Effect of Simultaneous Exposure of Pigs to Streptococcus suis Serotypes 2 and 9 on Their Colonization and Transmission, and on Mortality.

The distribution of Streptococcus suis serotypes isolated from clinically infected pigs differs between geographical areas, and varies over time. In several European countries, predomination of serotype 2 has changed to serotype 9. We hypothesize a relation, with one serotype affecting the other in colonization and invasion. The aim of this study was to evaluate whether simultaneous exposure of pigs to serotypes 2 and 9 affects colonization and transmission of each type, and mortality. Thirty-six caesarean-derived/colostrum-deprived piglets were randomly assigned to three groups, and there housed pair-wise. At six weeks old, one pig per pair was inoculated with either one (serotype 2 or 9; mono-group) or two serotypes simultaneously (dual-group); the other pig was contact-exposed. Tonsillar and nasal samples were collected within three weeks post inoculation. Bacterial loads in samples were quantified using multiplex real-time polymerase chain reaction (PCR). Transmission rates of the serotypes among pigs were estimated using a mathematical Susceptible-Infectious (SI) model. Bacterial loads and transmission rates did not differ significantly between serotypes. Compared to the mono-group, in the dual-group the average serotype 2 load in tonsillar samples from contact pigs was reduced on days 1 to 4 and on day 6. Simultaneous exposure to the serotypes reduced the mortality hazard 6.3 times (95% C.I.: 2.0-19.8) compared to exposure to serotype 2 only, and increased it 6.6 times (95% C.I.: 1.4-30.9) compared to exposure to serotype 9 only. This study indicates that serotype 2 load and mortality were affected in pigs exposed to these two serotypes.

Atypical Porcine Pestivirus: A Possible Cause of Congenital Tremor Type A-II in Newborn Piglets.

Congenital tremor type A-II in piglets has been regarded as a transmissible disease since the 1970s, possibly caused by a very recently-described virus: atypical porcine pestivirus (APPV). Here, we describe several strains of APPV in piglets with clinical signs of congenital tremor (10 of 10 farms tested). Piglets on a farm with no history of congenital tremor were PCR-negative for the virus. To demonstrate a causal relationship between APPV and disease, three gilts were inoculated via intramuscular injection at day 32 of pregnancy. In two of the three litters, vertical transmission of the virus occurred. Clinical signs of congenital tremor were observed in APPV-infected newborns, yet also two asymptomatic carriers were among the offspring. Piglets of one litter were PCR-negative for the virus, and these piglets were all without congenital tremors. Long-term follow up of farm piglets born with congenital tremors showed that the initially high viremia in serum declines at five months of age, but shedding of the virus in feces continues, which explains why the virus remains present at affected farms and causes new outbreaks. We conclude that trans-placental transmission of APPV and subsequent infection of the fetuses is a very likely cause of congenital tremor type A-II in piglets.

Spatio-temporal patterns and movement analysis of pigs from smallholder farms and implications for African swine fever spread, Limpopo province, South Africa.

Infectious and zoonotic disease outbreaks have been linked to increasing volumes of legal and illegal trade. Spatio-temporal and trade network analyses have been used to evaluate the risks associated with these challenges elsewhere, but few details are available for the pig sector in South Africa. Regarding pig diseases, Limpopo province is important as the greater part of the province falls within the African swine fever control area. Emerging small-scale pig farmers in Limpopo perceived pig production as an important means of improving their livelihood and an alternative investment. They engage in trading and marketing their products with a potential risk to animal health, because the preferred markets often facilitate potential longdistance spread and disease dispersal over broad geographic areas. In this study, we explored the interconnectedness of smallholder pig farmers in Limpopo, determined the weaknesses and critical control points, and projected interventions that policy makers can implement to reduce the risks to pig health. The geo-coordinates of surveyed farms were used to draw maps, links and networks. Predictive risks to pigs were determined through the analyses of trade networks, and the relationship to previous outbreaks of African swine fever was postulated. Auction points were identified as high-risk areas for the spread of animal diseases. Veterinary authorities should prioritise focused surveillance and diagnostic efforts in Limpopo. Early disease detection and prompt eradication should be targeted and messages promoting enhanced biosecurity to smallholder farmers are advocated. The system may also benefit from the restructuring of marketing and auction networks. Since geographic factors and networks can rapidly facilitate pig disease dispersal over large areas, a multi-disciplinary approach to understanding the complexities that exist around the animal disease epidemiology becomes mandatory.

Efficiency indices and indicators of poor performance among emerging small-scale pig farmers in the Limpopo Province, South Africa.

