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Background: Transmission of canine heartworm (Dirofilaria immitis) from infected to naïve dogs is dependent on successful mosquito feeding and survival., Methods: To determine whether treating heartworm-infected dogs with fluralaner (Bravecto ® ) limits the survival of infected mosquitoes, and potentially the transmission of D. immitis, we allowed female mosquitoes to feed on microfilaremic dogs and evaluated mosquito survival and infection with D. immitis. Eight dogs were experimentally infected with D. immitis. On day 0 (~ 11 months post-infection), four microfilaremic dogs were treated with fluralaner according to label directions while the other four were non-treated controls. Mosquitoes (Aedes aegypti Liverpool) were allowed to feed on each dog on days -7, 2, 30, 56, and 84. Fed mosquitoes were collected, and the number of live mosquitoes determined at 6 h, 24 h, 48 h, and 72 h post-feeding. Surviving mosquitoes held for 2 weeks were dissected to confirm third-stage D. immitis larvae; PCR (12S rRNA gene) was performed post-dissection to identify D. immitis in mosquitoes., Results: Prior to treatment, 98.4%, 85.1%, 60.7%, and 40.3% of mosquitoes fed on microfilaremic dogs were alive at 6 h, 24 h, 48 h, and 72 h post-feeding, respectively. Similarly, mosquitoes fed on microfilaremic, non-treated dogs were alive 6 h post-feeding (98.5-100%) throughout the study. In contrast, mosquitoes fed on fluralaner-treated dogs 2 days after treatment were dead or severely moribund by 6 h post-feeding. At 30 and 56 days post-treatment, > 99% of mosquitoes fed on treated dogs were dead by 24 h. At 84 days post-treatment, 98.4% of mosquitoes fed on treated dogs were dead by 24 h. Before treatment, third-stage larvae of D. immitis were recovered from 15.5% of Ae. aegypti 2 weeks after feeding, and 72.4% were positive for D. immitis by PCR. Similarly, 17.7% of mosquitoes fed on non-treated dogs had D. immitis third-stage larvae 2 weeks after feeding, and 88.2% were positive by PCR. Five mosquitoes fed on fluralaner-treated dogs survived 2 weeks post-feeding, and 4/5 were from day 84. None had third-stage larvae at dissection, and all were PCR-negative., Conclusion: The data indicate that fluralaner treatment of dogs kills mosquitoes and thus would be expected to reduce transmission of heartworm in the surrounding community., (© 2023. Merck & Co., Inc., Rahway, NJ, USA and its affiliates.)

Background: Ticks are common on horses, but recent publications characterizing equine tick infestations in North America are lacking., Methods: To further understand attachment site preferences of common ticks of horses, and to document the seasonality of equine tick infestation in northeastern Oklahoma, horses from eight farms were evaluated twice a month over a 1-year period. Each horse was systematically inspected beginning at the head and moving caudally to the tail. Attachment sites of ticks were recorded and all ticks collected were identified to species and stage., Results: Horses (26 males and 62 females) enrolled in the study ranged in age from 1 to 23 years (mean = 12, 95% CI 11-13). A total of 2731 ticks were collected; 84.1% (74/88) of the horses were infested (median = 3 ticks) at one or more examinations. Five tick species were identified, including Amblyomma americanum (78.2%; 2136/2731), Ixodes scapularis (18.2%; 497/2731), Dermacentor albipictus brown variant (2.6%; 71/2731), Dermacentor variabilis (0.7%; 20/2731), and Amblyomma maculatum (0.3%; 7/231). Most ticks were adults (83.6%; 2282/2731), but immature A. americanum (436/2136; 20.4%), D. albipictus (12/71; 16.9%), and A. maculatum (n = 1) were occasionally recovered. Amblyomma americanum were most often attached to the inguinal area, and I. scapularis and D. albipictus were most commonly found on the chest and axillary region (P < 0.0001). Ticks were found on horses in every month of the year. The largest number of ticks (638/2731; 23.4%) were collected in May (P < 0.0001). Amblyomma americanum, primarily immature, was the only tick recovered in September, I. scapularis and D. albipictus predominated October through February, and both A. americanum and I. scapularis were common in March. In the warmer months, April through August, A. americanum was the most common tick, followed by D. variabilis and A. maculatum., Conclusions: This research confirms that ticks common on horses in North America have attachment site preferences and that ticks infest horses in Oklahoma throughout the year, including during the winter. Additional research is warranted to fully understand the risk these infestations pose to equine health., (© 2021. The Author(s).)

Background: Various heartworm (HW) diagnostic testing modalities detect products of, or reactions to, different life cycle stages of Dirofilaria immitis. Microfilariae (Mf) can be directly visualized in blood, antigen (Ag) from immature and adult heartworms may be detected on commercial assays, and antibody (Ab) tests detect the host immune response to larval stages. Ag and Mf tests are commonly used in dogs, which frequently carry adult HW infections, but Ab tests have only been validated for use in cats. In some HW-infected dogs, Ag is blocked by immune complexing leading to false-negative results. Heat-treatment (HT) to disrupt these complexes can increase the sensitivity of HW Ag tests. The aim of this study was to compare different methods for diagnosing HW infection in dogs at high risk using individual and paired diagnostic tests, including an exploration of using Ab tests designed for cats to test canine samples., Methods: One hundred stray adult (≥ 2-year-old) dogs in Florida shelters were tested using Mf, HW Ag, and HW Ab tests (feline HW Ab tests currently not commercially validated/approved for use in dogs); two versions of each test platform were used., Results: Fourteen dogs tested positive using point-of-care (POC) Ag tests; an additional 2 dogs tested positive with microtiter well assay, and an additional 12 dogs tested positive using HT Ag testing. For individual tests, Ag test sensitivity/specificity compared to HT Ag was 50-57%/100%, and Ab tests were 46-64%/82-94%. Sensitivity estimates for individual tests were higher when comparing to non-HT Ag. Pairing POC Ag tests with Mf tests improved sensitivity without loss of specificity, while pairing POC Ag and Ab tests modestly increased sensitivity at the expense of specificity., Conclusions: Screening dogs for HW infection using both POC Ag and Mf detection, which is recommended by the American Heartworm Society, improved diagnostic performance in this study compared to single Ag test use, but may have missed more than one in four infected dogs. The need to improve access to highly accurate, rapid, and inexpensive large-scale HW testing for dogs in animal shelters remains largely unmet by current testing availability. The development of practical and validated protocols that incorporate heat or chemical treatment to disrupt Ag-Ab complexes in POC testing or decreasing the cost and time required for such testing in reference laboratories might provide solutions to this unmet need. Similar studies performed in countries where the prevalence of parasites such as D. repens or A. vasorum is different to the USA could potentially yield very different positive predictive values for both HT and non-HT Ag tests.

Background: Cercopithifilaria bainae is a filarioid nematode of dogs. Infection with the parasite was not reported in the USA until 2017, when a dog with skin lesions in Florida was diagnosed. Brown dog ticks, Rhipicephalus sanguineus (sensu lato), are the purported tick vectors, and are widespread in the USA. Therefore, C. bainae is likely present in additional states. Here, we tested dogs and ticks in Oklahoma for evidence of C. bainae infection., Methods: Dermal punch biopsies were opportunistically collected from municipal shelter and client-owned dogs. Multiple skin samples collected from interscapular and head regions were tested by saline sedimentation to recover live microfilariae for morphometric identification and by PCR to amplify a 330 bp region of the filarioid 12S rRNA gene. Also, ticks observed on surveyed dogs were collected, identified to species level, and tested for filarioid DNA., Results: A total of 496 saline sedimentations were performed on 230 shelter and 20 client-owned dogs. Cercopithifilaria bainae infections were identified in 2.6% (6/230) of shelter dogs by morphometry of microfilariae in sedimentations and/or amplification of DNA from skin. DNA sequences amplified from PCR positive skin samples were 99-100% identical to C. bainae reported in Italy. All skin samples from client-owned dogs were negative for filarioid infection by saline sedimentation and PCR. A total of 112 ticks, comprised of four species, were collected. Two of 72 R. sanguineus (s.l.), both engorged females found attached to a C. bainae infected dog, harbored C. bainae DNA (99-100% identity). One attached R. sanguineus (s.l.) male on the same dog harbored filarioid DNA sequence which was difficult to interpret at numerous base-pair locations, but was closest in identity (~80%) to C. bainae., Conclusions: The distribution of C. bainae is more widespread than previously known. To our knowledge, we document C. bainae infections in dogs and DNA in brown dog ticks in Oklahoma for the first time. As brown dog ticks are commonly found throughout the USA, veterinarians in this region should consider C. bainae infection as a differential diagnosis in canine patients with dermatitis or polyarthritis.

Background: A variety of tick species infest dogs and cats in North America. Although most of these species also readily feed on people, national data regarding the species and abundance of ticks on dogs and cats are lacking. Here we report a large-scale study of ticks from dogs and cats in the USA over a 12-month period., Methods: Tick submissions were invited from veterinary practices in all 50 states. Ticks were submitted with information about the pet and the attachment sites of each tick marked on a biopsy chart. Upon receipt, ticks were identified to species and stage using morphologic keys; when necessary, species identification was confirmed molecularly., Results: From February 2018 through January 2019, 10,978 ticks were submitted from 1494 dogs and 336 cats in 49 states and ticks were collected in every month. Dog and cat infestation intensities ranged from 1 to 4765 and from 1 to 38 (median = 1, mean = 6.7 and 2.6), respectively. Dogs were primarily infested with Dermacentor variabilis (532/1494; 35.6%), Ixodes scapularis (409/1494; 27.4%), Amblyomma americanum (345/1494; 23.1%) and Rhipicephalus sanguineus (172/1494; 11.5%). Cats were primarily infested with I. scapularis (156/336; 46.4%), A. americanum (99/336; 29.5%) and D. variabilis (60/336; 17.9%). Other submitted ticks included A. maculatum, Haemaphysalis longicornis, Otobius megnini, and less common Dermacentor spp. and Ixodes spp. Co-infestations were documented in 93 dogs and 14 cats. Reported attachment sites of common tick species differed. In dogs, A. americanum was most commonly attached to the abdomen, axillary, and inguinal regions; D. variabilis and I. scapularis to the head, neck, and back; and R. sanguineus to the head, neck, abdomen, legs, and feet. In cats, I. scapularis was most commonly attached to the head and A. americanum was most commonly attached to the tail and perianal region., Conclusions: These data confirm that dogs and cats in the USA are at risk of tick infestation throughout the year and that tick species present in the region have apparent attachment site preferences.