Chung Hyun Kim

Outbreaks of highly pathogenic avian influenza (H5N1) in the Republic of Korea in 2003/04

AVIAN influenza is considered to be an emerging exotic viral disease in chickens and turkeys because of increasing reports of outbreaks of highly pathogenic avian influenza (HPAI) in Europe, Asia and North America. HPAI is a systemic disease of high morbidity and mortality in domestic poultry, caused by some viruses of the H5 and H7 subtypes. In addition, avian influenza viruses are zoonotic agents; in particular, subtype H5N1 has caused great concern worldwide since its first occurrence in human beings in Hong Kong in 1997 (Li and others 2004). Since December 2003, continuing outbreaks of HPAI caused by H5N1 subtype viruses in a number of Asian countries have presented a serious risk to animal and public health. In early 2005, the outbreaks were still ongoing among bird populations in Vietnam and Thailand, and human cases have also been reported in these countries (FAO 2005, OIE 2005). In Korea, an outbreak of HPAI caused by H5N1 was first reported on December 10, 2003. This short communication describes HPAI outbreaks in Korea and the actions taken to control the disease. A total of 19 cases (10 in chickens and nine in ducks) in seven provinces were reported from the first outbreak until the last outbreak on March 20, 2004. The viruses isolated from dead chickens were confirmed as being of subtype H5N1 (OIE 2004) by the National Veterinary Research and Quarantine Service of Korea. Fourteen cases, including the first reported outbreak, occurred during the first two weeks of the epidemic. From then, cases were reported sporadically (three cases in January 2004, one in February and one in March) (Fig 1), probably due to the prompt and effective control measures introduced by the authorities. Although the HPAI outbreaks were widely distributed throughout the country in terms of administrative divisions, they could be mostly grouped into three zones by the boundaries of cities and provinces (Fig 2). The basic control measures practised against HPAI outbreaks during 2003/04 in Korea included depopulation of all infected or suspected flocks, movement restrictions and disinfection of the infected farms and for a radius of 500 m around the farms. If suspected cases were notified, the premises were quarantined by the prompt application of movement controls and disinfection of all the animals, vehicles and persons entering or leaving the premises. When suspected cases were confirmed as HPAI, all susceptible animals on the infected farms were slaughtered immediately. In addition, stringent control measures, including movement restrictions, were applied to two designated zones: the protection zone (an area within a 3 km radius of the outbreak farm) and the surveillance zone (an area between a 3 and 10 km radius of the outbreak farm). Pre-emptive stamping-out of all susceptible animals within the protection zone was practised, which resulted in a total of 5,285,000 susceptible animals from 392 farms being culled. In addition, 16 hatcheries and poultry slaughterhouses linked epidemiologically to the infected farms were forcibly closed, and hatching in duck hatcheries was halted, to prevent spread of the disease. Of the 19 HPAI-positive cases, 14 (nine of the 10 outbreaks on chicken farms and five of the nine in duck farms) were identified as a result of the farmers notifying the authorities. Most of these farmers’ reports were motivated by the advice of their veterinary practitioners, who had examined poultry showing clinical signs and suspected HPAI on the farms. The farm with the first reported outbreak and other outbreaks notified during January and March 2004 were included in this category. Veterinarians who were specialists in poultry diseases played a crucial role in the early reporting of HPAI outbreaks in Korea. Veterinary Record (2006) 158, 341-344

Comparative efficacy of commercial Mycoplasma hyopneumoniae and porcine circovirus 2 (PCV2) vaccines in pigs experimentally infected with M. hyopneumoniae and PCV2.

The efficacies of two commercial Mycoplasma hyopneumoniae bacterins and porcine circovirus 2 (PCV2) vaccines were compared in conventional pigs immunized at different ages based on humoral response, pathological observation, and growth performance from birth to finishing (175 days of age) using a M. hyopneumoniae and PCV2 co-infection challenge model. One-week-old pigs (n=110) were randomly assigned to five groups: three vaccinated and challenged (VC), and one each of non-vaccinated and challenged (NVC) and negative control. A significant difference was found in the number of genomic copies of M. hyopneumoniae in nasal swabs and PCV2 in serum samples, the average daily weight gain (gram/pig/day) between 63 and 133 dpi, gross and histopathological lung lesion scores, histopathological lymph node lesion scores, and the immunohistochemical analysis of PCV2 among the three VC groups. The single dose schedule for M. hyopneumoniae bacterins and PCV2 vaccines have the advantages of (i) improving daily weight gain (122.4%) and slaughter weight (120.5%), and (ii) reducing the incidence of clinical signs and lung and lymph node lesions.

