How good are we at detecting strongyles?

Effective control of strongyles is essential to maintain healthy, productive horses. To mitigate increasing global anthelmintic resistance, anthelmintic use based on improved parasite surveillance is recommended. Targeted anthelmintic use is considered the gold standard for equine strongyle control in the developed world. This involves the use of faecal egg counts (FEC) to estimate strongyle egg excretion, thereby identifying individuals requiring an anthelmintic. If future treatment decisions are to be based on regular parasite surveillance, review of the availability and accuracy of our current diagnostic tools is required. Current in vivo strongyle detection is based on coprological techniques, namely faecal egg counts (FEC), larval cultures, and molecular techniques such as polymerase chain reaction (PCR).

Faecal egg counts (FEC)

Presently the FEC is the principal in vivo test used to provide an estimation of strongyle burden. However, it has many limitations. Faecal egg counts do not provide an accurate gauge of total strongyle burdens within individual animals [1]. Faecal egg counts only detect eggs released by mature female worms i.e. a patent infection. There is no significant correlation between magnitude of FEC and mucosal larval burdens [2]. This is of particular importance during winter months in the northern hemisphere when cyathostomin encysted larvae are abundant and can comprise up to 90% of the total burden [1]. The FEC process follows a hierarchical structure from faecal pile to microscopic analysis, with potential sources of variation at each level [3]. Sources of variability in FEC methodology and interpretation must be appreciated, and if possible reduced, to prevent incorrect decision making regarding anthelmintic use or determination of anthelmintic sensitivity or resistance. […]