Toshiyuki Tsutsui

Bovine epizootic encephalomyelitis caused by Akabane virus in southern Japan

BackgroundAkabane virus is a member of the genus Orthobunyavirus in the family Bunyaviridae. It is transmitted by hematophagous arthropod vectors such as Culicoides biting midges and is widely distributed in temperate to tropical regions of the world. The virus is well known as a teratogenic pathogen which causes abortions, stillbirths, premature births and congenital abnormalities with arthrogryposis-hydranencephaly syndrome in cattle, sheep and goats. On the other hand, it is reported that the virus rarely induces encephalomyelitis in cattle by postnatal infection. A first large-scale epidemic of Akabane viral encephalomyelitis in cattle occurred in the southern part of Japan from summer to autumn in 2006. The aim of this study is to define the epidemiological, pathological and virological properties of the disease.ResultsNonsuppurative encephalomyelitis was observed in cattle that showed neurological symptoms such as astasia, ataxia, opisthotonus and hypersensitivity in beef and dairy farms by histopathological analysis. Akabane viral antigen and genome were consistently detected from the central nervous system of these animals, and the virus was isolated not only from them but also from the blood samples of clinically healthy calves in the epidemic area. The isolates were classified into genogroup I a containing the Iriki strain, which caused encephalitis of calves almost twenty years ago in Japan. Most of the affected cattle possessed the neutralizing antibody against Akabane virus. Seroconversion of the cohabitated and sentinel cattle in the epidemic area was also confirmed during an outbreak of the disease.ConclusionThe ecological and epidemiological data we have obtained so far demonstrated that the Akabane virus is not endemic in Japan. No evidence of Akabane virus circulation was observed in 2005 through nation-wide serological surveillance, suggesting that a new strain belonging to genogroup I a invaded southern Japan from overseas in the summer of 2006 and caused an unprecedented epizootic of encephalomyelitis mainly in susceptible calves. It will be necessary to reconsider the vaccine strategy to control the disease effectually.

Risk factors associated with within-herd transmission of bovine leukemia virus on dairy farms in Japan.

BackgroundAlthough several attempts have been made to control enzootic bovine leukosis (EBL) at the local level, a nationwide control program has not been implemented in Japan, except for passive surveillance. Effective control of EBL requires that the transmission routes of bovine leukemia virus (BLV) infection should be identified and intercepted based on scientific evidence. In this cross-sectional study, we examined the risk factors associated with within-herd transmission of BLV on infected dairy farms in Japan. Blood samples taken from 30 randomly selected adult cows at each of 139 dairy farms were tested by enzyme-linked immunosorbent assay (ELISA). Information on herd management was collected using a structured questionnaire.ResultsInfected farms were defined as those with more than one ELISA-positive animal and accounted for 110 (79.1%) of the 139 farms in the study. Completed questionnaires obtained from 90 of these 110 farms were used for statistical analysis. Seroprevalence, which was defined as the proportions of animals that tested positive out of all animals tested on the farm, was 17.1%, 48.1%, and 68.5% for the 25th, 50th, and 75th percentiles, respectively. A mixed logistic regression analysis implicated a loose housing system, dehorning, and a large number of horseflies in summer as risk factors (coefficient = 0.71, 1.11, and 0.82; p = 0.03, < 0.01, and 0.01, respectively) and feeding of colostrum to newborn calves from their dams as a protective factor (coefficient = -1.11, p = 0.03) against within-farm transmission of BLV on infected farms.ConclusionControl of EBL in infected dairy farms in Japan will be improved by focusing particularly on these risk and protective factors.

The recent prevalence of bovine leukemia virus (BLV) infection among Japanese cattle

A seroepidemiological survey of bovine leukemia virus (BLV) infection was conducted in Japan in 2007 using an enzyme-linked immunosorbent assay (ELISA) and an agar gel immunodiffusion (AGID) test. A total of 5420 cattle (dairy, 3966; breeding beef, 797; fattening beef, 657) from 209 farms in seven prefectures in Japan were tested. The overall prevalence of BLV infection was 28.6%. The prevalence of BLV infection in dairy cattle (34.7%) was higher than for both fattening beef cattle (7.9%) and breeding beef cattle (16.3%). Age-specific prevalence showed that BLV prevalence increased with age in all types of cattle and was notably different between dairy and beef cattle under 1 year of age. Among 207 farms, 141 herds (68.1%) had one or more positive animals. The proportion of these positive farms was significantly higher among dairy farms (79.1%) than among beef breeding farms (39.5%) and beef fattening farms (51.9%) (P<0.001). Dairy farms (40.5%) also showed a significantly higher within-herd prevalence than beef breeding (27.4%) and fattening (14.9%) farms (P=0.001). This study indicated that BLV is more widely spread in dairy cattle than in beef breeding cattle in Japan. Given the prevalence of BLV infection in dairy and beef cattle was 8- and 1.7-fold higher, respectively, than rates previously found in 1980-1982, BLV appears to be spreading particularly among the dairy cattle population during the last two decades. Further investigation is required to determine the risk factors necessary to control BLV infection that take into account the different farming practices that exist between dairy and beef sectors.

