Spatial transcriptomics reveals antiparasitic targets associated with essential behaviors in the human parasite Brugia malayi

Lymphatic filariasis (LF) is a chronic debilitating neglected tropical disease (NTD) caused by mosquito-transmitted nematodes that afflicts over 60 million people. Control of LF relies on routine mass drug administration with antiparasitics that clear circulating larval parasites but are ineffective against adults. The development of effective adulticides is hampered by a poor understanding of the processes and tissues driving parasite survival in the host. The adult filariae head region contains essential tissues that control parasite feeding, sensory, secretory, and reproductive behaviors, which express promising molecular substrates for the development of antifilarial drugs, vaccines, and diagnostics. We have adapted spatial transcriptomic approaches to map gene expression patterns across these prioritized but historically intractable head tissues. Spatial and tissue-resolved data reveal distinct biases in the origins of known drug targets and secreted antigens. These data were used to identify potential new drug and vaccine targets, including putative hidden antigens expressed in the alimentary canal, and to spatially associate receptor subunits belonging to druggable families. Spatial transcriptomic approaches provide a powerful resource to aid gene function inference and seed antiparasitic discovery pipelines across helminths of relevance to human and animal health.

Parasites as niche modifiers for the microbiome: A field test with multiple parasites

Parasites can affect and be affected by the host’s microbiome, with consequences for host susceptibility, parasite transmission, and host and parasite fitness. Yet, there are two aspects of the relationship between parasite infection and the host microbiome that remain little understood: the nature of the relationship under field conditions, and how the relationship varies among parasite species. To overcome these limitations, we assayed the within-leaf fungal community in a grass population to investigate how diversity and composition of the fungal microbiome are associated with natural infection by fungal parasites with different feeding strategies. We hypothesized that parasites that more strongly modify niches available within a host will thereby alter the microbial taxa that can colonize the community and be associated with greater changes in microbiome diversity and composition. A parasite that creates necrotic tissue to extract resources (necrotrophs) may act as a particularly strong niche modifier whereas one that does not (biotrophs) may not. Barcoded amplicon sequencing of the fungal ITS region revealed that the microbiome of leaf segments that were symptomatic of necrotrophs had lower fungal diversity and distinct composition compared to segments that were asymptomatic or symptomatic of other parasites. There were no clear differences in fungal diversity or composition between leaf segments that were asymptomatic and segments that were symptomatic of other parasite feeding strategies. This supports the hypothesis that within-host niches link infection by parasites to the host’s microbiome. Together, these results highlight the importance of parasite traits in determining parasite impacts on the host’s microbiome.

Multiple isotope analyses of the pike tapeworm Triaenophorus nodulosus reveal peculiarities in consumer–diet discrimination patterns

Previous studies of dietary isotope discrimination have led to the general expectation that a consumer will exhibit enriched stable isotope levels relative to its diet. Parasite–host systems are specific consumer–diet pairs in which the consumer (parasite) feeds exclusively on one dietary source: host tissue. However, the small numbers of studies previously carried out on isotopic discrimination in parasite–host (ΔXP-HT) systems have yielded controversial results, showing some parasites to be isotopically depleted relative to their food source, while others are enriched or in equilibrium with their hosts. Although the mechanism for these deviations from expectations remains to be understood, possible influences of specific feeding niche or selection for only a few nutritional components by the parasite are discussed. ΔXP-HT for multiple isotopes (δ13C, δ15N, δ34S) were measured in the pike tapeworm Triaenophorus nodulosus and two of its life-cycle fish hosts, perch Perca fluviatilis and pike Esox lucius, within which T. nodulosus occupies different feeding locations. Variability in the value of ΔXP-HT calculated for the parasite and its different hosts indicates an influence of feeding location on isotopic discrimination. In perch liver ΔXP-HT was relatively more negative for all three stable isotopes. In pike gut ΔXP-HT was more positive for δ13C, as expected in conventional consumer–diet systems. For parasites feeding on pike gut, however, the δ15N and δ34S isotope values were comparable with those of the host. We discuss potential causes of these deviations from expectations, including the effect of specific parasite feeding niches, and conclude that ΔXP-HT should be critically evaluated for trophic interactions between parasite and host before general patterns are assumed.

