Fine structure and cytochemical analysis of the intestinal wall along the body of adult female of Litomosoides chagasfilhoi (Nematoda: Filarioidea)

Microbiota and gut ultrastructure of Anisakis pegreffii isolated from stranded cetaceans in the Adriatic Sea

BACKGROUND

Inferring the microbiota diversity of helminths enables depiction of evolutionarily established ecological and pathological traits that characterize a particular parasite-host interaction. In turn, these traits could provide valuable information for the development of parasitosis control and mitigation strategy. The parasite Anisakis pegreffii (Nematoda: Anisakidae) realizes the final stage of its life-cycle within gastric chambers of aquatic mammals, causing mild-to-moderate granulomatous gastritis with eosinophilic infiltrate, to severe ulcerative gastritis with mixed inflammatory infiltrate, often associated with bacterial colonies. However, its interaction with the host microbiota remains unknown, and might reveal important aspects of parasite colonization and propagation within the final host.

METHODS

MySeq Illumina sequencing was performed for the 16S rRNA gene from microbiota isolated from larvae, and uterus and gut of adult A. pegreffii parasitizing stranded striped dolphins (Stenella coeruleoalba). To assess the potential presence of Brucella ceti within isolated microbiota, Brucella-targeted real-time PCR was undertaken. In addition, TEM of the gastrointestinal tract of the infective third-stage (L3) and transitioning fourth-stage larvae (L4) was performed to characterize the morphological differences and the level of larval feeding activity.

RESULTS

In total, 230 distinct operational taxonomic units (OTUs) were identified across all samples (n = 20). The number of shared taxa was lower than the number of taxa found specifically in each parasite stage or organ. The dominant taxon was Mycoplasmataceae (genus Mycoplasma) in the gut and uterus of adult A. pegreffii, whereas Fusobacteriaceae (genus Cetobacterium) was the most abundant in 40% of larvae, alongside Mycoplasmataceae. No B. ceti DNA was detected in any of the microbiota isolates. TEM revealed differences in gut ultrastructure between L3 and L4, reflecting a feeble, most likely passive, level of feeding activity in L3.

CONCLUSIONS

Microbiota from L3 was more related to that of the gut rather than the uterus of adult A. pegreffii. Taxa of the larval microbiota showed qualitative and quantitative perturbations, likely reflecting the propagation through different environments during its life-cycle. This suggests an ontogenetic shift in the alpha and beta diversity of microbial communities from uterus-derived towards cetacean-derived microbiota. Although TEM did not reveal active L3 feeding, microbiota of the latter showed similarity to that of an actively feeding adult nematode.

Effects of albendazole on Litomosoides chagasfilhoi (Nematoda: Filarioidea) females in vivo

Gerbils (Meriones unguiculatus) experimentally infected with Litomosoides chagasfilhoi were treated with a single oral dose of 40 or 80 mg of albendazole, respectively. Observation of the microfilaremia after the treatment showed that both single oral doses of albendazole decreased the microfilaremia in L. chagasfilhoi infection. The body wall was composed of a cuticle, a hypodermis, and a muscular layer, and treated nematodes showed no morphological alterations. The ultrastructural alterations produced by treatment with 40 mg of albendazole included a higher number of membrane invaginations in the basal labyrinth of the uterine epithelium and the presence of myelin figures in this region. Inside the uterus, most embryos and microfilariae were disintegrated. The treatment with 80 mg of albendazole did not produce alterations in the uterine wall, and the number of vesicles near the microfilariae sheath was smaller than that observed in the untreated and in the 40-mg treatment groups. However, all the microfilariae observed in the uterus were extensively damaged with cytoplasmic vacuolization and cellular degeneration. No alterations in the intestinal cells were observed after treatment with 40 or 80 mg of albendazole. The present study contributes to the knowledge of albendazole's effects in filariids and demonstrates the potential embryotoxic and microfilaricidal consequences of this drug.

Ultrastructure of reproductive system of female Litomosoides chagasfilhoi Moraes-Neto, Lanfredi and De Souza, 1997 (Nematoda: Filarioidea)

The ultrastructure of the female reproductive system of the filariid Litomosoides chagasfilhoi by transmission electron microscopy (TEM) is described for the first time. The ovary is composed of primary oocytes surrounded by a single layer of epithelial cells apposed on the basal laminae. The ovarian wall is completely filled with primary oocytes, which are arranged radially and are centrally connected around the rachis. The uterine wall consists of muscular fibers surrounded by a basal lamina and the epithelium underlying the lamina. Ameboid and aflagellate spermatozoa are present inside the distal portion of the uterus, some of them near oocytes, which present bacteria in its cytoplasm. An eletrondense well-defined eggshell covers the zygotes, which presents in its cytoplasm bacteria arranged in groups. These bacteria are also observed in embryos and in the hypodermal cord. These ultrastructural aspects of L. chagasfilhoi female worms presented herein contribute to the knowledge of the morphology and embryonary development of this filariid, providing means for further comparative analyses of the action of anti-filarial drugs. Besides this, the presence of bacteria Wolbachia-like is being reported for the first time in this species, showing the great importance of this experimental model of study.