Refresh Rate-Based Caching and Prefetching Strategies for Internet of Things Middleware

One of the research directions in Internet of Things (IoT) is the field of Context Management Platforms (CMPs) which is a specific type of IoT middleware. CMPs provide horizontal connectivity between vertically oriented IoT silos resulting in a noticeable difference in how IoT data streams are processed. As these context data exchanges can be monetised, there is a need to model and predict the context metrics and operational costs of this exchange to provide relevant and timely context in a large-scale IoT ecosystem. In this paper, we argue that caching all transient context information to satisfy this necessity requires large amounts of computational and network resources, resulting in tremendous operational costs. Using Service Level Agreements (SLAs) between the context providers, CMP, and context consumers, where the level of service imperfection is quantified and linked to the associated costs, we show that it is possible to find efficient caching and prefetching strategies to minimize the context management cost. So, this paper proposes a novel method to find the optimal rate of IoT data prefetching and caching. We show the main context caching strategies and the proposed mathematical models, then discuss how a correctly chosen proactive caching strategy and configurations can help to maximise the profit of CMP operation when multiple SLAs are defined. Our model is accurate up to 0.0016 in Root Mean Square Percentage Error against our simulation results when estimating the profits to the system. We also show our model is valid using the t-test value tending to 0 for all the experimental scenarios.

Adaptive Context Caching for IoT-Based Applications: A Reinforcement Learning Approach

Making internet-of-things (IoT)-based applications context-aware demands large amounts of raw data to be collected, interpreted, stored, and reused or repurposed if needed from many domains and applications. Context is transient but interpreted data can be distinguished from IoT data in many aspects. Managing context in cache is a novel area of research that has been given very little attention. Performance metric-driven adaptive context caching (ACOCA) can have a profound impact on the performance and cost efficiency of context-management platforms (CMPs) when responding to context queries in realtime. Our paper proposes an ACOCA mechanism to maximize both the cost and performance efficiency of a CMP in near realtime. Our novel mechanism encompasses the entire context-management life cycle. This, in turn, distinctively addresses the problems of efficiently selecting context for caching and managing the additional costs of context management in the cache. We demonstrate that our mechanism results in long-term efficiencies for the CMP that have not been observed in any previous study. The mechanism employs a novel, scalable, and selective context-caching agent implemented using the twin delayed deep deterministic policy gradient method. It further incorporates an adaptive context-refresh switching policy, a time-aware eviction policy, and a latent caching decision management policy. We point out in our findings that the additional complexity of adaptation introduced to the CMP through ACOCA is significantly justified, considering the cost and performance gains achieved. Our algorithm is evaluated using a real-world inspired heterogeneous context-query load and a data set based on parking-related traffic in Melbourne, Australia. This paper presents and benchmarks the proposed scheme against traditional and context-aware caching policies. We demonstrate that ACOCA outperforms the benchmarks in both cost and performance efficiency, i.e., up to 68.6%, 84.7%, and 67% more cost efficient compared to traditional data caching policies to cache context, redirector mode, and context-aware adaptive data caching under real-world-like circumstances.

Curative-Intent Radiotherapy for Squamous Cell Carcinoma of the Head and Neck in Sri Lanka: The Impact of Radiotherapy Technique on Survival

AIMS

We conducted a retrospective analysis of patients with squamous cell carcinoma of the head and neck (SCCHN) treated with curative-intent radiotherapy at the National Cancer Institute of Sri Lanka to determine the impact of the treatment technique on disease-free survival (DFS).

MATERIALS AND METHODS

SCCHN patients treated with radical radiotherapy or adjuvant postoperative radiotherapy from 2016 to 2017 were included in the study. Data on the following variables were collected by reviewing clinical and radiotherapy treatment records: age, gender, tumour site, stage, time to delivery of radiotherapy, use of neoadjuvant chemotherapy, use of concurrent radiosensitising chemotherapy and treatment technique. DFS, defined as the time to death, tumour recurrence or loss to follow-up, was the primary end point and outcomes were compared between patients treated with intensity-modulated radiotherapy (IMRT) in linear accelerators and those treated with conventional radiotherapy in cobalt teletherapy units. Univariate and multivariate analyses were carried out on known prognostic variables.

