Asymptomatic and Submicroscopic Plasmodium Infections in an Area Before and During Integrated Vector Control in Homa Bay, Western Kenya

Background Long lasting insecticidal bednets (LLINs) have been the primary vector control strategy until indoor residual spraying (IRS) was added in Homa Bay and Migori Counties in western Kenya. The objective of this study was to evaluate the impact of LLINs integrated with organophosphate-based (Actellic 300 CS) IRS on the prevalence of asymptomatic and submicroscopic Plasmodium species infections in Homa Bay County. Methods Four consecutive community cross-sectional surveys for Plasmodium species infection were conducted in residents of Homa Bay County, Kenya commencing immediately before and 2 years after introduction of annual IRS. Finger-prick blood samples were obtained to prepare thick and thin smears for microscopic determination and qPCR diagnosis of Plasmodium genus, P. falciparum, P. malariae and P. ovale infection. Results Plasmodium spp. infection prevalence by microscopy was 18.5% before IRS and 14.2%, 3.3% and 1.3% after two annual rounds of IRS (χ²= 186.9, df = 3, p < 0.0001). Submicroscopic (blood smear negative, qPCR positive) parasitemia was 50.4% before IRS and 43.2%, 68.0% and 80.7% after IRS (χ²= 31.98, df = 3, p < 0.0001). Geometric mean density of P. falciparum parasitemia decreased over the 2-year study period (ANOVA, F = 28.95, df = 3, 243, p < 0.0001). The proportion of blood smear positive asymptomatic infections that included P. falciparum did not significantly change over the study period. In contrast, the proportion of asymptomatic submicroscopic P. falciparum infections trended upward following introduction of IRS (pre-IRS 48.2% versus post-IRS 41.6%, 61.3% and 75.4%; (χ²= 24.00, df = 3, p = 0.0002). Conclusions These data suggest that two annual rounds of IRS integrated with LLIN significantly reduced the prevalence of Plasmodium parasitemia, whereas the proportion of submicroscopic infections that included P. falciparum parasite increases. Strategies that aim at reducing the number of asymptomatic submicroscopic infections should be considered to diminish cryptic P. falciparum transmission and enhance malaria control.

Haemagogus leucocelaenus (Diptera: Culicidae), the potential wild vector of yellow fever in the border zone of northern Misiones, Argentina

Haemagogus leucocelaenus (Diptera: Culicidae) is considered the primary vector of yellow fever virus (Flaviviridae) in wild environments in South America. Previous research has defined Hg. leucocelaenus as a wild species with phytotelmata-type breeding sites. The objective of this study was to report the temporal and space occurrence of Hg. leucocelaenus at the microscale in the wild-periurban fringe through a systematic and spatially stratified sampling using 81 ovitraps between April 2019 and February 2 020 in the locality of Puerto Iguazú, Argentina. Of the total ovitraps, eight were positive for Hg. leucocelaenus, six in the wild environment and two in the periurban environment. Regarding the time distribution, 98.5% of the occurrence was concentrated in November and December 2019 towards the beginning of the rainy season. The results confirm the habitat plasticity of Hg. leucocelaenus and establish the aptitude of artificial containers as a methodology in monitoring studies, since they illustrate the potential of wild populations to deposit fertile eggs in them at least up to 300 m from the wild-periurban fringe. This work is a contribution to determine the temporal and space risk of yellow fever virus transmission in the region, based on the distribution patterns of this species as a function to the ecotone associated with forest borders and climatic variables.

Modelling interference between vectors of non-persistently transmitted plant viruses to identify effective control strategies

Aphids are the primary vector of plant viruses. Transient aphids, which probe several plants per day, are considered to be the principal vectors of non-persistently transmitted (NPT) viruses. However, resident aphids, which can complete their life cycle on a single host and are affected by agronomic practices, can transmit NPT viruses as well. Moreover, they can interfere both directly and indirectly with transient aphids, eventually shaping plant disease dynamics. By mean of an epidemiological model, originally accounting for ecological principles and agronomic practices, we explore the consequences of fertilization and irrigation, pesticide deployment and roguing of infected plants on the spread of viral diseases in crops. Our results indicate that the spread of NPT viruses can be i) both reduced or increased by fertilization and irrigation, depending on whether the interference is direct or indirect; ii) counter-intuitively increased by pesticide application and iii) reduced by roguing infected plants. We show that a better understanding of vectors’ interactions would enhance our understanding of disease transmission, supporting the development of disease management strategies.

