In the present study, we describe intraperitoneal development of the FR3 strain of Brugia malayi ... more In the present study, we describe intraperitoneal development of the FR3 strain of Brugia malayi in Mongolian jirds (Meriones unguiculatus). The third molt for male worms occurred between 4 and 7 days postinfection (dpi) and between 4 and 8 dpi for females. The fourth and final molt occurred between days 21 and 29 for males and 25 and 34 for females, considerably earlier than the times reported for subcutaneous infection models using cats and jirds. The timing of the third molt coincided largely with reports for subcutaneous Brugia pahangi infections of cats and jirds, but the final molt occurred considerably later and lasted longer than those reported for subcutaneous B. pahangi models. Spermatogenesis occurred by at least 50 dpi in adult males, and insemination of females likely occurred between 50 and 60 dpi. Microfilariae were observed in the uteri and ovejectors of adult females at 65 dpi. Keywords Brugia malayi. Brugia pahangi. Meriones unguiculatus. Wuchereria bancrofti Odile Bain is deceased.
Since the definitive identification in 1995 of the bacterial endosymbiont Wolbachia that resides ... more Since the definitive identification in 1995 of the bacterial endosymbiont Wolbachia that resides in different tissues of the filarial worm Dirofilaria immitis, there has been increasing interest to understand whether and what role it plays in the pathogenesis of and immune response to heartworm infection. The present study evaluated the effects of treatments on lung pathology in 20 beagle dogs experimentally infected with D. immitis. Dogs in Group 1 were treated with doxycycline (10 mg/kg/day) orally from weeks 0-6, 10-12, 16-18, 22-26, and 28-34. Dogs in Group 2 served as infected, non-treated controls. Dogs in Group 3 were given doxycycline as described for Group 1 combined with weekly oral doses of ivermectin (6 mcg/kg) for 34 weeks and intramuscular (IM) melarsomine (2.5 mg/kg) at week 24, followed by two additional melarsomine injections 24 h apart 1 month later. Group 4 received only melarsomine as described for Group 3. Lung lesion criteria, scored by two independent blinded pathologists, included perivascular inflammation and endothelial proliferation. Doxycycline treatment alone had no effect on lesion scores, whereas the combination of doxycycline and ivermectin resulted in less severe perivascular inflammation. All lungs were evaluated for positive immunostaining for the Wolbachia surface protein (WSP). Control dogs showed numerous thrombi, intense perivascular and interstitial inflammation and, occasionally, positive staining for WSP. Interestingly, dogs receiving doxycycline/ivermectin/melarsomine showed significantly less severe arterial lesions and the virtual absence of thrombi.
ABSTRACTUse of experimental cats and dogs in veterinary heartworm preclinical drug research is in... more ABSTRACTUse of experimental cats and dogs in veterinary heartworm preclinical drug research is increasing. As a potential alternative primaryin vivoheartworm preventative drug screen, we assessed lymphopenic mice with ablation of the interleukin-2/7 common gamma chain (γc) as susceptible to the larval development phase ofD. immitis. Non-obese diabetic (NOD) Severe Combined ImmunoDeficient (SCID)γc-/-(NSG / NXG) mice consistently yielded viableD. immitislarvae at 2-4 weeks post-infection across multiple experiments, different batches of infectious larvae inoculates, different isolates ofD. immitisand at independent laboratories. Mice did not display any overt clinical signs associated with infection up to 4 weeks. Developing larvae were found in subcutaneous and muscle fascia tissues, the natural site of this stage of heartworm in dogs. Larvae retrieved from NSG / NXG mice were mid-L4 stage of development. Compared with 14-dayin vitropropagated larvae,in vivoderived L4 were significa...
Background: Microfilarial (mf) counts were monitored over 21.3 months for any rebound that might ... more Background: Microfilarial (mf) counts were monitored over 21.3 months for any rebound that might occur in counts and adulticidal efficacy was assessed following administration of low dosage with short- and long-treatment regimens of doxycycline and ivermectin to heartworm microfilaremic dogs. Methods:Twelve heartworm-naïve Beagles infected with 10 pairs of adult Dirofilaria immitis by IV transplantation were randomly allocated to 3 groups of 4 dogs. All treatments started on Day 0. On Day 0, Group 1 (short-treatment regimen) received doxycycline orally at 10 mg/kg once daily for 30 days plus ivermectin orally (min., 6 mcg/kg) on Days 0 and 30. Group 2 (long-treatment regimen) received doxycycline orally at 10 mg/kg once daily until individual dogs became mf negative (72-98 days) and ivermectin every other week until individual dogs became mf negative (6-7 doses). Group 3 was the untreated control. Mf counts and antigen (Ag) tests were conducted. Dogs were necropsied for recovery and...
Background Administration of four to six consecutive monthly doses of 24 µg/kg moxidectin alone s... more Background Administration of four to six consecutive monthly doses of 24 µg/kg moxidectin alone shows high effectiveness in preventing the maturation of macrocyclic lactone (ML)-resistant heartworm strains, Dirofilaria immitis JYD-34 and ZoeLA. This laboratory study evaluated the efficacy of six consecutive monthly oral doses of Simparica Trio® (moxidectin/sarolaner/pyrantel) compared to six monthly doses of either Heartgard® Plus (ivermectin/pyrantel) or Interceptor® Plus (milbemycin oxime/praziquantel) against ML-resistant D. immitis ZoeLA strain. Methods Beagle dogs were inoculated with 50 third-stage (L3) D. immitis larvae (ZoeLA) 30 days prior to the first treatment. Dogs were randomized to treatment (six animals in each group) with six monthly oral doses of placebo, Simparica Trio, Heartgard Plus, or Interceptor Plus at their respective label doses. Microfilaria (MF) and antigen tests were conducted periodically, and efficacy was evaluated by necropsy for adult heartworms appr...
BackgroundThe current studies compared ProHeart®12, Heartgard®Plus and Interceptor®Plus for preve... more BackgroundThe current studies compared ProHeart®12, Heartgard®Plus and Interceptor®Plus for preventive efficacy against JYD-34, a macrocyclic lactone (ML)-resistant strain ofDirofilaria immitisin dogs.MethodsIn two studies, each using 24 adult beagles, dogs were allocated to four treatment groups (n = 6): placebo-treated control; ProHeart 12 as per label (0.5 mg/kg moxidectin); Heartgard Plus (HGP) as per label (minimum 6 µg/kg ivermectin); and Interceptor Plus (INP) as per label (minimum 0.5 mg/kg milbemycin oxime). In both studies, ProHeart 12 was administered as a single subcutaneous dose on day 0, and HGP and INP were administered orally on days 0, 30, 60, 90, 120 and 150. In Studies 1 and 2, dogs were inoculated with 50 third-stage heartworm larvae (JYD-34 strain) on days −30 and 165, respectively. In Study 2, treatment for both HGP and INP was continued on days 180, 210, 240, 270, 300 and 330. Adult heartworm recoveries were performed on day 185 in Study 1 and on day 360 in St...
International Journal for Parasitology: Drugs and Drug Resistance, 2021
Despite being considered one of the most pathogenic helminth infections of companion animals, mem... more Despite being considered one of the most pathogenic helminth infections of companion animals, members of macrocyclic lactone class are the only drugs available for the prevention of heartworm disease caused by Dirofilaria immitis. Alarmingly, heartworm prevention is at risk; several studies confirm the existence of macrocyclic lactone resistance in D. immitis populations across the United States. To safeguard the long term prevention and control of this disease, the identification and development of novel anthelmintics is urgently needed. To identify novel, resistance-breaking drugs, it is highly desirable to: Unfortunately, none of the three above statements can be answered sufficiently for D. immitis and most of our hypotheses derive from surrogate species and/or in vitro studies. Therefore, the present study aims to improve our fundamental understanding of the neuromuscular system of the canine heartworm by establishing new methods allowing the investigation of body wall and pharyngeal muscle responses and their modulation by anthelmintics. We found that the pharynx of adult D. immitis responds to both ivermectin and moxidectin with EC 50 s in the low micromolar range. We also demonstrate that the somatic muscle cells have robust responses to 30 μM acetylcholine, levamisole, pyrantel and nicotine. This is important preliminary data, demonstrating the feasibility of electrophysiological studies in this important parasite. a) Understand the mode of action of the gold-standard b) Understand the mechanism(s) of resistance against the goldstandard, and c) Implement a highly predictive screening cascade.
Background Aedes aegypti is one of the main species responsible for the transmission of mosquito-... more Background Aedes aegypti is one of the main species responsible for the transmission of mosquito-borne pathogens worldwide. The isoxazoline Sarolaner has excellent efficacy as an acaricide against ticks and mites and as an insecticide against fleas, and potential efficacy against other insects. Methods In each of two laboratory studies, 24 dogs were randomly allocated (n = 8/group) to an untreated control group, a Simparica-treated group (at the minimum dose of 2.0 mg/kg sarolaner), or a Simparica Trio-treated group (at the minimum dose of 1.2 mg/kg sarolaner, 24 µg/kg moxidectin and 5 mg/kg pyrantel), based on pre-treatment mosquito counts. Treatments were administered orally once on day 0. Each dog was exposed to 50 unfed female adult A. aegypti mosquitoes for 1 h on days 1, 7, 14, 21, 28 and 35. After each exposure, mosquitoes were counted for each dog and characterized as live, moribund or dead, and as fed or unfed. Dead mosquitoes were counted and removed at 12, 24 and 48 h pos...
The antifilarial effects of tetracycline drugs were first demonstrated when they were found to be... more The antifilarial effects of tetracycline drugs were first demonstrated when they were found to be highly effective against L(3) and L(4) of Brugia pahangi and Litomosoides sigmodontis in rodent models. Tetracyclines are also now known to have activity against microfilariae and adult Dirofilaria immitis, but assessment of their activity against larval and juvenile heartworms has not been reported previously. This study assessed the effects of doxycycline administered orally at 10mg/kg twice daily for 30-day periods at selected times during the early part of the life cycle of D. immitis in dogs with dual infections of D. immitis and B. pahangi. Twenty beagles were randomly allocated by weight to four groups of five dogs each. On Day 0, each dog was given 50 D. immitis L(3) and 200 B. pahangi L(3) by SC injection. Dogs received doxycycline on Days 0-29 (Group 1); Days 40-69 (Group 2); or Days 65-94 (Group 3). Group 4 served as untreated controls. Blood samples were collected for microfilariae counting and antigen testing. Necropsy for collection of adult heartworms and selected tissues were performed Days 218-222. Heartworms recovered were examined by immunohistology, conventional microscopy/transmission electron microscopy, and molecular biology techniques. No live heartworms were recovered from dogs in Group 1; dogs in Group 2 had 0 to 2 live worms (98.4% efficacy), and dogs in Group 3 had 0-36 live worms (69.6% efficacy). All control dogs had live adult heartworms (25-41). The live worms recovered from dogs in Groups 2 and 3 were less developed and smaller that worms from control dogs. Microfilariae were not detected in any dogs in Groups 1 and 2; one dog in Group 3 had 1 microfilariae/ml at necropsy. All control dogs had microfilariae at necropsy. One dog in Group 1 was antigen positive at one sampling (Day 166). One dog in Group 2 was antigen positive Days 196 and 218-222 and three dogs in Group 3 were antigen positive at one or more samplings All five control dogs were antigen positive at all three sampling times. These findings suggest that doxycycline at 10mg/kg orally twice daily for 30 days has efficacy against migrating tissue-phase larvae and juvenile worms and will delay or restrict microfilarial production.
This nationwide, post-marketing, epidemiological study using >11 million electronic medical re... more This nationwide, post-marketing, epidemiological study using >11 million electronic medical records for dogs visiting >500 Banfield veterinary hospitals indicates that both moxidectin and ivermectin are highly effective for the prevention of heartworm infection in dogs. As expected, however, the 100% effectiveness reported for both drugs in limited pre-clinical laboratory studies with experimentally induced infections and
To better understand the efficacy of doxycycline and 10% imidacloprid+2.5% moxidectin (Advantage ... more To better understand the efficacy of doxycycline and 10% imidacloprid+2.5% moxidectin (Advantage Multi(®); Bayer Animal Health, Shawnee Mission, Kansas) on immature adult Dirofilaria immitis parasites and the results of antigen tests, 12 healthy, randomly selected dogs were experimentally infected with D. immitis and monitored for 407 days. Two dogs in each of three subgroups of four dogs were each infected with six (total of 6 dogs) or 12 (total of 6 dogs) D. immitis infective third-stage larvae (L3) obtained from infected mosquitoes. Doxycycline (10mg/kg per os twice daily×30 days) and 10% imidacloprid+2.5% moxidectin (1ml/kg by topical application every 30 days) treatment was initiated at 105 (Group A) and 149 (Group B) days post infection (PI) in two groups. One subgroup of two dogs given 6 L3 and one subgroup of two dogs given 12 L3 remained as untreated controls (GroupC). Serum obtained regularly throughout the study was evaluated by ELISA (PetChek(®) Heartworm-PF Antigen Test...
Experimental heartworm infection was established in ten dogs. Five had mild infections (8 to 21 w... more Experimental heartworm infection was established in ten dogs. Five had mild infections (8 to 21 worms) and five had severe infections (41 to 96 worms). After larval inoculation, dogs were radiographed each month for 1 year to evaluate cardiopulmonary changes occurring as the heartworm disease developed. Changes seen radiographically during the first year of heartworm infection were related to the magnitude of the worm burden. In mild infections, changes mainly involved the terminal portion of the right caudal lobar pulmonary artery and were minimal. In severe infections, changes mainly involved the entirety of the right caudal lobar pulmonary artery. In some dogs, an increase in size of the right cranial lobar pulmonary artery was seen. Gross changes in the size of the right ventricle and main pulmonary artery did not frequently occur during the first year.
This compilation of articles consists of four papers presented at the 19th International Conferen... more This compilation of articles consists of four papers presented at the 19th International Conference of the World Association for the Advancement of Veterinary Parasitology (WAAVP) (held in New Orleans, LA, USA, on 10-14 August 2003) in a symposium session titled "Recent Advances in Heartworm Disease," organized and chaired by John W. McCall and Jorge Guerrero. The first paper (Guerrero) covered the American Heartworm Society's most recent revision of their guidelines for the diagnosis, prevention, and management of heartworm infection in dogs, based on new research and clinical experience, particularly in the areas of heartworm chemoprophylaxis, adulticide therapy, and serologic testing and retesting. The entire updated 2003 "Guidelines" are presented herein. One paper (McCall) reviewed the "soft-kill" adulticidal and "safety-net" (reach-back, retroactive, clinical prophylactic) activity of prolonged dosing of prophylactic doses of macrocyclic lactones, concluding that ivermectin is the most effective in this way, milbemycin oxime is the least effective, and the activity of injectable moxidectin and selamectin lies between that of ivermectin and milbemycin oxime. The two remaining papers provided an overview of the discovery, rediscovery, phylogeny, and biological association between Wolbachia endosymbionts and filarial nematodes (Genchi and co-authors) and compelling evidence that Wolbachia may play a major role in the immunopathogenesis of filarial diseases of man and animals (Kramer and co-authors).
Dipetalonema reconditum is a filarid nematode residing subcutaneously in dogs, and is transmitted... more Dipetalonema reconditum is a filarid nematode residing subcutaneously in dogs, and is transmitted by fleas. Previous studies on experimental infections are limited to those by Pennington (1972, Diss. Abst. 33B: 772-B) and Farnell and Faulkner (1978, J. Parasit. 64: 565567). Thus the purposes of our study were: 1) to determine whether dogs could be infected experimentally with D. reconditum by subcutaneous and transmucosal inoculation; 2) to determine whether cats and jirds were susceptible to D. reconditum following subcutaneous inoculation; and 3) to compare microfilaremias during the course of infection in dogs inoculated subcutaneously or transmucosally. A stray dog with a naturally acquired infection was the original source of D. reconditum. Microfilariae were identified by morphological features (Redington, B. C., et al., 1978. In Proceedings of the heartworm symposium '77, G. F. Otto (ed.). Veterinary Medicine Publishing Co., Bonner Springs, Kansas, pp. 14-21) and acid phosphatase activity (Chalifoux and Hunt, 1971, J. Am. Vet. Med. Assoc. 158: 601-605). Ctenocephalides felis pupae were purchased from Environmental Consultants, Inc., Norfolk, Virginia, and reared to adulthood (Smith and Eddy, 1954, Bull. Wld. Hlth. Org. 10: 127-137). Adult fleas were placed on the infected dog and rem ved 10 to 14 days later. Procedures for harvesting infective nematode larvae were similar to those described for Brugia pahangi by McCall (1981, J. Georgia Entomol. Soc. 16: 283-293). In the first experiment, 11 microfilaria-free dogs were inoculated (Table I). Transmucosal and transcutaneous inoculations were performed by placing infective nematode larvae on the vestibular mucosa and shaved skin, respectively, of anesthetized dogs. In addition, two cats and six Mongolian jirds were inoculated subcutaneously with 22 to 25 larvae per animal. In the second experiment, six microfilaria-free Beagles were inoculated subcutaneously and four were inoculated transmucosally with 30 larvae per animal. Modified Knott tests were performed weekly for 28 wk PI. The degree of microfilaremia was com-
cis-and trans-1,2-cyclobutanediamines bearing appropriate N-methyl and N-acyl substituents were p... more cis-and trans-1,2-cyclobutanediamines bearing appropriate N-methyl and N-acyl substituents were prepared as analogues of diethylcarbamazine (DEC). None displayed activity against Litomosoides carinii in the gerbil despite substantial structural and sterochemical similarities to the parent drug. The inactivity of these drugs is rationalized in terms of eclipsed pharmacophore configurations and the increased population of unfavorable rotational conformations made possible by the exocyclic position of both pharmacophores. To provide perspective for these conclusions, the literature on DEC analogues is briefly summarized and structure-activity data are discussed in terms of critical structural factors associated with microfilaricidal activity. Generalizations on structural principles governing activity are advanced which encompass test results for the large majority of DEC analogues.
Background: This study assessed the influence of a topical ectoparasiticide (dinotefuran-permethr... more Background: This study assessed the influence of a topical ectoparasiticide (dinotefuran-permethrin-pyriproxyfen, DPP, Vectra®3D, Ceva Animal Health) on the acquisition of heartworm microfilariae by mosquitoes exposed to microfilaremic dogs weekly for 1 month. Methods: Six beagle dogs (9.2 ± 1.6 kg body weight) infected with Dirofilaria immitis were allocated to two groups of three dogs: an untreated control group and a DPP-treated group. Dogs were treated on Day 0 and exposed under sedation for 1 h to 80 ± 20 unfed Aedes aegypti. Each dog was exposed to mosquitoes released into mosquito-proof containers on Days −7 (pretreatment), 7, 14, 21 and 28. Up to 20 engorged mosquitoes were aspirated from the cage as soon as they were blood-fed. They were dissected and the blood from each midgut was stained for a microfilaria (MF) count. After each exposure, mosquitoes were classified as live, moribund or dead and engorged or nonengorged. The number of dead mosquitoes was recorded daily for 16 days, when the live mosquitoes were dissected to count the infective third-stage larvae (L3). Results: Prior to treatment, 95% of the engorged mosquitoes in both groups had MF. After treatment, engorgement rates for the treated group were 0%, 2.3%, 2.7% and 2.2% for Days 7, 14, 21 and 28, respectively, with anti-feeding efficacy (repellency) of 100%, 98.0%, 95.8% and 97.0%, respectively. A total of 22 mosquitoes fed on treated dogs; most of them were dead within 24 h, and all were dead within 72 h. Only 2 unfed mosquitoes exposed to treated dogs survived the incubation period and no L3 were found in them. A total of 121 of the 132 (91.6%) surviving mosquitoes that had engorged on untreated dogs had an average of 12.3 L3 per mosquito (range, 0-39).
This study assessed the influence of a topical ectoparasiticide (dinotefuran-permethrin-pyriproxy... more This study assessed the influence of a topical ectoparasiticide (dinotefuran-permethrin-pyriproxyfen, DPP, Vectra® 3D, Ceva Animal Health) combined with a macrocyclic lactone (milbemycin oxime, MBO, Interceptor®, Virbac) on transmission of heartworm L3 from mosquitoes to dogs and subsequent development of worms in treated dogs exposed to infected mosquitoes. Thirty-two beagle dogs were allocated to four groups of eight: Group 1, untreated controls; Group 2, treated topically with DPP on Day 0; Group 3, treated orally with MBO on Day 51; and Group 4, treated with DPP on Day 0 and MBO on Day 51. Dogs were exposed under sedation for 1 h to Dirofilaria immitis (JYD-34)-infected Aedes aegypti on Days 21 and 28. At the end of each exposure, mosquitoes were classified as live, moribund, or dead and engorged or non-engorged. Live or moribund mosquitoes were incubated for daily survival assessment for 3 days. Mosquitoes were dissected before and after exposure to estimate the number of L3 tr...
In the present study, we describe intraperitoneal development of the FR3 strain of Brugia malayi ... more In the present study, we describe intraperitoneal development of the FR3 strain of Brugia malayi in Mongolian jirds (Meriones unguiculatus). The third molt for male worms occurred between 4 and 7 days postinfection (dpi) and between 4 and 8 dpi for females. The fourth and final molt occurred between days 21 and 29 for males and 25 and 34 for females, considerably earlier than the times reported for subcutaneous infection models using cats and jirds. The timing of the third molt coincided largely with reports for subcutaneous Brugia pahangi infections of cats and jirds, but the final molt occurred considerably later and lasted longer than those reported for subcutaneous B. pahangi models. Spermatogenesis occurred by at least 50 dpi in adult males, and insemination of females likely occurred between 50 and 60 dpi. Microfilariae were observed in the uteri and ovejectors of adult females at 65 dpi. Keywords Brugia malayi. Brugia pahangi. Meriones unguiculatus. Wuchereria bancrofti Odile Bain is deceased.
Since the definitive identification in 1995 of the bacterial endosymbiont Wolbachia that resides ... more Since the definitive identification in 1995 of the bacterial endosymbiont Wolbachia that resides in different tissues of the filarial worm Dirofilaria immitis, there has been increasing interest to understand whether and what role it plays in the pathogenesis of and immune response to heartworm infection. The present study evaluated the effects of treatments on lung pathology in 20 beagle dogs experimentally infected with D. immitis. Dogs in Group 1 were treated with doxycycline (10 mg/kg/day) orally from weeks 0-6, 10-12, 16-18, 22-26, and 28-34. Dogs in Group 2 served as infected, non-treated controls. Dogs in Group 3 were given doxycycline as described for Group 1 combined with weekly oral doses of ivermectin (6 mcg/kg) for 34 weeks and intramuscular (IM) melarsomine (2.5 mg/kg) at week 24, followed by two additional melarsomine injections 24 h apart 1 month later. Group 4 received only melarsomine as described for Group 3. Lung lesion criteria, scored by two independent blinded pathologists, included perivascular inflammation and endothelial proliferation. Doxycycline treatment alone had no effect on lesion scores, whereas the combination of doxycycline and ivermectin resulted in less severe perivascular inflammation. All lungs were evaluated for positive immunostaining for the Wolbachia surface protein (WSP). Control dogs showed numerous thrombi, intense perivascular and interstitial inflammation and, occasionally, positive staining for WSP. Interestingly, dogs receiving doxycycline/ivermectin/melarsomine showed significantly less severe arterial lesions and the virtual absence of thrombi.
ABSTRACTUse of experimental cats and dogs in veterinary heartworm preclinical drug research is in... more ABSTRACTUse of experimental cats and dogs in veterinary heartworm preclinical drug research is increasing. As a potential alternative primaryin vivoheartworm preventative drug screen, we assessed lymphopenic mice with ablation of the interleukin-2/7 common gamma chain (γc) as susceptible to the larval development phase ofD. immitis. Non-obese diabetic (NOD) Severe Combined ImmunoDeficient (SCID)γc-/-(NSG / NXG) mice consistently yielded viableD. immitislarvae at 2-4 weeks post-infection across multiple experiments, different batches of infectious larvae inoculates, different isolates ofD. immitisand at independent laboratories. Mice did not display any overt clinical signs associated with infection up to 4 weeks. Developing larvae were found in subcutaneous and muscle fascia tissues, the natural site of this stage of heartworm in dogs. Larvae retrieved from NSG / NXG mice were mid-L4 stage of development. Compared with 14-dayin vitropropagated larvae,in vivoderived L4 were significa...
Background: Microfilarial (mf) counts were monitored over 21.3 months for any rebound that might ... more Background: Microfilarial (mf) counts were monitored over 21.3 months for any rebound that might occur in counts and adulticidal efficacy was assessed following administration of low dosage with short- and long-treatment regimens of doxycycline and ivermectin to heartworm microfilaremic dogs. Methods:Twelve heartworm-naïve Beagles infected with 10 pairs of adult Dirofilaria immitis by IV transplantation were randomly allocated to 3 groups of 4 dogs. All treatments started on Day 0. On Day 0, Group 1 (short-treatment regimen) received doxycycline orally at 10 mg/kg once daily for 30 days plus ivermectin orally (min., 6 mcg/kg) on Days 0 and 30. Group 2 (long-treatment regimen) received doxycycline orally at 10 mg/kg once daily until individual dogs became mf negative (72-98 days) and ivermectin every other week until individual dogs became mf negative (6-7 doses). Group 3 was the untreated control. Mf counts and antigen (Ag) tests were conducted. Dogs were necropsied for recovery and...
Background Administration of four to six consecutive monthly doses of 24 µg/kg moxidectin alone s... more Background Administration of four to six consecutive monthly doses of 24 µg/kg moxidectin alone shows high effectiveness in preventing the maturation of macrocyclic lactone (ML)-resistant heartworm strains, Dirofilaria immitis JYD-34 and ZoeLA. This laboratory study evaluated the efficacy of six consecutive monthly oral doses of Simparica Trio® (moxidectin/sarolaner/pyrantel) compared to six monthly doses of either Heartgard® Plus (ivermectin/pyrantel) or Interceptor® Plus (milbemycin oxime/praziquantel) against ML-resistant D. immitis ZoeLA strain. Methods Beagle dogs were inoculated with 50 third-stage (L3) D. immitis larvae (ZoeLA) 30 days prior to the first treatment. Dogs were randomized to treatment (six animals in each group) with six monthly oral doses of placebo, Simparica Trio, Heartgard Plus, or Interceptor Plus at their respective label doses. Microfilaria (MF) and antigen tests were conducted periodically, and efficacy was evaluated by necropsy for adult heartworms appr...
BackgroundThe current studies compared ProHeart®12, Heartgard®Plus and Interceptor®Plus for preve... more BackgroundThe current studies compared ProHeart®12, Heartgard®Plus and Interceptor®Plus for preventive efficacy against JYD-34, a macrocyclic lactone (ML)-resistant strain ofDirofilaria immitisin dogs.MethodsIn two studies, each using 24 adult beagles, dogs were allocated to four treatment groups (n = 6): placebo-treated control; ProHeart 12 as per label (0.5 mg/kg moxidectin); Heartgard Plus (HGP) as per label (minimum 6 µg/kg ivermectin); and Interceptor Plus (INP) as per label (minimum 0.5 mg/kg milbemycin oxime). In both studies, ProHeart 12 was administered as a single subcutaneous dose on day 0, and HGP and INP were administered orally on days 0, 30, 60, 90, 120 and 150. In Studies 1 and 2, dogs were inoculated with 50 third-stage heartworm larvae (JYD-34 strain) on days −30 and 165, respectively. In Study 2, treatment for both HGP and INP was continued on days 180, 210, 240, 270, 300 and 330. Adult heartworm recoveries were performed on day 185 in Study 1 and on day 360 in St...
International Journal for Parasitology: Drugs and Drug Resistance, 2021
Despite being considered one of the most pathogenic helminth infections of companion animals, mem... more Despite being considered one of the most pathogenic helminth infections of companion animals, members of macrocyclic lactone class are the only drugs available for the prevention of heartworm disease caused by Dirofilaria immitis. Alarmingly, heartworm prevention is at risk; several studies confirm the existence of macrocyclic lactone resistance in D. immitis populations across the United States. To safeguard the long term prevention and control of this disease, the identification and development of novel anthelmintics is urgently needed. To identify novel, resistance-breaking drugs, it is highly desirable to: Unfortunately, none of the three above statements can be answered sufficiently for D. immitis and most of our hypotheses derive from surrogate species and/or in vitro studies. Therefore, the present study aims to improve our fundamental understanding of the neuromuscular system of the canine heartworm by establishing new methods allowing the investigation of body wall and pharyngeal muscle responses and their modulation by anthelmintics. We found that the pharynx of adult D. immitis responds to both ivermectin and moxidectin with EC 50 s in the low micromolar range. We also demonstrate that the somatic muscle cells have robust responses to 30 μM acetylcholine, levamisole, pyrantel and nicotine. This is important preliminary data, demonstrating the feasibility of electrophysiological studies in this important parasite. a) Understand the mode of action of the gold-standard b) Understand the mechanism(s) of resistance against the goldstandard, and c) Implement a highly predictive screening cascade.
Background Aedes aegypti is one of the main species responsible for the transmission of mosquito-... more Background Aedes aegypti is one of the main species responsible for the transmission of mosquito-borne pathogens worldwide. The isoxazoline Sarolaner has excellent efficacy as an acaricide against ticks and mites and as an insecticide against fleas, and potential efficacy against other insects. Methods In each of two laboratory studies, 24 dogs were randomly allocated (n = 8/group) to an untreated control group, a Simparica-treated group (at the minimum dose of 2.0 mg/kg sarolaner), or a Simparica Trio-treated group (at the minimum dose of 1.2 mg/kg sarolaner, 24 µg/kg moxidectin and 5 mg/kg pyrantel), based on pre-treatment mosquito counts. Treatments were administered orally once on day 0. Each dog was exposed to 50 unfed female adult A. aegypti mosquitoes for 1 h on days 1, 7, 14, 21, 28 and 35. After each exposure, mosquitoes were counted for each dog and characterized as live, moribund or dead, and as fed or unfed. Dead mosquitoes were counted and removed at 12, 24 and 48 h pos...
The antifilarial effects of tetracycline drugs were first demonstrated when they were found to be... more The antifilarial effects of tetracycline drugs were first demonstrated when they were found to be highly effective against L(3) and L(4) of Brugia pahangi and Litomosoides sigmodontis in rodent models. Tetracyclines are also now known to have activity against microfilariae and adult Dirofilaria immitis, but assessment of their activity against larval and juvenile heartworms has not been reported previously. This study assessed the effects of doxycycline administered orally at 10mg/kg twice daily for 30-day periods at selected times during the early part of the life cycle of D. immitis in dogs with dual infections of D. immitis and B. pahangi. Twenty beagles were randomly allocated by weight to four groups of five dogs each. On Day 0, each dog was given 50 D. immitis L(3) and 200 B. pahangi L(3) by SC injection. Dogs received doxycycline on Days 0-29 (Group 1); Days 40-69 (Group 2); or Days 65-94 (Group 3). Group 4 served as untreated controls. Blood samples were collected for microfilariae counting and antigen testing. Necropsy for collection of adult heartworms and selected tissues were performed Days 218-222. Heartworms recovered were examined by immunohistology, conventional microscopy/transmission electron microscopy, and molecular biology techniques. No live heartworms were recovered from dogs in Group 1; dogs in Group 2 had 0 to 2 live worms (98.4% efficacy), and dogs in Group 3 had 0-36 live worms (69.6% efficacy). All control dogs had live adult heartworms (25-41). The live worms recovered from dogs in Groups 2 and 3 were less developed and smaller that worms from control dogs. Microfilariae were not detected in any dogs in Groups 1 and 2; one dog in Group 3 had 1 microfilariae/ml at necropsy. All control dogs had microfilariae at necropsy. One dog in Group 1 was antigen positive at one sampling (Day 166). One dog in Group 2 was antigen positive Days 196 and 218-222 and three dogs in Group 3 were antigen positive at one or more samplings All five control dogs were antigen positive at all three sampling times. These findings suggest that doxycycline at 10mg/kg orally twice daily for 30 days has efficacy against migrating tissue-phase larvae and juvenile worms and will delay or restrict microfilarial production.
This nationwide, post-marketing, epidemiological study using >11 million electronic medical re... more This nationwide, post-marketing, epidemiological study using >11 million electronic medical records for dogs visiting >500 Banfield veterinary hospitals indicates that both moxidectin and ivermectin are highly effective for the prevention of heartworm infection in dogs. As expected, however, the 100% effectiveness reported for both drugs in limited pre-clinical laboratory studies with experimentally induced infections and
To better understand the efficacy of doxycycline and 10% imidacloprid+2.5% moxidectin (Advantage ... more To better understand the efficacy of doxycycline and 10% imidacloprid+2.5% moxidectin (Advantage Multi(®); Bayer Animal Health, Shawnee Mission, Kansas) on immature adult Dirofilaria immitis parasites and the results of antigen tests, 12 healthy, randomly selected dogs were experimentally infected with D. immitis and monitored for 407 days. Two dogs in each of three subgroups of four dogs were each infected with six (total of 6 dogs) or 12 (total of 6 dogs) D. immitis infective third-stage larvae (L3) obtained from infected mosquitoes. Doxycycline (10mg/kg per os twice daily×30 days) and 10% imidacloprid+2.5% moxidectin (1ml/kg by topical application every 30 days) treatment was initiated at 105 (Group A) and 149 (Group B) days post infection (PI) in two groups. One subgroup of two dogs given 6 L3 and one subgroup of two dogs given 12 L3 remained as untreated controls (GroupC). Serum obtained regularly throughout the study was evaluated by ELISA (PetChek(®) Heartworm-PF Antigen Test...
Experimental heartworm infection was established in ten dogs. Five had mild infections (8 to 21 w... more Experimental heartworm infection was established in ten dogs. Five had mild infections (8 to 21 worms) and five had severe infections (41 to 96 worms). After larval inoculation, dogs were radiographed each month for 1 year to evaluate cardiopulmonary changes occurring as the heartworm disease developed. Changes seen radiographically during the first year of heartworm infection were related to the magnitude of the worm burden. In mild infections, changes mainly involved the terminal portion of the right caudal lobar pulmonary artery and were minimal. In severe infections, changes mainly involved the entirety of the right caudal lobar pulmonary artery. In some dogs, an increase in size of the right cranial lobar pulmonary artery was seen. Gross changes in the size of the right ventricle and main pulmonary artery did not frequently occur during the first year.
This compilation of articles consists of four papers presented at the 19th International Conferen... more This compilation of articles consists of four papers presented at the 19th International Conference of the World Association for the Advancement of Veterinary Parasitology (WAAVP) (held in New Orleans, LA, USA, on 10-14 August 2003) in a symposium session titled "Recent Advances in Heartworm Disease," organized and chaired by John W. McCall and Jorge Guerrero. The first paper (Guerrero) covered the American Heartworm Society's most recent revision of their guidelines for the diagnosis, prevention, and management of heartworm infection in dogs, based on new research and clinical experience, particularly in the areas of heartworm chemoprophylaxis, adulticide therapy, and serologic testing and retesting. The entire updated 2003 "Guidelines" are presented herein. One paper (McCall) reviewed the "soft-kill" adulticidal and "safety-net" (reach-back, retroactive, clinical prophylactic) activity of prolonged dosing of prophylactic doses of macrocyclic lactones, concluding that ivermectin is the most effective in this way, milbemycin oxime is the least effective, and the activity of injectable moxidectin and selamectin lies between that of ivermectin and milbemycin oxime. The two remaining papers provided an overview of the discovery, rediscovery, phylogeny, and biological association between Wolbachia endosymbionts and filarial nematodes (Genchi and co-authors) and compelling evidence that Wolbachia may play a major role in the immunopathogenesis of filarial diseases of man and animals (Kramer and co-authors).
Dipetalonema reconditum is a filarid nematode residing subcutaneously in dogs, and is transmitted... more Dipetalonema reconditum is a filarid nematode residing subcutaneously in dogs, and is transmitted by fleas. Previous studies on experimental infections are limited to those by Pennington (1972, Diss. Abst. 33B: 772-B) and Farnell and Faulkner (1978, J. Parasit. 64: 565567). Thus the purposes of our study were: 1) to determine whether dogs could be infected experimentally with D. reconditum by subcutaneous and transmucosal inoculation; 2) to determine whether cats and jirds were susceptible to D. reconditum following subcutaneous inoculation; and 3) to compare microfilaremias during the course of infection in dogs inoculated subcutaneously or transmucosally. A stray dog with a naturally acquired infection was the original source of D. reconditum. Microfilariae were identified by morphological features (Redington, B. C., et al., 1978. In Proceedings of the heartworm symposium '77, G. F. Otto (ed.). Veterinary Medicine Publishing Co., Bonner Springs, Kansas, pp. 14-21) and acid phosphatase activity (Chalifoux and Hunt, 1971, J. Am. Vet. Med. Assoc. 158: 601-605). Ctenocephalides felis pupae were purchased from Environmental Consultants, Inc., Norfolk, Virginia, and reared to adulthood (Smith and Eddy, 1954, Bull. Wld. Hlth. Org. 10: 127-137). Adult fleas were placed on the infected dog and rem ved 10 to 14 days later. Procedures for harvesting infective nematode larvae were similar to those described for Brugia pahangi by McCall (1981, J. Georgia Entomol. Soc. 16: 283-293). In the first experiment, 11 microfilaria-free dogs were inoculated (Table I). Transmucosal and transcutaneous inoculations were performed by placing infective nematode larvae on the vestibular mucosa and shaved skin, respectively, of anesthetized dogs. In addition, two cats and six Mongolian jirds were inoculated subcutaneously with 22 to 25 larvae per animal. In the second experiment, six microfilaria-free Beagles were inoculated subcutaneously and four were inoculated transmucosally with 30 larvae per animal. Modified Knott tests were performed weekly for 28 wk PI. The degree of microfilaremia was com-
cis-and trans-1,2-cyclobutanediamines bearing appropriate N-methyl and N-acyl substituents were p... more cis-and trans-1,2-cyclobutanediamines bearing appropriate N-methyl and N-acyl substituents were prepared as analogues of diethylcarbamazine (DEC). None displayed activity against Litomosoides carinii in the gerbil despite substantial structural and sterochemical similarities to the parent drug. The inactivity of these drugs is rationalized in terms of eclipsed pharmacophore configurations and the increased population of unfavorable rotational conformations made possible by the exocyclic position of both pharmacophores. To provide perspective for these conclusions, the literature on DEC analogues is briefly summarized and structure-activity data are discussed in terms of critical structural factors associated with microfilaricidal activity. Generalizations on structural principles governing activity are advanced which encompass test results for the large majority of DEC analogues.
Background: This study assessed the influence of a topical ectoparasiticide (dinotefuran-permethr... more Background: This study assessed the influence of a topical ectoparasiticide (dinotefuran-permethrin-pyriproxyfen, DPP, Vectra®3D, Ceva Animal Health) on the acquisition of heartworm microfilariae by mosquitoes exposed to microfilaremic dogs weekly for 1 month. Methods: Six beagle dogs (9.2 ± 1.6 kg body weight) infected with Dirofilaria immitis were allocated to two groups of three dogs: an untreated control group and a DPP-treated group. Dogs were treated on Day 0 and exposed under sedation for 1 h to 80 ± 20 unfed Aedes aegypti. Each dog was exposed to mosquitoes released into mosquito-proof containers on Days −7 (pretreatment), 7, 14, 21 and 28. Up to 20 engorged mosquitoes were aspirated from the cage as soon as they were blood-fed. They were dissected and the blood from each midgut was stained for a microfilaria (MF) count. After each exposure, mosquitoes were classified as live, moribund or dead and engorged or nonengorged. The number of dead mosquitoes was recorded daily for 16 days, when the live mosquitoes were dissected to count the infective third-stage larvae (L3). Results: Prior to treatment, 95% of the engorged mosquitoes in both groups had MF. After treatment, engorgement rates for the treated group were 0%, 2.3%, 2.7% and 2.2% for Days 7, 14, 21 and 28, respectively, with anti-feeding efficacy (repellency) of 100%, 98.0%, 95.8% and 97.0%, respectively. A total of 22 mosquitoes fed on treated dogs; most of them were dead within 24 h, and all were dead within 72 h. Only 2 unfed mosquitoes exposed to treated dogs survived the incubation period and no L3 were found in them. A total of 121 of the 132 (91.6%) surviving mosquitoes that had engorged on untreated dogs had an average of 12.3 L3 per mosquito (range, 0-39).
This study assessed the influence of a topical ectoparasiticide (dinotefuran-permethrin-pyriproxy... more This study assessed the influence of a topical ectoparasiticide (dinotefuran-permethrin-pyriproxyfen, DPP, Vectra® 3D, Ceva Animal Health) combined with a macrocyclic lactone (milbemycin oxime, MBO, Interceptor®, Virbac) on transmission of heartworm L3 from mosquitoes to dogs and subsequent development of worms in treated dogs exposed to infected mosquitoes. Thirty-two beagle dogs were allocated to four groups of eight: Group 1, untreated controls; Group 2, treated topically with DPP on Day 0; Group 3, treated orally with MBO on Day 51; and Group 4, treated with DPP on Day 0 and MBO on Day 51. Dogs were exposed under sedation for 1 h to Dirofilaria immitis (JYD-34)-infected Aedes aegypti on Days 21 and 28. At the end of each exposure, mosquitoes were classified as live, moribund, or dead and engorged or non-engorged. Live or moribund mosquitoes were incubated for daily survival assessment for 3 days. Mosquitoes were dissected before and after exposure to estimate the number of L3 tr...
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Papers by John McCall