Expression of Mucins and Trefoil Factor Family Protein-1 in the Colon of Pigs Naturally Infected with Salmonella typhimurium

The expression patterns of different mucins (MUC1, MUC2, MUC4, MUC5AC, MUC5C and MUC6) and trefoil factor family protein-1 (TFF1) in the colon of healthy pigs and pigs naturally infected with Salmonella typhimurium is reported. Twenty infected pigs approximately 80-160 days of age from 20 different herds were studied. These animals had similar microscopical change in colonic tissue characterized by mucosal erosion or sloughing and acute inflammation. S. typhimurium was cultured from all lesions and the identity of each isolate was confirmed by serotyping. Immunohistochemical studies of colonic tissue revealed reduced expression of MUC4 on the surface of the cryptal epithelium of S. typhimurium-infected pigs compared with non-infected pigs (P<0.001). By contrast, colon from infected animals had increased expression of MUC5AC (P<0.0001) and TFF1 (P=0.0095) relative to controls and there was a significant positive correlation between expression of these two molecules (Spearman coefficient 0.64, P<0.0001). Further studies are needed to evaluate the functional relationship between altered expression of these molecules and inflammation in Salmonella-infected pigs.

Outbreaks of classical swine fever in the Republic of Korea in 2003

CLASSICAL swine fever (CSF) is an economically important viral disease that occurs in many parts of the world, including Europe and Asia (Moennig and others 2003, Paton and Greiser-Wilke 2003). In the Republic of Korea, CSF was first reported in 1947, and subsequent outbreaks have made CSF one of the most devastating diseases to affect the South Korean pork industry. In an effort to rid the country of the disease, a nationwide, three-stage CSF eradication campaign was initiated in 1996: the first stage consisted of the wider use of vaccination and culling of infected animals, to reduce the number of outbreaks; the second stage consisted of mandatory nationwide vaccination and testing, to bring the disease under control; and the final stage consisted of a complete vaccination ban, so that the country could be declared free from CSF. Vaccination was conducted throughout mainland South Korea, but not in the Je-ju Islands, with the purpose of achieving 100 per cent compliance. Serological surveillance was also conducted to detect infection and monitor compliance with the vaccination programme. As a result of the campaign, the number of cases of CSF decreased until none was reported in 2000 and 2001. On the basis of this situation, the South Korean authorities decided to ban all CSF vaccination on December 1, 2001, and notified the Office International des Epizooties (OIE) that South Korea had achieved all the OIE requirements to declare the country free from CSF. Unfortunately, in April 2002, two cases of CSF were confirmed in Gang-won province, and 11 more cases were reported between October and December of the same year in Gyeong-gi province. The low temperatures at that time made cleaning and disinfection of premises difficult, thus increasing the risk of the disease spreading to other areas. The decision was therefore made in December 2002, to implement emergency CSF vaccination in the surrounding regions, while implementing a stamping-out policy on the infected and neighbouring farms. The outbreaks were restricted to confined areas and it was assumed that they represented isolated cases, such as might be expected after the cessation of vaccination. No change in the overall policy was considered at that time and, once these outbreaks had been contained, efforts to declare the country free from CSF were resumed. However, CSF was confirmed in 65 pig farms across the country, between March and May 2003, resulting in the resumption of the nationwide vaccination policy. This short communication describes the epidemiological investigations into the outbreak, which attempted to locate the source of the infection. On March 18, 2003, a suspect case of CSF was reported at a farm located in Ik-san city, Jeon-buk province, and samples were sent to the National Veterinary Research and Quarantine Service (NVRQS) for laboratory testing to confirm CSF. Additional suspect cases were then reported on farms located in Ham-an county (Gyeong-nam province), Sang-ju city (Gyeong-buk province) and Dang-jin county (Chungnam province). The epidemiological investigation of the four farms with suspected CSF revealed that they had all purchased young breeding pigs on February 18 or 19, 2003, from a breeding farm (farm S) located in Kim-po city, Gyeong-gi province, in the region where the CSF outbreak between October and December 2002 had occurred. Consequently, the NVRQS began investigations to