Effect of PPID on egg shedding after deworming

It has been suggested that horses with hormonal disorders, such as insulin dysregulation and
Pituitary Pars Intermedia Dysfunction (PPID), may be more susceptible to worm infections. 

Horses with PPID often have a weakened immune system, which can allow worms, such as cyathostomes, to thrive more easily compared to healthy horses. These horses may also not respond as effectively to standard deworming treatments due to their altered immune function.

 

A study conducted in Australia aimed to determine whether horses with PPID had increased strongyle faecal egg counts (FEC) compared with control horses.

 

The study, led by Adelaina Horner, took place over a fourteen-week period and involved adult horses and ponies over eight years old in Victoria, Australia. All horses lived on pasture and had not been dewormed for at least three months prior to the study. A total of 45 privately owned horses and ponies met the criteria for inclusion, with 14 horses diagnosed with PPID and 31 serving as controls. PPID diagnosis was confirmed by elevated plasma ACTH concentrations (above 120 pg/mL) along with at least one clinical sign of the disorder.

 

All horses were dewormed with a standard dose of a commercially available ivermectin product. Faecal egg counts were taken before treatment and then every two weeks for 14 weeks. A FEC of 200 eggs per gram (EPG) or higher was used as the cutoff for significant worm burden.

 

The results showed that the egg reappearance period (ERP) after deworming was shorter in PPID horses, and cumulative FEC after deworming was higher in these horses. However, the researchers noted that some PPID horses consistently had no detectable eggs or low EPG (≤ 200) throughout the study, and this could not be explained by observed husbandry practices.

 

Worm eggs collected during the study were cultured in the laboratory, and examination of the larvae confirmed that all worms were cyathostomin species.

 

The researchers advise monitoring egg shedding before anthelmintic treatment in PPID horses, in line with sustainable worm management guidelines, as some PPID horses consistently showed low FEC results.

 

While hormonal disorders like PPID do not directly cause an increase in parasitic infections, they can impair the horse’s immune system and overall health, making them more vulnerable to worm infections and potentially reducing the effectiveness of treatments. Effective management of both the hormonal disorder and parasitic infections is crucial for maintaining the health of affected horses.

 

 

For more details, see: 

 

Strongyle egg shedding and egg reappearance periods in horses with pituitary pars intermedia dysfunction

Adelaina Horner, Nicholas J. Bamford, Michael J. Stear, David Piedrafita, Abdul Jabbar, Kristopher J. Hughes, Charles M. El-Hage, Sarah Preston

Veterinary Parasitology (2024) Vol 328, 110176

 

https://doi.org/10.1016/j.vetpar.2024.110176

Chicory: a natural anthelmintic?

(C) Malsa et al CC BY-NC-ND 4.0

Recent research in France suggests that chicory shows promise as a natural anthelmintic for horses.

 

Cyathostomes (small redworms) are the most common gastrointestinal parasites in horses and are now the leading cause of parasite-related equine diseases. The larval stages of these worms can damage the large intestinal wall, leading to diarrhoea, colic, and loss of condition.

 

These parasites are also important because they are the most likely to develop resistance to the anthelmintics used to control them. Consequently, there is a shift away from regular deworming to reduce the development of anthelmintic resistance. Limiting unnecessary anthelmintic use is also important due to its environmental impact, particularly on insects that feed on horse manure.

 

Chicory (Cichorium intybus), a common forage plant, has been studied for its potential anthelmintic (anti-parasitic) properties, particularly in ruminants. Research has shown that certain compounds in chicory, such as sesquiterpene lactones, may have effects against gastrointestinal parasites.

 

Joshua Malsa and colleagues investigated the effect of horses grazing pasture containing a high proportion of chicory on faecal worm egg production and larval development. The research is reported in the International Journal for Parasitology: Drugs and Drug Resistance.

 

Twenty naturally infected 2-year-old saddle horses were used in the study. All horses were born and raised on the premises where the study took place and were naturally exposed to the same parasite populations. They had not been dewormed for 264 days before the onset of the trial. The last treatment given had been moxidectin.

