Molecular survey of Dirofilaria immitis and Dirofilaria repens by direct PCR for wild caught mosquitoes in the Republic of Korea

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.

The new invasive mosquito species Aedes koreicus as vector-borne diseases in the European area, a focus on Italian region: What we know from the scientific literature

The increased mobility of goods, people, and animals worldwide has caused the spread of several arthropod vectors, leading to an increased risk of animal and human infections. Aedes koreicus is a common species in South Korea, China, Japan, and Russia. Due to its cold-resistant dormant eggs, the adults last from the late summer until the autumn seasons. For these reasons, it seems to be better adapted to colder temperatures, favoring its colonization of hilly and pre-alpine areas. Its first appearance in Europe was in 2008 in Belgium, where it is currently established. The species was subsequently detected in Italy in 2011, European Russia, Germany, the Swiss–Italian border region, Hungary, Slovenia, Crimea, Austria, the Republic of Kazakhstan, and the Netherlands. The role of A. koreicus in the transmission of vector-borne pathogens remains unclear. The available scientific evidence is very old, often not available in English or not indexed in international databases, and therefore difficult to find. According to the literature reviewed, A. koreicus can be considered a new invasive mosquito species in Europe, establishing populations on the European continent. In addition, experimental evidence demonstrated its vector competence for both Dirofilaria immitis and Chikungunya and is relatively low for ZIKA but not for Western Nile Virus. On the other hand, even if the field evidence does not confirm the experimental findings, it is currently not possible to exclude with absolute certainty the potential involvement of this species in the spread, emergence, or re-emergence of these vector-borne disease agents.

Emergence of Dirofilaria repens (Spirurida: Onchocercidae) in dogs in Eastern Thailand

Background and Aim:

Dirofilaria repens is a zoonotic vector-borne parasite of dogs and cats. It is not commonly found in every part of Thailand, except the southern part. This study was conducted to investigate the prevalence of this parasite in Eastern Thailand in 2019.

Materials and Methods:

A total of 8003 blood samples were collected from private veterinary clinics and animal hospitals in Eastern Thailand. Blood parasites were examined using buffy coat thin blood smears with Wright-Giemsa staining. D. repens was morphologically identified and confirmed using the acid phosphatase activity technique.

Results:

The first case of D. repens was found in March 2019. The prevalence of D. repens from January to December 2019 was 0.44% (35/8003) (95% confidence interval 0.30-0.61).

Conclusion:

The prevalence data of D. repens in Eastern Thailand indicate that this parasitic infection should be considered as a zoonotic vector-borne disease. A strategic plan to control zoonotic transmission alongside a preventive program should be emphasized and encouraged among pet owners and veterinarians.

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.

Co-infection of Dirofilaria immitis and Japanese encephalitis virus in a spotted seal (Phoca largha) in the Republic of Korea

A 10-year-old male spotted seal presented with loss of appetite and decreased activity. Grossly, the internal organs revealed several filarial nematodes in the right ventricle of the heart and the pulmonary vessels. Histopathological examination of the brain revealed moderate nonsuppurative meningoencephalitis with glial nodules and neuronophagia. Japanese encephalitis virus (JEV) of genotype I was isolated from the brain. All nematodes were identified as Dirofilaria immitis. This is the first clinical case of co-infection with D. immitis and JEV in a seal, suggesting that the seal, may be a dead-end host, like the human and horse, for JEV.

Metagenomic Analysis Reveals Three Novel and Prevalent Mosquito Viruses from a Single Pool of Aedes vexans nipponii Collected in the Republic of Korea

Arboviruses continue to be a significant global health concern. The unbiased metagenomic analyses of mosquito-borne and mosquito-specific viruses are useful to understand viral diversity and for the surveillance of pathogens of medical and veterinary importance. Metagenomic analysis was conducted on 6368 mosquitoes (736 pools), covering 16 species from 18 locations throughout the Republic of Korea (ROK) in 2016. In this report, we describe three viruses detected in a single pool of Aedes vexans nipponii collected at Yongsan U.S. Army Garrison, located in a densely populated district of Seoul, the ROK. The three novel viruses, designated as Yongsan bunyavirus 1 (YBV1), Yongsan picorna-like virus 3 (YPLV3) and Yongsan sobemo-like virus 1 (YSLV1), share sequence and structural characteristics with members belonging to the family Bunyaviridae, order Picornavirales, and family Solemoviridae, with shared RNA-dependent RNA polymerase (RdRp) amino acid identities of 40%, 42% and 86%, respectively. The real-time reverse transcription and polymerase chain reaction (RT-PCR) of 3493 Aedes vexans nipponii (257 pools) showed a high prevalence of YBV1 and YSLV1 viruses, which were present in 65% and 62% of tested pools, respectively. This study highlighted the utility of a metagenomic sequencing approach for arbovirus discovery and for a better understanding of the virome of potential medically relevant vectors.

