Australian Magpie (Gymnorhina tibicen) with severe Leucocytozoonosis

Registry case number TARZ_9585.1

HISTORY

Juvenile fledgling magpies from the Nowra region in rehabilitation with experienced carers showing sudden onset inappetence, lethargy and death. All animals being reported with heavy throat worm loads. Some animals appear to recover slowly from the lethargy and begin to gain weight again but die suddenly, while others experience sudden onset anorexia and weight loss before being found dead, despite supportive care.

3 animals submitted live for blood collection and euthanasia. Multiple animals submitted fresh dead or frozen.

INDIVIDUALS HISTORY

This individual entered care 15/10/13 and was noted to have heavy throat worm burden – treated with removal of the worms by hand, and oral Ivermectin.  Sudden onset weakness, difficulty eating and weight loss.  Euthanasia elected due to poor condition, history of poor recovery for affected birds and mortality event investigation.

GROSS FINDINGS

External examination:  The keel feels prominent.  The beak is very flexible. The primary and secondary feathers of the wings are almost fully developed.  There are several very low submucosal nodules within the ventral oral cavity.

Hydration: good

Muscle mass: thin

Fat deposits: absent

Internal examination:  The bursa is small.  The gastrointestinal tract is devoid of ingesta.  The spleen is very large.  The skeletal and cardiac muscles appear pale.

HISTOPATHOLOGY

The tissues are very well preserved.

Within blood vessels in most organs there are large numbers of leucocytes with eccentric, semilunar nuclei and the cytoplasm is largely displaced by large oval basophilic organisms that have a very small nucleus.

Lesions are not evident within the following tissues: skeletal muscle – cross and longitudinal sections (A), pancreas, duodenum, brain – sagittal section, (B), ventriculus, kidney, ovary (C), eye (D).

The following observations are notable:

Heart (A): Within the epicardium at the heart base there are several focal mononuclear cell aggregates.  Air sac is evident attached to the greater vessels.  Focally the air sac epithelium is thickened and may contain a small number of mononuclear cells.

Spleen (B):  The splenic parenchyma contains numerous perivascular lymphoid cuffs, but few discrete lymphoid follicles.  Numerous cells with pyknotic or karyorrhectic nuclei are scattered throughout the lymphoid aggregates.  Reticuloendothelial cells surrounding penicillar arterioles appear prominent.  The mesentery between the spleen and pancreas contains a small number of small mononuclear cell clusters.

Lung (B): The tissue is congested.  Segmentally the air sac mucosa contains heterophils apparently migrating through the lamina propria and mucosa to form a thin exudate on the surface.

Small intestine (B, C): Moderate numbers of coccidial gametocytes are scattered throughout the villar mucosa.

Ileum and caecae (C): The caecal serosa contains scattered mononuclear cells.  The caecal lamina propria contains dense infiltrates of lymphocytes.  One caeca contains a luminal aggregate of heterophils and heterophils are evident migrating through the superficial lamina propria and mucosa.  A large blood vessel in the mesentery contains a focal subendothelial mononuclear cell infiltrate.

Liver (C): Multifocal portal tracts contain small aggregates of mononuclear cells.

Oesophagus, proventriculus (C):  The lamina propria contains multifocal small lamina proprial infiltrates of lymphocytes and plasma cells.

Cloaca – good section (D): The bursa is very well populated with lymphoid follicles.   A single blood vessel in the connective tissue adjacent to the bursa is surrounded by a cuff of lymphocytes and plasma cells.

ANCILLARY TESTS

Newcastle’s Disease Real Time PCR – Negative

Influenza A Real Time PCR – Negative

DIAGNOSIS

Euthanasia, Leucocytozoonosis – severe, Air sacculitis – mild, focal, heterophilic, Intestinal coccidiosis – moderate

COMMENT

The young bird had a very soft beak and was in very poor body condition.  The animal had a history of heavy throat worm infection, but had very few oral lesions at necropsy.   The bird had a very severe blood parasite infection with leucocytozoon and moderate intestinal coccidiosis.   These single celled parasites are not uncommon in young magpies and the infections can be quite severe in debilitated birds.

There was no evidence of systemic non-suppurative inflammation in this bird that might be suggestive of an underlying viral infection.

It seems more likely that a combination of malnutrition and parasitism contributed to the poor condition and debility of this bird.