MODEL FOR EXPERIMENTAL DISEASE AND IMMUNOGENICITY OF ACTINOBACILLUS SUIS FOR SWINE

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: ANIMAL HEALTH
• Reporting Frequency: Annual
• Accession No.: 0205237
• Project Start Date: Jun 1, 2005
• Project End Date: May 30, 2006
• Program Code: [(N/A)]- (N/A)

Recipient Organization
IOWA STATE UNIVERSITY
S. AND 16TH ELWOOD
AMES,IA 50011

Performing Department
VETERINARY MEDICINE

Non Technical Summary
Actinobacillus suis has been recognized as a nagging cause of septicemic, pleuropneumonic and other septic processes in swine for 100 years. The organism has emerged as a particularly difficult problem in high health status herds. Lack of a consistent model for experimental induction of disease has thwarted researchers and diagnosticians in their attempts to clearly understand the role of A. suis in swine disease and limited development of effective control measures. Tabulation of cases submitted to the Iowa Diagnostic Laboratory during the past 8 years indicates striking increases in numbers with 26 cases from 10 months in 1996; 67 cases in 1997; 219 in 2002; 191 in 2003; and 151 during the first 7 months of 2004. The work currently proposed will build on exciting results obtained in two recent trials that now form the basis for a more refined study of the method for disease induction and for determination of the efficacy of vaccination. Improved methods for control of the disease are urgently needed

Animal Health Component

100%

Research Effort Categories

Basic

(N/A)

Applied

100%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
311	3510	1090	100%

Knowledge Area
311 - Animal Diseases;

Subject Of Investigation
3510 - Swine, live animal;

Field Of Science
1090 - Immunology;

Keywords

immunogenicity actinobacillus suis

swine

Goals / Objectives
The hypothesis of this research is that A. suis will induce experimental pleuropneumonia in swine following intranasal inoculation, possibly, with a large dose, similar to that developed following intratracheal inoculation as described in our preliminary work. The second hypothesis is that vaccination with a killed or antibiotic treated autogenous vaccine will induce protection in swine against challenge with the organism.

Project Methods
The first objective of our work would be to attempt to induce pleuropneumonia by intranasal inoculation of pigs. The widespread occurrence of A. suis infection and the frustration of swine veterinarians and swine producers related to nagging, repeated losses associated with this disease in the field indicate a need for better strategies for control. While there is no defined serotyping system for isolates of A. suis, the potential for immunoprophylaxis, at least on an autogenous basis needs now to be explored. The extent of use of autogenous preparations in the field indicates a need for rigorous experimental evaluation. Therefore, the second objective of this project would be to determine the potential protective efficacy of experimental autogenous vaccines that protect pigs against experimental intratracheal (or intranasal) challenge with a homologous strain of A. suis. Evidence that protection can be induced under such circumstances should be sufficient to interest biologics companies, the pork producers, or possibly, the USDA in funding more comprehensive research on the factors involved in induction of protection against A. suis disease. The experimental model for induction of pleuropneumonia that we have developed now provides a basis for further study of the disease with an eye toward reduction of losses caused by A. suis, possibly through development and marketing of licensed, commercially available bacterins.

Progress 06/01/05 to 05/30/06

Outputs
The numbers of swine cases with Actinobacullus suis - disease submitted to the Iowa State University Veterinary Diagnostic Laboratory have increased substantially in recent years. Review of these cases indicated that A. suis was most frequently isolated from the lungs and associated with pneumonia and pleuropneumonia; however, the organism was often isolated from extra-pulmonary sites such as liver, kidney, spleen, blood, and brain. These findings indicate that some A. suis strains might have a proclivity for septicemia. The research objective was to utilize A. suis field isolates to develop an experimental disease model to study the pathogensis of A. suis - associated diseases and specifically determine the effect of dose and route of delivery on clinical disease, and gross and microscopic lesions. The studies were concluded in April 2006. The outcome of experimental inoculation of 103 seven to nine-week-old, high-health status pigs with one of two isolates of A. suis was evaluated. The animals were evaluated over four experiments. Challenge doses of A. suis, ranging from 104, 105, 106, 107, and 108 cfu, were administered by intratracheal and intranasal routes. The pigs were necropsied four days post-inoculation. Multiple tissues were evaluated for gross and microscopic lesions and cultured for recovery of bacteria. Intratracheal administration of high doses (107-108cfu) of A. suis in pigs resulted in acute pleuropneumonia similar to that observed in swine field cases and resembled pleuropneumonia induced by A. pleuropneumoniae. Pigs inoculated with high doses (107-108cfu) of A. suis intranasally also developed pleuropneumonia. A dose of 106 cfu of A. suis given intranasally and intratracheally resulted in less extensive clinical disease, fewer gross and microscopic lesions, and dramatic reduction in bacterial recovery from the organs. Pigs receiving a low dose (104-105cfu) of A. suis were unaffected clinically and had no gross or microscopic lesions suggestive of A. suis infection. In conclusion, the results generated from this study indicate a dose dependent relationship with A. suis to the development of pleuropneumonia and larger doses of A. suis are required to induce pleuropneumonia. A high dose (107-108 cfu) of A. suis delivered intratracheally caused severe pleuropneumonia. Yet, when 108 cfu was delivered intranasally, gross lesions of pneumonia were about 50% less than in the intratracheal inoculated pigs. Furthermore, the lesions are less extensive, less severe and bacterial recovery is dramatically reduced. Medium doses of A. suis delivered by intranasal inoculation did not achieve as reproducible clinical disease and lesions as did the high dose administered intratracheally. These results provide a basis for further investigation of the pathogenesis, virulence attributes and immunogenicity of A. suis infections in swine.

Impacts
The diagnosis of Actinobacillus suis infection has risen in the last five years and has become a cause of significant loss in growing pigs. The disease can affect both nursery and finishing age pigs, with results of death loss and elevated numbers of culls/low value animals. Therapeutic interventions which are successful would benefit health, livability and growth of affected animals and may reduce disease spread as well. Currently there are no swine antibiotics for labeled treatment or vaccine products specifically of A. suis. Limiting the duration and impact of disease and curbing reductions in weight gain due to illness are significant strategies to improving production performance and animal well being. These studies accomplished the establishment of a workable model to investigate antimicrobial therapies, vaccine development and intervention strategies.

Publications

• Jordan, D.M., Taylor-Vokes, R. J., Halbur, P.G., Hoffman, L.J.,. Ross, R.F. 2007. Experimental Challenge Model for Actinobacillus suis in Pigs. AJVR. Submitted.
• Jordan, D.M., Taylor-Vokes, R. J., Halbur, P.G., Hoffman, L.J.,. Ross, R.F. 2006. Experimental Challenge Model for Actinobacillus suis in Pigs. AAVLD 49th Annual Conference Proceedings, presentation.