The latest medical research on Tropical Medicine
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Request AccessAge, period, and cohort effects of Clonorchis sinensis infection prevalence in the Republic of Korea: Insights and projections.
PLoS Neglected Tropical DiseasesWith decades of containment efforts, the prevalence of C. sinensis infection in Korea has shown a declining trend. However, well-tailored intervention assessments remain challenging, particularly when considering the potential impacts of cohort variations in raw freshwater fish consumption behavior, a major transmission route to humans, on this observed decline.
We applied an age-period-cohort modeling approach to nationally representative C. sinensis infection prevalence data from 1981-2012 in Korea to assess age, period, and cohort effects on its secular trend and to project the age-stratified prevalence up to 2023.
Our analysis suggests that both cohort and period effects have substantially contributed to the declining prevalence of C. sinensis infection in Korea. Age-stratified projections up to 2023 suggest a decline in prevalence across all age groups, while those aged over 40 are anticipated to maintain prevalences above the elimination threshold of 1%.
Our study highlights the importance of incorporating cohort effects into intervention assessments aimed at controlling C. sinensis infection. The effectiveness of interventions remains evident in Korea despite adjusting for the cohort effect. This approach, applicable to other endemic countries, would provide valuable insights for intervention assessments and inform future public health planning to eliminate C. sinensis infection.
Lagged effects of climate factors on bacillary dysentery in western China.
Transactions of theEvidence has shown that the incidence of bacillary dysentery (BD) is associated with climatic factors. However, the lagged effects of climatic factors on BD are still unclear, especially lacking research evidence from arid and semi-arid regions. Therefore, this study aims to add new insights into this research field.
Spatial autocorrelation, time series analysis and spatiotemporal scans were used to perform descriptive analyses of BD cases from 2009 to 2019. On the basis of monthly data from 2015 to 2019, multivariable distributed lag non-linear models were used to investigate the lagged effects of climatic factors on BD.
The hot spots for BD incidence are gradually decreasing and becoming increasingly concentrated in the southern part of Gansu Province. The maximum cumulative relative risks for monthly average temperature, sunshine duration, average relative humidity and precipitation were 3.21, 1.64, 1.55 and 1.41, respectively. The lagged effects peaked either in the current month or with a 1-month lag, and the shape of the exposure-response curve changed with the increase in maximum lag time. After stratification by per capita gross domestic product, there were differences in the effects.
Climatic factors can influence the incidence of BD, with effects varying across different lag times. It is imperative to vigilantly track the disparities in the incidence of BD attributable to economic factors.
Building capacity for testing sterile insect technique against Aedes-borne diseases in the Pacific: a training workshop and launch of sterile insect technique trials against Aedes aegypti and arboviral diseases.
Infectious Diseases of PovertyVector-borne diseases cause morbidity and mortality globally. However, some areas are more impacted than others, especially with climate change. Controlling vectors remains the primary means to prevent these diseases, but new, more effective tools are needed. The World Health Organization (WHO) prioritized evaluating novel control methods, such as sterile insect technique (SIT) for control of Aedes-borne diseases. In response, a multiagency partnership between the U.S. Centers for Disease Control and Prevention (CDC), the Special Programme for Research and Training in Tropical Diseases (TDR), WHO, and the International Atomic Energy Agency (IAEA) supported the operational implementation and evaluation of SIT against Aedes aegypti and arboviral diseases in the Pacific through a consortium of regional partners (PAC-SIT Consortium).
A workshop was held from 2 to 6 May 2023, during which PAC-SIT country participants, researchers, and stakeholders in SIT, scientific advisory committee members, and organizational partners came together to review the principles and components of SIT, share experiences, visit field sites and the SIT facility, and officially launch the PAC-SIT project. Working in groups focused on entomology, epidemiology, and community engagement, participants addressed challenges, priorities, and needs for SIT implementation.
The PAC-SIT workshop brought together researchers and stakeholders engaged in evaluating SIT for arboviral diseases in the Pacific region and globally. This training workshop highlighted that many countries are actively engaged in building operational capacities and phased testing of SIT. The workshop identified a key need for robust larger-scale studies tied with epidemiological endpoints to provide evidence for the scalability and impact on mosquito-borne diseases.
The impact of the RTS,S malaria vaccine on uncomplicated malaria: evidence from the phase IV study districts, Upper East Region, Ghana, 2020-2022.
Malaria JournalThe RTS,S malaria vaccine has been prequalified for use in endemic settings prioritizing areas with moderate to high disease transmission. The impact of a vaccine at the population level may differ from observations during clinical trial due to programmatic, and individual-related factors, among others. The objective of this study was to assess the impact of the RTS,S malaria vaccine on uncomplicated malaria among children aged 12-59 months in the Phase IV study districts, Upper East Region, Ghana.
