ShapeShapeauthorShapecrossShapeShapeShapeGrouphamburgerhomeGroupmagnifyShapeShapeShapeShape

Keeping up to date with changing science

by
01 July 2009, at 12:00am

MARK TABACHNIK reports on a day spent learning about equine influenza and worming strategies

WARNINGS against complacency were the take-home message from world-class speakers at a stimulating one-day course held at Alton Towers on 30th April. 

The focus of this “Learn and Earn” CPD day run by Merial Animal Health was to deliver up-todate information primarily concerning equine influenza (EI) and worming strategies. These topics, so fundamental to the working lives of equine vets, are ever changing as the science is constantly being updated.

Dr Richard Newton from the Animal Health Trust kicked off the day with a talk entitled “Equine ’flu – the latest developments”. 

There are still three main ways to diagnose EI infection: virus isolation is performed using embryonated hens’ eggs or in cell culture; ELISA tests detect EI nucleoproteins present in respiratory samples; quantitative polymerase chain reaction (qPCR) is used to quantify EI RNA in respiratory samples. All three techniques compare favourably. 

Dr Newton went on to describe the importance of haemagglutinin (HA) sequencing. The HA segment of EI, as the dominant and major influenza antigen used for cellular attachment, changes its structure over time to evade the host’s immune response. This antigentic drift accounts for the evolution of EI and can be represented as an EI family (phylogenic) tree. This tree has branched into two distinct lineages: American and European. 

In 1995 the World Health Organisation recommended that representatives of both lineages be included in vaccinations. The EI outbreaks in both Newmarket and South Africa in 2003 confirmed further evolution of the virus. In 2004, the Expert Surveillance Panel recommended updating the American lineage component to include either Ohio 03 or South Africa 03. 

New technology 

Dr Jules Minke from Merial Equine Health Europe spoke about the new technology used in the Merial Protequflu EI vaccines. Protequflu is the first EI vaccine to use a recombinant viral vector, the canarypox virus, coding for the HA glycoprotein of both American and European strains. The inclusion of Ohio 03 makes it the first and only EI vaccine to be updated in Europe. 

The canarypox virus is a nonreplicative vector. The virus vector enters horse cells and is processed by the cytoplasm. HA glycoproteins are synthesised de novo and presented on the cell’s surface. This leads to a powerful cell-mediated immunity. Dr David Homer from Merial Australia described the time-line of events when EI struck Australia in 2007. Australia is one of the few countries where EI is not endemic, with the majority of the equine population unvaccinated and naïve to the virus. 

EI was imported in a clinically healthy stallion to a quarantine station near Sydney. Here, due to lax quarantine restrictions, the virus spread through the quarantine facilities and into the outside world. Within two months more than 76,000 horses were affected. Dr Homer described the setting up of a buffer zone to allow the disease to exhaust itself, surrounded by a ring vaccination zone.

The Australian authorities used Proteqflu as their main vaccination programme. Since that time, EI has been eradicated and Australia is now again EI free. 

In the afternoon, Professor Sandy Love from the University of Glasgow gave us an update on current issues in equine parasite control.

Prof. Love felt that whilst Strongylus vulgaris was largely extinct, issues such as anthelmintic resistance, wormer usage rates, herbal wormers and serial overuse of moxidectin were of greatest relevance to the veterinary profession. 

There is now widespread cyathastome resistance in horses to benzimidazoles and pyrantel, with one reported case of moxidectin resistance and some cases of reduced efficacy of ivermectin. Anthelmintic resistance is irreversible as the genetic advantage is passed on from one generation of worms to the next. 

Prof. Love discussed the concept of “refugia”. This is the proportion of parasites not exposed to anthelmintics at the point when the animal is dosed. There can be a high percentage of parasites in refugia at any time due to the number of eggs in faeces and larvae on the pasture (depending on the amount of poo picking). 

Although not perfect, one way to detect anthelmintic resistance is using a faecal egg count reduction test. Take a faecal worm egg count on day 0 and days 10-14 post worming. A less than 95 % reduction indicates resistant worms. 

Opportunity 

In the UK, anthelmintic usage rates are poor with an average of just one wormer purchased per horse per year. Herbal de-wormers are sold in considerable quantities but without any evidence that they work. 

Prof. Love felt that “serial” deworming programmes with moxidectin are a bad idea as they will drive pressure for worm resistance. His advice is to use moxidectin once a year in the autumn. 

Prof. Love described “best practice” in equine parasite control. This would involve customising programmes based on management conditions specifically targeting cyathostomins and tapeworms. 

This would entail monthly worm egg counts on all animals, with dosing only those with counts over 200 eggs per gram. Pasture hygiene and, where possible, mixed species co-grazing are good ways to keep worm numbers low. 

Tapeworms should be either targeted on the basis of serological results or annually treated using praziquantel in the worming programme. Prof. Love warned that serological evidence of tapeworm infection can take several months to return to normal. 

The “Earn” part of the day was a presentation by Caroline Johnson from Prescription Marketing focusing on the changing face of equine practice. A strategy embracing opportunities to change and becoming more competitive in the face of increasing competition and financial uncertainty was discussed. 

Caroline emphasised the importance of communication and presentation skills when dealing with clients, and the fact that vets are well placed to add value through their transactions. 

This could be achieved not only through provision of medicines, but advice, reminders and after-sales support. Referring to the current economic climate, Caroline’s takehome message was, “Where there’s change there is opportunity.” 

Summary 

This was a fascinating day’s CPD with many interesting subjects. Dr Emma Batson from Merial quoted that only 38 % of the equine population is vaccinated against EI. There are many reasons why we should not be complacent – this poor level of coverage of the equine population leaves us unprotected in the event of a mass EI outbreak. 

Vaccines using old strains of EI are common. The Australian ’flu outbreak is an example of the repercussions of lax biosecurity. 

Even our approach to de-worming, with the overuse of moxidectin and the emergence of anthelmintic resistance, proves that the responsible equine vet needs to exercise caution in the approach to the modern de-worming programme.