VetInfo Digest January 2001
This Month:
Understanding and controlling Fleas
PalmOS® Website With a Lot of Veterinary Information for Downloading
This Month's Note:
I have spent the last two weeks preparing to give a continuing education program to a group of veterinarians on computer applications in veterinary medicine. One of the things I have been trying to emphasize is the importance of working with clients to find all the information applicable to their pet's health problems, including searching the Internet for information. I am glad that so many of you have chosen to become proactive participants in your pet's health care. Given the vast amount of information available now, the only way that anyone, pet or person, can expect to acquire most of the information available is by seeking it out personally. Your physician and your veterinarian both have too many patients and too much information to deal with to always provide you with all the information you need. Our newsletter and online services are also only a part of the puzzle. Don't give up on learning as much as you can, through as many sources are you have available to you.
Understanding Fleas and Winning the Battle to Control Them
It may seem strange to devote the January issue of the VetInfo Digest to flea control, at least in the Northern Hemisphere, but it is important to be ready for flea season before it arrives and fleas are an all year problem in some areas of the country. We continue to see some cases of flea allergy in our practice, even at this time of the year in Virginia, so flea control can be necessary all year, in some cases, even in temperate climates.
As in all warfare, it is usually best to understand your enemy when making battle plans for defeating him. Fleas are no exception. There are over 2000 species of fleas, but only a few of them actually parasitize pets and/or humans. The most common flea found on pets is Ctenocephalides felis, or the "cat flea". In most areas of the world, this flea represents over 80% of the flea infestation found in pets. This flea can not survive solely on humans but it doesn't mind making an occasional snack of human blood. Surprisingly, this flea does not infect wildlife much, either, which means that most cases of flea infestation are associated with contact with an infested dog or cat, not a squirrel or raccoon that happens to share the same territory. The next most common flea is Pulex irritans, or the "human flea", which is found mostly in tropical and subtropical climates. In the United States, Pulex irritans is the most common flea found on pets in the deep South, where it nearly displaces the cat flea in many areas. Oddly, Ctenocephalides canis, or the "dog flea" is not usually found on dogs or on cats, although it can occur on either species. Echidnophaga gallinacea, which is also referred to as the "stick-tight flea" and associated with poultry, will infest dogs, cats and humans, if it needs to in order to survive.
Most of the species of fleas have similar biology, so the following information applies to all of them, except where differences are pointed out. Adult fleas prefer to stay on the pet their entire life, if possible. Since the goal of most pets is to rid themselves of fleas, causing scratching, chewing and biting of the hair and skin in a search for fleas, it is logical to expect that many adult fleas are unsuccessful in their attempts to remain on the pet. An adult flea can live for at least a year, and probably longer, under ideal circumstances but the "real world" life span of fleas is probably around one to three months. An adult female flea requires blood meals in order to produce eggs. She usually produces about a few eggs at a time but may produce hundreds of eggs over the course of her lifetime. Flea eggs are white and oblong in shape. They are usually between 0.5 and 2mm in length, making them visible to the naked eye, although very difficult to see. Flea eggs are small enough to fit in the cracks in most flooring, making linoleum and wood floors potential reservoirs of infestation, although carpeting is obviously a better environment for immature fleas. Flea larvae must molt at twice before reaching the third instar phase, in which they spin a miniature cocoon and develop in it for a few days, changing into the pupal stage of the flea and then becoming an adult before emerging from the cocoon. The development of the pupal stage is influenced by both heat and humidity and may be as short as few days or as long as several months. Pupae are responsive to vibration and may wait to emerge from the cocoon until they are stimulated to do so, which may explain why people are often bitten around the ankles and why there seems to be a huge hungry population of fleas in a household when pets and humans have been gone for a while and then return.
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It is possible to achieve flea control with imidacloprid, fipronil or lufenuron in combination with an adulticide, without concomitant treatment of the surroundings. ..... per Michael Dryden, DVM, PhD, Kansas State University, July 1999. Dr. Dryden is considered to be the "flea guru" of veterinary medicine.
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When the temperature is between 60° Fahrenheit ( 16° degrees Celsius) and 85° F (30°) it is ideal for flea reproduction. However, fleas also require a relative humidity of about 75 to 85% for reproduction, which is why many areas of the world have limited flea populations or limited times in which fleas can reproduce. In some areas, flea populations can reproduce all year, making the battle against them much harder to win. Most people keep their homes warm enough for flea reproduction to occur in the winter but the humidity levels are usually lower than 75% in heated homes, so pets that stay indoors all year still usually get a break from fleas in the cooler months in temperate climates.
