Selection of suitable reference genes for normalization of RT-qPCR in three tissues of Northern bobwhite (Colinus virginianus) infected with eyeworm (Oxyspirura petrowi)

BACKGROUND

The Northern bobwhite (Colinus virginianus) is an economically important, and popular game bird in North America. Northern bobwhites have experiencing declines of > 3.5% annually in recent decades due to several factors. The eyeworm Oxyspirura petrowi is a nematode parasite frequently found in the eyes of bobwhites. Although reported frequently in wild bobwhites, there is no research to understand the host-parasite mechanism. Hence, it is important to investigate mechanisms of eyeworm invasion and immune modulation in bobwhite. Cytokine gene expression using RT-PCR is widely used to identify the innate immune response of a host to an infection.

METHODOLOGY

In this study, we evaluated ten reference genes (HMBS, RPL19, RPL32, RPS7, RPS8, TATA, SDHA, YWHAZ, GAPDH, and ACTB) for their stability across three tissues (liver, spleen, and caecal tonsils) of control and O. petrowi infected Northern bobwhites. Primer efficiency and reference genes stability were assessed using GeNorm, NormFinder, and BestKeeper.

RESULTS

Expression of these reference genes with respect to O. petrowi infection in bobwhites showed RPL32 and HMBS were the most stable genes in the liver, HMBS and SDHA were the most stable genes in the spleen, and HMBS and YWHAZ were equally stable reference genes in the caecal tonsils.

CONCLUSION

Based on the geometric mean of all three analyses, our results indicate that the combination of RPL32 and HMBS for the liver, HMBS and SDHA for the spleen, and YWHAZ and HMBS for caecal tonsils might be used as reference genes for normalization in gene expression investigations on Northern bobwhites.

Emergence of Thelaziosis Caused by Thelazia callipaeda in Dogs and Cats, United States

We report 2 autochthonous feline thelaziosis cases caused by the eyeworm Thelazia callipaeda and discuss the spread among dogs in the northeastern United States. Phylogenetic analysis suggests the parasite was introduced from Europe. Adopting a One Health approach is needed to limit further spread of T. callipaeda eyeworms in North America.

Occurrence of Thelazia callipaeda and its vector Phortica variegata in Austria and South Tyrol, Italy, and a global comparison by phylogenetic network analysis

The zoonotic nematode Thelazia callipaeda infects the eyes of domestic and wild animals and uses canids as primary hosts. It was originally described in Asia, but in the last 20 years it has been reported in many European countries, where it is mainly transmitted by the drosophilid fruit fly Phortica variegata. We report the autochthonous occurrence of T. callipaeda and its vector P. variegata in Austria. Nematodes were collected from clinical cases and fruit flies were caught using traps, netting, and from the conjunctival sac of one dog. Fruit flies and nematodes were morphologically identified and a section of the mitochondrial cytochrome c oxidase subunit I gene (COI) was analysed. A DNA haplotype network was calculated to visualize the relation of the obtained COI sequences to published sequences. Additionally, Phortica spp. were screened for the presence of DNA of T. callipaeda by polymerase chain reaction. Thelazia callipaeda and P. variegata were identified in Burgenland, Lower Austria, and Styria. Thelazia callipaeda was also documented in Vienna and P. variegata in Upper Austria and South Tyrol, Italy. All T. callipaeda corresponded to haplotype 1. Twenty-two different haplotypes of P. variegata were identified in the fruit flies. One sequence was distinctly different from those of Phortica variegata and was more closely related to those of Phortica chi and Phortica okadai. Thelazia callipaeda could not be detected in any of the Phortica specimens.

A human corneal ulcer caused by Thelazia callipaeda in Southwest China: case report

In this study, we describe a rare human case with corneal ulcer caused by thelaziosis in a 69-year-old man in Southwest China. A male nematode was discovered and removed from the patient's right eye with a long spicule and further identified by sequencing mitochondrial cox1 gene. The ophthalmologic and molecular biological evidence demonstrates the corneal ulcer caused by T. callipaeda infection, which is mainly distributed in Asian and European countries. Most T. callipaeda infections are emerged in the conjunctiva, leading to conjunctivitis. To the best knowledge of the authors, corneal ulcers caused by T. callipaeda have not been reported yet.