High genetic diversity in the Dirofilaria repens species complex revealed by mitochondrial genomes of feline microfilaria samples from Narathiwat, Thailand

Dirofilaria repens is a zoonotic, mosquito-borne filaria infecting carnivores, particularly dogs. It is expanding its range in Europe but epidemiological information is sparse for other Eurasian regions. In Hong Kong and India, the closely related species Candidatus Dirofilaria hongkongensis was proposed. Previous analysis of 2.5 kb partial mitochondrial genome sequences containing the particularly variable non-coding control region revealed low diversity in European D. repens while Asian nematodes showed high diversity. Sequences derived from feline blood samples from Narathiwat (Thailand) led to the proposal of a third potential species, Dirofilaria sp. "Thailand II". To avoid bias from rapidly evolving non-coding regions, this study aimed to compare Dirofilaria sp. "Thailand II" with D. repens and C. D. hongkongensis based on complete mitochondrial genomes. Using PCRs and Sanger sequencing, three complete mitochondrial genomes (13,651 bp) were assembled from DNA obtained from different feline blood samples. Mitochondrial genome organization was identical to other onchocercids with eleven protein-coding, two rRNA and 22 tRNA genes and no atp-8 gene. All genes were on the same strand showing an extremely high thymidine content (56.7%). Maximum-likelihood phylogenetic analysis using protein and rRNA sequences confirmed closer relationship of Dirofilaria sp. "Thailand II" to C. D. hongkongensis than to D. repens. All distances between these three putative species were considerably larger than the distance between the valid sibling species Onchocerca volvulus and Onchocerca ochengi. Sequencing of a 2.5 kb fragment containing the control region from microfilarial DNA from additional feline blood samples from Narathiwat 3-4 years later revealed that these also fell into the C. D. hongkongensis clade but were remarkably different from C. D. hongkongensis and Dirofilaria sp. "Thailand II". Since D. repens-like filaria are absent from dogs in Narathiwat, further field studies are required to confirm if these genotypes represent locally circulating cat-specific Dirofilaria genotypes or species.

Molecular characterization of human Dirofilaria isolates from Kerala

Background & objectives:

Human dirofilariosis is a well-recognized zoonosis caused by several species of the genus Dirofilaria. The disease is prevalent among canines and human beings in Kerala. The objective of the present study was to confirm the human Dirofilaria isolates by molecular characterization.

Methods:

The worms or segments obtained from human sources were subjected to diagnostic polymerase chain reaction (PCR) targeting the cytochrome oxidase subunit 1 (COI) and 5S ribosomal RNA (rRNA) genes of Dirofilaria repens. The amplicons were sequenced and analyzed.

Results:

The filariid nematodes recovered from ocular as well as subcutaneous tissue of human origin were identified as D. repens based on PCR targeting COI as well as 5S rRNA genes. The phylogenetic analysis of the COI gene nucleotide sequence obtained in the present study showed that D. repens shared the closest evolutionary relationship with D. honkongensis.

Interpretation & conclusions:

Molecular identification of D. repens isolated from human source assumes significance from the point of zoonotic threat of this mosquito-borne nematode. Phylogenetic analysis revealed a close evolutionary relationship with Asian isolate of D. honkongensis. Timely detection and treatment of infection in dogs, together with mosquito control, should be an integral part of the control strategy of this disease.

Population dynamics of Armigeres subalbatus (Diptera: Culicidae) across a temperate altitudinal gradient

Understanding the impacts of weather fluctuations, and environmental gradients, on the abundance of vectors is fundamental to grasp the dynamic nature of the entomological risk for disease transmission. The mosquito Armigeres subalbatus (Coquillet) is a common vector of filariasis. Nevertheless, its population dynamics have been relatively poorly studied. Here, we present results from a season long study where we studied spatio-temporal abundance patterns of Ar. subalbatus across the altitudinal gradient of Mt. Konpira in Nagasaki, Japan. Spatially, we found that abundance of adult Ar. subalbatus decreased with altitude and increased in areas where the ground was rich in leaf litter. Similarly, adult activity was observed only when relative humidity was over 65%. Temporally, we found that peaks in abundance followed large rainfall events. Nevertheless, this mosquito was under significant density dependence regulation. Our results suggest that Ar. subalbatus population peaks following large rainfall events could reflect the recruitment of individuals that were dormant as dry eggs. We did not find a clear signal of temperature on abundance changes of this mosquito, but only on its phenology. Since ground cover seemed more critical than temperature to its spatial distribution, we propose that this mosquito might have some degree of autonomy to changes in temperature.

