Science and Art of Flea and Tick Control:

Transcription

1 Science and Art of Flea and Tick Control: Michael W. Dryden, DVM, Ph.D. Professor of Veterinary Parasitology Department of Diagnostic Medicine/Pathobiology College of Veterinary Medicine, Kansas State University, Manhattan KS Introduction: Historically, in order to achieve elimination of fleas we had to treat both the animal and the environment with a combination of insecticides and insect growth regulators. But today, in most cases topical and/or systemic therapy may be all that is required. Flea control can now be achieved with several highly effective, relatively safe insect growth regulators and adulticides. Several compounds that have demonstrated considerable effectiveness against fleas and/or ticks are permethrin, imidacloprid, fipronil, selamectin, nitenpyram, amitraz, lufenuron, methoprene and pyriproxifen. In addition several of these compounds also provide additional control or prevention of internal nematode parasites, elimination of mites and louse infestations. Therefore, while efficacy and ease of administration have dramatically improved, selection of products has become more complicated. Veterinarians must adjust parasite management programs to fit pet and clients needs. Product Overview: Permethrin (several formulations) Control of fleas, ticks, Cheyletiella and lice. Efficacy and duration are highly variable, based on formulation and resistance. Dogs only Imidacloprid (Advantage; Bayer Animal Health) 10mg/kg; spot-on formulation. Approved for monthly flea control. Has remarkable efficacy against lice, two applications at 30 days intervals. Dogs and cats.

2 Fipronil (Frontline Topspot or Frontline Spray; Merial Animal Health) 7.5mg/kg; spot-on and spray formulations. Approved for monthly flea and tick control. Efficacy also reported against lice. Reports of efficacy against Sarcoptes (variable efficacy) and Cheyletiella. Dogs and cats. Selamectin (Revolution; Pfizer Animal Health) 6mg/kg; spot-on formulation. Approved for monthly flea control and heartworm prevention in dogs and cats. Also approved for control of Sarcoptes on dogs, Otodectes on cats, Toxocara sp. and Ancylostoma sp. in cats, and tick control in dogs. Nitenpyram (Capstar; Novartis) A neonicotinoid, is a new systemically active, orally administered insecticide. Dosage: Dogs & cats <11.0kg: 11.4mg tablet; Dogs & cats >11.0kg: 57mg tablet Administered orally, rapid absorption within 10 min. Maximum blood levels are reached within 1.4 hrs and 0.6 hrs in fasting dogs and cats, respectively. The half-life of the drug in dogs and cats is 4.5 hrs and 7.7 hrs, respectively. Eliminated unchanged in urine within 24 36hrs. Insect Growth Regulators: Disrupt egg and larva development: Two distinct classes; Juvenile hormone (mimetics) analogs (JHA) and Chitin synthesis inhibitors (CSI). Lufenuron (Program; Novartis Animal Health) 10 mg/kg dogs, 30mg/kg cats; Oral CSI or insect development inhibitor. Prevents fleas from producing viable eggs Approved for control of flea populations. Used in integrated programs for removal of fleas and as long term preventative. Also combined with milbemycin. Methoprene (Precor) JHA & Pyriproxyfen (Nylar, Sumilar) JHA: Both on-animal and environmental applications. Prevent larval maturation and egg development. Eggs laid by female fleas that are on an animal treated topically with a JHA produce nonviable eggs. Eggs and developing larvae are non-viable before egg deposition.

