FLEA ALLERGY DERMATITIS
contributed by John Macdonald
Cuordha Goldens
Nova Scotia, Canada

Allergies are life long afflictions. Once they start they never disappear. Allergies are not curable and they are expansive. They get worse with age. About 10% of dogs are allergic to pollens.

The primary allergic agent is the skin in dogs and cats - the lung in humans. Flea allergy is the most common allergy in dogs and cats.

Flea allergy dermatitis has existed as long as the dog has. It is now more prevalent because we have more fleas. It has no pure genetic basis. Any animal can become allergic to fleas. Dogs with an allergic predisposition from their parents will develop allergies younger. There is a variable animal magnetism. Some dogs are more attractive to fleas than others. One dog can be virtually flea free while one next to it can be riddles with them. Different dogs also have a variable tolerance to exposure. Some can tolerate more fleas than others, often with little or no apparent discomfort. With age some get better due to autoimmune response.

Often there is no genetic basis for flea allergy dermatitis, but dogs with atopic diseases are very prone to flea allergy dermatitis.

Flea allergy dermatitis typically starts easy and gets worse with time. The typical allergic phenomenon is progressive & non-curable.

Flea allergy dermatitis is a tail-head-tummy disease. These areas are the primary feeding areas and the areas where the dog itches and consequently scratches. Flea allergy is a back end disease and if you don't have this pattern you don't have flea allergy dermatitis.

The allergen is the saliva of the flea. When the flea bites for its blood meal saliva is injected into the skin to prevent blood clotting. The saliva from the flea bite will persist in the animal's body for up to a week. Thus itching can last for up to a week afterwards. There are many types of fleas, such as the dog flea, cat flea, rat flea, etc. but all are very similar. An adult flea if given a choice will never leave the dog's body. Why would it want to leave its food supply?.

A flea after it bites the dog lays eggs. Those eggs are not sticky. They will roll off the dogs back and start to go through the larval and pupal stage in the environment. If the environment is heavily infested, treatment of the dog alone is a waste of time. You must treat the environment as well as the dog.

After the female flea feeds she lays eggs. Feeding is the stimulus to lay eggs. If you left a flea in a locked room for 6 months you would come back to a room full of very hungry fleas. The flea can survive up to 6 months in a state of suspended animation but at least in this state it cannot lay eggs.

The eggs are gelatinous and are impenetrable to insecticides. We can't do much to kill the egg. After the eggs hatch they go through a larval stage. We can kill larvae in the environment and we can kill larvae on the dog. That's fairly easy to do. Then comes the pupal stage where they go into the final stage of the development leading to the adult flea. In this stage in their cocoon they are impenetrable to insecticides so that once they get into the pupal stage there is nothing you can do to kill the flea. This is the big problem with flea allergy dermatitis. You can get rid of the flea on the dog but once the dog is replaced in an untreated environment it is immediately reinfested.

The flea can only be killed in the larval and adult stage which is about 58% of its total life cycle as the following table shows.

        1% as an adult
        8% as a pupa
        57% as a larva
        34% as an egg
 

The flea bite is like a mosquito bite. It will leave tiny red blotches. As the dog scratches there is initially usually no infection but the act of scratching will eventually result in the skin becoming broken and consequently infected. Thus it is important to determine whether or not skin infections are present in conjunction with the flea allergy. If there is it has to be treated with antibiotics while at the same time eradicating the fleas. So treatment can become more complicated than just insecticidal warfare.

Diagnosis of flea allergy dermatitis can be easy or complicated. The best way to find fleas is to use a flea comb. All pet owners should have one. Parting hair to look for fleas is not very effective. Flea combs also find and collect flea dirt. Use one regularly in flea season.

Therapy.

If an animal is very itchy we must break the itch cycle. Even if we get rid of all the fleas at once, remember that the saliva of the flea is travelling through they dog's system and the dog can remain itchy for up to 1 week. The dog can create very many hot spots during that week's period of time. For the very itchy dog the itch must be suppressed.

A wide variety of things may be used. Steroids are the recommended choice. Most dogs can not be hurt by a week of steroids as long as the dog is not diabetic, does not have heart disease, and does not have a severe metabolic problem. It's when you take steroids over extended periods of time that they can be a problem. So a vet will typically institute flea control and give the dog a week of corticosteroids. As mentioned before dogs with flea allergy can get infected skin, so frequently the vet will find that they have to prescribe antibiotics at the same time to combat the skin infection.

