bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2022‒09‒18
twenty-one papers selected by
Richard Halfpenny
Staffordshire University

  1. PLoS One. 2022 ;17(9): e0270882
      Characterizing persistent malaria transmission that occurs after the combined deployment of indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) is critical to guide malaria control and elimination efforts. This requires a detailed understanding of both human and vector behaviors at the same temporal and spatial scale. Cross-sectional human behavior evaluations and mosquito collections were performed in parallel in Magude district, Mozambique. Net use and the exact time when participant moved into each of five environments (outdoor, indoor before bed, indoor in bed, indoor after getting up, and outdoor after getting up) were recorded for individuals from three different age groups and both sexes during a dry and a rainy season. Malaria mosquitoes were collected with CDC light traps in combination with collection bottle rotators. The percentage of residual exposure to host-seeking vectors that occurred in each environment was calculated for five local malaria vectors with different biting behaviors, and the actual (at observed levels of LLIN use) and potential (i.e. if all residents had used an LLIN) personal protection conferred by LLINs was estimated. Anopheles arabiensis was responsible for more than 74% of residents' residual exposure to host-seeking vectors during the Magude project. The other four vector species (An. funestus s.s., An. parensis, An. squamosus and An. merus) were responsible for less than 10% each. The personal protection conferred by LLINs prevented only 39.2% of the exposure to host-seeking vectors that survived the implementation of both IRS and LLINs, and it differed significantly across seasons, vector species and age groups. At the observed levels of bednet use, 12.5% of all residual exposure to host-seeking vectors occurred outdoor during the evening, 21.9% indoor before going to bed, almost two thirds (64%) while people were in bed, 1.4% indoors after getting up and 0.2% outdoor after leaving the house. Almost a third of the residual exposure to host-seeking vectors (32.4%) occurred during the low transmission season. The residual bites of An. funestus s.s. and An. parensis outdoors and indoor before bedtime, of An. arabiensis indoors when people are in bed, and of An. squamosus both indoors and outdoors, are likely to have sustained malaria transmission throughout the Magude project. By increasing LLIN use, an additional 24.1% of exposure to the remaining hosts-seeking vectors could have been prevented. Since An. arabiensis, the most abundant vector, feeds primarily while people are in bed, increasing net use and net feeding inhibition (through e.g. community awareness activities and the selection of more effective LLINs) could significantly reduce the exposure to remaining host-seeking mosquitoes. Nonetheless, supplementary interventions aiming to reduce human-vector contact outdoors and/or indoors before people go to bed (e.g. through larval source management, window and eave screening, eave tubes, and spatial repellents) will be needed to reduce residual exposure to the outdoor and early biting An. funestus s.s. and An. parensis.
  2. Zootaxa. 2022 May 10. 5134(2): 275-285
      Nyssorhynchus (Nyssorhynchus) jamariensis, a new species of the Nuneztovari Complex, previously known as Anopheles (Nyssorhynchus) nuneztovari A, is described and validated using morphological characters of the adult male and female, male genitalia and immature stages. The species is recorded from the western Brazilian Amazon, where it was collected in pastures in the vicinity of the Jamari River, municipality of Monte Negro, Rondnia State, Brazil. Illustrations of the male genitalia, fourth-instar larva and pupa are provided. Nyssorhynchus jamariensis may be involved in malaria transmission, but its vector status needs further investigation.