 

 The horses were divided into two groups, each of ten horses, and were grazed either a field of chicory or a control field of mixed pasture

 

The researchers found a significant reduction in FEC after 16 days of grazing on chicory. By the end of the study grazing on chicory had an efficacy slightly lower than that of pyrantel treatment (85.5% vs 99.3% FECR for chicory and pyrantel respectively). 

 

The chicory diet also reduced the development of eggs into third-stage larvae in faeces and affected the diversity of the cyathostomin community.

 

They conclude: “Our study demonstrated the efficacy of grazing chicory (cv. Puna II) to reduce cyathostomins egg excretion and larval development in horses. The magnitude of this effect was almost as high as expected from synthetic drugs, although we identified differential sensitivity between species.”

 

Integrating chicory into a broader parasite management plan could be beneficial, especially in reducing reliance on chemical dewormers and combating drug resistance.

 

 However, while it might complement conventional parasite control methods, it should not yet be considered a replacement for standard anthelmintics without further research.

 

 

For more details, see:

 

Joshua Malsa, Leslie Boudesocque-Delaye, Laurence Wimel, Juliette Auclair-Ronzaud, Bertrand Dumont, Núria Mach, Fabrice Reigner, Fabrice Guégnard, Angélique Chereau, Delphine Serreau, Isabelle Théry-Koné, Guillaume Sallé, Géraldine Fleurance,

Chicory (Cichorium intybus) reduces cyathostomin egg excretion and larval development in grazing horses.

International Journal for Parasitology: Drugs and Drug Resistance, (2024) Vol 24,100523

 

https://doi.org/10.1016/j.ijpddr.2024.100523

New internal parasite guidelines from AAEP

The American Association of Equine Practitioners (AAEP) has issued revised Internal Parasite Control Guidelines to help minimise the risk of parasitic disease and maintain the effectiveness of current drugs for as long as possible by delaying further development of anthelmintic resistance.

The guidelines, originally created in 2013 and last revised in 2019, account for recent advances in knowledge concerning increased anthelmintic resistance and optimisation of parasite control management practices. They also address common misconceptions and offer parasite control program recommendations for senior horses (over 15 years old), mature horses (between 5 and 15 years old), and young horses (under 5 years old).

The guidelines were reviewed and updated by the AAEP Internal Parasite Control Guidelines Task Force, chaired by Dr. Nielsen and comprised of 10 AAEP members predominantly board certified in veterinary internal medicine, veterinary parasitology and/or veterinary microbiology. 

“We have seen dramatic development in the field of equine parasite control over the past 10 years, since we first launched these guidelines, and we work hard to keep our recommendations up to date,” said Martin Nielsen, DVM, PhD, DVSc, DAVCM, DEVPC, Schlaikjer Professor of Equine Infectious Diseases at the University of Kentucky.

Important conclusions to be drawn from the revised guidelines are to:

• Perform fecal egg count reduction tests annually to ensure that you are using effective dewormers in every herd or barn.
• Recognize that no anthelmintic will eliminate all parasitic stages from a horse.
• Continue using fecal egg counts once or twice per year to stratify horses into low, medium and high shedders to reduce pasture contamination.
• Deworm all horses at a baseline rate and target selected horses more often based on fecal egg counts.
• Not use fecal egg counts to diagnose disease in horses as there is no correlation between fecal egg counts and disease-causing parasite life stages.
• Discontinue deworming all horses with fixed intervals year-round and stop blindly rotating anthelmintic classes.

View the guidelines at https://aaep.org/resource/internal-parasite-control-guidelines.

You can access the entire guidelines document by clicking the Download Resource button.

Effect of anthelmintics on the gut microbiome

 While anthelmintic treatments are invaluable for controlling parasitic worm infections, new research shows they can also have unintended consequences on the gut microbiota. 

Michel Boisseau and colleagues conducted a study to explore how helminths, particularly cyathostomins, interact with the gut microbiota in their host animals. 