trace farms that had purchased pigs from farm S since February 1, 2003, and conducted clinical examinations and CSF laboratory tests on pigs from these farms as part of a proactive surveillance programme. Farm S consisted of three farm units, a great-grandparent (GGP) unit, a grandparent (GP) unit and the parent stock (PS) unit. Piglets born at the GGP unit were either kept on the unit to be used as GGP stock or supplied to the GP unit. Piglets born at the GP unit were allocated to nearby pig farms, which were under contract to rear the pigs until 150 days of age; at the time of the investigation, there were 20 such farms. Piglets suitable for breeding were then selected from these farms and moved to the PS unit to be reared until 180 days of age, when they were sold to ordinary pig farms, that is, not a pig-breeding or parent stock farm. Laboratory tests were conducted using an ELISA to detect high antibody levels, and reverse transcriptase-PCR and an antigen ELISA to detect CSF virus (CSFV), from blood and tissue samples collected from the GGP, GP and PS farm units. Initial laboratory tests of 100 pigs on the PS unit showed that two pigs were CSFV positive; subsequent testing of the whole herd the following day showed that 81 of 921 (8·8 per cent) pigs were CSFV positive. Some of the piglets produced from the GGP unit were sold through the PS unit to a pig farm located in Sang-ju city, Gyeong-buk province. This farm (designated as farm SJ) had already been confirmed as having CSF when the epidemiological link was discovered, and further investigations showed some of the pigs bought from farm S had been sold on to nearby farms as breeding pigs. A total of 81 pig farms had purchased young breeding pigs from farm S since February 1, 2003, and 38 of these were confirmed as being CSFV positive. Farm SJ had sold young breeding pigs to nine different pig farms, and five of these had CSFV confirmed. From the epidemiological studies of farm S, one additional pig farm that had purchased pigs during January 2003, was also confirmed positive for CSFV. Consequently, a total of 44 confirmed cases of CSF, accounting for 68 per cent of the total number of cases of CSF, were directly linked to farms S and SJ through the purchase of breeding pigs between March and May 2003. Fig 1 shows the course of the CSF outbreak from March 19 to May 8, 2003; the 65 confirmed cases were spread across six provinces. The number of reported cases peaked on March 21, with 14 cases. The pattern of CSF cases could be classified into three groups: group 1, consisting of 44 cases reported between March 18 and 28; group 2, consisting of 18 cases reported between April 5 and 20; and group 3, consisting of three cases reported on May 8. In group 1, there were 39 CSF positive cases related to the purchase of young breeding pigs from farms S and SJ, which accounted for 89 per cent of the cases in this group. In group 2, seven cases were linked to farm S, accounting for 39 per cent of this group, while nine cases were due to local spread; the cause of the other two cases was unknown. In group 3, all three cases were due to local spread. Fig 2 shows the number of CSF cases by region. Of the nine provinces in South Korea, only three, Gang-won, Chung-buk and Je-ju, were unaffected. Jeon-buk province had the largest number of cases, followed by Gyeong-nam; most of the pig farms in these areas are small in size (fewer than 1000 pigs per farm), are densely populated and had frequent visits by other farmers, which could explain the relatively large number of cases attributed to spread from neighbouring farms. This finding concurs with similar observations that farms located in herd-dense regions are at high risk of acquiring CSF from neighbouring infected farms (Mintiens and others 2003). Local spread of infection can be a major transmission route, as demonstrated by the 1997/98 epizootic of CSF in the Veterinary Record (2005) 157, 113-115

Effects of a modified live CSFV vaccine on the development of PMWS in pigs infected experimentally with PCV-2

The objective of this study was to determine the effect of vaccination against classical swine fever virus (CSFV) on the development of postweaning multisystemic wasting syndrome (PMWS) in conventional pigs infected experimentally with porcine circovirus type 2 (PCV-2). The pigs infected with PCV-2 and immunised with modified live CSFV developed mild to moderate PMWS, whereas none of the pigs infected with PCV-2 alone or immunised with modified live CSFV alone developed PMWS. Lesions histologically characteristic of PMWS were observed in lymph nodes from the pigs infected with PCV-2 and immunised with modified live CSFV vaccine, and extensive replication of PCV-2 was detected in the nodes by in situ hybridisation.

