Seasonal Abundance of Mosquitoes (Diptera: Culicidae) at a High and Low Prevalence Site for La Crosse Encephalitis in Eastern Tennessee

La Crosse (LAC), a California (CAL) serogroup bunyavirus, is the most prevalent pediatric arboviral disease in the United States and accounts for virtually all encephalitis cases associated with CAL serogroup arboviruses. In Tennessee, USA, prior to the drastic increase of confirmed La Crosse (LAC) encephalitis cases in 1997, the sum of documented cases reported to the Tennessee Department of Health totaled 9. During subsequent years in Tennessee (1997 to 2003), an average of 12 cases has been reported annually. Approximately 62% of these reported cases have occurred in the months of July and August. The native, container-inhabiting mosquito Ochlerotatus triseriatus (Say) is a proven vector of the LAC. Recently, the LAC virus was isolated from Aedes albopictus (Skuse) in Tennessee and North Carolina and it has been postulated that an increase in both incidence and distribution of LAC virus throughout Tennessee coincided with an expansion of the exotic and ubiquitous Ae. albopictus (Gerhardt et al. 2001, Erwin et al. 2002). Weekly collections of container-inhabiting mosquitoes were conducted from 19 May to 24 November, 2003, in an attempt to quantify differences in seasonal patterns of Oc. triseriatus and Ae. albopictus populations between a high (Knox County) and low (Blount County) prevalence area for reported cases of LAC encephalitis in eastern Tennessee. When eggs found in ovitraps (n = 108,973) were utilized as an index of population density, the data showed that Oc. triseriatus populations were highest from 26 May to 23 June and are abundant during the early onset dates of LAC encephalitis cases in eastern Tennessee. Collections of Oc. triseriatus eggs declined throughout July with a smaller peak in August. In contrast, Ae. albopictus egg collections gradually increased in density from May to July and sustained high levels until September. Egg densities of both Oc. triseriatus and Ae. albopictus were abundant during July and August and increased the opportunities for vertical and horizontal transmission throughout the mosquito season. Adult females of Oc. triseriatus and Ae. albopictus were collected weekly with host-seeking and gravid traps from each sites in both Knox and Blount County. A total of 5,187 adult Oc. triseriatus and Ae. albopictus was collected from all adult trapping techniques. The proportion of parous females for each species was determined via dissection. Monthly parity averages were above 40% and based upon the general increase from May to October, opportunities for vertical and horizontal transmission by Oc. triseriatus and Ae. albopictus should have increased throughout the mosquito season. The blood-engorged females (n = 8) successfully tested by polymerase chain reaction (PCR) contained mammalian blood. Furthermore, each site contained sufficient populations of sciurids and potentially allowed for LAC virus amplification. This research suggests that there are no differences between the high and low prevalence area for LAC encephalitis in regards to egg or adult collections, parity rates, host selection preferences. Seasonal abundance, occurrence, and diversity of all mosquito species were evaluated between 19 May and 17 November, 2003, and 24 May and 5 July, 2004, at the two forested sites in Knox and Blount County. Nineteen species representing 7 genera were identified between the 2 collection seasons with an accumulation of 4,961 host-seeking and 296 gravid females. The overall abundance of adult mosquitoes collected and identified to species was similar between Knox (n = 2590) and Blount (n = 2667) counties. Diversity of collected species was highest in June. Aedes vexans (Meigen), a potential bridge vector of West Nile virus (WNV), was the most commonly collected species in 2003 and accounted for approximately 28% of all host-seeking and gravid females collected. In 2004, Ae. vexans numbers were extremely low at both sites and was likely affected by lower amounts of precipitation in the early portion of the mosquito season. Neither a high abundance nor diversity of Culex species were found in gravid traps in either year. The proven and potential LAC vectors, Oc. triseriatus and Ae. albopictus, constituted 59.3% and 73.8% of all adult species collected in the 2003 and 2004 season, respectively. In Knox County, Oc. japonicus japonicus (Theobald) was collected during both seasons and was the first reported occurrence of this species in the state of Tennessee

Improving \u3ci\u3eAedes\u3c/i\u3e Mosquito Surveillance and La Crosse Virus Screening in Eastern Tennessee

