Frontiers in parasitology最新文献

Introduction: Pathogens and parasites play a crucial role in shaping ecological and evolutionary processes, influencing the behavior, physiology, and survival of their hosts across diverse ecosystems. Despite their taxonomic and functional diversity, non-passerine birds remain underrepresented in pathogen/parasite ecological research, providing an opportunity to explore how their unique life histories influence host-parasite dynamics. Investigating the susceptibility of non-passerines to infections, particularly in relation to physiological stress indicators such as heterophil-to-lymphocyte (H/L) ratios and microhematocrit levels, offers valuable insights into the complex interplay between health state, environmental conditions, and disease dynamics.

Methods: We evaluated the occurrence of haemosporidian parasite (avian malaria) infections (Plasmodium spp. and Haemoproteus spp.) in individuals from six non-passerine bird species - Red-legged Seriema (Cariama cristata), Crested Caracara (Caracara plancus), Yellow-headed Caracara (Daptrius chimachima), Dusky-legged Guan (Penelope obscura), Gray-necked Wood-Rail (Aramides cajaneus), and Tropical Screech Owl (Megascops choliba) - that were admitted to the Wildlife Screening Center in Belo Horizonte, Minas Gerais, Brazil. We assessed whether blood-parasite infection occurrence was associated with hematological parameters (e.g. microhematocrit, H/L ratio), major injuries, age, body condition, season, co-occurrence of Trichomonas spp. infections, and presence of ectoparasites.

Results: Of the 75 individuals analyzed, 37% were infected with haemosporidian parasites (Plasmodium spp. and Haemoproteus spp. combined). Age was a significant predictor of haemosporidian infection, with adults exhibiting higher overall haemosporidian parasite occurrence (both Plasmodium spp. and Haemoproteus spp. together), likely due to age-related chronic infection accumulation or higher mortality among infected juveniles. Also, individuals infected with Haemoproteus spp. only showed elevated H/L ratios, suggesting a physiological response to infection, and were more frequently infected during the rainy season, likely reflecting optimal vector conditions. No significant associations were observed between blood-parasite infection occurrence and other factors such as physical condition, major injuries, co-occurring Trichomonas spp., or the presence of ectoparasites.

Discussion: These findings highlight the importance of considering physiological, environmental, and life-history factors when investigating malaria infections in non-passerine birds. By advancing our understanding of host-parasite interactions in these underrepresented species, this study contributes valuable knowledge to inform conservation, rehabilitation, and wildlife-management strategies for these less-studied birds.

Introduction: The increasing resistance of Plasmodium falciparum to existing antimalarial drugs drives the urgent need for novel therapeutic strategies. The purine salvage pathway in P. falciparum is essential for the parasite's survival due to its complete reliance on host-derived purines for nucleic acid synthesis and other essential processes. Although the purine salvage system has been intensively researched, no purine-based antimalarial drugs have been taken into preclinical development. The current study evaluated the chemotherapeutic potential of some purine nucleobase analogues against P. falciparum.

Methods: In vitro sensitivity assays were conducted using the 72-hour SYBR Green drug assay on laboratory-adapted P. falciparum strains 3D7 and Dd2. The most potent nucleobase analogues were docked into PfENT1 using the PyRx software suite.

Results: The analogues 8-azaguanine, 7-deazaguanine, and 6-thioguanine exhibited average EC₅₀ values of 1.71 µM, 14.9 µM and 15.7 µM, respectively, for 3D7 and 5.2 µM, 16.3 µM and 18.6 µM, respectively, for the Dd2 strain, and subsequently tested against field isolates of P. falciparum. These ex vivo tests showed EC₅₀ values ranging from 0.5 - 4.5 µM for 8-azaguanine, 3.8 - 12.3 µM for 7-deazaguanine, and 4.1 - 15.0 µM for 6-thioguanine. To understand their cellular targeting, molecular docking of the same analogues was performed using the structure of P. falciparum Equilibrative Nucleoside Transporter 1 (PfENT1). This demonstrated that guanine, 8-azaguanine and 7-deazaguanine formed five hydrogen bonds each with the same amino acid residues of PfENT1, whereas 6-thioguanine's orientation allowed only two hydrogen bonds with PfENT1. The binding pose of inosine was different from these nucleobases.