  3. Infect Dis Poverty. 2022 Sep 14. 11(1): 97
      BACKGROUND: An outbreak of Plasmodium malariae infection among forest goers in Sanya City of Hainan Island, China was reported in 2015. In response to this outbreak, an innovative three-layer strategy (TLS) targeted forest goers was adapted based on the 1-3-7 approach.MAIN TEXT: Key elements of TLS are: (i) The village with five malaria cases and adjacent villages were set as the first layer. All residents including forest goers were taken as the high-risk population (HRP). Active case detection (ACD) by blood smear microscopy and PCR was selected as the primary measure, and passive case detection (PCD) as complementary measure. One case was identified under TLS implementation. (ii) The township with cases (Gaofeng Town) and the nearby towns were chosen as the second layer. Only forest goers were screened by ACD, while PCD as a routine screening method. 7831 blood smears collected by ACD and PCD and tested with negative results. (iii) The city with cases (Sanya City) and others 12 counties/county-level cities were selected as the third layer. Malaria cases were monitored passively. A total of 77,555 blood slides were screened by PCD with zero positive sample. For each layer, the malaria vector mosquitoes were monitored using light traps, cattle-baited/human-bait traps. Anopheles minimus (dominant species), An. sinensis and An. dirus were captured. Vector control measures mainly include insecticide residual spraying and long-lasting insecticide nets. The capacity of clinicians, public health practitioners and laboratory technicians has been improved through training. During 2016‒2018, TLS and chemoprophylaxis were implemented in the same areas. In the first layer, all residents were monitored by ACD, and malaria chemoprophylaxis were distributed, 89.5% of forest goers were using chemoprophylaxis against malaria. The blood smears (3126 by ACD plus 1516 by PCD) were with zero positive results. Chemoprophylaxis and ACD were offered to forest goers once a year, and PCD in residents as a complementary measure in the second and third layer, 77.8% and 95.1% of forest goers received chemoprophylaxis. In each layer, vector surveillance and control of malaria and trainings for medical staff were still in place.
    CONCLUSIONS: TLS was effective in blocking the outbreak by P. malariae among forest goers in Hainan in malaria elimination stage. However, whether it could prevent the malaria resurgence in the post-elimination phase needs to be further assessed.
    Keywords:  Elimination; Hainan, China; Malaria; Outbreak; Three-layer strategy
  4. PLoS Negl Trop Dis. 2022 Sep 12. 16(9): e0010715
      The Aedes aegypti mosquito is the main vector for several diseases of global importance, such as dengue and yellow fever. This species was first identified on Madeira Island in 2005, and between 2012 and 2013 was responsible for an outbreak of dengue that affected several thousand people. However, the potential distribution of the species on the island remains poorly investigated. Here we assess the suitability of current and future climatic conditions to the species on the island and complement this assessment with estimates of the suitability of land use and human settlement conditions. We used four modelling algorithms (boosted regression trees, generalized additive models, generalized linear models and random forest) and data on the distribution of the species worldwide and across the island. For both climatic and non-climatic factors, suitability estimates predicted the current distribution of the species with good accuracy (mean area under the Receiver Operating Characteristic curve = 0.88 ±0.06, mean true skill statistic = 0.72 ±0.1). Minimum temperature of coldest month was the most influential climatic predictor, while human population density, residential housing density and public spaces were the most influential predictors describing land use and human settlement conditions. Suitable areas under current climates are predicted to occur mainly in the warmer and densely inhabited coastal areas of the southern part of the island, where the species is already established. By mid-century (2041-2060), the extent of climatically suitable areas is expected to increase, mainly towards higher altitudes and in the eastern part of the island. Our work shows that ongoing efforts to monitor and prevent the spread of Ae. aegypti on Madeira Island will have to increasingly consider the effects of climate change.
  5. Parasite. 2022 ;29 42
      Control of invasive species relies partly on permanent surveillance at international points of entry. We report the exceptional trapping of one adult mosquito (Diptera: Culicidae) in the port of Marseille, France, in July 2018, during a routine survey conducted according to International Health Regulations. Morphological and molecular identification classified the specimen as a female Aedes (Stegomyia) aegypti (L.), vector of many arboviruses, absent from Europe and the Mediterranean rim since the 1950s. A world reference panel of approximately 23,000 genome-wide single nucleotide polymorphisms determined that the mosquito originated from Cameroon, west Africa. Cross-reference of this geographic location with boats traveling from Central Africa to Marseille during the trapping period suggests that the mosquito travelled within an identified merchant ship, a vehicles carrier connecting Douala, Cameroon to Marseille, France. This ship left Douala on June 25, 2018 and arrived 20 days later in Marseille on July 15. The mosquito was captured 350 m away from the dock. The interception of a propagule of an invasive species is a rare event that must be considered a priority to prevent its successful establishment.