RESULTS

In total, 408 patients were included in the study, with 138 (34%) being treated with IMRT in the linear accelerator. More than 75% of patients were of stage III or IV at diagnosis. The 2-year DFS of the whole cohort was 25% (95% confidence interval 21-30%). Patients treated with IMRT in the linear accelerator had a superior DFS in comparison with those treated with conventional radiotherapy in the cobalt teletherapy units (P < 0.001, hazard ratio 0.64, 95% confidence interval 0.5-0.82). Higher stage, cobalt treatment and use of neoadjuvant chemotherapy were adversely associated with DFS on multivariate analysis.

CONCLUSION

A large proportion of patients with SCCHN treated with curative-intent radiotherapy in Sri Lanka had locally advanced disease and DFS was superior in patients treated with IMRT in the linear accelerator.

A study on knowledge, attitudes and practices regarding dengue fever, its prevention and management among dengue patients presenting to a tertiary care hospital in Sri Lanka

Background

The World Health Organization (WHO) has ranked dengue as one of the top ten threats to Global health in 2019. Sri Lanka faced a massive dengue epidemic in 2017, the largest outbreak in the country during the last three decades, consisting of 186,101 reported cases, and over 320 deaths. The epidemic was controlled by intense measures taken by the health sector. However, the reported dengue cases and dengue deaths in 2019 were significantly higher than that of 2018. Deaths were mostly due to delay in hospitalization of severe dengue patients. The mortality of dengue hemorrhagic fever is 2–5% if detected early and treated promptly, but is high as 20% if left untreated.

Methods

A descriptive cross-sectional study was done among patients with dengue fever presenting to the Sri Jayawardenepura General Hospital during October 2019. Data was collected using a questionnaire comprising 20 questions based on knowledge, attitudes and practices on dengue, which were categorized into questions on awareness of mortality and severity of dengue burden, prevention of dengue vector mosquito breeding and acquiring the infection, patient’s role in dengue management, and warning signs requiring prompt hospitalization.

Results

The mean KAP score on all questions was 55%, while a majority of 65.2% patients scored moderate KAP scores (50–75%) on all questions, and only 7.6% had high KAP scores (> 75%). The highest categorical mean score of 62% was on awareness of dengue prevention, followed by 54% on awareness of dengue burden, and only 51% on dengue management. Only 5.3% patients scored high scores on awareness of dengue management, followed by 28.5%, and 40.9% patients scoring high scores on awareness of dengue burden, and awareness of prevention of dengue respectively. The mean KAP scores on all questions increased with increasing age category.

Conclusion

The population relatively has a better awareness of dengue prevention, as compared to awareness of dengue mortality and dengue management. The identified weak point is patient awareness of the patients’ role in dengue management, and identifying warning signs requiring prompt hospitalization. This results in delay in treatment, which is a major cause for increased mortality. There was a correlation between those who had good knowledge on dengue burden and those who were aware of patients’ role in dengue management. An action plan should be implemented to improve public awareness through education programs on the role of the public and patients in dengue management to drive a better outcome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06685-5.

An In-Silico Approach to Evaluate the Inhibitory Potency of Selected Hydroxamic Acid Derivatives on Zinc-Dependent Histone Deacetylase Enzyme

Histone deacetylase (HDAC) enzymes modify the histone by removing the acetyl group from the lysine residues, known as histone deacetylation. HDACs have been involved in altering gene expressions, resulting in cancer cells in the body. This study focuses on HDAC inhibitors’ impact on histone deacetylase-like protein (HDLP) stability through computational techniques. Molecular dynamics (MD) analyses were used to examine the atomic-level description of drug binding sites and how the HDAC inhibitors change the HDLP enzyme environment. In this study, two hydroxamic acid-derived inhibitors, such as [Formula: see text]-Carboxycinnamic acid bis-hydroxamide (CBHA) and scriptaid (GCK1026), were selected to examine the inhibition ability in terms with suberanilohydroxamic acid (SAHA) as a reference drug. The crystal structure of the HDLP was downloaded from the Protein Data Bank. The structures of inhibitors were optimized using the G09W package. Docking studies were done by AutoDock-Vina, and the resultant complex was used to initiate MD studies. The trajectories obtained from MD simulation were used to perform the structural analysis. Root-mean-square deviation (RMSD), radius of gyration, hydrogen bond, binding free energy and interaction energy studies revealed that the stability of HDLP-SAHA and HDLP-CBHA is higher than the free HDLP enzyme. The HDLP-CBHA complex shows an increased number of hydrogen bonds (5), high MM-PBSA binding free energy ([Formula: see text][Formula: see text]kJ/mol), high interaction energy ([Formula: see text][Formula: see text]kJ/mol), and an increased number of alpha-helical amino acids (130) compared with HDLP-SAHA. It concluded that the CBHA has the relatively same potential as SAHA to inhibit the HDLP. Consequently, the use of CBHA in clinical application is recommended through this in-silico method.

