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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.

ABSTRACT: 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.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.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%.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.

SUBMITTER: Greiman SE

PROVIDER: S-EPMC3924192 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

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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 Stephen E SE Tkach Vasyl V VV Vaughan Jefferson A JA

Parasites & vectors 20131022

<h4>Background</h4>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.<h4>Methods</h4>L ...[more]

PMID: 24383453

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Project description:Neorickettsia (formerly Ehrlichia) risticii is an obligatory intracellular bacterium of digenetic trematodes. When a horse accidentally ingests aquatic insects containing encysted trematodes infected with N. risticii, the bacterium is transmitted from trematodes to horse cells and causes an acute and often fatal disease called Potomac horse fever (PHF). Since the discovery of N. risticii in the United States in 1984, using immunofluorescence and PCR assays, PHF has been increasingly recognized throughout North America and South America. However, so far, there exist only a few stable N. risticii culture isolates, all of which are from horses within the United States, and the strain diversity and environmental spreading and distribution of pathogenic N. risticii strains remain poorly understood. This paper reports the isolation of N. risticii from the blood of a horse with acute PHF in Ontario, Canada. Intracellular N. risticii colonies were detected in P388D1 cells after 47 days of culturing and 8 days after the addition of rapamycin. Molecular phylogenetic analysis based on amino acid sequences of major surface proteins P51 and Ssa1 showed that this isolate is distinct from any previously sequenced strains but closely related to midwestern U.S. strains. This is the first Canadian strain cultured, and a new method was developed to reactivate dormant N. risticii to improve culture isolation.Neorickettsia risticii is an environmental bacterium that lives inside flukes that are parasitic to aquatic snails, insects, and bats. When a horse accidentally ingests insects harboring flukes infected with N. risticii, the bacterium is transmitted to the horse and causes an acute and often fatal disease called Potomac horse fever. Although the disease has been increasingly recognized throughout North and South America, N. risticii has not been cultured outside the United States. This paper reports the first Canadian strain cultured and a new method to effectively culture isolate N. risticii from the horse blood sample. Molecular analysis showed that the genotype of this Canadian strain is distinct from previously sequenced strains but closely related to midwestern U.S. strains. Culture isolation of N. risticii strains would confirm the geographic presence of pathogenic N. risticii, help elucidate N. risticii strain diversity and environmental spreading and distribution, and improve diagnosis and development of vaccines for this dreadful disease.

Project description:BackgroundNeorickettsia are a group of intracellular α proteobacteria transmitted by digeneans (Platyhelminthes, Trematoda). These endobacteria can also infect vertebrate hosts of the helminths and cause serious diseases in animals and humans. Neorickettsia have been isolated from infected animals and maintained in cell cultures, and their morphology in mammalian cells has been described. However, limited information is available on the morphology and localization of Neorickettsia in the trematode host.MethodsWe used a Neorickettsia-infected strain of the model trematode Plagiorchis elegans to infect Syrian Golden hamsters to produce adult worms. Ultrastructure of Neorickettsia was assessed by transmission electron microscopy of high pressure freezing/freeze substitution fixed specimens. A Neorickettsia surface protein from P. elegans (PeNsp-3) was cloned and antibodies against the recombinant protein were used to localize Neorickettsia by immunohistochemistry.ResultsUltrastructural analysis revealed moderate numbers of pleomorphic endobacteria with a median size of 600 × 400 nm and characteristic double membranes in various tissue types. Endobacteria showed tubular membrane invaginations and secretion of polymorphic vesicles. Endobacteria were unevenly localized as single cells, or less frequently as small morula-like clusters in the ovary, Mehlis' gland, vitelline follicles, uterus, intrauterine eggs, testis, cirrus-sac, tegument, intestine and the oral and ventral sucker. Examination of hamster small intestine infected with P. elegans showed many endobacteria at the host-parasite interface such as the oral and ventral sucker, the tegument and the excretory pore.ConclusionsWe conclude that adult P. elegans trematodes carry Neorickettsia endobacteria in varying numbers in many tissue types that support vertical transmission, trematode to trematode transmission via seminal fluid, and possibly horizontal transmission from trematodes to vertebrate hosts. These means appear to be novel mechanisms of pathogen transmission by endoparasitic worms.

Project description:Background and objectivesLymnaeid snails are the known intermediate hosts of the liver fluke Fasciola spp. and therefore play an important role in the parasite's life cycle. The study is conducted to determine specificity of snail host-parasite interaction and to determine the snail-trematode infection rate by cercarial emergence, characterizing the emerging larvae using standardized key.Materials and methodsA total of 750 snails were collected from a rice field in Barangay Cawongan, Padre Garcia, Batangas, from November 2016 to March 2017 (n=150/month). Preliminary snail identification was based on morphological features of the shell. Each snail was acclimatized for 24 hours in a 50-ml capacity container before being exposed to strong artificial light. The 150 snails collected per month were grouped into 5 batches (n=30/batch) with each batch receiving different number of light exposures. Emerging cercariae were described and characterized using photo-referencing and standardized keys. All statistical tests were performed at p<0.05 level of significance using SPSS ver. 20.ResultsThe total cercarial shedding rate of the snails studied, as a measure of the infected snails, was found to be 35.6% and was positively associated with the length of the snail shell [OR = 1.809; 95% CI: 1.471-2.225; p<0.001], but not with the weight [OR = 0.003; 95% CI: 0.00-0.275; p=0.012] and width of the shell [OR = 0.937; 95% CI: 0.672-1.305]. The rates varied from 29.3% to 38.0% based on the frequency of 6-hour light exposure. Appearance of encysted forms increased with increasing number of light exposures [OR = 10.27, 95% CI: 3.04-34.76, p<0.001]. Three distinct cercariae were identified, namely, echinostome, longifurcate-pharyngeate distome cercariae (Strigea cercariae), and the virgulate xiphidiocercaria, with 26.4%, 2.27%, and 0.67% infection monitored by cercarial emergence, respectively.ConclusionLocal lymnaeid snails were infected with a single type of trematode larvae and coinfection with multiple larvae was rare but was encountered.

Dataset Information

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

Publications

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

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