Avian chlamydiosis outbreak in a breeding flock of African grey parrots
Hein Synman, Pauline Delnatte, Christopher Dutton
Animal Health Laboratory, University of Guelph, Guelph, ON (Snyman); Ontario Veterinary College (Delnatte, Dutton)
AHL Newsletter 2023;27(1):18.
Over a 6-week period in the early fall of 2022, a breeding flock of approximately 30 adult African grey parrots (Psittacus erithacus) started to experience sudden and unexplained mortalities. The first death occurred in September, and was followed by two more in early and then late October. One bird was found dead with no premonitory signs, and two birds exhibited a short preceding course of non-specific clinical signs consisting of weight loss, ruffled feathers, and lethargy. At the time of the third mortality, two additional birds had also started showing the same non-specific clinical signs. One of these birds died 3 days later. All birds were young adults (~ 8-12 years old), with no significant preceding medical history. During the summer, birds were housed in a free-flight barn with fine mesh windows, and in the winter, birds were pair-housed in cages in a heated barn. The move from summer to winter housing occurred about a week before the third mortality. The flock was considered to be a closed flock with no new birds introduced into the flock for more than 6 years. There had been no mortalities in the flock over the previous 10 years.
At the time of the third mortality, an onsite veterinary visit was scheduled, and a postmortem was performed. On external postmortem examination, this male bird was found to be in poor body condition with severe dehydration, unilateral left lenticular opacification, and a small amount of dry discharge was present around the right nostril. Internally, the liver was markedly enlarged and friable with diffuse yellow-tan mottling and fibrinous adhesions. The pericardial sac was thickened, opaque and filled with a large amount of yellow-green gelatinous exudate (Fig. 1A). The spleen was also markedly enlarged (~ 2 cm diameter) and friable with dark red congestion and similar pale mottling (Fig. 1B). The lungs were diffusely congested and edematous (Fig. 1B). Representative formalin-fixed and fresh tissue samples were taken and submitted to the Animal Health Laboratory for further analysis.
Bacterial culture of the spleen did not yield any significant pathogens and salmonellosis was ruled out by enriched media culture. Histological sections of the liver and spleen contained widespread coalescing foci of acute parenchymal necrosis with moderately dense mixed infiltrates of macrophages, fewer heterophils, fibrinous exudate, and karyorrhectic nuclear debris (Figs. 2A, 2B). Many macrophages in addition to viable marginal hepatocytes were distended by densely-aggregated fine granular pale basophilic cytoplasmic bacterial colonies. Similar fibrino-inflammatory exudate and intra-histiocytic bacteria were also present on the surface of the pericardial sac (Figs. 2C, 2D). These features are highly suggestive of avian chlamydiosis, a diagnosis that was subsequently confirmed by PCR testing of the spleen (Ct = 15.82). Postmortem findings in the fourth mortality were very similar. Histology was not performed in this parrot. Chlamydia psittaci was confirmed by PCR testing of the spleen (Ct = 16.25).
Avian chlamydiosis is a zoonotic disease that is caused by the obligate intra-cellular bacterium Chlamydia psittaci. Aerosol inhalation and ingestion represent the primary routes of transmission / infection, and carriers are capable of excreting the organism intermittently for several months post infection. Given that immunity post infection is short lived, intermittent shedding also often results in rapid reinfection which can lead to prolonged recirculation of the disease in an affected population. C. psittaci elementary bodies can remain infectious for several months.
Clinical signs vary widely within and among individuals in an affected population, and may include: sinusitis, dyspnea, conjunctivitis, polyuria, diarrhea, lethargy, anorexia, yellow to dark green droppings, poor feathering, chronic weight loss, various neurological abnormalities (flaccid paralysis, opisthotonos, tremors, convulsions), or peracute death.
Although this group of birds was predominately housed indoors, infection was still likely related to incidental contact with wild birds, either directly through fine mesh windows or indirectly through contaminated dust, dried saliva, feathers, mucous and/or feces. The outbreak was reported to the Ontario Ministry of Health and Long-Term Care, and appropriate follow-up precautions were undertaken to limit any human contact with the remaining birds. The remaining symptomatic bird received intensive care for 5 days (supportive care and doxycycline orally) and improved quickly. The entire flock was immediately started on a 6-week course of doxycycline administered in drinking water and no additional mortality or morbidity occurred. AHL
Figure 1. Postmortem findings in a 10-year-old male African grey parrot with avian chlamydiosis. A. In-situ coelomic organs. Hepatomegaly with rounded lobar margins and pale yellow-tan mottling (arrow). The pericardial sac is thickened, opaque and is filled with light yellow-green gelatinous exudate (star). B. Lung (top) and spleen (bottom). Lungs are congested and edematous; spleen is markedly enlarged with mottled and friable parenchyma.
Figure 2. Histological findings in a 10-year-old male African grey parrot with avian chlamydiosis (H&E stain). A. Spleen contains large foci of acute parenchymal necrosis, associated with a mixed cellular infiltrate of macrophages and fewer heterophils (circle). B. Liver contains similar foci of necrosis and histiocytic inflammatory infiltrate (circle). C. & D. The pericardial cavity is filled with fibrino-cellular exudate (star) and numerous macrophages that are distended by densely-aggregated, fine granular pale basophilic cytoplasmic bacterial colonies (arrows).
References
1. Reavill DR, Dorrestein G. Chapter 32: Psittacines, Coliiformes, Musophagiformes, Cuculiformes. In: Pathology of Wildlife and Zoo Animals. Terio KA, McAloose D, St. Leger J, eds. Academic Press, 2018:789.
2. Schmidt RE, Reavill DR, Phalen DN. Chapter 4: Liver. In: Pathology of Pet and Aviary Birds, 2nd ed. Schmidt RE, Reavill DR, Phalen DN, eds. Wiley Blackwell, 2016:106-107.