Prevention of transmission of Ehrlichia canis by Rhipicephalus sanguineus ticks to dogs treated with a combination of fipronil, amitraz and (S)-methoprene (CERTIFECT®)

Advanced approaches for the diagnosis and chemoprevention of canine vector-borne pathogens and parasites-Implications for the Asia-Pacific region and beyond

Vector-borne pathogens (VBPs) of canines are a diverse range of infectious agents, including viruses, bacteria, protozoa and multicellular parasites, that are pernicious and potentially lethal to their hosts. Dogs across the globe are afflicted by canine VBPs, but the range of different ectoparasites and the VBPs that they transmit predominate in tropical regions. Countries within the Asia-Pacific have had limited prior research dedicated to exploring the epidemiology of canine VBPs, whilst the few studies that have been conducted show VBP prevalence to be high, with significant impacts on dog health. Moreover, such impacts are not restricted to dogs, as some canine VBPs are zoonotic. We reviewed the status of canine VBPs in the Asia-Pacific, with particular focus on nations in the tropics, whilst also investigating the history of VBP diagnosis and examining recent progress in the field, including advanced molecular methods, such as next-generation sequencing (NGS). These tools are rapidly changing the way parasites are detected and discovered, demonstrating a sensitivity equal to, or exceeding that of, conventional molecular diagnostics. We also provide a background to the armoury of chemopreventive products available for protecting dogs from VBP. Here, field-based research within high VBP pressure environments has underscored the importance of ectoparasiticide mode of action on their overall efficacy. The future of canine VBP diagnosis and prevention at a global level is also explored, highlighting how evolving portable sequencing technologies may permit diagnosis at point-of-care, whilst further research into chemopreventives will be essential if VBP transmission is to be effectively controlled.

Field trial investigating the efficacy of a long-acting imidacloprid 10%/flumethrin 4.5% polymer matrix collar (Seresto®, Elanco) compared to monthly topical fipronil for the chemoprevention of canine tick-borne pathogens in Cambodia

The tropical brown dog tick, Rhipicephalus linnaei, commonly infests canines in the tropics and is an important vector for disease-causing and sometimes lethal pathogens including Babesia spp., Ehrlichia canis, Hepatozoon canis and Anaplasma platys. In tropical climates ticks and their pathogens exert an extremely high infection pressure on unprotected dogs. To protect canines in such regions, effective acaricidal products possessing a speed of kill that blocks pathogen transmission is paramount. We conducted a 12-month community trial to compare the chemoprophylactic efficacy of two topical commercial acaricidal formulations: an imidacloprid 10% and flumethrin 4.5%, 8-month acting collar (Seresto®) against a monthly spot-on containing 12% w/v fipronil (Detick, Thailand). In a separate analysis, we used baseline data collected at the start of the trial to quantify tick-borne pathogen (TBP) infection status in dogs with a prior history of being administered a systemically-acting (isoxazoline) versus a topically-acting ectoparasiticide. We found that both topical products in the community trial demonstrated high efficacy at protecting dogs from ticks and TBP, with Seresto® demonstrating a moderate increase in protection at 3 (95% confidence interval (CI): 1–5) TBP-positive dogs per 100 dog-years at risk compared to 11 (95% CI: 4–26) TBP-positive dogs per 100 dog-years at risk for those on fipronil. Additionally, at baseline dogs treated with commercial systemic isoxazoline acaricides prior to the trial’s commencement were 2.7 (95% CI: 0.5–15.0) times more likely to be TBP-positive compared to dogs that had been topically treated, highlighting such isoxazoline products as being less efficacious than topical products at preventing canine TBP acquisition in a tropical setting.

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Chemopreventive products against ectoparasite infestation are essential for dog health in the tropics.

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Prevalence of canine tick-borne pathogens was higher in dogs on systemic ectoparasiticides than those on topical ones.

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Seresto® demonstrated better protection against canine tick-borne pathogen infection than a fipronil formulation.

