Improved detection of Dirofilaria repens DNA by direct polymerase chain reaction

Human Pulmonary Dirofilariasis Due to Dirofilaria immitis: The First Italian Case Confirmed by Polymerase Chain Reaction Analysis, with a Systematic Literature Review

Dirofilariasis is a zoonosis caused by nematodes of the genus Dirofilaria.Dirofilaria immitis is cosmopolitan as regards its distribution in animals, being responsible for human pulmonary dirofilariasis in the New World. However, human infections by Dirofilaria immitis are exceptional in Europe, and the previously reported Italian cases of pulmonary dirofilariasis were due to Dirofilaria repens. We performed a systematic literature review of the Italian cases of human dirofilariasis due to Dirofilariaimmitis according to the PRISMA guidelines. We also report the first autochthonous case of human pulmonary dirofilariasis due to Dirofilariaimmitis, confirmed by polymerase chain reaction analysis. The patient was a 60-year-old man who lived in the Po river valley and had never traveled abroad; on histological examination, the 2-cm nodule found in his right upper lung was an infarct due to a parasitic thrombotic lesion. Only one other autochthonous (but conjunctival) case due to Dirofilariaimmitis (molecularly confirmed) was previously found in the same geographic area. Climatic changes, the increasing movements of animal reservoirs and vectors, and new competent carriers have expanded the geographic distribution of the Dirofilaria species, increasing the risk of human infections. Our report demonstrates that at least some pulmonary Italian cases of human dirofilariasis are due to Dirofilaria immitis, as in the New World.

Autochthonous Human Dirofilaria repens Infection in Austria

PURPOSE

This report describes a rare autochthonous case of human D. repens infection in Austria. Dirofilariosis is a mosquito-borne parasitic infection that predominantly affects dogs. Human D. repens infections have primarily been reported in Mediterranean countries, but are emerging throughout Central and Northern Europe.

METHODS

The worm was removed surgically and identified using PCR and DNA sequencing. The consensus sequences were compared against reference sequences of Dirofilaria repens from GenBank.

RESULTS

The 56-year-old woman acquired the infection, which presented as a subcutaneous nodule, in Vienna, Austria. This is the second autochthonous case of human D. repens infection in Austria.

CONCLUSION

The reasons for the emergence of D. repens and other parasitic infections in Central and Northern Europe are manifold, including climate change and globalization. This case demonstrates that with the growing number of D. repens infections, health care professionals must place further emphasis on emerging infectious diseases to ensure appropriate diagnostics and treatment in the future.

Anthology of Dirofilariasis in Russia (1915-2017)

Dirofilariasis is a helminths vector-borne disease caused by two species of Dirofolaria—D. repens and D. immitis. The former is overwhelmingly associated with human dirofilariasis. The vector of the worm are mosquitoes of the family Culicidae (largely Culex, Aedes and Anopheles). The definitive hosts of Dirofilaria are dogs and to a lesser extent cats. Humans are an accidental host. A total of 1200 human cases caused by Dirofilaria were registered in the territory of the ex-USSR during the period 1915–2016. Zonal differences have been seen in the prevalence of infected dogs and mosquitoes. Studies undertaken in the southern part of the Russian Federation (RF) revealed the prevalence of Dirofilaria in dogs to be 20.8% with wild variations of larva density. Studies carried out in the central part of the RF found that the prevalence of parasites in dogs was 4.1%. Aedes mosquitoes were infected less than Culex and Anopheles mosquitoes. The latter were infected by D. repens more often than Culex and Aedes. Zonal differences were also traced in regard to Dirofilaria prevalence in humans, thus allowing identification of three zones of risk of infection (low, moderate, and stable), reflected in a series of constructed maps. Although Dirofilariasis was known on the territory of Russia from 1915, only sporadic cases of the disease were reported occasionally. Its number was showed an increasing trend only during the 1980s–1990s, reaching the level of hundreds of cases. The majority of cases were confined to the southern parts of Russia with geographic coordinates of 43°–45° on the northern latitude. Comparison of the timing of the global trend of climate warming during the 1990s with the temporal pattern of Dirofilaria on the territory of Russia during the same period demonstrated a close association between two phenomena. With the continuous process of global climate warming, the incidence of dirofilariasis both in man and dogs goes unabated exemplified by the territorial expansion of the disease northwards and eastwards attaining the latitude of 56°–57° on the northern latitude in the European and Asian parts of Russia. It appears that within the period of the last 20–25 years, the population at risk has doubled. Under these circumstances, dirofilariases in Russia should be considered as an emerging public health problem necessitating the establishment of a comprehensive epidemiological monitoring system with strong entomological and veterinary components. Based on the results obtained, an appropriate control intervention could be developed.

