bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2021‒05‒09
nineteen papers selected by
Richard Halfpenny
Staffordshire University

  1. PLoS One. 2021 ;16(5): e0250059
      BACKGROUND: More than 85% of the malaria cases in Panama occur in poor, rural and indigenous regions like Darien Province. Vector diversity, infection rate and spatial distribution are important entomological parameters of malaria transmission dynamics. Their understanding is crucial for the development of effective disease control strategies. The objective of this study was to determine the composition of Anopheles species, their natural infection rate and their geographic distribution to better understand the malaria transmission dynamics in Darién, Panama.METHODS: Anophelines mosquitoes were captured during the rainy and dry season of 2016. We selected five communities where adult anophelines were collected using CDC light-traps, and through protective human-baited traps. Detection of natural infection and Plasmodium genotype were detected via nested PCR through the amplification of ssrRNA and the circumsporozoite protein gene (csp), respectively.
    RESULTS: A total of 1,063 mosquitoes were collected mosquitoes were collected for the detection of natural infection with Plasmodium spp. Nine Anophelines species were identified, with the predominant species being: An. (Nys.) darlingi (45.0%) and An. (Nys.) albimanus (42.6%). Natural infection in An. (Nys.) albimanus with P. vivax was detected in one mosquito pool from the community Pueblo Tortuga (0.6%), three from Marraganti (1.7%), two from Bajo Chiquito (1.1%) and three pools from Alto Playona 3 (1.7%). For An. (Nys.) darlingi mosquitoes, we detected seven positive pools from the community Bajo Chiquito (4.0%), two pools from Marraganti (1.1%) and two pools from Alto Playona (1.1%). The P. vivax allelic variant VK210 was detected in infected mosquitoes.
    CONCLUSION: The results from this study provide new information on the transmission dynamics associated with anophelines vectors in the Darién region. This is the first report of natural P. vivax infection in An. (Nys.) darlingi and its incrimination as a potential malaria vector in this region of Panama. Additional studies are necessary to expand our knowledge and determine crucial parameters in malaria transmission in Darién, which in turn will aid the National Malaria Program in attaining an adequate malaria control strategy towards malaria elimination.
  2. Vector Borne Zoonotic Dis. 2021 Apr 30.
      A clinical and entomological investigation was performed to identify flavivirus infections in humans and mosquitoes in impoverished areas of Guerrero, a coastal state in southwestern Mexico. A total of 639 patients with acute febrile illness and 830 resting female mosquitoes in low-income communities of Guerrero in 2019 were tested for evidence of flavivirus infection. Sera were collected from all patients and screened at a dilution of 1:20 by plaque reduction neutralization test (PRNT) using dengue virus (DENV)2. A total of 431 (67.4%) patients were seropositive. Sera from a subset of seropositive patients (n = 263) were tested for flavivirus NS1 by enzyme-linked immunosorbent assay. Forty-eight (18.3%) sera contained viral antigen. All NS1-positive sera were titrated and further tested by PRNT using DENV-1 to -4, St. Louis encephalitis virus, West Nile virus, and Zika virus (ZIKV). Seven patients were seropositive for DENV-1, five patients were seropositive for DENV-2, one patient was seropositive for DENV-3, and two patients each were seropositive for DENV-4 and ZIKV. The remainder had secondary flavivirus infections or antibodies to an undetermined flavivirus. Comparative PRNTs were also performed on 60 randomly selected NS1-negative sera, identifying patients seropositive for DENV-2, DENV-3, and ZIKV. The entomological investigation yielded 736 Aedes aegypti and 94 Culex quinquefasciatus that were sorted into 183 pools and 20 pools, respectively. Mosquitoes were assayed for flavivirus RNA by RT-PCR and Sanger sequencing. DENV-2 RNA was detected in three pools of A. aegypti. In summary, we provide evidence for the concurrent circulation of all four DENVs and ZIKV in Guerrero, Mexico. The public health authorities reported no cases of DENV-3, DENV-4, and ZIKV in Guerrero in 2019 and thus, we provide evidence of under-reporting in the region.
