This paper focuses on the species diversity among the Trichostrongylidae Leiper, 1912 (Nematoda: Strongylida), and complexity of the family systematics. Polymorphism (subfamilies: Ostertagiinae, Cooperiinae and Haemonchinae), the presence of cryptic species (genus: Teladorsagia) and hybridization (genera: Cooperia, Haemonchus and Ostertagia) are presented and discussed, considering both morphological and molecular evidence. Some of these phenomena are common, nevertheless not sufficiently understood, which indicates the need for expanding the current state of knowledge thereof. Within the Trichostrongylidae, species distinction supported merely by morphological features is difficult, and requires confirmation by means of molecular methods. The parasitic nematode taxonomy is complicated mainly by the genus Teladorsagia, but complexity may also be expected among other Ostertagiinae (e.g. in the genera Ostertagia and Marshallagia). The data presented here show that the members of the Trichostrongylidae can significantly complicate unambiguous species identification. Hence, it is essential to consider the phenomena mentioned, to gather valid and comparable data on the biodiversity of this family.

Symbiotic bacteria are a common feature of many animals, particularly invertebrates, from both aquatic and terrestrial habitats. These bacteria have increasingly been recognized as performing an important role in maintaining invertebrate health. Both ecto- and endoparasitic helminths have also been found to harbour a range of bacterial species which provide a similar function. The part symbiotic bacteria play in sustaining homeostasis of free-living invertebrates exposed to anthropogenic pressure (climate change, pollution), and the consequences to invertebrate populations when their symbionts succumb to poor environmental conditions, are increasingly important areas of research. Helminths are also susceptible to environmental stress and their symbiotic bacteria may be a key aspect of their responses to deteriorating conditions. This article summarizes the ecophysiological relationship helminths have with symbiotic bacteria and the role they play in maintaining a healthy parasite and the relevance of specific changes that occur in free-living invertebrate–bacteria interactions under anthropogenic pressure to helminths and their bacterial communities. It also discusses the importance of understanding the mechanistic sensitivity of helminth–bacteria relationships to environmental stress for comprehending the responses of parasites to challenging conditions.

Conventional identification of Paragonimus species and their natural definitive hosts is based on the morphological features of adult parasites isolated from the lungs of wild mammalian hosts. However, wild animals are protected by strict regulations and sampling is not always possible. Recently, molecular techniques have been developed to identify the internal transcribed spacer (ITS) sequences of Paragonimus eggs in faeces/sputum of human patients. Also, mammalian hosts can be identified using the D-loop sequence of mitochondrial DNA in faecal samples. In this study, we used molecular techniques on faeces from wild animals collected in Da Krong Nature Reserve, Quang Tri province, central Vietnam, where Paragonimus metacercariae are highly prevalent in mountain crabs, to identify Paragonimus species and their natural definitive hosts. The results indicated that wild cats, Prionailurus bengalensis, were infected with at least three different Paragonimus species, P. westermani, P. skrjabini and P. heterotremus. Because all of these species can infect humans in Asian countries, human paragonimiasis should be considered in this area.

The present study focuses on the nematode community in the stomachs of three sympatric anatid bird species from the Central Patagonian coast, Argentina. The bird species include the Chubut steamer duck, Tachyeres leucocephalus, the crested duck, Lophonetta specularioides, and the black-necked swan, Cygnus melancoryphus. Up to 138 nematodes representing five species were recovered from 10 of the 13 ducks examined, with an overall prevalence of 77% and a mean intensity of 13.8. Nematodes isolated from the gizzard were Streptocara formosensis and Sciadiocara legendrei (Acuariidae) in T. leucocephalus, and Epomidiostomum vogelsangi (Amidostomatidae) in C. melancoryphus, whereas Echinuria uncinata (Acuariidae) and Tetrameres (Petrowimeres) fissispina (Tetrameriidae) were found in the proventiculus of L. specularioides. In particular, S. legendrei was registered for the first time in South America and T. leucocephalus, whereas T. fissispina represents a new record in Argentina and L. specularioides. Moreover, E. vogelsangi and E. uncinata were isolated in Patagonia for the first time. The birds studied herein are sympatric in their distribution, and two of them are syntopic breeders; however, they were infected with different parasite species. This situation could be partially due to their diet or their seasonal movements, or a combination of both. Despite the low number of hosts examined, this work enhances our knowledge about parasites from a frequently occurring group of birds on the Patagonian coast, a subject that has not been studied extensively in South America.