 

The research team observed naturally infected ponies to track changes in this relationship over time, both before and after treating them with pyrantel. (Pyrantel targets adult cyathostomins without affecting larval stages in the gut wall.) 

 

They also looked at how the ponies' blood gene expression responded to the anthelmintic treatment. Their work is reported in iScience.

 

The study involved 40 naturally infected Welsh pony mares, divided into four groups based on their worm burden and whether they received pyrantel treatment. 

 

Among the high shedding ponies, the researchers identified 14 species of cyathostomins, the most abundant of which was Cylicocyclus nassatus. They found that ponies with high cyathostomin egg counts had a richer and more dynamic gut microbiota. The presence of butyrate-producing Clostridia seemed to play an important role in maintaining stability within the ecosystem, while also bolstering host tolerance towards cyathostomin infections. Genes involved in B-cell activation and IgA synthesis were upregulated in high shedding ponies.

 

The administration of anthelmintic treatment induced a dramatic shift in the gut environment and microbial community dynamics, with the population being less stable. These changes were still present 7 days after treatment, and to a lesser extent after 15days. Anthelmintic treatment only had a limited effect on the host blood gene expression.

 

The researchers conclude: “These observations highlight how anthelmintic treatments alter the triangular relationship of parasite, host, and gut microbiota and open new perspectives for adding nutritional intervention to current parasite management strategies.”

 

 

For more details, see:

 

Michel Boisseau, Sophie Dhorne-Pollet, David Bars-Cortina, Élise Courtot, Delphine Serreau, Gwenolah Annonay, Jérôme Lluch, Amandine Gesbert, Fabrice Reigner, Guillaume Sallé, Núria Mach,

Species interactions, stability, and resilience of the gut microbiota - Helminth assemblage in horses,

iScience, Vol 26, 2, (2023), 106044.

 

https://doi.org/10.1016/j.isci.2023.106044

 

Signs of anthelmintic resistance in tapeworms?

Horses frequently carry tapeworm infections, particularly Anoplocephala perfoliata. While these parasites can be linked to colic, most infected horses generally tolerate them well and show no adverse signs.. 

Tapeworms are commonly found in horses grazing on pasture because the intermediate host, an oribatid mite, resides in the pasture environment. In contrast, tapeworms are seldom observed in horses in dry and arid conditions.

 

Two drugs, praziquantel and pyrantel, are commonly employed for tapeworm control and are generally acknowledged as effective in managing these parasites.

 

While the issue of anthelmintic resistance has garnered widespread attention concerning roundworms, it has not received as much consideration in relation to tapeworms. Anthelmintic resistance in equine tapeworms, as in other parasites, poses a significant challenge in the management of horse health. 

 

In contrast to roundworms, which can be easily diagnosed and assessed through a faecal egg count, tapeworms present a greater challenge as they excrete eggs sporadically. This erratic pattern not only complicates diagnosis but also poses challenges in evaluating the response to treatment and identifying anthelmintic resistance.

 

In a report from North America, Martin K. Nielsen, affiliated with the M.H. Gluck Equine Research Center in the Department of Veterinary Science at the University of Kentucky in Lexington, USA, sheds light on an apparent treatment failure involving praziquantel and pyrantel pamoate against tapeworms. The report relates to animals on a Thoroughbred stud farm in Central Kentucky in 2023. The findings have been published in the "International Journal for Parasitology: Drugs and Drug Resistance."

 

Fifty-six young horses were initially dewormed using a combination of ivermectin and praziquantel, followed by a treatment with pyrantel pamoate. The effectiveness of the deworming was assessed by checking the number of parasite eggs in their faeces on the day of treatment and again 14 days later.

 

Two groups of female horses, consisting of 39 and 45 individuals, were also given the ivermectin/praziquantel treatment, and their faeces were examined before and after treatment.

 

In the yearlings, the overall effectiveness against tapeworms, measured by FECR levels, was 23.5% for praziquantel and 50.9% for pyrantel pamoate. 

 

Praziquantel successfully removed tapeworm eggs in three out of 17 yearlings, but five other yearlings changed from having no tapeworm eggs to having them after treatment. 

