Dirofilaria immitis and Onchocercidae spp. in wild felids from Brazil

Among the species described within the Onchocercidae family, Dirofilaria immitis is regarded as the most common worldwide, causing severe and often fatal conditions in dogs, cats, and occasionally humans. Dirofilaria spp. are vectored by mosquitoes, simulids, and culicoids, with their epidemiology dependent on the geographical distribution of competent vectors. Eight species of Dirofilaria have been reported so far in Brazil, of which six parasitize non-human primates, deer, procyonids, and marsupials. Here, we investigated the occurrence of Onchocercidae in wild felids (i.e., Panthera onca, Puma concolor, Herpailurus yagouaroundi, Leopardus geoffroyi, Leopardus guttulus, Leopardus pardalis, Leopardus wiedii, Leopardus munoai) from different locations in Brazil. Overall, 82 samples (n = 63 blood; n = 19 tissues) were molecularly screened for cytochrome c oxidase subunit-1 (cox1) gene. Four (i.e., 4.8%) wild felid samples were positive, and at BLAST analysis, the obtained sequences showed varying percentage of nucleotide identity with the genera Brugia (i.e., 87-88%), Setaria (i.e., 89%), and D. immitis (i.e., 94.4%). Phylogenetic analyses clustered sequences obtained into three distinct clades, one with D. immitis and the remaining two with other Onchocercidae spp. Data herein obtained highlight the need for a more comprehensive understanding of the diversity and biology of Onchocercidae in South America in order to assess the potential impact that these species may have for domestic and wild animals, as well as humans.

Development of adult Dirofilaria immitis worms in the Rag2/Il-2rγ-/- mouse model

Dirofilaria immitis is the causative agent for one of the major parasitic infections in dogs. It is currently not possible to reliably diagnose the infection before the development of fertile adult female worms and the presence of microfilariae which takes six to 7 months. However, at this point adult worms already reside in the pulmonary arteries and can cause significant damage. Novel in vivo models may facilitate the development of new diagnostic tools and improve treatment options for both the early and late stages of D. immitis infections. In this paper, we aimed to increase the capabilities of recently published mouse models in which severely immune-deficient mice were shown to be susceptible to D. immitis. Our data shows that D. immitis may grow into fully developed mature male and female worms in C57BL/6 Rag2/Il-2rγ-/- mice with comparable growth rates to the natural canine host. The adult worms of D. immitis were shown to migrate into body cavities as well as the heart in this model. However, the presence of adult worms inside the heart of infected mice led to the development of caval syndrome in 36% of infected mice after five to 6 months. Overall, the current study complements recently published efforts to establish a D. immitis mouse model by extending the development of D. immitis into mature adult stages and will facilitate further preclinical research.

Genome structure and population genomics of the canine heartworm Dirofilaria immitis

The heartworm, Dirofilaria immitis, is a filarial parasitic nematode responsible for significant morbidity and mortality in wild and domesticated canids. Resistance to macrocyclic lactone drug prevention represents a significant threat to parasite control and has prompted investigations to understand the genetic determinants of resistance. This study aimed to improve the genomic resources of D. immitis to enable a more precise understanding of how genetic variation is distributed within and between parasite populations worldwide, which will inform the likelihood and rate by which parasites, and in turn, resistant alleles, might spread. We have guided the scaffolding of a recently published genome assembly for D. immitis (ICBAS_JMDir_1.0) using the chromosomal-scale reference genomes of Brugia malayi and Onchocerca volvulus, resulting in an 89.5 Mb assembly composed of four autosomal- and one sex-linked chromosomal-scale scaffolds representing 99.7% of the genome. Publicly available and new whole-genome sequencing data from 32 D. immitis samples from Australia, Italy and the USA were assessed using principal component analysis, nucleotide diversity (Pi) and absolute genetic divergence (Dxy) to characterise the global genetic structure and measure within- and between-population diversity. These population genetic analyses revealed broad-scale genetic structure among globally diverse samples and differences in genetic diversity between populations; however, fine-scale subpopulation analysis was limited and biased by differences between sample types. Finally, we mapped single nucleotide polymorphisms previously associated with macrocyclic lactone resistance in the new genome assembly, revealing the physical linkage of high-priority variants on chromosome 3, and determined their frequency in the studied populations. This new chromosomal assembly for D. immitis now allows for a more precise investigation of selection on genome-wide genetic variation and will enhance our understanding of parasite transmission and the spread of genetic variants responsible for resistance to treatment.

Exploring multiplex qPCR as a diagnostic tool for detecting microfilarial DNA in dogs infected with Dirofilaria immitis: A comparative analysis with the modified Knott's test

Current recommendations to diagnose cardiopulmonary dirofilariosis in dogs caused by Dirofilaria immitis involves tandem antigen and circulating microfilariae tests. The modified Knott's test is an important tool in heartworm diagnosis, allowing identification of circulating microfilariae. However, the subjective nature of the modified Knott's test affects its accuracy and diagnostic laboratories usually do not provide a quantitative outcome. Quantitative enumeration of microfilariae enables clinicians to track treatment progress and acts as a proxy for detecting emerging macrocyclic lactone resistance. There is a need for better diagnostic tools suitable for routine use to efficiently and accurately quantify the presence of D. immitis microfilaremia. The aim of this study was to determine whether the quantitative modified Knott's test can be substituted by multiplex quantitative polymerase chain reaction (qPCR) targeting D. immitis and associated Wolbachia endosymbiont DNA in canine blood samples. To do this, genomic DNA samples (n = 161) from Australian dogs, collected as part of a previous 2021 study, were assessed in a TaqMan qPCR targeting DNA of D. immitis, Wolbachia sp. and Canis lupus familiaris. Of the 161 genomic DNA samples, eight were considered positive for D. immitis microfilariae. The qPCR assay demonstrated good efficiency (E = 90 to 110%, R2 > 0.94). Considering the performance and efficient use of bench time, this TaqMan qPCR assay is a suitable alternative to the modified Knott's test for quantitative enumeration of microfilariae (Cohen's kappa coefficient [κ]: κ = 1 using D. immitis qPCR marker, κ = 0.93 using Wolbachia qPCR marker). The qPCR data demonstrated a comparable result to that of the quantitative modified Knott's test in a 2022 survey of D. immitis in Australian dogs (n = 23) before and after macrocyclic lactone (ML) administration. Improving the detection and diagnosis of canine heartworm infections will assist veterinarians in better managing and controlling disease outcomes and will be valuable for tracking the spread of ML resistance in Australia.

Dirofilaria immitis conquering the regions in Slovakia previously endemic for D. repens

The present study was focused on the current state of Dirofilaria species distribution in the territory of the Slovak Danubian Lowland, a region previously identified endemic for Dirofilaria repens. For the research, blood samples of 330 dogs tested positive for dirofilariosis using concentration tests or "rapid heartworm tests" were sent by private veterinary practitioners for further DNA analyses and species determination. The results revealed an unquestionable change in the pattern of Dirofilaria species distribution with Dirofilaria immitis, diagnosed as the agent of mono- and co-infections with D. repens, responsible for 60.00% of all cases. The results showed that in the course of the last 5 years, D. immitis has spread significantly in Slovakia and has become the dominant causal agent of dirofilariosis in the former endemic areas of D. repens distribution, which increases infection risk for both dogs and humans.