Tylodelphys aztecae n. sp. (Digenea: Diplostomidae) is described from adult specimens obtained from the intestine of the pied-billed grebe (Podilymbus podiceps) and the metacercariae found in the body cavity of freshwater fishes of the families Goodeidae and Cyprinidae in eight localities across central and northern Mexico. The new species is mainly distinguished from the other four described species of Tylodelphys from the Americas (T. adulta, T. americana, T. elongata and T. brevis) by having a forebody slightly concave, a larger ventral sucker, two larger pseudosuckers and by having between 2 and 7 eggs in the uterus. Partial DNA sequences of the mitochondrial gene cytochrome c oxidase subunit I (cox1), and the internal transcribed spacers (ITS1+5.8S+ ITS2) of the ribosomal DNA, were generated for both developmental stages and compared with available sequences in GenBank of other congeners. The genetic divergence estimated among Tylodelphys aztecae n. sp. and other congeneric species varied from 12 to 15% for cox1, and from 3 to 11% for ITS. In contrast, the genetic divergence among metacercariae and adults of the new species was very low, ranging between 0 and 1% for cox1 and between 0 and 0.3% for ITS. Phylogenetic analyses inferred with both molecular markers using maximum likelihood and Bayesian inference placed the adults and their metacercariae in a single clade, confirming that both stages are conspecific. The morphological evidence and the genetic divergence, in combination with the reciprocal monophyly in both phylogenetic trees, support the hypothesis that the diplostomids found in the intestines of the pied-billed grebe bird and the body cavity from goodeid and cyprinid fishes in central and northern Mexico represent a new species.

Parasitic infections influence the health of captive forest musk deer (Moschus berezovskii) and affect population increases. Nevertheless, there are few quantitative studies regarding forest musk deer parasites, and there is no common preservation method or flotation solution used for detection of faecal parasites because of the biology of the worms and the host physiological state. The objective of this study was to evaluate preservation and flotation methods for the detection of nematode eggs and coccidian oocysts in faeces of the forest musk deer. The McMaster technique was used to count nematode eggs and coccidian oocysts in 33 samples of faeces. For the nematode eggs, the differences among flotation solutions were significant (P< 0.01), with sodium nitrate being the best flotation solution, and the combination of freezing and sodium nitrate resulted in the greatest number of eggs per gram (EPG = 209.4 ± 67.8). For the coccidian oocysts, the interaction between preservation method and flotation solution was significant (P< 0.01), and the combination of formalin and sodium chloride yielded the greatest number of oocysts per gram (OPG = 1010.7 ± 162.3). The forest musk deer had a high prevalence of parasitic infections, with the parasite load of coccidia (96.4%) significantly greater than that of nematodes (71.9%, P< 0.01). These results confirm that captive forest musk deer suffer from serious parasitic invasions and demonstrate that the novel method described here could be utilized for parasitological diagnosis, detection and prevention in species of Moschidae and Cervidae.