Eliminasi Endosimbion Wolbachia sp. pada Nyamuk Aedes albopictus dengan Antibiotik Tetrasiklin

Dengue Hemorrhagic Fever (DHF) is a disease caused by the dengue virus which is transmitted through the bite of the Aedes mosquito. Aedes aegypti, which is known as the primary vector of dengue virus, is naturally not infected by Wolbachia sp. endosymbiont, while Ae. albopictus which is a secondary vector naturally infected with Wolbachia sp. The Wolbachia sp. known to inhibit the transmission of Dengue virus, to study the mechanism, it is necessary to eliminate Wolbachia sp. from Ae. albopictus, then infects the Ae. albopictus with the Dengue virus. The aim of the study was to determine the ability of tetracycline antibiotics to eliminate Wolbachia sp. from the Ae. albopictus mosquito. Ae. albopictus eggs was obtained in the Ciamis area by survey method using ovitrap which was installed outside the house. The Ae. albopictus eggs are then incubated in the laboratory and reared until they become adult mosquitoes. Mosquitoes were treated with sugar feeding which had been given tetracycline 0.25mg/ml every two days alternated with blood feed. Detection of the presence of Wolbachia sp. on mosquitoes carried out in first to third generations by the polymerase chain reaction (PCR) method using Wsp-specific primers. The results showed that the first to third generation mosquitoes were still infected with Wolbachia sp. This shows that the dose of tetracycline antibiotics used has not been able to eliminate Wolbachia sp. from the Ae. albopictus mosquito.

Starvation at the larval stage increases the vector competence of Aedes aegypti females for Zika virus

Aedes aegypti is the primary vector of Zika virus (ZIKV), a flavivirus which typically presents itself as febrile-like symptoms in humans but can also cause neurological and pregnancy complications. The transmission cycle of mosquito-borne arboviruses such as ZIKV requires that various key tissues in the female mosquito including the salivary glands get productively infected with the virus before the mosquito can transmit the virus to another vertebrate host. Following ingestion of a viremic blood-meal from a vertebrate, ZIKV initially infects the midgut epithelium before exiting the midgut after blood-meal digestion to disseminate to secondary tissues including the salivary glands. Here we investigated whether smaller Ae. aegypti females resulting from food deprivation as larvae exhibited an altered vector competence for blood-meal acquired ZIKV relative to larger mosquitoes. Midguts from small ‘Starve’ and large ‘Control’ Ae. aegypti were dissected to visualize by transmission electron microscopy (TEM) the midgut basal lamina (BL) as physical evidence for the midgut escape barrier showing Starve mosquitoes with a significantly thinner midgut BL than Control mosquitoes at two timepoints. ZIKV replication was inhibited in Starve mosquitoes following intrathoracic injection of virus, however, Starve mosquitoes exhibited a significantly higher midgut escape and population dissemination rate at 9 days post-infection (dpi) via blood-meal, with more virus present in saliva and head tissue than Control by 10 dpi and 14 dpi, respectively. These results indicate that Ae. aegypti developing under stressful conditions potentially exhibit higher midgut infection and dissemination rates for ZIKV as adults, Thus, variation in food intake as larvae is potentially a source for variable vector competence levels of the emerged adults for the virus.

Factors Contributing to Community None Acceptance for Indoor Residual Spraying (IRS) for Malaria prevention in Chipushi Area of Mpika, Zambia

Indoor residual spraying (IRS) is one of the primary vector control interventions for reducing and interrupting malaria transmission. In recent years, however, it has received relatively little attention. Just like it is the case in the 17 villages of the Chipushi area of Mpika district in Muchinga province, Zambia. In community work, among the things that attracted my attention are the non-acceptance and perceived negative attitudes towards acceptance for indoor residual spraying. The purpose of this study was to analyze and establish the factors that contribute to none acceptance for Indoor Residual Spraying (IRS) in the Chipushi area of Mpika, Zambia. None acceptance, in this case, refers to a widespread negative response to having indoor residual spraying performed in people’s homes at the community level. Simple random sampling was used to come up with the study population. And after executing the study through the questionnaire and semi-structured interviews on the 97 respondents, findings revealed that 12 (12.4%) respondents believed that chemicals used in IRS increase mosquitoes and bed bugs instead of controlling them. Other 22 (22.7%) never believed IRS could reduce the incidence of malaria. 18 (18.6%) respondents avoided being in-convenience by the spray operators and health personnel. 10 (10.3%) respondents don’t want to be seen how wrecked their houses are or fear of being embarrassed due to lack of sanity in their homes. Similarly, 17 (17.5%) respondents believed that by the culture, they could not allow strangers to expose their privacy in their homes. Surprisingly 26 (26.8%) respondents never just wanted to participate in spray operations. Keywords: Community, Households, Indoor Residual Spraying, Malaria elimination, Prevention.

