Capsid coding sequences of foot-and-mouth disease viruses are determinants of pathogenicity in pigs

The surface exposed capsid proteins, VP1, VP2 and VP3, of foot-and-mouth disease virus (FMDV) determine its antigenicity and the ability of the virus to interact with host-cell receptors. Hence, modification of these structural proteins may alter the properties of the virus.In the present study we compared the pathogenicity of different FMDVs in young pigs. In total 32 pigs, 7-weeks-old, were exposed to virus, either by direct inoculation or through contact with inoculated pigs, using cell culture adapted (O1K B64), chimeric (O1K/A-TUR and O1K/O-UKG) or field strain (O-UKG/34/2001) viruses. The O1K B64 virus and the two chimeric viruses are identical to each other except for the capsid coding region.Animals exposed to O1K B64 did not exhibit signs of disease, while pigs exposed to each of the other viruses showed typical clinical signs of foot-and-mouth disease (FMD). All pigs infected with the O1K/O-UKG chimera or the field strain (O-UKG/34/2001) developed fulminant disease. Furthermore, 3 of 4 in-contact pigs exposed to the O1K/O-UKG virus died in the acute phase of infection, likely from myocardial infection. However, in the group exposed to the O1K/A-TUR chimeric virus, only 1 pig showed symptoms of disease within the time frame of the experiment (10 days). All pigs that developed clinical disease showed a high level of viral RNA in serum and infected pigs that survived the acute phase of infection developed a serotype specific antibody response. It is concluded that the capsid coding sequences are determinants of FMDV pathogenicity in pigs.     

Swine vesicular disease: an overview

Swine vesicular disease (SVD) is a notifiable viral disease of pigs included on the Office International des Epizooties List A. The first outbreak of the disease was recognized in Italy in 1966. Subsequently, the disease has been reported in many European and Asian countries. The causative agent of the disease is SVD virus which is currently classified as a porcine variant of human coxsackievirus B5 and a member of the genus enterovirus in the family picornaviridae. From a clinical point of view, SVD is relatively unimportant, rarely causing deaths and usually only a minor setback to finishing schedules. However, the clinical signs which it produces are indistinguishable from those caused by foot-and-mouth disease, and its presence prevents international trade in pigs and pig products. This article reviews recent findings on all aspects of the virus and the disease which it causes.     

Infection of pigs by Aujeszky's disease virus via the breath of intranasally inoculated pigs

Aujeszky's disease is a worldwide problem in the pig industry. In this experiment, four pigs chosen to act as shedder pigs were intranasally infected with Aujeszky's disease virus. Next, on three consecutive days, eight recipient pigs were exposed to the breath of a pair of shedder pigs via a mask-to-mask module. Except for the virtual absence of CNS signs, shedder pigs expressed clinical signs that were similar to pigs infected naturally or experimentally. Only mild respiratory signs occurred in recipient pigs, but all were infected by aerosols of Aujeszky's disease virus as evidenced by seroconversion. The pig is a much more sensitive indicator of airborne virions than our aerosol collection methods. We conclude that the mild respiratory disease acquired by the aerogenous route in recipient pigs is an easily managed model for studying the transmission of airborne respiratory infections and the immune responses to this type of infection.     

Vesicular stomatitis.

Vesicular stomatitis is an infrequent yet important vesicular disease of cattle, horses, and swine. Periodic outbreaks of this disease in the United States have caused economic losses in cattle herds because of decreased production, movement restrictions, and trade embargoes. Vesicular stomatitis causes clinical signs indistinguishable from those of foot-and-mouth disease. It is of utmost importance that appropriate samples are collected from clinical cases of vesicular disease in cattle and swine so a rapid laboratory diagnosis can be made.     