Largemouth bass, Micropterus salmoides, is a native fish species with special importance for sport fishing competitions in Nuevo León, Mexico. However, no study has investigated the parasitic fauna of M. salmoides, and no reports are available on monogenean parasites in this fish species. Therefore, we described the monogenean parasites of M. salmoides and the effects of season and fish condition factor in five reservoirs: La Boca (LB), El Cuchillo–Solidaridad (CS), Sombreretillo (S), Laguna Salinillas (LS) and Cerro Prieto (CP). The monogeneans infecting M. salmoides were Clavunculus unguis and Acolpenteron ureteroecetes (collected in all localities), as well as Syncleithrium fusiformis, Haplocleidus furcatus, Clavunculus bifurcatus and Urocleidus principalis (CS). Clavunculus unguis had the highest prevalence in fish from all reservoirs. The abundance of monogeneans was generally greater in late spring to autumn than in winter. Although season was not correlated with abundance (rs = 0.0934, P <  0.0154), the months of highest temperature (from May to September) were positively correlated with parasite abundance. A significant association was observed between fish condition factor and the presence of monogeneans (P <  0.05), except for A. ureteroecetes. Our findings include five new geographic records for C. unguis, S. fusiformis, H. furcatus and C. bifurcatus.

Urocleidoides ectoparasites are mainly found on fish of the neotropical regions. Although molecular research on monogeneans is available, no genetic data exist characterizing species in the Urocleidoides genus. Some DNA sequences have been efficacious in systematic studies and in the reconstruction of phylogenies of fish parasites. Relevant roles have been given to the sequence of the mitochondrial gene of cytochrome c oxidase I (COI). This study characterized COI sequences of the parasites Urocleidoides malabaricusi and U. cuiabai in trahira fish Hoplias aff. malabaricus of the flood plain of the Upper River Paraná, Brazil. The two species under analysis were distinguished by sequencing and analysing a 420-bp fragment of the COI gene, which suggested the existence of the cryptic species U. malabaricusi.

The aim of this study was to determine the role in contractions of postsynaptic nicotinic acetylcholine (nACh) and γ-aminobutyric acid (GABA) receptors, in the bag region of Ascaris suum muscle cells, as well as the role of synaptic receptors between interneurons and motor neurons in the dorsal and ventral nerve cord. We have measured the isometric contractions of isolated segments of A. suum, with or without the nerve cord (dorsal or ventral). Contractions were caused by increasing concentrations of ACh or by electrical field stimulation (EFS). Based on our results, the presence of the nerve cord is essential for the contractile effects of ACh. The EC50 value of ACh for innervated muscle strips was 10.88 μm. Unlike intact (innervated) preparations, there was no contraction of the muscle flaps when the nerve cord was mechanically removed. Furthermore, continuous EFS produced stable contractions of innervated muscle strips, but they are not sensitive to mecamylamine (100 μm). However, GABA (30 μm) significantly inhibited the EFS-induced contractions. EFS with the same characteristics did not cause muscle contractions of denervated muscle strips, but EFS with a wider pulse induced the increasing of tone and irregular contractions. These contractions were completely insensitive to the effect of GABA. The EC50 for ACh did not differ between the dorsal and ventral segments (9.83 μm and 9.45 μm), while GABA exhibited features of competitive and non-competitive antagonists, regardless of whether it acted on the dorsal or ventral segments of A. suum. It is obvious that drugs will be more effective if they act on both the synaptic and extrasynaptic nACh and GABA receptors.

The possible environmental effects of the massive use of Duddingtonia flagrans for controlling sheep nematodes were evaluated in two regions. Non-supplemented faeces and faeces from sheep supplemented with D. flagrans were deposited three times on pasture plots and samples were collected 7 and 14 days post-deposition. Samples were cultured in agar-water (2%) with Panagrellus spp. to recover D. flagrans and other nematophagous fungi, and soil nematodes were extracted using Baermann funnels and counted. No significant differences in the populations of soil nematodes and fungi colonizing sheep faeces (P > 0.05) were observed between supplemented and non-supplemented groups, except in one sample. The topsoil in contact with the faeces was sampled 1–4 months post-deposition, revealing that, with one exception, D. flagrans did not persist in soil beyond 2 months post-deposition. Duddingtonia flagrans does not affect faecal colonization by other fungi and soil nematodes and, once deployed on pasture, does not survive for long periods in the environment.