Discussion: These findings highlight the potential of guanine-based scaffolds, particularly 8-azaguanine and 7-deazaguanine, as promising leads for purine-based antimalarial drug development and the versatility of the PfENT1 transporter in the uptake of purine antimetabolites.

Introduction: Cryptosporidium spp. and Cystoisospora spp. are significant unicellular parasites that cause gastrointestinal infections in both humans and animals globally. Among these, Cryptosporidium felis and Cystoisospora felis are particularly important for feline health and pose potential zoonotic risks, especially for individuals with compromised immune systems. Kazakhstan, characterized by its diverse climate zones and an increasing population of pets, provides an excellent context for studying the epidemiology and genetic diversity of these parasites. In Kazakhstan, the mandatory registration of pets offers a valuable opportunity to explore the distribution and molecular characteristics of these parasites. This study focuses on the prevalence, genetic diversity, and zoonotic potential of Cryptosporidium and Cystoisospora from companion and shelter cats across five major cities in Kazakhstan.

Methods: Overall, from five cities, 1301 fecal samples were collected and studied. Samples were study by direct modified Sheather's flotation technique was applied using a sugar solution. Samples were screened using the 18S rRNA gene for Cryptosporidium and the ITS-1 gene for Cystoisospora. Nucleotide sequences were aligned with the MUSCLE multiple sequence alignment program. Phylograms were constructed with the MEGA11 software using the Maximum Likelihood (ML) method.

Results and discussion: In total, we examined 1,301 fecal samples and found that 31 (2.4%) contained Cryptosporidium spp., including 10 identified as Cryptosporidium felis. Additionally, 121 samples (9.3%) tested positive for Cystoisospora felis. The studied Cryptosporidium parvum isolates obtained in this study belong to subtype IIdA15G1, which is dominant and clusters well with previously reported sequences from different countries on the gp60 gene. Shelter cats are more susceptible to these parasites, with a prevalence of 3.1% for Cryptosporidium and a notably higher rate of 19.0% for Cystoisospora. In contrast, companion cats showed lower rates, at 1.6% for Cryptosporidium and 5.1% for Cystoisospora. Our findings identified the species Cystoisospora felis, Cryptosporidium parvum, and Cryptosporidium felis, with a determined subtype of XIXa.

Introduction: Eimeria pragensis, an intestinal protozoa infecting mice, induces colitis and reduces goblet cell numbers in the large intestine. In the present study, we investigated the pathogenesis and the mechanisms underlying goblet cell down-regulation in the early phase of infection.

Methods: Male C57BL/6 mice were orally infected with 300 oocysts. Fecal oocyst shedding and body weight were monitored daily. Colon tissues were collected at 3, 8, and 13 days post-infection (dpi) to assess pathological changes. Parasite burden was assessed by histological analysis (H&E staining) and qPCR targeting 5S rRNA. Goblet cells were visualized using PAS-Alcian Blue staining and Muc2 immunohistochemistry. To elucidate mechanisms of goblet cell dysfunction, we performed RNA sequencing of large intestine tissue to examine host as well as parasite transcriptomes.

Results: Fecal oocyst excretion peaked at 8-9 dpi. Body weight decreased from 6 to 11 dpi, with recovery after 12 dpi. Maximal parasite accumulation in the proximal colon was observed at 8 dpi in histological examination as well as qPCR. Colon length was significantly shortened at 3 dpi. Goblet cell area significantly reduced at 8 dpi (p < 0.05). RNA sequencing of infected large intestines revealed that E. pragensis produced enzymes that were known to degrade mucin and tight junctions, and proteins that could activate the Notch-Hes1 signaling pathway. As for host responses, genes associated with Th1-type inflammation, epithelial barrier disruption, and immune regulation were up-regulated as early as 3 dpi.

