An index for multidimensional assessment of swine health

Pork accounts for almost one-third of the meat consumed worldwide. Infectious diseases have a marked impact on pig production. Epidemiological indicators are considered the most useful criteria in decision-making; however, a health status assessment remains a challenge at the national and regional levels. This study proposes a health index including herd-losses, morbidity, fatality, and type of diseases, to rate the health situation in a region or country; it contributes to assessing the effectiveness of control, damage manifestation, and trends. It is a multidimensional index with a structure of triads and simple quantitative, semi-quantitative, and qualitative expressions that use flexible and dynamics limits. With it, we analyzed twenty-one countries in 2005-2018, focusing on African swine fever, classical swine fever, foot-mouth-disease, and porcine respiratory and reproductive syndrome, diseases that caused 72% of the morbidity. Our multidimensional approach estimates farm, local, and regional impact from infectious agents and outbreaks, and apprises trends aiming to be useful to control measures, strategic actions, and animal health policies.

Classical swine fever virus E2 glycoprotein antigen produced in adenovirally transduced PK-15 cells confers complete protection in pigs upon viral challenge

E2 is the major envelope glycoprotein present on the outer surface of the classical swine fever virus (CSFV). It is exposed as a homodimer originated by disulfide linkage and represents an important target for the induction of neutralizing immune responses against the viral infection. The E2his glycoprotein nucleotide sequence used in this work contains the CSFV E2 extracellular domain preceded by the tissue plasminogen signal peptide and a hexa-histidine tag in the 3' terminus. The recombinant antigen was produced at a range of 120-150 microg/mL in the culture media of epithelial kidney pig cells, transduced with a replication defective adenoviral vector (Ad-E2his) generated by means of cloning the E2his sequence in the vector genome. The glycoprotein was obtained from clarified culture media as a homodimer of 110 kDa with purity over 95% after a single affinity chromatography step in Ni-NTA Agarose column. The E2his characterization by lectin-specific binding assay showed the presence of N-linked oligosaccharides of both hybrid and complex types. The protective capacity of E2his was demonstrated in two immunization and challenge experiments in pigs using doses of 15 or 30 microg of the glycoprotein, emulsified in Freund's adjuvant. The intramuscular immunization followed by a unique boost three weeks later, elicited high titers of neutralizing antibodies between the second and the fourth week after the primary vaccination. The immunized animals were fully protected from the viral infection after challenge with 10(5) PLD(50) of homologous CSFV "Margarita" strain administered by intramuscular injection. Consequently, no clinical signs of the disease or viral isolation from lymphocytes were detected in the vaccinated pigs. These results suggest that the E2his antigen produced in mammalian cells may be a feasible vaccine candidate for CSF prevention.

Epidemiological survey of viral diseases of pigs in the Mekong delta of Vietnam between 1999 and 2003

In the Mekong delta, backyard pig rearing plays an integral role in recycling nutrients in farming systems and generating valuable cash income. However, development has been hampered by fatal epizootics of piglets and reproductive failure of sows. Diseases are named by symptoms and blindly treated with antibiotics. As antibiotics are often ineffectual, involvement of viral diseases are suspected. To identify the causative agent, we first sero-surveyed porcine reproductive and respiratory syndrome (PRRS) and pseudorabies with 478 sera from non-vaccinated pigs collected from backyard farms, state farms and slaughterhouses in Can Tho province between 1999 and 2002. Antibodies for PRRS were first detected in 2002 in backyard farms and at high prevalence in state farms with increased piglet mortality. A few backyard breeder pigs had antibodies for pseudorabies in 2000 and 2002. With compulsory classical swine fever (CSF) vaccination, we examined the relationship between vaccination and antibodies in 70 serum samples. Seventy-nine percent of vaccinated breeders had CSF antibodies-higher than expected with irregular vaccination. Since circulation of CSF virus was suspected, isolation was attempted at 10 farms with fatal epizootics between 2002 and 2003. The viruses were detected at all farms and clustered within genogroup 2, despite vaccines corresponding to genogroup 1. This study demonstrated virologically/serologically the existence of PRRS, pseudorabies and CSF viruses in the Mekong delta of Vietnam. We also identified CSF as a cause of piglet mortality that disastrously affected backyard farming. Vaccine standardization and proper instructions are needed to simplify diagnosis and complement established simultaneous vaccination of sows with piglets.