The nervous systems of three Tylodelphys metacercariae (T. mashonense, Tylodelphys spp. 1 and 2) co-occurring in the cranial cavity of the catfish, Clarias gariepinus, were examined by the activity of acetylthiocholine iodide (AcThI), with the aim of better understanding the arrangement of sensillae on the body surface and the nerve trunks and commissures, for taxonomic purposes. Enzyme cytochemistry demonstrated a comparable orthogonal arrangement in the three metacercariae: the central nervous system (CNS) consisting of a pair of cerebral ganglia, from which anterior and posterior neuronal pathways arise and inter-link by cross-connectives and commissures. However, the number of transverse nerves was significantly different in the three diplostomid metacercariae: Tylodelphys sp. 1 (30), Tylodelphys sp. 2 (21) and T. mashonense (15). The observed difference in the nervous system of the three metacercariae clearly separates them into three species. These findings suggest that consistent differences in the transverse nerves of digenean metacercariae could enable the differentiation of metacercariae to the species level in the absence of molecular techniques. This, however, might require further testing on a larger number of species of digenean metacercariae.

In this study we present the first approach to exploration of the genetic diversity of Cuban Fasciola hepatica populations using microsatellite markers, coupled with observed prevalence in slaughterhouses. Nine populations of flukes recovered from cows and buffalos were studied in the central-western region of Cuba. The observed infection rates of definitive hosts (bovines) were 70–100% in most cases. An important amount of polymorphism was found in the four loci explored. However, no apparent genetic differences were found between populations from different provinces or bovine species. The absence of deviations from Hardy–Weinberg equilibrium suggests a high rate of cross-fertilization between F. hepatica individuals. This result was confirmed when all multilocus genotypes were tested for clonal reproduction and only four individuals differed statistically (Psex< 0.05). High values of expected heterozygosity coupled with highly probable mixing among strains make the metapopulation genetically diversified but similar in terms of certain alleles (low FST values). These results suggest a close relationship between parasite diversity and cattle management in Cuba. Our findings should be taken into consideration by veterinary authorities to help mitigate fasciolosis transmission.

The life cycle of Proctoeces maculatus (Looss, 1901) (Digenea, Fellodistomidae) was studied in Bizerte Lagoon (Tunisia). Three sequential hosts appear to be involved: the Mediterranean mussel Mytilus galloprovincialis Lamarck, 1819 (Mytilidae) as the first intermediate host; the polychaete Sabella pavonina Savigny, 1822 (Sabellidae), as the second intermediate host; and fishes (Lithognathus mormyrus (Linnaeus, 1758) (Sparidae), Trachinotus ovatus (Linnaeus, 1758) (Carangidae) and Sparus aurata Linnaeus, 1758 (Sparidae) as the definitive hosts. It should be noted that S. pavonina was recorded as second intermediate host for P. maculatus for the first time. Molecular confirmation of the morphological identification of the life-cycle stages of this digenean was obtained using partial 28S rDNA sequences. Comparative sequences revealed that the sporocysts and the metacercariae are conspecific but they diverged by 0.3% from the adults. The present results raised the possibility of the existence of cryptic species within the different developmental stages. However, all the present isolates differed from material from Archosargus probatocephalus in the Gulf of Mexico identified as P. maculatus.

Angiostrongylus cantonensis is primarily considered an emerging infectious agent of eosinophilic meningitis or meningoencephalitis with a worldwide distribution. Rodents and snails are important invasive hosts for transmission and expansion of A. cantonensis. The objective of this study was to investigate infection levels of A. cantonensis in snails, the most important natural intermediate host. Our study location was Mueang Kamphaeng Phet district, Kamphaeng Phet Province, and was undertaken between October and December 2012. A total of 2228 freshwater and terrestrial snails were collected, comprising 1119 Filopaludina spp., 409 Pomacea caniculata, 275 Achatina fulica and 425 Cryptozona siamensis. Angiostrongylus larvae were isolated by artificial digestion methods following Baermann's techniques. A low prevalence and intensity of A. cantonensis were observed in A. fulica, while higher numbers were found in C. siamensis. None of the Filopaludina spp. and Pomacea caniculata were infected with A. cantonensis. Molecular characterization was performed by analysing the 264 bp of cytochrome c oxidase subunit I (COI). Three COI sequences of Angiostrongylus were identical to A. cantonensis with 91–99% identity. Cryptozona siamensis has not previously been recorded as an intermediate host for A. cantonensis in Thailand. The infection of A. cantonensis identified in the natural intermediate hosts is new and important information to assist in the prevention and control of human angiostrongyliasis.

