Risk factors associated with highly pathogenic avian influenza subtype H5N8 outbreaks on broiler duck farms in South Korea.

Highly Pathogenic Avian Influenza (HPAI) subtype H5N8 outbreaks occurred in poultry farms in South Korea in 2014 resulting in significant damage to the poultry industry. Between 2014 and 2016, the pandemic disease caused significant economic loss and social disruption. To evaluate the risk factors for HPAI infection in broiler duck farms, we conducted a retrospective case-control study on broiler duck farms. Forty-three farms with confirmed laboratories on premises were selected as the case group, and 43 HPAI-negative farms were designated as the control group. Control farms were matched based on farm location and were within a 3-km radius from the case premises. Spatial and environmental factors were characterized by site visit and plotted through a geographic information system (GIS). Univariable and multivariable logistic regression models were developed to assess possible risk factors associated with HPAI broiler duck farm infection. Four final variables were identified as risk factors in a final multivariable logistic model: "Farms with ≥7 flocks" (odds ratio [OR] = 6.99, 95% confidence interval [CI] 1.34-37.04), "Farm owner with ≥15 years of raising poultry career" (OR = 7.91, 95% CI 1.69-37.14), "Presence of any poultry farms located within 500 m of the farm" (OR = 6.30, 95% CI 1.08-36.93) and "Not using a faecal removal service" (OR = 27.78, 95% CI 3.89-198.80). This highlights that the HPAI H5N8 outbreaks in South Korea were associated with farm owner education, number of flocks and facilities and farm biosecurity. Awareness of these factors may help to reduce the spread of HPAI H5N8 across broiler duck farms in Korea during epidemics. Greater understanding of the risk factors for H5N8 may improve farm vulnerability to HPAI and other subtypes and help to establish policies to prevent re-occurrence. These findings are relevant to global prevention recommendations and intervention protocols.

Epidemiology of the Foot-and-Mouth Disease Serotype O Epidemic of November 2010 to April 2011 in the Republic Of Korea.

The largest epidemic of foot-and-mouth disease (FMD) in Korea since the first record in 1911 occurred between November 2010 and April 2011. The outbreak was confirmed in 153 farms, and more than three million animals were destroyed. This study presents the temporal and spatial distribution patterns, epidemiological investigation and the control measures for the 2010/2011 epidemic in Korea. The index case of this 2010/2011 FMD epidemic was reported in a pig-farming complex with five piggeries in Andong, GyeongBuk Province, on 28 November 2010, and the outbreak lasted 145 days. The largest number of new detection of the infected farms per day was recorded in mid-January. Epidemiological investigation revealed that the FMD virus had spread from farm to farm through routine movements associated with animal husbandry operations. In contrast to FMD epidemics in other countries in which movement of the infected animals largely contributed to the spread of the disease, human behaviours were major factors in the spread of the FMD virus in the Korean epidemic. The 2010/2011 epidemic was first confirmed in a local small and medium city where share of smallholder producers is higher than that of other provinces. Although Korea had a well-developed emergent response system with the experience of controlling infection and re-obtaining FMD-free status after the previous epidemics, Korea was prompted to revise their contingency plan by tailoring it to its unique livestock environment. Practical contingency plans tailored to Korea for control of FMD can be fully effective when farmers, livestock-related agencies, veterinary service providers and the general public work together.

Development and application of a multiplex PCR assay for rapid detection of 4 major bacterial pathogens in ducks.

Infections with Pasteurella multocida, Salmonella enterica, Riemerella anatipestifer, and Escherichia coli result in high morbidity and mortality, which cause significant economic loss in the poultry industry. It can be difficult to distinguish these pathogens based on clinical signs because these pathogens can cause similar clinical signs and coinfections can occur. Thus, rapid and sensitive detection of these 4 major bacterial pathogens are important in ducks. The aim of this study was to develop a multiplex PCR (mPCR) assay for simultaneously detecting and identifying these 4 pathogenic bacteria in a single tube reaction. The target genes used were KMT1 of P. multocida, the invasion protein gene of S. enterica, 16S rDNA of R. anatipestifer, and the alkaline phosphatase gene of E. coli. The detection limit of the assay for all bacterial DNA was 10 pg. The mPCR did not produce any nonspecific amplification products when tested against other related pathogens, including Staphylococcus aureus, Streptococcus pyogenes, Clostridium perfringens, Mycoplasma gallinarum, Mycoplasma synoviae, and Mycoplasma gallisepticum, which can also infect ducks. We applied mPCR to field samples, and the results were the same as the single PCR results. These results suggest that mPCR for the 4 bacteria is a useful and rapid technique to apply to field samples.

