Diarrhea that mimics ileitis continues to be a problem despite a variety of treatments.
Although several antimicrobials have been shown to control the clinical disease known as porcine proliferative enteropathy, outbreaks of diarrhea that mimic ileitis amongst growing and finishing pigs have been frustratingly frequent.
When these outbreaks occur, in spite of vaccination or treatment with antimicrobials, the first question generally asked is: “Why did this tool (vaccine/antimicrobial) fail?”
The first question that should be asked is: “Is this clinical diarrhea due to ileitis?”
Granted, ileitis due to Lawsonia intracellularis is widespread, and is the most commonly diagnosed cause of diarrhea in growing pigs. So it rightfully should be at the top of our differential diagnosis list, especially when the feces contain blood.
However, there are other pathogens and syndromes that can mimic the various faces of ileitis. Therefore, when a control strategy that has worked in the past appears to have failed, we need to first gain an accurate diagnosis.
Since ileitis can present symptoms in various forms from acute to chronic, it opens up a wider array of potential imitators. Several of these such as salmonella are common, while others such as porcine circovirus type 2 (PCV2) are less common.
The following case studies demonstrate how antimicrobials and the avirulent vaccine don't always prevent clinical signs. They also show how important it is to properly work up a case that on the surface, appears to be merely problems with efficacy of your current control program.
A farm raising its own replacement gilts called to report problems with clinical ileitis in gilts despite receiving an antimicrobial in the ration at a level approved for control of Lawsonia. The gilts had “puddly” diarrhea within a week or so after arrival in the gilt developer and fallout and death loss was at an unacceptable level. Oral medication via the drinking water and individual injections aimed at treating ileitis, also failed to control diarrhea.
At the site, I discovered widespread evidence of chronic diarrhea with nearly 10% of the gilts showing significant loss of body condition. Several gilts were immediately euthanized for postmortem examination and submission of tissues to the diagnostic lab.
The results of the necropsies did not reveal any of the classic ileitis lesions such as thickened or proliferated intestinal linings. But enlargement of the mesenteric lymph nodes was significant.
As suspected, the lab confirmed a diagnosis of salmonella typhimurium. There were no lesions or laboratory findings indicating ileitis or other enteric pathogens. While the diarrhea looked clinically identical to ileitis, salmonella was the real culprit, and treatment aimed specifically at the root cause resolved the issue.
A grow-finish system was experiencing widespread diarrhea and fallback of pigs, which looked like a classic case of an ileitis outbreak. Pigs in mid to late finishing would develop runny stools and grow poorly to the point of appearing to waste away.
The owner was upset, since the pigs had been vaccinated with the avirulent live ileitis vaccine, which appeared to have no effect. The herd veterinarian contacted the technical services veterinarian for the company that produced the vaccine, and accompanied him to the most recently affected finishing site.
The finishing site manager was perplexed and frustrated as well, since the ileitis vaccine had been very efficacious since they instituted its use over a year ago, up until this recent “break.” The manager had attempted to “rescue treat” the group of pigs with feed-grade antimicrobials for ileitis control as well as oral antibiotics through the water, but all was to no avail.
Upon necropsy of several of the affected pigs, the veterinarians were surprised to find no gross lesions indicative of ileitis, but instead found lymph nodes throughout that were extremely enlarged. Submissions of tissues to the state diagnostic lab revealed that these pigs were suffering from extreme lymphoid depletion caused by porcine circovirus type 2 (PCV2).
The lab diagnosis surprised everyone, but as soon as PCV2 vaccine became available, the pigs were vaccinated and the issue was resolved.
Diseases can produce clinical signs that are similar or identical, even to the trained eye of a swine veterinarian. It is imperative to evaluate each outbreak on a case-by-case basis and utilize the diagnostic lab to confirm or negate a diagnosis based solely on clinical symptoms and what the textbooks describe.
As an old pathology professor of mine once said: “Diseases do not always read the book!”