Detection of Rickettsia asembonensis in Fleas (Siphonaptera: Pulicidae, Ceratophyllidae) Collected in Five Counties in Georgia, United States

We conducted a molecular survey of Rickettsia in fleas collected from opossums, road-killed and live-trapped in peridomestic and rural settings, state parks, and from pet cats and dogs in Georgia, United States during 1992-2014. The cat flea, Ctenocephalides felis (Bouché) was the predominant species collected from cats and among the archival specimens from opossums found in peridomestic settings. Polygenis gwyni (Fox) was more prevalent on opossums and a single cotton rat trapped in sylvatic settings. Trapped animals were infested infrequently with the squirrel flea, Orchopeas howardi (Baker) and C. felis. TaqMan assays targeting the BioB gene of Rickettsia felis and the OmpB gene of Rickettsia typhi were used to test 291 flea DNAs for Rickettsia. A subset of 53 C. felis collected from a cat in 2011 was tested in 18 pools which were all bioB TaqMan positive (34% minimum infection prevalence). Of 238 fleas tested individually, 140 (58.8%, 95% confidence interval [CI]: 52.5-64.9%) DNAs were bioB positive. Detection of bioB was more prevalent in individual C. felis (91%) compared to P. gwyni (13.4%). Twenty-one (7.2%) were ompB TaqMan positive, including 18 C. felis (9.5%) and 3 P. gwyni (3.2%). Most of these fleas were also positive with bioB TaqMan; however, sequencing of gltA amplicons detected only DNA of Rickettsia asembonensis. Furthermore, only the R. asembonensis genotype was identified based on NlaIV restriction analysis of a larger ompB fragment. These findings contribute to understanding the diversity of Rickettsia associated with fleas in Georgia and emphasize the need for development of more specific molecular tools for detection and field research on rickettsial pathogens.

Laboratory studies evaluating the efficacy of a novel orally administered combination product containing sarolaner, moxidectin and pyrantel (Simparica Trio™) for the treatment and control of flea infestations on dogs

BACKGROUND

Five studies were conducted to evaluate a novel oral combination tablet containing sarolaner, moxidectin and pyrantel (Simparica Trio™), for efficacy against induced flea infestations, speed of kill and effects on flea reproduction on dogs.

METHODS

Based on pre-treatment flea counts, dogs were randomly allocated to treatment with a single, oral dose of either placebo or Simparica Trio™ at the minimum label dose of 1.2 mg/kg sarolaner, 24 µg/kg moxidectin and 5 mg/kg pyrantel (as pamoate salt) on Day 0. All dogs were infested with approximately 100 unfed, adult fleas (C. felis or C. canis) prior to treatment and weekly for 5 weeks post-treatment. In Studies 1, 2 and 3, the number of viable fleas were comb-counted at 24 h after treatment and after each weekly infestation; Study 2 also included groups treated with tablets containing sarolaner-alone (1.2 mg/kg), moxidectin-alone (24 µg/kg) or pyrantel-alone (5 mg/kg). In Study 4, flea counts were conducted at 3, 4, 8 and 12 h after treatment and subsequent weekly infestations to establish speed of kill. In Study 5 (flea reproduction), dogs were housed in an enclosure designed to facilitate collection of flea eggs.

RESULTS

Efficacy of Simparica Trio™ against C. felis was ≥ 99.7% and against C. canis was 100% at 24 h after treatment and after subsequent infestations for at least 35 days. Treatment with sarolaner-alone had similar efficacy to Simparica Trio™, while moxidectin-alone and pyrantel-alone were no different from placebo at most time points. In Study 4, significant flea killing started at 4 h after treatment; by 8 h after treatment, all treated dogs were free of fleas. Following weekly re-infestation, the combination product reduced fleas by ≥ 97.8% within 12 h for 28 days. Simparica Trio™ reduced flea egg-laying by 100% for 35 days. No treatment-related adverse reactions occurred in any study.

CONCLUSIONS

A single dose of Simparica Trio™ at the recommended minimum dose provided highly efficacious and rapid treatment within 4 h of existing flea infestations and persistent control of fleas on dogs for 5 weeks. The efficacy against fleas resulted in 100% prevention of flea reproduction for over a month following a single oral dose.