Comparison of the vector potential of different mosquito species for the transmission of heartworm, Dirofilaria immitis, in rural and urban areas in and surrounding Stillwater, Oklahoma, U.S.A

Dirofilaria immitis Leidy (Spirurida: Onchocercidae), or heartworm, is a mosquito-borne nematode that causes a fatal disease in carnivores. Although infection is preventable through prophylactic drugs, compliance and the spectre of resistance suggest vector control is a viable alternative. There were two main objectives in this study: (a) to evaluate the relationships between landscape and social factors and the number and species of heartworm-positive mosquitoes, with a specific focus on the importance of the invasive Asian tiger mosquito, Aedes albopictus (Skuse) (Stegomyia albopicta) (Diptera: Culicidae), and (b) to test the hypothesis that dog heartworm is more prevalent in suburban than in rural areas. To achieve these objectives, mosquitoes were collected from May to November 2010 at 16 rural and 16 urban locations in Payne County, Oklahoma, U.S.A. using three trapping methods that utilized, respectively, resting boxes, carbon dioxide traps and BG Sentinel traps. Urban areas showed greater numbers of Ae. albopictus and a higher overall likelihood of infection with D. immitis. Because many species of mosquito are responsible for heartworm transmission, current prophylactic treatment remains the best method of controlling this parasite.

Update on temporal and spatial abundance of dengue vectors in Penang, Malaysia

It is important to obtain frequent measurements of the abundance, distribution, and seasonality of mosquito vectors to determine the risk of disease transmission. The number of cases of dengue infection has increased in recent years on Penang Island, Malaysia, with recurring epidemics. However, ongoing control attempts are being critically hampered by the lack of up-to-date information regarding the vectors. To overcome this problem, we examined the current situation and distribution of dengue vectors on the island. Residences throughout the urban, suburban, and rural areas were inspected through wet and dry seasons between February 2009 and February 2010. Two vectors were encountered in the survey, with Aedes aegypti present in especially high numbers mostly in urban areas. Similar observations were noted for Ae. albopictus in rural areas. The former species was more abundant in outdoor containers, while the latter showed almost equivalent abundance both outdoors and indoors. The dengue virus was active in both urban and rural areas, and the number of cases of infection was higher in areas where Ae. aegypti was predominant. The abundance of immature Ae. albopictus was positively correlated with rainfall (r2 = 0.461; P < 0.05), but this was not the case for Ae. aegypti. For both species, the size of immature populations tended to increase with increasing intensity of rain, but heavy rains resulted in population loss. In addition to updating data regarding the larval habitats and locations (outdoors and indoors), this study highlighted the importance of spatial vector control stratification, which has the potential to reduce costs in control programs.

Molecular xenomonitoring of Dirofilaria immitis and Dirofilaria repens in mosquitoes from north-eastern Italy by real-time PCR coupled with melting curve analysis

Background

Dirofilaria immitis and Dirofilaria repens are transmitted by bloodsucking culicid mosquitoes belonging to Culex, Aedes, Ochlerotatus, Anopheles and Mansonia genera.

The detection of filarioids in mosquitoes for assessing distribution of vectors and/or of pathogens in a given area (also known as “xenomonitoring”), when based on individual dissection of wild-caught female mosquitoes is time consuming and hardly applicable in large epidemiological surveys.

Our study aimed to evaluate the recently developed duplex real-time PCR for screening large number of culicids and to assess their positivity for D. immitis and D. repens in an area where both species are endemic.

Methods

A duplex real-time PCR was used to detect and differentiate D. immitis and D. repens in mosquitoes collected in six provinces of the Veneto region using 43 carbon dioxide-baited traps under the frame of an entomological surveillance program to monitor the vectors of West Nile disease. From early May till October 2010, unfed female mosquitoes (n = 40,892) were captured in 20 selected sites.