Survival rate of H5N1 highly pathogenic avian influenza viruses at different temperatures.

The survival rate of Korean H5N1 highly pathogenic avian influenza (HPAI) viruses was investigated at different temperatures under the laboratory conditions. The estimated survival days for a starting viral concentration of 10(6.5) 50% egg infectious dose/0.1 mL were 930, 1,042, and 3,213 d at 4 degrees C; 226, 232, and 293 d at 20 degrees C; and 51, 55, and 58 d at 30 degrees C for A/chicken/Korea/ES/03, A/chicken/Korea/IS/06, and A/chicken/Korea/Gimje/08 (Gimje/08) viruses, respectively. The stability of the Gimje/08 virus was statistically significant compared with the other 2 viruses except for the data between Gimje/08 and A/chicken/Korea/IS/06 virus at 30 degrees C. This result indicated that the survival rate of 3 Korean HPAI viruses is different at various temperatures, which might have partially influenced the large scale of HPAI outbreak in Korea in 2008.

An outbreak of highly pathogenic avian influenza at a public animal exhibit in seoul, Korea, during 2008.

This study describes the first recorded outbreak of HPAI in the city of Seoul, in captive birds held in an exhibition for public viewing at a local district office. The index cases were two pheasants, which had been introduced into the exhibit on 24 April, 4 days prior to death, from a store in a local market in Gyeonggi-do. Ducks and chickens from an HPAI outbreak farm, subsequently confirmed on 4 May, had also been held in this store. This outbreak highlights the potential role of local markets in AIV transmission. This outbreak led to considerable public health concern in Korea, however, no human cases were reported. The non-commercial poultry sector needs to be considered in national plans for preparedness and response.

Prediction of the nutrients value and biochemical characteristics of swine slurry by measurement of EC--electrical conductivity.

Slurry samples, collected from 41 commercial swine farms in South Korea, were characterized in various physico-biochemical, macro and micronutrients, heavy metals and microbial parameters. Interestingly, significant variations were observed in all the parameters. However, positive relationships were noticed between EC and ammonia nitrogen (NH(3)-N), total nitrogen (TN), total potassium (TK), specific gravity (SG), total solids (TS), volatile solids (VS), fixed solids (FS), total dissolved solids (TDS) at R(2)=0.91, 0.74, 0.69, 0.60, 0.50, 0.48, 0.55, and 0.52, respectively. Whereas phosphorous and other nutrients shown poor correlation. Escherichia coli and Salmonella were counted at an average of 5.04 log(10) colony forming unit (CFU)/mL and 3.55 log(10) most probable number (MPN)/mL, respectively. Equations for predicting nutrients content in swine slurries are presented with EC, because it is an easily determinable parameter. The data obtained in this study could be used as a guideline for Good Management Practices in South Korean swine farms as well as other countries.

Surveillance and control of bovine brucellosis in the Republic of Korea during 2000-2006.

Bovine brucellosis is a major animal health problem in the Republic of Korea. Further, a number of human cases of brucellosis have recently been detected. This paper provides an overview of surveillance (to detect new cases) and control (to clear infection following case detection) of bovine brucellosis in the Republic of Korea during 2000-2006. Using data from AIMS (the national animal infectious disease data management system), we conducted separate descriptive analyses, initially using farm and then episode as our unit of interest. An episode was defined as a period of compulsory herd trading restriction, following detection of infection with Brucella abortus in one or more cattle. We also identified risk factors for two measures of disease control: episode duration (logistic generalised estimating equation model) and time to re-restriction (Cox's proportional-hazard model). There were 8530 and 52,739 reactor farms and reactor cattle, respectively, during 2000-2006. From 2004 to 2006, there was a substantial increase in the number of new outbreaks, particularly within the beef sector. The probability of a prolonged episode (>150 days) and the hazard of a second episode each increased with herd size. Further, the hazard of a second episode was higher in 2005 (compared with other years) and in the southeast of Korea (compared with other provinces). The effect of outbreak size on control varied between the beef and dairy sectors. The increase in beef cattle reactors in 2004-2006 is closely aligned to an increase in surveillance effort. Nonetheless, it is likely that this is a genuine reflection of the recent establishment and spread of brucellosis in the Korean beef cattle population. The recent increase in surveillance coverage in the beef sector is central to national eradication efforts. Current strategies to control infection following detection have generally been effective, leading to rapid clearance of infection on most farms. Control becomes problematic with increasing herd size. This work provides a detailed insight into surveillance and control of bovine brucellosis in Korea, and should assist both policy-makers and field veterinarians to improve the effectiveness of national eradication efforts.

