Characterization of the endogenous DAF-12 ligand and its use as an anthelmintic agent in Strongyloides stercoralis

A prevalent feature of Strongyloides stercoralis is a life-long and potentially lethal infection that is due to the nematode parasite’s ability to autoinfect and, thereby, self-replicate within its host. Here, we investigated the role of the parasite’s nuclear receptor, Ss-DAF-12, in governing infection. We identified Δ7-DA as the endogenous Ss-DAF-12 ligand and elucidated the hormone’s biosynthetic pathway. Genetic loss of function of the ligand’s rate-limiting enzyme demonstrated that Δ7-DA synthesis is necessary for parasite reproduction, whereas its absence is required for the development of infectious larvae. Availability of the ligand permits Ss-DAF-12 to function as an on/off switch governing autoinfection, making it vulnerable to therapeutic intervention. In a preclinical model of hyperinfection, pharmacologic activation of DAF-12 suppressed autoinfection and markedly reduced lethality. Moreover, when Δ7-DA was administered with ivermectin, the current but limited drug of choice for treating strongyloidiasis, the combinatorial effects of the two drugs resulted in a near cure of the disease.

Characterization of the Endogenous DAF-12 Ligand and Its Use as an Anthelmintic Agent in Strongyloides stercoralis

ABSTRACTA prevalent feature of Strongyloides stercoralis is a life-long and potentially lethal infection that is due to the nematode parasite’s ability to autoinfect and, thereby, self-replicate within its host. Here, we investigated the role of the parasite’s nuclear receptor, Ss-DAF-12, in governing infection. We identified Δ7-DA as the endogenous Ss-DAF-12 ligand and elucidated the hormone’s biosynthetic pathway. Genetic loss of function of the ligand’s rate-limiting enzyme demonstrated that Δ7-DA synthesis is necessary for parasite reproduction, whereas its absence is required for development of infectious larvae. Availability of the ligand permits Ss-DAF-12 to function as an on/off switch governing autoinfection, making it vulnerable to therapeutic intervention. In a preclinical model of hyperinfection, pharmacologic activation of DAF-12 suppressed autoinfection and markedly reduced lethality. Moreover, when Δ7-DA was administered with ivermectin, the current but limited drug of choice for treating strongyloidiasis, the combinatorial effects of the two drugs resulted in a near cure of the disease.

In vitro infection of Madin-Darby bovine kidney (MDBK) cells with Eimeria acervulina sporozoites: quantitative analysis of parasite cellular invasion and replication using real-time polymerase chain reaction (PCR)

Poultry coccidiosis causes considerable economical losses to the livestock industry. Eimeria parasites are responsible for this disease. On a global scale, E. acervulina and E. tenella are amongst the most common Eimeria spp. infecting broilers. E. tenella is commonly used as infection model in in vivo and in vitro studies. On the other hand, E. acervulina has barely been studied under in vitro conditions. A well established and widely used in vitro model for E. tenella infection is the Madin-Darby bovine kidney cell line (MDBK); however, little is known regarding suitability of MDBK cells as host cells for E. acervulina. We infected MDBK monolayers with two different doses, 5 × 104 and 2 × 105, of E. acervulina sporozoites and evaluated cultures at 24 and 96 h post infection (hpi). For comparison, we ran an identical infection assay using E. tenella sporozoites. To assess parasite reproduction, the number of DNA copies of E. acervulina SCAR marker and E. tenella ITS-1 gene was quantified using real-time quantitative PCR. We found that the number of E. acervulina copies increased significantly at 24 hpi in comparison to E. tenella (p < 0.05). After 96 hpi, E. acervulina gene copies were considerably reduced while E. tenella continued to multiply (p < 0.05). Our results show that MDBK monolayers could be used for in vitro research aimed to study E. acervulina sporozoite cell invasion. Nevertheless, modifications of in vitro cultivation appear necessary to allow qualitative and quantitative studies over longer periods of parasite reproduction.

Downstream Effects: Impact of Antibiotic Pollution on Aquatic Host-Parasite Interactions

The global increase in antibiotic use has led to contamination of freshwater environments occupied by parasites and their hosts. Despite the identified impacts of antibiotics on humans and wildlife, the effect of antibiotics on host-parasite life cycles is relatively unexplored. We utilize the trematode parasite Schistosoma mansoni, and its snail intermediate host Biomphalaria glabrata to explore the influence of an ecologically relevant antibiotic concentrations on the life history characteristics of both parasite and host. Our results demonstrate that antibiotics not only accelerate parasite development and have a positive effect on parasite reproduction, but also increase the likelihood of host egg laying, and delay parasite-induced host castration. Using a mathematical model, we suggest that these life history alterations associated with antibiotics are likely to increase parasite transmission and disease burden.

Vector dynamics influence spatially imperfect genetic interventions against disease

Background and objectives Genetic engineering and similar technologies offer promising new approaches to controlling human diseases by blocking transmission from vectors. However, in spatially structured populations, imperfect coverage of the vector will leave pockets in which the parasite may persist. Movement by humans may disrupt this local persistence and facilitate eradication when these pockets are small, spreading parasite reproduction outside unprotected areas and into areas that block its reproduction. Here we consider the sensitivity of this process to biological details: do simple generalities emerge that may facilitate interventions? Methodology We develop formal mathematical models of this process similar to standard Ross-Macdonald models, but (i) specifying spatial structure of two patches, with vector transmission blocked in one patch but not in the other, (ii) allowing temporary human movement (travel instead of migration), and (iii) considering two different modes of mosquito biting. Results We find that there is no invariant effect of disrupting spatial structure with travel. For both biting models, travel out of the unprotected patch has different consequences than travel by visitors into the patch, but the effects are reversed between the two biting models. Conclusions and implications Overall, the effect of human travel on the maintenance of vector-borne diseases in structured habitats must be considered in light of the actual biology of mosquito abundances, biting dynamics, and human movement patterns. Lay summary Genetic interventions against pathogens transmitted by insect vectors are promising methods of controlling infectious diseases. These interventions may be imperfect, leaving pockets where the parasite persists. How will human movement between protected and unprotected areas affect persistence? Mathematical models developed here show that the answer is ecology-dependent, depending on vector biting behavior.