First report of Spirocerca vulpis in red foxes (Vulpes vulpes) in Portugal

Recent studies have described Spirocerca lupi-like nematodes in the stomach of red foxes (Vulpes vulpes) in Europe. A phylogenetic analysis of those specimens using mitochondrial DNA and their morphological reexamination allowed their characterization as a different species, Spirocerca vulpis. Between the years of 2010 and 2017, roundworms were collected from seven red foxes of northeastern Portugal found at necropsy with nodular lesions on their stomach wall. Histopathological analysis of four foxes revealed granulomatous lesions of the gastric nodules. On morphological assessment, by light microscopy, nematodes revealed the presence of six triangular teeth-like buccal capsule structures, which are absent in S. lupi. Polymerase chain reaction was run to amplify a 551 bp partial fragment of the cytochrome c oxidase subunit 1 gene. Sequences were 99% similar to S. vulpis (85% coverage) of red foxes from Spain and Bosnia and Herzegovina, 99% similar (99% coverage) to sequences of Spirocerca sp. of red foxes from Denmark and 93% similar (99% coverage) to S. lupi from South Africa. This is the first report of S. vulpis in foxes or any other host from Portugal.

[Sequential analysis of genome of Thelazia callipaeda]

OBJECTIVE

To investigate the molecular characteristics of genome sequence of Thelazia callipaeda (T. cp).

METHODS

The obtained T. cp genome assembling data were annotated by using a combination of ab initio gene by softwares, GeneMark and GeneID, and the homology of the experimentally confirmed genes was predicted by software GeMoMa. The results were integrated by software EVM to predict all genes of genome. The obtained genes were annotated in the common public database and three dedicated databases (CAZyme, TCDB and PHI), respectively.

RESULTS

The Scaffolds and Contigs gene structure of T. cp genome (79.34 Mb) was analyzed, and a total of 6 333 genes were obtained. The sequence search was conducted in the public databases using BLASTx, of which 97.85% of the genes could be annotated. The genes annotated in the NR database were the most (98.69%), and those enriched in the KEGG pathway were the least (50.50%). The functional genes were blasted by KOG database and totally 4 517 genes were found. The three special databases (CAZyme, TCDB and PHI) were used to annotate all the genes, and 136, 139 and 1 498 genes were assigned respectively, and the number of genes in the PHI database was the largest. In the cytochrome proprietary database, 238 cytochrome P450 genes were predicted.

CONCLUSIONS

We have preliminarily revealed the T. cp genome structure characteristics and annotation information, and totally 6 333 genes are obtained.

The eyeworm Thelazia callipaeda in Portugal: Current status of infection in pets and wild mammals and case report in a beech marten (Martes foina)

Ocular thelaziosis is caused by nematodes of the genus Thelazia (Spirurida, Thelaziidae), which inhabit the surface of the eyes and associated tissues. Thelazia callipaeda affects a range of mammal species, including humans, and in the last two decades has been reported in multiple European countries, being classified as an emergent vector-borne pathogen. In Portugal T. callipaeda is endemic in north-eastern areas, where it has been reported in domestic dogs, cats, red foxes (Vulpes vulpes) and wild European rabbits (Oryctolagus cuniculus). We report, for the first time, T. callipaeda in a beech marten (Martes foina) from Portugal and highlight the presence of haplotype 1 as the only one found in Europe, irrespective of the host species and geographical area of provenience.

Population structure analysis of the neglected parasite Thelazia callipaeda revealed high genetic diversity in Eastern Asia isolates

Background

Thelazia callipaeda is the causative agent of thelaziasis in canids, felids and humans. However, the population genetic structure regarding this parasite remains unclear.

Methodology/principal findings

In this study, we first explored the genetic variation of 32 T. callipaeda clinical isolates using the following multi-molecular markers: cox1, cytb, 12S rDNA, ITS1 and 18S rDNA. The isolates were collected from 13 patients from 11 geographical locations in China. Next, the population structure of T. callipaeda from Europe and other Asian countries was analyzed using the cox1 sequences collected during this study and from the GenBank database. In general, the Chinese clinical isolates of T. callipaeda expressed high genetic diversity. Based on the cox1 gene, a total of 21 haplotypes were identified. One only circulated in European countries (Hap1), while the other 20 haplotypes were dispersed in Korea, Japan and China. There were five nucleotide positions in the cox1 sequences that were confirmed as invariable among individuals from Europe and Asia, but the sequences were distinct between these two regions. Population differences between Europe and Asian countries were greater than those among China, Korea and Japan. The T. callipaeda populations from Europe and Asia should be divided into two separate sub-populations. These two groups started to diverge during the middle Pleistocene. Neutrality tests, mismatch distribution and Bayesian skyline plot (BSP) analysis all rejected possible population expansion of T. callipaeda.