A case of human Dirofilaria repens infection, causing an asymptomatic subcutaneous nodule

We present a case of subcutaneous dirofilariasis, a vector-borne zoonotic disease, in a young woman from Austria. The diagnosis was confirmed by ultrasound and histology of the excised subcutaneous nodule. The parasite species was identified as Dirofilaria repens by polymerase chain reaction. We expect to see more cases of human dirofilariasis also due to climate change and associated increase of the spectrum of suitable mosquito vectors.

Dirofilaria and Wolbachia in mosquitoes (Diptera: Culicidae) in central European Russia and on the Black Sea coast

Dirofilariasis is endemic in Russia, as well as in many other European countries. The aim of this study was to assess the ability of mosquitoes to transfer Dirofilaria immitis and Dirofilaria repens in regions with temperate and subtropical climates. The possible impact of the symbiotic bacterium Wolbachia on Dirofilaria transmission was also investigated. 5333 female mosquitoes were collected at 11 points in central European Russia and on the Black Sea coast during the period 2013–2017. Out of 20 mosquito species examined, 14 were infected with D. repens and 13 with D. immitis. Both species of Dirofilaria were found in different climatic regions. The total Dirofilaria spp. estimated infection rate (EIR) in the central part of Russia varied from 3.1% to 3.7% and, in the southern region, from 1.1% to 3.0%. The highest estimated infection rate was found in Anopheles messeae, the lowest in Culex pipiens. The greatest epidemiological danger was represented by Aedes aegypti, Ae. geniculatus, An. messeae and Ae. communis. Six out of 20 mosquito species were infected with Wolbachia. Pools of Aedes albopictus, Cx. pipiens and Coquillettidia richiardii were simultaneously infected with Dirofilaria and Wolbachia. After checking mosquitoes individually, it was found that there was no development of Dirofilaria to the infective larval stage in specimens infected with Wolbachia. Twenty-two Dirofilaria-infective pools were Wolbachia-free and only two mosquito pools were Wolbachia-infected. The potential for transmission of Dirofilaria in mosquito species naturally uninfected with the symbiotic bacterium Wolbachia is higher than in species infected with the bacterium.

Whether Dirofilaria repens parasites from South India belong to zoonotic Candidatus Dirofilaria hongkongensis (Dirofilaria sp. hongkongensis)?

The canine and zoonotic dirofilarioses are arthropod-borne parasitic infections caused by nematodes of the genus Dirofilaria, infecting canines, felines and humans throughout the world. Dirofilaria repens was considered as the most common cause of human dirofilariosis in Kerala. In the present study, molecular characterization of Dirofilaria isolates causing dirofilariosis in humans, dogs and jackal from Kerala, South India was undertaken by performing sequence and phylogenetic analysis based on cytochrome oxidase subunit I (COI) gene. The live worms from swellings/ nodules in subconjunctiva or subcutaneous tissue or scrotum were recovered from humans (n = 3), dogs (n = 4) and one jackal. The PCRs targeting a repetitive fragment, 18S rRNA and COI genes yielded products of ~246 bp, ~875 bp and ~350 bp respectively in all the samples. The sequence analysis of 18S rRNA gene revealed the closest identity (98 to 99%) with an already published sequence of D. repens isolated from a human in Japan. However, based on the sequence and phylogenetic analysis of partial sequences of COI gene, the Dirofilaria infecting both animals (dogs, jackal) and humans native to Kerala, South India were identified as genetically conserved and closely related to Dirofilaria sp. hongkongensis. Hence, the results of the present study suggested the existence of Candidatus Dirofilaria hongkongensis (Dirofilaria sp. hongkongensis) in Kerala, South India causing zoonotic filariosis in canines and humans.