A young girl with chronic isolated cervical lymphadenopathy found to have lupus lymphadenopathy, progressing to develop lupus nephritis: a case report

BACKGROUND

Systemic lupus erythematosus is a rare autoimmune disorder, with the prevalence in Asia ranging from 30 to 50/100,000. The diagnosis of systemic lupus erythematosus is made according to the 2019 European League Against Rheumatism/American College of Rheumatology classification criteria, and it does not contain lymphadenopathy as diagnostic criteria. However, lupus lymphadenopathy has an estimated prevalence of 5-7% at the onset of disease, and 12-15% at any stage of the disease.

CASE PRESENTATION

A 19-year-old Sinhalese girl had neck nodules since the age of 5 years, which increased in size and became tender since 1 year. She had alopecia and joint stiffness for 6 months. She presented with a 5-day history of worsening joint pain, fever, and painful, enlarging cervical nodules. She had tender cervical lymphadenopathy, and a vasculitic rash on both lower limbs. She had pancytopenia, an erythrocyte sedimentation rate of 92, positive antinuclear antibody titer, and high anti-double-stranded deoxyribonucleic acid (DNA), with low C3 and C4 complements. She had a high reticulocyte count of 5%, with direct and indirect antiglobulin tests being positive, indicating autoimmune hemolytic anemia. Lymph node biopsy showed moderate reactive follicular hyperplasia, with scattered plasma cells and immunoblasts, with varying degree of coagulative necrosis, suggestive of lupus lymphadenopathy. On immunohistochemistry of the lymph node biopsy, Bcl2 was negative, excluding lymphoma. Contrast-enhanced computed tomography of abdomen and chest was normal with no hepatosplenomegaly or lymphadenopathy. Skin biopsy showed leukocytoclastic vasculitis. Later, with development of generalized edema, she was found to have impaired renal function, and renal biopsy showed lupus nephritis. She was started on hydroxychloroquine, prednisolone, and mycophenolate mofetil, and her symptoms improved and lymphadenopathy regressed.

CONCLUSION

In the case of cervical lymphadenopathy in a patient with systemic lupus erythematosus, the possibilities of lupus lymphadenopathy, Kikuchi-Fujimoto disease, and lymphoma should all be considered, after excluding secondary infection due to immunosuppression. Histology confirms the differentiation of these pathologies. It is important to differentiate the cause for lymphadenopathy in systemic lupus erythematosus as the outcome and treatment varies. Lupus lymphadenopathy is usually generalized, but isolated cervical lymphadenopathy could also rarely be the first presentation of systemic lupus erythematosus. Lupus lymphadenopathy can be the only presenting feature, and needs a high index in suspecting systemic lupus erythematosus, though it is not included in the diagnostic criteria.

Palliative care consultation and aggressive care at end of life in unresectable pancreatic cancer

Background

Palliative care (pc) consultation has been associated with less aggressive care at end of life in a number of malignancies, but the effect of the consultation timing has not yet been fully characterized. For patients with unresectable pancreatic cancer (upcc), aggressive and resource-intensive treatment at the end of life can be costly, but not necessarily of better quality. In the present study, we investigated the association, if any, between the timing of specialist pc consultation and indicators of aggressive care at end of life in patients with upcc.

Methods

This retrospective cohort study examined the potential effect of the timing of specialist pc consultation on key indicators of aggressive care at end of life in all patients diagnosed with upcc in Nova Scotia between 1 January 2010 and 31 December 2015. Statistical analysis included univariable and multivariable logistic regression.