    Keywords:  Guerrero; Mexico; Zika; dengue; diagnosis; flavivirus
  3. PLoS Negl Trop Dis. 2021 May 05. 15(5): e0009397
      The world's most important mosquito vector of viruses, Aedes aegypti, is found around the world in tropical, subtropical and even some temperate locations. While climate change may limit populations of Ae. aegypti in some regions, increasing temperatures will likely expand its territory thus increasing risk of human exposure to arboviruses in places like Europe, Northern Australia and North America, among many others. Most studies of Ae. aegypti biology and virus transmission focus on locations with high endemicity or severe outbreaks of human amplified urban arboviruses, such as dengue, Zika, and chikungunya viruses, but rarely on areas at the margins of endemicity. The objective in this study is to explore previously published global patterns in the environmental suitability for Ae. aegypti and dengue virus to reveal deviations in the probability of the vector and human disease occurring. We developed a map showing one end of the gradient being higher suitability of Ae. aegypti with low suitability of dengue and the other end of the spectrum being equal and higher environmental suitability for both Ae. aegypti and dengue. The regions of the world with Ae. aegypti environmental suitability and no endemic dengue transmission exhibits a phenomenon we term 'aegyptism without arbovirus'. We then tested what environmental and socioeconomic variables influence this deviation map revealing a significant association with human population density, suggesting that locations with lower human population density were more likely to have a higher probability of aegyptism without arbovirus. Characterizing regions of the world with established populations of Ae. aegypti but little to no autochthonous transmission of human-amplified arboviruses is an important step in understanding and achieving aegyptism without arbovirus.
  4. Am J Transplant. 2021 May;21(5): 1959-1974
      PROBLEM/CONDITION: West Nile virus (WNV) is an arthropod-borne virus (arbovirus) in the family Flaviviridae and is the leading cause of domestically acquired arboviral disease in the contiguous United States. An estimated 70%-80% of WNV infections are asymptomatic. Symptomatic persons usually develop an acute systemic febrile illness. Less than 1% of infected persons develop neuroinvasive disease, which typically presents as encephalitis, meningitis, or acute flaccid paralysis.REPORTING PERIOD: 2009-2018.
    DESCRIPTION OF SYSTEM: WNV disease is a nationally notifiable condition with standard surveillance case definitions. State health departments report WNV cases to CDC through ArboNET, an electronic passive surveillance system. Variables collected include patient age, sex, race, ethnicity, county and state of residence, date of illness onset, clinical syndrome, hospitalization, and death.
    RESULTS: During 2009-2018, a total of 21 869 confirmed or probable cases of WNV disease, including 12 835 (59%) WNV neuroinvasive disease cases, were reported to CDC from all 50 states, the District of Columbia, and Puerto Rico. A total of 89% of all WNV patients had illness onset during July-September. Neuroinvasive disease incidence and case-fatalities increased with increasing age, with the highest incidence (1.22 cases per 100 000 population) occurring among persons aged ≥70 years. Among neuroinvasive cases, hospitalization rates were >85% in all age groups but were highest among patients aged ≥70 years (98%). The national incidence of WNV neuroinvasive disease peaked in 2012 (0.92 cases per 100 000 population). Although national incidence was relatively stable during 2013-2018 (average annual incidence: 0.44; range: 0.40-0.51), state level incidence varied from year to year. During 2009-2018, the highest average annual incidence of neuroinvasive disease occurred in North Dakota (3.16 cases per 100 000 population), South Dakota (3.06), Nebraska (1.95), and Mississippi (1.17), and the largest number of total cases occurred in California (2819), Texas (2043), Illinois (728), and Arizona (632). Six counties located within the four states with the highest case counts accounted for 23% of all neuroinvasive disease cases nationally.
    INTERPRETATION: Despite the recent stability in annual national incidence of neuroinvasive disease, peaks in activity were reported in different years for different regions of the country. Variations in vectors, avian amplifying hosts, human activity, and environmental factors make it difficult to predict future WNV disease incidence and outbreak locations.
    PUBLIC HEALTH ACTION: WNV disease surveillance is important for detecting and monitoring seasonal epidemics and for identifying persons at increased risk for severe disease. Surveillance data can be used to inform prevention and control activities. Health care providers should consider WNV infection in the differential diagnosis of aseptic meningitis and encephalitis, obtain appropriate specimens for testing, and promptly report cases to public health authorities. Public health education programs should focus prevention messaging on older persons because they are at increased risk for severe neurologic disease and death. In the absence of a human vaccine, WNV disease prevention depends on community-level mosquito control and household and personal protective measures. Understanding the geographic distribution of cases, particularly at the county level, appears to provide the best opportunity for directing finite resources toward effective prevention and control activities. Additional work to further develop and improve predictive models that can foreshadow areas most likely to be impacted in a given year by WNV outbreaks could allow for proactive targeting of interventions and ultimately lowering of WNV disease morbidity and mortality.
