ALLERGIC DERMATITIS CAUSED BY FLEAS IN DOGS

FLEA ALLERGIC DERMATITIS IN DOGS

Introduce
Flea allergic dermatitis (FAD) is caused by a hypersensitive reaction of the animal's skin to the allergen, flea saliva (Flea), at the skin sites bitten by fleas. Characteristics of flea-borne diseases are severe itching and papular dermatitis.

Pathogen characteristics 
Fleas are small dark brown insects about 2.5 mm in size and can be seen with the naked eye. Although fleas have no wings and cannot fly, they have powerful hind legs and can jump long distances. Fleas move through fur quickly and are difficult to catch. Most dog fleas are of the species Ctenocephalides felis.

Fleas survive by jumping on host animals, cutting open their skin, and feeding on their blood. In many dogs, the bite causes only mild itching, but in puppies it can cause severe infection or severe anemia and even death. Some dogs develop marked hypersensitivity to flea saliva and experience intense itching leading to skin abrasions, hair loss, and secondary pyoderma. Fleas are also an intermediate host for tapeworms.

Life cycle
The average flea life cycle is 21–30 days, varying from 12–174 days (Blagburn and Dryden, 2009). Adult fleas can live up to 115 days on a dog, but only leave them for a day or two. After drinking blood, fleas mate on the dog's skin. Females lay eggs within 24-48 hours, and can lay up to 2,000 eggs in a month. Eggs are released and incubated under furniture and in carpets and cracks. In 10 days, the eggs hatch into larvae that feed on local debris. The larvae spin cocoons and enter the pupal stage, which lasts for days or months. Under ideal temperature and humidity conditions, fleas can appear quickly, and live immature fleas can live for 12 days if they have not found a host to attach to.

(1) After finding a host and sucking blood, adult fleas will mate and begin to lay eggs in the fur (2) After hatching from eggs, fleas enter the larval stage, moving freely and feeds on blood to continue growing (3) Larva spins a cocoon and enters the pupal stage (4) Adult fleas emerge from the cocoon in the apparent presence of the host. (5) Adult females begin feeding on the host within a few hours of emerging from the cocoon and will soon mate and begin laying eggs (CDC, 2023)

Fleas are vectors for bacterial species such as Bartonella sp. Rickettsia felis and Haemoplasma species, Yersinia pestis and Dipylidium caninum (Otranto and Wall, 2008).

Clinical pathology
Dogs allergic to fleas develop severe itching and seborrheic dermatitis papules. The caudal fin, perineum, and umbilical area are commonly affected, although lesions may also be found around the neck. The primary lesion is a scaly papule, but self-trauma (a dog scratching or biting the skin due to itching) quickly leads to pain, scabbing, hair loss, and secondary bacterial or fungal skin infections.

Chronic inflammation leads to skin thickening and hyperpigmentation. Dogs who are allergic to fleas often have concurrent atopic dermatitis or food allergies. Cats allergic to fleas often develop symmetrical, scaly papular dermatitis along the caudal-dorsal midline causing hair loss, eosinophilic plaques, and granulomas. Fleas should therefore be considered in all cases of suspected hypersensitivity dermatitis

Diagnose
Flea allergic dermatitis can be diagnosed when fleas or their feces are detected on the animal with appropriate clinical signs. A flea infestation can be diagnosed by looking for fleas on the dog or by looking at black-and-white particles, like salt and pepper, in the coat. These particles are flea feces ("pepper") and flea eggs ("salt"). Stool is made up of digested blood, and when it sticks to wet paper, it turns reddish brown.

Diagnosis can be difficult because animals often have concurrent allergies and, especially in cats, it can be difficult to find fleas because the cat's licking behavior causes the fleas to adhere closely to the skin. Therefore, you can check for pieces of flea excrement by using a comb or using wet paper or tape to stick to pieces of flea feces.