Hyposensitization vaccines at present do not work in dogs. The reason is because the vaccines are very crude. There is not enough of the flea saliva in the vaccines. If they do become available and effective, and it is possible that they may within the next 5 years then a whole new way of dealing with the flea allergic animal will open up. Right now all we have is flea control, not only on the affected animal, but on all contact animals and the environment. With a severely infested environment you have lost the battle. There is nothing you can do to instantaneously change that situation. With the best environmental control that anyone can give you have at least 60 days of misery and it can last longer than that. Once cleared up a course of action to prevent reinfestation and maintain control in the future must be instituted. Prevention is the most important part of treatment of flea allergy dermatitis.

What do we do for the affected dog? Many of the gimmicky things we hear about may not be effective on the average dog and certainly will not be effective on the flea allergic dog. Ultrasonic collars may decrease the flea burden but they don't decrease it to zero. Brewers yeast, the old time B vitamin deficiency story, does indeed in some dogs seem to reduce the flea population by up to 50% but in the flea allergic dog this is inadequate. Garlic may work but you must give the dog enough garlic perles so that you can smell the garlic coming through the dog's skin. That gives you a fairly pronounced doggy odour. The other thing is that too much garlic will cause a form of anaemia. It is the product which is probably the most effective but it also has a significant potential for harm.

Many people object to using flea dips on the dogs because they tend to dry the coat out. It is a natural phenomenon as all flea dips have petroleum distillates and these dry coats. There is a product marketed for people called Avon Skin So Soft. Hunters found out that this is the best mosquito repellant on the market. If you take it out of the jar and slather it on your dog, your dog will slide right out through your hands and stain everything in the house. If you use it at 1.5 oz. per gallon, a gallon being the typical flea dip, and add Skin So Soft to it, it does have some repellent effects as well as counteracting some of the drying effects, but at 1.5 oz. per gallon it is about 50% effective in reducing fleas. So again it is not 100% but it has two useful benefits and it also makes the dog smell good. If you want to bump it up to 2-4 oz. per gallon it will become much more effective as a flea repellant but the dog will become very greasy.

When dealing with insecticides we have a bunch of ideal criteria, none of which are available for us. these are the ideal criteria:

     1. effective
     2. minimally toxic
     3. no environmental effects
     4. inexpensive
     5. easy to apply
 

Today there are insecticides which meet all of the above except inexpensive. Flea collars are a waste in any flea allergic dog. During warm weather mix up a bucket of flea dip, put some Avon Skin So Soft in it and you can do any dog very thoroughly in about 2 minutes. Pick up the sponge and saturate the dog and let dry on the dog. You can guarantee that if you get the dog soaking wet that there is flea dip on every square inch of its skin. There is absolutely no doubt that the dip technology is the best way to go. During the winter months powders and sprays are preferred because of the time required for the dog to air dry. Proban made a resurgence about three years ago although it has been licensed since the mid-60's. It is an oral insecticide. You give it twice a week. The theory behind it is that the flea bites the dog, gets a lethal dose of insecticide and dies. This may be sufficient for the average dog but not for the flea allergic dog. Remember that when the flea bites the dog it leaves some of its saliva in the skin before it starts to suck blood, otherwise the blood will clot and it is the saliva that affects the flea allergic dog. Proban will help and in some dogs it may be enough but in the severely flea allergic dog it is not sufficient. Proban is also an organo-phosphate, When you use a systemic organo-phosphate on the dog, that means that you cannot use an organo-phosphate in the environment nor can you use an organo-phosphate dip on the dog. So as you pump it in to the dog you have to be very careful what products you use in the environment or on the pet. Proban is not normally used on flea allergic dogs.

As Proban was not effective in the flea allergic dog, the manufacturers brought out Prospot, which is an organo-phosphate but it goes on through trans-dermal application where you run a strip of it down the dogs back. It is the result of work done by veterinarians in Texas and Florida using an insecticide on cattle for flea control which was very effective. Like any other organo- phosphate it is potentially toxic. Research indicated that it needed to be applied at the dosage of 20mg/kg and was effective in eradicating fleas for 1-2 weeks. But it has side effects and is now outlawed in Texas and Florida. Prospot has a dosage of 4-8 mg/kg and is only 50% effective and lasts for about a week. It may or may not be satisfactory for the flea allergic dog. It is only effective for 5-7 days but is licensed for application once every two weeks. It is not good enough for severely flea allergic dogs. It, as with Proban, may be adequate for contact animals who are not flea allergic.