  5. Vector Borne Zoonotic Dis. 2021 May 03.
      Dengue virus (DENV) is transmitted to humans by the bite of the vector Aedes aegypti. Several researchers have suggested that the mechanism of vertical transmission of DENV in the vector is a key aspect for the prevalence of the virus in the environment and the potentiation of epidemic outbreaks of the disease. In this context and as part of an integrated study of DENV serotypes in mosquitoes of urban areas in Sinaloa, Mexico, the presence of DENV-4 in larval stages of Ae. aegypti was evaluated to demonstrate the vertical transmission of this serotype. In total, 672 larvae of Ae. aegypti were collected in 16 sectors and were grouped into 36 pools, of which 41.66% (15/36 pools) tested positive for DENV-4, with a minimum infection rate = 22.32. The analysis of the obtained sequences showed a 98% similarity to the DENV-4 with sequences previously reported in GenBank. These results show that Ae. aegypti acts as a natural reservoir for DENV-4 in this region.
    Keywords:  Aedes aegypti; dengue virus 4; natural reservoir; urban areas; vertical transmission
  6. J Arthropod Borne Dis. 2020 Dec;14(4): 325-343
      Background: Malaria has long been regarded as one of the most important public health issues in Iran. Although the country is now in the elimination phase, some endemic foci of malaria are still present in the southeastern areas of the country. In some endemic foci, there are no data on the malaria vectors. To fill this gap, the present study was designed to provide basic entomological data on malaria vectors in the southeastern areas of Iran.Methods: Adult and larval stages of Anopheles mosquitoes were collected by using different catch methods. Resistance of the main malaria vector in the study area to selected insecticides was evaluated using diagnostic doses advised by the World Health Organization in 2013-2014.
    Results: A total of 3288 larvae and 1055 adult Anopheles mosquitoes were collected, and identified as: Anopheles stephensi (32.1%), Anopheles culicifacies s.l. (23.4%), Anopheles dthali (23.2%), Anopheles superpictus s.l. (12.7%), and Anopheles fluviatilis s.l. (8.6%). Anopheles stephensi was the most predominant mosquito species collected indoors at the study area, with two peaks of activity in May and November. This species was found to be resistant to DDT 4%, tolerant to malathion 5% and susceptible to other tested insecticides.
    Conclusion: All the five malaria vectors endemic to the south of Iran were collected and identified in the study area. Our findings on the ecology and resting/feeding habitats of these malaria vectors provide information useful for planning vector control program in this malarious area.
    Keywords:  Anopheles; Bio-ecology; Iran; Malaria; Malaria vectors
  7. Parasit Vectors. 2021 May 06. 14(1): 236
      BACKGROUND: Environmental disturbance, deforestation and socioeconomic factors all affect malaria incidence in tropical and subtropical endemic areas. Deforestation is the major driver of habitat loss and fragmentation, which frequently leads to shifts in the composition, abundance and spatial distribution of vector species. The goals of the present study were to: (i) identify anophelines found naturally infected with Plasmodium; (ii) measure the effects of landscape on the number of Nyssorhynchus darlingi, presence of Plasmodium-infected Anophelinae, human biting rate (HBR) and malaria cases; and (iii) determine the frequency and peak biting time of Plasmodium-infected mosquitoes and Ny. darlingi.METHODS: Anopheline mosquitoes were collected in peridomestic and forest edge habitats in seven municipalities in four Amazon Brazilian states. Females were identified to species and tested for Plasmodium by real-time PCR. Negative binomial regression was used to measure any association between deforestation and number of Ny. darlingi, number of Plasmodium-infected Anophelinae, HBR and malaria. Peak biting time of Ny. darlingi and Plasmodium-infected Anophelinae were determined in the 12-h collections. Binomial logistic regression measured the association between presence of Plasmodium-infected Anophelinae and landscape metrics and malaria cases.
