RECENTLY, I watched the Elancosponsored webinar on “real world flea control”, delivered by Dr Michael Dryden and produced by The Webinar Vet.
Webinars have become an increasingly popular medium for CPD in the last few years, and make an attractive tool for both vets and pharmaceutical companies alike.
For the pharmaceutical companies they allow them to offer sponsored CPD to a huge audience of veterinary professionals at relatively low cost, while for the individual practitioner they provide a handy means to make up CPD hours free of charge.
That the content of the webinars usually promotes some product of the company that sponsors it should not detract from the quality of the lecture nor indeed the science therein; to me it seems a genuine win-win situation.
As a locum vet, CPD hours are precious, and the convenience of sitting down to lunch in practice, or sipping a cuppa at home while catching up on some often very relevant material, is a huge bonus. Especially given that the speakers are frequently experts in their field, keen to share the most up to date thinking.
The real world flea control webinar covered three areas: the history of flea treatment leading up to our current understanding and rationale of flea control; a scientific trial comparing the efficacy of two products – spinosad and fipronil; and finally a question and answer session with Dr Dryden.
It is interesting to see how far flea control has come in the last 30 years, but more fundamentally it is useful to remind oneself of the reasons for using flea products in the manner we do. As with so many parts of daily general practice, repetition of seemingly mundane practices can lead one to forget the reasoning that underpins them and the reasons why we do them.
In this case, flea control is important, if not essential in the day-to-day wellbeing of most pets. Fleas cause pruritus, or in some cases allergic dermatitis, and no animal should be allowed to suffer the indignity of having to live with that, especially as freedom from disease is one of the pillars of animal welfare and something it is our duty to maintain.
In order to prevent this we now have an armoury of safe and effective products at our disposal. Whatever the product though, the aim of treatment is the same: to break the reproductive cycle of the flea and thus make the population of fleas living on that pet and in that household extinct.
Broadly speaking, the products can be divided into those that kill the adult fleas on the pet, and those that prevent maturation of the juveniles (the insect growth regulators or IGRs). Both effectively break the life-cycle of the flea and prevent further generations from reproducing.
The main thrust of the webinar looked at the results of a study undertaken by Dr Dryden into the efficacy of spinosad. The study had been prompted by a bit of a paradox. The initial laboratory trials of spinosad had been very good, yet some more recent ones had cast doubt on its efficacy, particularly in relation to its residual activity on the pet.
Puzzling
More puzzlingly, however, Dr Dryden was still hearing excellent reports of spinosad from vets in general practice (and this is a man who answers over 500 e-mails and phone calls every year)! So it was decided to put together a study to decide one way or another.
With this in mind, an in-home (rather than a laboratory) investigation was undertaken, comparing spinsoad to fipronil in a head-to-head study in clientowned dogs. The results were surprising. In the more than 120 households assessed across the southern USA (where fleas can be particularly bad), spinosad gave statistically better results than fipronil in the three objectives examined:
- the number of flea-free dogs at the end of the study (95% with spinosad v. 38% with fipronil);
- the reduction of owner reported pruritus; and
- the reduction in the mean flea count on each dog (99.9% with spinosad v. 88.4% with fipronil after three treatments over 90 days).
The results clearly demonstrate that spinosad provides a better level of flea control under conditions of natural challenge – ultimately what is most important to the owner.
Dr Dryden went on to highlight a number of points, illustrated by individual cases, which are important for vets to remember when administering flea control in practice.
A naive animal will typically acquire fleas from a reservoir of infection, either within the home or outside. Untreated pets, strays and wildlife vectors such as foxes, ensure that such outdoor reservoirs remain plentiful.
For fleas to reproduce, the minimum of only one male and one female must be present on the same animal. After only 24 hours the pair will breed and the female will begin to suck the vast quantities of blood she needs to produce her 40 to 50 eggs per day. These eggs rain off the animal like salt from a shaker.
Where they land in shady, protected areas, they hatch into larvae, which feed and eventually spin the cocoons from which the adult fleas will emerge, some 21 to 56 days later (although there will be scattered emergence for up to 60 to 90 days).
The outcome? It doesn’t take many fleas on an animal to create a substantial reservoir of infection in the home, and these eggs will continue to develop into adult fleas for up to 90 days following the commencement of any treatment.
This highlights the importance of routine flea control. On the one hand, any animal going outdoors will regularly be coming into contact with emerging adult fleas, and with as little as two adults, an infestation can start.
On the other side, where fleas already exist in a home, a single course of treatment is not likely to be enough to kill the few remaining fleas hatching 90 days later.
Another point to come out of this was the phenomenon of “red line homes”. These are cases where fleas are identified on an animal, and the appropriate treatment given, but the animal comes back a month later with as many, or even more, fleas than before. It is tempting in such a situation to blame this on resistance, although this is not the case. It occurs simply because the infestation within the home when the pet was first seen, was on an upward trajectory.
Short of poor compliance, the product given was likely to have been effective, but the sheer number of eggs already laid right up until its application mean that over the coming weeks even more fleas will be emerging than before, and so the problem gets worse before it gets better.
Indeed, when any infestation is treated, the owner needs to understand that there exists this “development window” – the time between the instigation of treatment and the emergence of the last adult flea, 21-56 days later.
In such cases as red line homes, but also those with heavy infestations, where animals are suffering from significant or allergic pruritus, or owners themselves are being bitten, it is often worthwhile to address the reservoir of infection within the house.
Biomass reduction
Dr Dryden speaks of “biomass reduction” – reducing the numbers of eggs, larvae and adults within the home. This can be achieved by daily vacuuming and disposal of the bag; washing pet bedding; and steam cleaning, targeted to areas where pets spend most of their time. Inverted aerosol sprays, again targeted to areas of likely infestation, can also be used.
Finally, we were also given a useful recap of the current thinking regarding flea allergy dermatitis (FAD). It had been thought that this was an anaphylactic type of allergic condition, requiring only one flea to bite to produce an allergic response lasting up to two weeks. This is no longer thought to be true.
In fact FAD now appears similar to atopy, in that it requires a certain degree of flea saliva to take a given animal above its pruritic threshold. Therefore both the number of fleas present, but also the length of time they bite, is important when it comes to preventing FAD from occurring.
Systemic products, such as spinosad, kill very rapidly as the flea ingests large quantities of it as soon as it starts to suck. Topical products, such as fipronil, tend to kill a little slower since they have to permeate across the flea’s waxy cuticle. Interestingly this rapidity of action makes systemic products a better firstline flea control for those pets that suffer from FAD.
This was a very well presented and informative talk. Dr Dryden is a great communicator, obviously at the forefront of his area of expertise and with a passion for what he does. CPD like this needs to be relevant to the general practitioner, and what could be more so than fleas?
Having up to date knowledge allows us to treat effectively, but also gives us the ability to sell, with confidence, products which we know will improve the lives of our patients.
