Natural Final Host Research Articles

Discovery of natural infection by Metagonimus hakubaensis Shimazu, 1999 (Trematoda: Heterophyidae) in Japanese water shrews (Chimarrogale platycephala) in Japan.

ABSTRACTABSTRACT. A total of 611 preserved adult Metagonimus spp. specimens recovered from 32 of 53 Japanese water shrews (Chimarrogale platycephala) that had previously been collected in Aomori Prefecture between June 1994 and August 1996, were examined in this study. Morphological examination revealed that 603 of these flukes were identical to M. hakubaensis Shimazu, 1999, and that the others were M. takahashii Suzuki, 1930 (n=4), M. otsurui Saito et Shimizu, 1968 (n=2), and M. miyatai Saito et al., 1997 (n=2). Each of the 32 Japanese water shrews infected with M. hakubaensis contained between 1 and 83 flukes. This is the first record of the natural final host for M. hakubaensis, since this fluke species was described.

Toxascaris leonina in Rodents, and Relationship to Eosinophilia in a Human Population

On St. Lawrence Island, U.S.A. (Bering Sea), following definition of the cycle of Echinococcus multilocularis and its identification as the cause of alveolar echinococcosis, we intensified the investigation of helminths in the northern vole (Microtus oeconomus), the major intermediate host of that cestode. Natural infections of the voles by larvae of Toxascaris leonina were first observed by us on the island in 1956, and subsequently on the mainland of Alaska. The natural final host is the arctic fox; sledge dogs were kept in large numbers by the Yup'ik residents of the island, and voles were most commonly affected where dogs were present. Larvae of the nematode were often macroscopically visible in the walls of the cecum and in skeletal muscle. Results of experimental infection of laboratory-reared voles, with the use of embryonated eggs of nematodes obtained from dogs, indicated that the larvae tended to migrate anteriad in voles, from the cecum to muscles anterior to the diaphragm. Repeated exposure of voles apparently intensified the immune response to the extent that larvae from exposure subsequent to the first were retarded in development and might have been prevented from completing migration to the musculature. The possibility of vole-to-vole transmission of third-stage larvae (determined by feeding of somewhat dried eviscerated bodies of infected animals) was confirmed in 11 of 29 trials. Because the rather high prevalence of eosinophilia in the people was not correlated with cases of alveolar echinococcosis (formerly hyperendemic on the island), we consider that the larva of T. leonina was its probable cause.

High prevalence of Sarcocystis calchasi sporocysts in European Accipiter hawks

The emerging Sarcocystis calchasi induces a severe and lethal central nervous disease in its intermediate host, the domestic pigeon (Columba livia f. domestica). Experimental studies have identified the Northern goshawk (Accipiter g. gentilis) as final host. Phylogenetically closely related European sparrowhawks (Accipiter n. nisus) and wood pigeons (Columba palumbus) have been found to harbor genetically closely related Sarcocystis spp. However, data on the prevalence and potential interspecies occurrence of these parasites are lacking. Here, we report that European Accipiter hawks (Accipitrinae) are highly infected with S. calchasi, S. columbae and Sarcocystis sp. ex A. nisus in their small intestine. Thirty-one of 50 (62%) Northern goshawks necropsied during 1997-2008 were positive for S. calchasi in a newly established species-specific semi-nested PCR assay based on the first internal transcribed spacer region. Unexpectedly, 14 of 20 (71.4%) European sparrowhawks tested also positive. In addition, birds of both species were found to be infested with S. columbae and an, as yet, unnamed Sarcocystis sp. recently isolated from European sparrowhawks. These findings raise new questions about the host specificity of S. calchasi and its high virulence in domestic pigeons, since sparrowhawks only rarely prey on pigeons. Notably, isolated sporocysts from both infected Accipiter spp. measured 8 μm × 11.9 μm, precluding a preliminary identification of S. calchasi in feces of Accipiter hawks based on morphology alone. Importantly, three of four Northern goshawks used in falconry tested positive for S. calchasi. In conclusion, the results indicate that both European Accipter spp. in Germany serve as natural final hosts of S. calchasi and suggest that falconry and pigeon sport may serve as risk factors for the spread of this pathogen in domestic pigeons.

