Consider the case where a high percentage of 40-lb. pigs placed in a facility 10 days ago are now coughing, gaunt, thumping and overall feed intake is decreased. Serum samples and nasal swabs from five affected pigs are submitted to the diagnostic laboratory to rule out swine influenza virus (SIV) and porcine reproductive and respiratory syndrome (PRRS) virus. The polymerase chain reaction test detects PRRS virus in serum, but SIV testing of nasal swabs turned out negative.
The purchaser of these pigs now has something (and perhaps someone) to blame, right? But does detection of PRRS tell the whole story? Be aware that PRRS virus acting alone does not cause pigs to cough.
To further the diagnosis, the veterinarian representing the pig source requested a complete necropsy and diagnostic workup. The gross necropsy findings 14 days after purchase confirmed the presence of numerous white spots on the liver, as well as multifocal hemorrhages and craniovental gray firmness (mycoplasma-like lesions) in the lung (Figure 1). A diagnosis of roundworm migration (liver-lung ascarid larval migration) is confirmed as the primary insult. PRRS virus is not identified as the cause of the clinical signs observed.
Four things to know about roundworms:
1. The roundworm larva (liver-lung) migration occurs from 5-21 days after exposure to eggs that are present within a feces-contaminated environment. The clinical signs (cough, gaunt) start about a week to 10 days after exposure. In this case, the exposure to roundworm eggs occurred at the buyer’s premises. Clinical signs are generally worse in pigs that are naïve to previous infection.
2. A “fecal examination” for roundworm eggs (ova) will not diagnose this condition. The feces will be negative for eggs for at least 7-8 weeks after exposure, since it takes that long for adult worms to mature and produce ova. The worms will not be visible in the intestine until at least six weeks after infection. Do not rely on fecal flotation to diagnose disease, but use this test method for surveillance. Necropsy is the only way to diagnose the active stages of liver-lung roundworm migration.
3. Roundworm larva migration can mimic other common diseases, including Mycoplasmal pneumonia and SIV. Roundworm migration has been shown to increase the severity of mycoplasma. Fibrosis of liver – white, hard liver – can compromise performance throughout the grow-finish phase and can be a cause for condemnations at slaughter.
4. Monitoring worm burdens is accomplished by timely, routine necropsies and fecal examination of market hogs. Strategic deworming programs control this disease quite effectively. Whipworms
Next to roundworms, whipworms are the second most common worm likely to be encountered in a swine operation. When affected, pigs do not grow well and may have soft feces with mucus or even flecks of blood. The most severe symptoms are seen 1-6 weeks after exposure. A fecal examination will not diagnose this problem until at least eight weeks after exposure. Necropsy and thorough examination are the only means of ruling out disease due to this parasite.
Coccidiosis is the most common parasitic disease in swine, caused by Isospora. This protozoan causes diarrhea in pigs from 4 days to 3 weeks of age. Diagnosis relies on necropsy and microscopic examination of small intestine from acutely affected pigs. The eggs (oocysts) build up in farrowing crates by fecal contamination from previous litters. The eggs become more rapidly infective in warm, moist environments, particularly during warm, humid weather (Figure 2). There is no approved treatment, so prevention is the key to control. Thorough cleaning of all surfaces in farrowing rooms after every litter is removed is the best defense against this disease.
Summertime Tips for Laboratory Submission
Accurate diagnosis of most diseases relies on necropsy and postmortem examination. After a cold winter, please be cognizant of how quickly animal samples decompose in hot weather. In the summer, necropsies should be viewed as “emergencies.” When planning a submission to a diagnostic laboratory, consider these tips:
1. Collect samples only from live or freshly dead animals.
2. Keep all specimens cold by collecting immediately onto ice.
3. Fresh tissues should not be larger than tennis balls to assure rapid chilling.
4. Intersperse fresh tissues and ice packs in the shipping container.
5. Do not “hide” swabs and serum within packing materials.
6. Double-bag specimens to prevent leakage; carriers will not deliver leaky packages (Figure 3).
7. Use insulated shipping containers, lined with a large bag (Figure 4). Pack specimens and ice packs inside the liner bag to avoid leaking and water (ice pack sweat) damage to box.
8. Bag all paperwork/submission forms and use waterproof markers/pens.
9. Use extra ice packs when shipping specimens.
Click to view graphs and photos.
Kent Schwartz, DVM
Iowa State University Veterinary Diagnostic Laboratory