An unusual presentation of suspected oedema disease of swine in Kenya

From a group of 11 recently weaned pigs, 4 were reported to be sick. Clinical examination of the sick pigs revealed marked dyspnoea, bluish-red discolouration of the skin, incoordination and difficulty in walking. Bacteriological examination of the gut contents of 2 pigs that had died earlier yielded pure cultures of haemolytic Escherichia coli. Post mortem examination of the remaining 2 pigs that died subsequently revealed progressive pulmonary collapse. One of these also showed subcutaneous oedema of the head and marked oedema of the mesentery of the spiral colon and oedema of the brain. Microscopically there was pulmonary alveolar collapse and degenerative changes in the liver. On the basis of the clinical signs, isolation of haemolytic E. coli and the post mortem findings, a diagnosis of oedema disease was made.     

Malignant catarrhal fever in Switzerland: 2. Evaluation of the diagnosis]

Malignant catarrhal fever (MCF) is a mostly fatal lymphoproliferative disease of cattle. In 1995 a PCR based method was introduced for the detection of the ovine herpesvirus 2 (OvHV-2), which is regarded as the causative agent of the sheep-associated form of the disease. This PCR can be regarded as a gold standard for the in vivo diagnosis of sheep-associated MCF in cattle (Müller-Doblies et al., 1998). This semi-nested PCR was now used as a reference test for the reassessment of diagnostic criteria in the clinical and post mortem diagnosis that could previously not be quantitated. Based on 83 suspected cases with a complete clinical record the clinical signs were weighted and grouped according to their sensitivity and specificity into lead signs indicative of MCF and frequently accompanying signs supportive for the diagnosis of MCF and general clinical signs that were less reliable for the diagnosis. Differential diagnoses are discussed, which are of particular significance due to their status as OIE list A diseases e.g. foot-and-mouth disease or rinderpest. 38 PCR confirmed cattle with MCF served for the quantitative analysis of organ lesions. For the post mortem diagnosis an essential set of organ samples is defined to permit a reliable histological diagnosis, as the gross pathology often did not give any indication for the diagnosis. These criteria should help to improve the diagnostic efficiency and to select the appropriate laboratory diagnostic procedures for MCF-suspected cattle.     

Swine vesicular disease, studies on pathogenesis, diagnosis, and epizootiology: a review

Swine vesicular disease (SVD) is a contagious viral disease of swine. It causes vesicular lesions indistinguishable from those observed of foot-and-mouth disease. Infection with SVD virus (SVDV) can lead to viraemia within 1 day and can produce clinical signs 2 days after a pig has come into contact with infected pigs or a virus-contaminated environment. Virus can be detected 3.5 hours after infection using immunohistochemistry. In these in vitro studies, this technique was superior to in-situ hybridization. In SVDV-infected tissues, however, more infected cells were positive using in-situ hybridization, and these were already seen 4.5 hours after infection. For serological diagnosis of SVD several new enzyme-linked immunosorbent assays (ELISA's) have been developed. The newest ELISAs, based on monoclonal antibodies, are superior to the previous tests. The new tests produce fewer less false-negative results and enable large-scale serological screening. In screening programmes a small percentage of false positive reactors have been detected. The cause of these false-positive reactions has not been identified, though infections with human Coxsackie B5 virus can be excluded.     

牛口蹄疫病防治

牛口蹄疫是国家一类重特大传染性疾病,会严重威胁地区牛养殖产业的安全,给养殖户带来巨大经济损失,降低牛养殖产业的生产效益。再加上牛口蹄疫是一种人畜共患病,疾病传播流行中,如果没有做好个体防护很易造成病毒,向人扩散蔓延,威胁周边居民的生命财产安全。在充分掌握牛口蹄疫病发生现状的基础上,需要进行认真细致的分析,构建针对性的防控措施,降低疾病发生流行造成的危害。在充分掌握新宾县牛口蹄疫发生现状的基础上,对牛口蹄疫疾病的诊断和提出防治措施。     

An experimental infection in pigs using a foot-and-mouth disease virus isolated from the 2010 epidemic in Japan

In this study, we carried out an experimental infection in pigs using a foot-and-mouth disease virus isolated from the 2010 epidemic in Japan to analyze the clinical manifestation, antibody response and virus shedding patterns in pigs. We found that the virus was virulent in pigs, producing a synchronous disease in the inoculated pigs and efficient spread to direct contact pigs. These results are useful for epidemiologically investigating the 2010 epidemic in Japan and improving the measures for controlling possible future FMD outbreaks in Japan or elsewhere.     