World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) guidelines for studies evaluating the efficacy of parasiticides in reducing the risk of vector-borne pathogen transmission in dogs and cats

These guidelines are intended to provide an in-depth review of current knowledge and assist the planning and implementation of studies for evaluating the efficacy of parasiticides in reducing transmission of vector-borne pathogens (VBPs) to dogs and cats. At present, the prevention of VBP transmission in companion animals is generally achieved through the administration of products that can repel or rapidly kill arthropods, thus preventing or interrupting feeding before transmission occurs. The present guidelines complement existing guidelines, which focus on efficacy assessment of parasiticides for the treatment, prevention and control of flea and tick infestations, but also give guidance for studies focused on other vectors (i.e. mosquitoes and phlebotomine sand flies). The efficacy of parasiticides in reducing VBP transmission can be evaluated through laboratory or field studies. As such, the present guidelines provide recommendations for these studies, representing a tool for researchers, pharmaceutical companies and authorities involved in the research, development and registration of products with claims for reducing VBP transmission in dogs and cats, respecting the overall principles of the 3Rs (replacement, reduction and refinement). Gaps in our current understanding of VBP transmission times are herein highlighted and the need for further basic research on related topics is briefly discussed.

Arthropod-borne pathogens of dogs and cats: From pathways and times of transmission to disease control

Vector-borne pathogens have developed a close relationship with blood feeding arthropod ectoparasites (e.g., mosquitoes, ticks, phlebotomine sand flies, black flies, fleas, kissing bugs, lice) and exploited a huge variety of vector transmission routes. Therefore, the life cycles of these pathogens result in a long evolved balance with the respective arthropod biology, ecology and blood feeding habits, instrumentally to the infection of several animal species, including humans. Amongst the many parasite transmission modes, such as ingestion of the arthropod, with its faeces or secretions, blood feeding represents the main focus for this article, as it is a central event to the life of almost all arthropod vectors. The time frame in which pathogens are transmitted to any animal host is governed by a large number of biological variables related to the vector, the pathogen, the host and environmental factors. Scientific data available on transmission times for each pathogen are discussed relative to their impact for the success of vector-borne disease control strategies. Blocking pathogen transmission, and thus preventing the infection of dogs and cats, may be achievable by the use of chemical compounds if they are characterised by a fast onset of killing activity or repellence against arthropods. The fast speed of kill exerted by systemic isoxazoline, as well as the repellent effect of pyrethroids have renewed the interest of the scientific community and pharmaceutical companies towards reducing the burden of vector-borne diseases under field conditions. However, endosymbionts and vaccines targeting arthropods or pathogen antigens should be further investigated as alternative strategies towards the goal of achieving an effective integrated control of vector-borne diseases.

Five-month serological monitoring to assess the effectiveness of permethrin/fipronil (Frontline Tri-Act®) spot-on in reducing the transmission of Leishmania infantum in dogs

Canine vector-borne diseases are highly endemic in European countries of the Mediterranean basin. The use of repellent insecticides aids to reduce the risk of pathogen transmission. The primary objective of this 5-month serological field study conducted in a highly endemic area of canine leishmaniosis in Greece was to comparatively assess the effectiveness of a topical formulation of fipronil/permethrin (Frontline Tri-Act®/Frontect®) and of a deltamethrin collar (Scalibor®) for the prevention of Leishmania infantum transmission. Initially, 72 clinically healthy owned dogs were sampled for inclusion. Ten out of the 72 (13.8%) were seropositive according to the Snap Leish® ELISA test and removed. Ultimately, a total of 56 dogs were followed from May to October 2015 with monthly blood samples and serological tests based on Snap Leish® and Snap 4Dx® ELISA tests. Twenty-five dogs were treated with deltamethrin collar (Scalibor®) (Group 1) and 31 were treated monthly with the topical fipronil/permethrin formulation (Group 2). In group 1, three dogs out of 25 (12%) seroconverted for Leishmania whereas none of the dogs (0/31) seroconverted in group 2. In addition, this trial provided means to serological assess the transmission of other vector-borne pathogens. Regarding Anaplasma spp., one dog in each group was seropositive at the beginning of the study and no dogs became positive during the study. For Ehrlichia canis, 9/25 (36%) dogs in group 1 and 5/31 (16.1%) in group 2 were seropositive at inclusion time. Two out of 16 (11.8%) and 3/26 (11.5%) dogs became positive for E. canis after 3months in groups 1 and 2, respectively. No Borrelia burgdorferi sensu lato seropositive dog was found during the study. In regard to Dirofilaria immitis, 7/25 (28%) dogs and 12/31 (38.7%) were antigen-positive in groups 1 and 2, respectively, at inclusion. There was no significant difference between groups 1 and 2 in regard to new seroconversions during the trial. This study, conducted in a highly endemic area for vector-borne pathogen transmission, confirmed that the use of deltamethrin and permethrin is a suitable approach to reduce the risk of L. infantum infection by sandflies.

