Emerging and re-emerging diseases can cause sudden, potentially catastrophic illness and death in commercial poultry flocks, said R.M. “Mick” Fulton, DVM, PhD, with the Michigan State University Veterinary Diagnostic Laboratory in Lansing, Michigan.
“It is up to investigators to use all available assets to detect those diseases,” he noted during a presentation at the 2022 North Central Avian Disease Conference. Those assets or tools include scientific tests as well as the human senses.
“Human senses consist of sight, sound, smell, touch and taste ⸺ all should be used by investigators,” he added, giving these examples:
- Sight: Consider stance, lack of movement, feather cover, fecal pasting and limestone (size and amount), Fulton pointed out. During necropsy, notice the location, distribution and type of lesions that are present.
- Hearing: Is the barn quiet or are some birds snicking? Respiratory noises can tell a story as well.
- Smell: Are there “off” odors in the flock as you enter a barn or in the feed or manure?
- Touch: Consider breast size, abdomen softness, weight and litter moisture.
- Taste: Is there too much salt in the feed?
Don’t forget common sense
“When you hear hoof beats, don’t diagnose zebras,” Fulton joked, adding that “a good history taken is a diagnosis half made.”
In other words, using previous information can be helpful in identifying a new or re-emerging disease. Veterinarians and producers should look for changes in patterns including daily mortality, egg production, and water and feed consumption. Knowledge of the species, age, housing conditions and disease prevalence in the area is also important.
Posting sessions also can be invaluable.
“Important information can be gathered through the simple dissection of an animal” Fulton said. “Through gross necropsy, the investigator can determine which laboratory test will provide the appropriate information and the detection of what is causing the illness and/or death of those animals.”
Diagnostics are also key to keeping diseases in check.
“Serology tests and microscopy are key indicators of emerging or re-emerging disease,” Fulton said. “Serology tests are generally reliable and good for screening (sensitivity) but poor for specificity. It’s hard to make a diagnosis with serology alone. They’re great for detecting previous [historical] diseases but not recent challenges.”
Bacteriology tests include culture and identification (reactions), agglutination, immunofluorescence, antibiotype (response to antibiotics), pulse-field gel electrophoresis and MALDI-TOF (“MALDI” is matrix-assisted laser desorption/ionization and “TOF” stands for time-of-flight mass spectrometry), polymerase chain reaction (PCR) and genetic sequencing.
“You must be able to grow it to detect it,” Fulton stressed.
Other tests include agar gel immunodiffusion, reverse agar gel immunodiffusion; virus isolation; transmission electron microscopy; PCR; and genetic sequencing, he explained.
“Investigators need to understand the pros and cons of the tools of discovery at our disposal so they can become more efficient when searching for emerging or re-emerging diseases,” Fulton said.
For example, PCR tests require expensive equipment and also require accurate selection of the PCR-probe target. On the other hand, they are relatively clean compared to other techniques and the results are known in a very short time (4 to 12 hours).
“It is up to diagnosticians to use all of the tools available to them,” Fulton said. “The most important tool is the critical thought process ⸺ look at the big picture and not just one specific test.”