Experimental foot-and-mouth disease in fattening pigs, sows and piglets in relation to outbreaks in the field

The progression of foot-and-mouth disease in sows and their litters of piglets following exposure to O1 Lausanne virus has been investigated. The majority of piglets died with acute myocarditis but without developing vesicles. Deaths occurred before and also when sows began showing early evidence of vesicle formation. This clinical picture parallels that seen at the beginning of both the Normandy 1979 and Britanny 1981 epidemics in France and points to the necessity of including foot-and-mouth disease in the differential diagnosis of acute death among cloven-hoofed livestock and furthermore the importance of extending clinical inspections to adult animals on premises when such events take place. In investigations in which the susceptibility of fattening pigs to infection with O1 Lausanne virus given by the intramuscular route was examined it was found that the 50 per cent infective dose was log (10)4.8 TCID50. This finding suggests that large amounts of virus are required for successful initiation of disease. This is more likely to come from animals already infected than by inoculation with contaminated material.     

Aflatoxicosis in Iowa swine: eight cases (1983-1985)

During 1983, 1984, and 1985, aflatoxicosis was diagnosed in 8 Iowa swine herds after the herds were fed corn from the 1983 corn crop. As a result of the diagnosis, the associated environmental conditions, clinical signs of aflatoxicosis, macroscopic and microscopic lesions, aflatoxin concentrations detected in feeds, and management of affected swine were reviewed. Concentrations of aflatoxin in shelled corn and complete feed were as high as 2,020 ng and 1,200 ng of aflatoxin (B1 and B2)/g of feed, respectively. Clinical signs of aflatoxicosis included decreased feed consumption and weight loss. Some pigs died acutely, but death often was preceded by a period of clinical disease. Greater morbidity and mortality were observed in swine herds that consumed greater concentrations of aflatoxin.     

Association between transmission rate and disease severity for Actinobacillus pleuropneumoniae infection in pigs

A better understanding of the variation in infectivity and its relation with clinical signs may help to improve measures to control and prevent (clinical) outbreaks of diseases. Here we investigated the role of disease severity on infectivity and transmission of Actinobacillus pleuropneumoniae, a bacterium causing respiratory problems in pig farms. We carried out transmission experiments with 10 pairs of caesarean-derived, colostrum-deprived pigs. In each pair, one pig was inoculated intranasally with 5 × 10⁶ CFUs of A. pleuropneumoniae strain 1536 and housed together with a contact pig. Clinical signs were scored and the course of infection was observed by bacterial examination and qPCR analysis of tonsillar brush and nasal swab samples. In 6 out of 10 pairs transmission to contact pigs was observed, but disease scores in contact infected pigs were low compared to the score in inoculated pigs. Whereas disease score was positively associated with bacterial load in inoculated pigs and bacterial load with the transmission rate, the disease score had a negative association with transmission. These findings indicate that in pigs with equal bacterial load, those with higher clinical scores transmit A. pleuropneumoniae less efficiently. Finally, the correlation between disease score in inoculated pigs and in positive contact pigs was low. Although translation of experimental work towards farm level has limitations, our results suggest that clinical outbreaks of A. pleuropneumoniae are unlikely to be caused only by spread of the pathogen by clinically diseased pigs, but may rather be the result of development of clinical signs in already infected pigs.     

Interferon inducers and foot-and-mouth disease vaccines: influence of two synthetic polynucleotides on antibody response and immunity in guinea pigs and swine.