Comparative efficacy of oral administrated afoxolaner (NexGard™) and fluralaner (Bravecto™) with topically applied permethrin/imidacloprid (Advantix(®)) against transmission of Ehrlichia canis by infected Rhipicephalus sanguineus ticks to dogs

Background

The ability of the topical spot-on Advantix^® (50 % permethrin/10 % imidacloprid) to prevent transmission of Ehrlichia canis by infected Rhipicephalus sanguineus ticks to dogs has previously been reported. The recent market introduction of chewable tablets containing the novel compounds, afoxolaner (NexGard™) and fluralaner (Bravecto™) enabled us to conduct a comparative efficacy study with respect to the ability of these three products to block transmission of E. canis by ticks to dogs. The speed of kill, immediate drop-off rate and anti-attachment efficacy of the respective products were also studied.

Methods

The study was a blinded parallel group design, wherein 32 dogs were randomised into four different groups of eight dogs. Group 1 served as negative placebo control, group 2 and 3 were treated on Days 0, 28 and 56 with NexGard™ and Advantix^®, respectively. Group 4 was dosed once on Day 0 with Bravecto™. For tick efficacy assessments 50 non-infected ticks were placed onto the dogs on Days 30, 35, 42, 49, 56, 63, 70, 77 and 84 and on animal tick counts were performed at 3 h, 6 h and 12 h after infestation. To evaluate the ability to block transmission of E. canis, each dog was challenged by releasing 80 adult E. canis-infected R. sanguineus ticks into their sleeping kennels on Days 31, 38, 45 and 52. The animals were monitored for clinical signs of monocytic ehrlichiosis (pyrexia and thrombocytopenia) and were tested for E. canis DNA by PCR and for specific antibodies using IFA. A dog was considered infected with E. canis if both PCR and IFA yielded positive test results up to Day 84.

Results

Mean arithmetic tick counts on dogs treated with the Advantix^® spot-on were significantly (P < 0.0005) lower throughout the study as compared with the negative controls and was, with respect to the speed of kill and resulting onset of acaricidal efficacy, superior over NexGard™ and Bravecto™ at all time points in the 12 h period observed (3 h, 6 h and 12 h). None of the dogs treated with the Advantix^® spot-on became infected with E. canis, whereas six out of eight untreated control dogs acquired the infection. Furthermore, E. canis infection was diagnosed in four out of eight dogs treated with NexGard™ and in two out of eight dogs treated with Bravecto™.

Conclusions

The speed of kill of the two recently registered systemic compounds against R. sanguineus was not sufficiently fast to prevent transmission of E. canis and resulted in only low partial blocking and protection capacity while Advantix^® effectively blocked transmission of E. canis to dogs in the challenge period and thus provided adequate protection for dogs against monocytic ehrlichiosis.