Molecular characterization of pig epidemic diarrhoea viruses isolated in Japan from 2013 to 2014.

Since October 2013, approximately 1000 outbreaks of porcine epidemic diarrhoea (PED) have occurred, spanning almost all prefectures of Japan, after a period of seven years without a reported case. In order to consider occurrence factor of PED outbreaks, we determined the whole-genome sequences of 38 PED virus (PEDV) strains from diarrheal samples collected at swine farms in 18 prefectures between 2013 and 2014 using next-generation sequencing technology. Using these data, we investigated genetic variation among the recent Japanese PEDV strains and the genetic relationships between these strains and global PEDV strains isolated recently from multiple swine-industrial countries. Eleven out of 38 PEDV strains were isolated successfully on Vero cells with trypsin treatment and subjected to genome sequence analysis. In a comparative genome analysis, we detected two novel PEDV variants, TTR-2/JPN/2014 and MYG-1/JPN/2014, with large deletions in the spike and ORF3 genes, respectively. A phylogenetic analysis based on the spike gene showed that the 38 Japanese PEDV strains were classified into two PEDV types: the North American type with high virulence (n=34) and the INDEL type (n=4). In addition, the recent Japanese PEDV isolates had a close relationship to global PEDV strains isolated in recent years than to the classical PEDV strains detected in Japan the past decades ago. Moreover, the phylogenetic dendrogram of the complete genomes also indicated that the 38 Japanese PEDV strains, including the two novel PEDV variants discovered in this study, are closely related to the PEDV strains that were widespread in the United States and Korea in 2013-2014. These findings suggest that the re-emergence of PED outbreaks since the last reported case in 2006 was caused by the introduction of recent PEDV strains to Japan from overseas.

Evaluation of surveillance strategies for bovine brucellosis in Japan using a simulation model

Bovine brucellosis is caused by Brucella abortus and induces abortions in female cattle, with other cattle at risk of infection from the aborted fetus or contaminated placenta. In Japan, the number of cases has dramatically reduced due to national surveillance and eradication strategies. Bovine brucellosis is now believed to be eradicated in Japan. Here, we examine the surveillance strategies currently in place for early detection of infected cattle in the event of a future reintroduction of the disease. We compared current serological surveillance for the dairy population with bulk-milk surveillance and abortion surveillance, and used time to detection as the main criterion of surveillance efficacy. A stochastic individual-based model (IBM) was developed to simulate disease transmission within and between farms. Using outputs from the transmission model, a comparison of surveillance strategies was simulated. For evaluation of the robustness of the parameter values used in the transmission model, a sensitivity analysis was conducted. For the purpose of evaluating the direct costs of each surveillance strategy, the annual number of samples to be tested and the annual number of farms to be visited were estimated. Our results indicated that current serological surveillance with 60-month test intervals is not effective enough for rapid detection of a brucellosis outbreak. Bulk-milk surveillance appeared the most effective method based on the early detection of infected cows and a reduced number of samples required. The time to detection for abortion surveillance was greater than that of bulk-milk surveillance but varied widely depending on the reported ratio of abortions. Results from the surveillance model were consistent when alternative scenarios were applied to the transmission model. Although our model cannot exactly replicate an actual brucellosis outbreak, or the results of surveillance, our results may help decision-makers to choose the most effective surveillance strategy.

Risk factors for local spread of foot-and-mouth disease, 2010 epidemic in Japan

To provide a basis for effective foot-and-mouth disease (FMD) prevention measures, factors associated with local spread were investigated in this study using data of the 2010 FMD epidemic in Japan. Thirty-eight local clusters within a 500-m radius from source farms were selected. In the clusters with pig source farms, more neighboring farms were infected in a short time compared with the clusters with cattle source farms. The influence of distance and wind upon local spread did not show a significant difference between infected and noninfected neighboring farms. Large-size pig farms posed a greater risk of inducing local spread; the odds ratio with reference to small-size cattle farms was 16.73. Middle-size and large-size cattle farms had a greater risk of infection; odds ratios with reference to small-size cattle farms were 15.65 and 25.52, respectively. The present results are useful for understanding features of local spread and prioritizing farms for control measures.