Droplet digital PCR as a tool to detect resistant isolates of Dirofilaria immitis

Prevention of canine heartworm disease, caused by Dirofilaria immitis, relies on macrocyclic lactones for which drug resistance is now a concern. Although genetic polymorphisms have been associated with resistance in D. immitis populations, the mechanism is still not well understood. The lack of reliable in vitro assays to detect resistance is a limitation for confirming resistance. Ten single nucleotide polymorphisms (SNPs) were previously clinically validated in D. immitis resistant isolates, using the MiSeq platform. This technique although useful for research studies is expensive and does not facilitate rapid detection of these markers in small numbers of clinical samples. We developed a droplet digital PCR protocol for detecting SNPs correlating with ML resistance. Specific primers and hydrolysis probes encompassing the wildtype and mutant alleles were designed to amplify the SNP targets from genomic DNA of different D. immitis isolates. Allele frequencies were determined and the suitability of the ddPCR assay was assessed and compared with MiSeq data. The ddPCR assay accurately detected and quantified alternate nucleotides in two isolates of reference, the ML-susceptible Missouri (MO) and ML-resistant JYD-34, at the previously identified SNP positions. The presence of the SNPs was also determined in additional isolates with known or putative susceptible or resistant phenotypes. We observed SNP1 and SNP2 are more predictive markers and appear suitable for rapid detection and monitoring of drug resistance. Our results suggested that ddPCR could be employed to distinguish infection due to actual genetic resistance from infection with susceptible parasites and also for rapid detection of isolates not only with ML susceptible and resistant genotypes but also mixed genotypes that correspond to heterogeneous isolates containing a mixed population of ML susceptible and resistant parasites. DdPCR may be a useful tool for conducting surveys, or assessments of individual isolates, for genetic evidence of resistance or developing resistance.

First molecular characterization of Dirofilaria Immitis in Cuba

BACKGROUND

Dirofilarioses are widespread diseases caused by mosquito-borne nematodes of the family Onchocercidae, genus Dirofilaria. The major etiologic agent of canine dirofilariosis in the American continent is the zoonotic parasite Dirofilaria immitis. Existing reports of filarioid nematodes in Cuba are based solely on morphological and immunological analysis which do not allow unambiguous identification and/or direct detection of causal agents.

RESULTS

Here we present the molecular characterization of filarioid nematodes found in a dog in Cuba. Based on the molecular and phylogenetic analysis of the 5.8S-ITS2-28S region and cox1 gene fragments, the worms were unambiguously classified as D. immitis. Sequence analysis showed high identity of the gene fragments in this study with others previously obtained from D. immitis found in dogs, wolfs and jackals but also from mosquito vectors of D. immitis.

CONCLUSIONS

Further studies are guarantee to better understand the epidemiological impact of canine dirofilariosis in Cuba as well as the competence of different species of culicid mosquitoes as vectors of Dirofilaria in the country.

Dirofilaria immitis in pet dogs from the metropolitan area of the Colombian Caribbean

A cross-sectional study was carried out to determine the frequency and factors associated with Dirofilaria immitis infection in pet dogs in the metropolitan area of the Colombian Caribbean (northern Colombia). A total of 173 dogs were analyzed by a commercial rapid immunochromatographic test (RIT) and a nested PCR of the cytochrome oxidase subunit I gene, in parallel. Ninety-two (53.2%) of the dogs showed positive results to the RIT, while 59 (34.1%) animals had D. immitis DNA by PCR. Positivity to one or both diagnostic techniques was detected in 104 (60.1%; CI95%: 53.8-67.4) of the sampled dogs. In PCR-positive dogs, phylogenetic analyses evidenced high nucleotide identity (100%) with sequences previously obtained from mosquitoes, dogs and other mammals in different countries. Exercise intolerance (p = 0.002; OR: 2.33; CI95%: 1.37-3.96) and thrombocytopenia (p = < 0.001; OR: 1.95; CI95%: 1.11-3.43) were the main factors associated with D. immitis infection in dogs. The high frequency of D. immitis in dogs indicates a wide distribution of this parasite in the metropolitan area of the Colombian Caribbean, which can be of animal and public health concern. Our results highlight the need to combine different methods to increase the diagnostic accuracy of D. immitis.

The first report of Dirofilaria repens infection in dogs from Colombia

Dirofilariasis is a mosquito-borne disease caused by Dirofilaria parasites, affecting both wild and domestic animals, including humans considered as accidental hosts. Dirofilaria repens is the principal causative agent of dirofilariasis in the Old World, with increasing reports of the parasite in countries where it has not been previously identified, due to several factors such as the expansion of mosquito vectors' geographical distribution. By utilizing newly designed primers for molecular detection and confirming through next-generation sequencing, here, we report the first plausible cases of D. repens in dogs from Colombia. Our results support the classification of this species as an emergent pathogen in the Americas. Finally, we encourage an increase in diagnostic and surveillance efforts to prevent and control the current and future dirofilariasis cases in this region.

Genetic diversity and characterization of Wolbachia endosymbiont in canine filariasis

Canine filariasis is caused by nematodes from the family Onchocercidae, which is transmitted by arthropod vectors. The disease is commonly found in Southeast Asia and exists worldwide. Some filarial nematodes are associated with intracellular bacteria of the genus Wolbachia, which plays an important role in embryogenesis, molting, and the long-term survival of adult worms. This study aims to characterize Wolbachia sp. and determine the association between Wolbachia and canine filarial nematode species in Thailand. A total of 46 dog blood samples that were naturally infected with filarial nematodes were obtained to identify filarial nematode species by Giemsa stained under a light microscope and confirmed using the molecular technique. In order to characterize Wolbachia sp., the nested PCR assay targeting the 16S rRNA gene showed that all samples of Dirofilaria immitis and fifteen samples of Candidatus Dirofilaria hongkongensis were grouped into Wolbachia supergroup C. In addition, all samples of Brugia spp. and five samples of Candidatus Dirofilaria hongkongensis were classified into Wolbachia supergroup D. The genetic diversity analysis conducted using the 16S rRNA gene revealed a similar result when analyzed through phylogenetic tree analysis. This is the first genetic diversity study of Wolbachia of Candidatus Dirofilaria hongkongensis in infected dogs in Thailand.

Diversity and geographic distribution of haplotypes of Dirofilaria immitis across European endemic countries

BACKGROUND

Dirofilaria immitis, also known as heartworm, is one of the most important parasitic nematodes of domestic dogs, causing a potentially serious disease, cardiopulmonary dirofilariosis, which can be lethal. This species seems to be less 'expansive' than its sister species Dirofilaria repens, and it is believed that climate change facilitates the spread of this parasite to new non-endemic regions.

METHODS

In total, 122 heartworm isolates were analysed from nine endemic countries in Europe (Portugal, Spain, Italy, Greece, Hungary, Romania, Slovakia, and Ukraine) and a single isolate from Bangladesh by amplification and sequencing of two mitochondrial (mt) DNA markers: cytochrome c oxidase subunit 1 (COI) and dehydrogenase subunit 1 (NADH). The main aim of the current study was to determine the genetic diversity of D. immitis and compare it with D. repens haplotype diversity and distribution. DNA was extracted from adult heartworms or microfilariae in blood. Most isolates originated from dogs (Canis lupus familiaris) while 10 isolates originated from wildlife species from Romania, including eight isolates from golden jackals (Canis aureus), one isolate from a Eurasian otter (Lutra lutra) and one isolate from a red fox (Vulpes vulpes).

RESULTS

Median spanning network analysis was based on the combined sequence (1721 bp) obtained from two mt markers and successfully delineated nine haplotypes (Di1-Di9). Haplotype Di1 was the dominant haplotype encompassing 91 out of the 122 sequences (75%) from all nine countries and four host species. Haplotype Di2 was the second most common haplotype, formed solely by 13 isolates from Italy. The remaining sequences were assigned to Di3-Di9 haplotypes, differing by 1-4 SNPs from the dominant Di1 haplotype. There was evidence for geographical segregation of haplotypes, with three unique haplotypes associated with Italy and four others associated with certain countries (Di4 and Di7 with Slovakia; Di8 with Greece; Di6 with Hungary).

CONCLUSION

Diversity in D. immitis mt haplotypes was lower by half than in D. repens (9 vs. 18 haplotypes in D. immitis and D. repens, respectively), which may be associated with the slower expansion of heartworm in Central and NE Europe. NADH gene appears to be conserved in Dirofilaria sp. by showing lower genetic diversity than the analysed COI gene.

