Production diseases in smallholder pig systems in rural Lao PDR.

Pigs in Lao People's Democratic Republic are important for income and food security, particularly in rural households. The majority of pigs are reared in smallholder systems, which may challenge the implementation of any disease control strategies. To investigate risk factors for pig production diseases in such farming systems in the country a serological survey was conducted during 2011. A total of 647 pigs were sampled, accounting for 294 households in Luang Prabang and 353 in Savannakhet province representing upland and lowland, respectively. The results demonstrated that pigs in Lao PDR had antibodies against erysipelas (45.2%), CSF (11.2%), PRRS (8.6%), FMD O (17.2%) and FMD Asia 1, (3.5%). Differences in the housing systems influenced disease risk, for example, penned pigs had reduced odds of FMD and CSF, compared to those in scavenger systems. Pigs owned by farms using a sanaam (a communal area where pigs are kept for some time of the year) had 3.93 (95% confidence interval (CI): 1.09-14.7) times the odds of having pigs seropositive for FMD. Farms on which sudden piglet deaths had been experienced were more likely to have pigs seropositive for FMD O and erysipelas. These diseases constrain the development of village farming and the wider livestock industry due to their impact on productivity and trade. Vaccination coverage for FMD and CSF was low and there was a lack of national funding for livestock disease control at the time of the study. Further investigation into sustainable low-cost control strategies for these pathogens is warranted.

Pulmonary intravascular macrophages regulate the pathogenetic mechanisms of pulmonary lesions during acute courses of classical swine fever.

Classical swine fever (CSF) is a highly contagious and often fatal viral disease of domestic pigs and wild boar. Pulmonary oedema and haemorrhages in lung parenchyma are common lesions in the acute forms of CSF that may compromise pig survival and whose pathogenetic mechanisms remain unclear. The appearance of pulmonary lesions in pigs infected with Alfort/187 strain of classical swine fever virus (CSFV) euthanized between 2 and 17 days postinfection (dpi) and the role played by cytokines secreted by different pulmonary macrophage populations in the evolution of lesions was evaluated in this study. Microscopic changes of alveolar septal thickening along with oedema and haemorrhages became more severe at middle-late stages of the experiment. A significant increase in the number of pulmonary macrophages, mainly pulmonary intravascular macrophages (PIMs), was observed coinciding with the onset of alveolar septal thickening from Day 4 pi. PIMs were the main target of CSFV from initial stages of infection while the presence of infected pulmonary alveolar macrophages (PAMs) was scarce and late. Initial infection of PIMs induced phagocytic and biosynthetic activation with subsequent release of chemotactic cytokines. TNFα and, to a lesser extent, IL-1α secreted by PIMs were the major cytokines involved, while IL-6 played only a minor role. On the contrary, results suggested only a secondary role of PAMs as source of cytokines. The presence of vascular changes from Day 9 pi coincided with the highest levels of infected PIMs and the highest number of pro-inflammatory cytokines secreting PIMs. Activation and phagocytosis of platelets were observed in the lungs of infected pigs from early stages, also coinciding with the expression of cytokines with a proven procoagulant activity. The existence of intravascular coagulation phenomena in lung was ruled out.

Autophagy induces apoptosis and death of T lymphocytes in the spleen of pigs infected with CSFV.

Lymphocyte depletion and immunosuppression are typical clinical characteristics of pigs infected with classical swine fever virus (CSFV). The apoptosis of virus-infected and bystander cells plays a role in the immunopathology of classical swine fever (CSF). Here, we offer the first evidence that autophagy is involved in apoptosis and death of T lymphocytes in the spleen of pigs infected with CSFV. Using immunohistochemical assays, we observed that more LC3II-positive cells appear in the T-cell zone of spleens. Spleen cell apoptosis was demonstrated using flow cytometry and TUNEL staining. Confocal immunofluorescence revealed that partial LC3II-positive cells were simultaneously TUNEL-positive. By cultivating spleen cells ex vivo, we demonstrated that the inhibition of autophagy by 3-MA treatment inhibited apoptosis and death of T lymphocytes caused by CSFV infection but did not have this effect  on B lymphocytes. Further observations demonstrated that uninfected cells in the spleen were also undergoing autophagy in vivo. In summary, these results linked autophagy with the apoptosis and cell death of splenic T cells, providing a new outlook to understand the mechanism of T lymphocyte depletion and immunosuppression during CSF.

