RISK FACTORS FOR A COMPLEX DISEASE
Ileitis is a ubiquitous, complex disease affected by different management practices unique to each farm. Also called porcine proliferative enteropathy (PPE), ileitis is transmitted from pig to pig mostly by fecal-oral routes.
Estimates from the United States Department of Agriculture say 96 percent of all U.S. hog farms test positive for Lawsonia intracellularis, the organism that causes ileitis.
This intracellular bacterium is responsible for two different clinical forms that depend on age and immunity level of the pig. One form, and perhaps the most economically important, is the chronic form known as porcine intestinal adenomatosis (PIA). It affects young growing pigs by causing intermittent diarrhea and reduced rate and efficiency of growth. The other form, known as proliferative hemorrhagic enteropathy (PHE), is frequently seen in young adults such as newly introduced replacement gilts and is characterized by acute bloody diarrhea and sudden death.
The pathogen causes a thickened lining of the small and large intestine. Diagnostic work such as tissue submissions and serological profiling help diagnose the disease and determine when to implement prevention and control strategies.
A recent serology survey in Alberta, Canada, found that antibodies against Lawsonia were widespread in finishing pigs.
Results of their study, which involved samples from 1,041 finishing pigs, found:
Farrow-to-finish farms were more at risk for having seropositive pigs than farms with just grower-finishers, implicating sows as a source of infection.
Farms that used in-feed antibiotics had a lower risk of seropositive pigs than those that did not use in-feed antibiotics.
As area per pig in the pen increased, the odds of a finisher pig being seropositive decreased. Even one square meter increase per pig had a sparing effect.
Pressure washing and disinfecting pens had a greater effect than washing alone. It is important to remember that Lawsonia has the capability of surviving out of the enterocyte, but if quaternary ammonium or iodine-based compounds are used, the bacterial challenge can be decreased.
More than one finishing barn per site increased the likelihood for seropositivity.
Farms that housed their finishing pigs in fully slatted and solid concrete floors were 3.6 and 42.6 times more likely to test seropositive, respectively, than partial slats.
SUBCLINICAL IMPACT ON WEIGHT VARIATION
Although not obvious through signs of ill health, subclinical ileitis continues to be singled out as a major factor in weight variation. Diseases cause variation because they do not hit every pig in the group, explains John Deen, swine veterinarian at the University of Minnesota. This may be caused by varying immunity levels or because a disease spreads slowly through a system.
Ileitis is often linked with weight variation because of the way it attacks pigs by damaging the intestinal tract and disrupting nutrient absorption required for growth. The slowed growth and increased variation may not be obvious in continuous-flow operations, adds Deen. In extreme cases, low growth rates that lead to variation can result in losses up to $45 per head, he says. This would occur when pigs fail to reach minimum specifications for a primary market and must be discounted.
Out-of-feed events are not only a known cause of ulcers in pigs, but are also suspected of being associated with increased incidence of hemorrhagic bowel syndrome and ileitis.
There is little information on how long Lawsonia organisms can survive in the environment because of the limitation of techniques to differentiate live from dead bacteria. Currently, the viability status of Lawsonia is being identified by a combination of flow cytometry and specific fluorescence probes. Previously, positive fecal PCR results were found from pigs that had been orally inoculated with two-week-old feces stored at 5-15 degrees C. It implies that the organism could survive and still be infective outside the host for at least two weeks.
In the same study, Lawsonia was susceptible to a 3.3 percent wt./vol. quaternary ammonium compound and one percent povidone-iodine, but less sensitive to one percent potassium peroxymonosulfate or a 0.33 percent phenolic mixture.
References:
M Bronsvoort et al. Journal of Swine Health & Production 2001: 9(6):285-290.
CA Corzo et al. Proceedings, American Association of Swine Practitioners 2005: 373-374.
M Brumm et al. Nebraska Swine Report 2005: 9-11.
J Deen & S Wattanaphansak, “Ileitis-What We Know and What We Need to Learn,” AD Leman Swine Conference, September 2004.