Adult female fleas generally consume about 18% of their weight in blood when they eat. Male fleas can consume up to 33% of their weight in blood. Fleas do not have efficient digestive tracts, so much of this blood is excreted, which is why flea feces are dark black but turn red when mixed with water. Much of the nutrient value of the blood also remains, which is important to the flea life cycle. Larval fleas do not move much and are not able to seek out food. They have to stumble across it, so food must be readily available. Larval fleas mostly eat the feces of adult fleas, which have fallen off the pet in its immediate surroundings, just like the flea eggs that have now developed into flea larvae. So the pet provides the meals for all stages of the flea life cycle, although it does this indirectly in the case of the larvae. Due to the large amount of blood that adult fleas can consume in repeated feedings, fleas pose a serious risk to young animals. Kittens and puppies die from flea infestation, without any secondary disease, in many cases. A good flea control program is essential when kittens or puppies are going to be raised by family pets.
The largest population of Ctenocephalides felis and C. canis occurs in the late summer and early fall. Pulex irritans reaches maximum populations in the midsummer and Echidnophaga gallinacea has population rises in the early spring and late fall.
Cat and dog fleas are the intermediate host for the tapeworm Dipylidium caninum, which is the most common tapeworm found in dogs and cats. Flea larvae ingest the tapeworm eggs and then a dog or cat ingests the flea as it tries to get it off of its skin. The tapeworm then finds itself in the pet's digestive tract, where it can develop into an adult, resulting in completion of the tapeworm life cycle. It can take as little as two weeks for a tapeworm ingested in this manner to begin to produce the egg sacs that most people associate with tapeworm infestation. These are short, 1 to 1.5cm (about ½ to ¾ inch) long white egg cases that have a muscular action, allowing them to move. These are usually seen around the rectum of the dog, or on its feces, and most clients think of these egg cases as "tapeworms", even though the actual tapeworm remains attached to the intestinal wall and just sheds the short segments that are actually seen. Fleas can carry other diseases, as well. The only one of major significance, probably, is the bubonic plaque organism, Yersinia pestis.
Many of my clients believe that their pet has fleas when it is itching and that fleas are not a problem if they are not seeing itchiness among their pets, or in some cases, if they are not itchy themselves. Clients using these criteria frequently miss flea infestations in pets that are not sensitized to the flea bites or assume failure of flea control medications if itchiness continues, even though there may be other causes for the itchiness. There are several good ways to check for the presence of fleas in a household, or on pets. Using at least one of these methods to check for fleas is a good idea. Using itchiness to evaluate which pets to treat in a multiple pet household is an especially bad idea. If any pets have fleas in a multi-pet household, all the pets should be treated in order to eliminate the flea infestation. Treating only the itchy pet or pets is just asking for continued flea problems.
Flea combs are available for checking for fleas on pets. These are combs with very narrow gaps between the teeth of the combs (very fine combs) which capture fleas as they the hair coat is combed. Louse combs with at least 32 teeth per inch will also work well as flea combs. It is best to concentrate in the areas around the top of the neck and back of the head and around the base of the tail and down the length of the tail, since these are the places that fleas congregate and combing works well to find them. The use of a flea comb on a regular basis to check for fleas is a good idea, especially in multiple pet households or in when a pet is very sensitive to flea bites and total control of fleas is desirable. This method of looking for fleas is even more accurate if the debris collected by the combs is examined for flea feces or flea eggs. Flea feces is black granular debris that turns red when placed on a pre-moistened paper towel. Flea eggs, as mentioned previously, are white oval eggs about 0.5 to 2mm long, which are best seen with a magnifying lens, if possible.
Separating the hair by hand, against the way it normally lies and looking at the skin for signs of fleas, flea feces or flea eggs also works well, if the search is vigilant. It is usually best to check the area between the ears, around the shoulder blades, over the base of the tail and in the inquinal region, carefully examining each area for approximately one minute. If suspicious debris is noted, collecting some of it and examining for flea feces or flea eggs
Light traps are a good way to monitor for fleas in the environment. The commercial light traps work well but a homemade light trap can be constructed according to guidelines from Kansas State University, which consists of a 7 watt light bulb surrounded by a green-yellow filter, which cycles on for 10 minutes, then off for 5 seconds, repeatedly, works well. The light attraction is placed over something that can trap the fleas, such as a pan of water with a small amount of liquid dish soap mixed in it. For pets that are itchy, it is better to assume that fleas are at least part of the problem and treat for them, even if fleas are never seen on the pet or in the household. In some studies of flea allergic pets, no fleas were ever found on examination of affected pets, apparently because they are so bothered by flea bites that they will incessantly chew on themselves until fleas are eliminated. If Dipylidium species tapeworm segments are found it is also best to assume that fleas are a problem and to treat for them, even if fleas can not be found.
