Malaria vaccines: the 60-year journey of hope and final success-lessons learned and future prospects

BACKGROUND

The world has made great strides towards beating malaria, although about half of the world population is still exposed to the risk of contracting malaria. Developing an effective malaria vaccine was a huge challenge for medical science. In 2021 the World Health Organization (WHO) approved the first malaria vaccine, RTS,S/AS01 vaccine (Mosquirix™), for widespread use. This review highlights the history of development, and the different approaches and types of malaria vaccines, and the literature to date. It covers the developmental stages of RTS,S/AS01 and recommends steps for its deployment. The review explores other potential vaccine candidates and their status, and suggests options for their further development. It also recommends future roles for vaccines in eradicating malaria. Questions remain on how RTS,S vaccine will work in widespread use and how it can best be utilized to benefit vulnerable communities.

CONCLUSION

Malaria vaccines have been in development for almost 60 years. The RTS,S/AS01 vaccine has now been approved, but cannot be a stand-alone solution. Development should continue on promising candidates such as R21, PfSPZ and P. vivax vaccines. Multi-component vaccines may be a useful addition to other malaria control techniques in achieving eradication of malaria.

Scabies as a part of the World Health Organization roadmap for neglected tropical diseases 2021-2030: what we know and what we need to do for global control

Background

Scabies is an under-recognized global health problem with an unacceptably high prevalence in many settings worldwide. Fortunately, the World Health Organization (WHO) has formally designated scabies as a neglected tropical disease in 2017, in the hope of increasing awareness and encouraging efforts to eradicate it. Also, scabies has recently been included as part of the WHO roadmap for neglected tropical diseases 2021–2030, aimed at ending the neglect to attain the Sustainable Development Goals.

Main abstract body

This review article places scabies in focus. The literature was reviewed to explore discussions on controversial issues in scabies control, with the aim of clarifying whether global control of scabies is a feasible and worthwhile objective. The existing status of scabies and its burden are discussed along with future prospects for its global control. The article investigates the feasibility of scabies control and provides updates on the various impediments to this goal, such as challenges related to transmission, diagnosis, treatment, and vaccine development. Also examined are relevant research needs, success factors, and reasons for failure. This article aims to increase the global awareness of scabies and promote discussion, enhance coordinated international efforts, and ultimately, enact change at the national and worldwide levels toward the control of this preventable disease of the poor.

Conclusion

Despite the current challenges, scabies control is now within reach. With sustained interventions, continuous resources, and sincere commitment and support, scabies global control appears to be a worthwhile, realistic goal that is potentially achievable in the not so distant future.

Evaluation of the nitric oxide activity against Blastocystis hominis in vitro and in vivo

The effect of exogenous nitric oxide (NO) on growth, viability and ultra-structural of B. hominis was assessed in vitro by sodium nitrite (NaNO2) in 0.6 mM, 0.8 mM & 1 mM concentrations. The viability of B. hominis was identified using neutral red stain. The role of NO as an endogenous oxidant was assessed by identifying its level in cecum tissue, ileum tissue, blood and stool elutes of mice infected with B. hominis symptomatic human isolates using reactive nitrogen assay compared to control. In vitro study revealed that NaNO2 inhibited the growth and decreased viability of B. hominis with minimal lethal concentra-tion dose 1 mM on the 4th day while, minimal effects were detected with 0.6 and 0.8 mM. Transmission electron microscopy study proved that apoptotic-like features were observed in growing axenic culture of B. hominis upon exposure to NaNO2. These changes were not only found on the vacuolar (central body) form but also they were detected on granular, multi-vacuolar and cyst forms. In vivo study proved that high levels of NO were found in infected mice compared to low changes in control group. The high levels were in cecum tissue particularly. The mean levels of NO among infected mice were 211.8 +/- 20.7 microM in cecum, 90.4 +/- 11.6 microM in ileum, 60.1 +/- 4.7 microM in blood and 63.6 +/- 7.3 microM in stool elutes while, the mean levels of NO in control mice were 70.2 +/- 3.1 in cecum, 67.8 +/- 4.7 microM in ileum, 30.9 +/- 4.2 microM in blood and 28.1 +/- 2.9 microM in stool elutes. The differences were statistically highly significant. NO-donor drugs proved useful in treatment and increase the host resistance to B. hominis.

Effect of exogenous adminstration of antioxidants on Blastocystis hominis in vivo

The effect of exogenous administration of antioxidant (Anttox) on the course of B. hominis in experimentally infected mice was studied. B. hominis isolates were obtained from 10 gastrointestinal symptomatic adult patients. Three groups of 30 infected mice (3/isolate) were used. GI was untreated infected, GII was treated by antox for 4 weeks after infection diagnosis (treatment strategy), and GIII antox treated by for 4 weeks before infection (prophylactic strategy). Mild pathological changes were detected on 13.4%, 19.9% & 86.8% of mice in Gs I, II & III, respectively. Moderate pathological changes were found in 29.9%, 26.6% & 6.6% of mice in Gs I, II & III, respectively. While, the majority of severe pathological changes were in Gs I & II (56.7% & 53.5%) as compared to GIII (6.6%). Meanwhile, 86.8% of mice in GIII had B. hominis forms > 10/high power field compared to 3.3% in Gs I & II, respectively. Although 19.8% of mice in GII were positive for B. hominis by direct smear, no growth resulted in vitro and all the forms were non-viable by using neutral red stain. All the differences were statistically significant. So, antioxidant exacerbated B. hominis intensity but it decreased the pathological changes.

