Equine Science Update
Reports from the world of  equine research.
Monitoring cyathostomin treatment.
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A commonly used laboratory test is of little use in monitoring the response to treatment of cyathostominosis according to researchers in Scotland.

Larval cyathostominosis is one of the most serious parasitic problems of horses in temperate regions of the world. The cyathostomins (or small red worms) migrate into the large intestinal wall where they spend a variable length of time encysted before emerging. If large numbers emerge at the same time they can cause considerable damage to the gut wall.

As it is the larval stages that are responsible for the damage, no eggs are passed in the faeces. So unless the larvae themselves are found in the faeces, it is difficult to confirm a suspected diagnosis of larval cyathostominosis.

Electrophoresis of the serum proteins provides a way of separating different groups of proteins in the blood. Certain disease conditions produce changes in the relative proportions of the different bands. For example an increase in the alpha-2 globulins is associated with acute inflammation. Chronic liver disease often results in an increase in the gamma globulins. Horses with a heavy burden of large strongyles may show an increase in the beta globulins.

Serum Protein Electrophoresis (SPE) is a simple test, requiring only a blood sample.  It is frequently used to assess the extent of cyathostomin (small red worm) burdens, although there is little evidence to support its use.

John Abbott and colleagues at Glasgow University School of Veterinary Medicine have been assessing whether the test is useful for monitoring the response to treatment for cyathostominosis.

They were asked to investigate a problem at a riding school. The horses were believed to be heavily infested with cyathostomins. Indeed, it was the death of one pony in the group that had alerted the clinicians to the problem. Larval cyathostominosis was confirmed on post mortem examination.

The clinicians divided the horses into three groups according to pre-treatment worm egg counts and age. Three different anthelmintics were used:
Pyrantel - effective against adult cyathostomins.
Fenbendazole - effective against susceptible adult cyathostomins, although resistance is now widespread. (In fact the cyathostomins in this study were shown to be resistant.)
Moxidectin - typically highly effective against adult cyathostomins and moderately effective against larvae, including those in the gut wall.

Blood samples were taken for SPE on five occasions over a period of 80 days after treatment. Analysis of the results showed that although many of the horses had raised beta-2 globulin levels initially, they did not fall after treatment of adult (and larval) cyathostomins with pyrantel or moxidectin.

Perhaps changes in the plasma proteins would have been detected if blood samples had been taken more frequently or over a longer period. Nevertheless, these results suggest that SPE is not sufficiently sensitive to monitor changes in level of cyathostomin burden.

Abbott concludes that SPE appears to have little value for assessing the response on cyathostomins to anthelmintic treatment.

For more details see:

Assessment of serum protein electrophoresis for monitoring therapy of naturally acquired equine cyathostomin infections.
JB Abbott, DJ Mellor, S Love.
Veterinary Parasitology (2007) 147, 110 -117.

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