The first molecular confirmation of Culex pipiens complex as potential natural vectors of Dirofilaria immitis in Myanmar

Dirofilariosis, known as one of the most widespread vector-borne zoonotic diseases, is caused by several different species of the nematodes of the genus Dirofilaria, which can be transmitted by Culex, Anopheles and Aedes mosquito vectors. In order to identify key vector mosquitoes of filarial parasites in Myanmar, mosquitoes were collected during three different seasons (summer, rainy and winter) in three townships in Nay Pyi Taw area, Myanmar. DNA extraction and polymerase chain reaction (PCR) analyses were conducted for 185 mosquito pools, with each pool containing 1-10 mosquitoes. Dirofilaria immitis was detected in 20 pools of Culex pipiens complex mosquitoes. The minimum infection rate of mosquitoes was found to be 16.33. The small subunit ribosomal RNA (12S rDNA) gene targeted PCR revealed that the sequences obtained were completely identical to the sequences of D. immitis derived from dogs in China, Brazil and France. The sequences obtained from mitochondrial cytochrome oxidase subunit I (COI) gene PCR exhibited 100% identity with the sequences of D. immitis derived from dogs in Bangladesh, Iran, Japan and Thailand, as well as humans in Iran and Thailand, and mosquitoes in Germany and Hungary. The findings of this study demonstrated that the mosquito species of Cx. pipiens complex are potential mosquito vectors for dirofilariosis in Myanmar.

New paradigms in research on Dirofilaria immitis

BACKGROUND

Since the advent of ivermectin (along with melarsomine and doxycycline), heartworm has come to be viewed as a solved problem in veterinary medicine, diminishing investment into non-clinical research on Dirofilaria immitis. However, heartworm infections continue to pose problems for practitioners and their patients and seem to be increasing in frequency and geographic distribution. Resistance to preventative therapies (macrocyclic lactones) complicates the picture. The use of chemotherapy for other kinds of pathogens has benefitted enormously from research into the basic biology of the pathogen and on the host-pathogen interface. A lack of basic information on heartworms as parasites and how they interact with permissive and non-permissive hosts greatly limits the ability to discover new ways to prevent and treat heartworm disease. Recent advances in technical platforms will help overcome the intrinsic barriers that hamper research on D. immitis, most notably, the need for experimentally infected dogs to maintain the life cycle and provide material for experiments. Impressive achievements in the development of laboratory animal models for D. immitis will enhance efforts to discover new drugs for prevention or treatment, to characterize new diagnostic biomarkers and to identify key parasite-derived molecules that are essential for survival in permissive hosts, providing a rational basis for vaccine discovery. A 'genomics toolbox' for D. immitis could enable unprecedented insight into the negotiations between host and parasite that enable survival in a permissive host. The more we know about the pathogen and how it manipulates its host, the better able we will be to protect companion animals far into the future.

Prevalence of filarial parasites in field-caught mosquitoes in northwestern California

Mosquitoes were collected in Lake County, CA, in 2014 and tested using standard polymerase chain reaction for filarial parasite DNA. Filarial parasites were detected in 23 out of 1,008 total pools. DNA from Dirofilaria immitis, the parasite causing dog heartworm, was detected in Aedes increpitus (MIR=4.62), Aedes sierrensis (MIR=6.72), Anopheles freeborni (MIR=1.08), and Culex tarsalis (MIR=0.10). Setaria yehi, deer body worm, was detected in Ae. sierrensis (MIR=13.42), Anopheles franciscanus (MIR=0.55), An. freeborni (MIR=2.69), and Culex stigmatosoma (MIR=0.41). The avian parasite Splendidofilaria could not be identified to species but was detected in Cx. tarsalis (MIR=0.20). DNA was also detected for three unidentified filarial parasites in Culex. Filarial-positive pools spanned May-August, with Splendidofilaria earlier in the season and S. yehi later. For D. immitis, MIR tended to be highest in June, when the 130 HDU development threshold was reached. Interestingly, D. immitis was also detected prior to the HDU threshold, and D. immitis was not detected August-September, though HDU remained high enough for development. This suggests that there are other factors influencing dog heartworm transmission in the area.

Dirofilaria immitis in an Asian small-clawed otter (Aonyx cinereus) from southeastern Louisiana, United States

A single, male Dirofilaria immitis was found in the right ventricle of a captive, 10-month-old female Asian small-clawed otter (Aonyx cinereus) from East Feliciana parish in Louisiana, USA. Molecular analysis was performed for unequivocal species level identification using the cytochrome c oxidase subunit 1 (cox1) region of the mitochondrial DNA and comparing to known D. immitis cox1 sequences available on GenBank to which the specimen had a 99.54-100% pair wise identity. As there is no safe adulticidal treatment for D. immitis in mustelids, chemoprophylaxis using macrocyclic lactones is recommended to prevent infection. Further studies are needed to better characterize D. immitis infection and its propensity to cause disease in the Asian small-clawed otter.

Transporter gene expression and Wolbachia quantification in adults of Dirofilaria immitis treated in vitro with ivermectin or moxidectin alone or in combination with doxycycline for 12 hours

Due to their marked larvicidal activity, macrocyclic lactones (MLs) are used for the prevention of heartworm disease ( Dirofilaria immitis) in dogs. They have also been shown to eliminate adult parasites after long-term administration, with a so-called "slow-kill" effect. In addition, recent studies have established that a combination of doxycycline, which eliminates the endosymbiont Wolbachia, and MLs has superior adulticide effects when compared to MLs alone. It has been hypothesized that the apparent synergism between doxycycline/MLs may be due to interaction with drug efflux transport proteins. The aim of the present study was to evaluate gene expression of several transport proteins in D. immitis adults treated in vitro either with doxycycline alone, ivermectin alone, moxidectin alone, or a combination of ivermectin or moxidectin with doxycycline for 12h. Quantitative PCR analysis showed a sex-dependent response to treatments. In female worms, Dim-pgp-10, Dim-haf-1 and Dim-haf-5 were upregulated compared to controls with doxycycline alone and when combined with ivermectin. Moxidectin did not induce any changes in gene expression. In males, moxidectin administered alone induced a slight increase in Dim-pgp-10, Dim-pgp-11and Di-avr-14, while ivermectin in combination with doxycycline produced significant upregulation of the ML receptor Di-avr-14. These results suggest possible synergism between the two drug classes and different susceptibility of males vs. females to adulticide effects.

Filarids (Spirurida: Onchocercidae) in wild carnivores and domestic dogs from the Brazilian Atlantic forest

Onchocercidae nematodes are heteroxenous parasites with worldwide distribution, and some of the species associated to animals may present zoonotic potential. Climatic changes and anthropic influences on the environment may result in vectors’ proliferation, facilitating the spillover to humans and/or non-typical animal hosts. The Iguaçu National Park (PARNA Iguaçu), one of the most important Brazilian natural remanescents of Atlantic rainforest, is strongly affected by human activities such as tourism and agriculture. The complexity of this area is especially characterized by the close nexus between the rich wildlife, humans, and domestic animals, especially domestic dogs. Based on this, this research aimed to diagnose the Onchocercidae nematodes in wild carnivores and domestic dogs in the PARNA Iguaçu and the surrounding areas. For this, we collected 162 samples of seven species of wild carnivores and 225 samples of domestic dogs. The presence of microfilariae in the blood samples was diagnosed by the modified Knott’s test and molecular screening, and the specific identification was based on sequencing of the myoHC and hsp70 genes. Microfilariae were detected only in ring-tailed coatis, in which we found five species: Mansonella sp. 1, Mansonela sp. 2, Onchocercidade gen. sp. 1, Onchocercidade gen. sp. 2, and Dirofilaria immitis. The morphological analysis supported the molecular findings. The domestic dogs were parasitized by Acanthocheilonema reconditum, representing a new locality record for this species. Phylogenetic analysis showed high genetic similarity among the four undetermined species and Mansonella spp., Brugia spp., and Wuchereria bancrofti. The presence of D. immitis in ring-tailed coatis may be result of spillover from dogs, even though the parasite was not diagnosed in the sampled dogs. The presence of several undetermined Onchocercidae species indicates the necessity of continuous investigations on wild and domestic animals from Neotropical area, especially considering the growing anthropic influence on forest remnants.