Transovarial transmission of a core virome in the Chagas disease vector Rhodnius prolixus

Triatomine assassin bugs comprise hematophagous insect vectors of Trypanosoma cruzi, the causative agent of Chagas disease. Although the microbiome of these species has been investigated to some extent, only one virus infecting Triatoma infestans has been identified to date. Here, we describe for the first time seven (+) single-strand RNA viruses (RpV1-7) infecting Rhodnius prolixus, a primary vector of Chagas disease in Central and South America. We show that the RpVs belong to the Iflaviridae, Permutotetraviridae and Solemoviridae and are vertically transmitted from the mothers to the progeny via transovarial transmission. Consistent with this, all the RpVs, except RpV2 that is related to the entomopathogenic Slow bee paralysis virus, established persistent infections in our R. prolixus colony. Furthermore, we show that R. prolixus ovaries express 22-nucleotide viral siRNAs (vsiRNAs), but not viral piRNAs, that originate from the processing of dsRNA intermediates during viral replication of the RpVs. Interestingly, the permutotetraviruses and sobemoviruses display shared pools of vsiRNAs that might provide the basis for a cross-immunity system. The vsiRNAs are maternally deposited in the eggs, where they likely contribute to reduce the viral load and protect the developing embryos. Our results unveil for the first time a complex core virome in R. prolixus and begin to shed light on the RNAi-based antiviral defenses in triatomines.

Observational Characterization of the Ecological and Environmental Features Associated with the Presence of Oropouche Virus and the Primary Vector Culicoides paraenesis: Data Synthesis and Systematic Review

Oropouche virus (OROV), a member of the Orthobunyavirus genus, is an arthropod-borne virus (arbovirus) and is the etiologic agent of human and animal disease. The primary vector of OROV is presumed to be the biting midge, Culicoides paraenesis, though Culex quinquefasciatus, Cq. venezuelensis, and Aedes serratus mosquitoes are considered secondary vectors. The objective of this systematic review is to characterize locations where OROV and/or its primary vector have been detected. Synthesis of known data through review of published literature regarding OROV and vectors was carried out through two independent searches: one search targeted to OROV, and another targeted towards the primary vector. A total of 911 records were returned, but only 90 (9.9%) articles satisfied all inclusion criteria. When locations were characterized, some common features were noted more frequently than others, though no one characteristic was significantly associated with presence of OROV using a logistic classification model. In a separate correlation analysis, vector presence was significantly correlated only with the presence of restingas. The lack of significant relationships is likely due to the paucity of data regarding OROV and its eco-epidemiology and highlights the importance of continued focus on characterizing this and other neglected tropical diseases.

Microbes increase thermal sensitivity in the mosquito Aedes aegypti, with the potential to change disease distributions

The mosquito Aedes aegypti is the primary vector of many disease-causing viruses, including dengue (DENV), Zika, chikungunya, and yellow fever. As consequences of climate change, we expect an increase in both global mean temperatures and extreme climatic events. When temperatures fluctuate, mosquito vectors will be increasingly exposed to temperatures beyond their upper thermal limits. Here, we examine how DENV infection alters Ae. aegypti thermotolerance by using a high-throughput physiological ‘knockdown’ assay modeled on studies in Drosophila. Such laboratory measures of thermal tolerance have previously been shown to accurately predict an insect’s distribution in the field. We show that DENV infection increases thermal sensitivity, an effect that may ultimately limit the geographic range of the virus. We also show that the endosymbiotic bacterium Wolbachia pipientis, which is currently being released globally as a biological control agent, has a similar impact on thermal sensitivity in Ae. aegypti. Surprisingly, in the coinfected state, Wolbachia did not provide protection against DENV-associated effects on thermal tolerance, nor were the effects of the two infections additive. The latter suggests that the microbes may act by similar means, potentially through activation of shared immune pathways or energetic tradeoffs. Models predicting future ranges of both virus transmission and Wolbachia’s efficacy following field release may wish to consider the effects these microbes have on host survival.

Larvicidal Activities against Aedes aegypti of Supernatant and Pellet Fractions from Cultured Bacillus spp. Isolated from Amazonian Microenvironments

The Aedes aegypti mosquito is the primary vector of Dengue, Chikungunya and Zika causing major problems for public health, which requires new strategies for its control, like the use of entomopathogenic microorganisms. In this study, bacteria from various Amazonian environments were isolated and tested for their pathogenicity to A. aegypti larvae. Following thermal shock to select sporulated Bacillus spp., 77 bacterial strains were isolated. Molecular identification per 16S RNA sequences revealed that the assembled strains contained several species of the genus Bacillus and one species each of Brevibacillus, Klebsiella, Serratia, Achromobacter and Brevundimonas. Among the isolated Bacillus sp. strains, 19 showed larvicidal activity against A. aegypti. Two strains of Brevibacillus halotolerans also displayed larvicidal activity. For the first time, larvicidal activity against A. aegypti was identified for a strain of Brevibacillus halotolerans. Supernatant and pellet fractions of bacterial cultures were tested separately for larvicidal activities. Eight strains contained isolated fractions resulting in at least 50% mortality when tested at a concentration of 5 mg/mL. Further studies are needed to characterize the active larvicidal metabolites produced by these microorganisms and define their mechanisms of action.