Parasitism, Anthelmintics and Cushing’s in Horses

I have been waiting for this research: “Does Cushings impair a horse’s ability to resist parasitism?” Well, the answer is, “in some cases”. However, it still appears that there is a wide range of susceptibility among Cushinoid horses and testing should be done to identify those needing extra help, just like all horses.

In the second study below the efficacy of ivermectin in Cushinoid horses is examined. The disease does not seem to greatly affect efficacy though further work is suggested, as always.
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Strongyle egg shedding and egg reappearance periods in horses with pituitary pars intermedia dysfunction

Vet Parasitol. 2024 Mar 28:328:110176. doi: 10.1016/j.vetpar.2024.110176. Online ahead of print.
Authors
Adelaina Horner 1 , Nicholas J Bamford 2 , Michael J Stear 3 , David Piedrafita 1 , Abdul Jabbar 2 , Kristopher J Hughes 4 , Charles M El-Hage 5 , Sarah Preston 6
Affiliations

1 Institute of Innovation, Science and Sustainability, Federation University, Victoria 3350, Australia.
2 Melbourne Veterinary School, The University of Melbourne, Parkville, Victoria 3010, Australia.
3 School of Life Sciences, La Trobe University, Melbourne, Victoria 3086, Australia.
4 School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW 2678, Australia.
5 Melbourne Veterinary School, The University of Melbourne, Parkville, Victoria 3010, Australia. Electronic address: cmeh@unimelb.edu.au.
6 Institute of Innovation, Science and Sustainability, Federation University, Victoria 3350, Australia. Electronic address: s.preston@federation.edu.au.

PMID: 38603926
DOI: 10.1016/j.vetpar.2024.110176

Abstract

Pituitary pars intermedia dysfunction (PPID) is the most common endocrine disorder of older horses. Immune dysfunction in horses with PPID could increase susceptibility to infectious diseases, including strongyle infections; however, few data are available. The aim of this study was to determine if horses with PPID had increased strongyle faecal egg counts (FEC) compared with control horses, over a fourteen-week period in Victoria, Australia. Clinical signs and plasma adrenocorticotropic hormone (ACTH) concentrations were used to categorise horses into PPID (n=14) or control (n=31) groups. Faecal samples were collected for FEC determination prior to anthelmintic treatment, and fortnightly post-treatment for each horse. Generalised linear mixed modelling, using a gamma distribution, was used to compare differences between groups in the repeated measures study. The confounding variable of age was controlled for as a fixed effect. Following anthelmintic treatment, mean FEC was greater for the PPID group compared to the control group on day 56 (405 ± 756 eggs per gram [EPG] vs 40 ± 85 EPG, p=0.05) and day 70 (753 ±1598 EPG vs 82 ±141 EPG, p=0.04). There were no differences in mean FEC between groups on days 84 and 98. Cumulative FEC (day 14 to day 98) was significantly greater for the PPID horses than control horses (2118 ± 4016 EPG vs 798 ± 768 EPG, p<0.0001). Group egg reappearance period was shorter for PPID horses (day 56 post-anthelmintic treatment) compared to control horses (day 70) and 30% of the PPID horses reached a FEC threshold of >200 EPG on day 42, compared to 0% of control horses (p=0.02). These results suggest that the rate of a re-established patent infection between groups could be different due to a comprised immune response in PPID horses or differences in the host-parasite relationship regarding encysted stage larvae. However, despite differences between groups, some horses with PPID consistently had no detectable or low FEC (<200 EPG) during the study period. These findings highlight the importance of individual FEC monitoring to determine if anthelmintic treatment is required, in line with sustainable parasite management practices.

Keywords: Endocrine; Equine; Faecal egg count; Pituitary pars intermedia dysfunction; Strongyle.

Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.

Ivermectin performance in horses diagnosed with equine endocrine disorders

Vet Parasitol. 2024 Apr 5:328:110182. doi: 10.1016/j.vetpar.2024.110182. Online ahead of print.
Authors
M K Nielsen 1 , C A Finnerty 2 , N E Ripley 2 , A E Page 2 , M E McClendon 2 , A A Adams 2
Affiliations

1 Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, 1400 Nicholasville Rd, Lexington, KY 40503, USA. Electronic address: martin.nielsen@uky.edu.
2 Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, 1400 Nicholasville Rd, Lexington, KY 40503, USA.

PMID: 38603925
DOI: 10.1016/j.vetpar.2024.110182

Abstract

Anthelmintic performance against equine cyathostomins can be evaluated by two different non-terminal measures; the Fecal Egg Count Reduction Test (FECRT) and the Egg Reappearance Period (ERP). Most available FECRT and ERP data have been determined in populations of young horses, and very little information is available from mature and senior horses. Furthermore, it is unknown how commonly occurring equine endocrine disorders such as Insulin dysregulation (ID) and Pituitary pars intermedia dysfunction (PPID) may interfere with these measurements, but it has been suggested that horses with these conditions could be more susceptible to parasitic infections. A research population of senior horses and horses with or without PPID, ID, or both were enrolled in this study. All strongylid egg count positive horses were included in an ivermectin (200 μg/kg) efficacy study. These were distributed among the following groups: ID: six, PPID: three, PPID and ID: seven, and healthy controls: three. Strongylid fecal egg counts were determined on the day of ivermectin administration, at two weeks post deworming, and on weekly intervals until eight weeks post treatment. Determination of FECRT and ERP were carried out following World Association for the Advancement of Veterinary Parasitology guidelines. Results revealed high ivermectin efficacy with mean egg count reduction at 99.7% or above in all groups at two weeks post treatment. Egg reappearance was documented at six and seven weeks in the ID and PPID/ID groups, respectively, whereas the PPID and healthy control groups both had ERP at 8 weeks. Statistical analysis found no significant differences in egg count levels between groups during the study. The expected ERP for ivermectin is 8-10 weeks, meaning that two of the groups displayed shortened ERPs. However, due to the small group sizes, these data should be interpreted with caution. Nonetheless, results do indicate a need for further investigation of the possible influence of endocrine disorders on anthelmintic performance in horses.

Keywords: Anthelmintic; Cyathostomin; Efficacy; Egg reappearance period; Treatment.

Copyright © 2024 Elsevier B.V. All rights reserved.

• This topic was modified 6 months ago by Robert Oglesby DVM.