Further studies of Dirofilaria roemeri (Nematoda: Filarioidea) in naturally and experimentally infected Macropodidae.

Larval development of D. roemeri occurs in the subcutaneous and intermuscular connective tissue and intramuscularly in the pelvic region and hind limbs of the wallaroo and eastern grey kangaroo. Host response to developing larvae is not evident at 1, 14 and 28 days. The development of D. roemeri in the red kangaroo exhibits features previously observed in both normal and abnormal hosts. Low-level blood microfilaraemia of brief duration occurs in the red kangaroo, which may act as a secondary reservoir of infection for other kangaroo and wallaby species. Among commercially harvested Macropodidae in Queensland there is a greater prevalence of D. roemeri in wallaroos and grey kangaroos than in red kangaroos. Infection is most prevalent in animals from south-central and south-western districts.     

Distribution of third-stage Dirofilaria roemeri (Nematoda: Filarioidea) in the tissues of tabanidae (Diptera)

The distribution of third-stage D. roemeri in its tabanid intermediate host was observed in histological sections of naturally infected Dasybasis oculata and Tabanus parvicallosus. Larvae invade the brain, eye, nerve cord, muscles of the mouthparts, horizontal and indirect flight muscles, fat body, hind gut and gonad of flies. Third-stage D. roemeri migrate from the abdomen via the haemocoelic spaces of the thorax to the head of the fly. Evidence suggests that larvae escape from the intermediate host by rupturing the tip of the labrum or the labro-epipharyngeal membranes. Injury was observed in the eye, nerve cord and musculature. There was no evidence that the parasite had a detrimental effect on the host and tabanids showed no response to the presence of filarioids. Species of Dasybasis and Tabanus acting as intermediate host of D. roemeri in nature epitomize the concept of a ‘good’ host.     

Vermetid gastropods as key intermediate hosts for a lineage of marine turtle blood flukes (Digenea: Spirorchiidae), with evidence of transmission at a turtle rookery

Blood flukes of the family Spirorchiidae Stunkard, 1921 are significant pathogens of marine turtles, both in the wild and in captivity. Despite causing considerable disease and mortality, little is known about the life cycles of marine species, with just four reports globally. No complete life cycle has been elucidated for any named species of marine spirorchiid, but the group is reported to use vermetid and fissurellid gastropods, and terebelliform polychaetes as intermediate hosts. Here we report molecular evidence that nine related spirorchiid species infect vermetid gastropods as first intermediate hosts from four localities along the coast of Queensland, Australia. ITS2 rDNA and cox1 mtDNA sequence data generated from vermetid infections provides the first definitive identifications for the intermediate hosts for the four species of Hapalotrema Looss, 1899 and Learedius learedi Price, 1934. Additionally, we provide a new locality report for larval stages of Amphiorchis sp., and evidence of three additional unidentified spirorchiid species in Australian waters. Based on the wealth of infections from vermetids during this study, we conclude that the previous preliminary report of a fissurellid limpet as the intermediate host for L. learedi was likely mistaken. The nine species found infecting vermetids during this study form a strongly supported clade exclusive of species of the other two marine spirorchiid genera for which sequence data are available; Carettacola Manter & Larson, 1950 which falls sister to the vermetid-infecting clade + a small clade of freshwater spirorchiids, and Neospirorchis Price, 1934 which is distantly related to the vermetid-infecting clade. We provide further evidence that spirorchiid transmission can occur in closed system aquaria and show that spirorchiid transmission occurs at both an important turtle rookery (Heron Island, southern Great Barrier Reef, Australia) and foraging ground (Moreton Bay, Australia). We discuss the implications of our findings for the epidemiology of the disease, control in captivity, and the evolution of vermetid exploitation by the Spirorchiidae.     

