of antimicrobial-resistant E. coli, whereas the treatment processes and sampling seasons did not affect the prevalence of these isolates. A bias in the genotype distribution of E. coli was observed among the isolates obtained from STP3. In conclusion, hospital wastewaters should be carefully treated to prevent the contamination of Indian environment with antimicrobial-resistant bacteria.

A case-control study of the infection risk of H5N8 highly pathogenic avian influenza in Japan during the winter of 2020-2021.

In Japan, outbreaks of H5N8 highly pathogenic avian influenza (HPAI) were reported between November 2020 and March 2021 in 52 poultry farms. Understanding HPAI epidemiology would help poultry industries improve their awareness of the disease and enhance the immediate implementation of biosecurity measures. This study was a simulation-based matched case-control study to elucidate the risk factors associated with HPAI outbreaks in chicken farms in Japan. Data were collected from 42 HPAI-affected farms and 463 control farms that were within a 5-km radius of each case farm but remained uninfected. When infected farms were detected as clusters, one farm was randomly selected from each cluster, considering the possibility that the cluster was formed by farm-to-farm transmission within an epidemic area. For each case farm, up to three control farms were selected within a 5-km radius. Overall, 26 case farms (16 layer and 10 broiler farms) and 75 control farms (45 layer and 30 broiler farms) were resampled 1000 times for the conditional logistic regression model with explanatory variables comprising geographical factors and farm flock size. A larger flock size and shorter distance to water bodies from the farm were found to increase infection risk in layer farms. Similarly, in broiler farms, a shorter distance to water bodies increased infection risk. On larger farms, frequent access of farm staff and instrument carriages to premises could lead to increased infection risk. Waterfowl visiting water bodies around farms may also be associated with infection risk.

Risk factors for the transmission of foot-and-mouth disease during the 2010 outbreak in Japan: a case-control study.

BACKGROUND: In 2010, foot-and-mouth disease (FMD) occurred for the first time in a decade in Japan. Movement or shipment of people and animals around infected farms was restricted; however these contingency measures proved insufficient to prevent FMD spread. Consequently, a total of 292 farms were confirmed as infected during this outbreak. We conducted a case-control study to identify the risk factors associated with FMD transmission between farms during these restrictions. As there was discordance in the control measures taken, risk factors were examined separately for two areas. Analyses were also performed separately for cattle and pig farms given their different infectivity and susceptibility. RESULTS: For cattle farms in the movement restriction area, the odds of having the factor 'farm equipment was shared with other farms' was significantly higher for case farms than for control farms. For cattle farms in the shipment restriction area, the odds of having the factors 'feed transport vehicles visited the farm' and 'staff of livestock-related companies visited the farm' were significantly higher on case farms than control farms. In pig farms in the movement restriction area, the odds of having factor 'farm staff commuted from outside' was 20 times higher for case farms than control farms. In addition, case farms were less likely to have the factors 'fattening farm' and 'barn has physical barriers' compared with control farms. CONCLUSIONS: In the movement restriction area, the disease was likely to spread regardless of the movement of people and vehicles, and physical barriers were found to be a protective factor. Therefore, physical barriers from the surrounding environments seemed to prevent farms from being infected. Conversely, in the shipment restriction area, movement of people and vehicles was strongly associated with disease spread. These results allow a better understanding of the risk factors associated with FMD transmission and are useful to enhance future preventive measures against transmission during FMD outbreaks.