    Keywords:  Invasive species; Mosquito; Point of entry; Propagule; Surveillance
  6. Am J Trop Med Hyg. 2022 Sep 12. pii: tpmd220137. [Epub ahead of print]
      Many factors influence the success or failure of malaria vector control program such as political will, leadership, sustained funding, robustness of healthcare system and others. In addition, updated knowledge and information about the triad of host, parasite, and vector is of paramount importance. Vector bionomics studies that determine mosquito behavior in terms of feeding, resting, biting, mating, breeding, longevity, vectorial capacity, and response to different insecticides are a step toward enhancing our understanding. In the present work, we have compiled studies conducted in India over the past 2 decades (2000-2020) to identify gaps in our knowledge of malaria vector bionomics and the research that needs to be done in the future. We retrieved district-level data of India's six primary malaria vector species. According to our findings, vector bionomics studies have been undertaken in ∼50% and ∼15% of the country's high (annual parasite index > 1) and low (annual parasite index < 1) malaria-endemic districts, respectively. Most of the research studies focused on mosquito density, insecticide susceptibility status, and parasite detection, whereas other vital bionomics parameters were neglected. Surveys conducted were incomplete, and vector bionomics data were not captured sufficiently. The absence of vector bionomics data can be a blind spot and the lack or inadequate understanding of vector bionomics can sustain malaria transmission in these areas limiting the effectiveness of usual vector control tools. Thus, there is an urgent need to initiate comprehensive bionomics studies on India's primary and secondary malaria vectors.
  7. Vet Med Sci. 2022 Sep 14.
      BACKGROUND: Rift Valley fever virus (RVFV) is the cause of one of the most important mosquito-borne emerging diseases negatively affecting the health of humans and animals, particularly in Africa. In Ethiopia, the status of RVFV and the existence of potential vectors are unknown.OBJECTIVES: This study aimed to survey the mosquito vectors of RVFV and the detection of the virus in selected sites (Batu, Hawassa, Arba Minch and Borana) in Ethiopia.
    METHODS: CDC light traps baited with the sugar-yeast solution were set up at various locations for a total of 29 trap nights. Mosquitoes identification were made morphologically using a stereomicroscope and for RVFV detection by reverse transcriptase-polymerase chain reaction (RT-PCR).
    RESULTS: Among a total of 132 trap efforts conducted, 60 (45%) captured the mosquitoes. A total of 1576 adult mosquitoes were collected and identified. Including Aedes (n = 407; 25.8%), Anopheles (n = 493; 32.3%), Culex (n = 466; 29.6%) and Mansonia (n = 210; 13.32%). The genome material of RVFV was not detected by RT-PCR.
    CONCLUSIONS: The existence of a potential Aedes species may pose a risk for the occurrence of the RVF outbreak in Ethiopia. Based on the current study, we recommend further monitoring for potential mosquito vectors of RVFV, particularly with a view to targeting the seasons during which the mosquitoes can be abundant along with a serological survey of susceptible hosts.
    Keywords:  RVF virus; genome detection; habitats; mosquito
  8. Am J Trop Med Hyg. 2022 Sep 12. pii: tpmd220204. [Epub ahead of print]
      Zika virus (ZIKV) infections occurred in epidemic form in the Americas in 2014-2016, with some of the earliest isolates in the region coming from Haiti. We isolated ZIKV from 20 children with acute undifferentiated febrile illness who were part of a cohort of children seen at a school clinic in the Gressier region of Haiti. The virus was also isolated from three pools of Aedes aegypti mosquitoes collected at the same location. On phylogenetic analysis, three distinct ZIKV clades were identified. Strains from all three clades were present in Haiti in 2014, making them among the earliest isolates identified in the Western Hemisphere. Strains from all three clades were also isolated in 2016, indicative of their persistence across the time period of the epidemic. Mosquito isolates were collected in 2016 and included representatives from two of the three clades; in one instance, ZIKV was isolated from a pool of male mosquitoes, suggestive of vertical transmission of the virus. The identification of multiple ZIKV clades in Haiti at the beginning of the epidemic suggests that Haiti served as a nidus for transmission within the Caribbean.
