Trevor N. Petney

Opisthorchis viverrini: an underestimated parasite in world health

Infection with Opisthorchis viverrini and its associated cholangiocarcinoma (CCA) is an underestimated problem in the Mekong region of Southeast Asia, despite the widespread use of praziquantel and health education measures for parasite control. Although data from Cambodia, Laos and Vietnam are rare, data from Thailand often show wide-ranging variability in epidemiological parameters, including human morbidity and the prevalence and incidence of CCA. The recent discovery of high levels of population genetic variability in O. viverrini in different wetlands in Thailand and Laos, which indicates the presence of sibling species, suggests that we have underestimated the complexity of this epidemiological situation. Future research should determine the relationship between the genetic variability of O. viverrini and patterns of opisthorchiasis-related disease.

The zoonotic, fish-borne liver flukes Clonorchis sinensis, Opisthorchis felineus and Opisthorchis viverrini

Clonorchis sinensis, Opisthorchis felineus and Opisthorchis viverrini are the three most important liver flukes involved in human health, infecting more than 45 million people worldwide. Both C. sinensis and O. viverrini, and possibly O. felineus, can induce human cholangiocarcinoma as well as inducing other hepatobiliary pathology. Although the life cycles of all three species are similar, only that of O. felineus in Europe remains predominantly zoonotic, while O. felineus in Asia and C. sinensis have a stronger mixture of zoonotic and anthroponotic components in their life cycles. Opisthorchis viverrini from the Mekong area of southeastern Asia is predominantly anthroponotic. Here we discuss the comparative epidemiology of these three taxa comparing in detail the use of first, second and final animal hosts, and consider the potential role of humans in spreading these pathogens. In addition we discuss the genetic structure of all three species in relation to potentially cryptic species complexes.

The ecology of tick-borne diseases

Zoonotic diseases are major causes of infection related morbidity and mortality worldwide. Of the various arthropods capable of transmitting pathogens that cause such diseases to humans, ticks, which are vectors of more kinds of pathogens than any other group of invertebrate, have become an increasing focus of attention. This is particularly the case in the temperate northern hemisphere where they are a significant vector of human disease. Here, we provide an overview of the complex ecological systems defining the various epidemiological cycles of tick-borne diseases. We highlight the abiotic and biotic factors influencing the establishment and persistence of tick populations and their associated pathogens. Furthermore, we emphasize the dynamic nature of such systems, especially when they are under the influence of both small and large-scale anthropogenic changes to the environment. Although a great deal of work has been done on ticks and the diseases which they transmit, the very dynamism of the system means that new factors are continually arising which shift the epidemiological pattern within specific areas. We therefore consider that more detailed, long-term (i.e. at least 10 years), multidisciplinary studies need to be carried out to define why and how these pattern shifts take place and to determine their public health significance.

The taxonomic status of Rhipicephalus sanguineus (Latreille, 1806)

The brown dog tick, Rhipicephalus sanguineus sensu stricto, is a species with considerable public health and economic importance. However, the taxonomic status of this species is far from resolved. After more than 110 years of scientific work on R. sanguineus s.s., the situation is that there is no type, no solid description, nor is there a consensus about the range of morphological variability within the species. Recent findings based on laboratory crosses and molecular genetics strongly suggest that there are several entities grouped under the same name. Here we review the history of the taxon, and we point out the caveats behind any further work on this tick. The current taxonomic status of R. sanguineus s.s. thus lacks an informative original description, and is based on the existence of several morphological descriptions based on ticks originating from different populations, which show, in some cases, biological incompatibility and significant genetic divergence. We suggests that as a result it is not possible to assign the specific name R. sanguineus s.s. to any population. Further work is required based on the rules issued by the International Code of Zoological Nomenclature to clearly define the morphological range of the different populations.

Comments on controversial tick (Acari: Ixodida) species names and species described or resurrected from 2003 to 2008.