A new intermediate host for Echinococcus multilocularis: The southern red-backed vole (Myodes gapperi) in urban landscape in Calgary,Canada

Human Alveolar Echinococcosis (HAE) is a potentially fatal parasitic disease caused by Echinococcus multilocularis, a cestode characterized by a sylvatic life-cycle involving several species of rodents and lagomorphs as intermediate hosts and canids as definitive hosts. Despite the wide distribution of the parasite in North America, the number of competent intermediate host species identified to date is still relatively small, and mainly includes the northern vole (Microtus oeconomus), brown lemming (Lemmus sibiricus), northern red-backed vole (Myodes rutilus), deer mouse (Peromyscus maniculatus) and meadow vole (Microtus pennsylvanicus).By monitoring the infections in rodents in the city of Calgary (Alberta, Canada), we have detected a case of severe alveolar echinococcosis in a southern red-backed vole (Myodes gapperi), a species never reported before as an intermediate host for this parasite. Observation of protoscolices in the intra-abdominal multilocular cysts indicates that M. gapperi could act as a competent intermediate host for the transmission of E. multilocularis.Since M. gapperi can be found in close proximity to, and within metropolitan areas, this species could play a role in the establishment and maintenance of the sylvatic life-cycle of E. multilocularis in urban landscapes, where the potential for zoonotic transmission is higher. The new intermediate host reported needs to be taken into account in future surveys and transmission models for this parasite.     

Meteorological effects on the daily activity patterns of tabanid biting flies in northern Queensland,Australia

Information on the daily activity patterns of tabanid flies is important in the development of strategies that decrease the risk of pathogens transmitted by them. In addition, this information is useful to maximize numbers of tabanids trapped during short‐term studies and to target feeding behavior studies of certain tabanid species to their times of peak activity. The current study examined the effects of various meteorological factors on the daily activity patterns of common tropical species of tabanids in north Queensland. Each species studied responded differently to weather factors. Tabanus townsvilli Ricardo (Diptera: Tabanidae) was most active during late morning and early afternoon, whereas Pseudotabanus silvester (Bergroth) and Tabanus pallipennis Macquart were most active in the late afternoon. Tabanus dorsobimaculatus Macquart was most active in the morning and early afternoon. Data on daily activity patterns of tabanid flies indicates that in an area such as Townsville, North Queensland, where several species of tabanid are present concurrently in high numbers, the overlapping periods of high activity for these species indicate a high risk of pathogen transmission for most of the day (10.00–19.00 hours). Similarly, because each species responds differently to weather variables, only extreme weather conditions are likely to inhibit activity of all species. These data also indicate that for maximal results, trapping and feeding behavior studies should be tailored to the preferred activity period of the species under investigation.     

Non-Specific Manipulation of Gammarid Behaviour by P. minutus Parasite Enhances Their Predation by Definitive Bird Hosts

Trophically-transmitted parasites often change the phenotype of their intermediate hosts in ways that increase their vulnerability to definitive hosts, hence favouring transmission. As a “collateral damage”, manipulated hosts can also become easy prey for non-host predators that are dead ends for the parasite, and which are supposed to play no role in transmission strategies. Interestingly, infection with the acanthocephalan parasite Polymorphus minutus has been shown to reduce the vulnerability of its gammarid intermediate hosts to non-host predators, whose presence triggered the behavioural alterations expected to favour trophic transmission to bird definitive hosts. Whilst the behavioural response of infected gammarids to the presence of definitive hosts remains to be investigated, this suggests that trophic transmission might be promoted by non-host predation risk. We conducted microcosm experiments to test whether the behaviour of P. minutus-infected gammarids was specific to the type of predator (i.e. mallard as definitive host and fish as non-host), and mesocosm experiments to test whether trophic transmission to bird hosts was influenced by non-host predation risk. Based on the behaviours we investigated (predator avoidance, activity, geotaxis, conspecific attraction), we found no evidence for a specific fine-tuned response in infected gammarids, which behaved similarly whatever the type of predator (mallard or fish). During predation tests, fish predation risk did not influence the differential predation of mallards that over-consumed infected gammarids compared to uninfected individuals. Overall, our results bring support for a less sophisticated scenario of manipulation than previously expected, combining chronic behavioural alterations with phasic behavioural alterations triggered by the chemical and physical cues coming from any type of predator. Given the wide dispersal range of waterbirds (the definitive hosts of P. minutus), such a manipulation whose efficiency does not depend on the biotic context is likely to facilitate its trophic transmission in a wide range of aquatic environments.     