Results

In the 365 patients identified for inclusion in the study, specialist pc consultation was found to be associated with decreased odds of experiencing an indicator of aggressive care at end of life; however, the timing of the consultation was not significant. Residency in an urban area was associated with decreased odds of experiencing an indicator of aggressive care at end of life. We observed no association between experiencing an indicator of aggressive care at end of life and consultation with medical oncology or radiation oncology.

Conclusions

Regardless of timing, specialist pc consultation was associated with decreased odds of experiencing an indicator of aggressive care at end of life. That finding provides further evidence to support the integral role of pc in managing patients with a life-limiting malignancy.

Cumulative sum (CUSUM) analysis in the assessment of trainee competence in fetal biometry measurement

OBJECTIVE

To determine the value of cumulative sum (CUSUM) analysis in assessing trainee proficiency in fetal biometry measurement.

METHODS

Three primary healthcare doctors with no prior ultrasound training were recruited. Each trainee measured the fetal biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL) on 100 consecutive pregnant women. The supervisor repeated the measurements. The CUSUM for each set of trainee measurements was calculated at a set failure rate of 10%. The point at which the graph fell below two consecutive boundary lines indicated the number of examinations required to achieve competence.

RESULTS

The CUSUM graphs showed that the rate of learning measurement skills varied among the three trainees. The graph for the CUSUM series for BPD and HC measurement for all trainees fell below two consecutive boundary lines and remained there, indicating competence. The CUSUM series for AC measurement for two of the trainees indicated that competence was achieved; however, for the third trainee, while the graph fell below two consecutive boundary lines, indicating competence, it rose again, crossing two consecutive boundary lines. This indicated a loss of competence and the need for further training. FL measurements for the same trainee never fell below two consecutive boundary lines, indicating failure to achieve competence; the other two achieved competence, but failed to maintain it.

CONCLUSIONS

CUSUM is a useful tool for identifying points of competence and for quantifying the duration of ultrasound training required for each trainee. It provides an early indication of performance, and highlights difficulties in individual performance.

Incidence of cancer in Sydney and Cape Breton County, Nova Scotia 1979-1997

The primary purpose of this study was to assess whether Sydney, Industrial Cape Breton County excluding Sydney (ICBxS) and Cape Breton County (CBCo) residents were at increased risk for cancer compared to Nova Scotia (NS) residents over five-year periods during 1979 through 1997. Gender-stratified, age-standardized cancer incidence rates were calculated following the direct method. All-cause rates were higher for female and male residents of Sydney, ICBxS and CBCo compared to NS based upon both municipality and postal code methods of residence classification. A sensitivity analysis of residential coding yielded a high degree of consistency for all geographies except Sydney, limiting comparisons of Sydney rates with other local geographies except where consistencies were observed. The results of this ecological study support the need for further analysis of factors contributing to the increased risk for cancer in CBCo.

Incidence of cancer in Sydney and Cape Breton County, Nova Scotia 1979-1997

The primary purpose of this study was to assess whether Sydney, Industrial Cape Breton County excluding Sydney (ICBxS) and Cape Breton County (CBCo) residents were at increased risk for cancer compared to Nova Scotia (NS) residents over five-year periods during 1979 through 1997. Gender-stratified, age-standardized cancer incidence rates were calculated following the direct method. All-cause rates were higher for female and male residents of Sydney, ICBxS and CBCo compared to NS based upon both municipality and postal code methods of residence classification. A sensitivity analysis of residential coding yielded a high degree of consistency for all geographies except Sydney, limiting comparisons of Sydney rates with other local geographies except where consistencies were observed. The results of this ecological study support the need for further analysis of factors contributing to the increased risk for cancer in CBCo.

The health and nutritional status of school children in two rural communities in Sri Lanka

There is growing evidence of considerable burden of morbidity and mortality due to infectious diseases and undernutrition in school children. This study describes the nutritional status and parasitic infections of school children in two areas of rural Sri Lanka. All children in four primary schools in the Moneragala district of Sri Lanka were included in the study. The height and weight of children were measured and anthropometric indices calculated. Stool and blood samples were examined for evidence of intestinal helminthiasis, malaria and anaemia. A greater proportion of boys than girls were underweight, wasted and stunted. Over 80% of the children were anaemic but did not apparently have iron deficiency anaemia according to their blood picture. The prevalence of parasitic infections such as hookworm and Plasmodium spp that may contribute to anaemia was low.

