Equine roundworm, Parascaris

Introduction

Adult P. equorum in a four-year-old donkey that died of colic. Most worms were found blocking the ileocaecal junction and in the caecum, with a few in the small intestine. (Image courtesy of The Donkey Sanctuary)

Parascaris equorum and P. univalens are the two species of the genus Parascaris that affect equids. P. equorum was considered to be the most prevalent and common equine ascarid, however available evidence now suggests that P. univalens is the main ascarid (Nielsen, et al., 2014; Nielsen, 2016). Generally it is believed that it is the same species of ascarid that is found in horses affects donkeys. They are among the largest nematodes/roundworms up to 40 cm in length. Parascaris spp are considered to mainly affect foals, as adult horses develop a strong protective immunity. However, the situation in donkeys appears to be different.. High infection prevalence, patent infections with high egg counts and a high number of adult worms are a common finding in adult donkeys in Ethiopia and South Africa (Getachew, et al., 2008; Wells, et al., 1998). This indicates age-dependent immunity may not develop in donkeys like in horses, or they may have been immunocompromised. Anecdotal evidence from the UK over recent years suggests there has been a rise in the number of ascarid infections seen in mature donkeys.

Characterisation of ascarid infections:

Large number of eggs are produced, which can survive for years in the environment
The infective stage eggs containing L2, once ingested from grazing and hatched, migrate through the liver and lungs before returning to the small intestine
Infestations are usually derived from allowing foals to graze on the same pastures year after year, but adult donkeys can also be a source of infection.
There is no evidence of prenatal infection

Signalment

Affects both adults and foals

Diagnosis

Clinical signs

Diarrhoea associated with acute parascariasis in a collapsed one-year-old donkey. Note mature and immature ascarids. (Image courtesy of The Donkey Sanctuary)

Larvae can cause liver damage and signs of respiratory problems
Heavy infection can cause stunted growth, ill thrift and diarrhoea
Adult worms can block the gut, causing colic and even ruptures of the gut, which may be associated with anthelmintic administration
Recently transabdominal ultrasound technique was developed for monitoring ascarid burdens in foals and young horse (Nielsen et al., 2016), and found to be a useful clinical diagnostic tool as adult ascarids are highly echogenic and thus readily identifiable on the monitor screen

Laboratory tests

Thick-shelled eggs of Parascaris spp. Note:morulation. (Image courtesy of The Donkey Sanctuary)

Patent infection in the horse occurs at three months and diagnosis is via faecal examination identifying the typical thick-shelled eggs of the parasite
A rigorous faecal sampling programme should be implemented with young stock

Treatment

Anthelmintics used in horses are effective against adult ascarids in donkeys. Prophylactic treatment of foals is warranted due to the serious nature of the infection in immature animals. Recently there are many reports of resistance to macrocyclic lactones in multiple countries in the horse. The Donkey Sanctuary has also recently experienced treatment failure against P. equorum with ivermectin, moxidectin and pyrantel embonate in donkeys. Therefore, this must be taken into consideration while treating donkeys against ascarids. A special sampling and treatment protocol is advised for pregnant jennies and foals, this is available from The Donkey Sanctuary on request.

In conjunction with treatment, a practical approach to control parascariosis is manure disposal, since practically all worm eggs and larvae will be killed by the heat generated during fermentation of the manure. On the other hand, in climatic conditions favourable for the eggs’ survival, ascarid eggs can remain viable for over a year.

Literature Search

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Ascarids in donkeys publications

References

Getachew, A.M., Innocent, G.T., Trawford, A.F., Feseha, G., Reid, S.J.W. and Love, S. (2008) Equine parascarosis under the tropical weather conditions of Ethiopia: a coprological and post-mortem study. Vet. Rec. 162: 177-180.

Nielsen, M.K., Wang, J., Davis, R., Bellaw, J.L., Lyons, E.T., Lear, T.L. and Goday, C. (2014). Parascaris univalens — a victim of large-scale misidentification? Parasitol. Res. 113: 4485-4490.

Nielsen, M.K., 2016. Evidence-based considerations for control of Parascaris spp. infections in horses. Equine vet. Educ. 28: 224-231.Nielsen, M.K., Donoghue, E.M., Stephens, M.L., Stowe, C.J., Donecker, J.M. and Fenger, C.K. (2016). An ultrasonographic scoring method for transabdominal monitoring of ascarid burdens in foals. Equine Vet. J. 48:380-386.

Trawford, A. and Getachew, M. (2008) Parasites. In: Svendsen, E.D., Duncan, J. and Hadrill, D. (eds), The Professional Handbook of the Donkey (4th ed), , pp.82-110. Whittet Books, UK.

Wells, D., Krecek, R. C., Wells, M. & Guthrie, A. J. (1998) Helminth levels of working donkeys kept under different management systems in the Moretele 1 district of the north west province, South Africa. Veterinary Parasitology 77, 163-177.

ENDOPARASITES - DONKEY

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Ascarids - Donkey