Population genetic analysis informs the invasion history of the emerging trematode Dicrocoelium dendriticum into Canada.

Parasite distributions are constantly changing due to climate change, local and global movement of animals and humans, as well as land use and habitat change. The trematode Dicrocoelium dendriticum is a relatively recent invader of Canada, being first reported in eastern Canada in the 1930s and western Canada in the 1970s. However, historical records are scarce and its emergence is poorly understood. The establishment of this parasite in Canada provides an interesting opportunity to explore the use of population genetic approaches to help elucidate the invasion history of a relatively recently established helminth parasite. In this study, we compare the genetic diversity and population structure of a number of D. dendriticum populations from western and eastern Canada, and compare these with much longer established European populations. Two independent genetic marker systems were used; a microsatellite marker panel and a cytochrome c oxidase 1 (cox1) mitochondrial (mt)DNA sequence marker. We found distinct differences in both genetic diversity and population structure of the different Canadian populations that provide insights into their invasion histories compared with the European populations. Two populations from British Columbia, Canada - Salt Spring and Vancouver Islands - are of low diversity, show evidence of a population bottleneck and are closely related to each other, suggesting a shared recent history of establishment. These west coast populations are otherwise most closely related to those from eastern Canada and western Europe, and in contrast are genetically divergent from those in Cypress Hills, Alberta, Canada. Although the Alberta parasite population is the most recently reported in Canada, being first identified there in the early 1990s, it was the most genetically diverse of those examined and showed a strong pattern of admixture of genotypes present in western and eastern Europe. Overall, our results are consistent with a model in which western Europe is likely the source of flukes on the east coast of Canada, which were then subsequently translocated to the west coast of Canada. The most recently reported D. dendriticum population in Canada appears to have a different history and likely has multiple origins.

Relative Effects of Temperature, Light, and Humidity on Clinging Behavior of Metacercariae-Infected Ants.

The lancet fluke, Dicrocoelium dendriticum, is perhaps the best-known example of parasite manipulation of host behavior, which is manifested by a radically changed behavior that leaves infected ants attached to vegetation at times when transmission to an herbivore host is optimal. Despite the publicity surrounding this parasite, curiously little is known about factors inducing and maintaining behavioral changes in its ant intermediate host. This study examined the importance of 3 environmental factors on the clinging behavior of red wood ants, Formica polyctena , infected with D. dendriticum . This behavior, hypothesized to involve cramping of the mandibular muscles in a state of tetany, was observed in naturally infected F. polyctena under controlled temperature, light, and humidity conditions. We found that low temperature significantly stimulated and maintained tetany in infected ants while light, humidity, ant size, and infection intensity had no influence on this behavior. Under none of the experimental conditions did uninfected ants attach to vegetation, demonstrating that tetany was induced by D. dendriticum . Temperature likely has a direct impact on the initiation of clinging behavior, but it may also serve as a simple but reliable indicator of the encounter rate between infected ants and ruminant definitive hosts. In addition, temperature-sensitive behavior manipulation may protect infected ants from exposure to temperatures in the upper thermal range of the host.

Ancient dicrocoeliosis: Occurrence, distribution and migration.

This paper focuses on the lancet fluke, Dicrocoelium sp., and includes a complete review of the literature as well as numerous new research results. The compilation of all these data led to a global overview of ancient dicrocoeliosis history. The presence of the lancet fluke in Western Europe was attested from 550,000 years BP to the 16th century AD Moreover, the parasite was identified in the New World around the 17th century AD following the colonization of Canada by Europeans. The role of human and animal migrations is discussed.

Contributions to and review of dicrocoeliosis, with special reference to the intermediate hosts of Dicrocoelium dendriticum.