In an aquatic environment, there is a profound and inverse relationship between environmental quality and disease status of fish. Parasites are one of the most serious limiting factors in aquaculture. Therefore, the present investigation was carried out during the period of February–December 2014 to determine the parasitic infections in the African sharptooth catfish Clarias gariepinus, relative to the capability of internal parasites to accumulate heavy metals. Up to 100 catfish were examined for gastrointestinal helminths and 38% of fish were found to be infected with the cestode Polyonchobothrium clarias. The morphology of this parasite species, based on light and scanning electron microscopy, revealed that the adult worm was characterized by a rectangular scolex measuring 0.43–0.58 (0.49 ± 0.1) mm long and 0.15–0.21 (0.19 ± 0.1) mm wide, with a flat to slightly raised rostellum armed with a crown with two semicircles each bearing 13–15 hooks, followed by immature, mature and gravid proglottids which were about 29–55 (45), 16–30 (24) and 15–39 (28) in number, respectively. The mature proglottid contained a single set of genitalia in which medullary testes measured 0.09–0.13 (0.11 ± 0.01) mm long and 0.05–0.08 (0.06 ± 0.01) mm wide; a bi-lobed ovary was situated near the posterior margin of the proglottid, extending laterally up to the longitudinal excretory canals; the tubular uterus arose from the ootype up to the anterior margin of the proglottid; and vitelline follicles were cortical. The greater portion of the gravid proglottid was occupied by a uterus filled with unoperculate and embryonated eggs. Chemical analysis confirmed that the concentrations of heavy metals (Zn, Cu, Mn, Cd, Ni and Pb) accumulated in P. clarias were higher than in fish tissues and values recommended by FAO/WHO, with the exception of Zn, which was found to be higher in fish kidneys than in the cestode. This supports the hypothesis that cestodes of fish can be regarded as useful bioindicators when evaluating the environmental pollution of aquatic ecosystems by heavy metals.

Experimental co-infections of juvenile and pre-adult Pseudosuccinea columella with Calicophoron daubneyi and Fasciola hepatica (five miracidia of each digenean per snail) were carried out to determine the aptitude of this lymnaeid to ensure complete larval development of the former parasite, the latter or both. Snails infected with F. hepatica were found in the two groups of juveniles, i.e. 1 and 2 mm at exposure, and the four groups of pre-adults, i.e. 3–6 mm. The highest frequency of F. hepatica, i.e. 37.3%, was noted in the 4 mm group. Low frequencies were noted for C. daubneyi and co-infections of both digeneans in the 3, 4 and 5 mm groups. Two other groups of P. columella, measuring 3 and 4 mm at exposure, were also constituted to study the characteristics of these co-infections. Compared to controls infected only with F. hepatica, the frequency of this digenean infection and the mean number of metacercariae were significantly lower in co-infected snails, while the patent period was significantly shorter. In snails harbouring C. daubneyi only or both digeneans, lower values were noted for prevalence, the patent period and the number of metacercariae. Pre-adult P. columella (3–5 mm in shell height at exposure) were able to sustain larval development of C. daubneyi if they were co-infected with the sequence C. daubneyi +F. hepatica. Low values noted for the prevalence of C. daubneyi infection and the number of metacercariae would be in favour of a still incomplete adaptation between the snail population and the miracidial isolate.