Intrahepatic growth and maturation of Gnathostoma turgidum in the natural definitive opossum host, Didelphis virginiana

Gnathostoma turgidum is a gastric nematode parasite of opossums found in the Americas. We recently found that G. turgidum juveniles appear in the liver of the opossums where they become mature adults and almost synchronously move to the stomach during certain months of the year, suggesting the importance of the liver for the growth and maturation of this species in the final hosts. In this study we attempted to detect G. turgidum larvae in the liver of opossums, Didelphis virginiana that are the natural final hosts. The results show that tiny (<3mm in length) third stage larvae (L3) appeared in the liver of opossums around November and December. Also in the liver, we found large L3 of up to about 10mm in length together with juveniles and mature adults from February to March. In spite of their length, large L3 have 4 rows of hooklets, and their gonads remained undeveloped. Morphological features of the small and large L3 of G. turgidum are described including scanning electron microscope images. The seasonal switching of the several growth stages of G. turgidum from small L3 to adult worms in the liver and eventual migration to the stomach in opossums suggests the unique feature of G. turgidum utilizing the liver as the maturation site.

Discovery ofParvatrema duboisiandParvatrema homoeotecnum(Digenea: Gymnophallidae) from Migratory Birds in Korea

Adult worms of Parvatrema spp. (Digenea: Gymnophallidae) were found in the intestines of 2 species of migratory birds, i.e., a great knot, Calidris tenuirostris, and 2 Mongolian plovers, Charadrius mongolus, in the coastal area of Gunsan-si, Jeollabuk-do in October 2009. The recovered Parvatrema worms were 79 in total number and composed of 2 species. The worms from a great knot were 289 µm in length with the oral and ventral sucker ratio of 2 : 1. They had a single vitellarium, and their intrauterine eggs were 25.0 x 17.5 µm in size. These findings were compatible with P. duboisi (Dollfus, 1923) Bartoli, 1974 (syn. P. timondavidi Bartoli, 1963). The worms recovered from the Mongolian plovers were smaller in length than P. duboisi and had 2 vitellaria. The oral and ventral sucker ratio was 2.5:1, and the eggs were 17.5 x 8.8 µm in size. These worms were assigned to be P. homoeotecnum James, 1964. This is the first report on the natural final hosts of Parvatrema spp. in Korea.

Diphyllobothriasis associated with eating raw pacific salmon.

The incidence of human infection with the broad tapeworm Diphyllobothrium nihonkaiense has been increasing in urban areas of Japan and in European countries. D. nihonkaiense is morphologically similar to but genetically distinct from D. latum and exploits anadromous wild Pacific salmon as its second intermediate host. Clinical signs in humans include diarrhea and discharge of the strobila, which can be as long as 12 m. The natural life history and the geographic range of the tapeworm remain to be elucidated, but recent studies have indicated that the brown bear in the northern territories of the Pacific coast region is its natural final host. A recent surge of clinical cases highlights a change in the epidemiologic trend of this tapeworm disease from one of rural populations to a disease of urban populations worldwide who eat seafood as part of a healthy diet.

Schistosomes in the North: A unique finding from a prosobranch snail using molecular tools

Samples of schistosome cercariae from three different snail species (Lymnaea stagnalis, Radix auricularia and Valvata (Tropidina) macrostoma) collected from lakes in Central Finland were analyzed using molecular techniques. Based on sequences of ITS region of rDNA, the parasite isolates from L. stagnalis and R. auricularia belong to Trichobilharzia szidati and T. franki, respectively. This confirms a wide distribution of these two species in Europe. On the other hand, the isolates from V. macrostoma represent a unique finding--they belong to yet unknown schistosome species falling into the bird schistosome clade. Therefore, identification of natural final hosts and morphological characterization of particular developmental stages need to be performed in the future.

