Michael W. Dryden

The cat flea: biology, ecology and control.

Control failures and recurrences of infestation of dogs, cats and their home environment with the cat flea, Ctenocephalides felis felis are common. Attempts to control these infestations are often impaired by an inadequate understanding of the interaction of the cat flea with its hosts and environment. This review presents information on the medical and veterinary importance of the cat flea and discusses recent information on the environmental and host factors that affect its development and survival. Additionally, information is presented on the use and effectiveness of various insecticides and insect growth regulators against the four life stages.

Control of fleas on naturally infested dogs and cats and in private residences with topical spot applications of fipronil or imidacloprid.

Thirty-four flea-infested dogs and cats residing in 20 homes in Tampa, FL were randomly placed into 1 of 2 treatment groups during the summer of 1997. Pets were treated topically with either 10.0%w/v imidacloprid or 10%w/v fipronil spot-on on day 0, then once for every 28-30 days for 90 days. Flea populations were assessed in the environment using an intermittent-light trap, while pet flea burdens were assessed using visual area counts. A single application of imidacloprid was 95.3 and 97.4% effective in reducing flea populations on pets at 7 and 28 days, respectively. A single application of fipronil was 97.5 and 97.0% effective in reducing flea populations on pets at the same time points. Following 3 monthly applications of either imidacloprid or fipronil, flea burdens on pets were reduced by 99.5 and 96.5%, respectively. In addition, flea numbers in the in-home environment were reduced by 99. 0 and 98.6% in homes, where pets were treated with imidacloprid or fipronil, respectively.

Insecticide/acaricide resistance in fleas and ticks infesting dogs and cats

This review defines insecticide/acaricide resistance and describes the history, evolution, types, mechanisms, and detection of resistance as it applies to chemicals currently used against fleas and ticks of dogs and cats and summarizes resistance reported to date. We introduce the concept of refugia as it applies to flea and tick resistance and discuss strategies to minimize the impact and inevitable onset of resistance to newer classes of insecticides. Our purpose is to provide the veterinary practitioner with information needed to investigate suspected lack of efficacy, respond to lack of efficacy complaints from their clients, and evaluate the relative importance of resistance as they strive to relieve their patients and satisfy their clients when faced with flea and tick infestations that are difficult to resolve. We conclude that causality of suspected lack of insecticide/acaricide efficacy is most likely treatment deficiency, not resistance.

Flea and tick control in the 21st century: challenges and opportunities.

Historically, veterinarians have told their clients that one flea is all that is necessary to produce and maintain the clinical signs of flea allergy dermatitis (FAD). Newer adulticides, such as fipronil, imidacloprid, nitenpyram and selamectin, have had a positive clinical effect on dogs and cats with FAD. However, data on flea feeding and the effect of these products on flea feeding bring into question the once perceived dogma of the single flea bite concept. Current data would indicate that the primary role of these insecticides in managing FAD is in rapidly reducing flea numbers and reducing flea feeding rather than preventing flea bites. Controlling tick infestations is important not only because ticks are nuisance parasites of dogs and cats, but also because they are vectors of a variety of bacterial and protozoal diseases. Achieving satisfactory tick control is often difficult due to unrealistic expectations of pet owners, to residual acaricidal properties of products that are often less than 100% and because of constant re-infestation pressure. Some of the most important factors veterinarians must be aware of are regional changes in tick distributions, our inability to control wildlife tick hosts and expectation differences between flea and tick control. These factors probably cause most real and perceived product failures.

Seroprevalence of Ehrlichia canis, Ehrlichia chaffeensis and Ehrlichia ewingii in dogs in North America