    RESULTS: Ninety-one females of Ny. darlingi, Ny. rangeli, Ny. benarrochi B and Ny. konderi B were found to be infected with Plasmodium. Analysis showed that the number of malaria cases and the number of Plasmodium-infected Anophelinae were more prevalent in sites with higher edge density and intermediate forest cover (30-70%). The distance of the drainage network to a dwelling was inversely correlated to malaria risk. The peak biting time of Plasmodium-infected Anophelinae was 00:00-03:00 h. The presence of Plasmodium-infected mosquitoes was higher in landscapes with > 13 malaria cases.
    CONCLUSIONS: Nyssorhynchus darlingi, Ny. rangeli, Ny. benarrochi B and Ny. konderi B can be involved in malaria transmission in rural settlements. The highest fraction of Plasmodium-infected Anophelinae was caught from midnight to 03:00 h. In some Amazonian localities, the highest exposure to infectious bites occurs when residents are sleeping, but transmission can occur throughout the night. Forest fragmentation favors increases in both malaria and the occurrence of Plasmodium-infected mosquitoes in peridomestic habitat. The use of insecticide-impregnated mosquito nets can decrease human exposure to infectious Anophelinae and malaria transmission.
    Keywords:  Amazonian settlements; Deforestation; Nyssorhynchus benarrochi B; Nyssorhynchus darlingi; Nyssorhynchus konderi B; Nyssorhynchus rangeli; Plasmodium vectors
  8. R Soc Open Sci. 2021 Mar 03. 8(3): 201525
      The relative risk of disease transmission caused by the potential release of transgenic vectors, such as through sterile insect technique or gene drive systems, is assessed with comparison with wild-type vectors. The probabilistic risk framework is demonstrated with an assessment of the relative risk of lymphatic filariasis, malaria and o'nyong'nyong arbovirus transmission by mosquito vectors to human hosts given a released transgenic strain of Anopheles coluzzii carrying a dominant sterile male gene construct. Harm is quantified by a logarithmic loss function that depends on the causal risk ratio, which is a quotient of basic reproduction numbers derived from mathematical models of disease transmission. The basic reproduction numbers are predicted to depend on the number of generations in an insectary colony and the number of backcrosses between the transgenic and wild-type lineages. Analogous causal risk ratios for short-term exposure to a single cohort release are also derived. These causal risk ratios were parametrized by probabilistic elicitations, and updated with experimental data for adult vector mortality. For the wild-type, high numbers of insectary generations were predicted to reduce the number of infectious human cases compared with uncolonized wild-type. Transgenic strains were predicted to produce fewer infectious cases compared with the uncolonized wild-type.
    Keywords:  Plasmodium falciparum; Wuchereria bancrofti; dynamical systems; genetic vector control; next generation matrix; transient dynamics
  9. Cell Tissue Res. 2021 May 07.
      FMRFamide-related peptides (FaRPs) are a class of neuropeptides that participate in a variety of physiological processes in invertebrates. They occur in nerves of stomatogastric ganglia and enteroendocrine cells of the insect digestive tract, where they may control muscle functions. However, their direct involvement in muscle function has never been shown in situ. We studied the relationship between FaRPs and midgut muscle during larval-pupal transition of the mosquito Aedes aegypti. In late L4, FaRP-positive neuronal extensions attach to the bundles of the external circular muscle layer, and muscle stem cells start to undergo mitosis in the internal circular layer. Thereafter, the external muscle layer degenerates, disappearing during early pupal development, and is completely absent in the adult mosquito. Our results indicate that FaRP-based neural signals are involved in the reorganization of the muscle fibers of the mosquito midgut during the larval-pupal transition. In addition to confirming FaRP involvement in muscle function, we show that the mosquito midgut muscles are largely innervated, and that circular and longitudinal muscle have specific neuron bodies associated with them.
