DIAGNOSIS

5.1 History, clinical signs and faecal oocysts

A history of recent exposure to risk factors (Table 30.1) and disease in other echidnas will increase the index of suspicion of clinical coccidiosis in a sick echidna.

Subjective estimates of faecal oocyst numbers using standard wet preparation or faecal flotation techniques are quick and easy to perform (Fig. 30.2). The presence or number of faecal oocysts is not necessarily indicative of the presence of disease (Middleton 2008; Debenham et al. 2012; Taronga Zoo records; ARWH 2024). Healthy echid­nas can shed large numbers of oocysts while acute, fatal coccidiosis can occur before any oocysts are shed in the faeces. Large numbers of oocysts in echidnas with diar­rhoea, lethargy and inappetence should be considered significant and treatment initiated.

Fig. 30.2. Coccidial oocysts (arrows) in the faeces of a short-beaked echidna (Tachyglossus aculeatus). It is not possible to distinguish Eimeria echidnae and E. tachyglossi oocysts on wet preparation or floatation, as there is considerable variation in the oocyst size of each species. Note the presence of strongyle-type ova (faecal floatation, ?400 magnification). Image: Taronga Wildlife Hospital

5.2 Haematology and biochemistry

Neutrophilia or neutropenia with or without a left shift may occur in echidnas with clinical coccidiosis. Five echid­nas with systemic coccidiosis at Taronga Zoo had a relative and absolute monocytosis of up to 33% and 7.4 ? 10⁹∕L (reference range: monocyte 0-10%, monocytes 0.07-1.5 ? 10⁹∕L [ZIMS 2024]). There was moderate-marked (30­100%) intramonocytic Eimeria burden in all five echidnas.

Intramonocytic Eimeria are detected in up to 50% of healthy echidnas (Plate 30.1).

Myelocytes and metamyelocytes were observed in blood smears of one echidna that died of overwhelming systemic coccidiosis (ARWH 2024 case no. 10783). A second echidna with fatal systemic coccidiosis had a significant leucocytosis of 105 ? 10⁹∕L comprising immature myeloid or lymphoid cells. Although it is likely these cells reflected bone marrow response to severe systemic inflammation, particularly as the WBC count decreased to 44 ? 10⁹∕L a few days after treatment commenced, leukaemia could not be ruled out (ARWH 2024 case no. 9855).

There are no pathognomonic biochemistry abnormali­ties. Changes reflect metabolic derangements, dehydra­tion, organ failure and sepsis.

5.3 Necropsy

Gross findings in subclinical enteric coccidiosis in echid­nas that have died for other reasons have been described as prominent, pale, ‘frosty’ mucosal patches of the distal two-thirds of the small intestine (Barker et al. 1985; Ladds 2009). Changes associated with clinical enteric coccidio- sis include intestinal wall thickening; multifocal, pale mucosal nodules; haemorrhage; ulceration; and necrosis (Middleton 2008; ARWH 2024). Systemic changes are dependent on the organs affected, but generally include congestion, haemorrhage, necrosis and oedema.

Histopathology confirms enteric or systemic coccidio- sis. Subclinical infection is characterised by an absence of significant inflammation associated with coccidia (Barker et al. 1985). Detailed histopathological descriptions of enteric and systemic coccidiosis can be found in Barker et al.

6.