3.5. Tapeworms Tapeworm eggs are not shed directly into the intestinal tract; rather, gravid proglottids containing eggs break off and eggs are subsequently released into the feces. This has practical implications for the detection of tapeworm eggs in feces; the diagnostic sensitivity of the general McMaster technique is less than 10% for diagnosing equine tapeworm (A. perfoliata) infections (Nielsen, 2016a). A modification of a centrifugation-based egg counting technique using 40 grams of feces has been validated to have a diagnostic sensitivity and specificity of 0.61 and 0.98, respectively (Proudman and Edwards, 1992). For detecting tapeworm burdens of 20 worms and above, the sensitivity of this method was found to be 0.90, which is very good for a parasitological diagnostic test. Results are typically not reported as eggs per gram of feces, but rather as the number of eggs counted. Samples should generally be interpreted as being either negative or positive, since there is no correlation of tapeworm egg counts and number of worms infecting a horse. However, egg counts are useful when treatment efficacy is being evaluated. Studies have shown a higher proportion of positive samples in horses treated with effective anthelmintics 24 hours prior to sampling (Slocombe, 2006), and this represents a pragmatic approach to increasing diagnostic sensitivity of tapeworm FECs.
Validated serum and salivary ELISAs are commercially available in the United Kingdom (Proudman and Trees, 1996; Lightbody et al., 2016). These assays measure A. perfoliata-specific antibodies and titer levels and have been found to correlate with worm burdens. However, being antibody- based tests, they may reflect exposure rather than actual infection, and horses can remain positive for months after treatment (Abbott et al., 2008). A different serological test for the presence of antibodies to A. perfoliata is available at the University of Tennessee Diagnostic Laboratory Services, but the test lacks sufficient validation as a quantitative assay for use in detecting current infections or for measuring worm burdens in individual horses. More useful ELISAs may become available in the U.S. in the future.
3.6. Pinworms Pinworm eggs (O. equi) can sometimes be found on a fecal exam, but the Scotch tape test or a microscopic examination of perineal scrapings (using a tongue depressor and lube) are expected to be more sensitive.
3.7. Neck Threadworms Onchocerca spp. microfilariae can be detected by microscopic examination of skin biopsies collected from affected areas along the neck or ventral midline. This technique has been demonstrated to provide useful estimates of anti-microfilarial treatment efficacy (French et al., 1988; Monahan et al., 1995), but is rarely used as a standard test in practice.
4. Anthelmintic Treatment Evaluation
Anthelmintic treatment efficacy is evaluated for the parasite population, of which each horse is a biological sample. Conclusions are drawn for the given population, not the individual horses tested. A general and pragmatic rule of thumb is that any anthelmintic should reduce both ascarid and strongyle fecal egg counts by more than 95% at 14 days after treatment.
10
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