Real-time PCR and flow cytometry in detection of Cyclospora oocysts in fecal samples of symptomatic and asymptomatic pediatrics patients

The magnitude of Cyclospora oocysts excretion in relation to infection intensity among cyclosporiasis patients was assessed using flow cytometry and quantitative real-time PCR (RT-PCR). Oocysts from stool samples of 25 (14.8%) gastro-intestinal symptomatic pediatrics patients (169) and of 10 (2.8%) asymptomatic gastrointestinal ones (350) were identified by modified Ziehl-Neelsen (MZN) and modified Acid Fast Trichrome (MAFT) staining methods and confirmed by its auto-fluorescent characterizations. Also, 10 infants with negative stool samples were selected as controls. The intensity of infection was calculated as number of oocysts/200 microscopic filed with immersion 400. Flow cytometry and RT-PCR assessed relation between symptoms and oocysts excretions compared to MZN & MAFT. The infection severity in symptomatic patients were identified by MZN & MAFT as mild (16%), moderate (24%) and severe (60%) All asymptomatic patients had mild infection. Flow cytometry was done for stool samples and 100% Cyclospora oocysts were in symptomatic and asymptomatic patients. None was detected in controls. RT-PCR was done for stools with both a species-specific primer set and dual fluorescent labeled Cyclospora cayetanensis hybridization probe by unique regions of 18S rRNA gene sequence. DNA of C. cayetanensis was in 100% of symptomatic and asymptomatic patients and in 20% of controls. In repetitive examination of stools Cyclospora oocysts were neither detected by staining nor flow cytometry. Based on oocysts counts, no differences were found between flow cytometry and RT-PCR in compared to staining methods.

Molecular characterization of Egyptian Trichomonas vaginalis clinical isolates by HSP70 restriction fragment length polymorphism

Molecular typing of 20 Egyptian Trichomonas vaginalis clinical isolates was performed using the Restriction Fragment Length Polymorphism (RFLP) analysis employing a probe from the heat-inducible cytoplasmic HSP70 gene family hybridized with EcoR l-digested genomic DNA. In each of the isolates tested 5 to 6 distinct DNA fragments ranging from 2.7 Kb to 7.5 Kb in size were detected. Analysis of 13 isolates from symptomatic and 7 isolates from asymptomatic women revealed 6 distinct RFLP pattern subtypes of T. vaginalis. Eleven isolates (55%) showed the same RFLP pattern, teen of them (90.9%) were from symptomatic patients. T. vaginalis virus (TVV) was present in 7 isolates (35%). Only one isolate was considered resistant to Metronidazole. There were no relations between TVV infection or Metronidazole susceptibility and RFLP subtypes.

Detection of Fasciola-specific excretory/ secretory (E/S) protein fraction band (49.5 kDa) and its utilization in diagnosis of early fascioliasis using different diagnostic techniques

The objective of the present work is to evaluate Fasciola E/S antigens for diagnosis of early fascioliasis utilizing different diagnostic techniques. Using enzyme-linked immunoelectro-transfer blot (EITB), Fasciola-specific E/ S protein fraction band (49.5 kDa) was determined and electroeluted. The mono-specific antibodies against this specific fraction band were prepared by immunizing pathogen-free rabbit. Assessment of the prepared mono-specific antibodies in diagnosis of human fascioliasis was performed through the detection of E/S copro-antigens by enzyme-linked immunosorbent assay (ELISA) in stool eluates obtained from patients with confirmed fascioliasis, other parasites as well as from other healthy individuals. Serum samples were collected and tested to detect serum antibodies against Fasciola E/S antigen using EITB and counter immunoelectrophoresis (CIEP). Analysis of Fasciola adult worm E/S products by SDS/PAGE revealed a number of bands, the molecular weight (MW) of which ranged from 14-200 kDa; with three major bands (27.5, 32.5 and 55 kDa). Fasciola EIS 49.5 kDa protein fraction proved to be specific to F. gigantica. Cross reaction with S. mansoni was observed at higher MW (110-120 kDa). The sensitivity, specificity and diagnostic accuracy of EITB were 45.2%, 100% and 70.7%, respectively, while those of CIEP were 38.7%, 100% and 67.2%, respectively. ELISA technique using mono-specific anti-49.5 kDa to detect copro-antigens proved to be practical and reliable. It showed higher sensitivity (91.4%) and higher diagnostic accuracy (91.8%), while the specificity was 92.3%. In addition, ELISA had higher negative predictive value (88.9%) and fair positive predictive value (94.1%).