Emaciation and larval filarioid nematode infection in boreal owls (Aegolius funereus)

Figures & data

Figure 1.  Extremely high microfilarial burden in the lung vessels of an emaciated boreal owl. Scale bar = 200 µm; haematoxylin phloxine saffron. Insert: numerous intertwined microfilariae have completely filled the vascular lumen.

Figure 2.  Aggregation of microfilariae (arrows) in a vein of the pericardium of an emaciated boreal owl. Some microfilariae are embedded in a fibrinoid material (arrowhead). Scale bar = 50 µm; haematoxylin phloxine saffron.

Table 1.  Boreal owls submitted for histopathology to the Canadian Cooperative Wildlife Health Center—Quebec Region during winter 2008/09: intensity of microfilarial infection and summary of the morphological changes observed.

Date found	Weight (g)	Sex	Age^a	Intensity of microfilarial infection^b	Morphological changes	Cause of death
Mid-December	109	Female	AHY			Emaciation^c
17 December	113	Female	HY			Emaciation^c
5 January	134	Female	AHY			Unknown^c
5 January	92	Male	AHY			Emaciation^c
6 January	119	Female	AHY	+++	Intravascular fibrinoid material	Emaciation/microfilariae
11 January	142	Female	AHY	++	No changes	Unknown^d
12 January	140	Female	AHY	0	–	Unknown
13 January	92	Male	SY	++	No changes	Emaciation
14 January	99	Male	AHY			Emaciation^c
21 January	109	Female	AHY			Emaciation^c
26 January	117	Female	AHY			Emaciation^c
17 February	120	Female	ASY			Trauma^c
26 February	118	Female	AHY			Emaciation^c
28 February	93	Male	AHY	0	–	Emaciation
1 March	116	Female	AHY			Emaciation^c
9 March	110	Female	ASY	0	–	Emaciation
10 March	95	Male	AHY	+++	Intravascular fibrinoid material	Emaciation/microfilariae
10 March	82	Male	ASY	+++	Intravascular fibrinoid material	Emaciation/microfilariae
17 March	101	Male	AHY			Emaciation^c
1 April	109	Female	SY			Emaciation^c
9 April	87	Male	SY	++	No changes	Emaciation
^aHY, hatching year (owl born the previous summer); SY, second year (owl born during the summer of the previous year); ASY, after second year (adults); AHY, after hatching year (encompass SY and ASY).
^bThe intensity of microfilarial infection was graded on one histological section of lung, observed under 400×magnification, using the following scale: 0, absence of microfilariae;+, 1 to 50 microfilariae present;++, 50 to 200 microfilariae present;+++, over 200 microfilariae present.
^cDiagnosis based on gross examination.
^dThe owl was euthanized because of rapidly worsening debilitation. The cause of the clinical signs was not identified.

Figure 3.  (Colour online) Impression of thawed lung from an emaciated boreal owl showing a sheathed, round-tailed, round-headed microfilaria. Scale bar = 10 µm; modified Wright–Giemsa stain (Dip Quick; Jorgensen Labs. Inc., Loveland, Colorado, USA).