Enhancement of survival of stored dopaminergic cells and promotion of graft survival by exposure of human fetal nigral tissue to glial cell line--derived neurotrophic factor in patients with Parkinson's disease. Report of two cases and technical considerations

The authors have studied the ability of glial cell line-derived neurotrophic factor (GDNF) to promote survival of human fetal dopaminergic tissue after a storage period of 6 days and subsequent implantation into the human putamen. The results indicate that GDNF promotes survival of stored dopaminergic cells. Cells stored without GDNF had a 30.1% decrease in survival time compared with those exposed to GDNF. Two patients with Parkinson's disease received bilateral putaminal implants of fetal dopaminergic cells exposed to GDNF for 6 days and showed enhancement of graft survival as assessed by positron emission tomography scanning. A mean increase of 107% in putaminal fluorodopa uptake from baseline values was observed 12 months postgrafting.

The dietary habits of idiopathic calcium stone-formers and normal control subjects

OBJECTIVES

To examine the relationship between 12 macro- and micro-nutrients and the risk of recurrent calcium stone formation by comparing the diets of a large outpatient clinic-based group of patients who had formed calcium-based urinary tract calculi with that of a population-based control group matched for age, gender and body mass index.

PATIENTS, SUBJECTS AND METHODS

The dietary intake of 500 patients (cases) randomly selected from the adult population attending an outpatient renal-stone clinic and being evaluated and/or treated for biochemically or radiologically diagnosed calcium-based upper urinary tract calculi were compared with those of 500 control subjects selected to match for age, sex and body mass index from a stratified probability sample of 2212 adults (not institutionalized) living in the same geographical area.

RESULTS

Comparing the mean nutritional intakes showed a statistically higher consumption of energy, carbohydrates, sodium, fibre, vitamin C, fat and folic acid among cases than in controls. The intake of calcium, alcohol and vitamin A was significantly higher among the controls. There were no significant differences in the intake of protein, niacin or iron. The results of these comparisons varied when the groups were stratified by sex, age and body mass index.

CONCLUSIONS

Dietary risk factors for calcium-based urinary tract calculi are many and complex, and a detailed consideration of sex, age and body mass index is important in interpreting such data. While it is difficult to draw firm conclusions about causes and effects of individual nutrients from the available data, this study indicates a possibly more important role for dietary fat in stone formation than has been previously recognized. This relationship needs to be further explored in relation to urinary risk factors, as it may be possible to advise patients to reduce dietary fat as a prophylactic measure for stone formation. As dietary fat has been associated with cardiovascular diseases and possibly cancer, an overall recommendation to these patients for a low dietary fat intake may be easier to follow.

Features of recrudescent chloroquine-resistant Plasmodium falciparum infections confer a survival advantage on parasites and have implications for disease control

This paper reports on the features of recrudescent infections of chloroquine-resistant Plasmodium falciparum (CQRPf) malaria from a study in vivo of patients from a malaria endemic (n = 527) and non-endemic (n = 129) region of Sri Lanka where the incidence of RI resistance was 30% and 55%, respectively. In both groups of patients, the recrudescent infections which emerged after treatment of the primary infection with chloroquine (CQ) and primaquine had significantly lower peripheral parasitaemia (0.036% and 0.108% in endemic and non-endemic patients, respectively) compared to their primary infections (mean parasitaemia 0.13% and 0.49%; P = 0.021 and 0.002, respectively). The recrudescences of CQ resistant infections also gave rise to clinical disease of markedly reduced severity (average clinical scores of 10.1 and 8.2) compared to their primary infections (average clinical scores of 12.4 and 12.3; P = 0.003 and 0.001, respectively, in endemic and non-endemic patients). CQ resistant recrudescent infections therefore had a lower probability of being diagnosed and treated. In endemic patients, a higher proportion of CQRPf infections (57%) had gametocytaemia compared to the chloroquine sensitive ones (29%) (P = 0.014, chi 2 = 5.96) and were significantly more infective to mosquitoes (P = 0.047). these findings imply that, in areas where CQ resistance is prevalent, the continued use of the drug may confer a survival and propagation advantage on resistant parasites and favour the rapid expansion of their reservoir. In support of this, we also present epidemiological evidence showing that, in endemic areas, the proportion of P. falciparum patients carrying gametocytes has increased significantly since the emergence of chloroquine resistance. These findings are relevant to the management of drug resistance and malaria control in countries where P.falciparum is only partially resistant to CQ.