A retrospective study was conducted using routine malaria surveillance data for the period 2020-2022. The burden of uncomplicated malaria was compared between the implementing (Kasena Nankana East and West districts) and comparator areas (Builsa North and South districts). The impact of RTS,S malaria vaccine was assessed by estimating the percentage reduction in uncomplicated malaria and incidence averted in the implementing area, accounting for the effect of confounders.
Over 50,000 episodes of uncomplicated malaria among children aged 12-59 months were included in the study. Uncomplicated malaria was reduced by 33% (95%CI 29-36) over the entire study period, but the malaria incidence averted declined from 324/1,000 (95% CI 298-339; p < 0.0001) in 2020 to 287/1000 (95% CI 274-299; p < 0.0001) in 2022.
The RTS,S malaria vaccine significantly reduced the burden of uncomplicated malaria among children aged 12-59 months in the implementing area. The sequential marginal declines in malaria incidence averted over the study period might be due to waning of protective immunity and acquisition of natural immunity as children age. Strengthening uptake of the currently recommended vaccines and other malaria control interventions is required to improve public health impact.
Evaluation of a novel biplex rapid diagnostic test for antibody responses to Loa loa and Onchocerca volvulus infections.
PLoS Neglected Tropical DiseasesEndemic to Central Africa, loiasis, caused by the vector-borne worm Loa loa, affects approximately 10 million individuals. Clinical manifestations include transient angioedema (Calabar swellings), migration of the adult worm under the eye conjunctiva (eye worm) and less specific general symptoms. Loiasis presents a significant public health challenge because L. loa-infected individuals can develop serious adverse events after taking ivermectin, the drug used to combat onchocerciasis. In this context, alternative interventions and rigorous diagnostic approaches are needed. Diagnosing loiasis is challenging because its main clinical manifestations are sporadic and non-specific. The definitive diagnosis relies on identifying adult worms migrating beneath the conjunctiva, or microfilariae (pre-larvae) in blood smears. However, "occult loiasis" (infection without blood microfilariae) is frequent. Serological rapid antibody diagnostic tests (ARTs) can provide an alternative diagnostic method. We compared a novel ART simultaneously targeting onchocerciasis (IgG4 to Ov-16 and OvOC3261, test line 1) and loiasis (IgG4 to L1-SXP-1, test line 2), called IgG4-SXP-1 biplex test) to the already established Loa-ART (all IgG isotypes to Ll-SXP-1, called pan-IgG-SXP-1 test).
Blood samples underwent both ARTs, read qualitatively and semi-quantitatively. Additionally, blood smears, skin snips, Kato-Katz method for soil-transmitted helminthiases identification and eosinophilia measurements were performed. Questionnaires gathered demographic details and loiasis-related signs. ARTs performance was compared using specific loiasis-related signs and microfilaremia as references. Discordances between the two ARTs were investigated using logistic regression models.
Out of 971 participants, 35.4% had L. loa microfilaremia, 71.9% had already experienced loiasis-related signs, 85.1% were positive in the pan-IgG-SXP-1 test and 79.4% were positive in the IgG4-SXP-1 biplex test. In the microfilariae-positive population, the sensitivity of the rapid tests was 87.4% for the pan-IgG-SXP-1 test and 88.6% for the prototype IgG4-SXP-1 biplex test. Sensitivity was similar for both ARTs when using eye worm or Calabar swelling as references, but diagnostic performance varied based on microfilaremia levels and occult loiasis. Overall, IgG4-SXP-1 biplex test demonstrated a sensitivity of 84.1% and specificity of 47.6% for loiasis compared to the pan-IgG-SXP-1 test, leading to a Kappa coefficient estimated at 0.27 ± 0.03 for the qualitative results of the 2 ARTs. In the group that tested positive with the Pan-IgG test but negative with the IgG4-specific test, there was a lower prevalence of STH infection (p = 0.008) and elevated eosinophilia (p<0.001) compared to the general tested population.
The sensitivity of each test was good (84-85%) but the diagnostic agreement between the two ARTs was poor, suggesting that IgG and IgG4 antibody responses should be interpreted differently. The assessment of the innovative rapid diagnostic IgG4-SXP-1 biplex test, designed for onchocerciasis and loiasis, shows encouraging sensitivity but underlines the necessity for further in vitro assessment.
Water, sanitation, and hygiene (WASH) practices in Africa: exploring the effects on public health and sustainable development plans.