    Keywords:  Insects; Metamorphosis; Midgut neurons; Neuropeptides; Visceral muscle
  10. Malar J. 2021 May 01. 20(1): 212
      BACKGROUND: Understanding of the impacts of climatic variability on human health remains poor despite a possibly increasing burden of vector-borne diseases under global warming. Numerous socioeconomic variables make such studies challenging during the modern period while studies of climate-disease relationships in historical times are constrained by a lack of long datasets. Previous studies have identified the occurrence of malaria vectors, and their dependence on climate variables, during historical times in northern Europe. Yet, malaria in Sweden in relation to climate variables is understudied and relationships have never been rigorously statistically established. This study seeks to examine the relationship between malaria and climate fluctuations, and to characterise the spatio-temporal variations at parish level during severe malaria years in Sweden 1749-1859.METHODS: Symptom-based annual malaria case/death data were obtained from nationwide parish records and military hospital records in Stockholm. Pearson (rp) and Spearman's rank (rs) correlation analyses were conducted to evaluate inter-annual relationship between malaria data and long meteorological series. The climate response to larger malaria events was further explored by Superposed Epoch Analysis, and through Geographic Information Systems analysis to map spatial variations of malaria deaths.
    RESULTS: The number of malaria deaths showed the most significant positive relationship with warm-season temperature of the preceding year. The strongest correlation was found between malaria deaths and the mean temperature of the preceding June-August (rs = 0.57, p < 0.01) during the 1756-1820 period. Only non-linear patterns can be found in response to precipitation variations. Most malaria hot-spots, during severe malaria years, concentrated in areas around big inland lakes and southern-most Sweden.
    CONCLUSIONS: Unusually warm and/or dry summers appear to have contributed to malaria epidemics due to both indoor winter transmission and the evidenced long incubation and relapse time of P. vivax, but the results also highlight the difficulties in modelling climate-malaria associations. The inter-annual spatial variation of malaria hot-spots further shows that malaria outbreaks were more pronounced in the southern-most region of Sweden in the first half of the nineteenth century compared to the second half of the eighteenth century.
    Keywords:  Epidemic; GIS; History; Infectious disease; Malaria; Plasmodium vivax; Summer precipitation; Summer temperature; Sweden
  11. Med Vet Entomol. 2021 May 05.
      The present study aimed at identifying the members of the Anopheles maculipennis complex (Diptera: Culicidae) occurring in Belgium. Therefore, the second internal transcribed spacer of nuclear ribosomal DNA (ITS2) and the mitochondrial cytochrome oxidase subunit I (COI) loci were sequenced in 175 and 111 specimens, respectively, collected between 2007 and 2019. In parallel, the suitability of two species-diagnostic PCR-RFLP assays was tested. The identified specimens included: An. maculipennis s.s. (N = 105), An. daciae (N = 62), An. atroparvus (N = 6) and An. messeae (N = 2). Each species was characterized by unique ITS2 haplotypes, whereas COI only supported the monophyly of An. atroparvus, a historical malaria vector in Belgium. Species identification results were further supported by unique PCR-RFLP banding patterns. We report for the first time An. daciae in Belgium, where it was found to co-occur with An. maculipennis s.s. The latter was the most prevalent in the collection studied (60%) and appears to have the widest distribution in Belgium. As in other studies, An. daciae and An. messeae appeared the most closely related species, up to the point that their species status remains debatable, while their ecological differences, including vector competences, need further study.
    Keywords:  Anopheles maculipennis subgroup; cytochrome oxidase I (COI); internal transcribed spacer 2 (ITS2); malaria vector; occurrence; restriction fragment length polymorphism (RFLP)
  12. Wellcome Open Res. 2020 ;5 259
      Background: Malaria is a major public health threat in sub-Saharan Africa. Asymptomatic Plasmodium falciparum gametocyte carriers are potential infectious reservoirs for sustaining transmission in many malaria endemic regions. The aim of the study was to assess the prevalence of gametocyte carriage and some of its associated risk factors among asymptomatic schoolchildren in Western Kenya and further analyse the association between gametocyte density, multiplicity of infection (MOI) and mosquito infection prevalence. Methods: Rapid diagnostic tests were used to screen for P. falciparum parasite infection among schoolchildren (5-15 years old) and the results were verified using microscopy. Microscopy positive gametocyte carriers were selected to feed laboratory reared An. gambiae s.l. mosquitoes using membrane feeding method. Genomic DNA was extracted from dry blood spot samples and P. falciparum populations were genotyped using 10 polymorphic microsatellite markers. Assessment of the association between MOI and gametocyte density and mosquito infection prevalence was conducted. Results: A significantly higher prevalence of P. falciparum infection was found in males 31.54% (764/2422) ( p-value < 0.001) compared to females 26.72% (657/2459). The microscopy gametocyte prevalence among the study population was 2% (84/4881). Children aged 5-9 years have a higher prevalence of gametocyte carriage (odds ratios = 2.1 [95% CI = 1.3-3.4], P = 0.002) as compared to children aged 10-15 years. After challenging An. gambiae s.l. by membrane feeding assay on gametocyte positive patient blood, our results indicate that 68.1% of the variation in mosquito infection prevalence is accounted for by gametocyte density and MOI (R-SQR. = 0.681, p < 0.001). Conclusions: Age was a significant risk factor for gametocyte carriage, as indicated by the higher risk of gametocyte carriage among the younger children (5-9 years). Gametocyte density and MOI statistically significantly predicted mosquito infection prevalence. Both of the variables added significantly to the prediction ( p < 0.05).
