TREATMENT
The key to successful treatment is to start early in the course of disease, although the decision of whether to treat or not and when to start is not always clear. Once clinical coccidiosis is present, there is already significant enteric damage.
Healthy echidnas shedding faecal oocysts, with or without low-moderate parasitaemia (<30%), and without any predisposing identifiable risk factors (Table 30.1) do not require treatment. If exposed to risk factors, consideration should be given to commencing prophylactic treatment. Any sick echidna with inappetence, lethargy, diarrhoea or signs of pain, with or without faecal oocysts, and moderate to marked par- asitaemia should be treated, particularly if there is exposure to risk factors (Table 30.1). Treatment is still indicated in these cases if there is no parasitaemia.6.1 Anticoccidial drugs
The anticoccidial drugs most often used in echidnas are toltrazuril (Baycox 5% for piglets; Bayer Animal Health, Pymble, NSW) and trimethoprim-sulfonamide (TMS) combinations.
The mechanism of action of toltrazuril and its major metabolite ponazuril is unclear and it is considered both inhibitory and coccidiocidal (Litster et al. 2014). It affects all stages of the parasite (Slapeta 2016) and is documented to reduce faecal oocyte shedding. However, recurrence of faecal oocyst shedding is common, either because of reinfection or potential recrudescence of tissue stages (Debenham et al. 2012). Although toltrazuril is regarded as highly effective in macropods (Slapeta 2016), in echidnas the efficacy is inconsistent and may be ineffective (S Vitali pers. comm.; M Pyne pers. comm.; Taylor et al. 2019). It is therefore recommended as a preventative treatment for asymptomatic adult echidnas exposed to risk factors or in the face of an outbreak rather than for use in clinical cases (Slapeta 2016; M Pyne pers.
comm.). A derivative, ponazuril, has been used effectively in domestic species and may prove a more effective alternative in echidnas (Litster et al. 2014; Sykes and Papich 2014; Papich 2016).TMS is currently the drug of choice for treating clinical coccidiosis in echidnas. Reductions in oocyst shedding and intramonocytic coccidia are consistent unless treatment is commenced late in the disease or in severely affected echidnas. There is debate regarding the frequency of administration of TMS in domestic species and many clinicians consider it more efficacious if given twice daily (Plumb 2015).
Dosing is either 5 mg/kg of the trimethoprim portion or 15-30 mg/kg (combined TMS) PO sid-bid. Trimetho- prim-sulfamethoxazole (Bactrim Oral Suspension, Roche Products Pty Ltd, Dee Why, NSW) is readily accepted in food. Inappetent echidnas can be gavaged daily under light gaseous anaesthesia (see Chapters 9 and 29). Duration of treatment varies but should be continued for 1 wk after reduced oocyst shedding and resolution of clinical signs.
Parenteral TMS is not recommended because of the serious and sometimes fatal adverse effects (e.g. immune- mediated haemolytic anaemia [M Pyne pers. comm.; see Chapter 29]). However, it has been used effectively without adverse effects (Middleton 2008; S Vitali pers. comm.).
Many other antiprotozoal drugs are used for prevention and treatment of coccidiosis in other non-domestic species, production animals and aviculture (e.g. sulfa- chloropyrizidine and amprolium). There are no reports of their use in echidnas. Doxycycline is used to treat isosporosis in humans (Sykes and Papich 2014) who cannot tolerate sulfa-containing drugs and could be considered an alternative to TMS in echidnas.
6.2 Supportive care
Supportive care is fundamental to the survival of clinically affected echidnas. Dehydration and pain are significant causes of morbidity and mortality and must be addressed proactively.
Crystalloid fluids are administered SC and small IV boluses can be administered via the beak sinus (see Appendix 2).
Light anaesthesia will be required for this in all but the sickest echidnas. Isotonic replacement fluids such as Ringers lactated solution (Hartmann’s) or Plasma-Lyte 148 (Baxter Healthcare, Old Toongabbie, Qld) are used to replace fluid deficits over 18-24 hr plus estimated daily ongoing losses. The daily fluid requirement of echidnas is not reported but can be estimated based on that of eutherian mammals, although it is likely to be less due to the lower basal metabolic rate of echidnas (see Chapters 14 and 29). Appropriate maintenance fluids are 0.45% NaCl + 2.5% glucose with supplemental KCl at 20 mmol/L.Opioids are used to control pain (see Appendix 4). NSAIDs are not recommended, because of dehydration and intestinal inflammation.
Additional supportive measures include treatment for GIT ulceration (e.g. ranitidine, omeprazole, sucralfate), faecal transfaunation to re-establish microbiome balance (Lu et al. 2021) and specific treatments for concurrent infections (e.g. mycotic gastritis). Maropitant is also recommended.
7.