  9. Lancet Planet Health. 2022 Sep;pii: S2542-5196(22)00192-9. [Epub ahead of print]6(9): e739-e748
      BACKGROUND: Environmental degradation facilitates the emergence of vector-borne diseases, such as malaria, through changes in the ecological landscape that increase human-vector contacts and that expand vector habitats. However, the modifying effects of environmental degradation on climate-disease relationships have not been well explored. Here, we investigate the rapid re-emergence of malaria in a transmission hotspot in southern Venezuela and explore the synergistic effects of environmental degradation, specifically gold-mining activity, and climate variation.METHODS: In this spatiotemporal modelling study of the 46 parishes of the state of Bolívar, southeast Venezuela, we used data from the Venezuelan Ministry of Health including population data and monthly cases of Plasmodium falciparum malaria and Plasmodium vivax malaria between 1996 and 2016. We estimated mean precipitation and temperature using the ERA5-Land dataset and used monthly anomalies in sea-surface temperature as an indicator of El Niño events between 1996 and 2016. The location of suspected mining sites in Bolívar in 2009, 2017, and 2018 were sourced from the Amazon Geo-Referenced Socio-Environmental Information Network. We estimated measures of cumulative forest loss and urban development by km2 using annual land cover maps from the European Space Agency Climate Change Initiative between 1996 and 2016. We modelled monthly cases of P falciparum and P vivax malaria using a Bayesian hierarchical mixed model framework. We quantified the variation explained by mining activity before exploring the modifying effects of environmental degradation on climate-malaria relationships.
    FINDINGS: We observed a 27% reduction in the additional unexplained spatial variation in incidence of P falciparum malaria and a 23% reduction in P vivax malaria when mining was included in our models. The effect of temperature on malaria was greater in high mining areas than low mining areas, and the P falciparum malaria effect size at temperatures of 26·5°C (2·4 cases per 1000 people [95% CI 1·78-3·06]) was twice as high as the effect in low mining areas (1 case per 1000 people [0·68-1·49]).
    INTERPRETATION: We show that mining activity in southern Venezuela is associated with hotspots of malaria transmission. Increased temperatures exacerbated malaria transmission in mining areas, highlighting the need to consider how environmental degradation modulates climate effect on disease risk, which is especially important in areas subjected to rapidly rising temperatures and land-use change globally. Our findings have implications for the progress towards malaria elimination in the Latin American region. Our findings are also important for effectively targeting timely treatment programmes and vector-control activities in mining areas with high rates of malaria transmission.
    FUNDING: Biotechnology and Biological Sciences Research Council, Royal Society, US National Institutes of Health, and Global Challenges Research Fund.
    TRANSLATION: For the Spanish translation of the abstract see Supplementary Materials section.
  10. Nat Ecol Evol. 2022 Sep 15.
      Cues involved in mate seeking and recognition prevent hybridization and can be involved in speciation processes. In malaria mosquitoes, females of the two sibling species Anopheles gambiae s.s. and An. coluzzii mate in monospecific male swarms and hybrids are rare. Long-range sex pheromones driving this behaviour have been debated in literature but so far, no study has proven their existence or their absence. Here, we attempted to bring to light their existence. To put all the odds in our favour, we used different chemical ecology methods such as behavioural and electrophysiological assays as well chemical analyses, and we worked with mosquitoes at their optimal physiological mating state that is with swarming males during their natural swarming windows. Despite all our efforts, our results support the absence of long-range sex pheromones involved in swarm detection and recognition by females. We briefly discuss the implications of this finding in ecology, evolution and for control strategies.
  11. Public Health Pract (Oxf). 2020 Nov;1 100051
      Objectives: The objectives of the study were to explore knowledge, attitudes, and practice (KAP) of dengue fever among Dhaka city dwellers and the potential associated factors.Study design: A cross-sectional survey was conducted among the city dwellers in Dhaka north and south city corporations using a standardized questionnaire from November to December 2019.
    Methods: Households were selected by purposive sampling and interviewed face to face by the trained interviewers. The association between education and occupation with the dengue practice was tested using the chi-square test statistic.
    Results: Around 96% of respondents claimed that they heard about Dengue, and 80% of them correctly identified its causes. Nearly half of the people did not know the breeding season and ecology of dengue vector mosquitoes. Though the city dwellers were well-known about Dengue's burden, they were reluctant to take preventive measures to get rid of this disease. More than 70% of people mentioned that every family member regularly sleeps under a bed net. Moreover, we found a significant relationship between the education level (p<0.05), as well as the occupation of the respondents (p<0.05) with the practice to prevent and control Dengue. We did not find any information, education, and communication (IEC) activities in the city during our survey.