Self-assessment of disease activity by patients with rheumatoid arthritis

OBJECTIVE

To determine the reliability of self-assessment of disease by patients with rheumatoid arthritis (RA), with a particular emphasis on the assessment of articular swelling.

METHODS

A questionnaire was developed using components from validated instruments. Information was obtained on global function, global joint tenderness/swelling, and joint pain (10 cm visual analog scales), duration of musculoskeletal morning stiffness (grade 1-6), ACR functional score (grade 1-4), tender joint count (0-20), tender joint score (0-60), swollen joint count (0-20), and swollen joint score (0-60). Data were collected prospectively on 61 patients with RA in a teaching clinic or office practice by 4 staff rheumatologists. Patient questionnaires were completed within 24 h before physician assessments. Followup assessments were carried out on 27 patients after a mean interval of 3 months (range 0.5-6).

RESULTS

At the initial assessment there was a significant correlation between patient and physician assessments for global function (r = 0.83; p = 0.01) [intraclass correlation coefficient (ICC) = 0.83; p < 0.01], global joint tenderness/swelling (r = 0.83; p < 0.01) (ICC = 0.83; p < 0.01), global joint pain (r = 0.83; p < 0.01) (ICC = 0.81; p < 0.01), duration of morning stiffness (r = 0.83; p < 0.01) (ICC = 0.85; p < 0.01), ACR functional score (r = 0.61; p < 0.01) (ICC = 0.62; p < 0.01), tender joint count (r = 0.57; p < 0.01) (ICC = 0.31; p < 0.01), and tender joint score (r = 0.60; p < 0.01) (ICC = 0.35; p < 0.01). However, there was poor correlation between patient and physician assessments for both swollen joint count (r = 0.16; p > 0.05) (ICC = -0.02; p > 0.05) and swollen joint score (r = 0.24; p > 0.05) (ICC = 0.12; p > 0.05). Longitudinal analysis indicated significant correlation between changes in patient and physician assessments in all variables except swollen joint count and score.

CONCLUSION

Although there was good correlation between most variables for patient and physician assessments of disease activity in RA, there were substantial differences in the assessment of joint swelling. This objective determinant of disease activity cannot be ascertained in self-report measures of health status.

Structure and stability of a model pyrimidine-purine-purine DNA triple helix with a GC.T mismatch by simulation

A 1.5 ns long molecular dynamics simulation was conducted to compare the structure and stability of a model DNA triplex in saline solution with that found from experiments. The model DNA was an antiparallel py.pu.pu (CG.G) 7-mer structure which contained a GC.T mismatch triplet at the middle of the sequence. The local conformation of the mismatch triplet and the effects of this triplet on the global helical structure suggest that the GC.T triplet forms stable hydrogen bonds and shows distortions from an in-plane alignment. The overall rms deviation of the triplex is similar to one without a mismatch, although the thymine base in the mismatch triplet shows significantly higher mobility. A high coordination probability for water between the G and T bases in the mismatch triplet was observed to have an effect on the stability of non-hydrogen-bonded base pairs. Average helical parameters, sugar pucker, and backbone dihedral angles indicate that the CG.G triplets on the 3' side of the mismatch triplet possess different structural and dynamical properties than that of the 5' side. These observations are consistent with recently available experimental results and provide an interpretation of the observed experimental structure. They also suggest that inclusion of explicit water molecules is necessary in order to understand and predict the interaction between the third strand and duplex DNA.