 

Unfortunately, pyrantel pamoate did not eliminate tapeworm eggs in any of the 14 yearlings that tested positive for tapeworms.

 

Among the tested mares, nine out of 84 were found to have tapeworm eggs, and after praziquantel treatment, seven of them still tested positive for tapeworm eggs.

 

The results also showed that the ivermectin and pyrantel pamoate treatment was not very effective against roundworm (strongylid)  parasites in the young horses. The average reduction in the number of parasite eggs in their faeces was 75.6% or less, and the upper limit of the 95% credible interval was below 90% in all cases.

 

Nielsen highlights that the results differ significantly from the initial field efficacy studies conducted for both active compounds, raising concerns about the potential development of anthelmintic resistance.

 

He suggests the need for continued research and advancements in parasite management strategies to develop more sustainable approaches in addressing equine tapeworm infections.

 

 

 

For more details, see:

.

Apparent treatment failure of praziquantel and pyrantel pamoate against anoplocephalid tapeworms

M K Nielsen 

Int J Parasitol Drugs Drug Resist. 2023 Aug:22:96-101.

 doi: 10.1016/j.ijpddr.2023.06.002

Careful use of anthelminitcs can help limit resistance

 Recent research suggests that employing selective treatment regimens can significantly reduce the
development of anthelmintic resistance. This is particularly relevant in the context of parasites such as the cyathostomins (small redworms), which are among the most common internal parasites of horses. These parasites have developed resistance to various deworming drugs over the years due to their widespread and indiscriminate use.

In Sweden, a country known for its controlled approach to anthelmintic use, a study was conducted to investigate the presence of resistance to ivermectin, a commonly used deworming medication. The research found no evidence of resistance to ivermectin in cyathostomes in Sweden.

 

ML resistance has been observed in cyathostomins worldwide. However, the current situation in Sweden is unclear. Routine anthelmintic treatment of horses without prior diagnostic tests is rare in Sweden, since anthelmintic drugs were restricted to being available on prescription only in 2007. What effect would this have had on the development of ML resistance in the country?

 

To assess the effectiveness of deworming treatments, two common tests are used: the faecal egg count reduction test (FECRT) and the egg reappearance period (ERP) after treatment. FECRT evaluates whether a dewormer successfully reduces the number of internal parasite eggs in the horse's faeces. Samples are taken before treatment and around 10 to 14 days after deworming, and the two egg counts are compared. A high reduction percentage indicates that the dewormer is effective, while a low reduction percentage suggests potential resistance.

 

As internal parasites develop resistance to dewormers, the egg reappearance period (ERP) shortens, meaning that eggs reappear in the faeces more quickly after treatment.

 

A study led by Ylva Hedberg Alm and her colleagues aimed to assess FECRTs and ERPs following ivermectin (IVM) treatment in Swedish horses. Sixteen equestrian establishments, each with at least six horses excreting a minimum of 150 eggs per gram of faeces (EPG) during screening, were included in the study. FECRTs and ERPs were evaluated in faecal samples before and after IVM treatment (200 µg/kg) and for eight weeks afterward.

 

The questionnaire responses revealed that 69% of establishments administered anthelmintic treatments based on faecal diagnostics. All establishments achieved a high FECRT, exceeding 99.0%, and ERPs ranged from six to over eight weeks. Notably, younger horses were found to excrete cyathostomin eggs earlier after treatment than older horses.

 

The researchers also observed that riding schools, stud farms, and those not segregating summer and winter paddocks had shorter egg reappearance periods.

 

In conclusion, this study in Swedish equestrian facilities employing selective anthelmintic treatment revealed that the establishments maintained longer ERPs and showed no confirmed resistance to ivermectin. These findings support the use of selective deworming strategies as a means of reducing the risk of anthelmintic resistance in horses. The full report is available in Veterinary Parasitology.