Filarids are vector-borne Onchocercidae nematodes widely distributed around the world, related to several hosts, both wild and domestic, in different Biomes, including human-related species. In consequence to deforestation, environmental degradation, and climate changes, there has been an expansion in the distribution of vector-borne diseases around the world, such as those caused by filarids, in endemic tropical areas and even in temperate regions where they did not used to occur before. Thus, epidemiology and molecular genetic diversity studies of these filarial parasites are of great importance for three main reasons: zoonotic potential of many known species of filarids; the lack of data about the species inhabiting neotropical regions and the current worldwide deforestation and consequent habitat loss scenario, which favors the emergence or re-emergence of diseases resulting from the infection of domestic animals and humans by parasites that used to have as reservoirs only wild animals.

Potential Mosquito Vectors of Dirofilaria immitis and Dirofilaira repens (Spirurida: Onchocercidae) in Aras Valley, Turkey

Dirofilaria immitis (Leidy, 1856) and Dirofilaria repens (Railliet & Henry, 1911) are mosquito-borne filarial nematodes that primarily affect dogs, causing heartworm disease and subcutaneous dirofilariosis. The canine heartworm is reported in different provinces in Turkey. However, studies about the transmitting mosquito species are limited. Hence, this study aimed to investigate potential vectors of D. immitis and D. repens in Aras Valley, Turkey. In total, 17,995 female mosquitoes were collected from eight villages during three mosquito seasons (2012-2014) in Aras Valley, located in north-eastern Turkey. A total of 1,054 DNA pools (527 abdomen and 527 head-thorax) were tested with Dirofilaria primers by multiplex-polymerase chain reaction (PCR). Aedes caspius was the most abundant species in collection sites with 90%; this was followed by Culex theileri Theobald, 1903 (Diptera: Culicidae) (7.31%), Anopheles maculipennis Meigen 1818 (Diptera: Culicidae) (1.28%), Culex pipiens Linnaeus, 1758 (Diptera: Culicidae) (0.43%), (Anopheles) hyrcanus (Pallas, 1771) (Diptera: Culicidae) (0.37%), Aedes vexans (Meigen, 1830) (Diptera: Culicidae) (0.25%), and Culiseta annulata Schrank, 1776 (Diptera:Culicidae) (0.02%). Dirofilaria immitis and D. repens were detected in mosquito pools from five villages. The total Dirofilaria spp. estimated infection rate was 1.33%. The highest estimated infection rate was found in Ae. vexans (6.66%) and the lowest was in Ae. caspius (1.26%). The results show that An. maculipennis sl, Ae. caspius, Ae. vexans, Cx. theileri and Cx. pipiens are potential vectors of D. immitis and D. repens with DNA in head-thorax pools; An. hyrcanus is also a likely vector, but Dirofilaria DNA was found only in abdomen pools for the study area. This study revealed new potential vector species for D. immitis. Mosquitoes with natural infections of D. repens were reported for the first time in Turkey.

First Molecular Detection of Dirofilaria immitis and D. repens in Dogs from Kyrgyzstan

BACKGROUND

Dirofilaria immitis and Dirofilaria repens are the causative agents of cardiopulmonary and subcutaneous dirofilariosis, respectively. This neglected disease mainly seen in dogs, cats and wild carnivores is re-emerging recent years. No study was conducted on dirofilariosis in dogs in Kyrgyzstan.

PURPOSE

The goal of this study was to investigate Dirofilaria species using PCR and sequencing in dogs from Kyrgyzstan.

METHOD

Dirofilaria spp. infection in dogs was screened via convential PCR and sequencing in 337 dogs from Kyrgyzstan.

RESULT

The overall prevalence of Dirofilaria spp. was 0.59% (2/337): DNA of D. immitis was detected in one sample and DNA of D. repens in second positive sample. In second sample, parallel co-infection of D. repens with Wolbachia was also found. While D. immitis sequence showed 98.70-100% similarity with previously reported sequences of D. immitis from dog blood, D. repens shared 100% identity with other sequences of D. repens.

CONCLUSION

These results provided first evidence for Dirofilaria spp. in Kyrgyzstan and emphasized the veterinary and medical importance.

Prevalence and genetic characterization of Dirofilaria lutrae Orihle, 1965 in North American river otters (Lontra canadensis)

Dirofilaria lutrae Orihle, 1965 is a subcutaneous filarial worm found in North American river otters (Lontra canadensis). Previous studies reported the geographical range of this worm to include Louisiana, Florida, and North Carolina, USA. Although D. lutrae does not cause disease in otters, it must be distinguished from Dirofilaria immitis (Leidy, 1856), which causes heartworm disease in otters. The goal of this study was to determine the prevalence of D. lutrae in several states and to investigate the phylogenetic relationship of D. lutrae and other Dirofilaria species. Adult D. lutrae were collected from 32 of 40 (80%) otters from North Carolina (n = 38), South Carolina (n = 1), and Kentucky (n = 1), whereas all otters from Georgia (n = 1), Pennsylvania (n = 2), Arkansas (n = 184) and California (n = 1) were negative for D. lutrae. A portion of the cytochrome c oxidase I (COI) was amplified from nine North Carolina specimens and one South Carolina specimen. Sequence analysis indicated that all but one were identical to each other and D. lutrae was phylogenetically most closely related to D. immitis; however, few Dirofilaria sequences are available for comparison. Because other subcutaneous parasites may be detected in otters, parasites should be carefully examined to confirm their identity. Finally, given the high prevalence of D. lutrae in otters in some southeastern states, microfilaria found in blood samples of otters must be correctly identified because treatment for D. lutrae is generally not warranted and some pharmaceutical treatments can cause mortality in otters.

PREVALENCE AND MOLECULAR CHARACTERIZATION OF DIROFILARIA IMMITIS (FILARIOIDEA: ONCHOCERCIDAE) IN DOGS FROM ENDEMIC AREAS OF RIO DE JANEIRO STATE, BRAZIL

Canine dirofilariasis is common in Brazil, but molecular diagnosis is rare even though molecular studies increase our knowledge about molecular epidemiology and circulating genotypes from helminths worldwide. This study aims to estimate the prevalence of infection with a modified Knott's test and to perform molecular characterization of Dirofilaria immitis (Leidy, 1856) Railliet and Henry, 1911, in dogs from endemic areas of Maricá and Niterói municipalities, Rio de Janeiro State, Brazil. Molecular characterization was performed in 33 blood samples from dogs positive for microfilariae and 4 adult worms obtained from 2 other dogs. DNA extraction followed by PCR for mitochondrial target 12S rDNA and cytochrome oxidase subunit 1 (COI) of D. immitis were performed, and the amplified products were sequenced. All sequences were identical for both gene targets and showed 100% identity with D. immitis sequences from different animal species from various countries. The study concluded that this genotype of D. immitis might be dispersed worldwide.