Dirofilaria immitis in a child from the Russian Federation

An immature female worm, Dirofilaria immitis, was isolated from the scrotum of a 14-month-old child. This is the first identification of human dirofilariosis caused by D. immitis in a relatively Northern region (Moscow) of the Russian Federation. The parasite was diagnosed by means of morphological examination of the worm, confirmed by PCR assay. This case raises questions about the range of the D. immitis distribution among humans in Russia. To better understand the geographical distribution of dirofilarioses, detailed clinical and epidemiological information should be collected from human cases with appropriate laboratory confirmation.

Human ocular dirofilariasis due to Dirofilaria repens in Sri Lanka

OBJECTIVE

To identify worms obtained from patients with eye lesions and to describe the demographic factors of patients with ocular dirofilariasis.

METHODS

A retrospective descriptive study was conducted in 31 worm samples from 30 patients referred by consultant ophthalmologists between 2006 and February 2014. Data on age, sex and site of the lesion were ascertained from the details given in the referral letters. Morphological identification of the worm was based on the maximum width, length and appearance of the cuticle. The sex of the worm was determined by the width, length and presence or absence of vulva opening. PCR was performed using Dirofilaria repens specific primers to confirm the species of worms which couldnot be identified morphologically.

RESULTS

Most of the patients belonged to the age group of 40-49 years (mean age = 42 years). Majority of them were females (70%). Subconjunctival lesions were the most frequent presentation, while the rest (n = 4) were found on eyelids. Female worms were extracted from 18 cases, and 11 had male worms. One individual had both male and female worms in a single nodule. Adults were the most commonly affected. This pattern was different from the previous studies in Sri Lanka where the most common age group affected was younger than 9 years old.

CONCLUSIONS

The present study showed a considerably high incidence of ocular dirofilariasis, stressing the importance of implementing preventive measures to reduce the transmission of this zoonotic filarial disease.

A rare case of anterior chamber dirofilariasis

We report a rare case of anterior chamber live dirofilariasis presenting as anterior uveitis. A 60-year-old man presented with dimness of vision in the right eye for 1 month. Vision recorded was 6/18 P, N 18 in the right eye. Slit lamp examination of the right eye revealed anterior uveitis with a moving nemathelminthes. The worm was removed live from the anterior chamber under local anesthesia with assisted methyl cellulose delivery and post-operatively, the worm was examined directly under light microscope. Morphometric measurement showed length of the worm was 6.061 mm. A thin, pale, slender worm was diagnosed as immature female Dirofilaria repens and was documented completely. Patient had made an excellent recovery of vision and intraocular inflammation after the surgical removal of the worm. Intraocular infection of dirofilaria is a rare presentation and successful surgical removal of the worm resulted in complete recovery of uveitis and visual status in the affected eye.

Canine filarial infections in a human Brugia malayi endemic area of India

A very high prevalence of microfilaremia of 42.68 per cent out of 164 canine blood samples examined was observed in Cherthala (of Alappuzha district of Kerala state), a known human Brugia malayi endemic area of south India. The species of canine microfilariae were identified as Dirofilaria repens, Brugia malayi, and Acanthocheilonema reconditum. D. repens was the most commonly detected species followed by B. pahangi. D. immitis was not detected in any of the samples examined. Based on molecular techniques, microfilariae with histochemical staining pattern of "local staining at anal pore and diffuse staining at central body" was identified as D. repens in addition to those showing acid phosphatase activity only at the anal pore. Even though B. malayi like acid phosphatase activity was observed in few dogs examined, they were identified as genetically closer to B. pahangi. Hence, the possibility of dogs acting as reservoirs of human B. malayi in this area was ruled out.