    Conclusion: Many people didn't know the specific preventive measures to minimize potential exposure to Dengue. This lack of knowledge is likely due to inadequate coverage with IEC activities. So, IEC intervention programs may need to start soon in highly dengue-endemic cities to reduce the burden.
    Keywords:  Aedes; Bangladesh; Dengue; Dhaka; KAP; Mosquito
  12. Glob Chang Biol. 2022 Sep 15.
      In recent decades, the emergence and resurgence of vector-borne diseases have been well documented worldwide, especially in tropical regions where protection and defence tools for human populations are still very limited. In this context, the dynamics of pathogens are influenced by landscape anthropization (i.e., urbanization, deforestation, and agricultural development), and one of the mechanisms through which this occurs is a change in the abundance and/or diversity of the vectors. An increasing number of empirical studies have described heterogeneous effects of landscape anthropization on vector communities; therefore, it is difficult to have an overall picture of these effects on a global scale. Here, we performed a meta-analysis to quantify the impacts of landscape anthropization on a global scale on the presence/abundance and diversity of mosquitoes, the most important arthropods affecting human health. We obtained 338 effect sizes on 132 mosquito species, compiled from 107 studies in 52 countries that covered almost every part of the world. The results of the meta-analysis showed an overall decline of mosquito presence/abundance and diversity in response to urbanization, deforestation, and agricultural development, except for a few mosquito species that have been able to exploit landscape anthropization well. Our results highlighted that these few favoured mosquito species are those of global concern. They thus provide a better understanding of the overall effect of landscape anthropization on vector communities and, more importantly, suggest a greater risk of emergence and transmission of vector-borne diseases in human-modified landscapes.
    Keywords:  Diptera; Urbanization; agricultural development; deforestation; landscape changes; pathogen vectors
  13. PLoS Negl Trop Dis. 2022 Sep 12. 16(9): e0010746
      Dengue is a vector-borne disease present in most tropical countries, infecting an average of 50 to 100 million people per year. Socioeconomic, demographic, and environmental factors directly influence the transmission cycle of the dengue virus (DENV). In Brazil, these factors vary between regions producing different profiles of dengue transmission and challenging the epidemiological surveillance of the disease. In this article, we aimed at classifying the profiles of dengue transmission in 1,823 Brazilian municipalities, covering different climates, from 2010 to 2019. Time series data of dengue cases were obtained from six states: Ceará and Maranhão in the semiarid Northeast, Minas Gerais in the countryside, Espírito Santo and Rio de Janeiro in the tropical Atlantic coast, and Paraná in the subtropical region. To describe the time series, we proposed a set of epi-features of the magnitude and duration of the dengue epidemic cycles, totaling 13 indicators. Using these epi-features as inputs, a multivariate cluster algorithm was employed to classify the municipalities according to their dengue transmission profile. Municipalities were classified into four distinct dengue transmission profiles: persistent transmission (7.8%), epidemic (21.3%), episodic/epidemic (43.2%), and episodic transmission (27.6%). Different profiles were associated with the municipality's population size and climate. Municipalities with higher incidence and larger populations tended to be classified as persistent transmission, suggesting the existence of critical community size. This association, however, varies depending on the state, indicating the importance of other factors. The proposed classification is useful for developing more specific and precise surveillance protocols for regions with different dengue transmission profiles, as well as more precise public policies for dengue prevention.
  14. Front Genet. 2022 ;13 931163
      The tiger mosquito (Aedes albopictus) is one of the most invasive species in the world and a competent vector for numerous arboviruses, thus the study and monitoring of its fast worldwide spread is crucial for global public health. The small extra-nuclear and maternally-inherited mitochondrial DNA represents a key tool for reconstructing phylogenetic and phylogeographic relationships within a species, especially when analyzed at the mitogenome level. Here the mitogenome variation of 76 tiger mosquitoes, 37 of which new and collected from both wild adventive populations and laboratory strains, was investigated. This analysis significantly improved the global mtDNA phylogeny of Ae. albopictus, uncovering new branches and sub-branches within haplogroup A1, the one involved in its recent worldwide spread. Our phylogeographic approach shows that the current distribution of tiger mosquito mitogenome variation has been strongly affected by clonal and sub-clonal founder events, sometimes involving wide geographic areas, even across continents, thus shedding light on the Asian sources of worldwide adventive populations. In particular, different starting points for the two major clades within A1 are suggested, with A1a spreading mainly along temperate areas from Japanese and Chinese sources, and A1b arising and mainly diffusing in tropical areas from a South Asian source.