Screening of mosquitoes for filarioid helminths in urban areas in south western Poland-common patterns in European Setaria tundra xenomonitoring studies

In recent years, numerous studies screening mosquitoes for filarioid helminths (xenomonitoring) have been performed in Europe. The entomological monitoring of filarial nematode infections in mosquitoes by molecular xenomonitoring might serve as the measure of the rate at which humans and animals expose mosquitoes to microfilariae and the rate at which animals and humans are exposed to the bites of the infected mosquitoes. We hypothesized that combining the data obtained from molecular xenomonitoring and phenological studies of mosquitoes in the urban environment would provide insights into the transmission risk of filarial diseases. In our search for Dirofilaria spp.-infected mosquitoes, we have found Setaria tundra-infected ones instead, as in many other European studies. We have observed that cross-reactivity in PCR assays for Dirofilaria repens, Dirofilaria immitis, and S. tundra COI gene detection was the rule rather than the exception. S. tundra infections were mainly found in Aedes mosquitoes. The differences in the diurnal rhythm of Aedes and Culex mosquitoes did not seem a likely explanation for the lack of S. tundra infections in Culex mosquitoes. The similarity of S. tundra COI gene sequences found in Aedes vexans and Aedes caspius mosquitoes and in roe deer in many European studies, supported by data on Ae. vexans biology, suggested host preference as the most likely cause of the mosquito genus-biased infections. High diversity of the COI gene sequences isolated in the city of Wroclaw in south western Poland and the presence of identical or almost identical sequences in mosquitoes and roe deer across Europe suggests that S. tundra has been established in most of Europe for a very long time.

Clinical validation of molecular markers of macrocyclic lactone resistance in Dirofilaria immitis

Prophylaxis with macrocyclic lactone (ML) endectocides is the primary strategy for heartworm control. Recent evidence has confirmed that ML-resistant Dirofilaria immitis isolates have evolved. Comparison of genomes of ML-resistant isolates show they are genetically distinct from wild-type populations. Previously, we identified single nucleotide polymorphisms (SNPs) that are correlated with phenotypic ML resistance. Since reliable in vitro assays are not available to detect ML resistance in L3 or microfilarial stages, the failure to reduce microfilaraemia in infected dogs treated with an ML has been proposed as a surrogate clinical assay for this purpose. The goal of our study was to validate the genotype-phenotype correlation between SNPs associated with ML resistance and failure to reduce microfilaraemia following ML treatment and to identify a minimal number of SNPs that could be used to confirm ML resistance. In this study, 29 participating veterinary clinics received a total of 148 kits containing supplies for blood collection, dosing and prepaid shipping. Patients recruited after a diagnosis of heartworm infection were treated with a single standard dose of Advantage Multi® and a blood sample taken pre- and approximately 2-4 weeks post-treatment. Each sample was processed by performing a modified Knott's Test followed by isolation of microfilariae, genomic DNA extraction and MiSeq sequencing of regions encompassing 10 SNP sites highly correlated with ML resistance. We observed significant correlation of SNP loci frequencies with the ML microfilaricidal response phenotype. Although all predictive SNP combination models performed well, a 2-SNP model was superior to other models tested. The predictive ability of these markers for ML-resistant heartworms should be further evaluated in clinical and epidemiological contexts.

Urbanization impact on mosquito community and the transmission potential of filarial infection in central Europe

BACKGROUND

Despite long-term research on dirofilariosis in Slovakia, little attention has thus far been paid to Dirofilaria vectors. The particular aim of the present study was molecular screening for filarioid parasites in two different habitats of Bratislava, the capital city of Slovakia. In addition, the effect of urbanisation on mosquito species abundance and composition, associated with the risk of mosquito-borne infections, was studied and discussed.

METHODS

Mosquitoes were identified by morphological features, and molecular methods were also used for determination of selected individuals belonging to cryptic species from the Anopheles maculipennis and Culex pipiens complexes. The presence of filarioid DNA (Dirofilaria repens, Dirofilaria immitis and Setaria spp.) was detected using standard PCR approaches and sequencing.

RESULTS

A total of 6957 female mosquitoes were collected for the study. Overall, the most abundant mosquito species was Aedes vexans, closely followed by unidentified members of the Cx. pipiens complex and the less numerous but still plentiful Ochlerotatus sticticus species. Further investigation of mosquito material revealed 4.26% relative prevalence of Dirofilaria spp., whereby both species, D. repens and D. immitis, were identified. The majority of positive mosquito pools had their origin in a floodplain area on the outskirts of the city, with a relative prevalence of 5.32%; only two mosquito pools (1.26%) were shown to be positive in the residential zone of Bratislava. Setaria spp. DNA was not detected in mosquitoes within this study.

CONCLUSIONS

The study presented herein represents initial research focused on molecular mosquito screening for filarioid parasites in urban and urban-fringe habitats of Bratislava, Slovakia. Molecular analyses within the Cx. pipiens complex identified two biotypes: Cx. pipiens biotype pipiens and Cx. pipiens biotype molestus. To our knowledge, Dirofilaria spp. were detected for the first time in Slovakia in mosquitoes other than Ae. vexans, i.e. D. repens in Anopheles messeae and unidentified members of An. maculipennis and Cx. pipiens complexes, and D. immitis in Coquillettidia richiardii and Cx. pipiens biotype pipiens. Both dirofilarial species were found in Och. sticticus. The suitable conditions for the vectors' biology would represent the main risk factor for dirofilariosis transmission.

G-protein-coupled receptor genes of Dirofilaria immitis

The diversity and uniqueness of nematode heterotrimeric G-protein-coupled receptors (GPCRs) provides impetus for identifying ligands that can be used as therapeutics for treating diseases caused by parasitic nematode infections. In human medicine, GPCRs have represented the largest group of 'drugable' targets exploited in the market today. In the filarial nematode Dirofilaria immitis, which causes heartworm disease, the macrocyclic lactones (ML) have been used as the sole preventatives for more than 25 years and now there is confirmed ML resistance in this parasite. A novel anthelmintic emodepside, with antifilarial activity, can act on a GPCR. In view of the ML resistance, there is an urgent need to identify new drug targets and GPCRs of D. immitis may be promising receptors. Knowledge of polymorphism within the GPCR superfamily is of interest. A total of 127 GPCR genes have been identified, so far, in the genome of D. immitis. Whole genome sequencing data from four ML susceptible and four ML loss of efficacy populations was used to identify 393 polymorphic loci in 35 D. immitis GPCR genes. Out of 57 SNPs in exonic regions, 36 of them caused a change in an amino acid, out of which 2 changed the predicted secondary structure of the protein. Knowledge about GPCR genes and their polymorphism is valuable information for drug design processes. Further studies need to be carried out to more fully understand the implications of each of the SNPs identified by this study.

Can P-glycoprotein and β-tubulin polymorphisms be used as genetic markers of resistance in Dirofilaria immitis from Rio de Janeiro, Brazil?

OBJECTIVE

Dirofilaria immitis, the causative agent of canine heartworm infection, is worldwide the most important filarid to affect domestic dogs. Prevention of this infection is done by macrocyclic lactones, but some reports on the lack of efficacy have been published. Although the actual cause of resistance is unknown, single nucleotide polymorphisms (SNPs) on a P-glycoprotein ABC transporter and β-tubulin genes have been pointed out as candidates for genetic markers of resistance. We conducted a survey to verify the presence of these suggested genetic markers in microfilariae from 30 naturally infected dogs under macrocyclic lactones treatment living in an endemic area in the state of Rio de Janeiro.

RESULTS

The analysis of these specific SNPs demonstrated no sign of polymorphism on the P-glycoprotein loci, while 72 and 48% of the samples were polymorphic to the first and second SNPs on β-tubulin loci, respectively. This work demonstrates that the P-glycoprotein position 11 and 618 were not polymorphic and, therefore, not suitable as a genetic marker of resistance in Rio de Janeiro whereas both β-tubulin loci were polimorphic. This work points out the difficulty of finding a universal genetic marker for resistance.