Vector-borne pathogens in ticks and EDTA-blood samples collected from client-owned dogs, Kiev, Ukraine

Due to the availability of adequate habitats in urban environments, e.g. city parks and recreational green areas, ticks from such settings may also carry pathogens of veterinary and public health concern. Thus, tick-borne infections may readily be identified in companion animals residing in urbanised areas. To investigate the presence of vector-borne pathogens in Kiev, Ukraine, 52 engorged adult ticks, 33 Dermacentor reticulatus and 19 Ixodes ricinus, were collected from 15 dogs in the spring of 2010, and further 23 canine EDTA-blood samples were obtained in the spring of 2011 from client-owned patients presented in a veterinary clinic in Kiev. DNA of 9 pathogens was detected by PCR in ticks and canine EDTA-blood samples: Babesia canis canis, Anaplasma phagocytophilum, Rickettsia helvetica, Ri. monacensis, Ri. raoultii, and Dirofilaria repens (by proxy) were identified in engorged ticks and B. c. canis, Hepatozoon canis, Di. immitis, Di. repens, and Mycoplasma haemocanis in canine EDTA-blood samples. This is the first description of Ri. raoultii in the Ukraine. This study adds information on the occurrence of vector-borne pathogens of veterinary and public health importance in Kiev, Ukraine.

Histological and molecular confirmation of the fourth human case caused by Dirofilaria repens in a new endemic region of Slovakia

Dirofilariosis is considered to be the arthropod vector-borne disease with the fastest spread in Europe. Slovakia belongs to new endemic regions for canine and human infections. This paper reports the fourth human case, where diagnosis was confirmed using computed tomography (CT), histological and molecular examinations – for the first time in this endemic region. The epidemiological history of this case indicated the autochthonous origin, and infection manifested by intense swelling in the periocular region, where a subcutaneous nodule was localized. Microscopic analysis of cross-sections of the surgically removed nodule confirmed the presence of a single male worm of Dirofilaria repens, indicated by the external cuticular ridges, the robust muscle cells and a single male sex organ seen as one tube beside the intestine. Considering that the worm morphology was partially damaged, molecular study was performed using DNA isolated from formalin-fixed and paraffin-embedded tissue sections of the worm. In polymerase chain reactions (PCR) a set of primers specific for D. repens DNA for the CO1-encoding gene amplified the expected 246 bp product using a high concentration of DNA template. Our diagnostic approach, involving molecular techniques, showed that identification of D. repens from excised tissues is possible even when the morphology of the worm and DNA are damaged during tissue processing. It is expected that the spread of this disease will continue due to climatic changes in central Europe. This warrants higher awareness among clinicians, who will initially be approached by patients, and better co-operation with parasitologists in newly endemic countries.

Molecular diagnosis of infections and resistance in veterinary and human parasites

Since 1977, >2000 research papers described attempts to detect, identify and/or quantify parasites, or disease organisms carried by ecto-parasites, using DNA-based tests and 148 reviews of the topic were published. Despite this, only a few DNA-based tests for parasitic diseases are routinely available, and most of these are optional tests used occasionally in disease diagnosis. Malaria, trypanosomiasis, toxoplasmosis, leishmaniasis and cryptosporidiosis diagnosis may be assisted by DNA-based testing in some countries, but there are very few cases where the detection of veterinary parasites is assisted by DNA-based tests. The diagnoses of some bacterial (e.g. lyme disease) and viral diseases (e.g. tick borne encephalitis) which are transmitted by ecto-parasites more commonly use DNA-based tests, and research developing tests for these species makes up almost 20% of the literature. Other important uses of DNA-based tests are for epidemiological and risk assessment, quality control for food and water, forensic diagnosis and in parasite biology research. Some DNA-based tests for water-borne parasites, including Cryptosporidium and Giardia, are used in routine checks of water treatment, but forensic and food-testing applications have not been adopted in routine practice. Biological research, including epidemiological research, makes the widest use of DNA-based diagnostics, delivering enhanced understanding of parasites and guidelines for managing parasitic diseases. Despite the limited uptake of DNA-based tests to date, there is little doubt that they offer great potential to not only detect, identify and quantify parasites, but also to provide further information important for the implementation of parasite control strategies. For example, variant sequences within species of parasites and other organisms can be differentiated by tests in a manner similar to genetic testing in medicine or livestock breeding. If an association between DNA sequence and phenotype has been demonstrated, then qualities such as drug resistance, strain divergence, virulence, and origin of isolates could be inferred by DNA-based tests. No such tests are in clinical or commercial use in parasitology and few tests are available for other organisms. Why have DNA-based tests not had a bigger impact in veterinary and human medicine? To explore this question, technological, biological, economic and sociological factors must be considered. Additionally, a realistic expectation of research progress is needed. DNA-based tests could enhance parasite management in many ways, but patience, persistence and dedication will be needed to achieve this goal.