Freshwater fishes of thailand as experimental intermediate hosts for Capillaria philippinensis

Bhaibulaya M., Indra-Ngarm S. and Ananthapruti M. 1979. Freshwater fishes of Thailand as experimental intermediate hosts for Capillaria philippinensis. The International Journal for Parasitology9: 105–108. Nine species of freshwater fishes from Thailand have been exposed to infection with embryonated eggs of Capillaria philippinensis. The eggs were fed to fishes with food or through a polyethylene tube. After 10–30 days larvae capable of establishing intestinal capillariasis in Mongolian gerbils were recovered from six fish species: Cyprinus carpio, Puntius gonionotus, Aplocheilus panchax, Gambusia holbrookii, Rasbora borapelensis, and Trichopsis vittatus. Larvae were not recovered from Tilapia nilotica, Osteochilus hasseltii and Trichogaster trichopterus. Five human cases of intestinal capillariasis have been reported from widely scattered areas of Thailand and the natural intermediate and definitive hosts remain to be determined.     

Gastropod first intermediate hosts for two species of Monorchiidae Odhner, 1911 (Trematoda): I can’t believe it’s not bivalves!

The trematode superfamily Monorchioidea comprises three families of teleost parasites: the Monorchiidae Odhner, 1911, Lissorchiidae Magath, 1917, and Deropristidae Cable & Hunninen, 1942. All presently known lissorchiid and deropristid life cycles have gastropods as first intermediate hosts, whereas those of monorchiids involve bivalves. Here, we report an unexpected intermediate host for monorchiids; two species of Hurleytrematoides Yamaguti, 1954 use gastropods as first intermediate hosts. Sporocysts and cercariae were found infecting two species of the family Vermetidae, highly specialised sessile gastropods that form calcareous tubes, from two locations off the coast of Queensland, Australia. These intramolluscan infections broadly corresponded morphologically to those of known monorchiids in that the cercariae have a spinous tegument, oral and ventral suckers, a simple tail and distinct eye-spots. Given the simplified morphology of intramolluscan infections, genetic data provided a definitive identification. ITS2 rDNA and cox1 mtDNA sequence data from the gastropod infections were identical to two species of Hurleytrematoides, parasites of butterflyfishes (Chaetodontidae); Hurleytrematoides loi McNamara & Cribb, 2011 from Moreton Bay (south-eastern Queensland) and Heron Island (southern Great Barrier Reef) and Hurleytrematoides morandi McNamara & Cribb, 2011 from Heron Island. Notably, species of Hurleytrematoides are positioned relatively basal in the phylogeny of the Monorchiidae and are a sister lineage to that of species known to infect bivalves. Thus, the most parsimonious evolutionary hypothesis to explain infection of gastropods by these monorchiids is that basal monorchiids (in our analyses, species of Cableia Sogandares-Bernal, 1959, Helicometroides Yamaguti, 1934 and Hurleytrematoides) will all prove to infect gastropods, suggesting a single host switching event into bivalves for more derived monorchiids (17 other genera in our phylogenetic analyses). A less parsimonious hypothesis is that the infection of vermetids will prove to be restricted to species of Hurleytrematoides, as an isolated secondary recolonisation of gastropods from a bivalve-infecting lineage. Regardless of how their use arose, vermetids represent a dramatic host jump relative to the rest of the Monorchiidae, one potentially enabled by their specialised feeding biology.     