Bird schistosomes of wildfowl in the Czech Republic and Poland

In 2005, we dissected 102 wildfowl from the Czech Republic and 73 wildfowl from Poland including representatives of Anseriformes, Gruiformes and Gaviiformes. Schistosome infection was found in a total of 21 (29%) and 23 (23%) birds from Poland and the Czech Republic, respectively. All infected birds belonged to the order Anseriformes. The prevalences of nasal and visceral species were, respectively, 22% and 16% in Poland and 6% and 19% in the Czech Republic. Four species of schistosomes were found: Bilharziella polonica Kowalewski, 1895, Trichobilharzia regenti Horák, Koláfová et Dvorák, 1998, T. szidati Neuhaus, 1952, and an undetermined schistosome from the intestinal wall of Anas penelope L. The finding of T. szidati represents the first record of the parasite from natural final host since the species description.

Paragonimus westermani and Some Rare Intestinal Trematodes Recovered from Raccoon Dogs (Nyctereutes procyonoides viverrinus) Introduced Recently on Yakushima Island, Japan

Helminth parasites were collected from 9 raccoon dogs (Nyctereutes procyonoides viverrinus) and 2 Japanese weasels (Mustela itatsi sho) on Yakushima Island, Japan. The former carnivore was introduced to this World Natural Heritage Area presumably within the last two decades, expanding its population thence, although detailed process(es) of the introduction is unknown. The collected trematodes from raccoon dogs included the triploid form of Paragonimus westermani, Brachylaima tokudai, Maritrema eroliae, and Pseudocryptotropa sp. Simultaneously, Paragonimus ohirai was found in one weasel killed by a traffic accident. Although the triploid form of P. westermani and P. ohirai are known to be distributed in some river-mouth areas of Yakushima Island based on previous surveys on crab hosts, natural infection was detected for the first time in wild final hosts. Particularly, the raccoon dog infected with P. westermani was caught in a mountainous area, distant from human residence or river-mouth areas. Although it is possible that the infected raccoon dog moved from a river-mouth area endemic with P. westermani after infection, the alternative scenario remains to be pursued; the endemic area of this zoonosis is expanding along with the recent expansion of raccoon dogs or feral cats (Felis catus), that became prevalent recently on this island including the mountainous areas. Maritrema eroliae taking a variety of shorebirds as its natural final hosts, and a minute trematode, Pseudocryptotropa sp., taking unknown natural final host(s) were recorded for the first time in raccoon dogs.

In vitro study of the migratory and adherent responses of fish leucocytes to the eel-pathogenic acanthocephalan Paratenuisentis ambiguus (van Cleave, 1921) Bullock et Sammuel, 1975 (Eoacanthocephala: Tenuisentidae)

The migratory response of fish leucocytes to infective larvae of the eelpathogenic acanthocephalan Paratenuisentis ambiguus was tested in vitro. Leucocytes of the accidental hosts carp (Cyprinus carpio) and rainbow trout (Oncorhynchus mykiss) showed a significantly higher response than the leucocytes of the natural final host, eel (Anguilla anguilla). Carp leucocytes caused damage to the tegument of the parasite, manifest as electron-lucent cavities in the striped layer and localised detachment of the surface coat. It is postulated that in carp the cellular defense system limits the longevity of P. ambiguus and thus plays a role in the determination of the host-specificity of this acanthocephalan.