Conclusions

The Asian population of T. callipaeda has a high level of genetic diversity, but further studies should be performed to explore the biology, ecology and epidemiology of T. callipaeda.

Thelazia callipaeda is the causative agent of thelaziasis canids, felids and humans. Despite the existing threat of thelaziosis in China, the genetic diversity of T. callipaeda has not been investigated across its wide geographical distribution in China, yet such information may provide insight into the disease epidemiology and the development of specific control measures. In this study, the genetic variation of 32 T. callipaeda clinical isolates collected from 13 patients from 11 geographical locations in China were explored using the following multi-molecular markers: cox1, cytb, 12S rDNA, ITS1 and 18S rDNA. In addition, the population structure of T. callipaeda from Europe and other Asian countries was analyzed using the cox1 sequences collected during this study and from the GenBank database. In general, the Chinese clinical isolates of T. callipaeda demonstrated high genetic diversity. Based on the cox1 gene, a total of 21 haplotypes were identified, one circulated in European countries (Hap1), while the other 20 haplotypes were dispersed in Korea, Japan and China. There were five nucleotide positions in the cox1 that were confirmed as invariable among individuals from Europe and Asia, but the sequences were distinct between these two regions. Population differences between Europe and Asian countries were greater than those among China, Korea and Japan, such that the T. callipaeda population from Europe and Asia should be divided into two separate sub-populations. These two groups started to diverge during the middle Pleistocene.

[Genetic variation of Thelazia callipaeda among isolates collected from patients in Zunyi City, Guizhou Province]

OBJECTIVE

To identify the genetic variation and possible sources of Thelazia callipaeda isolates collected from patients in Zunyi City, Guizhou Province.

METHODS

Seven cases of T. callipaeda infection in Zunyi City, 2016 were verified, and DNA (s) were extracted from the T. callipaeda's body collected from the thelaziasis patients. A mitochondrial COX1 fragment was amplified and sequenced. The sequence alignment and phylogenetical analysis were performed to compare the genetic variation of the gene sequence with the homologous sequences downloaded from Genebank.

RESULTS

COX1 genes of T. callipaeda were differed among the samples from the seven cases, which had low variation.

CONCLUSIONS

Zunyi City is a new area with endemic of thelaziasis. The isolates from Zunyi City include either Asian origin or European origin of T. callipaeda. Moreover, at least four haplotypes are identified among the seven isolates.

Further spreading of canine oriental eyeworm in Europe: first report of Thelazia callipaeda in Romania

BACKGROUND

Despite the increasing number of reports of autochthonous cases of ocular thelaziosis in dogs in several European countries, and the evident emergence of human cases, the distribution and spreading potential of this parasite is far for being fully known. In Romania, despite intensive surveillance performed over recent years on the typical hosts of T. callipaeda, the parasite has not been found until now.

METHODS

In October 2014 a German Shepherd was presented for consultation to a private veterinary practice from western Romania with a history of unilateral chronic conjunctivitis. Following a close examination of the affected eye, nematodes were noticed in the conjunctival sac. The specimens collected were used for morphological examination (light microscopy) and molecular analysis (amplification of the cytochrome c oxidase subunit 1 gene, followed by sequencing).

RESULTS

Thirteen nematodes were collected, all identified morphologically as T. callipaeda. The history of the dog revealed no travel outside Romania, and during the last year, not even outside the home locality. The BLAST analysis of our sequence showed a 100% similarity T. callipaeda haplotype h1.

CONCLUSIONS

This is the first report of T. callipaeda in Romania, which we consider to be with autochthonous transmission. These findings confirm the spreading trend of T callipaeda and the increased risk of emerging vector-borne zoonoses.

Two cases of human thelaziasis as confirmed by mitochondrial cox1 sequencing in China

Two special cases of human thelaziasis were reported in China: an old farmer with heavy infection by 36 worms and a 7-year-old boy with infection by eight worms. Thelazia callipaeda was morphologically identified and confirmed by mitochondrial cox1 gene sequencing.