    Keywords:  MOI; Mbita; P. falciparum; asymptomatic; gametocyte density; mosquito infection prevalence
  13. Am J Trop Med Hyg. 2021 May 03. pii: tpmd210137. [Epub ahead of print]
      Since 2018, a dengue epidemic has been ongoing in the French overseas department of Reunion Island, in the Indian Ocean, with more than 25,000 serologically confirmed cases. Currently, three dengue serotypes have been identified in Réunion Island (DENV-1, DENV-2, and DENV-3) progressing in the form of epidemic outbreaks. This arbovirus is mainly transmitted by mosquitoes of the genus Aedes and may be responsible for serious clinical forms. To date, very few cases of kidney transplant-related dengue virus infection have been described. Here we report the first case of severe dengue virus infection related to kidney transplantation from a patient previously infected with dengue. Testing for dengue fever with PCR search in donor's urine may help complete the pretransplant assessment in areas where this disease occurs.
  14. PLoS Negl Trop Dis. 2021 May 03. 15(5): e0009371
      BACKGROUND: Malaria, disproportionately affects poor people more than any other disease of public health concern in developing countries. In resource-constrained environments, monitoring the occurrence of malaria is essential for the success of national malaria control programs. Militancy and military conflicts have been a major challenge in monitoring the incidence and controlling malaria and other emerging infectious diseases. The conflicts and instability in Afghanistan have resulted in the migration of refugees into the war-torn tribal districts of Pakistan's Khyber Pakhtunkhwa (KPK) province and the possible introduction of many contagious epidemics. Although malaria is very common in all tribal districts, molecular, clinical and epidemiological data are scarce in these high-burden districts. Therefore, for the proper surveillance, detection, and control of malaria, obtaining and analyzing reliable data in these districts is essential.METHODOLOGY/PRINCIPAL FINDINGS: All 1,127 malaria-suspected patients were sampled within the transmission season in the tribal districts of KPK province between March 2016 to December 2018. After a detailed demographic and clinical investigation of malaria-suspected patients, the data were recorded. The data of the control group was collected simultaneously at the same site. They were considered as uncomplicated cases for statistical analyses. Blood samples were collected from malaria-suspected patients for the detection of Plasmodium species using microscopy and nested PCR (nPCR). Microscopy and nPCR examination detected 78% (n = 882) and 38% (n = 429) Plasmodium-positive patients, respectively. Among1,127 of 429nPCR detected cases with both species of malaria, the frequency of complications was as follows: anemia (n = 71; 16.5%), decompensated shock (n = 40; 9%), hyperpyrexia (n = 117; 27%), hyperparasitaemia (n = 49; 11%) hypoglycemia (n = 45; 10.5%), jaundice (n = 54; 13%), multiple convulsions (n = 37; 9%), and petechia (n = 16; 4%). We observed that 37% (n = 157 out of 429) of those patients infected by both Plasmodium species were children between the ages of 1 and 15 years old. The results revealed that Bajaur (24%), Kurram (20%), and Khyber (18%) districtshada higher proportion of P. vivax than P. falciparum cases. Most of the malaria cases were males (74%). Patients infected by both Plasmodium species tended to less commonly have received formal education and ownership of wealth indicators (e.g., fridge, TV set) was lower.
    CONCLUSIONS/SIGNIFICANCE: Malaria in tribal districts of the KPK province largely affects young males. P. vivax is a major contributor to the spread of malaria in the area, including severe malaria. We observed a high prevalence of P. vivax in the Bajaur district. Children were the susceptible population to malaria infections whereas they were the least expected to use satisfactory prevention strategies. A higher level of education, a possession of TV sets, the use of bed nets, the use of repellent fluids, and fridges were all associated with protection from malaria. An increased investment in socio-economic development, a strong health infrastructure, and malaria education are key interventions to reduce malaria in the tribal districts.
