Gametocytes Research Articles

Current medicines for malaria including resistance issues

Malaria is an old disease and continues to be a major health problem in many countries. In spite of decrement in morbidity and mortality due to malaria, the transmission is still active throughout the world. Hence, appropriate treatment is needed to handle malaria in addition to preventive measures. However, unavailability of new drugs and the occurrence of resistant Plasmodium strains toward many conventional antimalarial drugs including artemisinins are the major obstacles in combating malaria infection. Thus, experts from all directions of our planet are in search of novel compounds, and many new chemical entities, such as artefenomel, ferroquine, KAE609, KAF156, DSM265, methylene blue, MMV39048, DDD107498, SJ733, and MMV253, have been under drug development process. While many agents are in the pipeline, most of them are not able to kill both gametocytes and hypnozoites.

Parasitic affections of domesticated pigeons (Columba livia) in Jammu, India

The parasitic fauna of domesticated pigeons in Jammu region were not recorded and so a survey was undertaken amongst a population of approximately 4000 birds in twelve areas around Jammu. Ectoparasites and haemoprotozoa from live birds, and endoparasites from dead birds were recorded. Ova shed in feces were also screened in four different seasons. Ectoparasites recovered include Columbicola columbae, Campanulotes bidentatus, Pseudolynchia canariensis, Ctenocephalides sp., Psoroptes sp. A total of 22 (36.67%) out 60 gastrointestinal tracts (GIT) of pigeons were positive for helminthic endoparasites including Raillietina sp. (25%; 15/60); Ascaridia sp. (5%; 3/60) and the hairworm Capillaria sp. (6.67%; 4/60). coccidian (58.3%; 35/60), cryptosporidian parasites (50.0%; 5/10), Trichomonas gallinae (40%; 12/30) and haemoprotozoal schizogony tissue stages (45.0%; 27/60) were observed in cloacal, oro-pharyngeal and tissue samples from post-mortem materials. Prevalence of cestodes was relatively more than nematodes perhaps due to the pigeon’s access to intermediate hosts of the cestodes. Blood smears showed the presence of Haemoproteus columbae gametocytes (26.6%; 8/30). Twenty-four pooled fecal samples examined from six select villages revealed presence of different parasitic ova. A higher prevalence of parasitic eggs was noted in the winters. Ascarid eggs were particularly prevalent during monsoon and post monsoon. Raillietina sp. was the most common cestode with lowered prevalence in the peak summers. It is speculated that close confinement of the domesticated birds are responsible for increased parasitic load and their dissemination. The parasitic data generated in the study may be helpful in estimating the faunistic prevalence of different parasites for strategic management of such parasitism during various seasons.

Comparative transcriptome analysis of Eimeria necatrix third-generation merozoites and gametocytes reveals genes involved in sexual differentiation and gametocyte development

Eimeria necatrix is one of the most pathogenic parasites causing high mortality in chicken older than 8 weeks. Eimeria spp. possess a coccidian lifecycle including both sexual and asexual stages. Sexual differentiation and development occupies a central place in the life cycle of the Eimeria parasite. However, our knowledge of the sexual differentiation and gametocyte development of Eimeria is very limited. Here using RNA sequencing, we conducted a comparative transcriptome analysis between third-generation merozoites (MZ-3) and gametocytes (GAM) of E. necatrix to identify genes with functions related to sexual differentiation and gametocyte development. Approximately 4267 genes were differentially expressed between MZ-3 and GAM. Compared with MZ-3, 2789 genes were upregulated and 1478 genes were downregulated in GAM. Approximately 329 genes in MZ-3 and 1289 genes in GAM were further analyzed in the evaluation of stage-specific genes. Gene Ontology (GO) classification and KEGG analysis revealed that 953 upregulated gametocyte genes were annotated with 170 GO assignments, and 405 upregulated genes were associated with 231 signaling pathways. We also predicted a further 83 upregulated gametocyte genes, of which 53 were involved in the biosynthesis of the oocyst wall, and 30 were involved in microgametocyte development. This information offers insights into the mechanisms governing the sexual development of E. necatrix and may potentially allow the identification of targets for blocking parasite transmission.

Sobre la presencia de un Dactylosoma en Bufo marinus

A Dactylosoma is reported from a specimen of Bufo marinus caught in Puntarenas, Costa Rica. The various evolutive forms of the agamic cycle are des­cribed, as well as what the author regards as gametocytes. Pending clarification of the taxonomy of the genus, the parasite under discussion is classified as Dactylosoma ranarum.