Mitochondrial genome of the eyeworm, Thelazia callipaeda (Nematoda: Spirurida), as the first representative from the family Thelaziidae

Human thelaziosis is an underestimated parasitic disease caused by Thelazia species (Spirurida: Thelaziidae). The oriental eyeworm, Thelazia callipaeda, infects a range of mammalian definitive hosts, including canids, felids and humans. Although this zoonotic parasite is of socio-economic significance in Asian countries, its genetics, epidemiology and biology are poorly understood. Mitochondrial (mt) DNA is known to provide useful genetic markers to underpin fundamental investigations, but no mt genome had been characterized for any members of the family Thelaziidae. In the present study, we sequenced and characterized the mt genome of T. callipaeda. This AT-rich (74.6%) mt genome (13,668 bp) is circular and contains 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes, but lacks an atp8 gene. All protein-coding genes are transcribed in the same direction; the gene order is the same as those of Dirofilaria immitis and Setaria digitata (Onchocercidae), but distinct from Dracunculus medinensis (Dracunculidae) and Heliconema longissimum (Physalopteridae). Phylogenetic analyses of the concatenated amino acid sequence data for all 12 protein-coding genes by Bayesian inference (BI) showed that T. callipaeda (Thelaziidae) is related to the family Onchocercidae. This is the first mt genome of any member of the family Thelaziidae and should represent a new source of genetic markers for studying the epidemiology, ecology, population genetics and systematics of this parasite of humans and other mammals.

Human thelaziosis is an underestimated parasitic disease caused by the eyeworm Thelazia callipaeda (Spirurida: Thelaziidae). Although this parasite is of significance in humans in many Asian countries, its genetics, epidemiology and biology are poorly understood. Mitochondrial (mt) DNA can provide useful genetic markers for fundamental investigations, but no mt genome had been characterized for any members of the family Thelaziidae. In this study, we sequenced and characterized the mt genome of T. callipaeda. This circular mt genome is 13,668 bp long and contains 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes, but lacks an atp8 gene. Phylogenetic analyses of the concatenated amino acid sequence data for all 12 protein-coding genes by Bayesian inference showed that T. callipaeda is closely related to the family Onchocercidae, consistent with previous study. This is the first mt genome of any member of the family Thelaziidae, and represents a new source of genetic markers for studies of the epidemiology, ecology, population genetics and systematics of this parasite of human and animal health significance.

Mitochondrial cytochrome c oxidase subunit 1 (cox1) gene sequence of Spirocerca lupi (Nematoda, Spirurida): avenues for potential implications

Canine spirocercosis is a life-threatening parasitosis caused by Spirocerca lupi (Nematoda, Spirurida) that is presently emerging in several countries. This study characterised an informative region within the mitochondrial (mtDNA) gene encoding for the cytochrome c oxidase subunit 1 (cox1) of S. lupi by Polymerase Chain Reaction (PCR)-coupled sequencing. Specimens from five different countries in Europe, Asia and Africa were examined and two different sequence variants of cox1 (i.e. haplotypes) were determined, displaying nucleotidic variation at 6 of 689 positions. All of these positions were invariable among all the parasite individuals from Europe (haplotype 1) and among the African and Asian individuals (haplotype 2), but differed between Europe and Asia/Africa. The S. lupi cox1 sequences were consistent with those of other common Spirurida previously reported at both nucleotidic and phylogenetic levels. This study provides molecular information essential for identification of the nematode, irrespective of its life cycle stage. Crucial implications for the specific molecular diagnosis of clinical spirocercosis and investigation of the evolution, population genetics, ecology and epidemiology of S. lupi are discussed.

Phortica variegata as an intermediate host of Thelazia callipaeda under natural conditions: evidence for pathogen transmission by a male arthropod vector

Knowledge about Phortica variegata (Drosophilidae, Steganinae), the intermediate host of the eyeworm Thelazia callipaeda (Spirurida, Thelaziidae), is confined to experimental studies. To investigate the role P. variegata plays in the transmission of T. callipaeda under natural conditions, the population dynamics of these flies in the natural environment and their feeding preferences (on vegetables and/or animal lachrymal secretions) were examined. From April to November 2005, a total number of 969 (557 males and 412 females) P. variegata flies were collected weekly in a region of southern Italy with a history of canine thelaziosis. The flies were identified and dissected or subjected to a PCR assay specific for a region within the ribosomal ITS-1 DNA of T. callipaeda. The zoophilic preferences of P. variegata were assessed by collecting flies around the eyes of a person or around a fruit bait. Seven hundred and twenty flies (398 males and 322 females) were dissected under a stereomicroscope; 249 flies (158 males and 91 females) that died prior to the dissection were subjected to molecular investigation. Only P. variegata males were infected with larval T. callipaeda both at dissection (six, 0.83%) and with the specific PCR (seven, 2.81%), representing a total percentage of 1.34% flies infected. Interestingly, only males were collected around the eyes, compared with a male/female ratio of 1:4 around the fruit. This survey indicated that P. variegata males act as intermediate hosts of T. callipaeda under natural conditions in Europe. Both the zoophilic behaviour of P. variegata males on lachrymal secretions and their role as vector of T. callipaeda have been discussed as they represent a peculiarity in medical and veterinary entomology. The synchrony between the fly population dynamics and the biology of the nematode in the definitive host provides an interesting model for exploring the co-evolution of Thelazia spp. with their hosts.