An epidemiological study on dicrocoeliosis caused by Dicrocoelium dendriticum was carried out on sheep, molluscs and ants in the mountains of León province (NW Spain) between 1987-1991. The results concerning the intermediate hosts and a review of some aspects of dicrocoeliosis are summarized. Mollusc collection for the helminthological study was random throughout the study area at fortnightly intervals. Twenty-nine Gastropoda species were identified. D. dendriticum infection was only detected in 2.98%, of the 2084 Helicella itala examined and in 1.06% of 852 H. corderoi. The highest infection prevalence was detected in H. itala in September and in H. corderoi in February. Daughter sporocysts with well-developed cercariae predominated in spring and autumn. Infection prevalence increased with mollusc age and size. Ants were collected from anthills or plants to which they were attached. The behaviour of ants in tetania was followed. Twenty-one Formicidae species were identified, but only the following harboured D. dendriticum: Formica cunicularia (1158 examined specimens, 0.69% infection prevalence, 2-56 metacercariae per ant); F. sanguinea (234, 1.28%, 2-63); F. nigricans (1770, 4.97%, 1-186); F. rufibarbis (288, 6.59%, 2-107). In a flat area close to León town, 95.39% of the 2085 F. rufibarbis specimens collected in tetania contained metacercariae (1-240) in the abdomen. These were used for parasite characterization by isoelectric focusing and to infect lambs and hamsters. Only one brainworm per ant was found.

Coprological study of the Dicrocoelium dendriticum (Digenea) egg elimination by cattle in highland areas in León Province, northwest Spain.

Dicrocoelium dendriticum egg output in cattle from five locations of the Porma river basin (León Province, Northwest Spain) was studied at monthly intervals between March 1986 and March 1987. We found D. dendriticum eggs in 37.64% of the 1251 samples examined, and the number of eggs per gram (epg) ranged from 10 to 1000 (average, 41.65 +/- 2.73). The main egg-elimination period, for prevalence, was autumn-winter. The average epg values were quite similar during all months except March, when the maximum was detected. The infection prevalence increased in cattle aged up to 2 years and then a slight, gradual decrease was observed with increasing host age. The average epg values ranged from 40.08 +/- 3.24 to 48.33 +/- 12.42 in all age groups except the oldest animals, for which the figures were lower. The rate of egg elimination was higher in animals that came from locations situated at a greater altitude.

Snail-borne parasitic zoonoses in Korea.

A total of 22 snail-borne parasites causing various parasitic zoonoses in Korea are listed and reviewed. All of these parasites are indigenous except Heterophyes heterophyes, H. dispar and Angiostrongylus cantonensis detected in patients who traveled outside of Korea.

[Seasonal occurrence of Dicrocoelium dendriticum in intermediate hosts]. / Zum jahreszeitlichen Auftreten von Dicrocoelium dendriticum in Zwischenwirten.

Epizootiological questions were studied on a permanent pasture of a farm situated in one of the dicrocoeliasis areas in the GDR during the 1986 grazing season. Helicella obvia snails and Formica fusca ants were found to be first and second intermediate hosts respectively. A total of 1,121 snails and 70 ants were dissected. The infestation rate with Dicrocoelium dendriticum stages in snails decreased in summer after the high spring peak and increased again in autumn. Paralysed ants were found only at temperatures below 20 degrees C. Parthenogenetic stages in snails were identified morphologically according to the structure of cercariae; the metacercariae isolated from the ants' body cavity were determined in animal experiments.

Dicroceliasis (lancet fluke disease) in an HIV seropositive man.

Dicroceliasis is an unusual zoonotic trematode infection caused by the lancet liver fluke, Dicrocoelium dendriticum. Grazing herbivores (usually sheep or cattle) are the definitive hosts. The life cycle proceeds through two intermediate hosts: the land snail and the field ant. Human infection is acquired by consuming the field ant. This case report describes a human immunodeficiency virus-seropositive patient who presumably acquired this parasite from bottled water contaminated with ants. A brief discussion of the parasitology, pathology, clinical findings and treatment is presented.

[Dicrocoelium dendriticum in sheep in the Democratic Republic of Germany district of Frankfurt/Oder]. / Dicrocoelium dendriticum beim Schaf im DDR-Bezirk Frankfurt/Oder

In the district of Frankfurt/Oder of the German Democratic Republic, faecal examinations of 143 sheep stocks revealed a 31.3 percent infection with Dicrocoelium dendriticum. In different territories of the district, the intensity of the infection with Dicrocoelium dendriticum varied remarkably. Detailed investigations demonstrated, that the parasite was limited to pastures with Brownearth soil. Routine examinations revealed the fact, that the egg-output of Dicrocoelium dendritcum was very variable during the pasture season. During the whole time of the examinations, the authors found eggs in the faeces of sheep belonging to Dicrocoelium dendriticun. In the German Democratic Republic, this helminth species is not restricted to hills with limestones. It occurs also in lowlands with small amounts of lime like the Brown-earth zones of the district Frankfurt/Oder.