Evaluation of the spatial patterns and risk factors, including backyard pigs, for classical swine fever occurrence in Bulgaria using a Bayesian model.

The spatial pattern and epidemiology of backyard pig farming and other low bio-security pig production systems and their role in the occurrence of classical swine fever (CSF) is described and evaluated. A spatial Bayesian model was used to explore the risk factors, including human demographics, socioeconomic and environmental factors. The analyses were performed for Bulgaria, which has a large number of backyard farms (96% of all pig farms in the country are classified as backyard farms), and it is one of the countries for which both backyard pig and farm counts were available. Results reveal that the high-risk areas are typically concentrated in areas with small family farms, high numbers of outgoing pig shipments and low levels of personal consumption (i.e. economically deprived areas). Identification of risk factors and high-risk areas for CSF will allow to targeting risk-based surveillance strategies leading to prevention, control and, ultimately, elimination of the disease in Bulgaria and other countries with similar socio-epidemiological conditions.

[Pathogenesis of classical swine fever--similarities to viral haemorrhagic fevers: a review]. / Pathogenese der Klassischen Schweinepest--Parallelen zu viralen hämorrhagischen Fiebern: eine Ubersicht.

In spite of differences in etiology, viral haemorrhagic diseases share similarities in their pathogenesis. Characteristic for these diseases are thrombocytopenia, petechia and increased vascular leakage. Most lesions can be attributed to cytokine-mediated interactions triggered by infected and activated monocytes and macrophages, rather than by virus-induced direct cell damage. Causative agents of viral hemorrhagic diseases are enveloped RNA viruses. In most cases, they are transmitted to humans from their animal hosts by rodents or arthropod vectors (Arboviruses). Due to the clinical picture, the acute lethal form of classical swine fever (CSF) is also considered as a viral haemorrhagic disease. CSF is caused by an RNA virus in the family Flaviviridae, and members of the Suidae family are the only ones clinically affected. It is a highly contagious, therefore notifiable disease. In contrast to other viral hamorrhagic diseases, it is mainly transmitted oro-nasally by contact with infected pigs, or by contaminated items (semen, swill feed, clothing). The present survey summarizes analogies between classical representatives of viral haemorrhagic fevers, and recapitulates current knowledge concerning the pathogenesis of classical swine fever.

Feed contaminated with classical swine fever vaccine virus (LOM strain) can induce antibodies to the virus in pigs.

In November 2004, antibodies to classical swine fever virus (csfv) were detected in finishing pigs during the annual serological surveillance in Jeju Province, Korea. In addition, csf vaccine viruses (lom strain) had recently been isolated from pigs raised on farms known to have csfv antibody-positive pigs. In contrast with mainland Korea, Jeju Province had been csf free and its pigs had not been vaccinated against csf for more than five years. An epidemiological investigation team from the National Veterinary Research and Quarantine Service investigated the current status of csf prevention on the Korean mainland and in Jeju Province to determine possible routes of introduction of the virus into the province. It was concluded that improperly processed blood meals, manufactured on mainland Korea, had been contaminated with the csf vaccine lom strain, and that the lom strain had been transmitted to pigs fed feed or feedstuffs containing the contaminated meal.

Prevalence of classical swine fever, Aujeszky's disease and brucellosis in a population of wild boar in Switzerland.

During two survey rounds of a national surveillance system for infectious diseases in wild boar in Switzerland, each lasting four months from November to February, between 2001 and 2003, 1949 blood samples and 62 tissue samples from the spleen and 50 from the reproductive organs were collected from hunted wild boar. The survey was designed so that freedom from infection could be detected with a probability of 95 per cent at a threshold prevalence of less than 1 per cent for classical swine fever and Aujeszky's disease and less than 1.5 per cent for brucellosis. There was no serological evidence of classical swine fever or Aujeszky's disease, but brucellosis due to Brucella suis biovar 2 was confirmed serologically and by bacterial isolation.

Statistical evaluation of classical swine fever surveillance plans in Italy (1995-2003).

