252


EQUINE VETERINARY EDUCATION / AE / MAY 2018


oedema, congestion, haemorrhage and necrosis). This prevented accurate interpretation of any underlying pathology that may have preceded the intussusception. It is therefore difficult to determine the relevance of the histological inflammatory infiltrates seen. The presence of chronic gastrointestinal symptoms in Cases 1, 2 and 7 may indicate chronic infection, but could alternatively be due to other factors, as discussed above. It was not possible to perform a comprehensive retrospective search for cases of caecal intussusception in the hospital records as electronic case records have only recently been introduced. However, cases of caecal intussusception at the OVAH are considered to be rare. Since 2000 all except one case of caecocaecal or caecocolic intussusception encountered at necropsy at the Section of Pathology had heavy burdens of G. aegyptiacus in the caecum and/or colon (J. Williams, personal communication). Heavy burdens of G. aegyptiacus are not regularly identified during necropsies of horses suffering from other conditions at the OVAH (J. Williams, personal communication). The epidemiology of G. aegyptiacus infestation is


incompletely understood. Three of the cases in this series (2, 3 and 5) had a history of having grazed a pasture in which standing water was present. Based on what is known of the life cycle of this parasite, it is highly likely that this represents a risk factor for G. aegyptiacus infestation. It is not known how long adult G. aegyptiacus parasites can persist in the horse. Certain other species of intestinal fluke such as Calicophoron in sheep are viable in the host for many years (Rojo-Vazquez et al. 2012). It is possible that the other cases in this series were previously exposed to risk factors under different ownership. There are important limitations to consider upon


interpretation of the current faecal sedimentation test for G. aegyptiacus. It is nonquantitative and has not been validated for this species against a gold standard of necropsy. One of the horses in this series (Case 2) was negative for G. aegyptiacus ova when tested antemortem. The relative roles of mature oviparous adults and immature stages are unknown. The prepatent period from infestation with metacercariae to mature egg laying adults was found to be 115 days in an experimental donkey (Malek 1971). As an egg detection test, faecal sedimentation would be negative with an infestation of immature parasites during the prepatent period. The lower detection limit of the test is also unknown. Further work is required to determine why some infested animals test positive and some do not. Case 7 had clinical findings consistent with caecal intussusception and following treatment for G. aegyptiacus and supportive care, both clinical and ultrasonographic evidence of intussusception resolved. This has not previously been reported. It is possible that caecal intussusception may spontaneously resolve if adhesions are absent, especially with concurrent medical support. Additionally, multiple cases of spontaneously resolving jejunojejunal intussusception were recently described in an ultrasonographic study of neonatal Standardbred foals (Abraham et al. 2014). An important difference between those foals and the case described here is the absence of abdominal pain or any evidence of tissue or vascular compromise. The findings of serosanguinous peritoneal fluid with increased lactate content are consistent with intra-abdominal vascular compromise. Reports of caecal intussusception treated surgically describe successful outcomes in horses without resection of the intussusception


© 2017 EVJ Ltd


from the abdomen (Lores and Ortenburger 2008). The degree of compromise of the caecum and colon were unfortunately not described in that case series. It is possible that the intussusception in Case 7 reduced, or alternatively, if it was a caecocaecal intussusception, became walled off and atrophied. The shortest follow-up time previously reported for an intussuscepted caecum left within the abdomen, was 2 months, at which point it was no longer evident (Lores and Ortenburger 2008). In a therapeutic trial, treatment of G. aegyptiacus


positive horses with oxyclozanide (a salicylanilide anthelmintic with anti-trematode activity [Mehlorn 2008]) or resorantel (a salicylanilide anthelmintic with anti-trematode and anti- cestode activity [Mehlorn 2008]) led to negative faecal sedimentation in all cases (Roberts et al. 1975). Poor efficacy of oxfendazole, albendazole and ivermectin has also been demonstrated (Malik et al. 2006). Whether or not oxyclozanide is effective against immature stages of G. aegyptiacus is unknown. Niclosamide has not been tested for treatment of G. aegyptiacus infestations and would therefore not be recommended. Neither oxyclozanide nor resorantel are licensed for use in horses in South Africa, therefore treatment with either drug is off licence. A product containing oxyclozanide without levamisole is not available in South Africa. The authors have not observed any adverse reactions when using a combined oxyclozanide and levamisole product2 at 7.5 mg/kg bwt of oxyclozanide and 5.6 mg/kg bwt levamisole. This is a marginally lower dose than that previously evaluated by therapeutic trial (Roberts et al. 1975) and was selected due to reports of anorexia following treatment at the evaluated dose (Van Laaren 2014). In the current series a repeat faecal sedimentation test was only performed for Case 7. Following treatment with a combined oxyclozanide/levamisole product (Tramizan10, oxyclozanide 7.5 mg/kg bwt, levamisole 5.6 mg/kg bwt) this test was negative, suggesting that oxyclozanide may be efficacious at this dose. Prophylactic treatment for G. aegypticaus infestation is not currently being recommended due to limited understanding of the relevant epidemiology, perceived low incidence of disease and absence of a licensed anthelmintic product. This report supports previous suggestions of a pathological


role of G. aegyptiacus in equine gastrointestinal disease and suggests that G. aegypticus should be considered as a differential diagnosis in cases of typhlocolitis or caecal intussusceptions. Awareness of this parasite may increase its detection and enable treatment in clinical cases. Future study of the epidemiology of this parasite is required and would be greatly facilitated by more advanced diagnostic testing and wider veterinary awareness.


Authors’ declaration of interests No conflicts of interest have been declared.


Source of funding None.


Acknowledgements


The authors wish to acknowledge Prof. K. van den Berg for sharing the details of Case 4 for inclusion in this series.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76