Premises

Concrete kennels and linoleum are easy. Just hose it and vacuum it. It is when you get into penetrable items, such as wood, carpets, etc. that flea control becomes more of a problem. Vacuuming is an excellent way to collect eggs in a short pile carpet. In a shag carpet it is more difficult. If you have your carpets truly steam cleaned, not by the grocery store cleaners which only use warm water, but by professionals you will kill every egg, larva and pupa in the carpet. Steam cleaning is the best product available for environmental control but is expensive and cumbersome at times.

As a result we tend to fall back on insecticides. Insecticides typically come in two fashions. They come with quick kill where you put it on, they kill for 24 hours and then they are gone. Those are worthless to you. The simple reason they are worthless is they will kill larvae and adult fleas only. We need to use a product that has residual effectivity. That can be either an insecticide or a growth regulator. They come in a number of forms such as pump sprays, aerosol cans or fogger technology. People thought that the foggers would be the easiest to use and the end of flea infestation in the house. Fat chance. Bomb placement is crucial to how well it will spread and disperse itself. All bombs need to be repeated at least twice. They do not work as well as expected because the dispersion pattern is circular and rooms are not. They do not cover under furniture or in furniture or penetrate shag carpets. To overcome their limitations you need to get a hand held sprayer and spray in the areas not effectively reached by the bombs, an added cost and added work. To do a good job will take 5-6 hours in the average house. A professional exterminator would be a better investment or your can by a tank sprayer and the chemicals and do it yourself. An added problem with the fogger technology is that the foggers have not been licensed for sale in Canada.

What do you need to put down in your environment? You need a quick kill insecticide plus something with residual effects to kill the eggs and the pupae. That can be an insecticide or a growth regulator such as methoprene. The classical insecticides are the organo-phosphates (not recommended in a house with children as it is too much exposure to insecticides which may be carcinogenic). The manufacturers have recognized this problem and now there are micro- encapsulated insecticides available. There are two versions. One is a pyrethrin which is made out of chrysanthemums, marketed under the name of Sectrol. The other is an organo-phosphate called Duratrol. It uses chlorpyrifos which is one of the most potent organo-phosphates known to man, but in the micro-encapsulated form it is not toxic, because children can swallow it and it does not digest in their gastro-intestinal tract. It is a timed release so it does not put concentrated levels of insecticide into the environment.

Methoprene is actually a birth control product for the flea. It is a juvenile hormone. It is a growth type of hormone. For the flea to mature to adulthood the hormone level has to drop. Methoprene in the environment keeps the growth hormone levels very high and that burns the flea out. It prevents development into the pupal stage and they all die. It is completely non-toxic. It in licensed by the WHO for addition to drinking water to control mosquitoes. it has prolonged activity for 8-90 days. Siphotrol is one name under which it is marketed. A recent development is the finding that methoprene is concentration dependent. It may be ovicidal. Triple the concentration shrivels the egg and kills it immediately. Ovitrol Plus is a pyrethrin insecticide which has methoprene in triple the concentration of an environmental spray. If the pyrethrin does not kill the flea the flea will lay the egg and when it touches the skin it will contact the methoprene and is effectively dead at that point. In the next year or two we should expect to see much different and much better flea sprays and dips.

Ovitrol Plus has the disadvantage that it is a pure pyrethrin spray and lasts only about 24 hours. For your flea allergic dog that is not enough. You need better flea control. The Ovitrol Plus is very useful to prevent environmental infestation but it's not good enough for the dog. What is recommended is that people use the Ovitrol Plus once every three weeks, as methoprene will last three weeks on the dog's skin, and a dip every week which has residual effectivity.

Prevention is the key to control. The important thing is to start your flea control program early before it is reasonable to expect fleas. Fleas typically start up as soon as the temperature and the humidity start to go up. They typically become a problem in late July with August - October being the worst time. With the flea allergic dog, owners should start control when they turn off their heaters from winter, typically about late April. The key is to start control early as the fleas know no calendar and next year could be a great year or a poor year for the flea.

FLEA PRODUCTS & THEIR INGREDIENTS

Classification of Insecticides
Short Acting - quick kill products - use on animals
Synergists - activity enhancers
Long Acting - residual action - use in premises
Growth Regulators - arrests development - use in premises

Short Acting Insecticides

Pyrethrins

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Last modified: 08/25/2004
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