Tropical Medicine and International HealthSuboptimal water, sanitation, and hygiene (WASH) practices constitute a serious public health risk, affecting one-third of the world's population. Remarkable progress has been made to improve WASH; however, challenges remain, with rapid population growth adding pressure on WASH systems. This study explores the current state of WASH practices and diseases in Africa, identifies challenges, and proposes public health recommendations for sustainable implementation.
The staggering burden of WASH-related diseases in low- and middle-income countries (LMICs), particularly in Africa, threatens public health, with millions of deaths and disability-adjusted life years (DALYs) attributed to poor WASH practices annually. Notable challenges plaguing WASH practices in the region include poverty, malnutrition, poor data reporting, illiteracy, climate change, and poor healthcare financing. This results in adverse health consequences, including waterborne infections like cholera, typhoid, dysentery, and diarrheal diseases. Additionally, neglected tropical diseases (NTDs) such as intestinal worms, schistosomiasis, trachoma, lost productivity, and environmental pollution from soil and underground water contamination have been implicated. Geographical disparities, cultural norms, and inadequate funding further complicate efforts to improve WASH infrastructure and practices. Globally concerted efforts are required to address these issues and permit WASH practices to protect human health by preventing infectious diseases and contributing to economic growth. Strong financial frameworks, skills training, and tools like WASH Fit are recommended for a stronger WASH approach in Africa.
The consequences of poor WASH extend beyond public health, impacting economic growth, gender equality, and environmental sustainability. WaterAid's policy recommendations prioritizing government administration, institutional capacity enhancement, and more financial resources are expedient.
Insecticide resistance status and mechanisms in Aedes aegypti and Aedes albopictus from different dengue endemic regions of Panama.
Tropical Medicine and International HealthDengue is a serious public health problem worldwide, including Panama. During the last years, the number of dengue cases has increased. This may be due to the presence of mosquito populations resistant to insecticides. The aim of this study was to characterize the resistance status, its enzymatic mechanisms and Kdr mutations in wild populations of Aedes aegypti and Aedes albopictus.
Standard WHO bioassays were performed using insecticide-treated filter papers to determine resistance in populations Ae. aegypti and Ae. albopictus to pyrethroids insecticides, organophosphates, to the carbamate propoxur and to the organochlorine DDT. Biochemical assays were conducted to detect metabolic resistance mechanisms and real-time PCR was performed to determine the frequencies of the Kdr mutations Val1016IIe and F1534C.
The strains Ae. aegypti El Coco showed confirmed resistance to deltamethrin (78.5% mortality) and lambda-cyhalothrin (81%), Aguadulce to deltamethrin (79.3%), David to deltamethrin (74.8%) and lambda-cyhalothrin (87.5%) and Puerto Armuelles to permethrin (83%). Aedes aegypti El Empalme showed confirmed resistance to pirimiphos-methyl (62.3% mortality), chlorpyrifos-methyl (55.5%) and propoxur (85.3%). All strains of Ae. albopictus showed possible resistance to PYs and five strains to DDT. Only Ae. albopictus Canto del Llano showed confirmed resistance to pirimiphos-methyl (70% mortality) and malathion (62%). Esterase activity was variable across sites with the most frequent expression of α-EST compared to β-EST in Ae. aegypti populations. In Ae. Albopictus, the expressed enzymes were β-EST and MFOs. Through ANOVA, significant differences were established in the levels of enzymatic activity of α- and β-EST, MFOs and GST, with p < 0.001 in the Ae. aegypti and Ae. albopictus. The Kdr Val1016IIe mutation was detected in Ae. aegypti Aguadulce, El Coco and David. The odds ratio for the Val1016Ile mutation ranged from 0.8 to 20.8 in resistant mosquitoes, indicating the association between pyrethroid phenotypic resistance and the kdr mutation.
The presence of a varied and generalized resistance, enzymatic mechanisms and the Val1016IIe mutation may be associated with the intensive use and possibly misuse of the different insecticides applied to control Aedes populations. These results highlight the need to develop a program for resistance management. Also, alternative approaches to mosquito control that do not involve insecticides should be explored.
Modern agriculture and One Health.
Infectious Diseases of PovertyThe development of modern agriculture has significantly contributed to improving global food security and safety, alleviating poverty, and enhancing human health and livelihoods. However, the rapid advancement of modern agriculture has also brought about various challenges that limit its sustainable development. This commentary aims to discuss these issues through the One Health lens, and provide valuable insights for balancing modern agricultural activities with the need to protect and promote the health of all the sectors.