Seasonal and ontogenetic dynamics in trophic transmission of parasites

Transmission rates from the intermediate (amphipods) to the definitive hosts (fish) were quantified for two helminth species ( Cyathocephalus truncatus , Cestoda, and Cystidicola farionis , Nematoda) both seasonally and through the ontogeny of the final hosts (arctic charr, Salvelinus alpinus , and brown trout, Salmo trutta ). Amphipods ( Gammarus lacustris ) were important prey for both fish species, especially in the autumn. Both parasite species had low infection levels in amphipods compared to high abundance in fish. The seasonal variations in transmission rate of C. truncatus procercoids from amphipods to fish were in accordance with the observed abundance in fish hosts, being highest in the autumn and lowest during late winter and early summer. During summer, however, the estimated monthly transmission rates of C. truncatus were higher than the observed infection levels in the fish, suggesting restricted establishment success and shorter development time and longevity of the cestode in fish at higher temperatures. The accumulated transmission of C. farionis over the ontogeny of arctic charr was similar to the observed age-specific infection levels, reflecting a high establishment success and longevity of this parasite in charr. In contrast, brown trout exhibited an infection level that was much lower than the estimated transmission rates, suggesting a high resistance against C. farionis in these fish. The magnitudes of the estimated transmission rates were sufficient to explain the paradoxical contrast between low infection levels in the intermediate and high in the final hosts.     

Focal Philophthalmus gralli infection possibly persists in Melanoides tuberculata over two years following the definitive hosts' removal

Philophthalmosis is a zoonotic disease associated largely with the spread of the invasive freshwater snail Melanoides tuberculata, serving as an intermediate host. Here we examined Philophthalmus gralli focal fenced infection site reported recently as being associated with Tinamus major and M. tuberculata in Alajuela, Costa Rica. Removal of the definitive hosts allowed us to address also the long-term survival strategy of the parasite. Initially, the snail intermediate hosts displayed high prevalence of P. gralli infection across all its age cohorts. Two years following the removal of definitive hosts, the infection rate decreased by one order of magnitude, while the snails aging less than one year displayed zero infection prevalence. Additionally, phylogenetic analysis of mitochondrial (ND1) and nuclear (ITS1, ITS2) DNA loci revealed negligible intrasite DNA variability of the specimens obtained at the study site in Costa Rica (but not of those obtained earlier in Peru or New Zealand), supporting strongly the hypothesis on focal origin of the infection. The observed dynamics of infection suggests the explanation for the high variability in P. gralli prevalence in intermediate hosts experienced worldwide. We noticed that the reports claiming > 20% prevalence of M. tuberculata infection by P. gralli originated exclusively from foci with known eye infection of the definitive hosts, while the P. gralli infection penetrance < 2% is typically associated with sites, where the infection of definitive hosts was not observed, suggesting that the infected definitive hosts were present onsite only in the past, or were present only at a site upstream or downstream of the respective sampling site. Thus, this is the first evidence on the possible persistence of eye-trematode infection site for over two years following the last confirmed outbreak in its adult hosts.     

Transmission of Schistosoma japonicum in Marshland and Hilly Regions of China: Parasite Population Genetic and Sibship Structure

The transmission dynamics of Schistosoma japonicum remain poorly understood, as over forty species of mammals are suspected of serving as reservoir hosts. However, knowledge of the population genetic structure and of the full-sibship structuring of parasites at two larval stages will be useful in defining and tracking the transmission pattern between intermediate and definitive hosts. S. japonicum larvae were therefore collected in three marshland and three hilly villages in Anhui Province of China across three time points: April and September-October 2006, and April 2007, and then genotyped with six microsatellite markers. Results from the population genetic and sibling relationship analyses of the parasites across two larval stages demonstrated that, within the marshland, parasites from cattle showed higher genetic diversity than from other species; whereas within the hilly region, parasites from dogs and humans displayed higher genetic diversity than those from rodents. Both the extent of gene flow and the estimated proportion of full-sib relationships of parasites between two larval stages indicated that the cercariae identified within intermediate hosts in the marshlands mostly came from cattle, whereas in the hilly areas, they were varied between villages, coming primarily from rodents, dogs or humans. Such results suggest a different transmission process within the hilly region from within the marshlands. Moreover, this is the first time that the sibling relationship analysis was applied to the transmission dynamics for S. japonicum.     