Prevention & treatment of disease

Treatment
Treating fleas on dogs
There are many safe and effective flea treatment products available. It is best to use insect growth regulators (IGR) in combination with long-acting pesticides. There are many oral and topical treatment methods, so pet owners can choose the most suitable products for each type of pet. The most common reason for treatment failure is failure to follow label directions and recommendations. The following products can be considered:

Shampoo only kills fleas when they are on pets. They are best used for mild to moderate flea infestations where the environment has also been thoroughly treated. In general, pyrethrin-based shampoos are safest, especially for puppies. However, dogs must be cleaned with water after shampooing because dogs that lick or chew themselves can ingest toxic doses of these chemicals. Sprays, foams and soaks: Most effective in killing and are the best choice for severe flea infestations and for dogs with flea allergic dermatitis.

Sprays and foams work best on dogs with short fur. Most sprays last up to 14 days. Water-based sprays are preferred over alcohol-based sprays (which are flammable and can dry out the coat). When using the spray, start near the back of the dog's head and work toward the tail. This prevents fleas on the body from escaping the treatment by moving to the face. Sprays and foams should not be used on puppies under 2 months of age, unless the manufacturer's label says it is safe to do so. Always use these chemicals exactly as directed, as some can be toxic if your dog licks their fur.

Topical medications: This group of medications is extremely effective in eliminating fleas. Dip penetrates the coat and has the most immediate killing action and the longest lasting action. However, this drug also has the greatest potential for toxicity. Before use, please read the instructions carefully. Use according to manufacturer's recommendations. If your dog shows signs of poisoning, bathe or rinse her immediately. Excessive drooling, weakness, or instability in walking are all signs of mild poisoning.

Flea collars: Most collars contain dichlorvos, which turns into a vapor that surrounds the dog. If your dog sleeps outdoors, the collar will not be effective. Flea collars lose effectiveness over time and should be changed every two months, or as recommended by the manufacturer. Never use a dog flea collar on a cat.

Dogs can become sensitive to the chemicals in flea collars and develop contact dermatitis. This can be prevented to some extent by airing the collar for 24 hours when first removing it from the package and applying it loosely. The collar must fit snugly (allowing at least two fingers between the collar and the skin of the dog's neck). Using a dichlorvos collar at the same time as dichlorvos deworming may result in the dog absorbing toxic concentrations of dichlorvos, so the collar should be removed one week before deworming. Also, do not let your dog chew or lick the collar because it can be toxic. Early signs of toxicity may include excessive drooling, unsteady gait, and diarrhea.

Some flea control chemicals 
Lufenuron: The active ingredient builds up under the dog's skin tissue and requires fleas to bite the dog to work. Lufenuron works by inhibiting flea eggs from growing and hatching. This results in a steady decrease in the number of new fleas in the environment. It has a limited effect on the outer hard shell of the flea, making it completely harmless to mammals. However, since the adult flea is not affected, it can take 30 to 60 days or longer. For extra immediate results, and especially if the dog is suffering from flea allergic dermatitis, Lufenuron should be combined with a flea shampoo or some other topical insecticide treatment.

An additional imidacloprid or fipronil can be used to get rid of fleas in the premises. Lufenuron is not intended for use in puppies under 6 weeks of age, but it is safe to use in pregnant and lactating female breeds.

Imidacloprid taken once a month has the effect of killing fleas due to direct contact without having to bite the dog. Drip the medicine into the dog's skin between the shoulder blades (separating the skin when dropping the medicine to make sure the liquid stays on the skin) and three or four additional positions along the dog's back if the dog is large. One use protects a dog up to 30 animals a day.

After treatment, 98-100% of adult fleas are killed within 12 hours. Therefore, any new fleas that infect the dog are killed before they have a chance to lay eggs. This disrupts the life cycle of fleas and ultimately removes them from the environment. The advantage is not absorbed into the dog's system, and therefore is not toxic. Humans do not absorb chemicals after petting a treated dog. Advantix is a new formula that also works against ticks.