Polyriboadenylic-polybouridylic acid enhanced the immunological response of guinea pigs to aqueous foot-and-mouth disease virus vaccine. Polyriboninosinic-polyribocytidylic acid enhanced the early antibody production of swine to oil emulsified foot-and-mouth disease virus vaccine. Polyriboninosinic-polyribocytidylic acid alone did not stimulate resistance to foot-and-mouth disease in swine.     

Inoculation of pigs with Streptococcus suis type 2 alone or in combination with pseudorabies virus.

Pigs (9 [+/- 1] weeks old) were inoculated with Streptococcus suis type 2, pseudorabies virus (PRV), or both. For each pig of groups A, B, and C the inoculum of S suis was 10(9) colony-forming units. For each pig of groups A, B, and D the inoculum of PRV was 5 x 10(3) TCID50 of either PRV strain 4892 (group A, n = 9) or PRV isolate B (group B, n = 9). The PRV strain 4892 is a highly virulent strain; isolate B causes mild clinical signs of infection in inoculated pigs. Group-C pigs (n = 9) were given S suis alone, and group-D pigs (n = 3) were inoculated only with PRV isolate B. Clinical signs of infection and development of lesions were readily seen in pigs of groups A, B, and C. Duration and severity of clinical signs of disease and lesions were reduced in pigs of group C, compared with those of the other 2 groups. Lesions, such as polyarthritis and fibrinous pericarditis, were more abundant and acute in the groups of pigs given mixed challenge exposure, compared with pigs inoculated exclusively with S suis type 2 (group C). The group of pigs inoculated with PRV isolate B alone did not manifest clinical signs of disease or lesions. Average daily gain for group-C pigs was higher, compared with that of other groups; the difference was statistically significant at P less than 0.02 and P less than 0.05 for groups B and D, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transmission of Sarcoptes scabiei in Swine by Fomites

Transmission of sarcoptic mange by fomites was investigated by placing mange-free piglets in pens for either fixed or variable periods of time during the first six days following removal of mange infected swine. Transmission occurred in pigs with as little as 24 hours exposure to fomites. Clinical signs of pruritis and focal erythematous skin lesions developed in various pigs from four and a half to 13 weeks after exposure. Pigs with the longer exposure developed clinical signs more rapidly than those with a shorter exposure. Four of six pigs developed a chronic form of the disease characterized by thickened encrustations and scurf from which mites were readily demonstrated. The remaining two pigs developed only the pruritic form and mites were never found in numerous skin scrapings examined.     

猪流感诊断方法研究进展

猪流感即猪流行性感冒,是由正黏病毒科A型流感病毒引起的一种急性呼吸道传染病。其特征为突发,高热,精神沉郁,食欲废绝,呼吸困难,阵发性咳嗽。猪流感的病死率不高,病猪可康复。近年来,随着集约化养猪规模的不断扩大,猪流感对养猪业构成了较大的威胁。此外,猪流感在人流感和禽流感之间发挥着关键性作用,具有重要的公共卫生意义。自1918年首次报道以来,猪流感一直受到人们的广泛关注。研究快速、科学、准确的诊断方法,对于本病的检测和控制具有重要的意义。除常规的临床症状及病理变化诊断外,流感的确诊依赖于实验室诊断方法。文章从病原学、血清学和分子生物学等几个方面对该病的诊断研究进展做了综述。     

O型口蹄疫疫苗免疫家畜抗体水平的检测

准确监测是防控口蹄疫的重要环节。采集某地区乡镇规模化养殖场及散养户的牛、羊、猪血清,采用正向间接血凝试验进行O型口蹄疫疫苗免疫抗体水平的检测。结果显示,该地区牛、羊的口蹄疫疫苗免疫合格率平均为76%,猪的口蹄疫疫苗免疫合格率平均为60％;规模化养殖场较个体散养户免疫效果好;牛口蹄疫O型灭活苗的免疫效果好于牛口蹄疫Asia I-O型双价灭活疫苗的免疫效果。     