Immune depression induced by acanthocephalan parasites in their intermediate crustacean host: consequences for the risk of super-infection and links with host behavioural manipulation

Parasite survival in hosts mainly depends on the capacity to circumvent the host immune response. Acanthocephalan infections in gammarids are linked with decreased activity of the prophenoloxidase (ProPO) system, suggesting an active immunosuppression process. Nevertheless, experimental evidence for this hypothesis is lacking: whether these parasites affect several immune pathways is unknown and the consequences of such immune change have not been investigated. In particular, the consequences for other pathogens are not known; neither are the links with other parasite-induced manipulations of the host. Firstly, using experimental infections of Pomphorhynchus laevis we confirmed that the lower immune activity in parasitised Gammarus pulex is induced by the parasite infection. Second, using natural infections of three different parasites, P. laevis, Pomphorhynchus tereticollis and Polymorphus minutus, we showed that acanthocephalan infection was associated with reduction of the activity of the ProPO system and the haemocyte concentration (two major parameters of crustacean immunity) suggesting that immune depression is a phenomenon affecting several immunological activities. This was confirmed by the fact that acanthocephalan infection (whatever the parasite species) was linked to a lower efficiency to eliminate a bacterial infection. The result suggests a cost of parasite immune depression. Finally, acanthocephalans are also known to induce behavioural alterations in the intermediate host which favour their transmission to definitive hosts. We did not find any correlation between behavioural and immunological alterations in both experimentally and naturally-infected gammarids. Overall, this study suggests that whilst immune depression might be beneficial to acanthocephalan survival within the intermediate gammarid host, it might also be costly if it increases host mortality to additional infections before transmission of the parasite.     

Male hosts are responsible for the transmission of a trophically transmitted parasite, Pterygodermatites peromysci, to the intermediate host in the absence of sex-biased infection

Field studies have identified that male-biased infection can lead to increased rates of transmission, so we examined the relative importance of host sex on the transmission of a trophically transmitted parasite (Pterygodermatites peromysci) where there is no sex-biased infection. We experimentally reduced infection levels in either male or female white-footed mice (Peromyscus leucopus) on independent trapping grids with an anthelmintic and recorded subsequent infection levels in the intermediate host, the camel cricket (Ceuthophilus pallidipes). We found that anthelmintic treatment significantly reduced the prevalence of infection among crickets in both treatment groups compared with the control, and at a rate proportional to the number of mice de-wormed, indicating prevalence was not affected by the sex of the shedding definitive host. In contrast, parasite abundance in crickets was higher on the grids where females were treated compared with the grids where males were treated. These findings indicate that male hosts contribute disproportionately more infective stages to the environment and may therefore be responsible for the majority of parasite transmission even when there is no discernable sex-biased infection. We also investigated whether variation in nematode length between male and female hosts could account for this male-biased infectivity, but found no evidence to support that hypothesis.     

Manipulation of host-resource dynamics impacts transmission of trophic parasites

Many complex life cycle parasites rely on predator–prey interactions for transmission, whereby definitive hosts become infected via the consumption of an infected intermediate host. As such, these trophic parasites are embedded in the larger community food web. We postulated that exposure to infection and, hence, parasite transmission are inherently linked to host foraging ecology, and that perturbation of the host-resource dynamic will impact parasite transmission dynamics. We employed a field manipulation experiment in which natural populations of the eastern chipmunk (Tamias striatus) were provisioned with a readily available food resource in clumped or uniform spatial distributions. Using replicated longitudinal capture-mark-recapture techniques, replicated supplemented and unsupplemented control sites were monitored before and after treatment for changes in infection levels with three gastro-intestinal helminth parasites. We predicted that definitive hosts subject to food supplementation would experience lower rates of exposure to infective intermediate hosts, presumably because they shifted their diet away from the intermediate host towards the more readily available resource (sunflower seeds). As predicted, prevalence of infection by the trophically transmitted parasite decreased in response to supplemental food treatment, but no such change in infection prevalence was detected for the two directly transmitted parasites in the system. The fact that food supplementation only had an impact on the transmission of the trophically transmitted parasite, and not the directly transmitted parasites, supports our hypothesis that host foraging ecology directly affects exposure to parasites that rely on the ingestion of intermediate hosts for transmission. We concluded that the relative availability of different food resources has important consequences for the transmission of parasites and, more specifically, parasites that are embedded in the food web. The broader implications of these findings for food web dynamics and disease ecology are discussed.     