Discussion: Our findings suggested that E. pragensis infection induces a mucosal barrier dysfunction in the early phase of the infection, which possibly causes the tissue invasion of bacteria in the large intestine. Th1-type inflammatory response, thus induced, reduces goblet cell numbers and mucin production. This model provides valuable insight into the mechanisms of mucosal barrier disruption during protozoan infection.

Introduction: In the far western United States of America, Ixodes pacificus is the primary vector of several pathogens of public health and veterinary importance including the Lyme disease spirochete Borrelia burgdorferi sensu lato (s.l.), as well as Borrelia miyamotoi and Anaplasma phagocytophilum. Ixodes pacificus is common in southern Oregon yet there are few published studies on the distribution of tick-borne pathogens in this region.

Methods: Using real-time quantitative PCR, we assessed the prevalence of B. burgdorferi s.l., B. miyamotoi, and A. phagocytophilum among 2,463 unfed I. pacificus adults and nymphs combined into 260 pools (131 nymph, 129 adult) with nearly equal numbers of each life stage from 12 locations in Jackson County, Oregon.

Results: In our study, 27.9% (36/129) and 29.8% (39/131) of adult and nymph pools, respectively, tested positive for at least a single pathogen. Nymph pools had a higher pool positivity rate (PPR) for B. burgdorferi s.l. with 15.3% (20/131) testing positive compared to 3.1% (4/129) of adult pools. Nymph pools also had a higher minimum infection rate (MIR) and maximum-likelihood estimate of pooled prevalence (EPP) for B. burgdorferi s.l. than adults. Interestingly, the prevalence of B. burgdorferi s.l. varied greatly in nymph pools across collection sites (0-70%). PPR of B. miyamotoi was 21.7% (28/129) for adults and 12.2% (16/131) for nymphs, making it the most frequently detected pathogen in adult pools and the most detected pathogen overall. Anaplasma phagocytophilum was the least frequently detected pathogen overall with a PPR of 3.1% (4/129) and 2.3% (3/131) for adults and nymphs, respectively.

Discussion: These findings underscore the importance of continued surveillance, pathogen testing, and public education regarding ticks in areas such as southern Oregon where I. pacificus is common but little research has been done.

Background: Rapid Diagnostic Tests (RDTs) remain the frontline tool for malaria diagnosis, but their performance in detecting low-density infections is variable and poorly characterized at the population level.

Objective: This study aimed to evaluate the diagnostic performance of HRP2-based RDTs by integrating high-throughput bead-based HRP2 quantification into school-based malaria surveys.

Methods: A cross-sectional study was conducted in three Senegalese districts (Diourbel, Tambacounda, and Kédougou), enrolling 3,748 school-aged children. All participants were tested using RDTs, and dried blood spots were analyzed with a multiplex bead-based HRP2 assay. A Gaussian mixture model was used to classify HRP2 positivity, and logistic regression assessed the relationship between HRP2 concentration and RDT outcome.

Results: The overall RDT positivity rate was 7.2%, with marked heterogeneity across districts (Diourbel: 3.0%, Kédougou: 15.9%, Tambacounda: 7.6%). HRP2 concentration was the strongest predictor of RDT positivity (aOR: 14.55 per log₁₀ increase, 95% CI: 11.14-19.00). RDT limits of detection (LOD₉₅) varied significantly: 3.9 ng/mL in Tambacounda, 121.2 ng/mL in Kédougou, and 204.3 ng/mL in Diourbel.

Conclusion: RDTs remain a useful surveillance tool, particularly in moderate- to high-transmission settings. However, reduced sensitivity at lower antigen concentrations in hypo-endemic areas highlights the value of complementary high-sensitivity assays for elimination-focused strategies. Future research should explore the application of these integrated diagnostic approaches in regions without seasonal malaria chemoprophylaxis intervention.