Assessment of the prophylactic speed of kill of Frontline Tri-Act(®) against ticks (Ixodes ricinus and Rhipicephalus sanguineus) on dogs

The objective of the study was to assess the speed of kill of a single topical treatment with a combination of fipronil and permethrin (Frontline Tri-Act^®/Frontect^®) against experimental infestations of Ixodes ricinus and Rhipicephalus sanguineus ticks on dogs. In this parallel group designed, randomised, single centre, controlled efficacy study, 16 healthy adult dogs were allocated to two groups: 8 dogs were treated with the topical combination on Day 0 and the other 8 dogs served as untreated controls. Each dog was exposed in a crate to 100 I. ricinus (50 females, 50 males) and 50 R. sanguineus (25 males, 25 females) on Days 2, 7, 14, 21 and 28. Ticks were counted in situ at 6 and 12 h after exposure and removed at 24 h after exposure. Frontline Tri-Act^® was effective (≥90%) against both R. sanguineus and I. ricinus tick infestations at 6, 12 and 24 h after exposure, from 2 to 28 days after treatment. This is the first time that a topical ectoparasiticide has demonstrated a preventive killing effect against these two tick species in 6 h for a full month.

A novel combination of fipronil and permethrin (Frontline Tri-Act®/Frontect®) reduces risk of transmission of Babesia canis by Dermacentor reticulatus and of Ehrlichia canis by Rhipicephalus sanguineus ticks to dogs

Background

The ability of Frontline Tri-Act®/Frontect®, a topical ectoparasiticide containing fipronil and permethrin for dogs, to prevent the transmission of Babesia canis as well as Ehrlichia canis was evaluated by infesting dogs with infected vector ticks.

Methods

For the Babesia canis study, 16 dogs were randomly allocated to two groups. Eight dogs were treated on day 0 with a topical spot-on formulation containing 6.76 % w/v fipronil plus 50.48 % w/v permethrin and eight dogs served as the untreated control group. Dermacentor reticulatus ticks, with a B. canis infection rate ranging between 2 and 10 %, were placed onto dogs on days 7, 14, 21 and 28. In situ tick counts were performed on Days 9, 16 and 23. Ticks were counted and removed on Day 30. Infection of the dogs with B. canis was monitored by rectal temperature readings, clinical examinations and blood smears as well as PCR and IFA (indirect fluorescent antibody assay).

For the Ehrlichia canis study, another 16 dogs were allocated to two groups. Eight dogs were treated with the fipronil and permethrin combination on days 0 and 28 and eight dogs served as untreated controls. Rhipicephalus sanguineus ticks, carrying an infection rate of 13 % for E. canis, were released in the sleeping kennels of the dogs on days 7, 14, 21, 28, 35, 42, 49 and 56. Ticks were counted in situ on the dogs on a weekly basis. All ticks were removed and counted on the final assessment day 58. Infection of the dogs with E. canis was monitored by rectal temperature, clinical examinations, and testing of blood samples by PCR, IFA and platelet counts.

Results

B. canis was transmitted by D. reticulatus ticks to all eight untreated control dogs and to one treated dog, which was confirmed by blood smears, PCR and IFA. E.canis was transmitted by R. sanguineus ticks to all eight untreated control dogs. Two of the dogs in the treated group were found positive based on PCR and/or IFA.

Conclusions

Frontline Tri-Act®/Frontect® significantly lowered the risk for dogs to acquire a B. canis infection by 87.5 % over a challenge period of 28 days. The risk for dogs to acquire E. canis was reduced by 75 % over a period of 56 days.

A Tick Vector Transmission Model of Monocytotropic Ehrlichiosis

BACKGROUND

Ehrlichioses are emerging, tick-borne diseases distributed worldwide. Previously established animal models use needle inoculation as a mode of infection; however, there is limited representation of natural transmission in artificially inoculated models compared with transmission by the tick vector. The objective of this study was to develop a tick vector transmission animal model of ehrlichial infection using a human pathogen, Ehrlichia muris-like agent (EMLA).

METHODS

Ixodes scapularis larvae were fed on EMLA-infected mice, and after molting, infected nymphs were used to infest naive animals.

