Economic analysis of an epizootic of pseudorabies and subsequent production following the institution of a vaccination program in a Pennsylvania swine herd

The economic impact of pseudorabies was examined in a commercial swine herd. At the onset of clinical signs, a modified-live virus vaccine was administered to the sow herd and repeated at 3-month intervals. According to production data from the 320-sow farrow-to-feeder unit, preweaning mortality increased twofold, and subsequently, the number of pigs weaned per litter decreased by 19% (P less than 0.005) during the 5-week epizootic. Also, the number of pigs born alive decreased by 6% during the epizootic (P less than 0.05). No significant differences in production were observed between the 6-month periods before and after the epizootic. Actual cash flow analysis for the farm under isomarket conditions revealed a decreased net return of $2.40/inventoried sow/week, which was attributed to the disease during the epizootic, and a $0.46 decrease in net return/inventoried sow/week in the postepizootic period. Most seropositive herds have clinical signs less severe than those described in this herd, and the cost of eradication of the virus from a swine herd can be in excess of $200/inventoried sow. Thus, we believe that sufficient financial incentives are not available to all swine producers to ensure their enthusiastic cooperation in the effort to eradicate pseudorabies from the US swine population.     

Natural history of influenza in swine in Hawaii: swine influenza virus (Hsw1N1) in herds not infected with lungworms

To obtain more information on mechanisms by which influenza virus is perpetuated in swine, retrospective and prospective seroepizootiologic observations were made in swine herds in Hawaii, beginning in 1974. An epizootic of swine influenza (Hsw1N1) virus was observed in November and December 1976, involving 31 of 41 herds. Features of the epizootic included (1) infection of all herds within one geographic location, during a short period; (2) no obvious introduction of virus from the outside in most herds; (3) epizootics mainly in herds with serologic history of infection; (4) no evidence that lungworms were involved; and (5) little clinical disease associated with infection. There was evidence of viral activity in some herds before the epizootic period and afterward in two of three herds monitored. Evidence of viral transmission by feral animals was not obtained. Data indicated that swine influenza virus persists through latently or chronically infected swine, with epizootics occurring when herd immunity reaches a critically low degree.     

An epizootic of bovine tuberculosis in Georgia.

A tuberculous beef animal was detected Aug 29, 1973, by a veterinary medical officer in a Georgia slaughter establishment. Animal identification and traceback eventually led to a purebred beef herd in Decatur County, Georgia. Investigation and tuberculin testing of 23,000 cattle in 350 herds revealed 11 Mycobacterium bovis-infected beef herds and resulted in the complete depopulation of 5 herds. The epizootic was confined to Georgia and was eradicated by April, 1975.     

Prevalence of pseudorabies virus infection and associated infections in six large swine herds in Illinois.

Sera were collected from 6 large farrow-to-finish swine herds infected with pseudorabies virus (PRV) in Illinois. All herds were participating in the Large Herd Cleanup Study, a USDA-initiated project to evaluate the feasibility of eradicating pseudorabies from large farms (greater than 400 sows) by use of a combination of vaccination and management changes. Herd size ranged between 425 and 1,500 breeding females. Between April and July 1990, sera for measurement of PRV antibodies were obtained from 113 to 156 sows and 112 to 162 finishing pigs (body weight greater than 70 kg)/herd. Duplicate sera from 30 sows and 30 market-weight pigs/herd were obtained for measurement of serum antibodies to the following associated organisms: swine influenza virus, transmissible gastroenteritis virus, encephalomyocarditis virus, Actinobacillus pleuropneumoniae, Eperythrozoon suis, and 6 serovars of Leptospira interrogans. Prevalence of PRV antibodies attributable to field virus infection ranged between 53.8 and 100% for sows and between 0.7 and 97.3% for finishing pigs, as determined by the appropriate differential test for the vaccine being used on each farm. In only 1 herd, PRV seroprevalence was increased with higher sow parity. For associated infections, the risk of seropositivity attributable to PRV was not significant (for most infections) on all farms and varied among farms. Thus, pseudorabies did not appear, in general, to increase susceptibility to infection with other disease agents.     