Vector dynamics influence spatially imperfect genetic interventions against disease

Background and objectivesGenetic engineering and similar technologies offer promising new approaches to controlling human diseases by blocking transmission from vectors. However, in spatially structured populations, imperfect coverage of the vector will leave pockets in which the parasite can persist. Yet movement by humans may disrupt this local persistence and facilitate eradication when these pockets are small, essentially distributing parasite reproduction out of unprotected areas and into areas that block its reproduction.MethodologyWe develop formal mathematical models of this process similar to standard Ross-Macdonald models, but (i) specifying spatial structure of two patches, with transmission blocked in one patch but not in the other, (ii) allowing temporary human movement (travel instead of migration), and (iii) considering two different modes of mosquito biting.ResultsWe find that there is no invariant effect of disrupting spatial structure with travel. For both biting models, travel out of the unprotected patch has different consequences than travel by visitors into the patch, but the effects are reversed between the two biting models.Conclusions and implicationsOverall, the effect of human travel on the maintenance of vector-borne diseases in structured habitats must be considered in light of the actual biology of mosquito abundances and biting dynamics.Lay summaryGenetic interventions against pathogens transmitted by insect vectors are promising methods of controlling infectious diseases. These interventions may be imperfect, leaving pockets where the parasite persists. How will human movement between protected and unprotected areas affect persistence? Mathematical models developed here show that the answer is ecology-dependent, depending on vector biting behavior.

Diversity patterns in parasite populations capable for persistence and reinfection with a view towards thehuman cytomegalovirus

Many parasites like thecytomegalovirus, HIVandEscherichia coliare capable to persist in and reinfect its host. The evolutionary advantage (if so) of these complicated mechanisms have not been quantitatively analyzed so far. Here we take a first step by investigating a host-parasite model for which these mechanisms are driving the evolution of the parasite population. We consider two variants of the model. In one variant parasite reproduction is directed by balancing selection, in the other variant parasite reproduction is neutral. In the former scenario reinfection and persistence have been shown to sustain the maintenance of diversity in the parasite population in certain parameter regimes (Pokalyuk and Wakolbinger, 2018). Here we analyse the diversity patterns in the latter, neutral scenario. We evaluate the biological relevance of both model variants with respect to thehuman cytomegalovirus(HCMV), an ancient herpesvirus that is carried by a substantial fraction of mankind and manages to maintain a high diversity in its coding regions.

Dual RNA-seq reveals no plastic transcriptional response of the coccidian parasiteEimeria falciformisto host immune defenses

ABSTRACTBackgroundParasites can either respond to differences in immune defenses that exist between individual hosts plastically or, alternatively, follow a genetically canalized (“hard wired”) program of infection. Assuming that large-scale functional plasticity would be discernible in the parasite transcriptome we have performed a dual RNA-seq study of the full lifecycle ofEimeria falciformisusing infected mice with different immune status (e.g. naïve versus immune animals) as models for coccidian infections.ResultsWe compared parasite and host transcriptomes (dual transcriptome) between naïve and challenge infected mice, as well as between immune competent and immune deficient ones. Mice with different immune competence show transcriptional differences as well as differences in parasite reproduction (oocyst shedding). Broad gene categories represented by differently abundant host genes indicate enrichments for immune reaction and tissue repair functions. More specifically, TGF-beta, EGF, TNF and IL-1 and IL-6 are examples of functional annotations represented differently depending on host immune status. Much in contrast, parasite transcriptomes were neither different between Coccidia isolated from immune competent and immune deficient mice, nor between those harvested from naïve and challenge infected mice. Instead, parasite transcriptomes have distinct profiles early and late in infection, characterized largely by biosynthesis or motility associated functional gene groups, respectively. Extracellular sporozoite and oocyst stages showed distinct transcriptional profiles and sporozoite transcriptomes were found enriched for species specific genes and likely pathogenicity factors.ConclusionWe propose that the niche and host-specific parasiteE. falciformisuses a genetically canalized program of infection. This program is likely fixed in an evolutionary process rather than employing phenotypic plasticity to interact with its host. In turn this might (negatively) influence the ability of the parasite to use different host species and (positively or negatively) influence its evolutionary potential for adaptation to different hosts or niches.

Sexual reproduction and genetic exchange in parasitic protists

SUMMARYA key part of the life cycle of an organism is reproduction. For a number of important protist parasites that cause human and animal disease, their sexuality has been a topic of debate for many years. Traditionally, protists were considered to be primitive relatives of the ‘higher’ eukaryotes, which may have diverged prior to the evolution of sex and to reproduce by binary fission. More recent views of eukaryotic evolution suggest that sex, and meiosis, evolved early, possibly in the common ancestor of all eukaryotes. However, detecting sex in these parasites is not straightforward. Recent advances, particularly in genome sequencing technology, have allowed new insights into parasite reproduction. Here, we review the evidence on reproduction in parasitic protists. We discuss protist reproduction in the light of parasitic life cycles and routes of transmission among hosts.