Summary Surveillance plans were carried out in Italy from 1995 to 2003, with the main aim of controlling the possible circulation of low-virulence classical swine fever viral strains. The repetition of a serological monitoring programme over several years, with constantly negative results, can prove the absence of the infection while increasing the degree of confidence. In our case, in 2003, after eight repetitions of the surveillance plan, the probability that there was at least one infected farm reached 0.006%. Therefore, on the basis of the results of the sampling carried out from 1995 to 2003, we may state that there is no endemic infection, even because of a low virulence virus, in continental Italy.

Incidence and persistence of classical swine fever in free-ranging wild boar (Sus scrofa).

Although veterinary authorities aim to limit persistence of classical swine fever (CSF) in wild boar (Sus scrofa), to avoid potential transmission to pigs, factors influencing CSF transmission and persistence are not clearly understood. Here we analyse incidence and persistence in a CSF epidemic that occurred in the French Vosges Forest. Higher incidence was found in large forests compared to smaller isolated ones, being highest near the starting point of the epidemic, but poorly related to the local density. We hypothesize that the spatial and social structure of wild boar populations may be responsible for this variability of incidence over space. Persistence was highest near the starting point of the epidemic and where initial density was highest. We hypothesize that persistence was favoured by the abundance of young wild boar, itself encouraged by CSF. Our results allow us to propose management measures aimed at limiting CSF persistence.

Long-term monitoring of classical swine fever in wild boar (Sus scrofa sp.) using serological data.

In the European Community, epizootics of classical swine fever (CSF) in the wild boar (Sus scrofa) are compulsorily monitored because transmission may occur between wild boars and domestic pigs, causing heavy economic losses to the pork industry. The estimation of incidence in populations of wild boars is generally based on viroprevalence. However, viral isolation becomes rare when the incidence is low because the virus cannot be detected for more than a few weeks following infection. On the contrary, seroprevalence is detectable at low incidence levels, because antibodies can be detected for the lifetime of the infected animal. We thus attempted to analyse the long-term evolution of CSF incidence using serological data. The data came from France, where CSF had been monitored from 1992 to 2002, and where the virus has not been detected since 1997. We assumed that the overall seroprevalence would estimate the proportion of immune wild boars, that seroprevalence in juveniles would approximate incidence and that seroprevalence in different age classes would show the evolution of incidence in a given cohort. Spatial and temporal trends of incidence and seroprevalence were explored using logistic modelling and the spatial trend was analysed using polynomial regression. In 1992, incidence peaked in the northern area. After 1993, incidence decreased but remained the highest in the northern area. After 2000, no seropositive juvenile was observed, suggesting the extinction of the epizootic. Our results support the reliability of serological monitoring since it allowed a longer detection of viral transmission and provided more information on the spatio-temporal evolution of incidence than did viral isolation. We advocate that the highest persistence of infection in northeastern France is not independent from infection persistence in Reinland-Pfalz (Germany). Such persistence may be due to favourable local conditions and/or the social organisation of wild boars.

Ability of veterinary pathologists to diagnose classical swine fever from clinical signs and gross pathological findings.

Clinical signs recorded in a classical swine fever (CSF)-suspect situation and the results of the subsequent post-mortem examination (PME) from swine submitted to post-mortem during the 1997-1998 CSF epidemic in the Netherlands, were presented in an experiment as anonymous cases (without knowledge of the actual infection status of the submission) to five veterinary pathologists for their judgment: CSF-suspect or non-suspect. It was presented to them in two hypothetical situations: country was free of CSF for 5 years and CSF was detected in the country 2 weeks ago. Subsequently, their judgment was compared to the gold standard (infection status of the submission on the basis of an immunofluoresence assay on tissue samples) and the sensitivity (Se) and specificity (Sp) of clinical diagnosis was estimated. Furthermore, intra- and inter-pathologist agreement on pathological diagnosis was measured. Adding information on clinical signs to information on PME resulted in a significant increase in median Se and a significant decrease in median Sp for a clinical judgment by pathologists. Also, median Se was significantly higher-and Sp significantly lower-for a clinical judgment by pathologists in a situation in which CSF was detected 2 weeks ago in the country compared to the situation in which the country had been free of CSF for 5 years. Apparently, the internal threshold of pathologists is severely adjusted depending on the actual disease situation in a country. Intra-rater agreement ranged from fair to almost perfect for a clinical diagnosis on the basis of PME. There was considerable variation between pathologists, especially if clinical diagnosis was based on the combined information on PME and clinical signs observed in the herd. Inter-rater agreement was substantial for the diagnosis based on information on PME. Inter-rater agreement was considerably lower for the diagnosis based on the combined information on PME and clinical signs observed in the herd.