La Crosse virus (LACV), transmitted by infected Aedes triseriatus, Ae. albopictus, and Ae. japonicus mosquitoes is the leading cause of pediatric arboviral encephalitis. Severe cases of LAC encephalitis occur in individuals 16-years-old or younger and may cause permanent neurological damage or fatality. No vaccines exist making mosquito control and disease prevention crucial to public health. Effective screening and surveillance practices are key components to these goals. While a number of standard mosquito surveillance methods exist, continuous testing and improved understanding of vector biology to determine the best ways to implement these methods is important. Additionally, the current standard for screening LACV, RT-PCR, is time consuming, expensive, and inaccessible by many laboratories. I hypothesized that different LACV vectors would be active at different times (objective 1) and that a more efficient molecular method for virus detection can be developed (objective 2). For objective 1, I collected mosquitoes from 19 sites around Knox County from June-September in 2015 using traps previously found to be effective for monitoring LACV vectors. Nets were changed twice a day during “work” or “off-work” hours (9:00-17:00 or 17:00-9:00). Mosquitoes were identified and trap and time of day recorded. A total of 1,223 Aedes albopictus, 49 Ae. japonicus, and 90 Ae. triseriatus were collected. Significantly more LACV vectors were collected from 17:00-9:00. For objective 2, using a positive control, a reverse transcriptase loop mediated isothermal amplification (RT-LAMP) method of virus detection was developed and a dilution series was conducted to compare the developed assay to the standard. Both assays were found equally effective at detecting LACV, but the RT-LAMP is preferable for cost effectiveness and reduced detection time. This thesis provides research laboratories, health departments, and citizens with important vector surveillance information and an accurate and inexpensive method of screening for the virus. Surveillance information will make it easier for mosquito control districts to effectively monitor vectors. The diagnostic assay can be used in field-lab settings and will provide accurate results in a shorter time than with traditional methods. Together, the increased efficiency in vector surveillance and virus detection provide rapid and accurate results for low cost

Modulation of La Crosse Virus Infection in Aedes albopictus Mosquitoes Following Larval Exposure to Coffee Extracts

The mosquito-borne La Crosse virus (LACV; Family Bunyaviridae) may cause encephalitis, primarily in children, and is distributed throughout much of the eastern United States. No antivirals or vaccines are available for LACV, or most other mosquito-borne viruses, and prevention generally relies on mosquito control. We sought to determine whether coffee extracts could interfere with LACV replication and vector mosquito development. Both regular and decaffeinated coffee demonstrated significant reductions in LACV replication in direct antiviral assays. This activity was not due to the presence of caffeine, which did not inhibit the virus life cycle. Aedes albopictus (Skuse; Diptera: Culicidae) mosquito larvae suffered near total mortality when reared in high concentrations of regular and decaffeinated coffee and in caffeine. Following larval exposure to sublethal coffee concentrations, adult A. albopictus mosquitoes had significantly reduced whole-body LACV titers 5 days post-infection, compared to larvae reared in distilled water. These results suggest that it may be possible to both control mosquito populations and alter the vector competence of mosquitoes for arthropod-borne viruses by introducing antiviral compounds into the larval habitat

Transmission Dynamics and Epidemiology of West Nile Virus in Ontario, Canada

The resurgence of West Nile virus (WNV; Family Flaviviridae, genus Flavivirus) in Ontario, Canada in 2012 demonstrated that there is a great need for a reassessment of the local mosquito fauna, estimation of risk of WNV transmission, and the creation of effective arboviral awareness campaigns. A review of the current literature and collection databases revealed that there are 68 mosquito species known from Ontario (Chapter 2). Ten species were added to the list of species including Culex erraticus (Chapter 3) and Aedes albopictus (Chapter 4), both of which are capable of transmitting West Nile virus. Ae. albopictus was repeatedly collected from Windsor, Ontario in 2016 (Chapter 4). Immatures (n=78) were collected from tires, StyrofoamTM containers, and discarded garbage. Adult female (n=17) and male (n=2) specimens were collected from light traps (n=7) and Biogents-Sentinel traps (n=10). Additional specimens were obtained from Franklin County, Ohio. The generated gene tree and Bayesian cluster analysis grouped sequences described from Ohio and Windsor together on the same branches. Together these data suggest that the population in Windsor originated as a founder population of North American origin by means of human-aided dispersal. Mosquito abundance predication surfaces and seasonal distributions were attempted for each vector species to identify where and when vector species are most abundant in southern Ontario (Chapter 5). Spatial prediction surfaces using kriging were created for Aedes vexans, Aedes japonicus, Culex pipiens, Culex restuans, and Ochlerotatus trivittatus. Proximity to landscape variables was observed to improve model prediction. An epidemiological analysis of WNV human case prevalence and mosquito infection was conducted (Chapter 6). A strong quadratic relationship between the number of human cases and positive mosquito pools at the end of each year was observed (R2=0.9783, p < 0.001). Spearman rank correlation tests identified mosquito infection rates as the strongest predictors of human case prevalence at a one-week lag period. Average temperature was a strong predictor of mosquito infection rates. Cumulative positive Culex pools recorded by epidemiological week 34 is a sufficient action threshold for West Nile virus epidemics. These data have the potential to contribute to a more efficient West Nile virus awareness campaign