[Culling of animals in large herds, experiences from the Netherlands]

The outbreaks of classical swine fever in 1997-1998 and foot- and mouth-disease in 2001 provided a lot of experiences in the culling of animals. These experiences, as well as the aspects of animal welfare and public acceptance are described. In the future these experiences will help to carry out culling in a more efficient way including improved aspects of animal welfare and public acceptance.

Estimation of a time-varying force of infection and basic reproduction number with application to an outbreak of classical swine fever

BACKGROUND

A method was developed for stochastically reconstructing the pattern of infection from observed epidemic data. This allowed for estimation of a time-dependent force of infection, or transmission rate, during an epidemic.

METHODS

A discrete-time mechanistic model was used to describe the spread of infection and a stochastic procedure, which utilised the latent and infectious period distributions, was used to reconstruct the dates of infection, becoming infectious and removal from the given data. The four equations describing the model were then solved to obtain least squares estimates of the transmission rate and the basic reproduction number (R0) throughout the epidemic. This process was repeated in order to assess the variability in these key epidemiological parameters. The stochastic epidemic reconstruction procedure was developed to account for changes in the distribution of the survival period over the course of the epidemic and adapted for application to epidemic data where not all infected individuals have yet been observed as cases.

RESULTS

The method was applied to a set of epidemic data from an outbreak of classical swine fever in Pakistan. Constant and time-varying estimates of the transmission rate were derived and compared. There was some evidence to suggest that the force of infection varied over time.

DISCUSSION

The method described can be applied to data from epidemics where observations are incomplete. The confidence limits obtained for the estimated force of infection provide a means of assessing the evidence for time variation in this parameter.

The 1997-1998 classical swine fever epidemic in The Netherlands--a survival analysis

The aim of this analysis was to characterise the temporal pattern of infection during the 1997/98 classical swine fever (CSF) epidemic in The Netherlands and hence identify and quantify risk factors for infection in different enterprise types and areas. Survival analysis and Cox proportional hazards regression were used to describe the epidemic. Substantial differences in temporal survival patterns (herd breakdown rate) were found between areas where different control policies operated. Factors with a significant influence on the infection hazard of individual herds included: sow numbers as a percentage of total sows and fatteners (HR = 3.38 for mixed herds (0.1-60% sows) vs. fattening herds (0% sows) and HR = 2.74 for breeding herds (60-100% sows) vs. fattening herds), the number of 'transport contacts per month' (>0.3 vs. <0.3; HR = 4.11), pig density (pigs/km2) in the area (HR1000 pigs 1.48) and herd size (HR100 pigs = 1.01). Pre-emptive slaughter in an area appeared to be associated with lower subsequent disease levels. Higher frequency of transport contacts for welfare slaughter during the epidemic, however, well regulated and controlled, was associated with a substantially higher risk of becoming infected. The positive association of a higher pig density with CSF indicates the potential importance of local spread as a factor in disease transmission and emphasizes that dilution of the pig population can contribute to reduction in CSF occurrence. This analysis suggests however, that if pre-emptive slaughter can promptly be applied effectively in an area after initial diagnosis, pig density is then not a significant factor. Mixed and breeding herds had a higher probability of becoming infected than fattening herds, possibly due to different types and frequencies of inter-herd contacts. These contacts continue to some extent during the epidemic, despite the standstill of animal movements.

An experimental infection with classical swine fever virus in weaner pigs. I. Transmission of the virus, course of the disease, and antibody response