Epidemiological characteristics of the 2002 outbreak of foot-and-mouth disease in the Republic of Korea.

The Republic of Korea experienced a foot-and-mouth disease (FMD) outbreak during May-June 2002. The present study describes epidemiological characteristics of the 2002 FMD outbreak in Korea, including the pattern of the outbreak in both time and space, transmission routes among infected farms, and control measures. One of the notable features of the 2002 FMD epidemic in Korea was that the virus infected mostly pigs [15 of 16 infected premises (IPs)], despite the presence of other susceptible animals on infected and neighbouring farms. The epidemic showed temporal clustering at 8-9 day intervals, suggesting five generations of infection during the outbreak, and 13 of 16 (81.3%) IPs were located within a 10 km-radius of the index case. The clinical signs that prompted notification of infection included vesicles around hooves and snouts. The age of lesions was significantly less among cases reported by farmers compared with veterinarians. The high awareness of farmers from an earlier FMD outbreak greatly helped the animal hygiene authority in efforts associated with disease control and eradication. The outbreak was eradicated within <2 months as a result of the intensive control efforts of the animal hygiene authorities and the cooperation of the Korean people. Although the outbreak was a costly lesson for the Korean people, the experience gained will contribute to future efforts in the prevention and control of animal infectious diseases.

Using field-based epidemiological methods to investigate FMD outbreaks: an example from the 2002 outbreak in Korea.

Relevant to foot and mouth disease (FMD), most published epidemiological studies have been conducted using quantitative methods and substantial regional or national datasets. Veterinary epidemiology also plays a critical role during outbreak investigations, both to assist with herd-level decision-making and to contribute relevant information to assist with ongoing national or regional control strategies. Despite the importance of this role, however, little information has been published on the use of applied (field-based) epidemiological methods during disease outbreaks. In this study, we outline an investigative template for FMD, and a case study of its use during the 2002 FMD outbreak in Korea. Suitable for use during field-based epidemiological investigations of individual farms within a broader regional/national response, the template considers three steps including confirming infection, estimating date of introduction and determining method of introduction. A case study was conducted on IP13 (the 13th infected premises), the only IP during the 2002 FMD outbreak in Korea that was geographically isolated from all other known cases. The authorities first became aware of FMD on IP13 on 2 June, however, infection may have been present from 12 May. Infection was confirmed on 3 June 2002. FMD was probably spread to IP13 by a contract worker who had participated during 2-4 May in the culling operations on IP1. Other routes of spread were ruled out during the investigation. The contract worker lived in the locality of IP13 and worked on a part-time basis at a pork-processing plant that was adjacent to this farm. The contractor became heavily contaminated during the cull, but did not comply fully with cleaning and disinfection requirements once the cull had been completed. The investigative template contributed structure and focus to the field-based investigation. Results from this case study demonstrate the need for strict management of personnel in disease control and adherence to the sanitary rules by all those involved.

Study of transneuronal passage of pseudorabies virus in rat central nervous system by use of immunohistochemistry and in situ hybridization.

We studied the uptake and sequential transneuronal passage of pseudorabies virus (PRV) in rat CNS by use of a combination of immunohistochemistry and in situ hybridization. Protocols for rapid detection of PRV by immunohistochemistry and in situ hybridization in rats with PRV infection of the CNS after intranasal instillation of a wild-type strain of PRV were optimized in vitro, using porcine kidney-15 cells. Pseudorabies virus-specific hybridization signals appeared in the cytoplasm and nucleus of PRV-infected porcine kidney-15 cells by postinoculation (PI) hour 6. In tissue sections of PRV-infected rats, PRV nucleic acids were detected in areas of the rat brain in close proximity to the areas in which PRV antigens were evident. The PRV was initially found in the nucleus of trigeminal ganglion neurons at PI hour 24. At PI hour 72, PRV antigens were observed in the mid-brain, and 24 hours later, in the telencephalon. We also found evidence of specific progressive transsynaptic transmission of the virus, and, on the basis of that, we have constructed a map of the synaptic contacts and pathways in the brain. Therefore, combined use of immunohistochemistry and in situ hybridization was useful for characterizing the pathogenesis of PRV in the CNS of rats after intranasal inoculation, following a pattern that mimics PRV infection of the natural host.