Factors affecting the geographic distribution of pseudorabies (Aujeszky's disease) virus infection among swine herds in Illinois

Data on the geographic distribution of swine herds tested for pseudorabies virus (PRV) in the state of Illinois (USA) were analyzed to determine whether the prevalence of PRV-infected herds was clustered geographically at the county level. Second-order analysis of spatial dependence indicated there was a spatial clustering of counties of high PRV prevalence rates and that this clustering was greater than the observed clustering of counties with a large number of swine herds. The clustering of county PRV prevalence rates was most apparent within a radius of 120 km (on the average, approximately two couties away). The association of county PRV prevalence rates with average herd size, geographic density of swine herds in the country and regional (within 120 km) density of PRV-infected herds was analyzed using multiple linear regression. The primary factor affecting county PRV prevalence rates was the regional PRV density, which interacted with the other model variables. For counties with a low regional density of PRV infection, county PRV prevalence rates charged little with a change in county herd density or average herd size. In contrast, for counties with a high regional density of PRV infection, PRV prevalence within a county increased with increasing average herd size and increasing geographic density of swine herds in the county. The results of the current and previous studies implicate an important role for the geographic proximity of infected herds in the spread of PRV among swine herds.     

Variation of Aujeszky's disease viruses in wild swine in USA

In the United States of America, Aujeszky's disease (pseudorabies) has been eradicated from all domestic swine. Some re-emergence of infection occurred as vaccine use diminished. Sporadic outbreaks have also occurred because of the reservoir of infection in feral swine that have spread across the southern two-thirds of the country and Hawaii. In order to be able to understand the origins of re-emerging virus, sequence analysis of variable genes in pseudorabies virus (PRV) has been used to differentiate strains. Most PRV from feral swine can be distinguished from virus circulating in domestic pigs during the national epizootic. However, several feral swine isolates of PRV from south central states are closely related or identical in sequence to strains from domestic pigs. Extensive study by PCR for the presence of virus in the oral cavity of feral pigs disclosed that the viral DNA is distributed widely in tonsils salivary glands, taste buds and even mucosa in the vicinity of tusks. Clearly the virus in feral swine has multiple mechanisms of transmission to insure persistent infection and the threat of re-emergence in domestic swine continues.     

The use of a geographic information system in an epidemiological study of pseudorabies (Aujeszky''s disease) in Minnesota swine herds

A geographic information system (GIS) is being developed to study the spread of pseudorabies virus (PRV) among swine herds in the state of Minnesota. This GIS features an interface with a database management system that stores and manages pertinent data. These data include herd size, type of production system, degree of confinement, topographical features surrounding the farm, density of swine herds and distance to the closest quarantined herd. A pilot study was conducted in one Minnesota county with 280 swine herds, of which the PRV status was known in 115. Cox regression analysis was used to determine factors associated with herd PRV status. Relative risks (RR) and 95% confidence intervals (CI) were calculated. No association was detected between the PRV status of the herd and distance to the nearest county road, highway or quarantined herd. However, the following factors were significant: located within 1 km of a river or lake (RR, 0.524; CI, 0.328–0.828); farrow to finish (RR, 2.120; CI, 1.194–3.791); complete confinement (RR, 3.423; CI, 1.639–7.139); density of swine herds within a 5 km radius (RR, 1.036 per herd; CI, 0.996–1.064).     