Single-Dose Primaquine to Block Transmission of Falciparum Malaria

Artemisinin combination therapy rapidly clears asexual-stage parasites but has inadequate activity against mature gametocytes, the parasite stage

A novel reverse transcription polymerase chain reaction reveals a high prevalence of Plasmodium vivax gametocyte carriage in an endemic area of Thailand

Background: Gametocytes are precursors of malaria sexual stages that are infective to mosquito vectors and play crucial roles in maintaining cycle of infection. Microscopy cannot determine the status of gametocyte carriage in those who had submicroscopic gametocytemia that may serve as infectious reservoirs in endemic areas. Meanwhile, gametocytes possess stage-specific mRNA that can be detected by molecular methods. Objective: To develop a sensitive method for detection of Plasmodium vivax gametocytes using reverse transcription polymerase chain reaction (RT-PCR) and determine its diagnostic performance in clinical samples. Materials and Methods: A nested RT-PCR was devised using primers targeting Pvs25, a mature gametocytespecific mRNA transcript of P. vivax (nested Pvs25 RT-PCR). Performance of the assay was evaluated using mRNA extracted from blood samples of 180 febrile patients attending a malaria clinic in Tak Province. Total RNA was extracted from blood samples that were preserved in RNAlater???? and from dried blood on filter papers. Malaria species was determined by microscopy from Giemsa stained blood smears and reaffirmed by nested PCR targeting mitochondrial cytochrome b (nested mtCytb PCR). Results: Of 180 blood samples, malaria was diagnosed in 120 patients (69 P. vivax and 51 P. falciparum) by microscopy and 125 patients by nested mtCytb PCR (69 P. vivax, 51 P. falciparum and 5 coinfections with both these species). Microscopy detected gametocytes in 30 of all 74 (40.5%) P. vivax positives by nested mtCytb PCR. Meanwhile, 67 of 74 (90.5%) P. vivax-positive isolates that were preserved in RNAlater???? gave positive results by nested Pvs25 RT-PCR. Therefore, nested Pvs25 RT-PCR identified mature P. vivax gametocytes more than twice as frequently as microscopy. The minimum detection threshold for nested Pvs25 RT-PCR was 10 copies of template DNA whereas no cross-reactivity with other human malaria species was observed. Dried blood collected on filter papers offered comparable results for Pvs25 mRNA detection with blood stored in RNA preservative with only 2.7% difference in positive rates. Conclusion: The nested RT-PCR targeting Pvs25 developed in this study is sensitive and specific for diagnosing mature P. vivax gametocytes and can be efficiently applied to both blood samples kept in RNA preservative and dried blood on filter paper. Keywords: Plasmodium vivax, Gametocyte, Pvs25, reverse transcription polymerase chain reaction, Thailand

A new P. falciparum gametocyte drug screening assay based on pLDH detection

Plasmodium gametocytes (GCT) have recently been proposed as a crucial target for the development of new antimalarials in order to achieve malaria elimination and eventually eradication. At present, however, a widely accepted and routinely used screening method for potential gametocytocidal drugs does not exist. The aim of our work was to adapt the parasite lactate dehydrogenase (pLDH), already standardised for drug screening on asexual stages, to measure gametocyte drug sensitivity. In clinics the GCT- pLDH, which is present during all the five stages of gametocyte development, can be measured with good sensitivity through OptiMAL, an immunochromatographic diagnostic test. The pLDH assay is fast, simple, not expensive and does not require complex equipment or special waste disposal. It can be applied to field isolates since transgenesis is not needed. Gametocytogenesis of two different strains of P. falciparum, 3D7 and NF54, was induced in vitro using a standardized protocol, asexual parasites were removed by N-acetylglucosamine treatment, and GCT were seeded in 96well plates. A linear correlation between the percentage of gametocytemia, microscopically counted by Giemsa staining, and the optical density, measured spectroscopically by pLDH assay, was demonstrated. A good signal to noise ratio was obtained with the pLDH assay, and the Z’factor was calculated as indicator of the robustness of the method. Our data also indicate that GCT have a pLDH activity higher than asexual parasites. GCT were treated for 48-72h with primaquine, the gold standard against mature gametocytes in vivo, which was used to validate most of the GCT screening methods in literature; dihydroartemisinin, active on young GCT; and methylene blue, an old antimalarial recently characterised also for its anti-GCT activity. Finally, epoxomicin was tested since its strong gametocytocidal effect has been recently reported. Dose-response curves were obtained with all the four drugs. However, some discrepancies were observed between the Giemsa staining and the pLDH detection at high concentrations of the drugs, suggesting that morphological abnormalities, detected microscopically, precede the decay of pLDH activity in drug-treated GCT. In order to better understand these observations, we prolonged the treatment for further 72h. This extra-incubation period allowed us to calculate, from the pLDH assay, the IC50 (as the 50% inhibition compared to control untreated GCT) of the tested compounds, which were comparable to those obtained by Giemsa staining. These results demonstrate the feasibility of pLDH assay to measure GCT content in culture. Although more specific probes for GCT viability need to be standardized for measuring stage-specific drug activity, pLDH can be used as the first, fast and cheap screening method to find potential gametocitocydal drugs.

