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Fleas in dogs & cats

Published on 8 Sep 2021

Despite their small size, fleas are a source of misery for many dogs, and their families.  As well as causing discomfort when they bite, fleas on dogs can also spread potentially serious diseases to people, making flea prevention important for the welfare and health of your entire family.  

This article will give you some tips on how to tell if your dog has fleas, how dogs get fleas, how to prevent fleas on dogs, and how flea treatments for dogs actually work. Along with some interesting (or revolting) flea facts...

Why are fleas a problem?

Fleas are small, wingless insects that must feed on the blood of a pet to grow and reproduce – their ultimate goal in life! Flea bites are painful and cause discomfort to many pets, with a single flea capable of biting hundreds of times a day. Some pets become allergic to the saliva the fleas inject when feeding, leading to a condition called flea allergy dermatitis (FAD). For pets with FAD, flea bites trigger intense itchiness leading to excessive grooming and self-trauma, causing pain and predisposing to secondary skin infections or “hot spots”.

Did you know that fleas on dogs can also transmit parasites and disease to pets and humans?

Fleas are the most common ectoparasite affecting dogs and cats and can transmit flea tapeworm, an intestinal worm, to dogs when they’re swallowed during grooming. But more importantly, fleas can spread diseases (e.g. the plague) between animals, and from animals to people. In the case of flea-borne spotted fever, dogs can be carriers of bacteria that don’t make them sick, but can be transmitted to people through the bite of an infected flea.  People that contract flea-borne spotted fever can develop a range of symptoms from non-specific flu-like illness to more severe disease involving multiple body systems. 

How to tell if your dog or cat has fleas

Fleas on dogs and fleas on puppies are small and very quick moving, so it can be hard to spot them. To the human eye, fleas look like little dark red or brownish ovals. If you look closely, you can make out their legs underneath them. If you do spot a flea, be prepared for it to disappear suddenly as it crawls or jumps away. 

Sometimes you may not see the fleas themselves, but you may see evidence of them:

  1. Observing your dog scratching themselves: flea bites can be painful, causing irritation and discomfort to your dog.
  2. Finding flea dirt: fleas can be found anywhere on a dog, but healthy fleas move quickly, and can be very difficult to spot.  Fleas that have just emerged from their protective cocoons and jumped onto a dog to feed for their first ever meal will be hungry and fast and much smaller than fleas that have been on the dog feeding for a while. Finding the blood-rich droppings of fleas, also known as flea dirt, can be an easier way to tell if your dog has fleas.  If present, you will typically catch some small blackish specks of flea dirt with a fine-toothed flea comb, going through the coat over their lower back and around the base of their tail. These specks can be confirmed to be flea dirt, if they turn reddish-brown when placed onto moist paper towel.
  3. Finding skin lesions (hair loss, reddening of the skin, wounds from scratching, hot spots): the most common locations in dogs with FAD are the insides and backs of the thighs, lower back and around the base of the tail. 

How do dogs get fleas?

Pets acquire fleas via contact with other dogs and cats, or through exposure to an infested area (inside the house or the outdoors!). By the time you notice fleas on your pet, it is likely that the immature stages have been present in the environment for at least 4 weeks. 

The Flea Lifecycle

To understand how dogs get fleas, and then how to control and prevent them, it’s important to think about the life cycle of this hard to eradicate parasite!

The typical life cycle of a flea, or the time it takes for fleas to reproduce and develop, takes around a month, but may be as long as a year or more.

1. Adult Fleas

Adult flea emerges from the pupa when they detect a nearby host, due to temperature increases, vibrations or increased carbon dioxide levels. Newly emerged adult fleas are ready to begin feeding within minutes of finding a host, with new eggs produced within 1 or 2 days of feeding.

Adult fleas are the only life cycle stage to live on a dog, and only account for about 5% of the whole flea population. The remaining 95% are the immature flea stages (eggs, larvae and pupae) that lie largely unnoticed in the dog’s environment - your home!

Although adult fleas can move from dog to dog, this isn’t the most common way that dogs get fleas.

Just 10 adult fleas on a pet, can become an infestation of  250,000 in only 30 days!

2. Eggs

Adult female fleas lay their eggs on the skin or fur of their host animal after they have enjoyed a good feed of blood. The tiny, light-coloured, oval eggs fall from the dog's coat into the environment, where they take between two days and two weeks to hatch.

Flea eggs are small, slippery and don’t stay on the dog, but fall off and are spread wherever they go, including into carpets, cracks in floorboards, bedding, furniture, dirt in the yard or dog park etc. 

3. Flea larvae

Larvae grow inside the eggs until they are ready to hatch. They hatch from eggs in 2-4 days, avoid light and feed on flea dirt, dead skin cells and other organic debris. After about 5-11 days living in the environment, a larva will spin a cocoon around itself to become a pupa.

4. Flea Pupae

The cocoon makes pupae the most resilient stage of the flea life cycle – they can survive chemical control (e.g. insecticides and flea bombs) and a range of temperature and humidity extremes. 

Fleas can complete their metamorphosis from larva to adult inside their protective cocoon within just 10 days, but if conditions are unfavourable they can remain inside for up to 12 months. For this reason, these horrible parasites can suddenly appear in a house that has been clean and flea free for some time. 

After emerging, adult fleas are ravenous, and will jump onto any animal (or person) they can find and start biting and feeding almost immediately! This is how dogs most commonly get fleas, when they enter an environment where an animal with fleas has dropped off some flea eggs.

The good news is that with proper flea control, it is possible to break the flea life cycle.