Dielectric response of triplex DNA in ionic solution from simulations

We have analyzed a 1.2-ns molecular dynamics simulation of 51 mM d(CG.G)7 with 21 Na+ counter-ions and 1 M NaCl in water. Via the dipole fluctuations, the dielectric constant for the DNA is found to be around 16, whereas that for the bases and sugars combined is only 3. The dielectric constant for water in this system is 41, which is much smaller than 71 for pure SPC/E water, because of the strong restriction imposed on the motion of water molecules by the DNA and the ions. Also addressed in the present work are several technical issues related to the calculation of the dipole moment of an ionic solution from molecular dynamics simulations using periodic boundary conditions.

Infectivity of Plasmodium vivax and P. falciparum to Anopheles tessellatus; relationship between oocyst and sporozoite development

The assessment of malarial infectivity, for example in the evaluation of transmission blocking immunity, is generally based on counting oocysts in mosquitoes fed on infected blood. Ultimate transmission of the disease may, however, depend on the sporozoite load in the mosquito and its relationship to the size of the inoculum introduced to man. We conducted a laboratory study on Anopheles tessellatus infected with 108 different natural isolates of Plasmodium vivax from patients and 24 of P. falciparum to determine the relationship between oocyst numbers, sporozoite loads, and the effect of these on mosquito mortality. It was found that the P. vivax parasite density was positively correlated with the proportion of mosquitoes infected by a given feed at both the midgut and gland stages of parasite development (correlation coefficient [r] = 0.77, P < 0.001 and r = 0.6, P < 0.05 respectively). A significant positive linear correlation was observed between the number of oocysts and sporozoites in P. vivax (r = 0.5; P < 0.05); the proportions of mosquitoes infected with oocysts and sporozoites were also similarly related, although in general about 15% of mosquitoes infected with oocysts failed to develop salivary gland infections with sporozoites. The number of mosquitoes infected with P. falciparum parasites was too low for statistical analysis. Infection with either species of parasite did not appear to affect mosquito survival, nor was parasite density in the mosquito correlated with mosquito mortality.

Anti-circumsporozoite protein antibodies measure age related exposure to malaria in Kataragama, Sri Lanka

Antibodies to two peptides DDAAD and (NANP)40 representing the repetitive sequence of circumsporozoite antigens (CS protein) of P. vivax and P. falciparum respectively were measured in a cohort of 149 and 107 individuals respectively at four, 6 monthly blood surveys performed on residents of Kataragama, a P. vivax malaria endemic region in southern Sri Lanka. The prevalence of antibodies to the CS protein of both species was relatively low being less than 20% to either peptide in the population as a whole, this being consistent with the low entomological inoculation rates in the area. A marked age related prevalence pattern was evident, with the prevalence of antibodies increasing with age to reach between 25 to 30% in the 25-50 year age group in both P. vivax and P. falciparum. The population had had a life long exposure to P. vivax malaria but not to P. falciparum, an epidemic of which occurred in this region a few months prior to the beginning of this study. Nevertheless, the age-related prevalence of these antibodies was identical with respect to the two species. This suggests that the age-related prevalence pattern reflected differences in inoculation rates between the age groups due to differences in exposure to inoculation rather than an age acquired response resulting from a cumulative experience over several years. An analysis of antibody prevalence in individuals showed first, that sporozoite inoculations must have been clustered rather than homogeneously distributed in the population and secondly, that sero-conversion did not correlate with malaria infections in these individuals.

A mathematical model for Plasmodium vivax malaria transmission: estimation of the impact of transmission-blocking immunity in an endemic area

We have developed a multi-state mathematical model to describe the transmission of Plasmodium vivax malaria; the model accommodates variable transmission-blocking/enhancing immunity during the course of a blood infection, a short memory for boosting immunity, and relapses. Using the model, we simulated the incidence of human malaria, sporozoite rates in the vector population, and the level of transmission-blocking immunity for the infected population over a period of time. Field data from an epidemiological study conducted in Kataragama in the south of Sri Lanka were used to test the results obtained. The incidence of malaria during the study period was simulated satisfactorily. The impact of naturally-acquired transmission-blocking immunity on malaria transmission under different vectorial capacities was also simulated. The results show that at low vectorial capacities, e.g., just above the threshold for transmission, the effect of transmission-blocking immunity is very significant; however, the effect is lower at higher vectorial capacities.