Characterization of three neutral proteases of Spirometra mansoni plerocercoid

SUMMARYIn the pathogenesis of sparganosis, proteases have been considered to play important roles in tissue migration and parasite feeding. Several bands of proteolysis were observed when crude extracts of Spirometra mansoni plerocercoid (sparganum) were examined using gelatin substrate gel at neutral pH, of which two proteases of 198 and 104 kDa were purified by two chromatographic steps, and a 36 kDa protease was purified by gelatin-affinity and DEAE–anion exchange chromatography. All the purified proteases exhibited optimal activity at pH 7·5 and 0·1 M Tris–HCI. Proteolytic activities at 198 and 104 kDa were inhibited specifically by serine protease inhibitors, and 4-(amidinophenyl)methansulfonyl fluoride (APMSF, 0·5 m) and N-α–p–tosyl-L-lysine chloromethyl ketone (TLCK, 1 mM), which strongly suggested that these two proteases were trypsin-like proteases. The activity of the 36 kDa protease was inhibited by N-tosyl-l-phenylalanine chloromethyl ketone (TPCK, I mM) and chymostatin (0·1 mM), and was potentiated in 10 mM Ca2+ which showed that the protease had a chymotrypsin-like property. All the proteases were Schiff(PAS) positive. Proteases of 198 and 104 kDa degraded collagen completely within 24 h. The 36 kDa enzyme cleaved human recombinant interferon-γ (rIFNγ) and bovine myelin basic protein. In addition, all the purified proteins elicited strong antibody responses in the infected patients.

Host–parasite relationships between burbot (Lota lota) and adult Salmincola lotae (Copepoda)

The pathology elicited by the parasitic copepod Salmincola lotae and its distribution within the oral cavity of the burbot, Lota lota, is described. Of 50 burbot examined from the Apostle Islands region, Lake Superior, near Bayfield, WI, 18 (36%) were infested with S. lotae. A total of 63 copepods were recovered. Burbot were examined from three Lake Michigan collecting sites: 70 from Sturgeon Bay, 9 from Manitowoc, and 60 from Sheboygan were not infested with S. lotae. Salmincola lotae appears to prefer middle regions of the roof of the mouth. Mechanical damage to host tissues resulting from copepod presence included epidermal shredding from parasite feeding and lesions from bulla excavation and implantation. Epidermal encapsulation of the second maxillae of S. lotae was the primary host tissue reaction. Increased dermal vascularization and leucocyte infiltration occurred in regions of parasite attachment. This is the first report of S. lotae from the Nearctic.

The structure and development of Histomonas meleagridis (Mastigamoebidae: Protozoa) in the female reproductive tract of its intermediate host, Heterakis gallinarum (Nematoda)

The ultrastrcuture and development of the protozoan Histomonas meleagridis in the reproductive system of the female nematode, Heterakis gallinarum, have been described. It has been shown that there is a distinct cycle of events in the reproductive system. The stage of Histomonas in the germinal zone of the ovary is extracellular; the protozoan feeds and multiplies here. The histomonads move down the ovary with the oogonia and become intracellular when they penetrate the developing oocytes in the growth zone of the ovary. This is apparently an active penetration of the oocyte by the parasite. Feeding and division of the histomonad occurs in the oocyte and also in the newly formed egg; apparently a gradual reduction in size occurs along the reproductive system. These stages in the parasite are similar to the tissue-inhabiting stages in the bird but are much smaller. There are no mitochondria present.There is strong circumstantial evidence that the nematode is able to repair damage to the wall of the reproductive system and to the oolemma caused by the protozoan.I wish to thank Dr E. E. Lund of Beltsville Parasitological Laboratory, Maryland, U.S.A., who very kindly sent me some of his Histomonas-free strain of Heterakis and Dr L. P. Joyner and Mr C. C. Norton of the Central Veterinary Laboratory, Weybridge, for the strain of Heterakis which was found to transmit Histomonas wenrichii. I also wish to thank Mrs B. Fisher, Mr B. Millard and Mr M. Shirley for technical assistance and Mr P. Rogers for assistance with the photography.