Seeing fleas on a treated pet

If you see fleas on your cat or dog after treating them, you might think the flea treatment isn't working. However, modern flea treatments that contain fipronil, such as FRONTLINE^® products, are effective at killing fleas within 24 hours of them jumping on pets. The reason why you're still seeing fleas is because new fleas can jump on your pet at any time from an infested environment. Each new flea takes up to 24 hours to kill.

The majority of the flea population is found in the environment and is subject to a large variation in conditions: different hosts, pets treated with different products or none at all. This means that repeated exposure to a single active ingredient (which is necessary to develop resistance) is low.

The active ingredient, fipronil, acts on three parts of the flea nervous system so it would take three mutations of flea DNA for the product to become ineffective. This would be an extremely rare situation.

Scientific studies prove that the fipronil in FRONTLINE products remains effective. These include manufacturer studies (Beugnet F. & Franc M.), competitor studies (Jernej Küzner. Michael W. Dryden) and studies by independent researchers and veterinary parasitologists.

Why am I seeing fleas on my treated pet, and what can I do about it?

• No product stops newly hatched adult fleas from jumping onto a treated pet.
• Most products kill an adult flea between 12 and 24 hours of it landing on a treated pet. You will see fleas during this period whenever your pet has been in an infested environment.
• The key to flea control products is that they kill fleas before they can lay eggs that would be shed from your pet's fur into your home. This prevents a home infestation from developing, providing all pets in your home are treated throughout the year at the intervals specified on product packaging.
• Any gaps in treatment mean that the product will start to wear off and, at some point, newly arriving fleas will survive long enough to lay eggs that will infest your home.
• After a home infestation has developed, it will take monthly treatment of all pets in the home for at least 3 months to break the life cycle due to the amount of flea life stages in the pet's environment. While new fleas hatch out of pupae around the home, you will continue to see fleas on your pet. The treatment will kill these fleas within 24 hours, before they themselves can lay new eggs.
• Pets cannot become immune to FRONTLINE products because they don’t act through the pet's bloodstream. FRONTLINE products kill fleas on direct contact with the skin and fur.

* Dryden M (2012) Talk Flea Facts Seminar – DVD recording, Sydney; 22nd Feb 2012

FAQs

• How often should I treat my pets to prevent a home infestation?

  Your product packaging should tell you the recommended treatment interval. When using FRONTLINE Spot On:

  • treat all dogs every 4 to 8 weeks throughout the year
  • treat all cats every 4 to 5 weeks throughout the year
  • if you live in a high flea risk area, at times when the outdoor flea population is higher than usual (such as summer) you should consider treating all pets in the home every 4 weeks, rather than the longer treatment interval that you use in autumn and winter.

  Other small furry pets can also carry fleas and need to be treated with a suitable product at regular intervals throughout the year. Rabbits, in particular, should not be treated with FRONTLINE Spot On – ask your vet for advice about a suitable product for them.

• What is the best way to resolve a home infestation?

  If there is a pre-existing home infestation or there has been a gap in treatment, follow these steps.

  • Treat all pets with a suitable product every 4 weeks for at least 3 months (sometimes it can take a bit longer).
  • Use a home spray that contains an adulticide and an insect growth regulator. These ingredients won’t kill the flea pupae already present in the home, but they do reduce the number of eggs and larvae that go on to develop into pupae and therefore decrease the time it takes for the infestation to be resolved.
  • Vacuum more than usual and focus on areas under furniture, nooks and crannies etc. As well as getting rid of the flea eggs and larvae, this will help stimulate the pupae to hatch faster. Remember to shake rugs, cushions and so on, too.
  • By allowing treated pets to access all parts of the home you usually let them into, your pet acts as a ‘living vacuum cleaner’ to kill the newly hatched fleas before they can lay more eggs. Because of this, it is normal to see fleas on treated pets during this time. These newly hatched fleas will die within 24 hours, before they are able to lay eggs which would infest your home.
  • Wash all pet bedding at 60°C to help kill eggs or larvae that may be present.
• I used a flea control product when I first saw fleas. I continued to see fleas, so I used a different product a few weeks later and the fleas disappeared overnight. This means the first product didn’t work, doesn’t it?

  No. It is impossible for a product to control a flea infestation overnight. Here’s what would have happened.

  The first treatment you applied killed the fleas jumping on your pet before they could lay more eggs. However, no product can stop the flea pupae (developed from flea eggs) that are already present in the home from hatching into new fleas. These new fleas will have continued to jump onto your pet, and you’ll have seen them and thought that the original fleas hadn’t yet been killed.

  So, the first product must have prevented new eggs contaminating the home before the second product was applied, in order for pupae numbers to have been depleted in the home by the time the second product was used. In other words, it was actually the first product that was working before the second one was applied.

• How do I know if I have a home infestation?

  If you haven’t been treating all pets in the home at the correct intervals throughout the year, someone in the home is being bitten regularly (especially around the ankles) and you’re seeing fleas in the home, these are strong signs that you may have a home infestation. Please see What is the best way to resolve a home infestation? for how to resolve it as quickly as possible.

  It is possible for people to get bitten while outdoors (and even walk adult fleas into the home on their socks and shoes) if they walk through an infested area. So you need to take all the signs into account before deciding if there is a problem in the home or not.

• I'm only seeing fleas on one pet, do I need to treat the other one?

  Yes. Some pets groom more than others so it is possible to see many fleas on one pet and not notice any at all on the other, despite them both being exposed to equal numbers outdoors. If you only treat one pet, the other one will be bringing fleas in that then go on to lay eggs and infest the home. This is especially common in cats due to their inquisitive nature. They can explore heavily infested areas before coming home and grooming most of the fleas off before you notice them.

• I never used to see any fleas on my pets before when using a product and now I am seeing some. Is this because the product has become less effective?

  No, it is normal for parasite populations outdoors to fluctuate. This is because flea numbers in the outdoor environment depend on temperature, humidity, number of hosts (such as wildlife and cats) and vegetation cover. If any of these change from one year to the next, you can see an explosion in parasite numbers so that they suddenly become noticeable on your pets (or, alternatively, decrease in number).