Results

Mosquitoes identified as Culex pipiens, Ochlerotatus caspius, Aedes vexans and Culex modestus were grouped into 995 pools according to species, day and site of collection (from minimum of 1 to maximum of 57). Out of 955 pools, 23 (2.41 %) scored positive for Dirofilaria spp. of which, 21 (2.2 %) for D. immitis and two (0.21 %) for D. repens. An overall Estimated Rate of Infection (ERI) of 0.06 % was recorded, being higher in Och. caspius and Ae. vexans (i.e., 0.18 % and 0.14 %, respectively). At least one mosquito pool was positive for Dirofilaria spp. in each province with the highest ERI recorded in Vicenza and Padova provinces (i.e., 0.42% and 0.16 %, respectively). Mosquitoes collected in all provinces were positive for D. immitis whereas, only two (i.e., Padova and Rovigo) provinces scored positive for D. repens. All mosquito species, except for Cx. modestus, were positive for D. immitis, whereas D. repens was only found in Cx. pipiens.

Conclusions

The results suggest that both Dirofilaria species are endemic and may occur in sympatry in the examined area. The molecular approach herein used represents a powerful tool for surveillance programs of D. immitis and D. repens in the culicid vectors towards a better understanding of the epidemiology of the infections they cause and their seasonal transmission patterns.

A multiplex PCR for the simultaneous detection of species of filarioids infesting dogs

The present study reports the applicability of a multiplex PCR for the simultaneous detection and differentiation of common filarioids infecting dogs, i.e., Dirofilaria immitis, Dirofilaria repens, Acanthocheilonema reconditum and Cercopithifilaria sp. Amplicons of different sizes (i.e., 170 bp, 480 bp, 590 bp and 300 bp, respectively) of regions within the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene were amplified on a single-step multiplex PCR using a mix of species-specific forward primers coupled with a single reverse primer. Experiments were carried out by amplifying genomic DNA extracted from blood or skin samples test-positive for microfilariae (mff). The number of mff present in each blood sample was quantified (from 800 to 25,000 mff/ml for A. reconditum and D. repens, respectively) and mixed blood samples were tested for the simultaneous detection of DNA from these mff. Specific amplicons for blood-circulating mff of A. reconditum, D. immitis and D. repens and for those whose adults are localized in skin (i.e., A. reconditum and Cercopithifilaria sp.) were simultaneously detected on agarose gel up to a dilution of 250 mff/ml for D. repens. The specific identity of the amplicons was confirmed by sequencing. The multiplex PCR assay reported herein represents a new tool for the molecular detection and differentiation of canine filarioids in blood and skin samples.

Induction of Fas mediated caspase-8 independent apoptosis in immune cells by Armigeres subalbatus saliva

BACKGROUND

It is widely recognized that the introduction of saliva of bloodsucking arthropods at the site of pathogen transmission might play a central role in vector-borne infections. However, how the interaction between salivary components and the host immune system takes place and which physiological processes this leads to has yet to be investigated. Armigeres subalbatus is one of the prominent types of mosquitoes involved in the transmission of parasitic and viral diseases in humans and animals.

METHODOLOGY/PRINCIPAL FINDINGS

Using murine peritoneal macrophages and lymphocytes, and human peripheral mononuclear cells (PBMCs), this study shows that saliva of the female Ar. subalbatus induces apoptosis via interaction with the Fas receptor within a few hours but without activating caspase-8. The process further activates downstream p38 MAPK signaling, a cascade that leads to the induction of apoptosis in capase-3 dependent manner. We further illustrate that Ar. subalbatus saliva suppresses proinflammatory cytokines without changing IL-10 levels, which might happen as a result of apoptosis.

CONCLUSIONS

Our study shows for the first time that saliva-induced apoptosis is the leading phenomenon exerted by Ar.subalbatus that impede immune cells leading to the suppression of their effecter mechanism.

Aedes vexans and Culex pipiens as the potential vectors of Dirofilaria immitis in Central Turkey