  15. Parasit Vectors. 2021 May 07. 14(1): 243
      BACKGROUND: West Nile (WNV) and Usutu (USUV) are emerging vector-borne zoonotic flaviviruses. They are antigenically very similar, sharing the same life cycle with birds as amplification host, Culicidae as vector, and man/horse as dead-end host. They can co-circulate in an overlapping geographic range. In Europe, surveillance plans annually detect several outbreaks.METHODS: In Italy, a WNV/USUV surveillance plan is in place through passive and active surveillance. After a 2018 WNV outbreak, a reinforced integrated risk-based surveillance was performed in four municipalities through clinical and serological surveillance in horses, Culicidae catches, and testing on human blood-based products for transfusion.
    RESULTS: Eight WNV cases in eight equine holdings were detected. Twenty-three mosquitoe catches were performed and 2367 specimens of Culex pipiens caught; 17 pools were USUV positive. A total of 8889 human blood donations were tested, and two asymptomatic donors were USUV positive.
    CONCLUSIONS: Different surveillance components simultaneously detected WNV only in horses and USUV only in humans and mosquitoes. While in endemic areas (i.e. northern Italy) entomological surveillance is successfully used as an early detection warning, this method in central Italy seems ineffective. To achieve a high level of sensitivity, the entomological trapping effort should probably exceed a reasonable balance between cost and performance. Besides, WNV/USUV early detection can be addressed by horses and birds. Further research is needed to adapt the surveillance components in different epidemiological contexts.
    Keywords:  Co-circulation; Culex pipiens; Italy; Surveillance; Usutu virus; West Nile virus
  16. PLoS Negl Trop Dis. 2021 May;15(5): e0009190
      After the unexpected arrival of West Nile virus (WNV) in the United States in 1999, the mosquito-borne virus quickly spread throughout North America. Over the past 20 years, WNV has become endemic, with sporadic epizootics. Concerns about the economic impact of infection in horses lead to the licensure of an equine vaccine as early as 2005, but few advances regarding human vaccines or treatments have since been made. There is a high level of virus transmission in hot/humid, subtropical climates, and high morbidity that may disproportionately affect vulnerable populations including the homeless, elderly, and those with underlying health conditions. Although WNV continues to cause significant morbidity and mortality at great cost, funding and research have declined in recent years. These factors, combined with neglect by policy makers and amenability of control measures, indicate that WNV has become a neglected tropical disease.
  17. BMC Public Health. 2021 May 03. 21(1): 856
      BACKGROUND: Vector control is an essential component in prevention and control of malaria in malaria endemic areas. Insecticide treated nets is one of the standard tools recommended for malaria vector control. The objective of the study was to determine physical integrity and insecticidal potency of long-lasting insecticidal nets (LLINs) used in control of malaria vector in Kirinyaga County, Kenya.METHOD: The study targeted households in an area which had received LLINs during mass net distribution in 2016 from Ministry of Health. A total of 420 households were sampled using systematic sampling method, where the household heads consented to participate in the study. A semi-structured questionnaire was administered to assess care and use while physical examination was used to determine integrity. Chemical concentration was determined by gas chromatography mass spectroscopy (GC-MS). Data analysis was done using Statistical Package for Social Sciences (SPSS) version 19.
    RESULTS: After 18 months of use, 96.9% (95% CI: 95.2-98.6%) of the distributed nets were still available. Regarding net utilization, 94.1% of household heads reported sleeping under an LLIN the previous night. After physical examination, 49.9% (95% CI: 43-52.8%) of the bed nets had at least one hole. The median number of holes of any size was 2[interquartile range (IQR) 1-4], and most holes were located on the lower part of the nets, [median 3 (IQR 2-5)]. Only 15% of the nets with holes had been repaired. The median concentration for α-cypermethrin was 7.15 mg/m2 (IQR 4.25-15.31) and 0.00 mg/g (IQR 0.00-1.99) for permethrin. Based on pHI, Chi-square test varied significantly with the manufacturer (X (6, N = 389) = 29.14, p = 0.04). There was no significant difference between nets with different number of washes (X2(2) = 4.55, p = 0.103).