Trichomonas vaginalis is a flagellated protozoan causing trichomoniasis, the most common non-viral sexually transmitted infection. It is associated with various complications, particularly in asymptomatic carriers. Another major cause of vaginitis is Candida albicans, a normal member of the vaginal microbiota, which causes vulvovaginal candidiasis when immune imbalances occur, leading to recurrent infections. Treatment-resistant strains of these pathogens pose a significant challenge. Lactobacillus crispatus, a dominant species in the vaginal microbiota, produces antimicrobial compounds that help protect the vaginal mucosa. This study establishes an in vitro co-culture of T. vaginalis, C. albicans, and L. crispatus to simulate the vaginal microenvironment at the site of infection. MRS medium was chosen for the co-culture, with initial cell densities determined as follows: T. vaginalis at 1.0 × 10⁶ trophozoites/mL (counted using a hemocytometer), 3.33 × 10⁴ CFU/mL for C. albicans, and either 5.53 × 10⁶ CFU/mL (for co-culture with the ATCC isolate) or 5.53 × 10⁷ CFU/mL (for co-culture with a fresh clinical isolate) for L. crispatus. The cell densities of C. albicans and L. crispatus were quantified as colony-forming units (CFU) on selective agar. The incubation period for co-culture, ensuring optimal growth of all microorganisms, was 24 hours. In co-culture, L. crispatus at both tested densities acidified the medium. The co-culture system demonstrated lower MIC values for metronidazole (50 µM in the ATCC isolate co-culture and 25 µM with the fresh clinical isolate) and lower MFC values for fluconazole (6.25 µM), compared to monocultures of T. vaginalis (100 µM) and C. albicans (12.50 µM). Furthermore, the triple co-culture increased the cytotoxicity to vaginal cell and erythrocytes for the ATCC isolate while significantly inhibited both biofilm formation and metabolic activity of C. albicans (by up to 92% and 90%, respectively), as well as its yeast-to-hyphae transition (by up to 70%). SEM analyses highlighted the morphological differences among T. vaginalis, C. albicans, and L. crispatus, including isolate-specific size variations in the protozoan. These findings suggest that this in vitro co-culture system is a valuable tool for evaluating the antimicrobial efficacy of novel compounds against vaginitis pathogens and for studying interactions within the vaginal microenvironment.

Diplotriaena spp. are nematode parasites of the abdominal and thoracic air sacs of numerous avian species worldwide. Dipoltriaena infections are generally subclinical, but high worm burdens can lead to morbidity and mortality. In this case series, Diplotriaena were recovered from a pileated woodpecker (Dryocopus pileatus) in 2017 and three northern flickers (Colaptes auratus) in 2023 and 2024 from Washington, USA. All four presented to a wildlife rehabilitation center with either respiratory signs or trauma with varied severity. A large number of worms (>44 worms) were surgically removed from the pileated woodpecker. The bird improved and was subsequently released. All three northern flickers were humanely euthanized due to poor prognosis and worsening conditions. Nematodes from Cases 1 and 4 were identified as a Diplotriaena sp. but they did not match any described species. Ethanol-fixed worms were available from one flicker case for genetic characterization. Partial 18S rRNA sequences (888bp) from two worms from a flicker were identical and 98-98.5% similar to numerous Diplotriaena obtusa sequences. The sample Diplotriaena sp. grouped separately from the three closest matches in the GenBank database, Diplotriaena anthreptis and two clades of Diplotriaena obtusa and Diplotriaena bargusinica. The partial COI sequences (674bp) were identical to each other and ~80-85% similar to numerous Spiruromorpha representatives. Due to a lack of available samples in the GenBank database and incomplete morphological descriptions of the genus, identification to species was not possible. In summary, all four cases in this case series occurred in free-ranging birds in Washington state and represented unusually high burdens of Diplotriaena sp. We believe that the high worm burden contributed to trauma, respiratory pathology, and weight loss. Additional surveillance is needed to determine the prevalence and impact of this parasite on woodpecker populations and to more accurately identify the parasite species in these two species of woodpeckers.