    Keywords:  Aedes albopictus spread; MtDNA variation; haplogroups; mitogenome; phylogeny; sources of adventive populations
  15. Infect Drug Resist. 2022 ;15 5221-5232
      Background: Malaria remains a major vector borne disease globally, with the majority of the casualties reported in Africa. Despite this fact, there is drastic reduction in malaria infection using Artemisinin combined therapies (ACTs). Malaria is characterized by significant inconsistency in different geographical locations due to different confounding factors. There is need to identify zone-specific malaria trends and interventions to completely eliminate the disease. Thus the study was aimed at assessing the 11-year trend of microscopically confirmed malaria cases in Kisii County, Kenya, so as to devise area-specific evidence-based interventions, informed decisions, and to track the effectiveness of malaria control programs.Methods: This was a retrospective study carried out to determine 11-year malaria trend rates centered on the admission and laboratory records from health facilities located at four Sub-Counties in Kisii County, Kenya. Parasitological positivity rates of malaria were determined by comparing with the register records in health facilities which recorded confirmed malaria cases with the total number of monthly admissions over the entire year. Data was analyzed by using descriptive tools and chi-square test.
    Results: There were 36,946 suspect cases, with 8449 (22.8%) confirmed malaria cases reported in this study. The overall malaria slide positivity rate over the last 11 years in the study area was 22.6%. The months of April and August showed the largest number of malaria cases (63%). The age group of ≥18 years contained the most positive confirmed cases, having a prevalence rate of 2953 (35.45%). Out of the confirmed malaria cases, 2379 (28.1%) were males and 6070 (71.9%) were females The highest malaria prevalence rate was recorded in 2014, with Marani Sub-County recording the highest positivity rate of 37.94%.
    Conclusion: From the observed trends, malaria prevalence and transmission still remains stable in the study area. Thus more interventions need to be scaled up.
    Keywords:  ACTs; artemisinin combined therapies; malaria burden; retrospective
  16. Biomed Res Int. 2022 ;2022 2881879
      Plasmodium species is an important causative agent of malaria in the world including Ethiopia, and the majority of people were at risk of infection. The study's general objective was to determine the occurrence and distribution of Plasmodium species in the study area through microscopic examination of blood films. A cross-sectional study was carried out in the study sites from September 2016 to February 2017. Out of 512 participants, 32 (6.25%) were malaria positive. Of these, 17 (53.12%, 95% CI: 0.358, 0.704) were P. vivax, 12 (37.5%, 95% CI: 0.207, 0.543) P. falciparum, and 3 (9.375%, 95% CI: -0.007, 0.195) mixed out of the total positive case. The occurrence of parasites was greater in rural villages (59.375%) than in urban villages (40.625%) but not significant (χ 2 = 1.2917, df = 1, p = 0.2557). More males were infected compared to females but not significant (χ 2 = 0.0005665, df = 1, p = 0.981). The monthly distribution of Plasmodium species was higher in September and October but there was no significant variation in each month (χ 2 = 10.142, p = 0.4281). Due to the high occurrence of Plasmodium vivax in the study area, the result contrasts with the national figure of the Plasmodium species report. The result of the current study may be useful to those individuals who work in Plasmodium species control and prevention program.