BackgroundThis study evaluated the exposure of dogs to three different Ehrlichia spp. in the south and central regions of the United States where vector-borne disease prevalence has been previously difficult to ascertain, particularly beyond the metropolitan areas.MethodsDog blood samples (n = 8,662) were submitted from 14 veterinary colleges, 6 private veterinary practices and 4 diagnostic laboratories across this region. Samples were tested for E. canis, E. chaffeensis and E. ewingii specific antibodies using peptide microtiter ELISAs.ResultsOverall, E. canis, E. chaffeensis and E. ewingii seroprevalence was 0.8%, 2.8%, and 5.1%, respectively. The highest E. canis seroprevalence (2.3%) was found in a region encompassing Arkansas, Louisiana, Oklahoma, Tennessee and Texas. E. chaffeensis seroreactivity was 6.6% in the central region (Arkansas, Kansas, Missouri, and Oklahoma) and 4.6% in the southeast region (Georgia, Maryland, North Carolina, South Carolina, Tennessee and Virginia). Seroreactivity to E. ewingii was also highest in the central region (14.6%) followed by the southeast region (5.9%). The geospatial pattern derived from E. chaffeensis and E. ewingii seropositive samples was similar to previous reports based on E. chaffeensis seroreactivity in white-tailed deer and the distribution of human monocytic ehrlichiosis (HME) cases reported by the CDC.ConclusionsThe results of this study provide the first large scale regional documentation of exposure to E. canis, E. chaffeensis and E. ewingii in pet dogs, highlighting regional differences in seroprevalence and providing the basis for heightened awareness of these emerging vector-borne pathogens by veterinarians and public health agencies.

Insecticide Susceptibilities of Cat Fleas (Siphonaptera: Pulicidae) from Several Regions of the United States

Abstract Eleven cat flea, Ctenocephalides felis (Bouchè), strains, seven field-collected and four laboratory-colonized, were assayed for susceptibilities to five insecticides (carbaryl, chlorpyrifos, malathion, permethrin, and pyrethrin) with an insecticide-treated, horizontally-oriented, Nylon 6,6 disk in a test tube. The pyrethrin was synergized using piperonyl butoxide (PBO). Flea mortality at two doses was recorded after 4 and 24 h exposures. The field strains from Texas and Florida tolerated carbaryl, chlorpyrifos, and malathion; and carbaryl and PBO-synergized pyrethrin, respectively. Tolerance was observed in a field strain from Kansas against malathion. Colonies from California and North Carolina were susceptible to malathion and PBO-synergized pyrethrin, and chlorpyrifos and permethrin, respectively, but three colonies showed tolerance. The insecticidal response of the California colony varied; when exposed to a chlorpyrifos dose of 10 mg (AI)/m2 for 24 h, at various times had mortality of 3–100%. With a PBO-synergized pyrethrin dose of 396 mg (AI)/m2 for 4 h, the mortality ranged between 4.2 and 97%. Colonized strains were more susceptible than field strains at 4 h exposure to all insecticides except PBO-synergized pyrethrin. Colonized strains survived better in control tubes. The colony strains’ susceptibility and variability are of considerable importance because these strains are used for flea product efficacy evaluations and bioassays. The differences in susceptibility between laboratory colonies and the field strains suggested development of both adaptation to colonization, and extensive, multiple cross-resistance to insecticides in field strains. Varying susceptibility of cat fleas may affect control success.

Development of a Larval Bioassay for Susceptibility of Cat Fleas (Siphonaptera: Pulicidae) to Imidacloprid

Abstract Strategies for controlling cat fleas, Ctenocephalides felis felis (Bouché), have undergone dramatic changes in the past 5 yr. With the advent of on-animal treatments with residual activity the potential for the development of insecticide resistance increases. A larval bioassay was developed to determine the baseline susceptibility of field-collected strains of cat fleas to imidacloprid. All four laboratory strains tested showed a similar level of susceptibility to imidacloprid. Advantages of this bioassay are that smaller numbers of fleas are required because flea eggs are collected for the test. Insect growth regulators and other novel insecticides can also be evaluated. Using a discriminating dose, the detection of reduced susceptibility in field strains can be determined with as few as 40 eggs.

Effect of 0.29% w/w fipronil spray on adult flea mortality and egg production of three different cat flea, Ctenocephalides felis (Bouché), strains infesting cats