RESULTS

Ehrlichiae were acquired by 90%-100% of feeding larvae. The majority of animals fed upon by infected nymphs developed sublethal infection with 27% lethality. Bacteria disseminated to all tissues tested with greatest bacterial loads in lungs, but also spleen, lymph nodes, liver, kidneys, brain, and bone marrow. Numerous foci of cellular infiltration, mitoses, and hepatocellular death were observed in liver. Mice infected by tick transmission developed higher antiehrlichial antibody levels than needle-inoculated animals. Tick-feeding-site reactions were observed, but there was no observed difference between animals infested with infected or uninfected ticks.

CONCLUSIONS

For the first time we were able to develop a tick transmission model with an Ehrlichia that is pathogenic for humans.

The speed of kill of fluralaner (Bravecto™) against Ixodes ricinus ticks on dogs

Background

Pathogens that are transmitted by ticks to dogs, such as Anaplasma phagocytophilum, Babesia spp., Borrelia burgdorferi sensu latu, and Ehrlichia canis, are an increasing problem in the world. One method to prevent pathogen transmission to dogs is to kill the ticks before transmission occurs. Fluralaner (Bravecto™) is a novel isoxazoline insecticide and acaricide that provides long persistent antiparasitic activity following systemic administration. This study investigated the speed of kill of fluralaner against Ixodes ricinus ticks on dogs.

Methods

A total of 48 dogs were randomized to 8 groups of 6 dogs and each dog was infested with 50 female and 10 male I. ricinus ticks. Two days later (day 0), 4 groups received a single treatment of 25 mg fluralaner/kg body weight as Bravecto™ chewable tablets; the dogs in the other 4 groups were left untreated. Separate control and treatment groups were paired at each time point (4, 8, 12, or 24 hours after treatment) for assessment of tick-killing efficacy. At 4, 8, and 12 weeks after treatment, all dogs were re-infested with 50 female I. ricinus ticks and subsequently assessed for live or dead ticks at either 4, 8, 12, or 24 hours after re-infestation. Efficacy was calculated for each assessment time point by comparison of the treatment group with the respective control group.

Results

Tick-killing efficacy was 89.6% at 4 hours, 97.9% at 8 hours, and 100% at 12 and 24 hours after treatment. Eight hours after re-infestation, efficacy was 96.8%, 83.5%, and 45.8% at 4, 8, and 12 weeks after treatment, respectively. At least 98.1% tick-killing efficacy was demonstrated 12 and 24 hours after re-infestation over the entire 12 week study period.

Conclusions

Fluralaner kills ticks rapidly after treatment at 4 hours, and over its entire 12-week period of efficacy, it achieves an almost complete killing effect within 12 hours after tick infestation. The rapid tick-killing effect together with the long duration of efficacy enables fluralaner to aid in the prevention of tick borne diseases.

New method using quantitative PCR to follow the tick blood meal and to assess the anti-feeding effect of topical acaricide against Rhipicephalus sanguineus on dogs

A 28-day study was conducted to assess the dynamic of blood feeding by Rhipicephalus sanguineus ticks on dogs treated or not with a novel topical combination of fipronil, amitraz and (S)-methoprene. Dogs were infested weekly through exposure to ticks in crates for 4h. Ticks were then counted in the crates at 2h and 4h post dog exposure. Ticks were also counted and removed from the dogs at 2h, 4h, 6h, 12h and 24h post tick exposure. The inhibition of blood feeding was assessed by both tick quantification and designing and performing a quantitative PCR (qPCR) to detect the canine hydroxymethylbilane synthase (HMBS) gene in ticks. The percentage of repellency sensu lato based on the ticks collected in crates at 2h varied from 4.7% at day 28 to 48.3% at day 7. The immediate mortality rate of the ticks expelled at 2h varied from 1.5% at day 21 to 31.7% at day 7. The efficacy calculation showed that the acaricidal combination started to kill ticks in as little as 2h. The average efficacy reached 90.0% at 12h post crate challenges and 100% at 24h post exposure in crates. The inclusion of an internal amplification control was used to ensure that no significant template-derived PCR inhibition (≤ 6.2%) affected the overall results. The reduction of blood feeding was significant at 4h (>80.0%) and >99.0% at 24h post tick exposure in the crate. The high repellency rate and the lethal efficacy of CERTIFECT(®) resulted in significantly fewer live attached ticks, consequently reducing blood intake and fluid exchanges.