近期部分规模化猪场猪伪狂犬病野毒抗体监测情况调查

猪伪狂犬病仍然是我国猪群的重要威胁性传染病，通常造成母猪繁殖障碍以及仔猪的神经症状和高死亡率，同时伪狂犬病病毒也是猪呼吸系统疾病综合征的重要原发性病原。用gE-ELISA野毒鉴别诊断方法共检测了来自8个省、市46个猪场1940份血清样品，其中阳性样品657份，样品总阳性率33.87%，阳性猪场25个。在检测的各场中，阳性率最高猪场达到75.76%(125/165)。而部分进行了科学的疫苗免疫和实施了严格的生物安全措施的猪场始终保持猪伪狂犬病阴性(0/135)。利用基因缺失疫苗科学免疫配合伪狂犬抗体鉴别诊断技术是控制和净化伪狂犬病的重要手段。     

Factors associated with the seroprevalence of pseudorabies virus in breeding swine from quarantined herds.

Strategies for the elimination of pseudorabies virus (PRV) from swine herds include test and removal, offspring segregation, and depopulation/repopulation. The prevalence of PRV in a herd is a major factor in selection of the most appropriate strategy. The purpose of the study reported here was to describe the prevalence of PRV in adult swine in PRV quarantined herds in Minnesota, and to determine herd factors associated with the seroprevalence. Questionnaires describing the health history of the herd, management practices, and design of the swine facilities were obtained from the owners of 142 quarantined herds. Blood was collected from 29 finishing pigs over the age of 4 months, up to 29 adult females, and all herd boars. Factors considered to be significant in a bivariate analysis were combined in a stepwise multiple logistic regression analysis. The prevalence of PRV-seropositive adults in each herd was bimodally distributed among the 142 herds. In 42 (30%) of the herds, none of the females tested was seropositive, which represented the lower mode. At least 90% of the adults tested were seropositive in 30 (21%) of the herds and represented the higher mode. The odds of the breeding swine of a given herd having a PRV seroprevalence of greater than or equal to 20% as compared with having a seroprevalence of less than 20% was 1.654 times higher per 50 adults in the herd, 13.550 times higher if the finishing pigs were seropositive, 2.378 times higher if sows were housed inside during gestation, and 1.481 times lower per number of years since the imposition of quarantine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induced latency in pseudorabies vaccinated pigs.

A latent pseudorabies virus infection was established in pigs despite vaccination with a modified-live pseudorabies virus vaccine. Although the vaccinated pigs developed high concentrations of antibody, virus was recovered from the tonsils and lungs of pigs treated with dexamethasone three months after inoculation with virulent virus. These results may explain why vaccination programs have failed to eliminate the persistence and spread of virulent pseudorabies virus in infected herds.     

Outbreaks of classical swine fever in Great Britain in 1986

Classical swine fever was confirmed in 10 herds in Britain between April 10 and June 25, 1986 and typical acute disease was seen in nine of them. Serological evidence of exposure to classical swine fever virus was found in a further seven herds which, together with another nine, were slaughtered as dangerous contacts. Altogether 7781 pigs in 26 herds were slaughtered at a cost of 450,101 pounds for compensation alone. In order to detect subclinical disease, the majority of traced herds were blood sampled as well as inspected. A total of 119,169 pigs were inspected in 506 herds and 8302 blood samples were collected. Three primary outbreaks were identified, all attributed to the feeding of unprocessed waste food containing imported pig meat products. There was no spread of disease from two of these primary outbreaks.     

Indirect fluorescence antibody studies of porcine cytomegalo virus infections in the Netherlands

Summary Sera from 683 pigs of 41 swine herds with clinical atrophic rhinitis (A R), from 477 pigs of 37 herds with no A R history, from 267 breeding sows and breeding boars for slaughtering, from 22 boars at an artifical insemination centre, and from 103 SPF pigs were tested for the presence of antibodies to porcine cytomegalo virus (PCMV). The herds examined were spread all over the Netherlands. For the presence of antibodies to PCM V the indirect fluorescence antibody test was used. To obtain the antigen, the PCMV had been grown in pig lung macrophage cultures in Petri dishes for 10-12 days. These macrophages were dropped into the wells of slides. The serum dilution 1:20 of all the 103 sera from SPF pigs were negative, but 93 per cent of the other sera were positive. No marked differences were found between swine herds with clinical atrophic rhinitis and herds with no A R history. The FA titres in both types of herds seem to be at a comparable level.     