Assessment of MALDI-TOF mass spectrometry for filariae detection in Aedes aegypti mosquitoes

Matrix Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) is an emerging tool for routine identification of bacteria, archaea and fungi. It has also been recently applied as an accurate approach for arthropod identification. Preliminary studies have shown that the MALDI-TOF MS was able to differentiate whether ticks and mosquitoes were infected or not with some bacteria and Plasmodium parasites, respectively. The aim of the present study was to test the efficiency of MALDI-TOF MS tool in distinguishing protein profiles between uninfected mosquitoes from specimens infected by filarioid helminths. Aedes aegypti mosquitoes were engorged on microfilaremic blood infected with Dirofilaria immitis, Brugia malayi or Brugia pahangi. Fifteen days post-infective blood feeding, a total of 534 mosquitoes were killed by freezing. To assess mass spectra (MS) profile changes following filariae infections, one compartment (legs, thorax, head or thorax and head) per mosquito was submitted for MALDI-TOF MS analysis; the remaining body parts were used to establish filariae infectious status by real-time qPCR. A database of reference MS, based on the mass profiles of at least two individual mosquitoes per compartment, was created. Subsequently, the remaining compartment spectra (N = 350) from Ae. aegypti infected or not infected by filariae were blind tested against the spectral database. In total, 37 discriminating peak masses ranging from 2062 to 14869 daltons were identified, of which 17, 11, 12 and 7 peak masses were for legs, thorax, thorax-head and head respectively. Two peak masses (4073 and 8847 Da) were specific to spectra from Ae. aegypti infected with filariae, regardless of nematode species or mosquito compartment. The thorax-head part provided better classification with a specificity of 94.1% and sensitivity of 86.6, 71.4 and 68.7% of D. immitis, B. malayi and B. pahangi respectively. This study presents the potential of MALDI-TOF MS as a reliable tool for differentiating non-infected and filariae-infected Ae. aegypti mosquitoes. Considering that the results might vary in other mosquito species, further studies are needed to consolidate the obtained preliminary results before applying this tool in entomological surveillance as a fast mass screening method of filariosis vectors in endemic areas.

Filariosis is a disease group affecting humans and animals, caused by nematode parasites of the family Onchocercidae, superfamily Filarioidea. These parasites can be transmitted, essentially, by mosquitoes during blood meals of infected female specimens. Screening vectors for these filariae currently relies on time- and resource-consuming methods such as dissection and polymerase chain reaction-based methods. Here, we applied matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to assess whether this tool can detect changes in the protein profiles of Aedes aegypti infected with filarioid helminths compared to those uninfected by testing different parts of mosquitoes. First a reference mass spectra database from Ae. aegypti infected or not infected by filariae was created using MS from 47 specimen compartments. Then we tested the remaining mass spectra (350 x 4) in a blind validation test. Regardless of filariae species, the best correct classification rate was obtained from the thorax-head part with a specificity of 94.1% and sensitivity of 86.6, 71.4 and 68.7% for non-infected and D. immitis, B. malayi and B. pahangi infected mosquitoes respectively. The results indicated that MALDI-TOF MS is potentially able to screen Aedes aegypti mosquitoes as being non-infected or filariae-infected. Furthermore, complementary works using other mosquito species infected with different filarioids are needed to reinforce these preliminary results prior to apply this tool on field samples.

[(HUMAN DIROFILARIASIS: CLINICAL DIAGNOSTIC FEATURES ASSOCIATED WITH DIFFERENT DEVELOPMENTAL STAGES OF THE PATHOGEN)]

To seek medical advice is due to the time when a person has become infected during the infection transmission season (July-August) and the duration of development of the pathogen Dirofilaria (N.) repens in his/her body Clinical manifes- tations occurred in 61% of the patients 6-10 months after infection, as confirmed by the maximum body sizes (125-160 mm) of removed females which have reached puberty. PCR-based diagnosis in conjunction with microscopic studies improves the efficiency of identifying the patients and the species of the pathogens D.repens and D.immitis. The use of these methods for the first time in 2016 could confirm D.immitis infestation in a 14-month-old infant living in the Solnechnogorsk District, Moscow Region.

Comparative Studies on Nucleic Acid Based Biosensors for Identification of Filarial Nematode

BACKGROUND

The microfilarial nematodes, found mainly in blood circulation, form a special group of human and veterinary parasitic diseases. Recently, the rapid nucleic acid based biosensors (NABs) have been established in our laboratory for the employment of a point-of-care diagnostic test. Herein, NABs involved in the exploitation of lateral flow dipstick (LFD), gold nanoparticle (AuNP) and turbidity in combination with PCR and LAMP amplification for detection of filarial nematodes. The validation of each NABs was investigated in comparison to that of standard detection methods using the same unknown blood specimens.

OBJECTIVE

To compare the sensitivity, specificity and accuracy of NABs with standard detection methods.

MATERIAL AND METHOD

In this study, the microfilariae of Dirofilaria immitis was used as the representative model for filarial nematode. The PCR and LAMP primers were designed and synthesized according to the specific nucleotide regions of a small subunit gene of the parasite as well as the DNA probes. The fifty unknown blood samples were sent as a gift from Prasu Arthorn Animal Hospital, Faculty of Veterinary Science, Mahidol University. The samples were tested by using PCR, PCRLFD, PCR-AuNP, LAMP, LAMP-LFD, LAMP-AuNP, LAMP-turbidity and film blood smear. The efficacy of NABs was compared to a standard film blood smear in terms of sensitivity, specificity and accuracy.

RESULTS

Upon detection of fifty unknown blood samples, LAMP-LFD assay presented 100% of sensitivity, specificity and accuracy. The data revealed that sensitivity, specificity and accuracy of NABs varied from 66.67-100.00% when compared to a film blood smear stained with Giemsa dye. The data clearly indicated that LAMP-LFD was a preferred choice for the use as a point-of-care NABs.

CONCLUSION

NABs were highly sensitive performing as a selective diagnostic tool that could be applied particularly as the rapid screening tests for filarial nematodes hence as a recommended epidemiological survey.

Detection of Dirofilaria repens and Dirofilaria immitis DNA in mosquitoes from Belarus

During the last two decades, Belarus faces an increase of human cases of Dirofilaria (Nematoda, Spirurida, Onchocercidae) infections. However, comprehensive analyses explaining this development and the identification of mosquito vector species are missing. Here, we present results using temperature data from Belarus and show that the annual number of human Dirofilaria cases is significantly correlated with the yearly average temperatures (Spearman's rho = 0.49, p < 0.05) and the average sum of potential Dirofilaria transmission days (Spearman's rho = 0.46, p < 0.05), suggesting that autochthonous transmission is at least in part responsible for the increasing number of clinical Dirofilaria cases in the country. In addition, 467 female mosquitoes were collected from different sampling sites in the regions of Brest and Minsk, which were analyzed by molecular methods for the presence of Dirofilaria repens and Dirofilaria immitis DNA, respectively. Two pools (5.56 %) were tested positive for Dirofilaria (estimated infection rate per 100 specimens = 0.44, 95 % confidence interval = 0.08-1.43), comprising one Anopheles claviger s.l. pool that was positive for D. repens and one Culex pipiens s.l./Culex torrentium pool positive for D. immitis DNA. This, to our knowledge, is the first molecular evidence for the presence of Dirofilaria in mosquitoes from Belarus, suggesting a high probability of autochthonous Dirofilaria transmission in the country.

[INFECTION OF BLOOD-SUCKING MOSQUITOES (DIPTERA: CULICIDAE) WITH DIROFILARIAE (SPIRURIDA, ONCHOCERCIDAE) IN THE TULA REGION]

Blood-sucking mosquitoes (n = 2277) collected in Tula and its Region in 2013-2014 were examined using a PCR assay for dirofilariae. A total of 12 species from 4 genera (Culiseta, Aedes, Ochlerotatus [foreign character] Culex) out of 18 found mosquito species were infected with Dirofilaria immitis and D. repens. The proportion of the infected mosquitoes was 2.5% (D. immitis, 1.5%; D.repens, 1%). According to preliminary data, the most efficient Dirofilaria vectors, in the Tula Region may be Ae. vexans, Ae. geniculatus, Och. cantans, and Cx. pipiens.

