TRACKING THE RECOVERY OF CYATHOSTOMIN SPECIES FOLLOWING ANTHELMINTIC TREATMENT
Date
2019-05
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Cyathostomin are ubiquitous gastrointestinal parasites of horses that can cause
damage to the intestinal mucosa, colic, diarrhea, and host mortality. There are 50
species of nematodes in this group, and a single horse can host up to 20 different taxa.
There are three classes of antiparasitic drugs (benzimidazoles, macrocyclic lactones
and tetrahydropyrimidines) called anthelmintics used to treat cyathostomin
infections. Cyathostomin are observed with resistance to all three classes, but levels
of resistance vary. Macrocyclic lactones are more efficient in treatment than other
classes of anthelmintics, but early indications suggest increased resistance is
developing. The pattern of species recovery following deworming has not been fully
explored and there is little understanding of how this relates to resistance. In this
study, three drugs (moxidectin, ivermectin, and pyrantel) under the classes of
macrocyclic lactones and tetrahydropyrimidines, were used to treat infected horses and
observe their effects on the cyathostomin population. The goal of this study was to
observe the patterns of recovery and presence the cyathostomin population exhibited
during anthelmintic treatment. The second goal of this study was to determine which
taxa are predicted to recover faster within and across treatments. The last goal of this
study was to determine if there were any shifts in cyathostomin populations following
anthelmintic treatment. Exploring the dynamics of cyathostomin populations in the
presence of these treatments may help develop better approaches to fighting
cyathostomin infections, reducing the amount of severe Cyathostominosis cases.
The primary methods of identifying cyathostomin populations were 5.8S
rRNA gene sequencing of DNA extracted from equine fecal material while also
monitoring the fecal egg counts of each individual. Several analyses were used to
compare the cyathostomin populations following treatment including Multivariate
Logistic Regression and Principle Coordinate Analysis. Multivariate Logistic
Regression was used to predict the recovery rates and presence of specific taxa within
and across treatments. Principle Coordinate Analysis was used to detect if there were
any shifts in beta diversity following the course of anthelmintic treatment.
Logistic regression displayed significant (P-values < 0.05) differences within
the cyathostomin population. Coronocyclus coronatus was used as the reference level
in this study because it did not belong to the genus Cylicocyclus, which has been
observed with less sensitivity to anthelmintic treatments. The interaction effect of
species with treatment, showed that in the presence of moxidectin, Cylicocyclus
auriculatus and Cylicocylus elongatus were less likely to be present than C. coronatus.
In the presence of pyrantel, C. elongatus, Cylicodontophorus bicornatus, and
Cylicostephanus minutus were less likely to be present than C. coronatus. The
interaction effect of treatment with days showed that in the presence of moxidectin,
with each unit increase in day, cyathostomin were less likely appear than
ivermectin. Species also showed differential recovery patterns by looking at the
interaction effect of treatment, species, and days. This interaction showed that in the,
presence of moxidectin, Cylicocyclus nassatus, Cylicocyclus radiatus, and
Cylicostephanus longibursatus were more likely to be present with each unit increase
in day than C. coronatus. This interaction also showed that C. nassatus, in the
presence of ivermectin, was less likely to be present with each unit increase in day
than C. coronatus.
Main effects of the regression were also significant such as species and
shedding status. C. nassatus and C. longibursatus had very positive relationships
indicating they were more likely to be present than C. coronatus regardless of
treatment or time. Shedding status showed that low shedders (EPG 0-200) and
moderate shedders (EPG 200-500) were less likely to have cyathostomin presence
than high shedders (EPG 500 +).
Description
Keywords
Cyantostomin, Anthelmintic treatment