 

For more details, see:

 

Retained efficacy of ivermectin against cyathostomins in Swedish horse establishments practicing selective anthelmintic treatment

Ylva Hedberg Alm, Eva Osterman Lind, Frida Martin, Rebecca Lindfors, Nina Roepstorff, Ulf Hedenström, Isabelle Fredriksson, Peter Halvarsson, Eva Tydén

Veterinary Parasitology (2023) Vol 322, 110007

 

https://doi.org/10.1016/j.vetpar.2023.110007

Ivermectin resistance in small redworms

 In a recent study conducted in Brazil, it was discovered that there is widespread resistance to ivermectin among cyathostomins (small redworms) in most of the properties evaluated. This finding is concerning, as it has been increasingly recognised that important equine worms are developing resistance to commonly used anthelmintics.

The severity of this issue is underscored by the fact that resistance to all currently available classes of anthelmintics has been reported not only in cyathostomins but also in ascarids (large roundworms). Compounding the problem is the lack of new drugs on the horizon to combat this resistance.

 

Brazil is home to one of the largest horse populations globally, estimated to range from 5 to 6 million. In light of this, Giordani Mascoli de Favare and colleagues undertook a year-long research study in the western region of São Paulo state. The study aimed to assess the effectiveness of ivermectin as an anthelmintic in naturally infected horses on 12 breeding farms, involving a total of 123 horses.

 

To evaluate resistance in cyathostomins, the standard faecal egg count reduction (FECR) test was employed. If the FECR does not show a reduction of 95% or more after treatment with a macrocyclic lactone like ivermectin, it is indicative of resistance. Prior to the study, the horses had not received any anthelmintic treatment for at least 60 days. Each horse was orally administered the recommended dose of ivermectin paste based on its weight. Faecal samples were collected at the beginning of the treatment and 14 days later.

 

The results of the study revealed that in five of the properties, the FECR was below 90%, indicating significant cyathostomin resistance to ivermectin. Additionally, three properties showed a FECR between 90% and 95%, further indicating the presence of resistance. Only on four of the twelve properties did the faecal egg count reduction exceed 95%.

 

The authors of the study explain that in Brazil, the control of equine gastrointestinal parasites typically involves treating the entire herd without prior diagnosis and regularly rotating anthelmintic drugs. However, these findings highlight the urgent need for alternative strategies and interventions to effectively manage anthelmintic resistance in horses.

For more details, see:

Anthelmintic resistance of horse strongyle nematodes to ivermectin in São Paulo state, Brazil

Giordani Mascoli de Favare , Isabela de Almeida Cipriano, Tábata Alves do Carmo,  Mateus Oliveira Mena,   Gabriel Jabismar Guelpa, Alessandro Francisco Talamini do Amarante,  Ricardo Velludo Gomes de Soutello

Veterinary Parasitology: Regional Studies and Reports

Vet Parasitol Reg Stud Reports. (2023) Jun;41:100864.

 https://doi.org/10.1016/j.vprsr.2023.100864

Can probiotics help reduce parasite shedding in foals?

Probiotics are frequently added to horses’ diets with the goal of promoting a healthy microbial environment in the intestinal tract. But does their use have any effect on the worm burden in the gut?

 Research by Dr Robert Jacobs and colleagues at the Purina Animal Nutrition Center suggests that giving probiotics to foals may reduce the number of intestinal parasites they carry.

 

The research was presented at the 2021 virtual Equine Science Symposium. An abstract is published in the Journal of Equine Veterinary Science.

 

Twenty-nine quarter horse foals took part in the study over three consecutive foaling seasons.  Fifteen foals chosen at random were given a probiotic paste twice daily for eight days starting two days after being born. Fourteen foals received no probiotic.

 

(Each dose of probiotic paste contained 2.5 × 109 cfu each of B. subtilis, B. infantis, and L. acidophilus.)

 

The groups were managed similarly – being fed twice daily and being turned out into dry lots during the day.

 

When the foals were 150 days old, the researchers collected faecal samples. The foals had not received any anthelmintic before then. 

 

Analysis showed that “foals in the treatment group had fewer strongyle (1.07 vs 4.57/gm of feces; P = 0.02) and roundworm eggs (101.33 vs 216.00/gm of feces; P = 0.01) than those from the control group.”

