Oocyst counts not necessarily reliable in suspect Cocci cases

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With lambing season underway for many already, diseases that affect a large proportion of the new crop of lambs can be distressing for both farmers and vets. Elanco Animal Health is reminding vets about the importance of correctly interpreting oocyst counts in the diagnosis of coccidiosis during the post lambing period.

Scouring lambs that are failing to thrive should immediately ring the alarm bells for coccidiosis. Typically, oocyst counts of >20,000 per gram are cited as diagnostic for coccidiosis in sheep, but counts of up to 100,000 oocysts per gram have been reported in apparently healthy lambs and disease can also occur in the presence of low or negligible counts where there is gut damage but before oocysts have been shed.1 These discrepancies can lead to misdiagnosis and as such, oocyst counts should always be interpreted with care.

Oocysts of the fourteen Eimeria species described as specific to sheep are indistinguishable from each other by eye and only two species – E. ovinoidalis and E. crandallis, are actually pathogenic.1 For this reason, diagnosing coccidiosis based on clinical signs of diarrhoea and oocysts in their faeces alone can generate false positives. This could lead to important differentials, such as Nematodirus battus infection (for lambs at pasture) being left untreated.

False negatives are also a concern, particularly as prompt treatment of clinical cases with an effective anti-coccidial, such as diclazuril (Vexocan® 2.5mg/ml oral suspension) has been proven to reduce the convalescence period.2 Shedding of oocysts varies with disease progression and faecal counts can fluctuate significantly.3 For example, a delay between the development of clinical signs and oocysts appearing in faeces is common. Another possibility is sub-clinical disease, with affected lambs showing no typical outward signs. The gut damage caused by the parasite can be significant in these animals though, adversely affecting growth rates.

For reliable diagnosis of coccidiosis, faecal oocyst counts should be considered alongside disease and farm history and followed with Eimeria species identification if possible. The disease typically affects groups of lambs aged between 3-8 weeks old and is often triggered by a stressor such as castration, weaning, turnout and/or bad weather. If clinical signs appear around three weeks after such an event, the suspicion of coccidiosis can be heightened. For some farms, predictable stressors cause disease outbreaks year after year and in these cases, a metaphylactic dose of Vecoxan® can be administered to susceptible lambs 14 days after the trigger event.

Vets should also not forget the importance of good management when advising farmers about coccidiosis control. Lambing pen and high traffic area hygiene and age batching lambs are essential for long term control.

Vecoxan® 2.5 mg/ml Oral Suspension contains diclazuril 2.5 mg/ml. Legal Category POM‐VPS. Vm 00006/4145

For further information contact Elanco Animal Health, Lilly House, Priestley Road, Basingstoke,

Hampshire, RG24 9NL, Tel 01256 353131, Fax 01256 779510 Email elancouk@lilly.com

Advice on the use of this or alternative medicines should be sought from the medicine prescriber

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References

1. Merck veterinary manual online edition – ‘Coccidiosis of sheep’, http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/21203.htm, 10.12.12

2. Platzer B, Prosl H, Cieslicki M, Joachim A, Epidemiology of Eimeria infections in an Austrian milking sheep flock and control with diclazuril, , Veterinary Parasitology 129 (2005) 1-9

3. Gauly. M. et al. Pattern of Eimeria Oocyst Output and Repeatability in Naturally Infected Suckling Rhön Lambs, Journal of Veterinary Medicine, Series B, Volume 48, Issue 9, pages 665–673, November 2001