This commentary explores the multifaceted impacts of modern agriculture on social development, as well as the associated various health challenges and environmental impacts within the One Health framework. Key issues include ecosystem degradation, increased risk of interspecies disease transmission like zoonoses, reverse zoonoses, and vector-borne diseases, and the escalated threat of antimicrobial resistance due to intensified agricultural production and increased antimicrobial use. To address these challenges, this commentary outlines potential solutions anchored in the development and implementation of modern technologies and good agricultural practices, such as precision farming, integrated pest management, biosecurity measures, vaccination programs, as well as surveillance and early detection of health risks.
Good agricultural practices supported by scientific and technological advancements are essential for aligning productivity with the One Health vision, ensuring the health and resilience of all the sectors. Enhancing stakeholder education, strengthening regulatory frameworks, and providing supportive policies and infrastructure for farmers to adopt sustainable practices are crucial for the long-term viability of agrifood systems. The Food and Agriculture Organization of the United Nations plays a pivotal role in guiding this sustainable transformation through the One Health approach.
Factors influencing the acceptability of the test, treat and refer practice for malaria among caregivers of under 5 children at community pharmacies and drug shops in Nigeria.
Malaria JournalMalaria affects children under the age of five and pregnant women, leading to high morbidity and mortality rates. In sub-Saharan Africa, Patent and Proprietary Medicine Vendors (PPMVs) have been identified as key players in the provision of malaria treatment due to their accessibility and availability in communities, but PPMVs are not usually tested before fever cases are treated as malaria or refer clients. The aim of this study was to explore the factors influencing caregivers' acceptance of the test, treatment and referral practices for malaria management provided by CPs and PPMVs in Kaduna and Lagos states, Nigeria.
A cross-sectional quantitative telephone survey was conducted among 150 caregivers of children under five years old who received malaria services from trained CPs and PPMVs between May and July 2022. Descriptive and bivariate analyses were performed to identify factors significantly associated with the acceptability of malaria management services. All statistically significant factors from the bivariate analysis were explored using logistic regression models, and odds ratios (ORs) with confidence intervals (CIs) were calculated to predict acceptability. The 95% level was used to define statistically significant associations (p ≤ 0.05).
All caregivers were asked questions that aided in obtaining a diagnosis of malaria. More than two-thirds of the caregivers (68%) reported that the child was tested by a CP/PPMV. Among those treated (148), 89% reported that the child was administered artemisinin combination therapy (ACT) irrespective of whether the child tested positive or negative for malaria. At the bivariate level, acceptability was greater among caregivers of children aged 13 months and older than among caregivers of children aged 0-12 months (93% vs. 76%, p = 0.004). Caregivers of children who prescribed ACT had greater acceptance than did those not prescribing ACT (92% vs. 69%, p = 0.010). Multivariate analysis revealed that these relationships held.
The adoption of the test, treat, and refer practice as a standard approach by CPs and PPMVs could replace the widespread practice of prescribing medications without conducting tests. This shift has the potential to improve the quality of malaria management services and enhance patient outcomes.
Influence of future climate scenarios using CMIP 5 data on malaria transmission in India.
Malaria JournalVector-borne diseases, such as malaria, pose a significant global threat, and climatological factors greatly influence their intensity. Tropical countries, like India, are particularly vulnerable to such diseases, making accurate estimation of malaria risk crucial.
This study utilized the well-known Vector-borne Disease Community Model, VECTRI, developed by the International Centre for Theoretical Physics in Trieste. The model was implemented to estimate malaria's Entomological Inoculation Rate (EIR). Future climatic prediction datasets, including CMIP 5 and population data sets, were used as inputs for the analysis. Three RCP scenarios are considered (Representative Concentration Pathways are climate change scenarios that project radiative forcing to 2100 due to future greenhouse gas concentrations). The projections covered the period from 1 Jan, 2020, to 31 Dec, 2029.
The estimated mean EIR for the years 2020-2029 ranged, and a significant decline in malaria risk was observed with all RCP 2.6, 4.5, and 8.5 scenarios. Each year 0.3 to 2.6 [min-max] EIR/person/day decline is observed with a strong decline in man rainfall ranging from 5 to 17 [min-max] mm/year and associated high temperatures ranging from 0.03 to 0.06 [min-max] °C/year. During the post-monsoon period, August to November were identified as highly prone to malaria transmission. Spatial analysis revealed that the east coast of India faced a higher vulnerability to malaria risk, which kept increasing through RCP scenarios. Thus, it is essential to exercise caution, especially in areas with heavy rainfall.
This research provides valuable insights for policy-makers, highlighting the need to implement future strategies to mitigate malaria risk effectively. By utilizing these findings, appropriate measures can be taken to combat the threat posed by malaria and protect public health.
