Signs of moxidectin resistance

 Experts have been warning for some time of the danger of ending up with no effective
anthelmintics (dewormers). 

All the available classes of anthelmintic have shown declining efficacy as worms, particularly the cyathostomins (small redworms), become resistant. Moxidectin, a more recent addition to the arsenal is particularly useful for its action against encysted larvae. Until now it has remained relatively unscathed in the battle to hold back the advance of anthelmintic resistance. 

 

However, it seems now that the doomsday scenario is getting nearer as researchers in Australia have shown signs of resistance to moxidectin and combinations of anthelmintics.

 

Ghazanfar Abbas and co-workers conducted a study to assess the efficacy of commonly used anthelmintics against cyathostomins in Australian thoroughbred horses.

They carried out drug efficacy trials on two Thoroughbred stud farms in Victoria, Australia.

Horses were treated with single and combinations of anthelmintics. The researchers used the faecal egg count reduction test (FECRT) to assess the efficacy and egg reappearance period (ERP) of the anthelmintics. 

 

After treatment with an effective anthelmintic the faecal worm egg count (FEC) would be expected to be substantially reduced a couple of weeks later. So, for moxidectin, anything less than a 95% reduction in FEC two weeks after treatment would be taken as an indication of resistance.

 

The worm egg reappearance period (ERP) is the time taken for eggs to reappear in the faeces after successful treatment. It gives an early indication of the development of resistance. 

 

The research team found resistance to various anthelmintics and anthelmintic combinations, (including oxfendazole, abermectin and an oxfendazole/pyrantel combination).  

 

Although moxidectin was highly effective in one farm, producing a 100%  reduction in egg count two weeks after treatment, it showed a shortened ERP. (5 weeks – compared with the expected ERP when the drug is effective of 10 – 12 weeks). Resistance to moxidectin was found on the second farm with reduced efficacy of 90%.

A full report is published in Parasites and Vectors.

 

The authors conclude that the study provides the first evidence of moxidectin and multidrug-resistant (abermectin and combinations of anthelmintics) in cyathostomins in Australia. They suggest the need for continuous surveillance of the efficacy of currently effective anthelmintics and large-scale investigations to assess the ERP for various anthelmintics.

 

For more details, see:

 

Cyathostomin resistance to moxidectin and combinations of anthelmintics in Australian horses

Ghazanfar Abbas, Abdul Ghafar, John Hurley, Jenni Bauquier, Anne Beasley, Edwina J. A. Wilkes, Caroline Jacobson, Charles El-Hage, Lucy Cudmore, Peter Carrigan, Brett Tennent-Brown, Charles G. Gauci, Martin K. Nielsen, Kristopher J. Hughes, Ian Beveridge & Abdul Jabbar 

Parasites & Vectors volume 14, Article number: 597 (2021)

https://doi.org/10.1186/s13071-021-05103-8

 

See also the American Association of Equine Practitioners Parasite Control Guidelines: 

 

https://aaep.org/sites/default/files/Guidelines/AAEPParasiteControlGuidelines_0.pdf

Treating sarcoids with IL-2

A feline interleukin-2 immunomodulator (ALVAC-fIL2) shows promise as a possible treatment for equine sarcoid, a pilot study has shown.

Sarcoids are the most common skin tumour in horses. Currently there is no universally effective treatment, and if treatment fails the sarcoids will often come back worse than they were in the first place. Although the disease is rarely life-threatening, many horses with sarcoids are euthanased because the condition is untreatable or because the horse is unsellable. 

 

Interleukin (IL)-2 is one of the key cytokines (proteins involved in cell signalling). It stimulates cell mediated immunity, activating a range of T-cells. IL-2 is used in human medicine, including for treating cancerous conditions such as metastatic renal cell carcinomas and metastatic melanoma.

 

A canarypox virus vector, which has been genetically modified to contain a gene to produce IL-2, was used in the study. (The product is licenced for use in the treatment of fibrosarcoma in cats.) The technology is widely used in the production of vaccines for horses and other species, including some equine influenza and West Nile virus vaccines.

 

Corey Saba, of the University of Georgia College of Veterinary Medicine, Athens Georgia, and colleagues conducted a pilot study, which has been reported in the Journal of Veterinary Internal Medicine. The work was funded by Boehringer Ingelheim. 

 

Fourteen otherwise healthy horses were included in the study. For a start, each sarcoid was measured and photographed, then injected with 1ml ALVAC-fIL2 divided between four or five different sites. Treatment was repeated 1,3 and 7 weeks later.

 

The research team monitored the response for at least a year after the final treatment. They found that size of the sarcoid reduced in 12 of the 14 horses in the study, with complete remission occurring in seven cases (50%). Partial remission occurred in a further five (35%) 

 

An initial response was noted 34 – 406 days (median 89 days) after starting the treatment, and the best response occurred after 56 – 406 days (median 211 days). 