Synergy between dinotefuran and fipronil against the cat flea (Ctenocephalides felis): improved onset of action and residual speed of kill in adult cats

BACKGROUND

The cat flea, Ctenocephalides felis felis (C. felis), is a cosmopolitan hematophagous ectoparasite, and is considered to be the most prevalent flea species in both Europe and the USA. Clinical signs frequently associated with flea bites include pruritus, dermatitis and in severe cases even pyodermatitis and alopecia. Ctenocephalides felis is also a vector for several pathogens and is an intermediate host for the cestode Dipylidium caninum. Treatment of cats with a fast-acting pulicide, that is persistently effective in protecting the animal against re-infestation, is therefore imperative to their health. In addition, a rapid onset of activity ("speed of kill") may also reduce the risks of disease transmission and flea allergic dermatitis. The aim of this study was to evaluate the in vitro insecticidal activity and potential synergism between dinotefuran and fipronil against C. felis. A further aim was to evaluate the onset of activity and residual speed of kill of the combination in vivo on cats artificially infested with C. felis.

METHODS

In the first study, the insecticidal activity of dinotefuran and fipronil separately and dinotefuran/fipronil (DF) in combination, at a fixed ratio (2:1), was evaluated using an in vitro coated-vial bioassay. In the second study, the onset of activity against existing flea infestations and residual speed of kill of DF against artificial flea infestations on cats was assessed in vivo. Onset of activity against existing flea infestations was assessed in terms of knock-down effect within 2 h post-treatment and onset of speed of kill assessed at 3 h, 6 h and 12 h post-treatment. Residual speed of kill was evaluated 6 h and 48 h after infestation, over a period of six weeks post-treatment.

RESULTS

In vitro results revealed that the DF combination was synergistic and more potent against fleas than either compound alone. The combination also proved effective when tested in vivo. Efficacy was > 97% [geometric mean (GM) and arithmetic mean (AM)] at 3 h after treatment, and ≥ 99.8% (GM and AM) at 6 h and 12 h post-treatment. At 6 h after flea re-infestations, the efficacy of DF remained ≥ 90.8% (GM and AM) for up to 28 days, and at 42 days post-treatment persistent efficacy was still ≥ 54.3% (GM and AM). At 48 h after flea re-infestations, DF remained almost fully effective for up to 28 days, with efficacies ≥ 99.4% (GM and AM) and was persistently ≥ 93.0% (GM and AM) effective for up to 42 days post-treatment.

CONCLUSIONS

The combination of dinotefuran and fipronil in a single formulation exhibited strong synergistic insecticidal activity against C. felis in vitro, and also proved effective on artificially infested cats. This activity had a rapid onset that persisted for 6 weeks against re-infestations of C. felis on cats. The rapid curative insecticidal effect was observed as early as 3 h after treatment, and as early as 6 h after re-infestations for up to 6 weeks post-treatment. The insecticidal activity profile of DF makes it an optimal candidate for the protection of cats against flea infestations, and possibly also associated diseases.

Influence of Bloodmeal Host on Blood Feeding, Egg Production, and Offspring Sex Ratio of Ctenocephalides felis felis (Siphonaptera: Pulicidae)

The cat flea, Ctenocephalides felis felis (Bouché), feeds on different host species, causing annoyance or transmitting disease agents. In this study, the influence of the host of the cat flea on blood feeding, egg production, and sex ratio of the offspring was investigated. Two strains of C. felis were domesticated on either rats or mice for >10 yr in the laboratory, and in this study, these fleas were placed in the following groups and fed on rats or mice continuously: Group A (rat-domesticated C. felis with rats as host); Group B (rat-domesticated C. felis with mice as host); Group C (mouse-domesticated C. felis with rats as host); and Group D (mouse-domesticated C. felis with mice as host). In total, 240 adult fleas were in each group at a sex ratio of female:male = 1.7:1. The mean egg production per flea of Groups A, B, C, and D was 55.0, 19.2, 62.5, and 13.2, respectively. A significant correlation between egg production and the volume of blood consumed was detected for Groups A, B, C, and D. The sex ratio (F:M) of the offspring in Groups A and C was 2.07 and 2.11, respectively, whereas in Groups B and D, the ratio was 1.04 and 1.03, respectively. In conclusion, the C. felis with rats as host consumed more blood, produced more eggs, and had higher sex ratios of the offspring than those with mice as the host.

Feeding Behavior Modulates Biofilm-Mediated Transmission of Yersinia pestis by the Cat Flea, Ctenocephalides felis

BACKGROUND

The cat flea, Ctenocephalides felis, is prevalent worldwide, will parasitize animal reservoirs of plague, and is associated with human habitations in known plague foci. Despite its pervasiveness, limited information is available about the cat flea's competence as a vector for Yersinia pestis. It is generally considered to be a poor vector, based on studies examining early-phase transmission during the first week after infection, but transmission potential by the biofilm-dependent proventricular-blocking mechanism has never been systematically evaluated. In this study, we assessed the vector competence of cat fleas by both mechanisms. Because the feeding behavior of cat fleas differs markedly from important rat flea vectors, we also examined the influence of feeding behavior on transmission dynamics.