Culex quinquefasciatus mosquitoes do not support replication of Zika virus

The rapid spread of Zika virus (ZIKV) in the Americas raised many questions about the role of Culex quinquefasciatus mosquitoes in transmission, in addition to the key role played by the vector Aedes aegypti. Here we analysed the competence of Cx. quinquefasciatus (with or without Wolbachia endosymbionts) for a ZIKV isolate. We also examined the induction of RNA interference pathways after viral challenge and the production of small virus-derived RNAs. We did not observe any infection nor such small virus-derived RNAs, regardless of the presence or absence of Wolbachia. Thus, Cx. quinquefasciatus does not support ZIKV replication and Wolbachia is not involved in producing this phenotype. In short, these mosquitoes are very unlikely to play a role in transmission of ZIKV

Effects of co-habitation between Anopheles gambiae s.s. and Culex quinquefasciatus aquatic stages on life history traits

<p>Abstract</p> <p>Background</p> <p>The effective measures for the control of malaria and filariasis vectors can be achieved by targeting immature stages of anopheline and culicine mosquitoes in productive habitat. To design this strategy, the mechanisms (like biotic interactions with conspecifc and heterospecific larvae) regulating mosquito aquatic stages survivorship, development time and the size of emerging adults should be understood. This study explored the effect of co-habitation between <it>An. gambiae </it>s.s. and <it>Cx. quinquefasciatus </it>on different life history traits of both species under different densities and constant food supply in the habitats of the same size under semi-natural conditions.</p> <p>Methods</p> <p>Experiments were set up with three combinations; <it>Cx. quinquefasciatus </it>alone (single species treatment), <it>An. gambiae </it>s.s. alone (single species treatment); and <it>An. gambiae </it>s.s. with <it>Cx. quiquefasciatus </it>(co-habitation treatment) in different densities in semi field situation.</p> <p>Results</p> <p>The effect of co-habitation of <it>An. gambiae </it>s.s. and <it>Cx. quinquefasciatus </it>was found to principally affect three parameters. The wing-lengths (a proxy measure of body size) of <it>An. gambiae </it>s.s. in co-habitation treatments were significantly shorter in both females and males than in <it>An. gambiae </it>s.s single species treatments. In <it>Cx. quinquefasciatus</it>, no significant differences in wing-length were observed between the single species and co-habitation treatments. Daily survival rates were not significantly different between co-habitation and single species treatments for both <it>An. gambiae </it>s.s. and <it>Cx. quinquefasciatus</it>. Developmental time was found to be significantly different with single species treatments developing better than co-habitation treatments. Sex ratio was found to be significantly different from the proportion of 0.5 among single and co-habitation treatments species at different densities. Single species treatments had more males than females emerging while in co-habitation treatments more females emerged than males. In this study, there was no significant competitive survival advantage in co-habitation.</p> <p>Conclusion</p> <p>These results suggest that co-habitation of <it>An. gambiae </it>s.s. and <it>Cx. quinquefasciatus </it>in semi-natural conditions affect mostly <it>An. gambiae </it>s.s. body size. Hence, more has to be understood on the effects of co-habitation of <it>An. gambiae </it>s.s. and <it>Cx. quinquefasciatus </it>in a natural ecology and its possible consequences in malaria and filariasis epidemiology.</p

AIMSurv: First pan-European harmonized surveillance of Aedes invasive mosquito species of relevance for human vector-borne diseases