Morphological and molecular identification of Dirofilaria immitis from Jackal (Canis aureus) in North Khorasan, northeast Iran

BACKGROUND & OBJECTIVES

The heartworm Dirofilaria immitis is an important mosquito-borne zoonotic nematode of domestic and wild mammals throughout the world, causing cardiopulmonary dirofilariasis. This parasite has been reported from carnivores in some provinces of Iran. However, in the present study, the occurrence of this filarial nematode is reported for the first time in wild canids of the North Khorasan Province, located in northeast Iran, based on morphological and molecular characteristics.

METHODS

The carcasses of 45 golden jackals (Canis aureus), 16 foxes (Vulpes vulpes), 15 dogs (Canis familiaris), and one wolf (Canis lupus) were necropsied between 2013 and 2014.

RESULTS

By gross examination, adult filarial nematodes were found in the cardiovascular system of four jackals (8.9%). The morphological characteristics of the recovered heartworms were compatible with D. immitis. DNA sequencing of the cytochrome c oxidase subunit I (cox1) gene of all four isolates was identical, showing 100% homology with several sequences registered in GenBank from other countries. No adult D. immitis was found in any of the other animals examined.

INTERPRETATION & CONCLUSION

D. immitis is circulating in wildlife of the study area, suggesting the relevance of developing control programmes to prevent transmission of the disease to humans and domestic animals.

[Human dirofilariasis: clinical and diagnostic signs and diagnostic methods]

The clinical and diagnostic signs caused by the tissue location and migration of adult Dirofilaria in the human body determine the use of different methods for the diagnosis of dirofilariasis. During their investigations, the authors modified polymerase chain reaction (PCR): they chose and synthesized primers and selected amplification regimens for them and obtained agarose gel bands that corresponded to PCR fragment length nucleotide sequences that were equal to 245 bp for D. (N.) repens and 656 bp for D. immitis. There was 100% agreement in the results of PCR and microscopic examination of sera from 32 dogs and 1 female patient with low parasitemia and in the blood nucleotide sequence characteristic of D. repens.

New insights onto cardiopulmonary nematodes of dogs in Sardinia, Italy

Dog heartworms Angiostrongylus vasorum and Dirofilaria immitis cause severe parasitological diseases; the importance of these parasitosis is growing due to their health impact on animals, the possible zoonotic implications and the recent spreading across several European countries and previously non-endemic areas. The aim of this study is to update the epidemiological scenario of cardiopulmonary nematodes A. vasorum and D. immitis in dogs of Sardinia island and to perform a morphological identification of larvae by the use of the Baermann and Knott techniques respectively and the molecular characterization of the mitochondrial cytochrome c oxidase subunit I (cox1) and the second ribosomal transcribed spacer region (ITS-2) of larvae L1 of A. vasorum. In the present study, 3.4% (5/146) of dogs resulted positive at Baermann technique for A. vasorum while 8.9% (61/684) to D. immitis. If on one side A. vasorum can be considered an emerging parasite in Sardinia, the parasitic pressure and the risk of infection for D. immitis in the island seems to be increased compared with the recent past.

Rapid detection and identification of Wuchereria bancrofti, Brugia malayi, B. pahangi, and Dirofilaria immitis in mosquito vectors and blood samples by high resolution melting real-time PCR

A simple, rapid, and high-throughput method for detection and identification of Wuchereria bancrofti, Brugia malayi, Brugia pahangi, and Dirofilaria immitis in mosquito vectors and blood samples was developed using a real-time PCR combined with high-resolution melting (HRM) analysis. Amplicons of the 4 filarial species were generated from 5S rRNA and spliced leader sequences by the real-time PCR and their melting temperatures were determined by the HRM method. Melting of amplicons from W. bancrofti, B. malayi, D. immitis, and B. pahangi peaked at 81.5±0.2℃, 79.0±0.3℃, 76.8±0.1℃, and 79.9±0.1℃, respectively. This assay is relatively cheap since it does not require synthesis of hybridization probes. Its sensitivity and specificity were 100%. It is a rapid and technically simple approach, and an important tool for population surveys as well as molecular xenomonitoring of parasites in vectors.

[Cloning and prokaryotic expression of casein kinase II subunit beta gene fragment of Dirofilaria immitis]

OBJECTIVE

To clone and express the partial fragment of Csnk2b gene of Dirofilaria immitis in prokaryotic cells, and analyze the immunoreactivity.

METHODS

The partial fragment of Csnk2b gene was amplified by PCR with a pair of specific primers. The PCR product was cloned into pMD18-T, and then sub-cloned to pGEX-4T-1 expression vector. The constructed plasmid pGEX-4T-1-Csnk2b was transformed into E. coli Rosetta (DE3) and followed by expression of the protein induced by IPTG. The recombinant protein was analyzed by SDS-PAGE and identified by Western blotting.

RESULTS

The PCR product was about 700 bp. Enzyme digestion and DNA sequencing confirmed that the recombinant plasmid pGEX-4T-1-Csnk2b was constructed. SDS-PAGE results showed that the relative molecular weight (M(r)) of the fusion protein (GST-Csnk2b) was about 45 000. GST-Csnk2b reacted positively with mouse anti-D. immitis serum.

CONCLUSION

The partial Csnk2b gene has been expressed in prokaryotic expression system and shows immunoreactivity.

Prevalence of Dirofilaria immitis (Nematoda: Filarioidea) in mosquitoes from northeast Arkansas, the United States

A mosquito survey was conducted to identify which species of mosquitoes carry Dirofilaria immitis (Leidy) (Nematoda: Filarioidea), dog heartworm, in northeast Arkansas. Using polymerase chain reaction, mosquitoes were analyzed for D. immitis, Dirofilaria repens Railliet & Henry, and Acanthocheilonema dracunculoides Cobbold. Mosquitoes were collected from April to October 2009 using black light ultraviolet traps baited with dry ice. Sixteen mosquito species were identified. D. immitis was identified in nine mosquito species, which included Aedes vexans (Meigen), Anopheles quadrimaculatus Say, Anopheles punctipennis (Say), Culex pipiens quinquefasciatus Say, Culex erraticus (Dyer & Knab), Culiseta inornata (Williston), Psorophora columbiae (Dyer & Knab), Psorophora ferox (Humboldt), and Psorophora howardii Coquillett. No D. repens or A. dracunculoides DNA was amplified. Of the 1,212 mosquito pools tested, 7.3% were positive for D. immitis. Frequency of D. immitis infections from six collection sites ranged from 2.1 to 19.4%. Ae. vexans and An. quadrimaculatus were the two most abundant species, composing 58.7 and 23.7% of the total mosquitoes collected, with 9.6 and 6.9% of pools positive for D. immitis, respectively. To investigate localized vector infection rates of D. immitis, mosquitoes were collected from inside the kennel of a heartworm-positive dog. Of the 114 mosquitoes collected, 84 (73.7%) were positive for D. immitis. The frequency of D. immitis-infected mosquitoes collected near a heartworm-positive dog was considerably higher than in the original six collection sites, suggesting a single heartworm-positive dog potentially increases infection pressure on susceptible animals sharing mosquito exposure.

Novel insights into the transcriptome of Dirofilaria immitis

Background

The heartworm Dirofilaria immitis is the causal agent of cardiopulmonary dirofilariosis in dogs and cats, and also infects a wide range of wild mammals as well as humans. One bottleneck for the design of fundamentally new intervention and management strategies against D. immitis may be the currently limited knowledge of fundamental molecular aspects of D. immitis.

Methodology/Principal Findings

A next-generation sequencing platform combining computational approaches was employed to assess a global view of the heartworm transcriptome. A total of 20,810 unigenes (mean length  = 1,270 bp) were assembled from 22.3 million clean reads. From these, 15,698 coding sequences (CDS) were inferred, and about 85% of the unigenes had orthologs/homologs in public databases. Comparative transcriptomic study uncovered 4,157 filarial-specific genes as well as 3,795 genes potentially involved in filarial-Wolbachia symbiosis. In addition, the potential intestine transcriptome of D. immitis (1,101 genes) was mined for the first time, which might help to discover ‘hidden antigens’.