There has been a great deal of information written about flea control in households and in the environment. Prior to the advent of the new flea control medications, it was always necessary to treat the pet, the house for house pets and the pet's environment in order to control fleas. Treating all these areas is still the quickest method of resolving a flea problem but several studies have shown that imidocloprid, lufenuron with an adulticide and fipronil are capable of eliminating flea infestations, even if the house or environment are not treated. For many veterinary clients this is a welcome relief, since treatment of the house is sometimes undesirable and treatment of the environment often undesirable.
If an effort is made to eliminate fleas in a household, vacuuming helps to eliminate adult fleas off of the pet and to eliminate flea eggs pretty efficiently, if the vacuum bag is changed after each time the house is vacuumed. Flea larvae in carpeting are not efficiently controlled by vacuuming, because flea larvae have hooks the bodies that cling well to carpeting, making them hard to dislodge and saving them from the vacuum cleaner. It is necessary to use a flea spray that can kill pre-adult stages of the flea to control the larvae in carpeting. Methoprene (Precor®) and pyriproxyfen (Nylar®) are two effective pre-adult flea control products. These ingredients can be found in many flea control products which are readily available. There are other insect growth regulators or products capable of killing pre-adult fleas, so reading the labels of household flea sprays carefully should allow you to find a product that will kill flea larvae.
Unfortunately, it is very hard to kill pupal fleas and these fleas are pretty efficient at finding a host quickly, since the presence of the host stimulates them to leave the cocoon, so they are not usually killed by pre-adult flea control products. For this reason, maintaining good adult flea control on the pet is really important when treating a flea infestation.
It usually takes about three months to totally (>99% flea reduction) control a flea infestation in a household, if all pets are treated with imidocloprid or fipronil once a month, or lufenuron once a month and an adulticide (pyrethrin spray or other method) used every couple of weeks, and there is no effort made to kill fleas in the environment. Fleas are usually reduced about 90 to 95% by the end of the first week. This is not enough to stop the itchiness associated with flea bite allergy in some pets, though. For these pets, a reduction in itchiness from flea control alone will usually take two to three months. If you know that your pet has an allergy to fleas, start your attempt to control fleas before the flea season and continue it until you are sure you are past the time when fleas are likely to be found in your climate.
If the flea advertising you see on TV and read in magazines was written by scientists, or by practicing veterinarians, it would probably be a lot different than what you see and read now. The ads for the best of the products might say something more like "Our product, used in conjunction with a total flea control plan, or for extended periods of time, will almost control flea related problems in your pets." For some products, the advertising would have to say, "Our product kills some of the fleas on your pet but not enough to ever control flea related problems your pet might have." Of course, that wouldn't be the greatest confidence builder in a product's prowess, so the marketing departments prefer to use slogans that are less than accurate. "Kills fleas instantly," is true for several products. Its just that none of them actually kill all the fleas. The ones that don't die instantly may not die at all. "Kills pre-adult fleas for up to 5 months," can be roughly translated to "Kills pre-adult fleas well for a month or two". There are lots of examples of this sort of truth-stretching in advertisements for flea killing products.
There are two flea products that kill adult fleas extremely effectively and have a proven track record with millions of doses sold. They are imidocloprid (Advantage™) and fipronil (Frontline Topspot™). These products each target weaknesses within the flea's nervous system that are not present, or not active, in mammals. This makes them safer than most flea products used in the past. Advantage is made by Bayer and Frontline Topspot is made by Merial, which is a spin-off of the animal health divisions of Merck and Rhone-Merieux. Frontline Spray® works better than Frontline Topspot®, when properly applied. However, application of Frontline Spray is difficult, so for many clients the Topspot version works better, just because dosing is more likely to be appropriate. There are two products capable of killing adult fleas that are newer on the market but are reported to work well. The first is selamectin (Revolution™) and the second is nitenpyram (Capstar™).
Revolution is a topical product that also kills several types of intestinal worms, at least one type of tick and prevents heartworms. It does not work as fast as imidocloprid and fipronil and it remains to be proven, over time, if it will be as effective, but for many clients the convenience of flea control and heartworm control in a single topical application once a month is appealing. For areas in which ticks are a major problem, this product will not work as well as Frontline Spray (best) or Frontline Topspot.