The spread of Classical Swine Fever (CSF) virus (strain Lorraine), originally isolated in the first CSF infected herd of the 1993-1994 Belgian epizootic, was examined in an isolation unit with three adjacent pens and 15 weaner pigs per pen. Virus was introduced through experimental inoculation of one weaner pig in the middle pen (pen 2). The experimentally inoculated pig became viraemic 4 days post-inoculation (dpi) and the pen mates at 12 (n = 9) and 14 dpi (n = 5). The first viraemia in pens 1 and 3 was observed 18 dpi. Pigs were found to be seropositive in pens 1, 2, and 3 from 24, 20, and 22 dpi onwards, respectively. The reproduction ratio (R0) for the pigs in pen 2, estimated according to the martingale method, was 81.3 (s.e. = 109.54). The rate ratio (Cox proportional hazard) of the first pigs to become viraemic in pen 3 (airborne contact plus contact via contaminated clothing and footwear with pen 2) versus pen 1 (airborne contact with pen 2 only) was 1.60 (P = 0.3342). Thus, the additional contact of contaminated clothing did not affect transmission of the CSF virus. The survivor function (Kaplan-Meier survival analysis) did not significantly differ per pen. The time from first detection of virus in plasma to death was not significantly different between pens. The mean rectal temperature of pigs in a pen increased 3 to 4 days prior to detection of virus. The proportion of seropositive pigs per pen (p) from the day the first weaner pig in a pen became viraemic (dpf) was examined as a function of time with a logistic regression model. The model parameter estimates did not differ between pens. Hence, the data from the three pens were pooled. The regression equation of the seroprevalence over time for the pooled data was p = 1/[1+e(4.65-0.39 *dpf)].

Epidemiological characteristics of an outbreak of classical swine fever in an area of high pig density

The objective of this study was to analyse an outbreak of classical swine fever under a policy of non-vaccination, intensive surveillance and eradication in an area of high pig density. The virus was found in 52 herds, where some 90,000 pigs were slaughtered. The clinical signs were vague and the reports of suspect herds generally coincided with increased mortality. The interval between the first occurrence of clinical signs and the report of a suspect herd was shorter when the disease was first diagnosed in fattening pigs than when it was diagnosed in sows, boars or suckling piglets. Among fattening pigs, mortality and morbidity appeared to increase with age. The proportion of clinically ill animals was positively correlated with the proportion of serologically positive animals in a pig house during the phase when the disease was spreading. Fifty-eight per cent of pig houses containing only clinically healthy but some virologically positive pigs were serologically negative. Antigen detection was therefore critical for early disease detection. Serology was nevertheless useful to ascertain that swine fever was not endemic in the area. The secondary cases were concentrated in the close neighbourhood of the herd initially infected.

[Postmortem findings in swine: non-selected submissions from hog cholera protection areas of 1992 versus selected submissions of 1991-1992]

This article presents a survey of death-causes of all spontaneously died pigs, n = 851, from a restricted area in the province of South Holland during a 2 1/2 months lasting hog-cholera epizoötic in 1992. 23 pigs from 5 submissions showed a positive IFT against hog-cholera virus. Those animals and pigs from sero-positive farms were excluded from this survey. The results of the post-mortems were compared with the post-mortem findings of the normally submitted, selected, animals in 1991 and 1992, n = 904 + 745, from the western parts of the Netherlands, in which the above mentioned province is situated. By means of classification of the animals in age-classes and of the post-mortem findings to disease or diseased organsystem, insight is gained in the prevalence of the various causes of death per age-class. No distinct differences were found between the findings in the groups of animals from 1991 and 1992. In the group of the hog-cholera-period comparatively more animals belonged to the neonatal and suckling period. In contrast to 1991-1992 the number of weaned and fattening pigs in the hog-cholera-group was lower. In both groups 40% of the death-causes was due to diseases of the digestive tract and 30% was a result of respiratory-tract infections. The third main cause of death in both groups was septicaemia and related diseases as endocarditis, pleuritis, peritonitis, polyserositis and polyarthritis. Comparison of the prevalence of infectious diseases per organsystem in successive age-classes demonstrated a similar tendency in the hog-cholera-group as in the year-groups 1991 and 1992.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of oxyamylose and polyacrylic acid on foot-and-mouth disease and hog cholera virus infections

Two interferon-inducing polycarboxylates were tested for antiviral activity on foot-and-mouth disease (FMD) virus infections in mice, guinea pigs, and swine. Polyacrylic acid, given intraperitoneally, had a protective effect on infection by FMD virus administered in the peritoneal cavity of mice and in the foot pad of guinea pigs. Chlorite-oxidized oxyamylose (COAM) was effective in mice at a dosage of 2 mg/kg. Swine were not protected against naturally transmitted FMD by 120 mg/kg of COAM nor by polyacrylic acid. Swine were not totally unresponsive to COAM since it delayed symptoms of hog cholera. Interferon was not detected in the serum of COAM-treated swine. With FMD virus, an example was found of activity of interferon inducers in experimental hosts and lack of activity in a natural host.