Population Genetics of Schistosoma japonicum within the Philippines Suggest High Levels of Transmission between Humans and Dogs

Background

Schistosoma japonicum, which remains a major public health problem in the Philippines and mainland China, is the only schistosome species for which zoonotic transmission is considered important. While bovines are suspected as the main zoonotic reservoir in parts of China, the relative contributions of various non-human mammals to S. japonicum transmission in the Philippines remain to be determined. We examined the population genetics of S. japonicum in the Philippines in order to elucidate transmission patterns across host species and geographic areas.

Methodology/Principal Findings

S. japonicum miracidia (hatched from eggs within fecal samples) from humans, dogs, pigs and rats, and cercariae shed from snail-intermediate hosts, were collected across two geographic areas of Samar Province. Individual isolates were then genotyped using seven multiplexed microsatellite loci. Wright''s F_ST values and phylogenetic trees calculated for parasite populations suggest a high frequency of parasite gene-flow across definitive host species, particularly between dogs and humans. Parasite genetic differentiation between areas was not evident at the definitive host level, possibly suggesting frequent import and export of infections between villages, although there was some evidence of geographic structuring at the snail–intermediate host level.

Conclusions/Significance

These results suggest very high levels of transmission across host species, and indicate that the role of dogs should be considered when planning control programs. Furthermore, a regional approach to treatment programs is recommended where human migration is extensive.     

Life cycle abbreviation in trematode parasites and the developmental time hypothesis: is the clock ticking?

The typical multi‐host life cycle of many parasites, although conferring several advantages, presents the parasites with a highly hazardous transmission route. As a consequence, parasites have evolved various adaptations increasing their chances of transmission between the different hosts of the life cycle. Some trematode species like the opecoelid Coitocaecum parvum have adopted a more drastic alternative strategy whereby the definitive host is facultatively dropped from the cycle, resulting in a shorter, hence easier to complete, life cycle. Like other species capable of abbreviating their life cycle, C. parvum does so through progenetic development within its intermediate host. Laboratory‐reared C. parvum can modulate their developmental strategy inside the second intermediate host according to current transmission opportunities, though this ability is not apparent in natural C. parvum populations. Here we show that this difference is likely due to the time C. parvum individuals spend in their intermediate hosts in the natural environment. Although transmission opportunities, i.e. chemical cues of the presence of definitive hosts, promoted the adoption of a truncated life cycle in the early stages of infection, individuals that remained in their amphipod host for a relatively long time had a similar probability of adopting progenesis and the abbreviated cycle, regardless of the presence or absence of chemical cues from the predator definitive host. These results support the developmental time hypothesis which states that parasites capable of facultative life cycle abbreviation should eventually adopt progenesis regardless of transmission opportunities, and provide further evidence of the adaptive plasticity of parasite transmission strategies.     

Infection Characteristics of Clonorchis sinensis Metacercariae in Fish from Republic of Korea

The infection nature of Clonorchis sinensis metacercariae (CsMc) in freshwater fish hosts is closely related to the transmission of human clonorchiasis. This article reviewed the infection characteristics of CsMc in freshwater fish in the Republic of Korea (Korea). The status of CsMc infection was examined in a total of 17,792 cyprinid fish of 49 species in 9 water systems, which included Hantan-/Imjin-gang, Han-gang, Geum-gang, Mangyeong-gang, Yeongsan-gang, Tamjin-gang, Seomjin-gang, Nakdong-gang, and streams in the east coastal areas from 2010 to 2020. The infection status of CsMc was examined according to cyprinid fish species and water systems, after which analyzed by endemicity and susceptibility index. The high endemicity was shown in the cyprinid fish from 3 regions (6.1%) in the upper reaches of Nakdong-gang, such as Banbyeon-cheon (stream), Yongjeon-cheon, and Wi-cheon. The moderate levels were observed in fishes from 8 regions (16.3%), and low endemicity was shown in fishes from 20 regions (40.8%). No CsMc were detected in fish from 18 regions (36.7%). The susceptibility of CsMc in index fish, Puntungia herzi, was found to be a reliable index without examination of other fish species. CsMc infection rates were closely related to subfamily groups in the cyprinid fish hosts in a highly endemic area. In Korea, a total of 58 fish species in 10 families has been listed as the second intermediate hosts for C. sinensis. This review provides several novel features of CsMc infection and clarifies the species of second intermediate freshwater fish host in Korea.     