One downside of Imidacloprid is that it loses some effectiveness if the dog's coat gets completely wet more than once a week. If this happens, the dog may be regulated.

Fipronil: Kills fleas upon contact within 24-48 hours. The effectiveness of the Frontline does not diminish if the dog's coat is wet. The product has a residual effect that lasts up to 90 days in some dogs. Like Imidacloprid, Fipronil is not absorbed and therefore non-toxic. An added benefit is that it can also kill ticks for up to 30 days. Fipronil should not be used on puppies under 10 weeks of age.

Fipronil has the addition of (S) methoctures, which kill adult fleas, eggs and larvae. Selamectin, a liquid preparation applied to the skin of the dog's neck between the shoulder blades, once a month also controls adult fleas and prevents flea eggs from hatching.

Treatment of fleas in the environment
Vacuuming will help remove adult fleas from the floor, reduce the number of eggs and larvae in the carpet, raise the carpet fibers and thus enhance the penetration of pesticides, and stimulate the appearance of adult pupae.

Environmental products are sprays that include Permethrin in combination with insect growth regulators such as Regimetho, Pyriproxifen or Cyromazine. Insecticides that help to quickly destroy larvae and adults can be effective for up to 2–3 months. IGR prevents the normal development of eggs, larvae, and pupae for up to 12 months. Spraying of environmental treatment with permethrin must be carried out in areas with small rodents, birds and shaded outdoor areas.

Prevention
Flea control includes treating all exposed animals (cats, dogs, ferrets, and rabbits, including any neighbors' pets) and the environment (indoors and possibly outdoors, depending on the climate). Complete removal of fleas can take several months. Itching can persist after flea eradication so anti-itch treatments should be considered to reduce itching in animals An effective flea control strategy requires an understanding of the life cycle of fleas. At any given time, about 1% of the flea population consists of adult fleas, while 99% remain in the eggs, larvae, and pupal stages. An effective flea control program must eliminate this large reservoir.

Carry out a monthly flea prevention procedure (before flea attacks), using one of the active ingredients as stated above. If fleas have settled on the dog, it is essential to kill them on the dog and prevent them from coming back. One way to do this is to wash or dip your dog to get rid of fleas instantly. Vacuum the environment thoroughly and wash all dog bedding. 24 to 48 hours later, spray the flea killer that has just hatched from the eggs at the facility.

For this method to be successful, it is essential to treat all dogs and cats in the family, as well as any mink or domestic rabbit. Note that many dog safe products are not safe for these other pets. Any product that contains permethrin, even if it is labeled as cat-safe, is still potentially toxic.

The following flea elimination procedure can be used

- All dogs, cats, ferrets, and rabbits must be treated. Dip all pets once every other week with a solution containing Chlorpyrifos or Permethrin. It is important to ensure the product is labeled as pet safe.

- Also, use sprays or foams containing pyrethrins and/or permethrin every week. Apply to the surface of your pet's skin, not just on the fur. For unaffected pets, dip or spray twice a month.

- Physically remove fleas using a flea comb that is effective for short-haired pets. Pets must be groomed at least every other day. Comb your face as well as your body. Kill fleas on the brush by dipping it in alcohol or liquid detergent.

- Insecticides must be applied monthly to all floor surfaces. If pyrethrins are used alone, weekly spraying for the first three weeks is necessary. A disadvantage of spraying is that the mist settles on the carpet and may not get into the cracks on the upholstery and under the furniture. To compensate for this disadvantage, it is necessary to wash the carpet and spray it underneath the furniture before misting.

- Mechanical cleaning and insecticidal cleaning must be repeated every 3 weeks. It can take 9 weeks to get rid of fleas. Outdoor control includes the handling of yards, kennels, barns, running tracks, and rest spots

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Source: Nguyen Duc Hien, Nguyen Ngoc Phu Vinh, Huynh Minh Tri, Pham Minh Thu, Tran Khanh Long (2023). The disease is common in dogs. Can Tho University Press.