Limpopo is a very important area for pig production in terms of animal populations and contributions to transboundary animal disease spread. Emerging small-scale pig farmers (ESSPF) are being encouraged to establish operations and spread in South Africa; however, for these farmers to perform optimally, they need to understand the basics of animal agriculture and contribute to enhancing biosecurity and efficient production systems. In the present study, the limitations to efficient production amongst ESSPF were evaluated and some improvements were suggested. It was found that the ESSPF are dominated by males and include a large percentage of older persons. A total of 26.54% of these farmers have post-matriculation qualifications. Undefined and indigenous breeds still dominate their animal genetics. The animal health technicians are the preferred channels by which farmers report diseases to the authorities (52.47%) and only one out of five (20.37%) will preferably report a disease situation direct to a veterinarian. These farmers do not vaccinate their stock, and knowledge of biosecurity is poor. Antimicrobials, especially tetracyclines, are abused. Animals that are slaughtered within the community or sold at local sale points, pension pay stations and auction markets are likely candidates for disease spread. It is recommended that the younger generations are retained and incentivised in animal agriculture. Improved training on management, health, biosecurity and better market access must be provided for the ESSPF, whilst efforts should made to consolidate these farmers into small cooperatives. The current government agricultural support system will need to be reworked to benefit the resource-poor farmers. Collaborative efforts in disease reporting and management among veterinarians, animal health technicians and extension officers will become necessary. Finally, the creation of a progressive quality grading system for ESSPF should be planned by the industry and this should be attached to a reward system that will encourage these farmers to target good farming practice.

Effect of spatial separation of pigs on spread of Streptococcus suis serotype 9.

The spread of an infectious agent in a population can be reduced by interfering in the infectiousness or susceptibility of individuals, and/or in their contact structure. The aim of this study was to quantify the effect of prevention of direct contact between infectious and susceptible pigs on the transmission of Streptococcus suis (S. suis). In three replicate experiments, S. suis-free pigs were housed in boxes either in pairs (25 pairs) or alone (15 pigs). The distance between the boxes was ±1 m. At 7 weeks of age, one pig of each pair was inoculated intranasally with S. suis serotype 9; the other pigs were exposed to S. suis by either direct (pairs) or indirect contact (individually housed pigs). Tonsillar brush and saliva swab samples from all pigs were collected regularly for 4 weeks post inoculation to monitor colonization with S. suis. All inoculated pigs became infected, and their pen mates became colonized within 2 days. Thirteen indirectly exposed pigs became positive within 7-25 days after exposure. The rate of direct transmission ßdir was estimated to be 3.58 per pig per day (95% CI: 2.29-5.60). The rate of indirect transmission increased in time, depending on the cumulative number of days pigs tested positive for the presence of S. suis. The estimate ß'ind was 0.001 (95% CI: 0.0006-0.0017) new infections per pig per day for each day that an infected pig was tested positive for S. suis. We conclude that prevention of direct contact reduces the rate at which susceptible pigs become colonized. Simulation studies using these parameters showed, however, that such intervention measure would not limit S. suis serotype 9 spread in a commercial pig farm to a relevant extent, implying that spatial separation of groups op pigs within a compartment would not be effective on a farm.

Pleuritis in slaughter pigs: relations between lung lesions and bacteriology in 10 herds with high pleuritis.

Pleuritis in slaughter pigs has increased in recent years in the Netherlands. The aim of the present study was to determine what respiratory pathogens were involved in pleuritis. In total, lungs of 968 slaughter pigs from 10 herds with high prevalence of pleuritis were morphologically examined for size, location, and type of lesions. Moreover, histology and bacteriology were performed. Examination of gross lung lesions showed 45% pleuritis, 14% pleuropneumonia and 38% catarrhal pneumonia. Peribronchiolar cuffing was found in 61 of 142 samples. Actinobacillus pleuropneumoniae was cultured from 22 lung samples from four herds. Pasteurella multocida was cultured from 55 lung samples in eight herds. No specific pattern with respect to the causal pathogens was found. In conclusion, no single infectious cause of pleuritis was found. A variety of infectious agents combined with environmental factors should be considered as a cause of pleuritis.

Clostridium difficile PCR ribotype 078 toxinotype V found in diarrhoeal pigs identical to isolates from affected humans.

In diseased piglets from two Dutch pig-breeding farms with neonatal diarrhoea for more than a year, culture and PCR analyses identified the involved microorganism as Clostridium difficile PCR ribotype 078 harbouring toxin A (tcdA) and B (tcdB), and binary toxin genes. Isolated strains showed a 39 bp deletion in the tcdC gene and they were ermB gene-negative. A number of 11 porcine and 21 human isolated C. difficile PCR ribotype 078 toxinotype V strains were found genetically related by multiple-locus variable-number tandem-repeat analysis (MLVA). Moreover, a clonal complex was identified, containing both porcine and human isolates. The porcine isolates showed an antimicrobial susceptibility profile overlapping that of isolates from Dutch human patients. On the basis of these pheno- and genotypical analyses results, it was concluded that the strains from affected piglets were indistinguishable from increasingly encountered C. difficile PCR ribotype 078 strains of human C. difficile infections in the Dutch population and that a common origin of animal and humans strains should be considered.