More than 2,000 types of fleas parasitise mammals and birds. Dogs are most commonly inhabited by the Ctenocephalides felis (cat flea), more rarely by the Ctenocephalides canis (dog flea), and occasionally by the Pulex irritans and Pulex simulans (human flea), as well as by the Echidnophaga gallinacea (hen flea) and (hedgehog flea).
Fleas are wingless, laterally flattened insects around 1-6mm in length with a strong talus and piercing-sucking mouth parts. They are light to dark brown in colour and feed off the blood of their host animal.
The development of fleas progresses from the egg to three larva stages to the pupa and then the adult form. Female fleas take just a few minutes to inhabit the dog's blood and start to lay eggs after around 24-48 hours. During its lifespan of around 50-100 days, it lays on average 30 eggs per day. The eggs are mostly laid during the dog's rest period and fall out on its sleeping spot or other areas where it frequently rests. Within a few days, the eggs hatch and become larvae, developing over three stages into pupa. The larvae feed off cell material and flea excrement with undigested blood, which is released from the dog along with the eggs. The adult flea hatches from the pupa and seeks to inhabit the nearest dog as soon as possible. In unfavourable conditions, such as cooler temperatures, the pupa can survive in its cocoon for up to 50 weeks until hatching. In ideal conditions, the duration of the cycle from egg to adult flea is around two to four weeks. Adult fleas from C. felis and C. canis permanently live on their host; they occasionally cross over to other hosts, but don't stay in the surrounding area for a long time. The flea's youthful stages (egg, larva, pupa) live in the environment, the larvae hole up into hiding places such as under cushions and carpets, as well as gaps in the flooring.
Dogs can bring fleas into the home through contact with other animals. The conditions in a living space are ideal for the development of fleas, and they multiply rapidly in this environment. C. felis, the most common type of flea, is not picky in its choice of host animal: it has been found on over 50 different types of animal all over the world, as well as on humans.
What are the symptoms of a flea infestation?
Flea bites cause dogs mainly itching and local skin reactions like red dots with a light ring. More severe reactions can also lead to pustules and scabs. Dogs constantly scratching and gnawing can lead to hair loss and weeping or even purulent eczema. Areas favoured by fleas are the ear and croup zone, the back and base of the tail, as well as the stomach and inner thigh. However, a flea infestation can go entirely unnoticed and not show any symptoms.
In addition, dogs can suffer from flea allergy dermatitis (FAD), a hyper-sensitivity reaction triggered by flea saliva allergens. FAD is one of the most significant and common allergic skin diseases that affect dogs. A single flea bite is sufficient to cause the affected dog very severe itching.
When it comes to massive flea infestations, puppies or dogs that are also suffering from other diseases can end up with anaemia due to fleas sucking the blood out of their body. Fleas can also transmit the tapeworm Dipylidium caninum to dogs.
Diagnosing a flea infestation
With severe flea infestations, it is possible to recognise fleas on the dog with the naked eye. Clinical symptoms like stings and redness on the areas preferred by fleas can also indicate a flea infestation. You can search for fleas or their excrement with the help of a flea comb. In order to distinguish flea excrement from dirt in the fur, tap the material that sticks to the flea comb onto a white piece of paper or kitchen roll and dampen it with water. If the material turns a reddish colour, it is flea excrement containing the blood that has been sucked up. Sometimes eggs or larvae that stick to the fur can be found and are recognisable under the microscope.
An allergy to flea saliva is more difficult to diagnose, because fleas or flea excrement can only be found in rare cases. Indications are the symptoms typical of FAD and areas showing alterations to the skin. However, other allergies or parasites must be taken into consideration when making a diagnosis. If suspicion of FAD arises, dermatologists are happy to carry out diagnostic treatment with medication or an intradermal test.
Treating flea infestations
Several measures are necessary when treating a flea infestation affecting a dog. On one hand, adult fleas on the dog must be fought, which can be done with suitable medications like spot-on treatments, tablets or sprays available from the vet. In addition, the young stages should also be killed off, meaning that the whole surrounding area inhabited by the dog must be treated too. In particular, think of cracks in the floorboards, the underside of rugs and other dark areas where larvae retreat to. Blankets and cushions should be washed, and floors and the car should also be thoroughly vacuumed. The vacuum bag should be emptied or frozen straight after use. After cleaning, it is recommended to treat the surrounding area with an insecticide like an environmental spray or fogger from a specialist store or the vet's.
Since fleas can also infest other animals living in the same household or entering into direct contact, it is advisable to treat these animals as well.
Fleas transmit the canine tapeworm Dipylidium caninum, so you should think about deworming procedures after a flea infestation.
In order to avoid a flea infestation, dogs can be given preventive treatment with different medications. These come in different forms like spot-on treatments, tablets and collars with different modes of action and duration.
Dogs with an allergy to flea saliva in particular should receive regular anti-flea treatment, because the bite of a single flea can trigger major symptoms.