Our Archives: fleas

Cats are known to be fastidious creatures, and regular grooming alongside the odd scratch is perfectly usual for our feline companions. However, excessive scratching and itchy skin is not, and can be very uncomfortable for our pets. Itching is a symptom, rather than a diagnosis. So some detective work may need to be undertaken by your vet to pinpoint the cause. 

Picture it: you’re locked down and at home a whole lot more; the dog is thrilled (the cat probably less so!). You’re getting to spend some quality time with the family, not to mention making the most of the exercise allowance. And then the dog starts itching. 

Hair loss in cats is almost always due to excessive grooming from itchiness (pruritus). They often do this in secret so may not be seen. In the UK, fleas are the most common cause of this over-grooming. The general veterinary approach to skin disease: fleas are the culprits until proven otherwise.

Dogs do occasionally scratch, but if it’s frequent, incessant or distressing then something is amiss. Some dogs will lick or nibble rather than scratch. Many do this in private so watch out for red, sore skin, bald patches, or brown saliva staining where the fur has been licked. Itching (technically called pruritus) is a sign, not a diagnosis or specific disease. It’s probably the most common reason for owners to take pets to the vet’s, making up a large proportion of our consultations.

Although it’s no longer Rabbit Awareness Week, we thought we’d cover some extra rabbity things this month! Rabbits are quite fastidious creatures. They love to groom and will have the odd scratch. It is important to know what is normal for your rabbit, so you are able to spot potential problems quickly. Scratching more than normal, overgrooming, dandruff, or fur loss may be signs of a parasite infestation. Mites and fleas are the most common parasites affecting rabbits.

Anne Stafferton asked: This one is a bit boring really I've spent hundreds of pounds on flea stuff only for it not to work I breed cats so it's a nightmare I'm now combing them all every day to get fleas out any suggestions on what really really works Answer: Hi Anne, thanks for your question about fleas in cats. I know exactly what you mean – they can be a real nightmare to get under control! I’m going to answer your question by (briefly!) discussing the flea life-cycle and how it can be broken, and then talking about the specific treatments that are available. As a warning, on a blog like this I am legally obliged to use the generic names for all the drugs and medicines (otherwise I would get nasty letters from the Veterinary Medicines Directorate, the government department who regulate advertising of veterinary medicines). You can, however, look up any of the generic names for the active substances and “translate” them into brand names on the VMD’s Product Information Database. What are fleas? Fleas are a group of obligate ectoparasites – this means that they live on the outside of other animals, and cannot survive in any other way but by sucking the blood of their hosts. Once an adult flea lays her eggs, they fall onto the floor, the carpet, and into the cat’s bedding. Here they hatch into larvae, which live, hidden deep in the fabric, in the dust, and in cracks in floorboards etc. The larvae survive primarily by eating the faeces of adult fleas, which fall off the cat as the “black sand” we all know and hate! This material is semi-digested blood, and is very nutritious for the larvae. After their final moult, they turn into pupae (like the chrysalis of a butterfly but less pleasant) and there they stay, waiting for a chance to hatch. Pupae can remain dormant for months or years, and in this state they are more or less impervious to virtually any treatment we can use against them (although apparently repeated steam cleaning can kill them). When they detect air movement, heat, or increased carbon dioxide levels (all indicators that a cat, dog or human is close), they hatch and leap on board, to feed, breed and repeat the cycle. Traditionally, we think of fleas as being a spring and summer problem; however, with modern insulation and central heating, nowadays we see them all year round. The flea life cycle can only complete in a relatively warm environment, but we kindly provide them with a nice warm, comfy house to grow up in. So how do you break the cycle? There are a number of points at which the cycle is vulnerable – however, it’s important to remember that if the cats go outside (even briefly) they can pick up new fleas (deposited by other cats, dogs, foxes and even small mammals such as rodents). It only takes one amorous flea couple to reinfest a whole household… The adult fleas are actually pretty easy to kill – even old-fashioned drugs like fipronil will kill most of the adults present, and many of the newer medications are much more potent. The larvae need to cut their way out of their eggs (using a special “egg tooth” made of chitin); if their synthesis of chitin is impaired (e.g. by lufenuron) they cannot hatch. The larvae cannot develop into adults in the presence of juvenile hormone – if this is chemically supplied (as an Insect Growth Regulator, e.g. S-Methoprene), they cannot make the change into adults. The number of eggs, larvae and pupae in the house can also be reduced, by washing of fabrics (especially bedding) in hot (60C) soapy water. Although it won’t kill all of them, it will reduce the numbers and wash a lot away down the drain where they can’t hurt anyone! The pupae themselves are pretty much impervious to any treatment, but they can be “tricked” into coming out as adults, which are then much easier to kill. The common method is regular vacuuming – the air movement and heat trick the pupae into hatching; you won’t catch many in the cleaner, but once out, they are vulnerable to environmental insecticides. In fact, if you keep a “closed household”, with all the cats (and dogs if you have any) living indoors 24/7, it is theoretically possible to break the life cycle without treating the adults at all… but it will take a long time (the adults may live for 4-6 months) and you’re always at risk of a new introduction (in your clothes, for example). So how do I kill them? As you’ve found, there are a huge range of different flea control products on the market! Broadly speaking, these can be divided into 5 categories: Environmental insecticides: These are products used to spray the infested house, killing adults, sometimes eggs, and larvae. They will not kill pupae, but if applied rapidly after vacuuming, they can be very effective. Most products contain permethrin, which is toxic to cats – this means that you have to be careful using them, by treating rooms one at a time and shutting the cats out until they have ventilated. The cans will explain how long to leave it for on the label, or talk to your vet, before reintroducing the cats. On-cat environmental treatments: These are applied to, or administered to, the cat, to treat the environment, and rely on the fact that the larvae are eating the flea’s droppings. There are 3 particularly important ones:

• Lufenuron – a chitin inhibitor, available as an oral liquid, a tablet, or an injection. Does not kill adults, but prevents larvae and pupae from hatching properly.
• Pyriproxifen – an Insect Growth Regulator, available in some prescription-only fipronil products.
• S-methoprene - another IGR, available in some prescription-only fipronil products.
• Imidacloprid – an insecticide available as a spot-on that kills adults and larvae in the vicinity of the treated cat.

Over-the-counter adulticides (products that kill adult fleas only): These are of various effectiveness; most contain piperonyl butoxide or dimpylate (not very potent but pretty harmless) but there are still some on the market containing permethrin, which although effective is potentially lethal to cats. In general, if it is available over-the-counter without any regulation, it’s probably not that powerful. The most popular products in this group are the spot-ons containing fipronil, which is an older drug but still fairly effective. Some of these products are over the counter, and others are classified “NFA-VPS” (which means there are certain restrictions on their supply, but they still do not require a prescription) Contrary to popular opinion, there is no conclusive evidence that resistance of fleas to fipronil is widespread – however, fipronil containing products are water soluble (so may wash off if the cat gets wet) and are much less effective than the modern prescription-only products. The other commonly used active ingredient is imidacloprid, which is a different class of insecticide that is active against adult and against the larvae. Again, it doesn’t suit every cat but may be useful. There is also an interesting product available as a tablet containing nitenpyam, which is very effective at killing adults – but only lasts 24 hours after being given. It is best used to kill off the bulk of the adults when starting a flea control program. Prescription-only products: Fipronil-combos – spot-on products containing fipronil plus an Insect Growth Regulator, to treat the adults and the environment simultaneously. Last between 4 and 8 weeks, but the adulticide (killing of adults) effect tends to wear off after about 4-5 weeks. Flumethrin/Imidacloprid combo collar – this is a collar containing flumethrin (a form of permethrin that is safe for cats) and imidacloprid. It lasts about 6-8 months, and is very effective – if the cat will keep it on! Imidacloprid/Moxidectin combo – another spot-on, that treats a wide range of different parasites. Lasts about 4 weeks. Selamectin – a spot-on product, but one that is absorbed into the cats system so it cannot be washed off – very useful for outdoor cats! It also treats roundworms and both mange- and ear-mites, but does require the flea to bite before it works. Lasts about 4 weeks. Indoxacarb – Another spot-on, but one that is utterly inactive in the cat’s body, until it is “turned on” by a unique metabolic action inside the flea, and the larvae if repeated every 4 weeks. Spinosad – a tablet, given once a month, that is really effective against fleas, but does cause some cats to vomit; if given with food, however, it normally stays down - it does require the flea to bite, but kills very, very fast (in a few hours). Herbal and homeopathic remedies: Available, but no proven effectiveness. I have heard garlic recommended, but, sadly, in my experience it just doesn’t work and is potentially toxic to cats. There’s so much choice! What do I do? Bottom line – you’ll never control fleas if you only attack one stage of the life cycle. You need to kill the adults (and I’d recommend you talk to your vet about the more potent, modern, prescription products rather than rely on older and less powerful medications); however, you also need to decontaminate the environment, with regular vacuuming, insecticidal sprays, and good old fashioned washing and cleaning! If you’re still struggling to get on top of the situation, talk to your vet – not every product suits every cat, and it’s sometimes necessary to try several alternatives until you find the product, and the control methods, that suit your cats and their lifestyle. All the best – I hope you can rid your cats of their unwelcome visitors! David Harris BVSc MRCVS