Herd-level seroprevalence of swine-influenza virus in Korea

A total of 911 serum samples from 130 herds (an average of nine serum samples per herd) in Korea were examined for antibody to swine H1N1-influenza virus using enzyme-linked immunosorbent assay (ELISA). The list of farms was obtained from the Korean Swine Association, and herds were included from all five of the country’s states. Farms were selected using a random-numbers table for swine within farms and for farms. All serum samples were collected from 22- to 24-week-old finishing pigs between September 2000 and March 2001. By ELISA, 93 out of 130 sampled herds (71.5%) were positive against swine H1N1-influenza virus. Our data suggested that seropositive herds for swine H1N1-influenza virus are distributed diffusely throughout the Republic of Korea.     

Detection of latent pseudorabies virus in swine using in situ hybridization

We have examined methods for detection of pseudorabies virus (PRV) latency in three groups of swine; naturally infected animals obtained from a field case; animals which have been experimentally infected with Becker or Iowa strains of PRV; and single reactors (single seropositive animals within PRV-free herds). In situ hybridization was shown to be more sensitive than explanation/co-cultivation for the detection of latent virus. Nervous tissues, in particular the trigeminal ganglia, were found to be the most reliable source for detecting latent PRV. The presence of latent PRV was not detected in lymphoid tissues examined.     

Field evaluation of test-and-removal and vaccination as control measures for pseudorabies in Missouri swine.

Eighteen Missouri swine herds were serologically monitored to determine the efficiency of two methods for the control of pseudorabies. A serum neutralization test-and-removal procedure was effective in ten of ten herds using this method. Vaccination procedures were less reliable. Virus still circulated in five of eight vaccinated herds and a thorough epidemiological evaluation of herd status was impossible. Titers caused by vaccination could not be distinguished from those by natural infection. Vaccination also was carried out in three seronegative herds. Antipseudorabies virus titers in these herds ranged from negative to 1:16 two to three months postvaccination. A majority of the sows in these herds responded with low 1:2 or 1:4 titers following vaccination. A direct comparison of "test and removal" farms and farms that used vaccination was not possible because of the differences between the two groups of farms.     

Survival of pseudorabies virus in the presence of selected diluents and fomites.

Because of the importance of environmental survival of pseudorabies virus to proposals to eradicate the virus from swine in the United States, survival of the virus was studied in various diluents and on combinations of diluents and solid fomites at 25 C. Suspensions of the virus in phosphate-buffered saline and saline G solutions remained infectious for at least 10 days. Infectivity of other virus/diluent suspensions decreased to less than 10 plaque-forming units/ml in 14 days (swine urine), 7 days (well water), 4 days (swine saliva), 2 days (lagoon water and swine nasal washings), and 1 day (swine pit effluent, chlorinated water, and bile). Suspensions of pseudorabies virus in saline G solution and on the solid fomites, whole corn, and steel remained infectious for at least 7 days. Infectivity of other virus/diluent/fomite combinations decreased to less than 10 plaque-forming units/ml in 7 days. The role of the fomites as vehicles for transmission of infection is discussed.     

Investigation of an outbreak of foot-and-mouth disease in vaccinated dairy cattle in Thailand

SUMMARY An outbreak of foot-and-mouth disease that spread between two related vaccinated dairy herds was investigated. Although the cattle were of similar vaccination status, in one herd there was high morbidity, whereas in the other there was considerably lower morbidity. The relationship between the vaccine virus and the outbreak virus was expressed as an r value determined by the two-dimensional neutralisation test. Bovine serum homologous to the vaccine virus indicated a close antigenic relationship between the vaccine virus and the outbreak virus (r = 0.61). The source of the outbreak virus was not determined. The investigation suggested a requirement for close contact between stock for foot-and-mouth disease to spread in a tropical environment, in contrast to the capacity of the disease to spread considerable distances by aerosol transmission in temperate climates.     