Conclusions/Significance

This study provides novel insights into the transcriptome of D. immitis and sheds light on its molecular processes and survival mechanisms. Furthermore, it provides a platform to discover new vaccine candidates and potential targets for new drugs against dirofilariosis.

[The molecular diagnosis of Dirofilaria immitis in vector mosquitoes in Felahiye district of Kayseri]

This study was designed to determine the potential vectors of Dirofilaria immitis by molecular techniques in Felahiye district of Kayseri. Mosquitoes were sampled from 11 points between June-August 2008 and collected live samples were brought to laboratory. In order to allow the larval development, mosquitoes were incubated in in vitro conditions for seven days. After this mosquitoes were killed and species identifications were done. Among the totally collected 301 mosquitoes, 96 (31.9%) were belonging to Aedes vexans and 205 (68.1%) to Culex pipiens. Head-thorax and abdomens of each sample were dissected to determine the infective and infected mosquitoes and totally 54 pools (2-17 sample/pool) were constituted according to species and collected region. Genomic DNA was extracted from pools and analyzed by PCR using species specific primers. Dirofilaria immitis DNA was found in 2/54 of the pools formed with one head-thorax and one abdomen pool of Ae. vexans. The minimum infection rate (MIRs) was calculated as 0.33 % in the study area. MIRs of 20 pools consisted from Ae. vexans was determined as 1.04 %. No filarial DNA was detected in 34 pools consisted from Cx. pipiens. Consequently, Ae. vexans was the active potential vector of D. immitis in the study area.

Identification and analysis of genes expressed in the adult filarial parasitic nematode Dirofilaria immitis

The heartworm Dirofilaria immitis is a filarial parasitic nematode infecting dogs and other mammals worldwide causing fatal complications. Here, we present the first large-scale survey of the adult heartworm transcriptome by generation and analysis of 4005 expressed sequence tags, identifying about 1800 genes and expanding the available sequence information for the parasite significantly. Brugia malayi genomic data offered the most valuable information to interpret heartworm genes, with about 70% of D. immitis genes showing significant similarities to the assembly. Comparative genomic analyses revealed both genes common to metazoans or nematodes and genes specific to filarial parasites that may relate to parasitism. Characterization of abundant transcripts suggested important roles for genes involved in energy generation and antioxidant defense in adults. In particular, we proposed that adult heartworm likely adopted an anaerobic electron transfer-based energy generation system distinct from the aerobic pathway utilized by its mammalian host, making it a promising target in developing next generation macrofilaricides and other treatments. Our survey provided novel insights into the D. immitis transcriptome and laid a foundation for further comparative studies on biology, parasitism and evolution within the phylum Nematoda.

Natural infection of Culex theileri (Diptera: Culicidae) with Dirofilaria immitis (Nematoda: Filarioidea) on Madeira Island, Portugal

Field and laboratory studies were performed to verify whether Culex theileri Theobald functions as a natural vector of Dirofilaria immitis (Leidy) on Madeira Island, Portugal. CO2-baited light traps (EVS traps) were use to sample mosquitoes monthly basis between February 2002 and February 2003 in the area of Quebradas (Funchal). Three mosquito species were captured, including 58 Culex pipiens L., 790 Cx. theileri, and three Culiseta longiareolata (Macquart). Only C. theileri tested positive for D. immitis. The presence of this filarial worm was detected by direct observation, infectivity assay dissection technique, and polymerase chain reaction methods. Infected mosquitoes were recovered in October and December 2002 and January 2003. These data provide evidence that Cx. theileri could be the main vector of D. immitis in Funchal, Madeira.

The First Record of Dirofilaria immitis Infection in a Humboldt Penguin, Spheniscus humboldti

Dirofilaria immitis infection is an important parastic disease in many mammals, especially canids, but has not been reported in bird hosts. Filarial worms were isolated from the lumen of the right atrium of the heart and the connective tissue of the lung of a captive female Humboldt penguin, Spheniscus humboldti, that died at a zoo in Japan. One of these worms was observed morphologically and identified as D. immitis by features such as 4 pairs of cephalic papillae, 1 pair of cervical papillae, esophagus divided into 2 regions, 4 pairs of pre-anal papillae, 5 pairs of post-anal papillae, and unequal spicules. In addition, the partial DNA sequence (234 bp) of mitochondrial CO / gene of the filarial worm was identical to that of D. immitis. This is the first report of D. immitis infection in a bird.

Serological and molecular survey of Dirofilaria immitis infection in stray cats in Gyunggi province, South Korea

The aim of this study was to carry out a serological and molecular survey for the presence of Dirofilaria immitis infection in stray cats using an ELISA kit and PCR assay. One hundred and fifty-five stray cats (77 females and 78 males) in Gyunggi province in South Korea, were used in this study. Four (2.6%) tested with the ELISA kit showed a positive reaction, and all positive samples by the ELISA kit showed a positive reaction by PCR analysis. No significant difference was observed between the male (2.6%) and female (2.6%) cat groups by ELISA kit. The positive rates for dirofilariosis were 2.8% in the 4-6-year-old group, and 18.2% in the > 6-year-old group by ELISA kit. With regard to the age element, older cats showed a higher prevalence of D. immitis infection in this study. A statistical analysis revealed that significant difference was observed in > 6-year-old group (p < 0.01). In conclusion, D. immitis infection in stray cats was present in Gyunggi province, although its incidence was low. Therefore, heartworm treatment and/or prophylaxis for stray cats captured are required in this area.

Dirofilaria immitis: identification of a novel ligand-gated ion channel-related polypeptide

We have isolated a cDNA from Dirofilaria immitis that encodes a predicted ion channel subunit, Di-LGR-1. Secondary structure predictions and database searches reveal that Di-LGR-1 is distantly related to ligand-gated anion channels, such as the GABA(A) receptors, though there are marked differences in the sequences of the putative channel forming regions. Di-LGR-1 has 52% sequence identity to the Caenorhabditis elegans predicted polypeptide, T27A1.4: neighbour-joining trees show that these two polypeptides are the most divergent members of the nematode ligand-gated anion channel family. No close homologues are present in vertebrates, suggesting that their function may be specific to nematodes. RNAi experiments using a fragment of T27A1.4 with C. elegans failed to reveal any obvious phenotype, so the function of these channels remains unknown.

An ivermectin-sensitive glutamate-gated chloride channel subunit from Dirofilaria immitis

Dirofilaria immitis is a filarial nematode that infects dogs and causes cardiopulmonary disease. The most effective way of controlling the infection is by chemoprophylaxis, using members of the avermectin/milbemycin (A/M) class of anthelmintics, which includes ivermectin; these drugs act at invertebrate glutamate-gated chloride channels (GluCl). We have cloned two cDNAs encoding D. immitis GluCl subunits and demonstrated that at least one may be an important molecular target for the A/Ms in vivo. The subunits are orthologues of the alternatively spliced GluClalpha3A and alpha3B subunits (encoded by the avr-14 gene) previously identified in Caenorhabditis elegans and in Haemonchus contortus. Although the alternative splicing of avr-14 is conserved across the species, the processing of the mature GluClalpha3A mRNA differs in D. immitis compared to C. elegans and H. contortus. Two-electrode voltage clamp recordings were made from Xenopus oocytes injected with subunit-specific cRNAs. The DiGluClalpha3B subunit formed channels that were gated by L-glutamate (1-100 mM) and ivermectin (1 microM). Oocytes injected with DiGluClalpha3A cRNA failed to respond to L-glutamate. The qualitative responses obtained were consistent with the pharmacology observed for the GluClalpha3 subunits from C. elegans and H. contortus.