In vitro study on the impact of fish sera on the survival and fine structure of the eel-pathogenic acanthocephalanParatenuisentis ambiguus

The effects of fish sera on the growth and fine structure of infective larvae of the eel-pathogenic acanthocephalan Paratenuisentis ambiguus (Eoacanthocephala: Tenuisentidae) were studied under in vitro conditions using sera from the final host Anguilla anguilla and from two accidental fish hosts as well as fetal calf serum. As controls larvae were also kept in medium in the absence of serum and in experimentally infected eels. Sera from the accidental fish hosts carp and rainbow trout exerted toxic effects on the acanthocephalans. Worms maintained in medium containing sera from these two fish were contracted and displayed inverted probosces. Moreover, the tegument exhibited vacuolization and the formation of necrotic areas, including lysis of the mitochondria. Due to these effects, the parasites died at 21 (rainbow trout) or 21-50 days (carp) post-incubation. Eel sera had no toxic effect on the infective larvae. The growth of the larvae in medium depended on the composition of the latter, but was reduced as compared with that in the natural final host. Based on these results, we conclude that components of the hosts' blood sera play a role in the determination of the host specificity of P. ambiguus.

The life-history ofMesorchis denticulatus (Rudolphi, 1802) Dietz, 1909 (Trematoda, Echinostomatidae)

Red-tailed gigantocercous cercariae which developed in the euryhaline snailHydrobia ulvae Pennant (Prosobranchia, Hydrobiidae) in Denmark developed intoMesorchis denticulatus (Rudolphi 1802) Dietz 1909 (Echinostomatidae). Synonyms areStephanoprora denticulata (Rudolphi 1802) Odhner 1910,M. pseudoechinatus (Olsson 1876) Dietz 1909, andS. pseudoechinata (Olsson 1876) Odhner 1910. The rediae are cannibals devouring whole extraredial cercariae. The cercariae are actively ingested by small fish or carried by the respiratory current into their gill chambers. They encyst in the gill filaments.Gasterosteus aculeatus L.,Pungitius pungitius L. andPomatoschistus microps Kroyer are the most important second intermediate hosts in Danish waters, but all species of small fish, exceptAnguilla anguilla L., exposed to the cercariae were experimentally infected. Chickens were suitable laboratory hosts, whereasLarus spp. and other piscivorous birds function as natural final hosts in Europe and North America. Mammals may also be suitable hosts.

The larval stages of Meiogymnophallus strigatus (M. V. Lebour, 1908) n. comb. (Trematoda: Gymnophallidae)

Cercariae and metacercariae of Meiogymnophallus strigatus (M. V. Lebour, 1908) have been found in some places along the coast of Camargue (South of France). Sporocysts and cercariae are parasites of Tellina tenuis. Metacercariae occur in various Bivalves, mainly in Donax trunculus and D. semistriatus. Cercariae and metacercariae are described. Relationship between cercariae and metacercariae is demonstrated. Metacercarial microhabitat is delimited. Reaction of D. trunculus in front of the metacercarial infection is studied. Some metacercariae are free-living in the extrapallial space, between the mantle and the shell. These larvae have an advanced genital maturity. Most of the metacercariae are massed together and are enclosed by the host's epithelium. Their excretory vesicle, which is packed with blackish granules, almost fills the entire body. Attempts to infect laboratory reared birds by feeding metacercariae from Donax trunculus were not successful. The natural final host is unknown. In consideration of the metacercarial anatomy, Cercaria strigata M. V. Lebour, 1908 is placed in the genus Meiogymnophallus H. L. Ching, 1965.

On the morphology and life-history ofStephanostomum caducum(Looss 1901) Manter 1934 (trematoda, acanthocolpidae)

Abstract The cercaria of Stephanostomum caducum (Looss 1901) Manter 1934, develops in redia in the marine prosobranch Natica alderi. The ocelate cercaria has two alternating rows of oral spines and a stylet. The distal part of the tail is able to invaginate and function as a sucker. The cercaria is probably identical with Cercaria obtusicaudata Pelseneer 1906. The cercariae encyst below the epidermis of the mouth of fish belonging to the family Gobiidae. The nietacercariae have 24 or 25 oral spines in each of the two rows. S. caducum developed in the pyloric caeca of cods fed on experimentally infected gobies. Cod, Gadus morhua, is the natural final host for S. caducum in Danish waters. The different developmental stages were studied using the scanning electron microscope.

