Chick Fung-EYE: You never know where it will go!
Emily Martin, Lisa Ledger, Nathan Bennoit, Hugh Cai, Hillary Schramm
Animal Health Laboratory, University of Guelph, Guelph, ON (Martin, Ledger, Bennoit, Cai);
Production Poultry Veterinary Services, Brucefield, ON (Schramm).
AHL Newsletter 2025;30(1):23.
A commercial chicken broiler flock had an ongoing history of wet litter shortly after placement due to leaking water lines. The referring veterinarian had evaluated various flocks on this farm over time and had identified occasional air sac plaques suspicious for fungal growth. These lesions were identified in birds from 3-4 days of age up to 2 weeks of age and the lesions were considered incidental. The bedding material consists of long straw.
The current flock was 15 days of age at the time of examination. Due to a mechanical problem, the temperature in the barn was below set point for the previous 24-48 hours and was considered cold for this age of bird. Mortality at the time of examination was within expected limits for a flock of this age (1.35%), and first week mortality was considered very good (0.41%).
Six birds were submitted to the practice for postmortem examination. The birds were notably variable in size. One bird was behaviourally normal but had pronounced unilateral periorbital swelling (Fig. 1). On postmortem examination, the left eye was markedly enlarged compared to the right. During dissection, discolouration of the brain was noted through the calvarium and involved both cerebral lobes (Fig. 2). Otherwise, the birds examined had mild bacterial lesions, and 2 birds had 1-2 plaques within the air sacs.
Tissue samples were submitted to the AHL for histopathology. Examination of multiple tissues revealed mycotic encephalitis, airsacculitis and panuveitis (Fig. 3). The areas of necrosis in the brain corresponded with the pale-yellow areas noted on postmortem examination while the enlarged eye had fungal organisms throughout the circumference of the transverse section. Due to the distribution of these lesions, further identification of the fungus was attempted using ITS sequencing on wax scrolls as fresh tissue was unavailable. The DNA sequence had 100% sequence similarity (558/558 bp) to the ITS region of Aspergillus fumigatus, the most common cause of aspergillosis in poultry.
In this case, the likely source of fungal organisms is the wet long straw bedding material. Aspergillus within the straw will multiply in wet conditions and when litter dries the fungal spores can become aerosolized and subsequently inhaled. Aspergillus fumigatus spores are small and easily inhaled, allowing deep penetration of the respiratory system. These birds were also stressed due to cold temperatures in the barn, likely resulting in immunosuppression and hematogenous spread of organisms infiltrating the vasculature. Considering the relatively mild respiratory lesions, spread from the upper respiratory system would be another potential source of organisms although upper respiratory lesions were not identified in this case. While brain lesions can often be identified in cases of young birds with aspergillosis, the extensive eye lesions identified in this case are an unusual distribution.
Figure 1. Ocular swelling and protrusion of the left eye. (Photos: Dr. Hillary Schramm).
Figure 2. Postmortem lesions: A. Enlarged left eye. B. Bilateral yellow discolouration in the cerebrum.
(Photos: Dr. Hillary Schramm).
Figure 3. Histologic lesions: A. Eye. Double headed arrow shows thick layer of inflammation between the sclera and cornea (H&E stain, 2X). B. Eye. Arrows indicate fungal organisms (PAS stain, 20X). C. Brain. Yellow lesions on gross examination are multiple abscesses within the cerebral lobes (H&E stain 2X). D. Brain. Oval surrounds fungal organisms within a cerebral abscess (PAS stain,40X) (Photos: Dr. Emily Martin).
Reference
1. Arné P, et al. Aspergillosis. In: Swayne DE, ed. Diseases of Poultry, 14th ed., Vol II. Wiley Blackwell, 2020:1112-1124