Dogs, cats, parasites, and humans in Brazil: opening the black box

Dogs and cats in Brazil serve as primary hosts for a considerable number of parasites, which may affect their health and wellbeing. These may include endoparasites (e.g., protozoa, cestodes, trematodes, and nematodes) and ectoparasites (i.e., fleas, lice, mites, and ticks). While some dog and cat parasites are highly host-specific (e.g., Aelurostrongylus abstrusus and Felicola subrostratus for cats, and Angiostrongylus vasorum and Trichodectes canis for dogs), others may easily switch to other hosts, including humans. In fact, several dog and cat parasites (e.g., Toxoplasma gondii, Dipylidium caninum, Ancylostoma caninum, Strongyloides stercoralis, and Toxocara canis) are important not only from a veterinary perspective but also from a medical standpoint. In addition, some of them (e.g., Lynxacarus radovskyi on cats and Rangelia vitalii in dogs) are little known to most veterinary practitioners working in Brazil. This article is a compendium on dog and cat parasites in Brazil and a call for a One Health approach towards a better management of some of these parasites, which may potentially affect humans. Practical aspects related to the diagnosis, treatment, and control of parasitic diseases of dogs and cats in Brazil are discussed.

The efficacy of Advantix® to prevent transmission of Ehrlichia canis to dogs by Rhipicephalus sanguineus ticks

The capacity of a topical combination of imidacloprid and permethrin (Advantix(®)) to prevent transmission of Ehrlichia canis was studied in two groups of six dogs. One group served as controls, whereas the other group was treated. All dogs were exposed to E. canis-infected Rhipicephalus sanguineus ticks on Days 7, 14, 21 and Day 28 post acaricidal treatment. The adult R. sanguineus ticks were released into the individual kennels of the dogs to simulate natural tick exposure. In situ tick counts were conducted on Day 9, 16 and 23 and any remaining ticks were counted and removed on Day 30. The efficacy of the acaricidal treatment against R. sanguineus ranged between 96.1% and 98.9% at 48 h post-application and lasted up to 4 weeks. Four out of six control dogs became infected with E. canis, as demonstrated by the presence of specific E. canis antibodies and the detection by PCR of E. canis DNA in blood samples. These dogs became thrombocytopenic and displayed fever and were consecutively rescue-treated by doxycycline. None of the six treated dogs became infected with E. canis, as confirmed by the lack of specific antibodies and absence of E. canis DNA in blood samples. Advantix(®) prevented transmission of E. canis and provided protection against monocytic ehrlichiosis for 4 weeks post acaricidal treatment.

Study of ehrlichiosis in kennel dogs under treatment and prevention during seven months in Dakar (Senegal)

In Dakar kennels where morbidity and mortality attributed to diseases transmitted by ticks were high, we conducted a field study to assess the prevalence of Ehrlichia canis, Anaplasma platys and Babesia spp. infections in two kennels (n = 34 dogs) and to study the impact of tick protection. The first day of the study, the E. canis PCR were positive in 18 dogs (53%). A. platys was found in one dog and all dogs were negative for Babesia spp. After one month of doxycycline treatment, the number of PCR positive dogs decreased significantly to 2 (5.9%). During seven months, all dogs were treated monthly topically with a novel combination (Certifect(®), Merial) delivering at least 6.7 mg fipronil/kg body weight, 8.0mg amitraz/kg and 6 mg (S)-methoprene/kg. The number of PCR positive dogs remained stable all over the seven months, with 4 dogs being positive at Day 90 and 2 at Day 210. The combination of treatment and monthly prevention had a significant effect in the two kennels. All dogs remained healthy, which was not the case in previous years.