There are numerous discrepancies in recent published lists of the ticks of the world. Here we review the controversial names, presenting evidence for or against their validity and excluding some altogether. We also address spelling errors and present a list of 17 species described or resurrected during the years 2003–2008. We consider the following 35 tick species names to be invalid: Argas fischeri Audouin, 1826, Ornithodoros boliviensis Kohls and Clifford, 1964, Ornithodoros steini (Schulze, 1935), Amblyomma acutangulatum Neumann, 1899, Amblyomma arianae Keirans and Garris, 1986, Amblyomma bibroni (Gervais, 1842), Amblyomma colasbelcouri (Santos Dias, 1958), Amblyomma concolor Neumann, 1899, Amblyomma cooperi Nuttall and Warburton, 1908, Amblyomma curruca Schulze, 1936, Amblyomma cyprium Neumann, 1899, Amblyomma decorosum (Koch, 1867), Amblyomma nocens Robinson, 1912, Amblyomma perpunctatum (Packard, 1869), Amblyomma striatum Koch, 1844, Amblyomma superbum Santos Dias, 1953, Amblyomma testudinis (Conil, 1877), Amblyomma trinitatis Turk, 1948, Dermacentor confractus (Schulze 1933), Dermacentor daghestanicus Olenev, 1928, Haemaphysalis himalaya Hoogstraal, 1966, Haemaphysalis vietnamensis Hoogstraal and Wilson, 1966, Hyalomma detritum Schulze, 1919, Ixodes apteridis Maskell, 1897, Ixodes donarthuri Santos Dias, 1980, Ixodes kempi Nuttall, 1913, Ixodes neotomae Cooley, 1944, Ixodes rangtangensis Teng, 1973, Ixodes robertsi Camicas, Hervy, Adam and Morel, 1998, Ixodes serrafreirei Amorim, Gazetta, Bossi and Linhares, 2003, Ixodes tertiarius Scudder, 1885, Ixodes uruguayensis Kohls and Clifford, 1967, Ixodes zealandicus Dumbleton, 1961, Ixodes zumpti Arthur, 1960 and Rhipicephalus camelopardalis Walker and Wiley, 1959. We consider the following 40 names valid: Argas delicatus Neumann, 1910, Argas vulgaris Filippova, 1961, Ornithodoros aragaoi Fonseca, 1960, Ornithodoros dugesi Mazzoti, 1943, Ornithodoros knoxjonesi Jones and Clifford, 1972, Ornithodoros marocanus Velu, 1919, Ornithodoros nattereri Warburton, 1927, Amblyomma beaurepairei Vogelsang and Santos Dias, 1953, Amblyomma crassipes (Neumann, 1901), Amblyomma echidnae Roberts, 1953, Amblyomma fuscum Neumann, 1907, Amblyomma orlovi (Kolonin, 1995), Amblyomma parkeri Fonseca and Aragão, 1952, Amblyomma pseudoconcolor Aragão, 1908, Bothriocroton oudemansi (Neumann, 1910), Bothriocroton tachyglossi (Roberts, 1953), Dermacentor abaensis Teng, 1963, Dermacentor confragus (Schulze 1933), Dermacentor ushakovae Filippova and Panova, 1987, Haemaphysalis anomaloceraea Teng, 1984, Haemaphysalis filippovae Bolotin, 1979, Haemaphysalis pavlovskyi Pospelova-Shtrom, 1935, Hyalomma excavatum Koch, 1844, Hyalomma isaaci Sharif, 1928, Hyalomma rufipes Koch, 1844, Hyalomma turanicum Pomerantzev, 1946, Ixodes arabukiensis Arthur, 1959, Ixodes boliviensis Neumann, 1904, Ixodes columnae Takada and Fujita, 1992, Ixodes maslovi Emel′yanova and Kozlovskaya, 1967, Ixodes sachalinensis Filippova, 1971, Ixodes siamensis Kitaoka and Suzuki, 1983, Ixodes sigelos Keirans, Clifford and Corwin, 1976, Ixodes succineus Weidner, 1964, Rhipicephalus aurantiacus Neumann, 1907, Rhipicephalus cliffordi Morel, 1965, Rhipicephalus pilans Schulze, 1935, Rhipicephalus pseudolongus Santos Dias, 1953, Rhipicephalus serranoi Santos Dias, 1950 and Rhipicephalus tetracornus Kitaoka and Suzuki, 1983.

The ecology of the Bithynia first intermediate hosts of Opisthorchis viverrini.

Opisthorchiasis, together with its associated cholangiocarcinoma, is one of the most important human parasitic diseases on continental Southeast Asia. A great deal of epidemiological data from humans is available on this disease, particularly from the northeast of Thailand, however, only limited information is available on those aspects of the life cycle relating to its Bithynia (Gastropoda) and cyprinid fish intermediate hosts. Here we review the information which is available on the Bithynia hosts of Opisthorchis viverrini. Only one major ecological study has been carried out at one site on a single species of Bithynia. We show not only that detailed ecological studies are required to clarify the epidemiology of opisthorchiasis, but also that the taxonomic status of the Bithynia species transmitting O. viverrini requires clarification.