Some effects of population density in infections of Diphyllobothrium dendriticum (Nitzsch) in golden hamster (Mesocricetus auratus Waterhouse) and common gull (Larus canus L.).

Golden hamsters were given plerocercoids of Diphyllobothrium dendriticum either singly or in groups of 2, 4, 8 or 15. There was a higher rate of recovery of worms from hamsters given many (8 and 15) than from those given few (1, 2 or 4) plerocercoids. The difference in rate of recovery of worms was present from 2 h after administration of plerocercoids and persisted up to day 20 when experiments were ended. Denser tapeworm populations had the smallest individuals and some of them contained worms with primary strobilae at the start of egg production. The size of the tapeworm population did not influence the prepatent time. Also, with the common gull there was a higher rate of recovery of worms when plerocercoids were given in groups. These results are discussed in relation to aspects of the life-cycle of D. dendriticum where the natural final host is most probably normally infected by a larger number of plerocercoids at the same time.

Life cycle of a new echinostome from Egypt, Echinostoma liei sp.nov. (Trematoda: Echinostomatidae).

A 37-spined Egyptian echinostome, Echinostoma liei sp.nov., is described in adult and larval stages. The parasite develops readily in the laboratory in chicks and ducklings, hamsters and rats. Its natural final host in or near irrigation ditches of the Nile delta involves the roof rat, Egyptian giant shrew and aquatic bird hosts. Developmental forms are described from infection of the NIH strain of Biomphalaria glabrata in the laboratory. B. alexandrina, is infected in the normal habitat in Egypt and contains both developmental stages in the heart or aorta and the hepatopancreas, and metacercariae encyst in the pericardium and kidney. E. liei sp.nov. is one of six very similar species characterized by 37 collar spines with a pattern of (3 + 2) corner spines in each lappet, six laterals on each side, and 15 dorsals in alternating rows; two pairs of dorsoventral and one small pair of ventro-lateral finfolds on the cercarial tail; and rodlike cystogenous material filling the cercarial encystation glands. In addition to distinctive intermediate-host specificity, differentiating characteristics of E. liei cercariae include presence of six sets of three flame cells each per side (total 36), seven oesophageal cells, eight penetration gland outlets on the dorsal lip of the oral sucker, and an absence of paraoesophageal gland cells as determined by intravital dyes. Significance of these and other cercarial traits is emphasized to aid in defining highly similar, but none the less distinct, sibling species.

Thysanoessa inermis and T. longicaudata (Euphausiidae) as First Intermediate Hosts of Anisakis sp. (Nematoda: Ascaridata) in the Northern North Sea, to the North of Scotland and at Faroe

REPORTS1,2 that live larvae of the nematode Anisakis from raw or inadequately cooked fish may cause eosinophilic granuloma of the alimentary tract in man have stimulated research into the ecology, taxonomy, physiology and pathogenesis of this genus in fish (natural second intermediate hosts), marine mammals (natural final hosts) and man and laboratory animals (abnormal hosts)3,4. But little attention has been paid to earlier stages in the life cycle or to a search for first intermediate hosts, A knowledge of early developmental stages of Anisakis might contribute to an understanding of geographical and other variations in abundance of the larvae in economically important fish. Uspenskaya5 reported larval Anisakis in one of 855 specimens of the amphipod Caprella septentrionalis Kroyer, 1838, in one of 990 specimens of the decapod Hyasaraneus (L.) and in one of an unspecified number of euphausiids Thysanoessa raschii (M. Sars, 1864) from the Barents Sea. Oshima et al.6 found five larvae in 3,247 specimens of T. raschii and T. longipes Brandt, 1851, collected in the northern North Pacific Ocean and Bering Sea. Kagei7, according to Gibson4, mentioned T. inermis (Kroyer, 1846) as a first intermediate host of Anisakis.