Epidemiological characteristics and financial costs of the 1997 foot-and-mouth disease epidemic in Taiwan

Between March and July 1997, a devastating outbreak of foot-and-mouth disease (FMD), serotype O, occurred in pigs in Taiwan. A total of 6,147 pig farms with more than 4 million pigs were infected, and 37.7 per cent of the pigs in Taiwan either died (0.18 million pigs) or were killed (3.85 million pigs). The epidemic reached its peak during the fifth week after it was first recognised. During the eighth and ninth weeks, a two-dose blanket vaccination programme was instituted which led to a large reduction in new outbreaks. Except for two cities, the whole of Taiwan was declared an FMD-infected zone. During the four months in which new farm outbreaks occurred, 21.7 per cent of the pigs on infected farms showed clinical signs, and there was an overall mortality of 3.95 per cent. During the early stages of the epidemic, the incubation period was as short as 24 hours and the case fatality rates for suckling piglets reached 100 per cent. The financial cost of the epidemic was estimated at US$ 378.6 million, including indemnities, vaccines, carcase disposal plus environmental protection, miscellaneous expenses, and loss of market value. Owing to the ban on exports of pork to Japan, it is estimated that the total economic cost to Taiwan's pig industry will be about US$ 1.6 billion.     

Associations between genetics, farm characteristics and clinical disease in field outbreaks of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is a disease of domestic swine characterized by exceptionally high clinical variability. This study addresses the question of whether clinical variability in PRRS results from (a) genetic variation among viral isolates and/or (b) variation in management practices among farms on which isolates are found. Genetic data (open reading frame 5 gene sequences) and data on farm characteristics and associated clinical disease signs were collected for 62 PRRS virus (PRRSV) field isolates, representing 52 farms. Clinical disease signs were interrelated — confirming that a true reproductive syndrome exists (involving abortions, infertility in sows, deaths of sows and preweaning mortality).

Pairs of farms experiencing deaths in their sow populations also tended to share viral isolates which were more similar to one another than expected by chance alone. This implies that sow death (one of the more-severe manifestations of PRRS) is under genetic influence. Large herd size was a significant risk factor for the death of sows and for respiratory disease in nursery pigs. All-in–all-out management practices in the nursery were protective against reproductive signs in the sow herd. All-in–all-out management practices in the finishing stages of production were protective against respiratory disease in nursery pigs — but were paradoxically associated with an increased risk of infertility in sows. These results suggest that farm-management practices can also influence which PRRS clinical signs are manifested during an outbreak. In general, signs associated with PRRS appear to result from a combination of genetic factors and herd-management characteristics. The relative contributions of these two influences differ depending on the specific clinical sign in question.     

Review of methods for the detection of Lawsonia intracellularis infection in pigs

Lawsonia intracellularis is an obligate intracellular bacterium associated with enteric disease in pigs. Clinical signs include weight loss, diarrhea, and, in some cases, sudden death. The hallmark lesion is the thickening of the intestinal mucosa caused by increased epithelial cell replication, known as proliferative enteropathy. The immune response to L. intracellularis is not well defined, and detection of the infection, especially in the early stages, is still a significant challenge. We review here the main approaches used to identify this important but poorly understood pathogen. Detection of L. intracellularis infection as the cause of clinical disease is confounded by the high prevalence of the pathogen in many countries and that several other pathogens can produce similar clinical signs. A single L. intracellularis–specific ELISA and several amplification assays are available commercially to aid detection and surveillance, although histopathology remains the primary way to reach a conclusive diagnosis. There are major gaps in our understanding of L. intracellularis pathogenesis, especially how the host responds to infection and the factors that drive infection toward different clinical outcomes. Knowledge of pathogenesis will increase the predictive value of antemortem tests to guide appropriate interventions, including identification and treatment of subclinically affected pigs in the early stages of disease, given that this important manifestation reduces pig productivity and contributes to the economic burden of L. intracellularis worldwide.