    CONCLUSION: More than three-quarters of the nets supplied had survived and insecticidal potency was adequate in vector control. Standard procedure for field evaluation of surface insecticidal content available to a mosquito after landing on a net to rest is recommended.
    Keywords:  Integrity; Long-lasting insecticide treated-nets; Mass distribution; Median concentration; Permethrin; α-Cypermethrin
  18. Malar J. 2021 May 01. 20(1): 211
      BACKGROUND: Malaria in endemic countries is often asymptomatic during pregnancy, but it has substantial consequences for both the mother and her unborn baby. During pregnancy, anaemia is an important consequence of malaria infection. In Burkina Faso, the intensity of malaria varies according to the season, albeit the prevalence of malaria and anaemia as well as their risk factors, during high and low malaria transmission seasons is underexplored at the household level.METHODS: Data of 1751 pregnant women from October 2013 to March 2014 and 1931 pregnant women from April 2017 to June 2017 were drawn from two cross-sectional household surveys conducted in 24 health districts of Burkina Faso. Pregnant women were tested for malaria in their household after consenting. Asymptomatic carriage was defined as a positive result from malaria rapid diagnostic tests in the absence of clinical symptoms of malaria. Anaemia was defined as haemoglobin level less than 11 g/dL in the first and third trimester and less than 10.5 g/dL in the second trimester of pregnancy.
    RESULTS: Prevalence of asymptomatic malaria in pregnancy was estimated at 23.9% (95% CI 20.2-28.0) during the high transmission season (October-November) in 2013. During the low transmission season, it was 12.7% (95% CI 10.9-14.7) between December and March in 2013-2014 and halved (6.4%; 95% CI 5.3-7.6) between April and June 2017. Anaemia prevalence was estimated at 59.4% (95% CI 54.8-63.8) during the high transmission season in 2013. During the low transmission season, it was 50.6% (95% CI 47.7-53.4) between December and March 2013-2014 and 65.0% (95% CI 62.8-67.2) between April and June, 2017.
    CONCLUSION: This study revealed that the prevalence of malaria asymptomatic carriage and anaemia among pregnant women at the community level remain high throughout the year. Thus, more efforts are needed to increase prevention measures such as IPTp-SP coverage in order to reduce anaemia and contribute to preventing low birth weight and poor pregnancy outcomes.
    Keywords:  Asymptomatic carriage; Community; Haemoglobin; Health district; Plasmodium; Pregnant
  19. PLoS One. 2021 ;16(5): e0250253
      BACKGROUND AND OBJECTIVES: The burden of dengue virus (DENV), a mosquito-borne pathogen, remains difficult to assess due to misdiagnosis and underreporting. Moreover, the large proportion of asymptomatic dengue cases impairs comprehensive assessment of its epidemiology even where effective surveillance systems are in place. We conducted a prospective community-based study to assess the incidence of symptomatic dengue cases in Zapopan and neighboring municipalities in the state of Jalisco, Mexico.METHODS: Healthy subjects aged 6 months to 50 years living in households located in the Zapopan and neighboring municipalities were enrolled for a 24-month follow-up study (NCT02766088). Serostatus was determined at enrolment and weekly contacts were conducted via phone calls and home visits. Participants had to report any febrile episode lasting for at least two days. Suspected dengue cases were tested by reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR), detection of non-structural protein 1 (NS1), anti-DENV immunoglobulin G and M (IgG and IgM) assays.
    RESULTS: A total of 350 individuals from 87 households were enrolled. The overall seroprevalence of anti-DENV IgG at enrolment was 19.4% (95% confidence interval [CI] 14.5-25.6) with the highest seroprevalence rate observed in the adult group. Over the 27-month study period from July 2016 to September 2018, a total of 18 suspected dengue cases were reported. Four cases were confirmed by RT-qPCR and serotyped as DENV-1. A fifth case was confirmed by the NS1 assay. The 13 remaining suspected cases were tested negative by these assays. Based on the 5 virologically confirmed cases, symptomatic dengue incidence proportion of 1.4% (95%CI 0.5-3.8) was estimated. No severe cases or hospitalizations occurred during the study.
    CONCLUSION: Community-based active surveillance was shown as efficient to detect symptomatic dengue cases.