To evaluate the effect of fipronil spray on adult flea mortality and flea egg production of three different cat flea, Ctenocephalides felis (Bouché) strains, 30 domestic short hair cats were randomly allocated into six groups of five cats each. On day 0, cats in groups 2, 4 and 6 were treated with fipronil at 5-6ml/kg. Cats in groups 1, 3 and 5 served as untreated controls. On days -2, 7, 14, 21, and 28 each cat was infested with 50 adult cat fleas. Groups 1 and 2 were infested with fleas from the Kansas1 Colony (KS1) strain. Groups 3 and 4 were infested with a recently colonized cat flea strain from Florida (R6). Groups 5 and 6 were infested with fleas from the ARC strain. The adulticidal activity of fipronil was determined by flea comb counts 48h after treatment and then 48h after each reinfestation. Any flea eggs produced during the infestations were collected and counted prior to the 48h comb counts. Fipronil spray was > or = 99.5% effective against adults of all three cat flea strains when applied during an active infestation. Fipronil spray provided > or = 98.2 and > or = 99.5% control of adult fleas and egg production, respectively, for all strains through week 2. On days 23 and 30 control of R6 adults and egg production was significantly lower than either the ARC or the KS1 strain. On day 30, control of R6 adults and egg production was 77.3 and 87.3%, respectively. Control of KS1 adults and egg production on day 30 was significantly lower than the ARC strain. Fipronil provided > or = 99.5 and > or = 99.9% control of ARC fleas and egg production, respectively, throughout the entire study. The susceptibility to fipronil for the three strains was also evaluated on filter paper pesticide bioassays. The R6 strain was found to be less susceptible than the KS1 and ARC strains. The LC(95) estimates for the strains were 10.13, 4.77 and 2.62mg/m(2) for the R6, ARC and KS1 strains, respectively.

Vaccination against the cat flea Ctenocephalides felis felis.

Non‐chemical control of haematophagous parasites is a desirable goal. We report here on the use of concealed antigens from the major digestive organ of the cat‐flea as vaccine components. Rabbits were immunized with various antigens from cat flea midguts, and immunoglobulin from these rabbits was fed to cat fleas in an artifical feeding system. Antibody produced against soluble antigens from the midguts of fed fleas was able to kill fleas in this system. Dogs were then immunized with various antigen preparations, and challenged for a week with live fleas. Significantly fewer live fleas were recovered from dogs immunized with fed midgut supernatant, and recovered live female fleas produced significantly fewer eggs. This study indicates the possibility of vaccination as a means of control of flea, and possibly other blood sucking insect populations.

Assessment of owner-administered monthly treatments with oral spinosad or topical spot-on fipronil/(S)-methoprene in controlling fleas and associated pruritus in dogs.

Monitoring of the performance of flea control products under conditions of natural challenge is valuable in assessing continued effectiveness and determining the ongoing relevance of laboratory studies. A multi-clinic, investigator-blinded study was undertaken in client-owned dogs to investigate and compare the flea control provided by 3 consecutive monthly treatments of oral spinosad (SPN) or fipronil/(S)-methoprene topical (FSM) spot-on. The first household dog meeting enrollment criteria and with at least 10 fleas (whole-body flea count) served as the index dog in a household against which primary objectives were set. Stratification was based on pruritus scores at the enrollment visit and on single or multiple pet household. Index pets were randomized to treatment with either SPN or FSM, dispensed on day 0 for at-home administration by owners. All other household dogs and cats, maximum 4 pets per household, were dispensed the same treatment as the index dog (spinetoram was dispensed for cats in SPN households). Subsequent treatments were dispensed when index dogs were returned for whole-body flea counts and pruritus-scoring at visits on days 30 and 60, with final assessments on day 90 (±5 days on each occasion). Primary endpoints were the number of flea-free index dogs in each group one month after the final treatment, the reduction in owner-reported pruritus, and the reduction from baseline mean flea counts. One hundred twenty eight index dogs were enrolled (65 in the SPN arm; 63 in the FSM arm) at 10 clinics in FL (6), NC (2), LA (1), and TX (1). On day 0, geometric mean flea counts were 57.7 (range: 10-1469) and 44.8 (10-717) for the SPN and FSM groups, respectively. On Day 90, 55 of 58 (95%) and 21 of 55 (38%) index dogs completing the study were flea-free in SPN and FSM groups, respectively; mean SPN pruritus scores declined to 0.92 (6.67 on day 0), and to 3.83 (6.33 on day 0) for FSM; geometric mean flea counts (% control) were 0.08 (99.9%) and 5.19 (88.4%), for SPN and FSM groups, respectively. Between-treatment differences were highly statistically significant (p<0.0001). In conclusion, SPN provided reliable flea control in client-owned dogs, regardless of challenge level.