How to prevent fleas on dogs and cats

Fleas can be difficult to control, because the majority of the flea population is in the home, rather than on the pet. Ideally, flea treatment for dogs should start early in the pet’s life, and as soon as they join your family.

Don’t wait until you see evidence of fleas on your dog to start flea prevention. Lapses in flea control can allow the flea population to establish or rebuild, leading to an infestation in the home that can take months to eliminate. This is why it’s important to continue using flea control all year-round, and on all pets in the household, even during the cooler winter months. 

How do flea treatments for dogs work?

Selecting a flea treatment for dogs can be overwhelming!

There are many products to choose between, coming in different formats (e.g. spot-ons, collars, tablets, chews, sprays), offering different lengths of protection, and with or without other parasite protection. But another thing to consider, that isn’t so obvious, is the way the products work to kill fleas.

Flea treatments for dogs and cats can be broadly divided into two groups, those that work from the inside of your dog (systemically-acting), and those that remain and work on the outside (topically-acting). Most products (e.g. all chews, all tablets and some spot-ons), are absorbed into the dog’s bloodstream, meaning fleas must bite and take a bloodmeal to be killed.

Did you know that a single flea can stay in one place on your dog for up to 3 hours, biting and feeding on your dog’s blood?!?

Fewer products (e.g. some spot-ons, including Advocate, and some collars, including Seresto), are not absorbed into the bloodstream but instead work on the outside of the dog, killing fleas as they come into physical contact with the skin and hair.

Another important consideration is how fast the product will work to kill fleas already on your dog, and even more importantly, kill new fleas that try to infest your dog between treatments. This information can often be found on the information on the product leaflet.

The topically-acting flea-killing ingredient in Advocate, imidacloprid, kills fleas on contact, meaning fleas don’t need to bite your dog to be killed. Imidacloprid localises in the skin and oils covering a pet’s skin and coat, and is not absorbed into the body. Imidacloprid is also the fastest-acting flea control active available, stopping adult fleas that jump onto the dog from biting within just 3 to 5 minutes, and killing them within 1 hour. As pets naturally shed their dead skin cells and hair, flea larvae in the pet’s environment are also killed. 

 

Depending on the product chosen the application or administration frequency will vary. 

NexGard Spectra ®, NexGard ® or Comfortis® kill adult fleas fast, before they can start to lay eggs, helping protect your dog and your home.

It is important to note that not all flea preparations are safe for cats, you should always check with your veterinarian about which flea prevention is best for your pet. 

Fleas infected dog scratching the ear.

Signs of flea infestation 

It may be possible to visualise the fleas on your pet.  

Adult fleas spend the majority of their time living on dogs and cats. Within 24 hours of infesting a pet, a flea will begin to lay eggs which then fall off the hair coat of the pet and into the environment. Female fleas can lay 40-50 eggs per day! 

Female fleas feed often and can consume up to 15 times their weight in blood in just 24 hours!

Within 3-8 weeks, under the right environmental conditions, these eggs develop into adult fleas. Fleas thrive in mild weather and prefer temperatures between 20C and 30C.  

As many pets have dense hair coats, or in the case of cats are fastidious groomers, it can be difficult to visualise fleas on pet. You may notice “flea dirt” which appears as black specks and is actually flea faeces!

Other signs of a flea infestation may include:

  • Scratching, licking and chewing particularly around the rump and tail base. This can lead to hair loss, secondary bacterial and less commonly yeast infections. Pets may also be allergic to flea saliva and this may cause a condition called flea allergy dermatitis 
  • Anaemia: when fleas feed they ingest the pets blood, with severe infestations this can lead to anaemia. Clinically your pet may have pale gums or they may become lethargic. Prompt veterinary attention is required 
  • Transmission of other parasites: fleas are intermediate hosts for other parasites including Dipylidium caninum (tapeworm). Tapeworm segments can appear as small grains of rice in your pets stool. 
  • Disease transmission: fleas are capable of transmitting other organisms that may results in Murine Typhus or Cat Scratch Disease 

Eliminate premises infestation 

If your pet has fleas, you may wish to consider environmental decontamination, this process should be focused on where your pet spends most of their time (their bed, kennel etc). Some helpful hints include:

  • Regular vacuuming- make sure you empty the vacuum cleaner cannister or bag – this will assist with discarding immature fleas 
  • Bedding- wash bedding weekly, preferably with hot water and after washing, the bedding should be dried in the dryer 
  • Carpets- steam cleaning will help to eliminate immature fleas
  • Consider a pest control professional for the exterior of your property 

References

  1. Dr Flea” Accessed on 25/11/20
  2. Purina, “Flea and tick prevention”, Accessed on 25/11/20
  3. DVM 360, “ How to conquer these blood-feeding, egg-laying machines” accessed on 25/11/20
  4. Vet Derm, Allergy Ears and Skin Specialists,  “Flea  bite pet allergies, what to be aware of”, accessed on 27/11/20

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Dr Dani Hoolahan Profile Pic

Dani Hoolahan

Veterinarian

Dr Dani has studied BVSc, BVMS and became a Diplomate of the American College of Veterinary Dermatology in 2013. She has worked in busy dermatology referral practice since 2014 and is the founder of the Veterinary Dermatology Clinic. She is currently the Chief Veterinary Officer for PetSure.

Dani is a proud Pet Parent to Spike, Daisy and Oliver (a trio of Labradors) , Ghost (a Lykoi kitten) and Hobbes (a domestic shorthair cat).

Dani Hoolahan's Pets

  • Dr Dani Hoolahan Spike Dog Pet Picture.Spike
  • Dani Hoolahan Ghost Cat Pet Picture.Ghost