Diagnosing neurologic disease in backyard chickens

Emily Martin, Marina Brash, Emily Brouwer, Kate Todd

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter, 2020;24(1):15-17.

Veterinarians who treat backyard flocks can encounter cases of neurologic disease due to a number of different etiologies. Neurologic signs can include tremors, circling, ataxia, twisting of the head and neck, falling over backwards, and paralysis.

Morbidity and mortality will be variable. How do you approach diagnosing neurologic disease in these flocks?

On physical examination, you can observe how the bird is moving. Determine whether it can stand and if so, whether it can walk. If the bird can only sit or lie down, observe how it is positioned. Is it hock sitting with both legs forward and the feet slightly off the ground (kinky back/spondylolisthesis)? Does it have one leg forward and one leg back (Marek’s disease, Fig. 1)? Is it lying on its side? Different positions can give you clues to the etiology. Also note if the bird is bright, alert and responsive. Determine if the neck muscles have good or flaccid tone (botulism). Look at the eyes and note if they are cloudy or if the bird is squinting and the corneas are irregular (ammonia burn). If there are multiple birds affected, determine if they are showing similar neurologic signs.

If there is no mortality, a thorough history will be important. Determine if the bird is outside or indoors, what the bird is being fed (commercially available or home-made feed, scraps; access to toxic plants) and if the bird has had any vaccinations.

If there is mortality, this is an opportunity for postmortem examination and more intensive sampling. Postmortem examination could be done at a clinic or birds could be shipped to the AHL. If birds are shipped, please refer to the AHL website for a PM submission form:

https://www.uoguelph.ca/ahl/submissions/submission-forms and packaging instructions:

https://www.uoguelph.ca/ahl/submissions/ahl-labnote-27-submission-instructions

Clinic Postmortem: On postmortem examination, examine the bird for any signs of trauma or puncture wounds (predation). Examine the skin for any raised nodules surrounding feather follicles (Fig. 2). Cut the skin between the breast muscle and leg and retract the leg laterally. Identify the triangular muscle along the medial thigh. Cut this muscle caudal to cranial next to the body wall and reflect it cranially. This will expose the femoral artery and sciatic nerve that can be collected for histology (Fig. 3). When the body cavity is opened and the breast is reflected cranially, the brachial plexus can be identified and collected for histology. Collecting peripheral nerve for histology is critical for diagnosing Marek’s disease (Fig. 4). Remove the skull cap and carefully remove the brain, including the brain stem and cerebellum. Examine the brain for any discolouration or nodules that could indicate bacterial or fungal infection. If the cerebellum is bright red in young birds, there is possible vitamin E deficiency. One half of the brain can be collected for histology. The cerebellum is needed to detect Baylisacaris procyonis migration (Fig. 5) in cases where birds have exposure to raccoon feces. The cerebellum and brain stem are needed to diagnose avian encephalomyelitis (Fig. 6) in young birds. The remaining half of the brain can be collected for culture or PCR testing. (Table 1).

Examine the internal organs and determine if there are any nodular lesions (Marek’s, other tumors; Fig. 7) that can be collected for histology. Examine the crop and gizzard contents to determine the type of feed or identify any foreign bodies that could be toxic. Once your examination of organs is complete, you can remove the soft tissues and cut longitudinally down the middle of the spinal column. Examine the area around the junction of the lungs and kidney to determine if there is developmental spinal compression (kinky back/spondylolisthesis) or if there is a vertebral abscess causing impingement of the spinal column (osteomyelitis).

For more information on neurologic diseases in chickens, please refer to the OAHN website:

https://oahn.ca/resources/neurologic-diseases-of-small-flock-poultry/ and

https://oahn.ca/resources/small-flock-poultry-veterinary-resources/ 

Table 1: List of chicken neurologic disease tests available at AHL

Sampling summary:

NOTE: If screening a flock for disease, up to 5 swabs or tissues can be pooled for PCR testing. PCR tests are generally preferred as they target specific diseases and can be done quickly.

Live bird diagnostics:

• Choanal slit/tracheal swab (use viral transport medium) for PCR. PCR is a fast test and screens for multiple diseases.

You can watch a video on how to collect samples with these swabs at: https://oahn.ca/resources/small-flock-poultry-veterinary-resources/

• Photos of affected birds can be submitted to AHL along with the case history.

Deceased bird diagnostics:

NOTE: If a postmortem is refused by the owner, swabs from the choanal slit could still be collected for PCR or bacterial culture.

• Postmortem: key test for lesion identification and sample collection.
• Histology: an option to screen tissues for lesions or determine the etiology of specific lesions such as nodular structures (bacterial, fungal, neoplastic). Collect a wide variety of tissues to place in formalin including brain, peripheral nerve, and all major organs: lung, liver, spleen, and kidney.
• PCR tests can be run on swabs or tissues. If you are sending tissues, package each tissue type separately and label the bag. Do not mix intestinal tissue with organ tissue.
• Bacterial/fungal culture can be run on gel swabs or tissues. Culture will screen for multiple bacterial organisms and the MALDI-TOF system is used for precise identification.

Reportable diseases in Canada include Salmonella Pullorum, Salmonella Gallinarum, influenza A and Newcastle disease. If high mortality and/or clinical signs lead you to suspect (avian) influenza A or Newcastle disease – quarantine the flock and phone CFIA!  AHL

Figure 1. Abnormal leg position (one forward, one back) suggestive of Marek's disease (AAAP Slide Set #26)	Figure 2. Swelling of individual feather follicles due to lymphoid infiltration (Marek's)
Figure 3. Sciatic nerve location (black arrow)	Figure 4. Lymphoid infiltration of a peripheral nerve is key to histologic diagnosis of Marek’s (H&E)
Figure 5. Baylisascaris procyonis larval migration in brain	Figure 6. Avian encephalomyelitis brain lesions: perivascular inflammation (solid black arrow); neuronal degeneration (open black arrow)
Figure 7. Marek’s disease: neoplastic lymphocytic infiltrates within the wall of proventriculus (black box)

Photos courtesy of Dr. Marina Brash and Dr. Emily Martin