My flea treatment isn't working

It can be frustrating, disappointing and expensive if you've bought flea products, only to find later that your pet still has fleas.

As a pet owner, you’ll probably come across the subject of fleas sooner or later. These small, blood-sucking parasites can spread diseases, cause anaemia (especially in young and small pets), set off allergic reactions and bite people.

However, there is an array of products designed to prevent fleas from infesting your pets and colonising your home. Using the right products for your pet's lifestyle, at the right time, exactly as they’re meant to be used, can keep fleas under control.

How do you know that flea treatment isn't working?

This might seem like an odd question, but flea treatments all work slightly differently, targeting different stages of the flea life cycle and killing or controlling fleas in specific ways. If you’ve recently treated your pet with a product that kills adult fleas when they suck blood, remember that there could still be thousands of fleas emerging to feed, and most products don’t kill fleas instantaneously.

When you have a flea infestation, it is normal for it to take at least two weeks before there’s much improvement and often, it takes even longer than that.

If you treat all your pets and your home, you will kill off the adults, the larvae and the eggs, however, the surviving pupae will still go on and hatch as adults, who will then feed on blood from treated pets and die off, but potentially lay viable eggs first. The eggs should die once in contact with the treated environment. It’s not uncommon for a flea problem to seem worse before it gets better, and this could be related to numbers of new adults hatching out.

So, if you’re still seeing adult fleas, or you’re being bitten, don’t panic! 

The flea life cycle

When you think of fleas, you might picture small, dark-coloured insects with long back legs, hopping or crawling through your pet’s fur.

But did you know that these are only the adult fleas, which represent about 5% of a typical flea population? The remaining 95% are hidden around your home, busy growing and developing.

Broken down further, flea eggs make up 50% of the population, larvae another 35% and pupae 10%, so when you see one flea on your pet, it’s possible there are another 19 fleas developing somewhere in the environment. In some cases, it has been estimated that cats’ bedding could contain up to 10,000 fleas, of which 2,000 are adults! 

  1. An adult flea climbs onto your pet to suck blood.
  2. After each blood meal, a female flea lays between four and eight oval-shaped, whitish eggs, which are about 0.5 mm long. They aren’t sticky, so they fall off into the environment when your pet shakes or scratches. In her lifetime, which can be up to two years, a female flea can produce 800-1000 eggs.
  3. After about a week, the eggs hatch into maggot-like larvae. These spend about three weeks living in dark, humid places, such as bedding and carpets, and feeding on adult fleas’ faeces and smaller insects, before they spin a silken cocoon, inside which they pupate. Flea pupae are quite tough.
  4. They can remain safely cocooned away all winter, the new, hungry adults only emerging when the temperature and humidity are favourable, and in response to physical vibrations produced by a nearby host animal.

In normal conditions, the flea life cycle can be completed within four weeks, but it can take longer during cooler periods.

What types of flea products are there?

Topical flea products (also known as 'spot-on') are those you put on your pet’s skin and coat. Most also control a range of other parasites at the same time. Spot-on treatments are applied to the back of the neck or shoulders, where they are either absorbed through the skin or remain on the surface, gradually covering the haircoat. Absorbable spot-ons enter the fat beneath the skin, from where they are released into the bloodstream over the following few weeks. When a flea drinks the pet’s blood, it also ingests some of the product. Spot-ons and sprays designed to remain on the surface kill fleas when they land on the pet’s coat or ingest the product.

Some topical products kill fleas by interfering with their nervous system. The fleas can appear active and mobile just before they die. This can make it seem as though the treatment isn’t working when, in fact, the fleas are responding to it as intended. 

Topical flea treatments can be easy to use effectively, particularly in pets who don’t like being given tablets. This product isn't ideal for dogs who swim or are bathed regularly though, as the product is then less effective.

A range of oral flea control products are available and they all have slightly different methods of action, onset times and persistence (how long they last). Many also include ingredients that target other parasites, besides fleas. For pets who don’t get on well with topical treatments, oral products can be a great solution.

Flea collars have been available for many years and some of the older types may not be as effective as newer flea treatments. However, advanced technology has been incorporated into a new generation of flea and tick collars, made from special plastics.

These allow effective flea- and tick-killing medications to be delivered without any smell and without anything noticeable on the coat. Importantly, they also repel insects – a bonus if your pets suffer from ticks, because preventing ticks from biting means they can’t pass on blood-borne infections.

The collars last for seven to eight months. Not all cats are suited to wearing collars, but many dogs could have a collar placed and virtually forgotten about for much of the year.

A special type of flea preventative can be given by six-monthly injection. It doesn’t kill fleas, but females that feed on the blood of a pet who has had the injection will be unable to lay viable eggs.

Injections can be a convenient way to prevent fleas from establishing in the environment and can be used alongside adult flea-killing products at first, if needed.

Normally, flea products to treat your home come as a can of spray and they can be effective for a year following treatment.