Eosinophilic meningitis caused by Angiostrongylus cantonensis: an emergent disease in Brazil

Eosinophilic meningitis (EoM) is an acute disease that affects the central nervous system. It is primarily caused by infection with the nematode Angiostrongylus cantonensis. This infection was previously restricted to certain Asian countries and the Pacific Islands, but it was first reported in Brazil in 2007. Since then, intermediate and definitive hosts infected with A. cantonensis have been identified within the urban areas of many states in Brazil, including those in the northern, northeastern, southeastern and southern regions. The goals of this review are to draw the attention of the medical community and health centres to the emergence of EoM in Brazil, to compile information about several aspects of the human infection and mode of transmission and to provide a short protocol of procedures for the diagnosis of this disease.     

The lifecycle of <Emphasis Type="Italic">Dichelyne minutus</Emphasis> (Rudolphi, 1819) (Nematoda: Cucullanidae) in the estuarine biocenosis of the Black Sea

The lifecycle, the host–parasite system, and the ecological features of the nematode Dichelyne minutus (Rudolphi, 1819), which parasitizes invertebrates and fish in the estuarine biocenosis located at the influx of the Chornaya River into the Black Sea (off Sevastopol), have been studied. The host–parasite system of D. minutus includes the polychaete Hediste diversicolor Müller, 1776 (as an obligatory intermediate host) and nine fish species, of which seven are definitive hosts and two are accidental or captive hosts. It has been found that the lifecycle of D. minutus in the biocoenosis of the Black Sea differs from the lifecycle of this nematode that inhabits the Baltic and North seas. In the studied biocoenosis, nematode larvae occur in polychaetes and fish only in the spring and summer; no larvae are found in the autumn (the study was not conducted in the winter). The nematode parasitizes the polychaete H. diversicolor in the spring; the main source of infection in this period is obviously nematode eggs that were laid in the autumn and have overwintered in the environment. The infection process ends by early summer. The seasonal and size–age dynamics of nematode infection of the round goby, Neogobius melanostomus (Pallas, 1814), are analyzed taking the specifics of fish biology into account. The short period of infection, as characterized by the active emission of nematode larvae, their low survival in polychaetes and fish, a short lifecycle and the mortality of mature nematodes after egg-laying in the autumn result in an over-scattered distribution (mostly of the negative-binomial type) of D. minutus in populations of all the hosts.     

Seasonal succession of tabanid species in equine infectious anaemia endemic areas of Italy

Equine infectious anaemia (EIA) is a disease with an almost worldwide distribution, with several outbreaks having been reported recently in European countries. In Italy, two regions, Lazio and Abruzzo, are considered as endemic areas for this disease. In nature, the EIA virus is mechanically transmitted by biting flies such as tabanids (Diptera: Tabanidae), although few studies have investigated the epidemiological implications. In the present study, several sites characterized by different levels of EIA prevalence were sampled. In sites with high tabanid populations, a seasonal succession of tabanid species with a dual‐peak corresponding to early active species (i.e. in June to July) and late active species (i.e. in August to September) was clearly observed. Moreover, a positive correlation was found between EIA prevalence and tabanid abundance and species richness, suggesting that tabanid diversity might extend the duration of the seasonal transmission period of EIA. Further observations are required to better assess how vector diversity influence EIA transmission.