Establishment and characterisation of two cDNA-derived strains of classical swine fever virus, one highly virulent and one avirulent.

The virulence of classical swine fever virus (CSFV) strains including established laboratory strains as well as field isolates ranges from avirulent to highly virulent. Here, we describe the construction and characterisation of two cDNA-derived CSFV strains, each corresponding to one of these extremes. The recombinant virus vEy-37 caused acute disease indistinguishable from that provoked by infection with the highly virulent parent strain Eystrup. In contrast, vRiems-3, a molecular clone of the CSFV vaccine strain Riems, was avirulent and induced protective immunity in pigs. After repeated passage of vEy-37 in porcine kidney SK-6 cells adaptive mutations in the E(rns) gene were observed. The respective reconstructed mutant virus grew to titres that were almost 4log units higher when compared to vEy-37. The mutation in the E(rns) gene had only a minor effect on the virulence of the virus. The complete genomic sequences of the two CSFV strains, Eystrup and Riems, have been deposited in GenBank (accession number AF326963 for CSFV Eystrup, AY259122 for CSFV Riems/IVI).

Neighbourhood infections of classical swine fever during the 1997-1998 epidemic in The Netherlands.

Data of the 1997-1998 epidemic of classical swine fever (CSF) in The Netherlands were analysed in survival analysis to identify risk factors that were associated with the rate of neighbourhood infections. The study population consisted of herds within 1000 m of exclusively one previously infected herd. Dates of virus introduction into herds were drawn randomly from estimated probability distributions per herd of possible weeks of virus introduction. (To confirm the insensitivity of the results for this random data-selection procedure, the procedure was repeated 9 times (resulting in 10 different data sets).) The data set had 906 non-infected and 59 infected neighbour herds, which were distributed over 215 different neighbourhoods. Neighbour herds that never became infected were right-censored at the last date of the infectious period of the infected source herd. Neighbour herds that became empty within the infectious period or within the following 21 days due to preventive depopulation or due to the implemented buying-out programme were right-censored 21 days before the moment of becoming empty. This was done as a correction for the time a herd could be infected without being noticed as such. The median time to identified infection of neighbour herds was 2 weeks, whereas the median time to right censoring of non-infected neighbour herds was 3 weeks. The risk factors, radial distance < or =500 m, cattle present on source herd and increasing herd size of the neighbour herd were associated multivariably with the hazard for neighbour herds to become infected. We did not find an association between time down wind and infection risk for neighbour herds. Radial dispersion of CSFV seemed more important in neighbourhood infections than dispersion along the road on which the infected source herd is situated. The results of this study support the strategy of preventive depopulation in the neighbourhood of an infected herd. Recommendations are presented to adapt the applied control strategy for neighbourhood infections.

Virulence of recent and former classical swine fever virus isolates evaluated by their clinical and pathological signs.

The clinical diagnosis of classical swine fever (CSF) still caused problems to the veterinarians during the last decade. The primary CSF outbreak was often detected too late and, meanwhile, the virus had spread. Consequently, the recent classical swine fever virus isolates (CSFV) were suspected to be of low virulence. The purpose of the study was to quantify the virulence of four recent CSFV by evaluating the clinical and pathological signs caused by different CSFV. Pigs of the same breed and age group were inoculated intranasally with CSFV from recent epidemics in European Union (EU) member states. The CSFV used are registered in the data base of the EU Reference Laboratory for CSF and belong to different genotypes: 2.1, 2.2 and 2.3 respectively. Clinical signs of CSF were evaluated by using a score system suggested previously (Mittelholzer et al., 2000: Vet. Microbiol. 74, 293). For the evaluation of pathological lesions, a new pathological score was introduced. The four CSFV tested here were classified as moderately virulent in general, although one CSFV may cause different clinical courses, ranging from highly virulent to avirulent. This indicates the importance of additional factors in the host animal for virulence. Differences in the clinical and pathological signs between these four recent CSFV were rather minor, emphasizing that the genetic typing of CSFV is absolutely essential. Differences towards former CSFV (e.g. reference virus strain Alfort 187) were more pronounced, especially regarding the onset and duration of the disease, the occurrence of skin haemorrhages and pathological lesions of kidney, subcutis and serosae. It is concluded that clinical diagnosis of CSF is rather difficult in pigs up to 14 days post-CSFV infection using these four CSFV, emphasizing the need for careful differential diagnosis and the laboratory investigation for CSF at an early stage.

