What flea control is best for dogs?
There is a huge range of different flea products on the market – and it can be really hard to decide which to use. Do you choose the cheapest? Or the most expensive? What formulation – collar, tablet, spot on? Where do you get it from – pet shop, pharmacy, vet? Are the fleas resistant to any drugs?
In this blog, we’ll take a look at the ever-thorny problem of flea control in dogs. We won’t look at every product on the market (because there are way too many now, and there’ll probably be another one along in a moment!), but we will look at some of the more important groups. However, to kill the flea you must first understand the flea, so let’s start with…
What are fleas? 
Fleas are a type of insect, with bodies that are flattened from side to side. They live by sucking blood from a variety of different hosts. Unlike most insects, they have no wings, but they can jump – the average jumping distance is 70 times their own length, but the record is a massive 250 times the body length – that’s equivalent to a human jumping almost 500m!
The most common in the UK is the Cat Flea (Ctenocephalides felis, which can actually live on dogs, cats and many other animals). There is also a Dog Flea (Ctenocephalides canis) which can also live on cats as well, just to be confusing. There are also other species, but their life-cycle is all pretty similar so we’ll deal with them all together,
What is their lifestyle?
The adults live on your dog, sucking blood. When a female flea lays her eggs, they fall off the dog and land in the environment – typically in the house, the car, or (most often) the dog’s bedding. These eggs mature and hatch, releasing worm-like maggots: the larvae. These crawl around wherever they are, living primarily off the faeces of the adults (which are, of course, comprised of partially digested blood).
Once they have grown enough, they form a pupa (like a chrysalis but with a nastier inhabitant) and reorganise themselves into adults. In this pupal form, they can remain dormant for days, months or even years – in this state they are virtually indestructible. They stay hidden away, inactive, until they detect air movement, vibration, and warmth – suggesting a potential meal is coming along. Then they hatch out and jump on board, ready to feed and start the cycle again.
….and why is that important?
Only about 5% of the fleas in a home are adults living on the dog – the remainder are living as eggs or larvae in the carpets, soft furnishings, upholstery or bedding. If you want to control a flea infestation, you can’t just kill the adults – there are many more larvae waiting to grow up and hop on board! Instead, you must try to break the life-cycle as well, killing them at all phases of their development.
It’s also worth remembering that, because the adults can jump species, you need to treat all the animals in the household, not just dogs but cats, rabbits and ferrets as well, to deny the fleas a safe hiding place.
Why do we want to kill them anyway?
Fleas cause itching, scratching and untold misery to their victims! They can also bite humans if they’re hungry enough, which is probably enough of a reason for most people by itself…
However, they can cause more serious problems as well. A certain percentage of dogs will develop Flea Allergic Dermatitis (an allergic reaction to flea saliva), causing more severe itching, a rash, self-trauma and skin infections). In addition, fleas carry the Dog Tapeworm (Dipylidium caninum) and may transmit other infections.
So, what types of flea product are available in the UK?
The most common and widespread treatments in the UK are based on the chemical fipronil* and are available as spot-on products. These spread in the grease layer of the skin and kill fleas that bite. Many people are nowadays disillusioned with this drug, and think that the fleas have become resistant to it – however, there is very little evidence for this. It is more likely that the reason it appears to work less well nowadays is due to a combination of factors, including the fact that is it water-soluble (and therefore lost if you wash your dog or they go swimming), and its relatively slow method of action (24-48 hours from exposure to kill). These are available on their own (over the counter) or in combination with…
Insect Growth Regulators (IGRs) are a group of chemicals that prevent flea larvae from developing properly. Although they have no effect on the adults, they are very effective at reducing the number of offspring they have – essentially, they act as flea contraceptives!
Avermectins like selamectin and moxidectin are also available as spot-ons; however, these are actively absorbed into the body and the dog’s blood. Therefore, whenever the flea takes a bite, they get a dose of the medication. These drugs are very safe, although there can be problems in Collies and similar herding dogs if they have a particular gene mutation – talk to one of our vets if you’re concerned. They also have a role in controlling flea larvae in the environment, as the drug residue that reaches the carpets will be fatal to larvae. These drugs are always prescription-only, and may be combined with…
Imidacloprid, which is available over the counter or in combination in some prescription products, is applied as a spot-on. This is toxic to fleas on contact, as well as after being swallowed.
The other common spot-on products contain permethrin or its derivatives; this is a synthetic version of a chemical found in chrysanthemum blossom! It is toxic to fleas on contact, but also to cats (so be very careful if you have a mixed household). It is also available in some flea collars, and as sprays for the house to kill larvae. Sometime formulations are available over the counter, but the more potent or concentrated forms require a prescription.
There is a range of prescription-only tablets, containing drugs such as fluralaner, alfoxolaner and spinosad – these drugs are easily absorbed from the dog’s intestine and protect against fleas for one to three months, depending on the formulation; they are only available on prescription. They kill the fleas so fast that they don’t have time to breed, so helping to break the life-cycle.
Another type of tablet contains nitenpyam. This is very, very effective at killing the adults (within a few hours!) but only lasts 24 hours, so it’s only useful in an emergency situation.
There are so many! What do I do next?!?!?!
Actually, there are several other drugs, but these are the more common ones!
How effective any product will be will depend not just on the drug, but also on our dog’s lifestyle. If one product doesn’t work, it may be that another one would suit your dog better. If you want good flea control, pop on down and talk to one of our vets, who will help you find the product that best suits your dog.
* Note: it is not legal for us to list the brand-names of prescription medications in a blog like this, in addition, many of these drugs are sold under different names by many different companies – so we are using the generic chemical names instead.