It’s important to follow the manufacturer’s directions when you use sprays like this, as they are also toxic to birds, fish and some other animals. Birds should be removed from the home while treatment takes place and for at least two hours afterwards. Fish are more difficult to move so, to protect them, switch off their filter pump to stop active water movement and cover their tank with thick blankets, leaving these in place for at least two hours after treatment. You could also contact the product manufacturer for advice about your individual circumstances, for example, if you keep reptiles or amphibians before you spray.

When you use the spray, it should kill all developmental stages of fleas, apart from pupae. You can make a few preparations to encourage these to hatch. Adult fleas emerge from their cocoons when they detect warmth, moisture and movement. So, before you use the spray, turn on the heating and increase the humidity by hanging damp towels on radiators, or by placing bowls of water in front of heaters. Vacuum thoroughly, paying special attention to areas where pets spend most time and where cats jump down from furniture or windowsills (shaking off flea eggs as they do so). Make sure you vacuum underneath furniture, in cracks and crevices and in any dark corners. Dispose of the vacuum contents in an outside bin bag. If you have access to a steam cleaner, use this on any surfaces and soft furnishings that can be safely steam cleaned – always testing an inconspicuous area first. Once you’ve done this, you’re ready to spray! 

Move pets and people out of rooms you’re treating and open windows for a couple of hours following treatment. Also, if you have asthma, it’s best if someone else does the spraying, as aerosol propellants can irritate the condition. If you have an asthmatic cat, keep them safely in their carrier somewhere like the garage until the rooms have been ventilated. 

If you have seen large numbers of fleas on your pets, or if you have a pet with flea allergic dermatitis (FAD), it’s especially important to treat the environment to remove as many developing and adult fleas as possible. 

Continue to vacuum at least twice a week following spraying, as the vibrations from the vacuum will help to get the remaining fleas to hatch. 

Are some flea treatments better than others?

One flea product could be more appropriate than another in certain situations so, if you’re sure you’ve taken all these steps with the product you’re using and you’ve treated the environment as described above, you might need to try a different type of product.

Does resistance to flea treatments occur?

In the past, resistance to certain environmental insecticides developed. Resistance to the commonly used spot-on treatments, while possible, hasn’t been proven. However, if a treatment is used on a population of fleas and not all succumb, the survivors can pass on their genetic traits to future generations and this could include some tolerance to certain treatments.

Flea product characteristics that can affect their success in some situations include: 

  • Which stages of the flea life cycle are targeted – some products kill adult fleas, others can prevent their eggs from developing, and yet others can affect all stages of development other than pupae 
  • How quickly the product kills adult fleas – this can influence how many eggs could be produced by a female flea before she dies
  • How long the product’s action persists – some products should be used monthly, others every three, six or 12 months, and there are even products that only work for 24-48 hours but kill adult fleas from 30 minutes after administration
  • How the product is administered and whether it’s appropriate for the pet’s temperament and lifestyle

What to expect when you use flea products as directed

When you have a flea infestation, it is normal for it to take at least two weeks before there’s much improvement and often, it takes even longer than that. If you treat all your pets and your home, you will kill off the adults, the larvae and the eggs and, if you’ve managed to get some of the pupae to hatch, you’ll have reduced the numbers of these. However, the surviving pupae will still go on and hatch as adults, who will then feed on blood from treated pets and die off, but potentially lay viable eggs first. The eggs should die once in contact with the treated environment. It’s not uncommon for a flea problem to seem worse before it gets better, and this could be related to numbers of new adults hatching out.

In homes where there have been no pets for some time, it’s common for there to be an explosion of flea numbers when pets move in, even if the pets have been given flea preventatives. This happens because fleas have been lying quietly in their cocoons, waiting for the opportunity to emerge and feed. The changes around them when mammals are suddenly around, cause them to hatch and seek a blood meal.

In cooler weather, pupae could stay in a ‘dormant’ state for several months, only hatching when they feel the conditions are right, so you could still see small numbers of adult fleas on your pet, or you could still get bitten, for months after treating both pets and environment. Provided you continue to treat your pets as often as your vet has advised, newly emerged adult fleas won’t go on to breed and build up the population again. 

Flea treatment failure

If you use flea treatments exactly as prescribed you should expect the signs of fleas gradually to lessen. 

Only treating your pets and not the environment can work as a preventative if you don’t have an established flea population in your home, but it’s not enough if you already have a problem. This is a common reason for people thinking their flea treatment isn’t working or that they must have a resistant flea population. If you don’t kill the developing fleas, you won’t prevent fleas emerging to bite you and your pets.

Even if you do treat the environment but only use treatments on your pets intermittently, you won’t be able to eradicate the fleas, as they will be able to feed and lay eggs, some of which will survive and go on to develop into a new generation of adults. For a flea treatment to work properly, it needs to be used as the manufacturer or your vet advises.

If the product is getting removed – perhaps because your dog is bathed or swims regularly, or the treated floors around your cat’s bed are mopped daily – it won’t be able to do its job properly. If you think this could be happening, ask your vet about alternative products.

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