African swine fever and classical swine fever: a review of the pathogenesis.

This paper describes major pathogenetic mechanisms of African and Classical Swine Fever virus infections. The interactions between both viruses and the monocyte-macrophage-system result in the release of mediator molecules, which are important for the further progression of the diseases. The causes of the thrombocytopenia and the mechanisms of the haemorrhages, which are characteristic in both infections, are described. Apoptotic cell death is regarded as the predominant cause of lymphopenia in both virus infections.

Apoptosis of thymocytes related to cytokine expression in experimental classical swine fever.

Atrophy of the thymic cortex and loss of thymocytes were studied in 32 pigs inoculated with the virulent strain "Alfort" of classical swine fever (CSF) virus and killed at intervals from 2 to 15 days after infection. Immunohistochemical, ultrastructural, ELISA and TUNEL methods were used. The results suggested that direct action of CSF virus on thymocytes played no more than a minor role. The massive lymphoid depletion observed in the thymus, may, however, have been associated with the numerical increase in monocytes-macrophages in this organ, and their secretory activation, leading to synthesis and release of tumour necrosis factor (TNF)-alpha, interleukin (IL)-1alpha and C1q complement component as main chemical mediators, and IL-1beta and IL-6 as minor mediators. These cytokines (TNF-alpha and IL-1alpha) may have played a role in the apoptosis of thymocytes, demonstrated by TUNEL and ultrastructural methods. The pathogenetic mechanism outlined may contribute to the lymphoid depletion observed in others organs in CSF and may explain the lymphopenia characteristic of the disease.

Simulated effect of pig-population density on epidemic size and choice of control strategy for classical swine fever epidemics in The Netherlands.

We examined the importance of pig-population density in the area of an outbreak of classical swine fever (CSF) for the spread of the infection and the choice of control measures. A spatial, stochastic, dynamic epidemiological simulation model linked to a sector-level market-and-trade model for The Netherlands were used. Outbreaks in sparsely and densely populated areas were compared under four different control strategies and with two alternative trade assumptions. The obligatory control strategy required by current EU legislation was predicted to be enough to eradicate an epidemic starting in an area with sparse pig population. By contrast, additional control measures would be necessary if the outbreak began in an area with high pig density. The economic consequences of using preventive slaughter rather than emergency vaccination as an additional control measure depended strongly on the reactions of trading partners. Reducing the number of animal movements significantly reduced the size and length of epidemics in areas with high pig density. The phenomenon of carrier piglets was included in the model with realistic probabilities of infection by this route, but it made a negligible contribution to the spread of the infection.

Morphological and immunohistochemical changes in splenic macrophages of pigs infected with classical swine fever.

Classical swine fever (CSF) was induced in 20 pigs by inoculation with a virulent strain of CSF virus to determine sequential changes (2, 4, 7, 10 and 14 days post-inoculation) in the number and morphology of splenic macrophages (red pulp and lymphoid marginal zone) and thus to assess the role of these cells in the pathogenesis of the disease. The first splenic cells to be infected with CSF virus were macrophages in the marginal zone followed by other macrophage populations. The initial phase of CSF was associated with an increase in splenic macrophage numbers in the marginal zone and a decrease in the red pulp. Subsequently, the numbers in the red pulp increased. The study suggested that infection, mobilization and apoptosis of splenic macrophages play an important role in the spread of CSF virus in vivo. Moreover, the secretory changes that occurred in macrophages in the initial phase of the infection suggested that macrophages release chemical mediators capable of modulating pathogenesis.