METHODOLOGY/PRINCIPAL FINDINGS

Groups of cat fleas were infected with Y. pestis and subsequently provided access to sterile blood meals twice-weekly, 5 times per week, or daily for 4 weeks and monitored for infection, the development of proventricular biofilm and blockage, mortality, and the ability to transmit. In cat fleas allowed prolonged, daily access to blood meals, mimicking their natural feeding behavior, Y. pestis did not efficiently colonize the digestive tract and could only be transmitted during the first week after infection. In contrast, cat fleas that were fed intermittently, mimicking the feeding behavior of the efficient vector Xenopsylla cheopis, could become blocked and regularly transmitted Y. pestis for 3-4 weeks by the biofilm-mediated mechanism, but early-phase transmission was not detected.

CONCLUSIONS

The normal feeding behavior of C. felis, more than an intrinsic resistance to infection or blockage by Y. pestis, limits its vector competence. Rapid turnover of midgut contents results in bacterial clearance and disruption of biofilm accumulation in the proventriculus. Anatomical features of the cat flea foregut may also restrict transmission by both early-phase and proventricular biofilm-dependent mechanisms.

Dynamics of Ctenocephalides felis felis (Siphonaptera: Pulicidae) Infestations on Urban Dogs in Southeastern Brazil

The cat flea, Ctenocephalides felis felis (Bouché, 1835), is an important ectoparasite of dogs and cats throughout the world, causing annoyance to the animals and acting as a vector of infections and a cause of allergic dermatitis in dogs and cats. Although climatic variability and seasonality are known to influence the diversity and abundance of fleas, few investigations of seasonal prevalence of cat flea infestation have involved the same group of dogs being examined regularly over an extended period. The aim of this study was to determine the effects of temperature, rainfall, and relative humidity on the infestation by C. felis felis on 88 outdoor dogs in southeastern Brazil. The dogs, which were of mixed breed, sex, and age, were examined for ectoparasites every month during the period August 2011 to July 2012, and samples of fleas were randomly collected and identified. Meteorological data, comprising mean temperature, total rainfall, and mean relative humidity, were recorded for the calendar month prior to that in which the examinations were performed. Dogs were found to be infested only with C. felis felis, with a higher prevalence in the months with lowest rainfall (July, August, and September). The data obtained in this investigation can be used in control programs in order to establish an efficient strategy for environmental management and the application of insecticides, particularly during the driest months of the year based on the seasonal pattern of infestation of dogs by C. felis felis.

Efficacy of a new combination of fipronil and permethrin against Ctenocephalides felis flea infestation in dogs

BACKGROUND

Five studies were conducted to evaluate the effect of a new combination of fipronil and permethrin on cat fleas, Ctenocephalides felis, when applied to dogs, including dogs that underwent water exposure or shampooing.

METHODS

In each study, 16 dogs were allocated to two groups. Each dog was infested with 100 unfed adult fleas on Days -1, 7, 14, 21 and 28. Eight dogs were treated with a new topical spot-on formulation containing 6.76% w/v fipronil + 50.48% w/v permethrinon Day 0; and eight dogs served as untreated controls. Twenty-four or 48 h after treatment or subsequent infestation, each dog was combed to remove and count live fleas. In addition, the dogs were subjected to different levels of water or shampoo exposure. In study 1, dogs were not subjected to any water exposure or shampooing; in study 2, dogs were water immersed twice during the month on Days 10 and 24; in study 3, dogs were water immersed three times on Days 10, 17 and 24; and in studies 4 and 5, dogs were shampooed once on Day 17.

RESULTS

All groups of dogs administered a single topical treatment with a combination of fipronil and permethrin had significantly (p < 0.005) lower flea counts than untreated controls 24 h and 48 h post-treatment or post-infestation, regardless of whether they underwent water exposure/shampooing or not. The reductions in C. felis counts were between 98.4% and 100% at all time points in all studies.

CONCLUSIONS

The new topical spot-on formulation of fipronil and permethrin maintains a high level of protection of dogs against C. felis flea infestations even when the dogs are exposed to environmental factors that are believed to adversely affect efficacy, such as water exposure or shampooing.