Analysis of genetic variability within Thelazia callipaeda (Nematoda: Thelazioidea) from Europe and Asia by sequencing and mutation scanning of the mitochondrial cytochrome c oxidase subunit 1 gene

This study investigated genetic variability within the 'eyeworm'Thelazia callipaeda (Nematoda: Thelazioidea) from Europe and Asia by polymerase chain reaction (PCR)-coupled sequencing and mutation scanning of the mitochondrial cytochrome c oxidase subunit 1 gene (cox 1). Eight different sequence variants of cox 1 (haplotypes) were determined for the 50 individual adult specimens of T. callipaeda (from dogs, foxes or cats from Italy, Germany and the Netherlands and from dogs from China and Korea). Nucleotide variation (0.3--2%) was detected at 23 of 649 positions in the cox 1. Six of these positions were invariable among all 37 individuals from Europe and among the 13 individuals from Asia (irrespective of host origin) but differed (five G<-->A and one C<-->T changes) between Europe and Asia. PCR-based single-strand conformation polymorphism (SSCP) analysis of the most variable portion (v-cox 1) of the cox 1 was validated (for a subset of samples) as a tool to rapidly screen for genetic (haplotypic) variability. The results for the SSCP analysis and sequencing were concordant, indicating that the mutation scanning approach provides a useful tool for investigating the population genetics and molecular ecology of T. callipaeda.

Molecular characterization of Thelazia lacrymalis (Nematoda, Spirurida) affecting equids: a tool for vector identification

Equine thelaziosis caused by the eyeworm Thelazia lacrymalis is a parasitic disease transmitted by muscid flies. Although equine thelaziosis is known to have worldwide distribution, information on the epidemiology and presence of the intermediate hosts of T. lacrymalis is lacking. In the present work, a PCR-RFLP based assay on the first and/or second internal transcribed spacer (ITS1 and ITS2) of ribosomal DNA was developed for the detection of T. lacrymalis DNA in its putative vector(s). The sensitivity of the technique was also assessed. The restriction patterns obtained readily differentiated T. lacrymalis from four species of Musca (Diptera, Muscidae) (i.e. Musca autumnalis, Musca domestica, Musca larvipara and Musca osiris), which are potential vectors of equine eyeworms. The molecular assay presented herein is a useful tool to identify the intermediate host(s) of T. lacrymalis in natural conditions and to study its/their ecology and epidemiology.

Molecular Characterization of the First Internal Transcribed Spacer of Ribosomal DNA of the Most Common Species of Eyeworms (Thelazioidea: Thelazia)

Spirurid nematodes of the genus Thelazia cause ocular infection in several mammals and are transmitted by dipteran flies. Of the 10 described species, T. gulosa, T. rhodesi, T. skrjabini (affecting cattle), T. lacrymalis (affecting horses), and T. callipaeda (affecting carnivores and humans) are the most common. The aim of this study was to characterize the first internal transcribed spacer (ITS1) ribosomal DNA sequences of these 5 species. The length of the ITS1 sequences ranged from 357 bp (T. lacrymalis) to 905 bp (T. callipaeda). Interspecific differences ranged from 35 to 77%. Polymorphic sites were detected in each species. Intraspecific variation varied from 0.3 to 2.5%. The characteristics of the ITS1 of Thelazia spp. show similarities to those of other Spirurida. The findings of this present study show that the ITS1 represent a powerful genetic marker for the molecular identification of eyeworms and a useful tool for developing molecular epidemiological techniques to study Thelazia spp. transmission patterns and prevalence in definitive and intermediate hosts.