  17. Ecol Evol. 2022 Sep;12(9): e9278
      Environmental temperature is a key driver of malaria transmission dynamics. Using detailed temperature records from four sites: low elevation (1800), mid elevation (2200 m), and high elevation (2600-3200 m) in the western Himalaya, we model how temperature regulates parasite development rate (the inverse of the extrinsic incubation period, EIP) in the wild. Using a Briére parametrization of the EIP, combined with Bayesian parameter inference, we study the thermal limits of transmission for avian (Plasmodium relictum) and human Plasmodium parasites (P. vivax and P. falciparum) as well as for two malaria-like avian parasites, Haemoproteus and Leucocytozoon. We demonstrate that temperature conditions can substantially alter the incubation period of parasites at high elevation sites (2600-3200 m) leading to restricted parasite development or long transmission windows. The thermal limits (optimal temperature) for Plasmodium parasites were 15.62-34.92°C (30.04°C) for P. falciparum, 13.51-34.08°C (29.02°C) for P. vivax, 12.56-34.46°C (29.16°C) for P. relictum and for two malaria-like parasites, 12.01-29.48°C (25.16°C) for Haemoproteus spp. and 11.92-29.95°C (25.51°C) for Leucocytozoon spp. We then compare estimates of EIP based on measures of mean temperature versus hourly temperatures to show that EIP days vary in cold versus warm environments. We found that human Plasmodium parasites experience a limited transmission window at 2600 m. In contrast, for avian Plasmodium transmission was not possible between September and March at 2600 m. In addition, temperature conditions suitable for both Haemoproteus and Leucocytozoon transmission were obtained from June to August and in April, at 2600 m. Finally, we use temperature projections from a suite of climate models to predict that by 2040, high elevation sites (~2600 m) will have a temperature range conducive for malaria transmission, albeit with a limited transmission window. Our study highlights the importance of accounting for fine-scale thermal effects in the expansion of the range of the malaria parasite with global climate change.
    Keywords:  climate change; extrinsic incubation period; malaria; western Himalaya
  18. Infect Dis Model. 2022 Sep;7(3): 510-525
      Dengue is a harmful tropical disease that causes death to many people. Currently, the dengue vaccine development is still at an early stage, and only intervention methods exist after dengue cases increase. Thus, previously, two scientific experimental field studies were conducted in producing a dengue outbreak forecasting model as an early warning system. Successfully, an Autoregressive Distributed Lag (ADL) Model was developed using three factors: the epidemiological, entomological, and environmental with an accuracy of 85%; but a higher percentage is required in minimizing the error for the model to be useful. Hence, this study aimed to develop a practical and cost-effective dengue outbreak forecasting model with at least 90% accuracy to be embedded in an early warning computer system using the Internet of Things (IoT) approach. Eighty-one weeks of time series data of the three factors were used in six forecasting models, which were Autoregressive Distributed Lag (ADL), Hierarchical Forecasting (Bottom-up and Optimal combination) and three Machine Learning methods: (Artificial Neural Network (ANN), Support Vector Machine (SVM) and Random Forest). Five error measures were used to evaluate the consistency performance of the models in order to ensure model performance. The findings indicated Random Forest outperformed the other models with an accuracy of 95% when including all three factors. But practically, collecting mosquito related data (the entomological factor) was very costly and time consuming. Thus, it was removed from the model, and the accuracy dropped to 92% but still high enough to be of practical use, i.e., beyond 90%. However, the practical ground operationalization of the early warning system also requires several rain gauges to be located at the dengue hot spots due to localized rainfall. Hence, further analysis was conducted in determining the location of the rain gauges. This has led to the recommendation that the rain gauges should be located about 3-4 km apart at the dengue hot spots to ensure the accuracy of the rainfall data to be included in the dengue outbreak forecasting model so that it can be embedded in the early warning system. Therefore, this early warning system can save lives, and prevention is better than cure.
    Keywords:  Early warning system; IoT; Machine learning; dengue; rainfall
  19. PLoS Negl Trop Dis. 2022 Sep 15. 16(9): e0010741
      BACKGROUND: Yellow fever is endemic in Africa and the Americas, occurring in urban or sylvatic environments. The infection presents varying symptoms, with high case-fatality among severe cases. In 2016, Brazil had sylvatic yellow fever outbreaks with more than 11 thousand cases, predominantly affecting the country's Southeast region. The state of Minas Gerais accounted for 30% of cases, even after the vaccine had been included in the immunization calendar for at least 30 years.METHODOLOGY AND PRINCIPAL FINDINGS: We applied parameters described in the literature from yellow fever disease into a compartmental model of vector-borne diseases, using namely generation time intervals, vital host and vector parameters, and force of infection, using macroregions as the spatial unit and epidemiological weeks as the time interval. The model permits obtaining the reproduction number, which we analyzed from reported cases of yellow fever from 2016 to 2018 in residents of the state of Minas Gerais, Brazil. Minas Gerais recorded two outbreak periods, starting in EW 51/2016 and EW 51/2017. Of all the reported cases (3,304), 72% were men 30 to 59 years of age. Approximately 27% of cases (905) were confirmed, and 22% (202) of these individuals died. The estimated effective reproduction number varied from 2.7 (95% CI: 2.0-3.6) to 7.2 (95% CI: 4.4-10.9], found in the Oeste and Nordeste regions, respectively. Vaccination coverage in children under one year of age showed heterogeneity among the municipalities comprising the macroregions.
