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Transmission rates of the bacterial endosymbiont, Neorickettsia risticii, during the asexual reproduction phase of its digenean host, Plagiorchis elegans, within naturally infected lymnaeid snails.

Greiman SE, Tkach VV, Vaughan JA - Parasit Vectors (2013)

Bottom Line: Prevalence of Neorickettsia infection in cercariae of Plagiorchis elegans was variable and never reached 100%.Reasons for this are speculative, however, the low prevalence of Neorickettsia observed in some of our samples (11 to 52%) differs from the high prevalence of other, related bacterial endosymbionts, e.g. Wolbachia in Wolbachia-dependent filariid nematodes, where the prevalence among progeny is universally 100%.This suggests that, unlike the Wolbachia-filaria relationship, the Neorickettsia-digenean relationship is not obligatory mutualism.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, University of North Dakota, 10 Cornell St,, Grand Forks, North Dakota 58202, USA. stephen.greiman@my.und.edu.

ABSTRACT

Background: Neorickettsia are obligate intracellular bacterial endosymbionts of digenean parasites present in all lifestages of digeneans. Quantitative information on the transmission of neorickettsial endosymbionts throughout the complex life cycles of digeneans is lacking. This study quantified the transmission of Neorickettsia during the asexual reproductive phase of a digenean parasite, Plagiorchis elegans, developing within naturally parasitized lymnaeid pond snails.

Methods: Lymnaea stagnalis snails were collected from 3 ponds in Nelson County, North Dakota and screened for the presence of digenean cercariae. Cercariae were identified to species by PCR and sequencing of the 28S rRNA gene. Neorickettsia infections were initially detected using nested PCR and sequencing of a partial 16S rRNA gene of pooled cercariae shed from each parasitized snail. Fifty to 100 single cercariae or sporocysts were isolated from each of six parasitized snails and tested for the presence of Neorickettsia using nested PCR to estimate the efficiency at which Neorickettsia were transmitted to cercariae during asexual development of the digenean.

Results: A total of 616 L. stagnalis were collected and 240 (39%) shed digenean cercariae. Of these, 18 (8%) were Neorickettsia-positive. Six Neorickettsia infections were selected to determine the transmission efficiency of Neorickettsia from mother to daughter sporocyst and from daughter sporocyst to cercaria. The prevalence of neorickettsiae in cercariae varied from 11 to 91%. The prevalence of neorickettsiae in sporocysts from one snail was 100%.

Conclusion: Prevalence of Neorickettsia infection in cercariae of Plagiorchis elegans was variable and never reached 100%. Reasons for this are speculative, however, the low prevalence of Neorickettsia observed in some of our samples (11 to 52%) differs from the high prevalence of other, related bacterial endosymbionts, e.g. Wolbachia in Wolbachia-dependent filariid nematodes, where the prevalence among progeny is universally 100%. This suggests that, unlike the Wolbachia-filaria relationship, the Neorickettsia-digenean relationship is not obligatory mutualism. Our study represents the first quantitative estimate of the Neorickettsia transmission through the asexual phase of the digenean life cycle.

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Natural life cycle of the digenean Plagiorchis elegans. Neorickettsia infection is represented by a red dot.
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Figure 1: Natural life cycle of the digenean Plagiorchis elegans. Neorickettsia infection is represented by a red dot.

Mentions: Bacteria in the genus Neorickettsia (Order Rickettsiales, Family Anaplasmataceae) are intracellular endosymbionts of digeneans. Neorickettsiae are presumably maintained throughout the digenean life cycle by vertical transmission during the sexual and asexual reproductive phases of the parasite. Digeneans are endoparasitic flatworms with complex life cycles involving asexual reproduction in mollusks (=first intermediate host) and sexual reproduction in vertebrates (=definitive host) (Figure 1). In some cases neorickettsiae are transmitted horizontally from digeneans to their vertebrate definitive hosts, where the bacteria can infect white blood cells and cause debilitating disease in horses, dogs, and humans [1-6]. Currently, Neorickettsia comprises three named species and several unnamed species level lineages [6,7].