Quantitative Risk Assessment of Vibrio parahaemolyticus in Finfish: A Model of Raw Horse Mackerel Consumption in Japan

The aim of this study was to evaluate the effects of implemented control measures to reduce illness induced by Vibrio parahaemolyticus (V. parahaemolyticus) in horse mackerel (Trachurus japonicus), seafood that is commonly consumed raw in Japan. On the basis of currently available experimental and survey data, we constructed a quantitative risk model of V. parahaemolyticus in horse mackerel from harvest to consumption. In particular, the following factors were evaluated: bacterial growth at all stages, effects of washing the fish body and storage water, and bacterial transfer from the fish surface, gills, and intestine to fillets during preparation. New parameters of the beta-Poisson dose-response model were determined from all human feeding trials, some of which have been used for risk assessment by the U.S. Food and Drug Administration (USFDA). The probability of illness caused by V. parahaemolyticus was estimated using both the USFDA dose-response parameters and our parameters for each selected pathway of scenario alternatives: washing whole fish at landing, storage in contaminated water, high temperature during transportation, and washing fish during preparation. The last scenario (washing fish during preparation) was the most effective for reducing the risk of illness by about a factor of 10 compared to no washing at this stage. Risk of illness increased by 50% by exposure to increased temperature during transportation, according to our assumptions of duration and temperature. The other two scenarios did not significantly affect risk. The choice of dose-response parameters was not critical for evaluation of control measures.

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.

Mathematical model of the 2010 foot-and-mouth disease epidemic in Japan and evaluation of control measures.

A large-scale foot-and-mouth disease (FMD) epidemic occurred in Japan in 2010. The epidemic arose in an area densely populated with cattle and pigs, continued for 3 months, and was contained by emergency vaccination. In this study, a mathematical simulation model of FMD transmission between farms was developed to generate the disease spread in the affected area. First, a farm-distance-based transmission kernel was estimated using the epidemic data. The estimated transmission kernel was then incorporated into the transmission model to evaluate the effectiveness of several control measures. The baseline model provided a good fit to the observed data during the period from imposition of movement restrictions until the implementation of vaccination. Our simulation results demonstrated that prompt culling on infected farms after detection could contribute to reducing the disease spread. The number of infected farms decreased to 30% of the baseline model by applying the 24-h prompt culling scenario. The early detection scenario resulted in a smaller-sized epidemic. However, the results of this scenario included a 35% chance of large-scale epidemic (more than 500 infected farms), even when the disease was detected 14 days earlier than in the baseline model. As additional options, preemptive culling could halt the epidemic more effectively. However, the preemptive culling scenario required substantial resources for culling operations. The 1-km preemptive scenario involved more than 50 farms remaining to be culled per day. Therefore, preemptive culling scenarios accompanied some difficulties in maintaining a sufficient capacity for culling in the affected area. A 10-km vaccination 7 days after the first detection of the disease demonstrated the potential to contain the epidemic to a small scale, while implementation of a 3-km vaccination on the same day could not effectively reduce epidemic size. In vaccination scenarios, the total number of farms that were either culled or vaccinated exceeded that of the baseline model. Vaccination scenarios therefore posed a problem of appropriate management of many vaccinated animals, whether these vaccinated animals would be culled or not. The present FMD transmission model developed using the 2010 FMD epidemic data in Japan provides useful information for consideration of suitable control strategies against FMD.

Analysis of risk factors associated with bovine leukemia virus seropositivity within dairy and beef breeding farms in Japan: A nationwide survey

This cross-sectional study evaluated risk factors associated with farm-level bovine leukemia virus (BLV) seropositivity in 563 dairy and 490 beef farms throughout Japan. Twenty randomly selected cattle on each farm were serologically tested, and farm epidemiologiocal information was obtained through face-to-face interviews. Due to the large number of zero-prevalence dairy and beef farms, data analysis was performed using a zero-inflated negative binomial model, which revealed that the common risk factors associated with higher within-farm seroprevalence were past detection of clinical leukemia and presence of blood-sucking insects. Loose housing on dairy farms and direct contact between calves and adult cattle on beef farms were also identified as risk factors. With regard to farm-level presence of BLV, the presence of purchased cattle was found to be a risk factor in both sectors. Sending heifers to a common ranch was identified as an additional risk factor for dairy farms.