    CONCLUSION: The outbreaks in multiple parts of the state and the estimated Re values raise concern since the state population was partially vaccinated. Heterogeneity in vaccination coverage may have been associated with the occurrence of outbreaks in the first period, while the subsequent intense vaccination campaign may have determined lower Re values in the second period.
  20. Int J Infect Dis. 2022 Sep 08. pii: S1201-9712(22)00505-7. [Epub ahead of print]
      BACKGROUND: A systematic literature review was conducted to assess the epidemiology and economic burden of dengue in Malaysia.METHODS: Embase, MEDLINE, Evidence-Based Reviews databases, and grey literature sources were searched for English and Malay studies and surveillance reports on the epidemiology (between 2012-2019) and costs (between 2009-2019) of dengue in Malaysia. Independent screening of titles/abstracts followed by full texts was performed using pre-specified criteria.
    RESULTS: A total of 198 publications were included (55 peer-reviewed and 143 grey literature). Dengue incidence has been increasing in recent years, with 130,101 cases (dengue fever [DF] 129,578 cases; dengue haemorrhagic fever [DHF] 523 cases) reported in 2019, which is the highest since 2012. All DENV serotypes co-circulated between 2004 and 2017, and major outbreaks occurred in a cyclical pattern, often associated with a change in the predominant circulating serotype. Economic impacts are substantial, including the societal impact of lost work (7.2-8.8 days) and school days (3.2-4.1 days) due to dengue.
    CONCLUSIONS: The rising incidence and high cost of dengue, coupled with overlapping diseases, will likely result in further pressures on the healthcare system. To appropriately mitigate and control dengue, it is critical to implement integrated strategies, including vaccination, to reduce the burden of dengue.
    Keywords:  Malaysia; costs; dengue; epidemiology; incidence; serotype
  21. Trans R Soc Trop Med Hyg. 2022 Sep 10. 116(9): 853-867
      BACKGROUND: Dengue is an acute viral disease of major relevance and impact on public health, causing major epidemics around the world, especially in tropical regions. Here we aimed to analyse the temporal trend and spatial risk, as well as social vulnerability factors, associated with the occurrence of dengue in the state of Bahia, Brazil between 2009 and 2018.METHODS: This is an ecological study carried out with all suspected cases of dengue in Bahia between 2009 and 2018. The data were obtained from the National Notifiable Diseases Information System, available on the website of the Health Department of the State of Bahia, and from the Brazilian Institute of Geography and Statistics. We used the Joinpoint regression model, local empirical Bayesian model for smoothing, global and local Moran statistics and spatial scanning statistics. The relationship between the dengue incidence rate and social determinants was tested using Moran's bivariate correlation.
    RESULTS: During the study period, 451 847 probable dengue cases were registered in Bahia. A declining trend was observed in 39.28% (n=11) of the state's health regions and 60.71% (n=17) showed a stationary tendency. The spatiotemporal scanning statistic showed nine clusters of dengue occurrence. The largest cluster had a radius of 342.14 km, consisting of 160 municipalities, 120 094 cases (710.20 cases/100 000 inhabitants) and a relative risk of 2.80. In the multivariate regression model, 11 variables showed a significant association: Social Vulnerability Index (SVI), Municipal Human Development Index (MHDI), SVI urban infrastructure, SVI human capital, MHDI longevity, MHDI education, proportion of people living in households with per capita income less than half the minimum wage (in 2010) and who spend more than 1 h commuting, proportion of mothers who are heads of household who did not complete elementary school and with children <15 y of age, activity rate of persons ages 10-14 y and per capita income.
    CONCLUSIONS: In the analysis of the spatial distribution, areas of risk of disease transmission throughout the state were identified. These results can provide subsidies for the strategic planning of actions, as well as for the implementation of programs and/or public policies in order to control the incidence of dengue in the population.
    Keywords:  Dengue; epidemiology; public health; spatial analysis