Assessing the prevalence, risk factors, and socio-demographic predictors of malaria among pregnant women in the Bono East Region of Ghana: a multicentre hospital-based mixed-method cross-sectional study.
Malaria JournalMalaria is one of the world's most lethal vector-borne diseases, causing significant health burdens in endemic countries. Several studies on the prevalence of malaria among pregnant women in Ghana have been conducted in various parts of the country, yielding evidence pointing to intra- and inter-regional variations. The current study assessed the prevalence, risk factors, and sociodemographic predictors of malaria among pregnant women in the Bono East Region of Ghana.
This multicentre hospital-based study employed a mixed-method cross-sectional design. A multistage sampling technique was used to select seven health facilities and recruited 1452 pregnant women who attended ANC at seven selected health facilities. Haematological examination, a structured closed-ended questionnaire, in-depth interviews (IDIs), and focus group discussions (FGDs) were used to obtain relevant data. Quantitative data were analysed with STATA 14 (StataCorp, College Station, USA). Likewise, the four-step thematic analysis was used to analyse qualitative data. A significant level was set at (p < 0.05) at a 95% confidence interval (CI).
The ages of the pregnant women at enrolment ranged between 17 and 40 years, with a mean (SD) of 28.8 ± 3.73 (95% C.I: 28.63-29.02). The overall prevalence of malaria infection among pregnant women was 10.8% (95% CI: 9.32-12.56). Presence of farm or domestic animals, living close to drainage tunnels, living near overgrown vegetation, not married, not having formal education, living in extended-type households, living in compound-type households, mud and thatch households, mud and iron sheet households, primigravidae, multiparity, first-time pregnant women, second-time, third-time, fourth-time, and fifth-time ANC visits, blood groups A, B, and AB were independent factors or predictors significantly associated with increased risk of malaria.
The current study revealed an approximately 10.8% prevalence of malaria among pregnant women. The prevalence revealed, was, however, higher than the national prevalence of 8.6%. The high prevalence of malaria, associated risk factors, and sociodemographic and maternal predictors highlight the need to strengthen screening for malaria, administer treatments, monitor maternal and foetal health, and provide education and counselling.
Urban malaria and its determinants in Eastern Ethiopia: the role of Anopheles stephensi and urbanization.
Malaria JournalMalaria prevention and control strategies have been hampered by urbanization and the spread of Anopheles stephensi. The spread of this vector into Africa further complicates the already complex malaria situation, that could put about 126 million Africans at risk of infection. Hence, this study aimed to assess the determinants of urban malaria, focusing on the role of urbanization and the distribution of An. stephensi in Eastern Ethiopia.
A matched case control study was conducted among febrile urban residents of Dire Dawa (malaria positive as cases and negative as a control). A capillary blood sample was collected for parasite identification using microscopic examination and an interviewer administered questionnaire was used to collect additional data. Centers for Disease Control and Prevention miniature light traps (CDC-LT) and Prokopack aspirator were used to collect adult mosquito vectors from the selected cases and control houses to identify the mosquito vector species. Then, the data were exported to STATA for analysis. Conditional logistic regression was done to identify determinants, and principal component Analysis (PCA) was done for some independent variables.
This study enrolled 132 cases and 264 controls from urban setting only. Of the 132 cases, 90 cases were positive for Plasmodium falciparum, 34 were positive for Plasmodium vivax and 8 had mixed infections. All cases and controls were similar with regard to their respective age and sex. Travel history (AOR: 13.1, 95% CI 2.8-61.4), presence of eves and holes on walls (AOR: 2.84, 95% CI 1.5-5.5), history of malaria diagnosis (AOR: 2.4, 95% CI 1.1-5.3), owning any livestock (AOR: 7.5, 95% CI 2.4-22.8), presence of stagnant water in the area (AOR: 3.2, 95% CI 1.7-6.1), sleeping under bed net the previous night (AOR: 0.21, 95% CI 0.1-0.6) and knowledge on malaria and its prevention (AOR: 2.2, 95% CI 1.2-4.1) were determinants of urban malaria infection. About 34 adult Anopheles mosquitoes were collected and identified from those selected cases and control houses and 27 of them were identified as An. stephensi.
Among the cases, the dominant species were P. falciparum. This study identified travel history, house condition, past infection, livestock ownership, stagnant water, bed net use, and malaria knowledge as determinants of infection. This study also found the dominance of the presence of An. stephensi among the collected mosquito vectors. This suggests that the spread of An. stephensi may be impacting malaria infection in the study area. Hence, strengthening urban-targeted malaria interventions should be enhanced to prevent and control further urban malaria infection and spread.
