How to better target ileitis control
Since the organism was first identified about a decade ago, progress has been made in diagnosing ileitis caused by Lawsonia intracellularis. The unique nature of the germ, particularly its ability to shelter itself inside the cells lining the gut and thus out of reach of most common antibiotics, has made long-term ileitis control a challenge. However, intervention strategies to reduce the productivity losses caused by the disease, without yesterday's over-reliance on continuous antibiotic feeding, have followed that diagnostic progress. Today's management strategies can control the emerging disease more effectively, including its insidious subclinical form which limits productivity without causing any obvious clinical signs such as diarrhea. Better yet, the newer management strategies control the disease more completely and more cost-effectively than outdated methods.
The evolution of ileitis control
Together with better diagnostics, strategically targeted medications and the recent commercial release of a highly effective oral vaccine against ileitis have greatly enhanced our ability to manage ileitis immunologically, eliminating the traditional need for continuous medication. In large-scale field studies the vaccine has shown long-lasting duration of immunity, improvements in productivity and survivability, and economic benefits that come from reducing — in many cases totally eliminating — routine feed antibiotics.
OLD METHODS
STRATEGY: Preventive antibiotic medication at effective inclusion rates
RATIONALE: Medication limits infection by Lawsonia, keeps pigs immunologically naïve.
DOWNSIDE: Effective drug levels cost-prohibitive and unapproved for prolonged continuous use. Short-term protection provided only during the actual medication period. No immune response, so pigs become susceptible soon after antibiotic withdrawal. Older, heavier pigs break with ileitis, increasing losses.
STRATEGY: Continuous antibiotic medication at sub-effective inclusion rates (“step-down” programs; typically following initial antibiotic use at higher, more effective inclusion rates)
RATIONALE: Permit “breakthrough” of infection to generate immune response, while antibiotics try to control clinical signs and severity.
DOWNSIDE: No consistent population immune response; some animals remain susceptible often resulting in ileitis outbreaks still occurring, subclinical ileitis widespread; inadequate short and long-term ileitis control, entire group underperforms. Antibiotics overused with poor outcomes. Increased likelihood of antibiotic resistance developing.
NEW METHODS
STRATEGY: Strategic medication
RATIONALE: Use diagnostics to identify most likely exposure period; time brief medication period(s) to control infection after exposure but before disease outbreak occurs. Captures partial population immunity but avoids setback of disease outbreak. Reduced, targeted antibiotic use. Reduced likelihood of antibiotic resistance.
DOWNSIDE: Reduces concerns about cost, antibiotic over-use, inhibiting the immune response to ileitis, and developing antibiotic resistance, but it doesn't entirely eliminate those issues. A useful step in the right direction.
STRATEGY: Targeted vaccination
RATIONALE: Use vaccination for long-term effective ileitis prevention and control. Uniform population immunity achieved for consistent, reliable long-term ileitis protection. Dramatically reduces or eliminates antibiotic use for ileitis. No antibiotic resistance selection pressure.
DOWNSIDE: Requires proper timing of vaccination and removal of antibiotics during vaccination period.
Walter D. 2003. Reducing reliance upon continuous feeding of antimicrobials in swine production. Proc AASV Applied Pharmacology Seminar 2003:19-25.