This study was carried out to investigate the potential vectors and relative mosquito infection rates of Dirofilaria immitis throughout two mosquito seasons (2008-2009) in Kayseri province where is located in Central Anatolian part of Turkey. For this aim, totally 1198 genomic DNA pools, extracted and grouped according to the species and collection site (1-17 specimens/pool) from 6153 mosquito specimens, were examined by PCR using species-specific primers for D. immitis. The captured mosquitoes from 46 focuses were survived under in vitro conditions for 7 days to allow the development of larval stages of D. immitis. DNA extraction was performed individually to both thorax-head and abdomens in order to determine infective and infected mosquito specimens, respectively. The most abundant mosquito species in the study area was determined as Ae. vexans (51.7%) and this was followed by Cx. pipiens (42.1%), Cx. theileri (3.1%), Cs. annulata (1.5%), An. maculipennis (1.0%) and Cx. hortensis (0.6%). The PCR results indicated that 9/312 and 12/312 pools from Ae. vexans abdomens and thorax-heads were positive for filarial DNAs, respectively where as 3/241 pools of each abdomens and thorax-heads from Cx. pipiens were positive for D. immitis DNAs. The minimum infection rates (MIRs) for Ae. vexans and Cx. pipiens were calculated as 0.41 and 0.12, respectively. Although D. immitis DNA's were found in both pools from Ae. vexans and Cx. pipiens, the calculated MIRs provide evidence that Ae. vexans could be the main potential vector of D. immitis in Kayseri.

Loop-mediated isothermal amplification applied to filarial parasites detection in the mosquito vectors: Dirofilaria immitis as a study model

Background

Despite recent advances in our understanding of the basic biology behind transmission of zoonotic infectious diseases harbored by arthropod vectors these diseases remain threatening public health concerns. For effective control of vector and treatment, precise sampling indicating the prevalence of such diseases is essential. With an aim to develop a quick and simple method to survey zoonotic pathogen-transmitting vectors, LAMP (loop-mediated isothermal amplification) was applied to the detection of filarial parasites using a filarial parasite-transmitting experimental model that included one of the mosquito vectors, Aedes aegypti, and the canine heartworm, Dirofilaria immitis.

Results

LAMP reactions amplifying the cytochrome oxidase subunit I gene demonstrated high sensitivity when a single purified D. immitis microfilaria was detected. Importantly, the robustness of the LAMP reaction was revealed upon identification of an infected mosquito carrying just a single parasite, a level easily overlooked using conventional microscopic analysis. Furthermore, successful detection of D. immitis in wild-caught mosquitoes demonstrated its applicability to field surveys.

Conclusion

Due to its simplicity, sensitivity, and reliability, LAMP is suggested as an appropriate diagnostic method for routine diagnosis of mosquito vectors carrying filarial parasites. This method can be applied to the survey of not only canine filariasis but also lymphatic filariasis, another major public health problem. Therefore, this method offers great promise as a useful diagnostic method for filarial parasite detection in endemic filariasis regions.

Ectopic migration of an adult heartworm in a dog with dirofilariasis (case report)

A 3-yr-old female mongrel dog was referred to the Veterinary Teaching Hospital of Chungnam National University in the Republic of Korea. An adult heartworm, Dirofilaria immitis, was found in the abdominal cavity of the dog during spaying. Dirofilariasis in this dog was also diagnosed by modified Knott's test, ELISA test, and PCR analysis. The present case is the first report on the migration of an adult dog heartworm to the abdominal cavity of a dog in the Republic of Korea.

Heartworm disease in animals and humans

Heartworm disease due to Dirofilaria immitis continues to cause severe disease and even death in dogs and other animals in many parts of the world, even though safe, highly effective and convenient preventatives have been available for the past two decades. Moreover, the parasite and vector mosquitoes continue to spread into areas where they have not been reported previously. Heartworm societies have been established in the USA and Japan and the First European Dirofilaria Days (FEDD) Conference was held in Zagreb, Croatia, in February of 2007. These organizations promote awareness, encourage research and provide updated guidelines for the diagnosis, treatment and prevention of heartworm disease. The chapter begins with a review of the biology and life cycle of the parasite. It continues with the prevalence and distribution of the disease in domestic and wild animals, with emphasis on more recent data on the spreading of the disease and the use of molecular biology techniques in vector studies. The section on pathogenesis and immunology also includes a discussion of the current knowledge of the potential role of the Wolbachia endosymbiont in inflammatory and immune responses to D. immitis infection, diagnostic use of specific immune responses to the bacteria, immunomodulatory activity and antibiotic treatment of infected animals. Canine, feline and ferret heartworm disease are updated with regard to the clinical presentation, diagnosis, prevention, therapy and management of the disease, with special emphasis on the recently described Heartworm Associated Respiratory Disease (HARD) Syndrome in cats. The section devoted to heartworm infection in humans also includes notes on other epizootic filariae, particularly D. repens in humans in Europe. The chapter concludes with a discussion on emerging strategies in heartworm treatment and control, highlighting the potential role of tetracycline antibiotics in adulticidal therapy.