Detection by In-situ Hybridization of Pasteurella multocida Toxin (toxA) Gene in the Lungs of Naturally Infected Pigs

In-situ hybridization with a non-radioactive digoxigenin-labelled probe was used to detect the Pasteurella multocida toxin (PMT) gene in tissue sections of pneumonic lung from pigs naturally infected with toxigenic P. multocida. The morphology of host cells was preserved despite the relatively high temperature used in the incubation procedure. Pulmonary abscessation was observed in 13 pigs naturally infected with toxigenic P. multocida type A (three pigs) or D (10 pigs). In these 13 pigs a strong hybridization signal for PMT DNA was detected, mainly in degenerate leucocytes in abscesses. Occasionally, PMT DNA was detected in degenerate neutrophils and macrophages in alveolar spaces. Detection of hybridization signals for PMT DNA would seem to be a potential indicator of the production of PMT. The study suggested that PMT plays an important role in pulmonary abscessation caused by P. multocida.

Expression of secreted and membrane-bound mucins in the airways of piglets experimentally infected with Mycoplasma hyopneumoniae.

Immunohistochemistry was used to demonstrate secreted mucins MUC2, MUC5AC and MUC5B and membrane-bound mucin MUC4 in the pulmonary bronchioles of piglets experimentally infected with Mycoplasma hyopneumoniae. Conventional status, Landrace-Duroc cross-bred piglets, 13 days of age, were randomised to two groups. One group (n=20) was infected by the intra-tracheal route with the SNU98703 strain of M. hyopneumoniae, and a group of 12 animals acted as uninfected controls. Five infected and three uninfected piglets were euthanased on the day of infection and at 7, 21, and 35 days post-inoculation (PI). Membrane-bound MUC4 and secreted MUC5AC were the predominant mucins produced in the bronchioles of the piglets in response to M. hyopneumoniae infection, but by day 35 PI, all labelled mucins had returned to pre-infection levels, contemporaneous with reduced pulmonary lesion scores. The increased mucin production may result from direct stimulation of the epithelium by mycoplasmal infection, or may arise indirectly following M. hyopneumoniae-induced ciliostasis.

Expression of mucins on the mucosal surface of lungs of 4-week-old pigs

The aim of this study was to determine the immunoreactivity of normal small bronchial, bronchiolar, respiratory bronchiolar, and interalveolar epithelium using antibodies to six mucins: MUC1, MUC2, MUC4, MUC5AC, MUC5B, and MUC6. The large, gel-forming secreted mucins MUC2, MUC5AC, and MUC5B were widely expressed in the lower respiratory tract. The results of this study demonstrate that these secreted mucins form a gel to cover and protect the mucosal surface in the lower respiratory tract of pigs.

Expression of secreted mucins (MUC2, MUC5AC, MUC5B, and MUC6) and membrane-bound mucin (MUC4) in the lungs of pigs experimentally infected with Actinobacillus pleuropneumoniae

The expression patterns of different secreted (MUC2, MUC5AC, MUC5B, and MUC6) and membrane-bound (MUC4) mucins were determined immunohistochemically in the lungs of pigs experimentally infected with Actinobacillus pleuropneumoniae. Forty-seven-week-old colostrum-deprived pigs were randomly allocated to infected (n=20) or control groups (n=20). Five infected and uninfected pigs were euthanized at 0, 6, 12, and 48 h post-inoculation (hpi). In the infected pigs, the expression of both types of mucins, which were invariably observed, was associated with bronchiolar and respiratory bronchiolar lesions. Strong positive mucin signals were seen on the surface of bronchiolar and respiratory bronchiolar epithelium with neutrophil infiltration. The mean mucin-positive area peaked at 6 hpi and decreased significantly to control levels by 48 hpi on the surface of the bronchiolar and respiratory bronchiolar epithelium. Further studies are needed to establish the functional relationship between mucin expression and the host defense mechanism against A. pleuropneumoniae in the lungs of infected pigs.

Prevalence of tir gene subtypes in Escherichia coli isolates from pigs

ATTACHING and effacing Escherichia coli (aeec) are characterised by their capacity to infect intestinal epithelial cells, resulting in attaching and effacing (ae) lesions. ae histopathology is characterised by intimate adherence of the bacteria to enterocytes and disruption of the underlying