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

Adult mosquito collections using New Jersey light traps and Black-hole light traps were conducted to determine the potential vectors and the relative mosquito infection rates of Dirofilaria immitis and Dirofilaria repens in Gyeonggi and Gangwon Provinces, Republic of Korea, 2005. Dirofilaria spp. were confirmed by polymerase chain reaction (PCR) using species-specific primers for D. immitis and D. repens. Minimum field infection rates (MFIR) [MFIR = (number infected pools/total number of mosquitoes) x 1000] of 12 pools/2059 total number mosquitoes (5.8) and 21 pools (10.1) of the wild caught mosquitoes were positive by PCR for D. immitis and D. repens, respectively. Dual infections of both D. immitis and D. repens were detected by PCR in eight pools (3.9). Anopheles sinensis sensu lato (includes An. sinensis s.s., An. pullus, An. kleini, An. belenrae, and An. lesteri), An. sineroides, Aedes vexans nipponi, Culex pipiens and Armigeres subalbatus were found to be infected and are potential vectors of D. immitis and D. repens in Korea. Infections observed in mosquitoes represent potential health risks for domestic animal and human populations.

Detection of Dirofilaria (Nochtiella) repens DNA by polymerase chain reaction in embedded paraffin tissues from two human pulmonary locations

We here report two new cases of human pulmonary dirofilariasis in men aged 62 and 64 from Northern and Central Italy, respectively. Both were asymptomatic and the infections were discovered incidentally when chest radiographs taken for another reason revealed the presence of a coin lesion. The initial clinical diagnosis was oriented towards a lung tumour, and an excisional lung biopsy after thoracotomy was necessary for the final diagnosis. Pathologically, the lesion consisted of a roundish subpleural infarct with a central thrombotic artery containing sections of an immature nematode: Dirofilaria repens was diagnosed histologically in one case, the necrotic condition of the worm allowing only genus identification, Dirofilaria, in the other case. In both samples, PCR analysis amplified a 246 bp product, specific for the IpS insert 11 of D. repens. The authors stress the role of PCR in the diagnosis of this parasite from paraffin samples, also in cases in which identification of the species was not possible by conventional morphology due to poor conservation of the worm. These cases represent the first PCR-based diagnosis of D. repens in a human pulmonary dirofilariasis on samples embedded in paraffin.

Discrimination between six species of canine microfilariae by a single polymerase chain reaction

Canine dirofilariasis caused by Dirofilaria immitis is usually diagnosed by specific antigen testing and/or identification of microfilariae. However, D. immitis and at least six other filariae can produce canine microfilaremias with negative heartworm antigen tests. Discriminating these can be of clinical importance. To resolve discordant diagnoses by two diagnostic laboratories in an antigen-negative, microfilaremic dog recently imported into the US from Europe we developed a simple molecular method of identifying different microfilariae, and subsequently validated our method against six different filariae known to infect dogs by amplifying ribosomal DNA spacer sequences by polymerase chain reaction using common and species-specific primers, and sequencing the products to confirm the genotype of the filariae. We identified the filaria in this dog as D. repens. This is the first case of D. repens infection in the United States. Additionally, we examined microfilariae from five additional antigen-negative, microfilaremic dogs and successfully identified the infecting parasite in each case. Our diagnoses differed from the initial morphological diagnosis in three of these cases, demonstrating the inaccuracy of morphological diagnosis. In each case, microfilariae identified morphologically as A. reconditum were identified as D. immitis by molecular methods. Finally, we demonstrated that our PCR method should amplify DNA from at least two additional filariae (Onchocerca and Mansonella), suggesting that this method may be suitable for genotyping all members of the family Onchocercidae.