Strong gametocytocidal effect of methylene blue-based combination therapy against falciparum malaria

With the availability of new preventive and curative interventions, global malaria control has been strengthened significantly in recent years. Drugs effective in reducing malaria gametocytaemia might contribute to local elimination and possible long-term eradication. We here report on the effects of methylene blue (MB)-based malaria combination therapy on gametocytaemia during a randomised-controlled trial in Burkina Faso. An open-label randomised controlled phase II study in 180 children aged 6-10 years with uncomplicated falciparum malaria was conducted in Nouna, north-western Burkina Faso. Children were randomised to MB-artesunate (AS), MB-amodiaquine (AQ), and AS-AQ (local standard of care). Overall follow-up was for 28 days, follow-up for gametocytaemia was for 14 days. The treatment groups were similar in baseline characteristics and there was only one loss to follow-up. Compared to AS-AQ, both MB-containing regimens were associated with significantly reduced gametocyte carrier rates during follow-up days 3, 7, and 14. This effect was seen both in patients with and without P. falciparum gametocytaemia at baseline. MB reveals pronounced gametocytocidal activity which appears to act against both existing and developing P. falciparum gametocytes. MB-based combination therapy thus has the potential to reduce transmission of P. falciparum malaria in endemic regions, which has important implications for future elimination and eradication strategies.

Ultrastructure of gametocytes of Leucocytozoon sabrazesi

Ultrastructure of gametocytes of Leucocytozoon sabrazesi

Additional Fallisia spp. (Apicomplexa: Plasmodiidae) of Neotropical lizards

Fallisia biporcati n. sp. parasitises thrombocytes and lymphocytes of Anolis biporcatus and A. lionotus in Panama. Round or oval schizonts average 13.3 × 11.5 (10.5–16 × 9–13) μm, with LW 153.8 (94–208) μm2, and produce 38.3 (28–60) merozoites. Gametocytes are variably shaped, from round or oval to nearly triangular or rectangular, and average 12.6 × 9.0 (10–15 × 6–12) μm, with LW 113.1 (82–150) μm2 and L/W ratio 1.43 (1.0–2.2). Thrombocytes and lymphocytes of A. poecilopus in Panama are parasitised by F. poecilopi n. sp. Schizonts, oval to elongate in shape, 7.7 × 4.7 (5.5–9 × 3–6) μm, with LW 36.5 (22–54) μm2, are filled with 31.0 (20–51) tiny nuclei or merozoites. Gametocytes are 10.1 × 8.0 (7.5–14 × 6–11) μm, with LW 82.0 (45–132) μm2, round to elongate with L/W ratio 1.27 (1.0–1.6). F. thecadactyli n. sp. parasitises thrombocytes and lymphocytes of Thecadactylus rapicaudus in Panama and Venezuela. Oval, oblong, or triangular schizonts average 10.3 × 8.0 (7–13 × 5–12) μm, with LW 86.6 (37–156) μm2, and produce 40.2 (26–61) merozoites. Gametocytes are round, oval, triangular or elongate, 10.4 × 7.0 (7–15 × 5–11) μm, with LW 74.8 (40–154) μm2 and L/W ratio 1.51 (1.1–2.2). F. dominicensis n. sp. parasitises thrombocytes of A. cybotes on Hispaniola. Schizonts, 6.0 × 4.8 (4–8 × 3–7) μm, with LW 29.1 (12–56) μm2, round, oval, elongate, oblong or lentiform in shape, produce 12.4 (8–22) merozoites. Gametocytes are 6.6 × 5.0 (5–9 × 4–7) μm , with LW 33.8 (20–56) μm2, round, oval or elongate, and L/W ratio of 1.34 (1.1–2.0).

The Comparative Incidence of Gametocytes in Untreated and in Briefly Treated Malaria

The Comparative Incidence of Gametocytes in Untreated and in Briefly Treated Malaria