Molecular epidemiological survey on the vectors of Thelazia gulosa, Thelazia rhodesi and Thelazia skrjabini (Spirurida: Thelaziidae)

A Polymerase Chain Reaction (PCR)- based assay developed for the specific identification of Thelazia gulosa, Thelazia rhodesi and Thelazia skrjabini (Nematoda, Spirurida), which cause bovine ocular thelaziosis, was evaluated for its usefulness in detecting the intermediate hosts and in estimating the infection prevalence of vectors in field conditions throughout 5 years (from 1997 to 2001). A total of 5190 flies were captured and identified as Musca larvipara, Musca osiris, Musca autumnalis, Musca tempestiva or Musca domestica. Genomic DNA was extracted from pools constituted by heads, thoraces, abdomens and wings of 10 flies of each species, and 2076 samples were subjected to a PCR assay to specifically detect the ribosomal ITS-1 sequence of bovine Thelazia. Amplicons were sequenced and subjected to digestion with CpoI restriction enzyme. M. autumnalis, M. larvipara, M. osiris and M. domestica species were shown to be PCR positive. T. gulosa was specifically detected by PCR in M. autumnalis, M. larvipara, M. osiris and M. domestica, whereas T. rhodesi is in M. autumnalis and M. larvipara. Of 27 positive samples, 23 were positive for T. gulosa and 4 for T. rhodesi, with a mean prevalence of 2·86% in the whole fly population collected. The highest mean prevalence values of infection were detected in M. autumnalis (4·46%) and M. larvipara (3·21%), and the former species was confirmed to be the vector of T. gulosa and T. rhodesi. This study is the first report of M. osiris as a vector of T. gulosa and M. larvipara as a vector of T. gulosa and T. rhodesi under natural conditions. The occurrence of Thelazia in fly populations in the Apulia region of Italy (in the 5 grazing seasons considered) indicates that cattle thelaziosis is enzootic in southern Italy. This molecular assay should be a useful epidemiological tool for assessing the role of different species of flies as intermediate hosts of thelaziae.

Differentiation among three species of bovine Thelazia (Nematoda: Thelaziidae) by polymerase chain reaction-restriction fragment length polymorphism of the first internal transcribed spacer ITS-1 (rDNA)

Thelazia gulosa, Thelazia rhodesi and Thelazia skrjabini are nematodes transmitted by some species of Musca (Diptera: Muscidae) which cause ocular infestations in bovines. Differences in the rDNA of these species were determined by a PCR using different sets of relatively conserved oligonucleotide primers. PCR on the first internal transcribed spacer (ITS-1) revealed differences in size in Thelazia species (437 bp for T. gulosa, 370 bp for T. rhodesi and 506 bp for T. skrjabini) while the DNA control of Musca spp. was not amplified. The ITS-1 amplicons of the three species were sequenced and then analysed. The GC contents ranged from 26 to 36% and the level of differences in the nucleotide sequences of ITS-1 was lower between T. skrjabini and T. gulosa (39%) than the latter and T. rhodesi (49-56%). Restriction fragment length polymorphism (RFLP) of ITS-1 amplicons was also carried out and the restriction profiles compared. Clear genetic differences among the three Thelazia examined were demonstrated by using the enzymes HpaII, CpoI and SspI. This PCR-RFLP for the delineation of T. gulosa, T. rhodesi and T. skrjabini offers prospects as a molecular epidemiological tool to study parasite transmission patterns and prevalence.

A phylogenetic analysis of filarial nematodes: comparison with the phylogeny of Wolbachia endosymbionts

Infection with the endosymbiotic bacteria Wolbachia is widespread in filarial nematodes. Previous studies have suggested concordance between the phylogeny of Wolbachia with that of their nematode hosts. However, there is only one published molecular phylogenetic study of filarial species, based on the 5S rRNA gene spacer. The phylogeny proposed by this study is partially incongruent with previous classifications of filarial nematodes, based on morphological characters. Furthermore, both traditional classifications and molecular phylogenies are, in part, inconsistent with the phylogeny of Wolbachia. Here we report mitochondrial cytochrome oxidase I (COI) gene sequences for 11 species of filaria and for another spirurid nematode which was included as an outgroup. In addition, 16S rRNA, wsp and ftsZ gene sequences were generated for the Wolbachia of several filarial species, in order to complete the available data sets and further resolve the phylogeny of Wolbachia in nematodes. We used these data to evaluate whether nematode and Wolbachia phylogenies are concordant. Some of the possible phylogenetic reconstructions based on COI gene were congruent with the phylogeny of Wolbachia and supported the grouping of the rodent filaria Litomosoides sigmodontis with the lymphatic filariae (i.e. Brugia spp. and Wuchereria spp.) and the sister group relationship of Dirofilaria spp. and Onchocerca spp. However, the placement of the Wolbachia-free filaria Acanthocheilonema viteae is ambiguous and dependent on the phylogenetic methods used.