Susceptibility of cat fleas (Siphonaptera: Pulicidae) to fipronil and imidacloprid using adult and larval bioassays

The monitoring of the susceptibility offleas to insecticides has typically been conducted by exposing adults on treated surfaces. Other methods such as topical applications of insecticides to adults and larval bioassays on treated rearing media have been developed. Unfortunately, baseline responses of susceptible strains of cat flea, Ctenocephalides felis (Bouchè), except for imidacloprid, have not been determined for all on-animal therapies and new classes of chemistry now being used. However, the relationship between adult and larval bioassays of fleas has not been previously investigated. The adult and larval bioassays of fipronil and imidacloprid were compared for both field-collected isolates and laboratory strains. Adult topical bioassays of fipronil and imidacloprid to laboratory strains and field-collected isolates demonstrated that LD50s of fipronil and imidacloprid ranged from 0.11 to 0.40 nanograms per flea and 0.02 to 0.18 nanograms per flea, respectively. Resistance ratios for fipronil and imidacloprid ranged from 0.11 to 2.21. Based on the larval bioassay published for imidacloprid, a larval bioassay was established for fipronil and reported in this article. The ranges of the LC50s of fipronil and imidacloprid in the larval rearing media were 0.07-0.16 and 0.11-0.21 ppm, respectively. Resistance ratios for adult and larval bioassays ranged from 0.11 to 2.2 and 0.58 to 1.75, respectively. Both adult and larval bioassays provided similar patterns for fipronil and imidacloprid. Although the adult bioassays permitted a more precise dosage applied, the larval bioassays allowed for testing isolates without the need to maintain on synthetic or natural hosts.

A survey of ectoparasites infesting urban and rural dogs of Maranhão state, Brazil

This study evaluated for the first time, ectoparasite infestations on dogs from urban and rural areas of the continental land of the state of Maranhão, northeastern Brazil. In total, 622 dogs were examined for ectoparasite infestations. Overall, 392 (63.0%) were infested with ectoparasites, 154 (51.3%) of 300 urban dogs and 238 (73.9%) of 322 rural dogs. Five species of ectoparasites were found, three ticks [Rhipicephalus sanguineus (Latreille), Amblyomma ovale Koch, and Amblyomma cajennense (F.)], one flea [Ctenocephalides felis (Bouché)], and one louse [(Heterodoxus spininger (Enderlein)]. The frequency of infestation by R. sanguineus tended to be higher in urban than in rural areas, whereas infestations by Amblyomma ticks and C. felis fleas tended to be higher among rural dogs. Louse (H. spininger) infestations were similarly low among all areas. Mixed infestations by at least two species of ectoparasites on the same dog were significantly more frequent on rural than on urban dogs. The most frequent mixed infestation was by R. sanguineus and C. felis, found on 11.4% of the dogs. Further studies are warranted to evaluate canine vector-borne agents in Maranhão, especially because most of the ectoparasites here reported are vectors of major vector-borne diseases, including zoonoses of continental importance.

Combining real-time polymerase chain reaction using SYBR Green I detection and sequencing to identify vertebrate bloodmeals in fleas

Programs that aim to control vector-borne zoonotic diseases require information on zoonotic hosts and on the feeding behavior of bridging vectors that are capable of transmitting pathogens from those hosts to humans. Here we describe an assay developed to identify bloodmeals in field-collected cat fleas (Ctenocephalides felis Bouché) to assess this species' potential role as a Yersinia pestis bridging vector in a plague-endemic region of Uganda. Our assay uses a single primer set and SYBR Green I-based real-time polymerase chain reaction to amplify a segment of the 12S mitochondrial ribosomal RNA gene for identification by sequencing. The assay capitalizes on the sensitivity of real-time polymerase chain reaction and the specificity of sequencing and can be used to differentiate vertebrate bloodmeals to the genus or species level without a priori knowledge of the host community. Because real-time assays that detect vertebrate DNA are highly sensitive to human DNA contamination, we analyzed detection in artificially fed and unfed fleas to establish a Ct cutoff that optimized specificity without completely sacrificing sensitivity. Using the established cutoff, our assay detected human, rat, and goat DNA in artificially fed C. felis up to 72 h postfeeding.

Understanding attraction stimuli of the cat flea, Ctenocephalides felis, in non-chemical control methods

Comparisons were conducted of flea catches of four commercially available flea traps in the laboratory and under field conditions, in both rural and urban locations. The results clearly showed the My Flea Trap™, which utilizes an intermittent light to attract fleas, to be far superior in trapping ability to the three continuous light traps; it caught up to 23 times as many fleas as the other traps. Altering the lighting mechanism to provide continuous rather than intermittent light significantly decreased the number of fleas captured. In addition, the use of a green filter significantly increased trapping efficiency, whereas the addition of a heat source had no apparent effect.