Capstar was just approved for use in the United States but has been available in Europe for a couple of years. Revolution is made by Pfizer and Capstar is made by Novartis. Capstar, which comes in tablet form, has no residual effect but is reported to kill all, or nearly all, adult fleas on the dog within a few hours of administration of the tablets. It is being marketed as part of a total flea control plan when combined with lufenuron ( Program™), which is a once-monthly tablet that prevents flea reproduction by causing damage to the eggs and developing larvae of fleas. Norvartis claims that Capstar may be given daily until the adult flea population is under control and then control can be maintained by continuous use of Program, along with "as necessary" use of Capstar.
Imidocloprid (Advantage) became available in the United States in 1996. Fipronil (Frontline) followed within a few months. Prior to the time these products were available, about 35% of the practice revenue of many veterinary hospitals related directly to the control of flea allergy dermatitis and secondary effects of this condition, such as chronic skin infections, in areas in which fleas were prevalent for at least a few months of each year.. I can not speak for all practices, but the reduction in chronic skin disease in our practice for clients who use these products on a regular basis from the time flea season starts until it ends, has been incredible.
In our practice, it has always been very hard to separate flea allergy dermatitis cases from other inhalant allergies (atopy), mange infestation and other chronic itchy conditions. This is no longer a major problem except when clients refuse to use the newer flea products due to cost concerns. We have discovered that the incidence of atopy is much lower than we would have thought and that we were not very good at distinguishing dogs and cats with atopy from dogs and cats with flea allergy. We have also discovered that we can control most, but not all, cases of atopy using lower dosages of prednisone or even alternatives to corticosteroids, while pets with flea allergy dermatitis do not respond well to alternatives to corticosteroids and almost always need higher dosages of corticosteroids to control their itching than atopic pets. The regular use of the newer flea control products has reduced the percentage of our cases that relate to flea allergy dermatitis to about 5 to 10% of the practice load from about 35%. We feel strongly that we could almost totally eliminate this condition except that imidocloprid and fipronil are expensive to use on very large dogs and in multiple cat households (unless the owners are adept at spraying the cats) so we have some resistance from clients who own big dogs or lots of cats.
The "typical" appearance of flea allergy in dogs is hair loss down the back of the thighs and along the top of the back, usually starting about the base of the tail and extending to about the level of the ribs or the shoulder blades in badly affected dogs. The based of the hair loss is usually includes some hair loss on the tail, is widest at the base of the tail and then tapers to a point somewhere along the back, leading to a "Christmas tree" appearance to the shape of the hair loss. The "typical" appearance of flea allergy dermatitis in cats is a bunch of small scabs on the skin, usually concentrated around the base of the tail and around the neck. Unfortunately, lots of dogs and cats don't develop typical patterns of reaction to flea bites, so almost any skin disease that involves itchiness should be considered as potentially a case of flea bite hypersensitivity or flea bite allergy.
There is some concern among veterinary clients, and a lot of concern among veterinary professionals, that resistance to these new flea products. The most recent studies (Vet Parasitology, Nov 2000, Dryden et. al.) do not show a resistance to these medications, yet, but it is logical, based on past experience, that it will eventually occur. Due to this concern, some veterinarians feel that it is best to use more than one of the products, or to use them on a rotating basis.
Using lufenuron and one of the adulticides is a frequently advocated method of reducing the potential for flea resistance to either medication, since fleas would have to become resistant to both in order to reproduce and thrive. This is expensive but may be worth considering for pets that are especially sensitive to flea bites. The alternative is to carefully monitor your pets for failure of the medication. You should expect to find an occasional adult flea, perhaps one every month or so, if you are carefully checking your pets and they are not confined entirely to your house. It takes a few hours for the flea products to work and new fleas will be picked up from the environment at times. However, if you are finding more fleas than this, you need to consult with your vet about the situation.
We find that the majority of the failures of lufenuron result from failure to give the tablets with a meal. Lufenuron is only absorbed from the digestive tract when it can hitch a ride on fat that is also being absorbed, so it must be given with a meal and the meal must contain at least a small amount of fat. Frontline Spray must be applied according to the label directions, which is one pump of the sprayer per pound of body weight for short haired pets and two pumps per pound for long haired pets. It is much better to error on the high side, since two pumps per pound is safe for pets even if they have short hair. Frontline Topspot and Advantage are absorbed better if they are placed directly on the skin, rather than spread across the top of the hair. The directions for Frontline Topspot seem to imply that it should all be put on one spot, but we find it is much more effective if it is applied in quantities that cover only the skin that can be exposed at one time by folding the hair back against its lie. This results in the need to apply about 2 to 3 spots on cats and up to 8 or 9 spots on large dogs, in order to try to apply the drops directly on the skin. It is possible to suck the liquid back into Topspot application vials if you aren't paying attention, so look at the vial before you throw it away, to make sure that it is empty.