Comparison of the Acid-phosphatase Staining and Polymerase Chain Reaction for Detection of Dirofilaria repens Infection in Dogs in Korea

This study was performed to compare acid-phosphatase staining with polymerase chain reaction (PCR) analysis for the diagnosis of Dirofilaria repens infection. The infection of D. repens was confirmed in Korean reared German shepherd dogs. Knott's tests were carried out for the detection of microfilaria in 543 Korean reared German shepherd dogs (255 females and 288 males). Eighty four of the 543 dogs (15.5%) showed microfilaria-positive reactions with the modified Knott's test, and the test-positive microfilariae were then examined by both acid phosphatase staining and PCR analysis. Six (7.1%) and 17 (20.2%) of the 84 microfilaria-positive samples, by the Knott's tests were positive to D. repens by acid-phosphatase staining and in D. repens-specific PCR analysis, respectively. All samples found to be positive by the acid-phosphatase staining were also found to be positive by PCR analysis. Therefore, we conclude that PCR analysis (20.2%) is more valuable for the diagnosis of D. repens infection than acid-phosphatase staining (7.1%) (p<0.001).

Diagnosis of human filariases (except onchocerciasis)

The traditional method of diagnosing filarial infections is to examine blood or skin samples for microfilariae and for many this is still the standard procedure. However, since the present global campaign to eliminate lymphatic filariasis new diagnostic tools have emerged like PCR, antigen detection using finger-prick blood taken during the day and ultrasound to visualize adult worms. The last two can be applied in endemic countries with limited resources and enable the detection of early infections. As well as their value in control schemes, the latter is particularly important for the individual since recent research has shown that damage is usually caused long before symptoms appear. The usefulness in different situations and the advantages and disadvantages of the various new tools for diagnosis of lymphatic filariasis are discussed. For loiasis, immunodiagnostic methods have not been very successful but repetitive DNA sequences in the Loa genome have been found to be species specific. Techniques based on them are particularly useful for diagnosing cases of occult infection without microfilaraemia. There have been no advances in the diagnosis of Mansonella perstans but both immunodiagnostic and PCR tests show promise in differentiating M. streptocerca, and the latter in differentiating M.ozzardi, from Onchocerca. In addition to the human filariae, the dog parasites Dirofilaria immitis and D. repens can also occur in humans but do not produce microfilariae in them. ELISAs and PCR probes have been devised and can usefully differentiate between pulmonary dirofilariasis and lung cancer.

Genotypic assignment of infection by Dirofilaria repens

Dirofilariasis is a parasitic disease, which if treated inappropriately due to misdiagnosis, can cause unwanted complications particularly when the infection is located in the breast. The numerous obstacles that can cause misdiagnosis of dirofilariases by standard morphological procedures prompted the development of a Dirofilaria repens-specific direct polymerase chain reaction (PCR)-based diagnostic approach using freshly infected dog blood. Reliable amplification of nematode DNA from formalin-fixed infected human specimens by this method is only possible from relatively fresh biological material, preserved in the fixative for up to 20 days. We report here our first case of dirofilariasis since the development of PCR genotyping, where the pathogen was morphologically unrecognizable and the diagnosis was based exclusively on DNA amplification. We complete our methodological contribution to the clinical laboratory diagnosis of dirofilariasis by presenting two more cases, where the primary genotypic assignment of infection by D. repens was further confirmed by conventional morphological means.

Characterisation of nuclear ribosomal DNA sequences from Onchocerca volvulus and Mansonella ozzardi (Nematoda: Filarioidea) and development of a PCR-based method for their detection in skin biopsies

The internal transcribed spacer region (ITS1, 5.8S gene and ITS2) of the two filarial nematodes Onchocerca volvulus and Mansonella ozzardi was sequenced, and two species-specific primers designed in the ITS2 to develop a PCR-based method for their specific detection and differentiation. When used with a universal reverse primer, the two species-specific primers gave amplification products of different size, which were readily separated in an agarose gel. The PCR was tested on skin biopsies from 51 people from three localities in Brazil where M. ozzardi is present, and results have been compared with those of parasitological examination of blood. The species-specific PCR gave a higher percentage of detection of infection by M. ozzardi than the parasitological examination of blood. No infection with O. volvulus was detected by PCR. This PCR-based assay may assist in determining the nature of infection in areas where both filarial species exist in sympatry.