Transmission rates of the bacterial endosymbiont, Neorickettsia risticii, during the asexual reproduction phase of its digenean host, Plagiorchis elegans, within naturally infected lymnaeid snails.

Greiman SE, Tkach VV, Vaughan JA - Parasit Vectors (2013)

Natural life cycle of the digenean Plagiorchis elegans. Neorickettsia infection is represented by a red dot.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3924192&req=5

Figure 1: Natural life cycle of the digenean Plagiorchis elegans. Neorickettsia infection is represented by a red dot.
Mentions: Bacteria in the genus Neorickettsia (Order Rickettsiales, Family Anaplasmataceae) are intracellular endosymbionts of digeneans. Neorickettsiae are presumably maintained throughout the digenean life cycle by vertical transmission during the sexual and asexual reproductive phases of the parasite. Digeneans are endoparasitic flatworms with complex life cycles involving asexual reproduction in mollusks (=first intermediate host) and sexual reproduction in vertebrates (=definitive host) (Figure 1). In some cases neorickettsiae are transmitted horizontally from digeneans to their vertebrate definitive hosts, where the bacteria can infect white blood cells and cause debilitating disease in horses, dogs, and humans [1-6]. Currently, Neorickettsia comprises three named species and several unnamed species level lineages [6,7].

Bottom Line: Prevalence of Neorickettsia infection in cercariae of Plagiorchis elegans was variable and never reached 100%.Reasons for this are speculative, however, the low prevalence of Neorickettsia observed in some of our samples (11 to 52%) differs from the high prevalence of other, related bacterial endosymbionts, e.g. Wolbachia in Wolbachia-dependent filariid nematodes, where the prevalence among progeny is universally 100%.This suggests that, unlike the Wolbachia-filaria relationship, the Neorickettsia-digenean relationship is not obligatory mutualism.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, University of North Dakota, 10 Cornell St,, Grand Forks, North Dakota 58202, USA. stephen.greiman@my.und.edu.

ABSTRACT

Background: Neorickettsia are obligate intracellular bacterial endosymbionts of digenean parasites present in all lifestages of digeneans. Quantitative information on the transmission of neorickettsial endosymbionts throughout the complex life cycles of digeneans is lacking. This study quantified the transmission of Neorickettsia during the asexual reproductive phase of a digenean parasite, Plagiorchis elegans, developing within naturally parasitized lymnaeid pond snails.

Methods: Lymnaea stagnalis snails were collected from 3 ponds in Nelson County, North Dakota and screened for the presence of digenean cercariae. Cercariae were identified to species by PCR and sequencing of the 28S rRNA gene. Neorickettsia infections were initially detected using nested PCR and sequencing of a partial 16S rRNA gene of pooled cercariae shed from each parasitized snail. Fifty to 100 single cercariae or sporocysts were isolated from each of six parasitized snails and tested for the presence of Neorickettsia using nested PCR to estimate the efficiency at which Neorickettsia were transmitted to cercariae during asexual development of the digenean.

Results: A total of 616 L. stagnalis were collected and 240 (39%) shed digenean cercariae. Of these, 18 (8%) were Neorickettsia-positive. Six Neorickettsia infections were selected to determine the transmission efficiency of Neorickettsia from mother to daughter sporocyst and from daughter sporocyst to cercaria. The prevalence of neorickettsiae in cercariae varied from 11 to 91%. The prevalence of neorickettsiae in sporocysts from one snail was 100%.

Conclusion: Prevalence of Neorickettsia infection in cercariae of Plagiorchis elegans was variable and never reached 100%. Reasons for this are speculative, however, the low prevalence of Neorickettsia observed in some of our samples (11 to 52%) differs from the high prevalence of other, related bacterial endosymbionts, e.g. Wolbachia in Wolbachia-dependent filariid nematodes, where the prevalence among progeny is universally 100%. This suggests that, unlike the Wolbachia-filaria relationship, the Neorickettsia-digenean relationship is not obligatory mutualism. Our study represents the first quantitative estimate of the Neorickettsia transmission through the asexual phase of the digenean life cycle.

Show MeSH
Related in: MedlinePlus