 

The authors conclude “that the administration of the probiotic paste to otherwise identically managed groups of foals may reduce their overall parasite load. “

 

They suggest that “further research is needed to understand the mechanisms by which this is occurring and to determine if these effects persist.”

 

For more details, see:

 

Probiotic administration post-foaling may reduce parasite shedding in foals

R.D.Jacobs, M.L.Jerina, B.A.Tremayne

Journal of Equine Veterinary Science (2021)

Volume 100, May 2021, 103565

https://doi.org/10.1016/j.jevs.2021.103565

Award for worm film series

A series of short films on horse worms has been awarded best educational film at the EQUUS International Film and Arts Festival.

Martin Nielsen, Schlaikjer Professor of Equine Infectious Disease, at the University of Kentucky’s Gluck Equine Research Center, set out to produce a series of films to put the record straight on best practices in equine parasitology.

Launching the series of 18 videos in October 2019 he said: “I wanted to try and address common misconceptions and myths in equine parasite control. In this series, I’ll address one myth or misconception at the time and in 45 seconds or less, I will explain why it is exactly that – a myth or misconception. These will be interspersed with a few longer videos providing more background information and highlighting recent research findings.”

 Deworm Debunk topics included: deworm at first frost? drug rotation; five-day dewormers; daily dewormers; and how the weather affects parasite transmission.

“As academics and scientists in today’s world, we need to make an effort to communicate our research findings to our end users,” he said. “We need to establish ourselves as the source of solid, evidence-based, and unbiased information. Communication on social media is a must for scientists because that platform is now an integrated part of society and where people acquire and exchange information."

He also showed that such films could be made on a limited budget: “I wanted to make a point out of not needing elaborate equipment or technical assistance. These videos were all shot by an iPhone, and I edited them myself on my laptop computer.”

The “Deworm Debunk” video series were awarded Best Educational Film at the 2019 International EQUUS Film Festival.

The EQUUS Film & Arts Fest took place over four days in December 2019 at the Kentucky Horse Park. Founded in 2013 by equestrian enthusiast, Lisa Diersen, the festival is billed as the first event of its kind to offer a home to the storytellers of the horse world, with films, documentaries, videos, commercials, and shorts from around the world and cultural elements of fine equestrian art and literature.

The first Deworm Debunk video can be found on YouTube, here:

https://www.youtube.com/watch?v=JsF8f7QdOrs

Blood test for small redworms

A new blood test for small redworms (cyathostomins) is due to be launched in the United Kingdom.

There is a welcome emphasis now on only deworming horses when they need it. This has become necessary because of the spread of anthelmintic-resistant parasites and the need to reduce the use of anthelmintics. 

Small redworms (cyathostomins)are the main culprits. Faecal worm egg counts can detect the presence of adult worms in the intestinal tract. But until now there has been no way of knowing whether a horse is carrying inhibited larvae in the gut wall. Consequently, routine treatment for larval stages during the winter has become the recommended tactic. However, this approach results in some horses being treated unnecessarily, risking stimulating anthelmintic resistance.

Scientists at the Moredun Research Institute in Scotland, led by Professor Jacqui Matthews, have been developing a blood test for larval cyathostomins. That work, largely funded by The Horse Trust, is now coming to fruition with a commercial version of the test due to be launched next month (September 2019) by Austin Davis Biologics (ADB).

The new test can detect all stages of small redworm infections, including, crucially, the encysted larval stage.

Dr Corrine Austin, of ADB said “We are thrilled to be making this test available to horse owners after extensive research has been conducted to achieve high accuracy.” 

Prof Matthews said: “It is great to see the commercialisation of this much-needed test to support sustainable worm control in horses.”

“The test fills an important gap in our diagnostic toolbox and will enable horse owners to work with their veterinarians in targeting anthelmintic treatments against cyathostomin infections and, hence, help protect these important medicines for the future.”

For more details, see:

https://www.austindavis.co.uk/