The present study tests the anti-inflammatory and anti-fibrotic effects of silymarin alone or combined with mefloquine on acute schistosomiasis by evaluating parasitological, histopathological, biochemical and immunological parameters. Male CDI Swiss mice were divided into seven groups, which included healthy controls, mice infected with Schistosoma mansoni or treated with silymarin (140 mg/kg body weight) or mefloquine (400 mg/kg body weight), or mice treated with a combination of both drugs and uninfected mice simply treated with mefloquine or silymarin alone. All mouse groups were sacrificed 8 weeks post-infection (pi) and/or post-treatment. Those infected mice treated with both silymarin and mefloquine showed a significant decrease (P <  0.001) in worm burden, immunoglobulins (IgG and IgM), liver function enzymes and granuloma diameter, with complete eradication of immature and mature eggs. In conclusion, treatment with silymarin combined with mefloquine in murine schistosomiasis was able to reduce granulomatous reactions and hepatic fibrosis. Hence, this combination is a new strategy to be studied as an efficient tool in the treatment of schistosomal liver fibrosis.

Experimental Echinococcus multilocularis infection and deworming was repeated three or five times in nine dogs at various re-infection schedules. The mean number of worms decreased more than 91% in dogs with repeated infection, compared to first infection controls (n= 6). The copro-antigen assay and the egg count in the faeces suggested that the worm burden gradually decreased each time the dogs were re-infected. To examine whether such worm exclusion was a non-specific response, five dogs were sequentially infected with the parasite four times and subsequently fed freely for 6 months. Even after the 6-month interval, the five dogs that were infected five times with the parasite were still able largely to exclude the adult worms. The results suggested that the ability of worm exclusion in dogs that developed a resistance did not become rapidly extinct. Observation of the condition of faeces and the excretion of hooks in the faeces of repeatedly infected dogs revealed that the exclusion of worms started at the first week after the re-infection, and it continued during the patent period. Serum antibodies specific to the parasite antigen increased gradually until the third infection and significantly decreased during the 6-month interval. There was little enhancement of serum antibodies after the fifth infection in most dogs, although no clear correlation was observed between the antibody response and the worm burden. These findings suggested the possibility of developing a vaccine.

Ocular lesions have been reported in patients with schistosomiasis; however, the problem with studying schistosomal infection of the human eye is that biopsies are almost impossible to take, and histopathological examination of suspicious lesions can only be undertaken post-mortem or after enucleation. This work aimed to study the possible effects and pathogenesis of schistosomiasis on the eye. This study involved 55 hamsters; five hamsters remained non-infected and the remaining 50 hamsters were infected with Schistosoma mansoni cercariae. Infected hamsters were sacrificed on weeks 8, 12, 16 and 20 post-infection (pi). Eye sections were prepared and stained for histopathological and immunohistochemical studies. Histopathological changes detected in hamsters infected after 16 and 20 weeks included looseness and oedema of the innermost retinal layers together with hyperplastic polypoid growth. Neither eggs nor granulomata were detected in eye sections throughout the experimental period. Deposition of S. mansoni antigen was revealed in 35% of infected hamsters. Later, on weeks 16 and 20 pi, moderate subepithelial conjuctival deposits and marked subchoroidal and scleral deposition were detected. In conclusion, the deposition of schistosomal antigen and immune complexes may play a pivotal role in the ocular changes that occur in schistosomiasis, even in the absence of detectable Schistosoma eggs. Schistosomiasis should be suspected in cases with unexplained ophthalmological findings, especially in endemic areas.

Parasites represent a great, unknown component of animal biodiversity. Recent efforts have begun to uncover patterns of infection by helminth parasites in several Neotropical lizards. The present study reports, for the first time, levels of helminth infection in a population of the flat lizard Tropidurus semitaeniatus. One hundred and thirty-nine lizards were examined and evidence of five intestinal helminth species was found, comprising four species of nematodes, one species of cestode and an unidentified encysted larval nematode. The most frequently occurring species was the intestinal nematode Parapharyngodon alvarengai, which did not exhibit differences in prevalence and intensity of infection relative to host sex or age/body size. Furthermore, helminth species richness was not related to host body size.