 

Other than transient mild-moderate focal inflammation in two horses, the injections were well-tolerated.

 

The researchers conclude “our results provide evidence that ALVAC-fIL2 is a safe, cosmetic, and effective treatment for sarcoid tumors in horses. Furthermore, our results provide a basis for a larger, placebo-controlled study to better define the role of this treatment in sarcoid tumors in horses.”

 

For more details, see:

 

ALVAC-fIL2, a feline interleukin-2 immunomodulator, as a treatment for sarcoids in horses: A pilot study

Corey Saba, Randall Eggleston, Andrew Parks, John Peroni, Eric Sjoberg, Shelbe Rice, Jesse Tyma, Jarred Williams, Deborah Grosenbaugh, A. Timothy Leard

Journal of Veterinary Internal Medicine (2022);1–6.

https://doi.org/10.1111/jvim.16425 

Wild parsnip and photo-dermatitis

Wild parsnip has been implicated as a cause of photodermatitis in horses.

 

Clinicians at the Freie Universität Berlin in Germany investigated a series of cases in which horses showed signs of inflammation of unpigmented skin.

 

Judith Winter and colleagues examined nine horses from stables in Berlin and Brandenburg, Germany, which showed variable degrees of erythema, scaling, crusting and necrosis of unpigmented skin on the head and prepuce. Most horses also showed signs of eye involvement: including conjunctivitis, photophobia and blepharitis (inflammation of the eyelids).

 

The clinicians found that, although the horses came from three separate yards, all stables were provided with hay from the same supplier.

 

Analysis of the hay showed that it contained large amounts of wild parsnip plants, including seeds and roots.

 

Wild parsnip (Pastinaca sativa) is widespread in Europe. It contains photodynamic pigments, known as furocoumarins. Contact with parts of the plant that contain the toxins, followed by exposure to sunlight, may cause photodermatitis, keratoconjunctivitis and uveitis. It is thought that lesions can occur due to both systemic uptake and direct topical contact.

 

Horses were treated with systemic anti-inflammatory medication as necessary, combined with topical treatment. They were protected from sunlight by being kept in a dark environment or by being treated with sunscreen and facemasks. Depending on the severity of the signs, treatment lasted from 6–30 days

 

Full details of the cases are published in BMC Veterinary Research. 

 

 

For more details, see: 

 

Photodermatitis and ocular changes in nine horses after ingestion of wild parsnip (pastinaca sativa)

JC Winter, K Thieme, JC Eule, E-M Saliu, O Kershaw, H Gehlen (2022).

BMC Vet Res 18, 80 

https://doi.org/10.1186/s12917-022-03162-2

Investigating worm control measures

 Horses and foals can carry many different parasitic worms in their intestines, some of which can cause severe disease. 

 

 Over recent years it has become recognised that some of the more important worms are developing resistance to the anthelmintics (dewormers) that are used to control them.

 

The seriousness of the problem is highlighted by the fact that resistance to all currently available classes of anthelmintics has been reported in both the cyathostomins (small redworm) and ascarids (large roundworm). Furthermore, there is currently no prospect of any new drugs in the pipeline.

 

It is becoming accepted that we need to adopt a more sustainable approach to deworming.

 

In a letter to the Veterinary Record, Dr Tim Mair and colleagues announced the launch of a collaborative project (ProjectWORMS) which they hope will produce recommendations about the best and safest way to prevent serious worm infestations, whilst limiting the further development of resistance to wormers.

 

The first step is to investigate current thinking and management practices with two online questionnaires – one for horse owner/keepers and one for stud owner/managers. This information is important to be able to develop and promote new and alternative ways of controlling worms that do not add to the problem of anthelmintic resistance

 

Dave Rendle, President Elect of the British Equine Veterinary Association (BEVA) said: “BEVA are pleased to be able to support this important piece of work which will inform decision-making around anthelmintic stewardship going forward. Anthelmintic resistance presents a serious and imminent threat to the equine industry."

 

To take part in the online survey, and for more information, see:

For horse owners/keepers: https://www.surveymonkey.co.uk/r/WORMSowner

And 

For stud owners/managers: https://www.surveymonkey.co.uk/r/WORMSstud

US vets help sought for back pain study

 Equine veterinarians in the United States are asked to complete a short online survey on the diagnosis, treatment and management of primary back pain.

 Marianne E. Marshall-Gibson is conducting the research as part of her American College of Veterinary Sports Medicine & Rehabilitation residency studies.

 

The goal is to determine 1) the preference of practitioners when treating primary back pain and 2) the preference of practitioners for treating impinging spinous processes ("kissing spine") in horses in the United States.

 

The survey is open until May 31^st, and can be accessed by the following link:

 

https://docs.google.com/forms/d/e/1FAIpQLSeaseBD40iLcO2VEO3B8zsMkO-4heQ-IfcqDEmM6sS_Lb-6hQ/viewform