3 Flea - Host interactions that play a role in understanding the importance of topical and systemic flea control: Adult cat fleas begin feeding almost immediately once they acquire a host and defecate flea feces (partially digested blood) in as little as 8 to 9 minutes of initiation of feeding (Dryden, 1990). Consumption of blood is necessary before cat fleas can initiate reproduction. Mating occurs after fleas have fed and egg production begins within 24 to 48 hours of females taking their first blood meal (Hudson and Prince, 1958; Akin, 1984). Female cat fleas remain on their host, laying 40 to 50 eggs per day within the pelage, with the eggs dropping off to be deposited anyplace the flea infested host has access (Dryden, 1989). Adult cat fleas are considered permanently host-associated external parasites. Since fleas cause considerable discomfort to their host and it is on the host where reproduction occurs, elimination of fleas and cessation of reproduction can both be accomplished at the host level. Flea Control Principles: Most insecticides do an excellent job of eliminating existing fleas from the host during the initial application. The problem is that reinfestation is a common occurrence. Historically, flea control was achieved through repeated application of on-animal products and application of insecticides and insect growth regulators into the premises. These programs were designed to eliminate existing populations on the host and reduce populations of developing and emerging adult fleas in the surrounding environment. The difficulty with this approach was getting pet owners to consistently following treatment protocols. Because pet owner compliance was problematic, pets repeatedly acquired new fleas from the premises and infestations became a recurring if not a continuous problem. The recent development of insecticides and insect growth regulators with convenient dosage forms (spot-ons, collars, pills, oral suspensions, and injections) and prolonged

4 residual activity, have improved dramatically pet owner compliance and have helped to eliminate recurrent infestations. Several of these new insecticides and insect growth regulators have even been shown to be extremely effective in eliminating flea infestations in even the most difficult climatic conditions. Field studies conducted in Tampa, FL (USA) demonstrated that fipronil, imidacloprid, and lufenuron (+pyrethrin spary or +nitenpyram tablets) were 100% effective in eliminating established flea populations, without the need for treatment of the premises (Dryden et al. 1999, Dryden et al 2000a, Dryden et al 2000b). Flea infestations can be eliminated using topical and systemic approaches because fleas are either killed prior to initiating reproduction or reproduction is directly inhibited. While providing the pet relief from fleas is one aspect of treatment, the other goal should be eliminating fleas before they can initiate reproduction. If flea products are applied at the appropriate dose and treatment intervals there should be adequate residual activity between applications to kill most if not all newly acquired fleas before egg production is initiated. However, flea survival and reproduction do occasionally occur for a variety of reasons. Infrequent product application commonly occurs because of owner concerns of pet toxicity or simple lack of compliance with label or veterinary instructions. The inabilities of some pet owners to adequately apply the insecticide and therefore under-dose the pet often allow fleas the opportunity to reproduce between product applications. Bathing and swimming can also reduce insecticide levels of most products. In addition, genetic variability of different flea populations means that none of the currently available residual flea products are 100% effective against all cat flea strains between labeled reapplication periods. These same factors that often allow flea infestations to be persistent and could possibly be the scenario that allows for genetic selection of resistant populations of fleas.

5 Tick control Control of recurrent or persistent tick problems usually starts with an understanding of the life history of the problem tick or ticks. It must be remembered that virtually all ticks infesting dogs in the U.S. are considered 3-host ticks. The larva feeds on one host, feeding for several days drops off and molts in the environment to a nymph. The nymph then gets on a second host, feeds for a few days, drops off into the environment, and molts to the adult stage. The adult gets on a third host, with female ticks feeding until they become engorged (large blood killed abdomens), and then drop off and lay eggs in the environment. Difficulty in controlling ticks often results from an inability to: 1) control immature stages of ticks in the environment, 2) eliminate alternative wildlife hosts, or 3) restrict movement of pets from infested environments. Several different species of ticks may infest dogs and less commonly cats. Historically the most common tick infesting dogs in North America was Dermacentor sp. Larval ticks usually feed on rats, mice, or other small wild mammals. Nymphs feed on dogs, rabbits, raccoons, opossums, and other medium to small sized mammals. Then the adult tick will feed dogs, horses, cattle and other large mammals, including man. Two other ticks with similar life histories are Ambylomma americanum and A. maculatum. Ambylomma americanum, Lone Star Tick, was once limited to Texas, Oklahoma, Arkansas, and other southern states. Recently however, this tick has been found as far north as Michigan and Wisconsin. A recent survey at KSU found that this tick accounted for 62% of ticks recovered (nymphs and adults) from dogs admitted to the teaching hospital. Of equal interest is that the Gulf Coast Tick, A. maculatum is also now found in Northeast Kansas. It is interesting to speculate that