Both Topspot and Advantage can be irritating to the skin at the spots they are applied. This is usually a reaction to the alcohol that the active ingredients are dissolved in. The irritation can last as long as 72 hours in some dogs and cats and is irritating enough that there have been scattered reports of self-mutilation at the site the product it applied. If a pet seems to be very sensitive to either product, washing the area thoroughly with shampoo and rinsing well, then repeating a couple of times, will eliminate most of the residual alcohol (and most of the active ingredient, too). For dogs and cats that are bathed regularly, Advantage may have to be reapplied after two baths, in order to maintain its effect. It should not be applied more than once a week, though. Frontline can usually withstand four or five baths before the active ingredient, fipronil, washes off enough to decrease its effectiveness. It is best not to bathe a dog for 48 hours before or after Frontline application. Frontline is not approved for use more than once a month, even if its effectiveness does seem to be waning after repeated bathing during the month. Swimming, or other exposure to water without shampoo or soap, does not seem to affect either product much.
There are a number of over-the-counter topical flea control products that claim to be effective for a month or more. Bio-Spot®, Control®, Defend®, are some of the products that make this claim. Almost all of these products are permethrin or permethrin in combination with something else, in the dog versions. This is simply not an effective flea control ingredient for dogs that really need flea control, such as flea allergic pets. Permethrin is reasonably effective if used every two weeks and may be suitable for dogs in which flea allergy problems are not an issue. Permethrin is toxic to cats and it is extremely important not to use the dog version of these products on cats. If there is an over-the-counter monthly flea control product for cats that has even moderate effectiveness, I am not aware of it.
Most of the products labeled for cats contain only a pre-adult flea control ingredient, which simply isn't adequate flea control protection for a cat that is sensitive to flea bites and does not work well enough to even recommend it for a cat that isn't particularly sensitive to flea bites.
I know that it is self serving for a veterinarian to tell you that the products that are available primarily through veterinarians are better but in this case, it is true. If you have a pet with flea allergy dermatitis, please use imidocloprid, fipronil, lufenuron and an adulticide (nitenpyram or pyrethrins work well) or possibly selamectin, to control the fleas on your pet. Start the month before flea season in your area and continue for one month past the time that fleas are prevalent. For some areas of the country and for a few people that keep the inside environment warm enough and humid enough, this will be all year. Monitor for fleas even though you are using a reliable product, in case resistance does develop some day and to be sure you are applying the products properly. For pets that live completely indoors or in areas in which fleas are only a minor problem, it may be possible to treat for a few months and then just monitor for return of the fleas, treating intermittently as necessary. Your vet can advise you on the best approach for your area and your pet's particular needs.
If You Own a PalmOS® Device:
For the last two months I have been collecting information on computer applications, telemedicine and computer peripherals that can aid veterinarians in their search for a definite diagnosis or help them practice better medicine through better client communications and record keeping. I will try to pass some of this information on over the next few months. For this month, since we have limited space left, I thought I'd stick to one topic, veterinary software for the Palm OS®.
There is a fair amount of detailed information on poisonings and pets available for use on PalmOS equipped devices available at this web site: http://www.anmldr.com , which is produced by Linda Cochran, DVM. The toxicology information is provided free of charge by Dr. Jill Richardson who works for the National Animal Poison Control Center. Dr. Greg Vogrin from Kansas State University has contributed a number of files, including the use of antibiotics, anesthetics, aging horses by their teeth and parasitology information. A collection of veterinary textbooks which have been converted to iSilo® format for Palm devices can be purchased on the site, including Dr. Plumb's "Veterinary Drug Handbook", which is a very valuable reference. If you have a PalmOS device it would definitely be worth checking out this site. I think that some of the files are also available in html format for folks who do not have a PalmOS device such as the PalmIII® or Handspring Visor®.
Thanks for Your Support!
If you send us e-mail, remember that Michal Justis answers the e-mail at vetinfo@vetinfo.com. E-mail sent to mervet@inna.net is answered by Dr. Michael Richards.