Spread of pseudorabies virus among breeding swine in quarantined herds.

In theory, pseudorabies virus (PRV) may be eliminated from any size of breeding herd by phased test and removal if replacement gilts are not infected with PRV, culling decisions are partially based on PRV status, and the cull rate is higher than the incidence rate of PRV. Annual cull rates are commonly at least 50%, but little information exists on the incidence of PRV within enzootically infected swine herds. The purpose of this study was to develop a method by which spread of PRV could be detected among breeding swine within enzootically infected herds and to determine the incidence of PRV infection in these herds. Data were collected from 17 herds that were quarantined for PRV and ranged in size from 120 to 1,100 sows. At each herd, within the first 5 days of introduction, a group of approximately 30 replacement gilts was identified, vaccinated with a glycoprotein X-deleted PRV vaccine, and blood sample was collected. The owner of 1 herd had a nonvaccinated breeding herd and elected to leave incoming gilts nonvaccinated. After vaccination, blood samples were collected every 1 to 2 months for an average of 13.6 months. Serum samples from vaccinated gilts were tested for antiglycoprotein X antibodies by a specific differential ELISA. Samples from nonvaccinated gilts were evaluated by serum neutralization test. Product-limit method was used to estimate the probability of not becoming infected with PRV. Spread was detected in 7 of 8 herds that had more than 400 sows and in 2 of 9 herds that had less than 400 sows.(ABSTRACT TRUNCATED AT 250 WORDS)     

A seroepizootiologic study of five viruses in a swine-evaluation station.

This serologic study was done to gain information on the spread, maintenance, and effect upon performance of five porcine viruses. Blood samples were taken from two groups of 8- to 11-week-old pigs from a large number of Indiana swine herds in a performance-testing station 1 week after entry, 7 weeks after entry (one group only), and at slaughter. The sera were tested by indirect fluorescent antibody tests for antibodies to transmissible gastroenteritis virus (TGEV), swine influenza virus (SIV), hemagglutinating encephalomyelitis virus (HEV), porcine adenovirus (PAV), and pseudorabies virus (PRV). Seroconversions to TGEV, HEV, and PAV occurred in a group of pigs entered in May and slaughtered in August (group 1). In the group that was entered in October and slaughtered in January (group 2), pigs developed antibodies to SIV, HEV, and PAV, but not to TGEV. Only 1 of the 434 pigs tested had antibodies to PRV, and there were no seroconversions to this virus. The only statistically valid effect of infection on performance was found in group 1 pigs, which had seroconverted to TGEV during the first 7 weeks of their stay. These pigs gained 0.077 kg less per day than pigs that did not develop antibodies to TGEV during that period. The pattern of serologic reactions was indicative of a relatively slow spread of these viruses in the groups. We interpret this as supporting the concept that a relatively slow spread of these viruses through large groups of pigs kept under conditions that are less than optimum for virus spread may be an important means of their interepizootic survival.     

光生物素标记的口蹄疫病毒cDNA探针的制备及其对口蹄疫病毒RNA检测的试验研究

本文首次报道了利用pF1034质粒制备FMDV O型特异性探针,并通过PCR反应扩增FMDO_1K株病毒基因组的第2962位与3071位之间共110bp序列,制备了能检测O型、A型和亚洲I型FMDV RNA的群(组)特异性探针。用硝酸纤维素膜斑点杂交试验表明,二者均能检测出10pg水平的O_9K毒株的纯RNA;但前者只与O型FMDV RNA杂交,与A型及亚洲I型FMDV RNA无交叉杂交现象;而后者则能与O型、A型和亚洲I型的FMDV RNA发生杂交反应。对照试验显示:此两种探针与SVDV ssRNA、BTV dsRNA、EHDV dsRNA、DHV ssRNA、PRV DNA、乳鼠组织细胞RNA、BHK_(21)克隆13细胞RNA及DNA等均不出现交叉杂交现象,但与IBR DNA有假阳性杂交反应。