6 the dramatic spread in Ambylomma sp. distribution and prevalence may be due to the remarkable increase in White Tail Deer populations, the natural host for the adult stages of these ticks. Another tick that is of considerable importance is the brown dog tick, Rhipicephalus sanguineous. It also is a 3-host tick but every stage (larva, nymph and adult) prefers to feed dogs. Larvae will feed on rats and nymphs on rabbits, but prefer on dogs. Because of this tick s ability to complete its lifecycle on one species of host and molt at much lower humidity than other three host ticks, it is the only species of tick that infests buildings in North America. The last 3-host tick of significant importance is Ixodes scapularis, the Deer tick or Lyme disease tick. This tick is found throughout the Midwest and Eastern US. It is a small 3-host tick, with larvae being the size of a pinhead and nonengorged adults being less than 2mm. Larvae feed on small mammals, (mainly mice, squirrels, voles, shrews, raccoons). Nymphs feed on mice, squirrels, chipmunks, raccoons, opossums, shrews, cats, and man. Adults feed primarily on white tail deer and rarely raccoons and dogs). Tick control can usually be accomplished with the regular topical application of residual insecticides such as permethrin, fipronil, amitraz or selamectin. Duration of activity varies considerable based upon formulation, dog activity, and acaracide tolerance or resistance in a given region. Occasionally topical application does not appear to control the problem. This may be real or perceived based upon pet owner expectations of product performance. If additional control measures are needed, products may be combined, frequency of application increased or the problem can be approached by attempting to eliminate ticks in the environment. If possible start by destroying tick habitat. Grass, weeds, brush piles in fence lines, between runs, and along buildings, should be removed because they provide a refuge for ticks and wild mammals that can also serve as hosts for ticks.

7 If brown dog ticks are the problem, these ticks can crawl up into the ceilings and cracks and crevices along floors to molt or lay eggs. Acaracides should be sprayed the cracks and crevices, behind and under cages and along the boards in the ceiling. Foggers may not get acaracides into these areas. Therefore, direct application of residual insecticide sprays is often necessary. Effective compounds for environmental tick include cyfluthrin, permethrin and cypermethrin. Following application, make sure the acaracide is dry before you allow animals back into the premises to minimize toxicity problems. These same compounds can also be used outdoors. Rarely is broadcast application of acaracides necessary in the yard. Spot treatment along fences, kennels or shaded areas is preferred. Finally, restricting pet access from tick infested environments may be necessary. The bottom line in persistent tick infestations is that environmental control is necessary. References: Akin DE Relationship between feeding and reproduction in the cat flea, Ctenocephalides felis (Bouche). M.S. Thesis, University of Florida, Gainesville, FL. pp 125. Dryden MW Host association, on-host longevity and egg production of Ctenocephalides felis felis. Vet. Parasitol. 34: Dryden MW Blood consumption and feeding behavior of the cat flea, Ctenocephalides felis felis (Bouché 1835). Ph.D. Dissertation, Purdue University, W. Lafayette, IN. pp 128 Dryden MW, Perez H, Ulitchny D Control of flea populations on naturally infested dogs and cats and in private residences with either topical Imidacloprid spot application or the combination of oral lufenuron and pyrethrin spray. Am. J. Vet. Med. Assoc.1;215(1):36-9. Dryden M, Magid-Denenberg T, Bunch S. Control of fleas on naturally infested dogs and cats and in private residences with topical spot applications of fipronil or imidacloprid. Veterinary Parasitology, Vol. 93:1; 69-75, 2000A. Dryden M, Maggid-Denenberg T, Bunch S, Schenker R. Control of Fleas on Dogs and Cats and in Private Residences with the Combination of Oral Lufenuron and Nitenpyram. Vet Therapeutics. In- Press. 2000B Hudson BW, Prince FM A method for large scale rearing of the cat flea, Ctenocephalides felis felis (Bouché). Bull. W.H.O., 19: