Key factors influencing canine heartworm, Dirofilaria immitis, in the United States

Temperature-bounded development of Dirofilaria immitis larvae restricts the geographical distribution and seasonality of its transmission: case study and decision support system for canine heartworm management in Australia

Dirofilaria immitis is the causative agent of canine heartworm disease. We used the established heartworm development unit (HDU) principle to map the extrinsic incubation period (EIP) of D. immitis in Australia using historical weather data from 2013-2022. We found weather conditions suitable for EIP completion showed substantial seasonality and geographical variability. Whilst a considerable percentage of the Australian territory showed suitable weather conditions to always support EIP completion (17%), only 2.7% of the 2021 Australian human population lived in this region. Therefore, 97% of the population lived in an area that changed its EIP suitability within the study period. EIP completion is required prior to D. immitis transmission, meaning that infection risk of D. immitis is seasonal and location-dependent, being disrupted each year for most of the human population's dogs. We developed an online, open access tool allowing us to visualise EIP completion across Australia historically and in near real-time. We aim to support veterinarians to make risk-based recommendations for dirofilariosis prevention by using the tool, available at https://heartworm-mapping.adelaide.edu.au/shiny/.

Seroprevalence, Blood Chemistry, and Patterns of Canine Parvovirus, Distemper Virus, Plague, and Tularemia in Free-Ranging Coyotes (Canis latrans) in Northern New Mexico, USA

Wildlife diseases have implications for ecology, conservation, human health, and health of domestic animals. They may impact wildlife health and population dynamics. Exposure rates of coyotes (Canis latrans) to pathogens such as Yersinia pestis, the cause of plague, may reflect prevalence rates in both rodent prey and human populations. We captured coyotes in north-central New Mexico during 2005-2008 and collected blood samples for serologic surveys. We tested for antibodies against canine distemper virus (CDV, Canine morbillivirus), canine parvovirus (CPV, Carnivore protoparvovirus), plague, tularemia (Francisella tularensis), and for canine heartworm (Dirofilaria immitis) antigen. Serum biochemistry variables that fell outside reference ranges were probably related to capture stress. We detected antibodies to parvovirus in 32/32 samples (100%), and to Y. pestis in 26/31 (84%). More than half 19/32 (59%) had antibodies against CDV, and 5/31 (39%) had antibodies against F. tularensis. We did not detect any heartworm antigens (n = 9). Pathogen prevalence was similar between sexes and among the three coyote packs in the study area. Parvovirus exposure appeared to happen early in life, and prevalence of antibodies against CDV increased with increasing age class. Exposure to Y. pestis and F. tularensis occurred across all age classes. The high coyote seroprevalence rates observed for CPV, Y. pestis, and CDV may indicate high prevalence in sympatric vertebrate populations, with implications for regional wildlife conservation as well as risk to humans via zoonotic transmission.

CANINE HEARTWORM INFECTION AND PROPHYLAXIS USE AMONG PET CARETAKERS FROM THE CUMBERLAND GAP REGION OF TENNESSEE, USA

The prevalence of infection with canine heartworm (CHW), Dirofilaria immitis, continues to increase across the United States, regardless of the availability of effective and affordable prophylactic products. Current reports of CHW prevalence as estimated by the Companion Animal Parasite Council (CAPC) are thought to under-represent the true magnitude of the issue because pet dogs that do not receive regular veterinary care are often excluded. This study estimated the prevalence of CHW in pet dogs and associated prophylaxis use in pet dogs in the Cumberland Gap Region with a combined doorstep diagnostic testing approach and caretaker survey. Dogs tested (n = 258) during the summers of 2018 and 2019 revealed a 2.3% (6/258) prevalence in the pet dog population with 33% (2/6) being microfilaremic. Questionnaire data from caretaker interviews revealed that 41.8% (108/258) of the dogs were not receiving CHW prophylaxis. Significant predictors of CHW prophylaxis use identified through logistic regression included pet caretaker awareness of CHW as an important health issue and the use of veterinary services in the year preceding participation in the survey. These results underscore the importance of veterinary-mediated client interaction to create risk awareness of CHW disease and association with prophylaxis compliance.

Treatment of dogs with Bravecto® (fluralaner) reduces mosquito survival and fecundity

BACKGROUND

Mosquitoes serve as the vector of canine heartworm (Dirofilaria immitis), which represents a significant and persistent threat to canine health. A reduction in the longevity and/or reproductive success of mosquitoes that take a blood meal from fluralaner-treated dogs may consequently reduce the local transmission of heartworm and prevent new infections. A novel secondary effect of an oral formulation of the ectoparasiticide fluralaner (Bravecto®) against a laboratory strain of the mosquito Aedes aegypti, a potential major vector of canine heartworm, was investigated in this study.

METHODS

Six dogs were administered a single dose of fluralaner orally in the form of Bravecto® Chews (at the labeled fluralaner dose of 25 mg/kg body weight), while six control dogs received no treatment. Mosquitoes were fed on blood that was collected from each dog prior to treatment and weekly for 15 weeks post-treatment to assess the continued effects of fluralaner as its serum level decreased. Mosquito fitness was assessed by three parameters: rate of successful blood-feeding, survival, and egg laying.

RESULTS

Successful blood-feeding rate was similar between control and treatment groups. In the fluralaner treatment, mosquito survival was significantly reduced within the first 24 h after blood-feeding, for the first 12 weeks post-treatment of the dogs (efficacy range = 33.2-73.3%). Survival of mosquitoes up until a potentially heartworm-infective timepoint (14 days post-blood-feeding) was significantly reduced in the fluralaner-treated group at several timepoints (1, 2, 5, 11, 12, 13, 14, and 15 weeks post-treatment; efficacy range = 49.4-91.4%), but was less consistently reduced at the other timepoints. Egg laying by mosquitoes was almost completely suppressed for the first 13 weeks following treatment of the dogs with fluralaner (treatment efficacy ≥ 99.8%).

CONCLUSIONS

Mosquitoes fed blood from fluralaner-treated dogs experienced a significant reduction in survival and fecundity. These findings support the potential for a reduction in heartworm transmission directly by lethal effects on the vector and indirectly through a reduction of the local vector population when mosquitoes are exposed to animals treated with fluralaner.

Prevalence of canine heartworm infection in Queensland, Australia: comparison of diagnostic methods and investigation of factors associated with reduction in antigen detection

BACKGROUND

The prevalence of Dirofilaria immitis infection in dogs is increasing globally and spreading into new areas. Prevalence of dirofilariosis in the state of Queensland, Australia, was as high as 90% before the introduction of macrocyclic lactones. Limited research on prevalence of D. immitis infection in dogs in Queensland has been reported in the last 30 years. Antigen testing is the most common method for detection of dirofilariosis but its accuracy is reduced by antigen getting trapped (blocked antigen) in immune complexes (ICs). The objectives of this research were to determine the prevalence of D. immitis infection in dogs from two geographical areas (Brisbane and Townsville) in Queensland, to determine the extent to which blocked antigen affects the validity of antigen testing, and to explore whether this was associated with microfilaraemia, location, age or sex.

METHODS

Blood samples from Brisbane (sub-tropical climate) and Townsville (tropical climate) shelter dogs were evaluated for the presence of D. immitis antigen before (conventional antigen testing, CAT) and after dissociation of ICs by heat treatment (antigen testing after heat treatment, ATHT), using a commercially available test. Microfilariae were detected using modified Knott's test (MKT). Test proportions were compared with McNemar's test and the association between antigen test-discordant results (positive for antigen after dissociation of ICs) and microfilaraemia, location, sex and age was modelled using logistic regression.

RESULTS

Dirofilaria immitis prevalence in dogs from Townsville (22% by CAT, 32.1% by ATHT and 16.7% by MKT) was significantly higher than in dogs from Brisbane (1.1% by CAT and MKT and 1.7% by ATHT) [Formula: see text]. Dissociation of ICs allowed detection of significantly more D. immitis infected dogs than either conventional antigen testing or microfilariae detection, or the combined antigen and microfilariae detection [Formula: see text]. The odds of dogs being positive for antigen after dissociation of ICs were significantly higher for microfilaraemic, 3-4-year-old female dogs from Townsville.

CONCLUSIONS

The high prevalence of infection with D. immitis in dogs from Townsville poses a health risk for local susceptible host species, including humans. Dissociation of ICs increases antigen detection and should be considered in dogs suspected of D. immitis infection but negative on routine testing.

High prevalence of canine heartworm, Dirofilaria immitis, in pet dogs in south Texas, USA, with evidence of Aedes aegypti mosquitoes contributing to transmission

Background

The canine heartworm Dirofilaria immitis, a filarioid nematode of dogs and other carnivores, is widespread in the USA and the world. Over 20 different mosquito species serve as intermediate hosts of D. immitis, but their contribution to transmission varies according to factors like host feeding patterns, geographic locations and climatic conditions. The yellow fever mosquito, Aedes aegypti, is a competent vector of D. immitis but is often dismissed as a vector of veterinary relevance given its anthropophilic feeding behavior. We evaluated the prevalence of D. immitis in pet dogs along the USA-Mexico border and assessed whether Ae. aegypti in the area are naturally infected with heartworm and are potentially acting as a vector.

Methods

A total of 200 whole blood samples collected from pet dogs in the Lower Rio Grande Valley in south Texas from 2016 to 2019 were included in this study. Canine serum samples for D. immitis were tested using the DiroCHEK® Canine Heartworm Antigen Test Kit pre- and post-immune complex dissociations (ICD) and blood samples were tested using high-resolution melt (HRM) quantitative PCR (qPCR) and a probe-based qPCR. Additionally, mosquito specimens were collected and identified, and Ae. aegypti heads, abdomens and pools were tested using conventional PCR (cPCR) and HRM qPCR.

Results

Overall, heartworm prevalence in dogs aged > 6 months was 40.8% (64/157) when the results from all testing modalities were considered. Heartworm antigen was detected in 33.5% and 40.7% of the dogs using DiroCHEK® pre- and post-ICD, respectively. By molecular screening, 20.1% of dogs tested positive with probe-based qPCR, while only one tested positive with HRM qPCR. Of the Ae. aegypti abdomens from blood-fed Ae. aeygpti tested, 20 (21.7%) from mosquitoes that fed on dogs and four (7%) from those that fed on humans tested positive for heartworm. Among Ae. aegypti heads from blood-fed Ae. aeygpti, two (1.1%) were positive based on cPCR and four (2.5%) were positive based on HRM qPCR. No D. immitis DNA was detected in the 208 pools of whole bodies (358 individuals) of Ae. aegypti gravid females.

Conclusions

Our study highlights a high prevalence of heartworm in dogs in south Texas and provides evidence that Ae. aegypti could be contributing to heartworm transmission in canine populations in this region.

Graphical Abstract

Ecological drivers of dog heartworm transmission in California

BACKGROUND

Effectively controlling heartworm disease-a major parasitic disease threatening animal health in the US and globally-requires understanding the local ecology of mosquito vectors involved in transmission. However, the key vector species in a given region are often unknown and challenging to identify. Here we investigate (i) the key vector species associated with transmission of the parasite, Dirofilaria immitis, in California and (ii) the climate and land cover drivers of vector presence.

METHODS

To identify key mosquito vectors involved in transmission, we incorporated long-term, finely resolved mosquito surveillance data and dog heartworm case data in a statistical modeling approach (fixed-effects regression) that rigorously controls for other unobserved drivers of heartworm cases. We then used a flexible machine learning approach (gradient boosted machines) to identify the climate and land cover variables associated with the presence of each species.

RESULTS

We found significant, regionally specific, positive associations between dog heartworm cases and the abundance of four vector species: Aedes aegypti (Central California), Ae. albopictus (Southern California), Ae. sierrensis (Central California), and Culiseta incidens (Northern and Central California). The proportion of developed land cover was one of the most important ecological variables predicting the presence or absence of the putative vector species.

CONCLUSION

Our results implicate three previously under-recognized vectors of dog heartworm transmission in California and indicate the land cover types in which each putative vector species is commonly found. Efforts to target these species could prioritize surveillance in these land cover types (e.g. near human dwellings in less urbanized settings for Ae. albopictus and Cs. incidens) but further investigation on the natural infection prevalence and host-biting rates of these species, as well as the other local vectors, is needed.

Detection of Dirofilaria immitis via integrated serological and molecular analyses in coyotes from Texas, United States

Wild canids serve as reservoir for various vector-borne pathogens of veterinary and medical importance, including the canine heartworm, Dirofilaria immitis. In North and Central America, coyotes (Canis latrans) may be a relevant reservoir host for heartworm transmission. The objective of this study was to determine the occurrence of D. immitis in coyotes across Texas using integrated antigen detection test and molecular assays. Matching whole blood and serum samples were collected from 122 coyotes from different locations across the state of Texas, United States, encompassing nine counties. Collections occurred from February to April 2016, and December 2016. Samples were assessed serologically using a commercial microtiter plate ELISA (DiroCHEK®), and molecularly by conventional PCR targeting the cytochrome oxidase c subunit 1 (cox1) and NADH dehydrogenase subunit 5 (nad5) of the mitochondrial DNA, and via a TaqMan© probe-based real-time PCR protocol, also targeting a fragment of the cox1 gene. Overall, 12 (9.83%) samples tested positive when serological and molecular results were combined. Seven of 122 samples (5.73%) were antigen-positive, 8 (6.55%) were qPCR-positive, and 4 (3.27%) were positive using conventional PCR. Of 12 positive samples, 4 tested antigen-positive by DiroCHEK® but were negative in all molecular tests, another 4 tested positive by at least one of the molecular assays but tested negative by DiroCHEK®, and 3 samples tested positive by both antigen test and at least one of the molecular assays. Two samples (16.67%) tested positive on both the antigen test and both conventional PCR and qPCR. Our study confirmed the presence of D. immitis infection in coyotes from southern and northern Texas. The combination of serologic and molecular diagnostic tests was proven synergistic for the identification of D. immitis infections, including occult dirofilariosis, and revealed a more accurate picture of heartworm occurrence in the sampled coyotes.

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Coyotes are an important wild reservoir for Dirofilaria immitis in North America.

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We collected 121 matching blood and serum samples of coyotes from Texas, USA.

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Twelve samples (9.92%) tested positive combining serology and molecular tests data.

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Probe-based qPCR was superior than conventional PCR for heartworm diagnosis.

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Combined DiroCHEK® and qPCR data showed a higher prevalence than each test alone.

Temporal trends in intake category data for animal shelter and rescue organizations in Colorado from 2008 to 2018

OBJECTIVE

To investigate trends in animal shelter and rescue organization intake for dogs and cats in Colorado from 2008 to 2018.

SAMPLE

482 animal shelters and rescue organizations that reported annual intake data to the State of Colorado Department of Agriculture for 1,086,630 dogs and 702,333 cats.

PROCEDURES

Total intake, intake for each of 5 Pet Animal Care and Facilities Act categories (stray, owner surrender, intrastate transfer, interstate transfer, or other), and community-based intake (total intake after exclusion of transfers) of dogs and cats were assessed in total and for each organization type (shelter or rescue organization). The number taken in per year, number taken in/1,000 capita (human residents)/y, and number in each intake category as a percentage of total intake for the same species per year were analyzed with linear regression models.

RESULTS

Trend lines indicated that total dog intake increased over the study period, but there was no change when these data were adjusted for the human population. Cat intake decreased over time according to both of these measures. Total community-based intake decreased, whereas total intake by interstate transfer from other organizations increased for both species during the study period.

CLINICAL RELEVANCE

Increased transfer of dogs and cats across state lines into regions with low community-based shelter intake suggested that regional and national animal disease trends could potentially impact disease profiles for recipient areas. Findings supported efforts toward collecting animal shelter and rescue organization intake and outcome data across larger systems.

Dirofilaria spp. and Angiostrongylus vasorum: Current Risk of Spreading in Central and Northern Europe

In the past few decades, the relevance of Dirofilaria immitis and Dirofilaria repens, causing cardiopulmonary and subcutaneous dirofilariosis in dogs and cats, and of Angiostrongylus vasorum, causing canine angiostrongylosis, has steadily increased in Central and Northern Europe. In this review, a summary of published articles and additional reports dealing with imported or autochthonous cases of these parasites is provided for Central (Austria, Czechia, Germany, Hungary, Luxemburg, Poland, Slovakia, Slovenia, and Switzerland) and Northern (Denmark, Finland, Iceland, Norway, and Sweden) Europe. Research efforts focusing on Dirofilaria spp. and A. vasorum have varied by country, and cross-border studies are few. The housing conditions of dogs, pet movements, the spread of competent vectors, and climate change are important factors in the spread of these nematodes. Dogs kept outside overnight are a major factor for the establishment of Dirofilaria spp. However, the establishment of invasive, diurnal, synanthropic, competent mosquito vectors such as Aedes albopictus may also influence the establishment of Dirofilaria spp. The drivers of the spread of A. vasorum remain not fully understood, but it seems to be influenced by habitats shared with wild canids, dog relocation, and possibly climatic changes; its pattern of spreading appears to be similar in different countries. Both Dirofilaria spp. and A. vasorum merit further monitoring and research focus in Europe.

Infection risk varies within urbanized landscapes: the case of coyotes and heartworm

BACKGROUND

Urbanization can have profound effects on ecological interactions. For host-pathogen interactions, differences have been detected between urban and non-urban landscapes. However, host-pathogen interactions may also differ within highly heterogeneous, urbanized landscapes.

METHODS

We investigated differences in infection risk (i.e., probability of infection) within urbanized landscapes using the coyote (Canis latrans) and mosquito-borne nematode, Dirofilaria immitis (the causative agent for canine heartworm), as a case study. We focused on a coyote population in Chicago for which extensive behavioral and heartworm infection data has been collected between 2001 and 2016. Our objectives were to: (i) determine how onset and duration of the heartworm transmission season varied over the 16-year period and across the urban-suburban gradient; and (ii) investigate how heartworm infection risk in coyotes varied over the years, across the urban-suburban gradient, by coyote characteristics (e.g., age, sex, resident status), and coyote use of the urbanized landscape (e.g., use of urban areas, mosquito habitats).

RESULTS

While onset of the heartworm transmission season differed neither by year nor across the urban-suburban gradient, it was longer closer to the core of Chicago. Of the 315 coyotes sampled, 31.1% were infected with D. immitis. Older coyotes and coyotes sampled in later years (i.e., 2012-2016) were more likely to have heartworm. While coyote location in the urban-suburban gradient was not a significant predictor of infection, the proportion of urban land in coyote home ranges was. Importantly, the size and direction of this association varied by age class. For adults and pups, infection risk declined with urbanization, whereas for subadults it increased. Further, models had a higher predictive power when focusing on resident coyotes (and excluding transient coyotes). The proportion of mosquito habitat in coyote home ranges was not a significant predictor of infection.

CONCLUSIONS

Our findings suggest that urbanization may affect host exposure to vectors of D. immitis, that risk of infection can vary within urbanized landscapes, and that urbanization-wildlife infection associations may only be detected for animals with certain characteristics (e.g., age class and resident status).

Heartworm disease - Overview, intervention, and industry perspective

Dirofilaria immitis, also known as heartworm, is a major parasitic threat for dogs and cats around the world. Because of its impact on the health and welfare of companion animals, heartworm disease is of huge veterinary and economic importance especially in North America, Europe, Asia and Australia. Within the animal health market many different heartworm preventive products are available, all of which contain active components of the same drug class, the macrocyclic lactones. In addition to compliance issues, such as under-dosing or irregular treatment intervals, the occurrence of drug-resistant heartworms within the populations in the Mississippi River areas adds to the failure of preventive treatments. The objective of this review is to provide an overview of the disease, summarize the current disease control measures and highlight potential new avenues and best practices for treatment and prevention.

Detection of Borrelia spp., Ehrlichia canis, Anaplasma phagocytophilum, and Dirofilaria immitis in Eastern Coyotes (Canis latrans) in Nova Scotia, Canada

Borrelia burgdorferi and Borrelia miyamotoi are tickborne zoonotic pathogens in Canada. Both bacteria are vectored by ticks, Ixodes scapularis in Atlantic Canada, but require wildlife reservoir species to maintain the bacteria for retransmission to future generations of ticks. Coyotes (Canis latrans) are opportunistic feeders, resulting in frequent contact with other animals and with ticks. Because coyotes are closely related to domestic dogs (Canis lupus familiaris), it is probable that coyote susceptibility to Borrelia infection is similar to that of dogs. We collected livers and kidneys of eastern coyotes from licensed harvesters in Nova Scotia, Canada, and tested them using nested PCR for the presence of B. burgdorferi, B. miyamotoi, and Dirofilaria immitis. Blood obtained from coyote livers was also tested serologically for antibodies to B. burgdorferi, Ehrlichia canis, Anaplasma phagocytophilum, and D. immitis. Borrelia burgdorferi and D. immitis were detected by both nested PCR and serology tests. Seroreactivity to A. phagocytophilum was also found. Borrelia miyamotoi and E. canis were not detected. Our results show that coyotes in Nova Scotia have been exposed to a number of vectorborne pathogens.

Prevalence of Dirofilaria immitis in mosquitoes (Diptera) - systematic review and meta-analysis

Knowledge of the vectors of dirofilariasis in the world beside the treatment of infected dog is crucial to establish mosquito vector-based control programs. The current systematic review and meta-analysis were conducted on published studies, documenting the prevalence of Dirofilaria immitis infected/infective mosquitoes from field surveys and laboratory experiments under controlled conditions. Articles up through 2019 from Scopus, PubMed, Embase, Web of Science, Google Scholar were screened systematically. The overall prevalence of D. immitis infected/infective mosquitoes was estimated using a random effect model. Meta-regression was used to identify factors related to high dirofilariasis prevalence in the vectors. In these studies, the detection method was not identified as a heterogeneity and the overall prevalence in both subgroups had overlap (7.9-34.9 and 1.5-48.5). The overall prevalence of infective stage was 2.6 (95% CI: 0.97-4.77 per 1,000) and 84.7 per 1000 (95% CI: 20.5-183.8 per 1,000) for the field survey/laboratory experiment, respectively. The higher overall prevalence of D. immitis infected/infective mosquitoes were reported across studies in which take place in Eastern Mediterranean Region office (EMRO), longitude: 80 to 110, latitude: 20 to 40, annual rainfall: 250 to 1000, sea level: 26 to 100 and <1,000, humidity: 66 to 70, during 2000 to 2005 by dissection methods. Our review determined that mosquito species within the genus Anopheles and to a less extent Culex were the main vectors of dirofilariasis.

Retrospective Analysis of Heartworm (Dirofilia immitis) Prevention Medication Compliance and Economic Value in Dogs in Veterinary Practices in Australia

Background: Canine heartworm (HW) is endemic in Australia. Prevention usually involves monthly topical or oral preventives, or annual injections of extended-release moxidectin (ProHeart SR-12^*1), hereafter referred to as injectable moxidectin (IM). Poor compliance can leave dogs susceptible to infection. This pharmacoeconomics study used retrospective transactional data from 52 Australian veterinary practices to examine the economic value of compliance, revenue, and patient retention associated with veterinarian-sourced canine HW prevention.

Methods: This longitudinal descriptive study utilized anonymized transaction records of 228,185 dogs identified to have visited a veterinary practice at least twice in the period 2010–2015. Purchase compliance against a benchmark of 12 months HW protection per year was measured for IM or monthly HW (MHW) preparations each year and for consecutive years. The average annual cost per dog by preventative modality was also determined.

Results: Between 2010 and 2015, of the 228,185 dogs identified, 73.0% recorded either zero or one purchase of HW preventive from their veterinary clinic; 18.7% recorded at least two IM purchases, and 10.6% purchased MHW prevention at least twice. Single-year purchase compliance was 92.8–96.9% for IM vs. 26.9–36.5% for dogs receiving MHW products. Consecutive-year purchase compliance was 76.7% for IM and 24.4% for MHW medications. Dog owners spent $AU108.29/dog/year (Australian dollars) on IM vs. $AU131.96/dog/year on MHW prevention products, which may have treated other parasites concurrently, although repeat MHW purchasers only purchased enough to cover an average of 7.2 months per year. Dogs recording at least two HW prevention transactions generated more revenue for veterinary practices/dog/year compared to dogs with less than two. Finally, dogs receiving IM, especially those that started at <15 months old, had the highest retention rate in this population.

Conclusions: In the 5 years from 2010 to 2015, 73% of dog owners who visited a veterinary practice at least twice made less than two purchases of HW preventatives from the veterinary practice. For those with at least two preventative purchases, 76.7% of dogs receiving IM and 24.4% of dogs prescribed with MHW products purchased enough doses to provide continuous protection over the observation period.

Recording drug responses from adult Dirofilaria immitis pharyngeal and somatic muscle cells

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 EC₅₀s 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.

Evaluation of the SNAP® 4Dx® plus test for the detection of Dirofilaria immitis antigen and characterization of exposure to tick-borne pathogens in wild canids in southern Ontario

Population-level surveys for Dirofilaria immitis in wild canids typically rely on identification of the parasite at necropsy. More recently, some studies have employed the use of the SNAP® 4Dx® Plus test. However, since the assay was designed for use with domestic dogs it needs to be validated for use with wild canids for accurate interpretation of results. We therefore evaluated the performance of the SNAP® 4Dx® Plus test for detection of D. immitis in wild canids in southern Ontario. Overall, 199 wild canid carcasses were collected from across the region and assessed for the presence of D. immitis parasites at necropsy; ten were infected. Lung tissue extract (LE) and thoracic fluid filter paper extract (TFE) prepared from each wild canid were tested via the SNAP® 4Dx® Plus test, which simultaneously tests for the presence of D. immitis antigen and antibodies to Borrelia burgdorferi, Anaplasma spp., and Ehrlichia spp. The prevalence adjusted bias adjusted kappa (PABAK) and Gwet's first-order-agreement coefficient (AC1) were used to assess the level of agreement between sample pairs. The PABAK and AC1 between LF and TFE applied to the SNAP® 4Dx® Plus test and the necropsy-confirmed D. immitis status indicated a very high level of agreement for all sample pairs. Compared to necropsy-confirmed D. immitis status, the estimated sensitivity and specificity of the SNAP® 4Dx® Plus test for D. immitis antigen in LE was 80 % (95 % CI 44.4-97.5%) and 98.9 % (95 % CI 96.2-99.9%), respectively. For the TFE, the sensitivity was 70 % (95 % CI 34.8-93.3%) and the specificity was 97.9 % (95 % CI 94.7-99.4%). With respect to the tick-borne pathogen components, 1.5 % (3/199; 95 % CI 0.3-4.5%) of wild canids tested positive for B. burgdorferi antibody; 1.0 % (2/199; 95 % CI 0-3.8%) of LE samples were positive and 0.5 % (1/199; 95 % CI 0-3.1%) of TFE samples were positive. No samples tested positive for antibody to Anaplasma spp. (95 % CI 0-2.3%) or Ehrlichia spp. (95 % CI 0-2.3%). Collectively, the results suggest that the SNAP® 4Dx® Plus test may be a suitable test for use with LE and TFE for the detection of D. immitis antigen in wild canids from southern Ontario.

A cross sectional study on Dirofilaria immitis and Acanthocheilonema reconditum in sheepdogs in a western region in Iran

Iran is one of the endemic areas of Dirofilariasis, and also one of the most important zoonotic infections. Dirofilaria immitis causes a severe and fatal disease called heartworm disease in dog. It also produces pulmonary nodules in humans. The worm is to be investigated as a potential infection of humans and animals in various provinces in Iran. In this research, the samples were studied with modified Knott's test and molecular method. The results of the modified Knott's test method indicated that 14.00% of sheepdogs were infected with filarial microfiler. The microfilers were characterized with basic morphological features, the length of the infective larva and tail ending. There was an estimated prevalence of 4.45% for Dirofilaria immitis and 9.55% for Acanthocheilonema reconditum microfiler. To verify the differential diagnosis, molecular method was performed using PCR with Dirofilaria specific primers for amplification of ITS2 locus. Gene locus sequencing results of D. immitis and sequence alignment recorded in GeneBank showed 97.00% similarity, and relatively 98.00% similarity was observed in A. reconditum. The results of the molecular method confirmed the result of modified Knott's test method. Low infection with D. immitis was observed the region, probably due to the fact that the annual temperature and precipitation in this area were not suitable for the proliferation of the vector mosquitoes. In general, there was less infection in the region compared to regions with relatively similar climatic conditions. Hence, the results suggested that alternative diagnostic tests are required to determine the occult infections.

Potential mosquito (Diptera: Culicidae) vectors of Dirofilaria immitis from residential entryways in Northeast Arkansas

The nematode Dirofilaria immitis causes serious disease of canines in the United States. Transmitted by a variety of mosquito species, several studies have examined the prevalence of D. immitis in mosquitoes. However, no prevalence studies have focused on diurnal mosquitoes that could potentially enter homes. Mosquitoes were collected under doorway awnings at four residences to identify the diurnal blood-feeding mosquito species and prevalence of potential vectors harboring D. immitis in Jonesboro, Arkansas. Mosquitoes were collected from May to December 2016 using pheromone traps and aerial nets. Each mosquito was individually dissected and observed for larvae in the head, thorax, and abdomen to identify infective and non-infective larvae. Ten mosquito species from five genera were identified. Larvae, presumed to be D. immitis, were observed in five mosquito species, including Aedes albopictus, Anopheles quadrimaculatus, Culex pipiens quinquefasciatus, Culiseta inornata, and Psorophora columbiae and four genera, including Anopheles spp., Culex spp., Culiseta spp., and Psorophora spp. The diurnal mosquito, Ae. albopictus composed 3.4% of the total mosquitoes collected. An. quadrimaculatus and Anopheles spp. were the most abundant mosquitoes, composing 59.7 and 19.6% of the total mosquitoes collected, respectively. Of the 536 mosquitoes dissected, 60 (11.2%) were observed with D. immitis, and 33 (55.0%) of the heartworm-positive mosquitoes harbored infective (L₃) larvae in the head or proboscis upon dissection. The high proportion of infective D. immitis larvae found in the mosquitoes aggregating under doorway awnings may increase the exposure of indoor dogs and cats to heartworm disease in northeast Arkansas.

Comparative Vector Efficiency of Two Prevalent Mosquito Species for Dog Heartworm in North Carolina

The dog heartworm, Dirofilaria immitis (Leidy) (Spirurida: Onchocercidae), is a devastating parasite of domestic and wild canines vectored by a multitude of mosquito species. Although many species are implicated as vectors, not all contribute equally to disease transmission, with demonstrated variation in vector efficiency between and within species. We investigated the vector efficiency of mosquitoes derived from wild-caught North Carolina populations of two known heartworm vectors: a native species, Aedes triseriatus (Say) (Diptera: Culicidae), and an invasive species, Aedes albopictus (Skuse). We compared the parasite developmental times within the mosquito, mosquito longevity and fecundity, and the vector efficiency index between the two species. We found that the tested composite North Carolina population of Ae. triseriatus was an efficient vector of D. immitis under laboratory conditions, whereas the local composite population of Ae. albopictus was a competent but relatively poor vector. Compared with Ae. triseriatus, Ae. albopictus showed a longer time for parasite development, lower infection rates, and lower vector efficiency. Additionally, Ae. albopictus was the sole species to exhibit significant parasite-induced mortality. These results are in contrast to prior studies of populations of Ae. albopictus from locations outside of North Carolina, which have implicated the species as a highly competent heartworm vector. The variation seen for different strains of the same species emphasizes the heritable nature of D. immitis vector competence and highlights the need for local infection studies for accurate transmission risk assessment in a particular locale.

Mosquito diversity and dog heartworm prevalence in suburban areas

Background

Urbanization is occurring rapidly on a global scale and is altering mosquito communities, creating assemblages that are characteristically less diverse. Despite high rates of urbanization and ample examples of vector-borne diseases transmitted by multiple species, the effects of urbanization-driven mosquito diversity losses on disease transmission has not been well explored. We investigated this question using the dog heartworm, a filarial parasite vectored by numerous mosquito species.

Methods

We trapped host-seeking mosquitoes in undeveloped areas and neighborhoods of different ages in Wake County, North Carolina, USA, analyzing captured mosquitoes for heartworm DNA. We compared within-mosquito heartworm infection across land-use types by Kruskal–Wallis and likelihood ratio tests. Using zip code level data acquired from dogs in a local shelter, we performed linear regressions of within-host heartworm prevalence by within-mosquito heartworm prevalence as well as by three mosquito diversity measures. We also determined the best predictor of host-level prevalence among models including within-mosquito infection, mosquito diversity and abundance, and socioeconomic status as variables.

Results

Suburban areas had lower within-mosquito heartworm prevalence and lower likelihood of heartworm-positive mosquitoes than did undeveloped field sites, although no differences were seen between suburban and undeveloped wooded sites. No relationships were noted between within-mosquito and within-host heartworm prevalence. However, mosquito diversity metrics were positively correlated with host heartworm prevalence. Model selection revealed within-host prevalence was best predicted by a positive relationship with mosquito Shannon–Wiener diversity and a negative relationship with household income.

Conclusions

Our results demonstrate that decreases in mosquito diversity due to urbanization alter vector-borne disease risk. With regard to dog heartworm disease, this loss of mosquito diversity is associated with decreased heartworm prevalence within both the vector and the host. Although the response is likely different for diseases transmitted by one or few species, mosquito diversity losses leading to decreased transmission could be generalizable to other pathogens with multiple vectors. This study contributes to better understanding of the effects of urbanization and the role of vector diversity in multi-vectored pathosystems.

Variation in Tolerance to Parasites Affects Vectorial Capacity of Natural Asian Tiger Mosquito Populations

Globally, diseases transmitted by arthropod vectors, such as mosquitoes, remain a major cause of morbidity and mortality [1]. The defense responses of mosquito and other arthropod vectors against parasites are important for understanding disease transmission dynamics and for the development of novel disease-control strategies. Consequently, the mechanisms by which mosquitoes resist parasitic infection (e.g., immune-mediated killing) have long been studied [2, 3]. However, the ability of mosquitoes to ameliorate the negative fitness consequences of infection through tolerance mechanisms (e.g., tissue repair) has been virtually ignored (but see [4, 5]). Ignoring parasite tolerance is especially taxing in vector biology because unlike resistance, which typically reduces vectorial capacity, tolerance is expected to increase vectorial capacity by reducing parasite-mediated mortality without killing parasites [6], contributing to the recurrent emergence of vector-borne diseases and its stabilization and exacerbation. Despite its importance, there is currently no evidence for the evolution of tolerance in natural mosquito populations. Here, we use a common-garden experimental framework to measure variation in resistance and tolerance to dog heartworm (Dirofilaria immitis) between eight natural Aedes albopictus mosquito populations representing areas of low and high transmission intensity. We find significant inter-population variation in tolerance and elevated tolerance where transmission intensity is high. Additionally, as expected, we find that increased tolerance is associated with higher vectorial capacity. Consequently, our results indicate that high transmission intensity can lead to the evolution of more competent disease vectors, which can feed back to impact disease risk.

Prevalence and distribution of Dirofilaria immitis infection in wild canids in southern Ontario

Wild canids represent a potential reservoir host for Dirofilaria immitis infection in dogs in Ontario. Since wild canids are not protected by chemoprophylaxis, understanding the epidemiology of D. immmitis in these populations may help elucidate the background risk of infection for dogs. The aim of this study was to determine the prevalence and distribution of D. immitis infection in wild canids across southern Ontario. From February 2016 to March 2017, 290 wild canid carcasses (273 coyotes and 17 foxes) were collected from across the region and assessed for the presence of D. immitis at the time of necropsy. Overall, D. immitis infection was identified in 4.8% (95% CI 2.8-8.0%) of these wild canid carcasses. Among coyotes, 5.1% (95% CI 3.0-8.5%) were positive; no evidence of D. immitis was found in the 17 foxes. Dirofilaria immitis infections in wild canids were detected in two regions of southern Ontario: 12 of the 14 D. immitis infections were detected in the south-western region and two were detected in the eastern region. Our findings provide preliminary insights into the prevalence and geographical distribution of D. immitis in coyotes and foxes in southern Ontario.

Ecological and Socioeconomic Factors Associated with Bartonella henselae Exposure in Dogs Tested for Vector-Borne Diseases in North Carolina

Bartonella henselae is a zoonotic vector-borne pathogen affecting both humans and dogs. Little is known about the epidemiology of B. henselae in dogs, including risk factors associated with exposure. The objectives of this study were to map the current distribution of B. henselae in dogs in North Carolina (NC) and to identify ecological and socioeconomic factors influencing B. henselae seroreactivity. Results from 4446 B. henselae serology samples from dogs in NC submitted by veterinarians for clinical diagnostic testing to the North Carolina State University College of Veterinary Medicine Vector Borne Disease Diagnostic Laboratory between January 1, 2004 and December 31, 2015 were retrospectively reviewed. These results were used to generate a map of B. henselae seroreactivity. To account for sparsely sampled areas, statistical smoothing using head banging and areal interpolation kriging was performed. Using previously described risk factors for exposure to canine tick-borne diseases, eight multivariable logistic regression models based on biologically plausible hypotheses were tested, and a final model was selected using an Akaike's Information Criterion weighted-average approach. Seroreactivity among dogs tested for vector-borne disease was variable across the state: higher along the southern/eastern coastal plains and eastern Piedmont, and lower in the western mountains. Of 25 explanatory factors considered, the model combining demographic, socioeconomic, climatic, and land use variables fits best. Based on this model, female intact sex and increasing percentage of the county with low-intensity development and evergreen forest were associated with higher seroreactivity. Conversely, moderate development, increasing median household income, and higher temperature range and relative humidity were associated with lower seroreactivity. This model could be improved, however, by including local and host-scale factors that may play a significant role in dogs' exposure.

Regional and local temporal trends in the prevalence of canine heartworm infection in the contiguous United States: 2012-2018

Background

Canine heartworm disease is a potentially fatal disease for which treatment is financially burdensome for many pet owners. Prevention is strongly advocated by the veterinary community along with routine testing for infection during annual wellness examinations. Despite the availability of efficacious chemoprophylaxis, recent reports have suggested that the incidence of heartworm disease in domestic dogs is increasing.

Results

Using data from tests for heartworm infection in the USA from January 2012 through September 2018, a Bayesian spatio-temporal binomial regression model was used to estimate the regional and local temporal trends of heartworm infection prevalence. The area with the largest increase in regional prevalence was found in the Lower Mississippi River Valley. Regional prevalence increased throughout the southeastern states and northward into Illinois and Indiana. Local (county-level) prevalence varied across the USA, with increasing prevalence occurring along most of the Atlantic coast, central United States, and western states. Clusters of decreasing prevalence were present along the Mississippi Alluvial Plain (a historically endemic area), Oklahoma and Kansas, and Florida.

Conclusions

Canine heartworm infection prevalence is increasing in much of the USA, both regionally and locally, despite veterinarian recommendations on prevention and testing. Additional steps should be taken to protect dogs, cats and ferrets. Further work is needed to identify the driving factors of the locally decreasing prevalence present along the Mississippi Alluvial plain, Florida, and other areas.

Refugia and anthelmintic resistance: Concepts and challenges

Anthelmintic resistance is a threat to global food security. In order to alleviate the selection pressure for resistance and maintain drug efficacy, management strategies increasingly aim to preserve a proportion of the parasite population in 'refugia', unexposed to treatment. While persuasive in its logic, and widely advocated as best practice, evidence for the ability of refugia-based approaches to slow the development of drug resistance in parasitic helminths is currently limited. Moreover, the conditions needed for refugia to work, or how transferable those are between parasite-host systems, are not known. This review, born of an international workshop, seeks to deconstruct the concept of refugia and examine its assumptions and applicability in different situations. We conclude that factors potentially important to refugia, such as the fitness cost of drug resistance, the degree of mixing between parasite sub-populations selected through treatment or not, and the impact of parasite life-history, genetics and environment on the population dynamics of resistance, vary widely between systems. The success of attempts to generate refugia to limit anthelmintic drug resistance are therefore likely to be highly dependent on the system in hand. Additional research is needed on the concept of refugia and the underlying principles for its application across systems, as well as empirical studies within systems that prove and optimise its usefulness.

Impact of Dog Transport on High-Risk Infectious Diseases

Translocation of dogs inherently poses infectious disease risks when pathogen distributions vary between regions, even within the same country. Concerns include introduction of novel pathogens that can infect dogs, zoonotic pathogens, pathogens that can become established in existing reservoirs or vectors, and vectors that might carry pathogens and/or become established in a new region. This article presents the drivers of canine movement and their relative risks, and provides examples of diseases to show how different pathogen characteristics and transmission pathways can affect the impact of movement of infected dogs.

The Dynamic Nature of Canine and Feline Infectious Disease Risks in the Twenty-first Century

Canine and feline infectious diseases are constantly changing in frequency and location. Numerous drivers or determinants of these changes are suspected, including emergence of new pathogens; change in virulence and resistance of existing pathogens; change in land use, climate, and weather; travel and trade; habitat destruction and urbanization; change in animal-animal contact networks; host susceptibility; availability and uptake of prevention measures; and change in ability to detect pathogens and track diseases. This article explores each of these proposed drivers and examines examples of feline and canine diseases likely to be influenced by them.

The prevalence and trends of canine heartworm (Dirofilaria immitis) in Kuala Lumpur, Malaysia (1970-2018)

Malaysia is considered a hyperendemic area for canine heartworm (Dirofilaria immitis) due to its favorable climate for the completion of the parasite life cycle. This study provides an updated prevalence data on D. immitis in owned dogs from Kuala Lumpur, Malaysia and compares the trends of D. immitis in Malaysia. In the period between December 2017 and June 2018, 3.85% (5/130) dog blood samples tested positive for the presence of D. immitis antigen. A majority of the tested dogs (122/130) were not on rigorous heartworm prevention. After collating and analyzing information from 10 historical studies (1970-2017), we identified a significant decline in prevalence of D. immitis antigen in Malaysia, after the year 2000. Historically, the prevalence of D. immits antigen in owned dogs was significantly lower than the prevalence seen in stray dogs in Malaysia. This study demonstrates that D. immitis remains active in Kuala Lumpur, implying that accurate compliance of heartworm prevention is essential in Malaysia.

Serological evidence of canine exposure to arthropod-borne pathogens in different landscapes in Rio de Janeiro, Brazil

Arthropod-borne infections are dependent on environmental conditions, and several combinations of natural and human-related variables play an important role in vector populations as well as the life cycle of agents carried by the arthropods. The top 5 canine arthropod-transmitted agents, Dirofilaria immitis, Leishmania spp., Ehrlichia canis, Anaplasma phagocytophilum, and Borrelia burgdorferi infect unprotected animals without propensity. The purpose of this study was to determine the prevalence of these parasite species in three different landscape settings (sandbanks, plains and mountains) along a 60-km line. During a 6-month period, blood samples were collected from dogs (>12months old) living in the different settings. Prevalence of D. immitis was determined by modified Knott test and ELISA. Prevalence of E. canis, A. phagocytophilum, and B. burgdorferi was determined by ELISA, and Leishmania spp. by ELISA, indirect immunofluorescence, and immunocromatographic assays. D. immitis was most prevalent in the sandbank (68.9%) as well as Leishmania spp. (34.5%), and tick-transmitted agents, A. phagocytophilum and E. canis in the plains (61.7%). B. burgdorferi was not detected. Depending on the resources for arthropods present in regions, dogs are likely to be exposed to different arthropod-borne parasites and should receive preventives tailored to the risk of infection in the region in which the dog resides.

Gray Wolf Exposure to Emerging Vector-Borne Diseases in Wisconsin with Comparison to Domestic Dogs and Humans

World-wide concern over emerging vector-borne diseases has increased in recent years for both animal and human health. In the United Sates, concern about vector-borne diseases in canines has focused on Lyme disease, anaplasmosis, ehrlichiosis, and heartworm which infect domestic and wild canids. Of these diseases, Lyme and anaplasmosis are also frequently diagnosed in humans. Gray wolves (Canis lupus) recolonized Wisconsin in the 1970s, and we evaluated their temporal and geographic patterns of exposure to these four vector-borne diseases in Wisconsin as the population expanded between 1985 and 2011. A high proportion of the Wisconsin wolves were exposed to the agents that cause Lyme (65.6%) and anaplasma (47.7%), and a smaller proportion to ehrlichiosis (5.7%) and infected with heartworm (9.2%). Wolf exposure to tick borne diseases was consistently higher in older animals. Wolf exposure was markedly higher than domestic dog (Canis familiaris) exposure for all 4 disease agents during 2001–2013. We found a cluster of wolf exposure to Borrelia burgdorferi in northwestern Wisconsin, which overlaps human and domestic dog clusters for the same pathogen. In addition, wolf exposure to Lyme disease in Wisconsin has increased, corresponding with the increasing human incidence of Lyme disease in a similar time period. Despite generally high prevalence of exposure none of these diseases appear to have slowed the growth of the Wisconsin wolf population.

Forecasting United States heartworm Dirofilaria immitis prevalence in dogs

Background

This paper forecasts next year’s canine heartworm prevalence in the United States from 16 climate, geographic and societal factors. The forecast’s construction and an assessment of its performance are described.

Methods

The forecast is based on a spatial-temporal conditional autoregressive model fitted to over 31 million antigen heartworm tests conducted in the 48 contiguous United States during 2011–2015. The forecast uses county-level data on 16 predictive factors, including temperature, precipitation, median household income, local forest and surface water coverage, and presence/absence of eight mosquito species. Non-static factors are extrapolated into the forthcoming year with various statistical methods. The fitted model and factor extrapolations are used to estimate next year’s regional prevalence.

Results

The correlation between the observed and model-estimated county-by-county heartworm prevalence for the 5-year period 2011–2015 is 0.727, demonstrating reasonable model accuracy. The correlation between 2015 observed and forecasted county-by-county heartworm prevalence is 0.940, demonstrating significant skill and showing that heartworm prevalence can be forecasted reasonably accurately.

Conclusions

The forecast presented herein can a priori alert veterinarians to areas expected to see higher than normal heartworm activity. The proposed methods may prove useful for forecasting other diseases.

Dirofilaria infections in dogs in different areas of Greece

Background

The nematodes Dirofilaria immitis and D. repens are enzootic in Greece. In the light of evidence of dirofilariosis spreading to new areas around the world, the aim of the present study was to update and enrich the current knowledge on the prevalence of Dirofilaria infections in dogs in Greece, to assess the risk factors of heartworm infection, and to initiate the drawing of the epizootiological map of canine dirofilariosis, investigating Dirofilaria infections in five locations along the north-south axis of the country, i.e. municipalities of Thessaloniki, Larissa, Achaia, Attica and Heraklion, associated with the five largest urban centres of Greece.

Methods

Blood samples collected from 750 dogs in total, were examined by the modified Knott’s method and by serology. A questionnaire including information about each examined dog was filled in and statistical analysis of the results was performed using the Chi-square test and a Binary Multiple Univariate Generalized Linear Model.

Results

In total, 31 (4.1 %) out of 750 examined animals were found positive for D. immitis by any of the tests applied (Knott’s method and serological examination). Moreover, microfilariae of D. repens and Acanthocheilonema reconditum were detected by the Knott’s method in 17 (2.3 %) and 10 (1.3 %) of the animals, respectively. At the municipality level, the prevalence of infection was 14, 7, 5.3, 0.7 and 0 % for D. immitis, 1, 2, 8.7, 0.3 and 0 % for D. repens, and 0, 3, 2.7, 0.7 and 1 % for A. reconditum in Thessaloniki, Larissa, Achaia, Attica and Heraklion, respectively. In addition, in three dogs (one each in Thessaloniki, Achaia and Attica) mixed D. immitis - D. repens infections were detected by the Knott’s method. The area of the country, dog’s usage and age were determined as risk factors for heartworm infection.

Conclusions

Northern areas of Greece have higher Dirofilaria prevalence and the prevalence in a western province (Achaia) is recorded for the first time. The mosquito population dynamics recorded in the past is likely to play an important role in the distribution of Dirofilaria infections in Greece, and needs further investigation. Similarly, the role of wild reservoirs of filarial parasites in different areas needs to be clarified. Promotion by veterinarians of preventive treatment and compliance by pet owners is essential in all parts of Greece, regardless of the recorded prevalence of infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1797-6) contains supplementary material, which is available to authorized users.

Canine heartworm disease in Porto Velho: first record, distribution map and occurrence of positive mosquitoes

The aim of this study was to make the first report on canine heartworm disease in the state of Rondônia and confirm its transmission in this state. Blood samples were randomly collected from 727 dogs in the city of Porto Velho. The samples were analyzed to search for microfilariae and circulating antigens, using three different techniques: optical microscopy on thick blood smears stained with Giemsa; immunochromatography; and PCR. Mosquitoes were collected inside and outside the homes of all the cases of positive dogs and were tested using PCR to search for DNA of Dirofilaria immitis. Ninety-three blood samples out of 727 (12.8%) were positive according to the immunoassay technique and none according to the thick smear method. Among the 93 positive dogs, 89 (95.7%) were born in Porto Velho. No difference in the frequency of infection was observed between dogs raised indoors and in the yard. PCR on the mosquitoes resulted in only one positive pool. This result shows that the transmission of canine heartworm disease is occurring in the city of Porto Velho and that there is moderate prevalence among the dogs. The techniques of immunochromatography and PCR were more effective for detecting canine heartworm than thick blood smears. The confirmation of canine heartworm disease transmission in Porto Velho places this disease in the ranking for differential diagnosis of pulmonary nodules in humans in Rondônia.

Detection of Dirofilaria immitis and other arthropod-borne filarioids by an HRM real-time qPCR, blood-concentrating techniques and a serological assay in dogs from Costa Rica

BACKGROUND

Canine filarioids are important nematodes transmitted to dogs by arthropods. Diagnosis of canine filariosis is accomplished by the microscopic identification of microfilariae, serology or PCR for filarial-DNA. The aim of this study was to evaluate a molecular assay for the detection of canine filariae in dog blood, to compare its performance to other diagnostic techniques, and to determine the relationship between microfilarial concentration and infection with other vector-borne pathogens.

METHODS

Blood samples from 146 dogs from Costa Rica were subjected to the detection of canine filarioids by four different methods: the microhematocrit tube test (MCT), Knott's modified test, serology and a high resolution melt and quantitative real-time PCR (HRM-qPCR). Co-infection with other vector-borne pathogens was also evaluated.

RESULTS

Fifteen percent of the dogs were positive to Dirofilaria immitis by at least one of the methods. The HRM-qPCR produced distinctive melting plots for the different filarial worms and revealed that 11.6% of dogs were infected with Acanthocheilonema reconditum. The latter assay had a limit of detection of 2.4x10⁻⁴ mf/μl and detected infections with lower microfilarial concentrations in comparison to the microscopic techniques and the serological assay. The MCT and Knott's test only detected dogs with D. immitis microfilaremias above 0.7 mf/μl. Nevertheless, there was a strong correlation between the microfilarial concentration obtained by the Knott's modified test and the HRM-qPCR (r = 0.906, p < 0.0001). Interestingly, one dog was found infected with Cercopithifilaria bainae infection. Moreover, no association was found between microfilaremia and co-infection and there was no significant difference in microfilarial concentration between dogs infected only with D. immitis and dogs co-infected with Ehrlichia canis, Anaplasma platys or Babesia vogeli.

CONCLUSIONS

This is the first report of A. reconditum and C. bainae in Costa Rica and Central America. Among the evaluated diagnostic techniques, the HRM-qPCR showed the most sensitive and reliable performance in the detection of blood filaroids in comparison to the Knott's modified test, the MCT test and a serological assay.

Concurrent transcriptional profiling of Dirofilaria immitis and its Wolbachia endosymbiont throughout the nematode life cycle reveals coordinated gene expression

Background

Dirofilaria immitis, or canine heartworm, is a filarial nematode parasite that infects dogs and other mammals worldwide. Current disease control relies on regular administration of anthelmintic preventives, however, relatively poor compliance and evidence of developing drug resistance could warrant alternative measures against D. immitis and related human filarial infections be taken. As with many other filarial nematodes, D. immitis contains Wolbachia, an obligate bacterial endosymbiont thought to be involved in providing certain critical metabolites to the nematode. Correlations between nematode and Wolbachia transcriptomes during development have not been examined. Therefore, we detailed the developmental transcriptome of both D. immitis and its Wolbachia (wDi) in order to gain a better understanding of parasite-endosymbiont interactions throughout the nematode life cycle.

Results

Over 215 million single-end 50 bp reads were generated from total RNA from D. immitis adult males and females, microfilariae (mf) and third and fourth-stage larvae (L3 and L4). We critically evaluated the transcriptomes of the various life cycle stages to reveal sex-biased transcriptional patterns, as well as transcriptional differences between larval stages that may be involved in larval maturation. Hierarchical clustering revealed both D. immitis and wDi transcriptional activity in the L3 stage is clearly distinct from other life cycle stages. Interestingly, a large proportion of both D. immitis and wDi genes display microfilarial-biased transcriptional patterns. Concurrent transcriptome sequencing identified potential molecular interactions between parasite and endosymbiont that are more prominent during certain life cycle stages. In support of metabolite provisioning between filarial nematodes and Wolbachia, the synthesis of the critical metabolite, heme, by wDi appears to be synchronized in a stage-specific manner (mf-specific) with the production of heme-binding proteins in D. immitis.

Conclusions

Our integrated transcriptomic study has highlighted interesting correlations between Wolbachia and D. immitis transcription throughout the life cycle and provided a resource that may be used for the development of novel intervention strategies, not only for the treatment and prevention of D. immitis infections, but of other closely related human parasites as well.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1041) contains supplementary material, which is available to authorized users.

Establishment of macrocyclic lactone resistant Dirofilaria immitis isolates in experimentally infected laboratory dogs

BACKGROUND

Strains of Dirofilaria immitis suspected of lack of efficacy (LOE) to macrocyclic lactone (ML) preventive drugs have been increasingly reported in dogs by practicing veterinarians since 2005 in the Lower Mississippi Delta region. If proven, and not controlled in the early stages, the emergence of ML drug resistance threatens to become a widespread problem in the US that may limit the effectiveness of current preventive drug treatment methods.

METHODS

To validate practice reports, a statewide survey of Louisiana veterinarians was done to define the extent of the problem and identify focal 'hotspots' of reported ML LOEs using Geographic Information Systems (GIS) methods. The present study then utilized microfilariae (Mf) from two canine field cases from different state locations that fit criteria for a high index of suspicion of LOE against heartworms by ML drugs. Blood containing Mf from the canine field cases was used to infect and produce L3 in Aedes aegypti for experimental infection of two groups of dogs, each of which contained two laboratory dogs, one treated with prophylactic ivermectin (12 μg/kg) monthly for 6 months at twice the label dose (6 μg/kg), and one untreated control.

RESULTS

Both treated and untreated dogs from Group I and Group II developed patent D. immitis infections by 218 DPI and 189 DPI, respectively, as evidenced by a positive occult heartworm antigen test and microfilaremia by the Knott's test. Mf counts gradually increased post-patency in test and control dogs. Infective larvae raised from microfilariae from the treated Group I dog were used to successfully establish a second generation isolate, confirming heritability of resistance in the face of a monthly ivermectin challenge dose of 24 μg/kg, given monthly for 3 months.

CONCLUSIONS

These experimental infection studies provide in vivo evidence of the existence of ML drug resistance in dogs infected by D. immitis L3 from suspect field LOE cases in the Lower Mississippi Delta. Results encourage further work on mechanisms underlying the emergence of ML resistance in D. immitis and development of evidence-based resistance management strategies for heartworm preventives in order to extend the useful life of current drugs.

Quantitative factors proposed to influence the prevalence of canine tick-borne disease agents in the United States

The Companion Animal Parasite Council hosted a meeting to identify quantifiable factors that can influence the prevalence of tick-borne disease agents among dogs in North America. This report summarizes the approach used and the factors identified for further analysis with mathematical models of canine exposure to tick-borne pathogens.

Prevalence and seasonal variations of canine dirofilariosis in Portugal

Dirofilariosis is a severe vector-borne emergent disease that is spreading worldwide and becoming a serious threat to human and veterinary public health. Portugal, a Mediterranean country, has favorable climate conditions for mosquito development and survival. At present, accurate data on the prevalence and epidemiological pattern of dirofilariosis in Portugal is scarce and outdated. To study these trends, a project was developed to assess the current prevalence of Dirofilaria immitis infection in shelter dogs as well as the prevalence of Dirofilaria species present in three coastal regions in central Portugal: Coimbra, Santarém, and Setúbal. Blood samples were collected from 696 shelter dogs during three consecutive years: 2011, 2012, and 2013. A rapid immunomigration technique was performed to detect female D. immitis antigens. Concurrently, to detect and identify circulating microfilariae, a modified Knott's technique and acid phosphatase histochemical staining were also performed. Of the 696 dogs sampled, 105 were positive for D. immitis, with an overall prevalence of 15.1%. Forty of the 105 dogs were antigen negative but were positive for D. immitis microfilariae. Three animals were co-infected with D. immitis and Acanthocheilonema dracunculoides, and there was also one dog infected only with A. dracunculoides, all confirmed by polymerase chain reaction. The highest prevalence of canine heartworm during the 3-y period was in Setúbal (24.8%), followed by Coimbra (13.8%), and Santarém (13.2%), with significant inter-district differences. Our results demonstrate a higher prevalence of dirofilariosis compared with findings of previous studies and show an increasing rate of infection in the southern areas of Portugal attributed, at least in part, to bioclimatic and ecological factors. The present study updates the epidemiological situation and correlates the risk of dirofilariosis transmission within each region. These findings are highly relevant to both human and veterinary public health, contributing to the general awareness of pet owners and veterinarian practitioners and reinforcing the need for effective control measures against vectors and preventive therapy in companion animals.

Climate suitability for the transmission of Dirofilaria immitis and D. repens in Germany

Recently concerns are increasing that dirofilarial nematodes may spread from endemic areas in southern, eastern and central Europe to countries in northern regions of Europe. The increasing number of autochthonous cases of canine Dirofilaria repens infections in Germany indicates that worms of this genus may invade new areas, and climate change may be a key factor in this scenario. Thus analysis of long term development of regional temperature is a pivotal factor in risk analysis related to transmission of these worms. Such information is important for suggestions of counteracting strategies, such as definition of periods of increased transmission risk and, consequently, time slots most suited for preventative measures. In this study, mean daily temperature data from 34 geographical clustered weather stations representing all parts of Germany were analyzed. It is concluded that the increasing trend for average daily temperatures observed in the period from 1984 to 2013 has led to climatic conditions that allow the completion of dirofilarial life cycles in large parts of Germany between May and October. Autochthonous infection with D. repens is already established in some regions and targeted diagnosis and medical prophylaxis is advisable for dogs assumedly exposed during risk of transmission periods. It appears likely that global warming will support further spread of D. repens. Furthermore for the population of dogs the spread of the more pathogenic species D. immitis in hitherto non-endemic Germany is a potential risk if mean temperatures rise to a level suitable for parasite development in the abundant vector mosquitoes during the warmer seasons.

Factors influencing U.S. canine heartworm (Dirofilaria immitis) prevalence

Background

This paper examines the individual factors that influence prevalence rates of canine heartworm in the contiguous United States. A data set provided by the Companion Animal Parasite Council, which contains county-by-county results of over nine million heartworm tests conducted during 2011 and 2012, is analyzed for predictive structure. The goal is to identify the factors that are important in predicting high canine heartworm prevalence rates.

Methods

The factors considered in this study are those envisioned to impact whether a dog is likely to have heartworm. The factors include climate conditions (annual temperature, precipitation, and relative humidity), socio-economic conditions (population density, household income), local topography (surface water and forestation coverage, elevation), and vector presence (several mosquito species). A baseline heartworm prevalence map is constructed using estimated proportions of positive tests in each county of the United States. A smoothing algorithm is employed to remove localized small-scale variation and highlight large-scale structures of the prevalence rates. Logistic regression is used to identify significant factors for predicting heartworm prevalence.

Results

All of the examined factors have power in predicting heartworm prevalence, including median household income, annual temperature, county elevation, and presence of the mosquitoes Aedes trivittatus, Aedes sierrensis and Culex quinquefasciatus. Interactions among factors also exist.

Conclusions

The factors identified are significant in predicting heartworm prevalence. The factor list is likely incomplete due to data deficiencies. For example, coyotes and feral dogs are known reservoirs of heartworm infection. Unfortunately, no complete data of their populations were available. The regression model considered is currently being explored to forecast future values of heartworm prevalence.