Occurrence of different Borrelia burgdorferi sensu lato genospecies including B. afzelii, B. bavariensis, and B. spielmanii in hedgehogs (Erinaceus spp.) in Europe.

In order to determine whether European hedgehogs (Erinaceus europaeus and E. roumanicus) play a role in the epidemiological cycle of Borrelia burgdorferi sensu lato in Central Europe and Great Britain, tissue samples of hedgehogs from Germany (n=211), Austria (n=4), the Czech Republic (n=22), and the U.K. (n=32) were tested for the presence of these tick-borne pathogens. PCR for amplification of the B. burgdorferi s.l.-specific 5S-23S intergenic spacer region as well as the outer surface protein A (ospA) gene were used. B. burgdorferi s.l. DNA was detected in 35 of the 259 E. europaeus and in 2 of 10 E. roumanicus. B. burgdorferi prevalences in E. europaeus ranged from 0% (U.K.) to 37.5% (Czech Republic), for E. roumanicus from 0% (Czech Republic) to 50.0% (Austria). Sequencing revealed the occurrence of 3 different B. burgdorferi genospecies in E. europaeus: B. afzelii was the dominant genospecies, followed by B. bavariensis (previously B. garinii OspA serotype 4) and B. spielmanii, the latter was detected for the first time in Hamburg (Germany). B. afzelii and B. bavariensis were also found in E. roumanicus. Our results suggest that hedgehogs modulate the epidemiology of certain species of the B. burgdorferi s.l. complex, potentially affecting the distribution and abundance of individual B. burgdorferi s.l. genospecies in various habitats. We hypothesise that juvenile or individuals with low immune competence in particular, have a high reservoir potential for the 3 genospecies identified here.

Comparative population dynamics of a generalist (Ixodes ricinus) and specialist tick (I. hexagonus) species from European hedgehogs

Although the population dynamics of the tick Ixodes ricinus are relatively well studied, those of other Western European tick species are largely unknown. Moreover, there is very little information related to the interactions between I. ricinus and other ticks. Such knowledge, however, is of special interest in respect to the epidemiology of tick-borne pathogens such as Borrelia spp. We compared the dynamics of the generalist I. ricinus with the nest-dwelling hedgehog specialist, I. hexagonus. Both species were collected from hedgehogs from a naturally infested experimental population between 2006 and 2008. Ticks were collected once a month from March to October from each hedgehog counted and the life history stage and species determined. All hedgehogs harboured both tick species. Nymphs, females and males of I. ricinus showed clear bimodal seasonal distributions with peaks in spring and autumn, while larvae peaked only in summer. The density of I. hexagonus life stages was low during the whole investigation period and seasonal fluctuations of population density were much weaker compared to I. ricinus. Nymphs and larvae showed comparatively little change in population size and no consistent period of peak density. Females showed a single peak in summer and males were found only occasionally on hedgehogs. We suggest density-dependent mechanisms regulating the population density of the specialist I. hexagonus but not of the generalist I. ricinus.

Molecular Detection of Anaplasma phagocytophilum in the European Hedgehog (Erinaceus europaeus) and its Ticks

The European hedgehog (Erinaceus europaeus) is a common wild mammal in Central Europe that shares habitats with humans in urban, peri-urban, and rural areas. Thus, this species may play a role in human contact with zoonotic diseases. Here we report the presence of the pathogen Anaplasma phagocytophilum in hedgehogs and their ticks in Germany.

Mitochondrial DNA sequence variation among geographical isolates of Opisthorchis viverrini in Thailand and Lao PDR, and phylogenetic relationships with other trematodes

The present study compared the genetic variation among 14 different geographical isolates of Opisthorchis viverrini sensu lato from Thailand and Lao PDR using sequence data for 2 mitochondrial DNA genes, the subunit 1 of NADH dehydrogenase gene (nad1) and cytochrome c oxidase gene (cox1). Four different nad1 haplotypes were detected among isolates, all of which were identical at the amino acid sequence level. Nucleotide sequence variation among 14 isolates ranged from 0 to 0.3% for nad1. Two different cox1 haplotypes were detected among isolates. These two haplotypes differed at 2 nucleotide positions, one of which resulted in a change in the amino acid sequence. Nucleotide sequence variation among isolates for cox1 ranged from 0 to 0.5%. Comparison of cox1 sequences of O. viverrini to those of other trematodes revealed nucleotide differences of 13-31%. A phylogenetic analysis of the cox1 sequence data revealed strong statistical support for a clade containing O. viverrini and 2 other species of opisthorchid trematodes; O. felineus and Clonorchis sinsensis.