Human and animal vector-borne diseases, particularly mosquito-borne diseases, are emerging or re-emerging worldwide. Six Aedes invasive mosquito (AIM) species were introduced to Europe since the 1970s: Aedes aegypti, Ae. albopictus, Ae. japonicus, Ae. koreicus, Ae. atropalpus and Ae. triseriatus. Here, we report the results of AIMSurv2020, the first pan-European surveillance effort for AIMs. Implemented by 42 volunteer teams from 24 countries. And presented in the form of a dataset named “AIMSurv Aedes Invasive Mosquito species harmonized surveillance in Europe. AIM-COST Action. Project ID: CA17108”. AIMSurv2020 harmonizes field surveillance methodologies for sampling different AIMs life stages, frequency and minimum length of sampling period, and data reporting. Data include minimum requirements for sample types and recommended requirements for those teams with more resources. Data are published as a Darwin Core archive in the Global Biodiversity Information Facility- Spain, comprising a core file with 19,130 records (EventID) and an occurrences file with 19,743 records (OccurrenceID). AIM species recorded in AIMSurv2020 were Ae. albopictus, Ae. japonicus and Ae. koreicus, as well as native mosquito species

Vector competence evaluation of mosquitoes for Tahyna virus PJ01 strain, a new Orthobunyavirus in China

IntroductionTahyna virus (TAHV), an arbovirus of the genus Orthobunyavirus, is a cause of human diseases and less studied worldwide. In this study, a new strain of TAHV was isolated from Aedes sp. mosquitoes collected in Panjin city, Liaoning province. However, the competent vector of TAHV in China is still unknown.MethodsThe genome of newly isolated TAHV was sequenced and phylogenetic analysis is performed. Aedes albopictus and Culex pipiens pallens were orally infected with artificial virus blood meals (1:1 of virus suspension and mouse blood), the virus was detected in the midgut, ovary, salivary gland and saliva of the mosquitoes. Then, the transmission and dissemination rates, vertical transmission and horizontal transmission of the virus by the mosquitoes were assessed.ResultsPhylogenetic analysis revealed that the virus shared high similarity with TAHV and was named the TAHV PJ01 strain. After oral infection with virus blood meals, Ae. albopictus showed positive for the virus in all tested tissues with an extrinsic incubation period of 2 days and a fluctuating increasement of transmission and dissemination rates. Whereas no virus was detected in the saliva of Cx. pipiens pallens. Suckling mice bitten by infectious Ae. albopictus developed obvious neurological symptoms, including inactivity, hind-leg paralysis and difficulty turning over, when the virus titer reached 1.70×105 PFU/mL in the brain. Moreover, TAHV was detected in the eggs, larvae and adults of F1 offspring of Ae. albopictus.DiscussionAe. albopictus is an efficient vector to transmit TAHV but Cx. pipiens pallens is not. Ae. albopictus is also a reservoir host that transmits the virus vertically, which further increases the risk of outbreaks. This study has important epidemiological implications for the surveillance of pathogenic viruses in China and guiding comprehensive vector control strategies to counteract potential outbreaks in future

Do topical repellents divert mosquitoes within a community? Health equity implications of topical repellents as a mosquito bite prevention tool.

OBJECTIVES: Repellents do not kill mosquitoes--they simply reduce human-vector contact. Thus it is possible that individuals who do not use repellents but dwell close to repellent users experience more bites than otherwise. The objective of this study was to measure if diversion occurs from households that use repellents to those that do not use repellents. METHODS: The study was performed in three Tanzanian villages using 15%-DEET and placebo lotions. All households were given LLINs. Three coverage scenarios were investigated: complete coverage (all households were given 15%-DEET), incomplete coverage (80% of households were given 15%-DEET and 20% placebo) and no coverage (all households were given placebo). A crossover study design was used and coverage scenarios were rotated weekly over a period of ten weeks. The placebo lotion was randomly allocated to households in the incomplete coverage scenario. The level of compliance was reported to be close to 100%. Mosquito densities were measured through aspiration of resting mosquitoes. Data were analysed using negative binomial regression models. FINDINGS: Repellent-users had consistently fewer mosquitoes in their dwellings. In villages where everybody had been given 15%-DEET, resting mosquito densities were fewer than half that of households in the no coverage scenario (Incidence Rate Ratio [IRR]=0.39 (95% confidence interval [CI]: 0.25-0.60); p<0.001). Placebo-users living in a village where 80% of the households used 15%-DEET were likely to have over four-times more mosquitoes (IRR=4.17; 95% CI: 3.08-5.65; p<0.001) resting in their dwellings in comparison to households in a village where nobody uses repellent. CONCLUSIONS: There is evidence that high coverage of repellent use could significantly reduce man-vector contact but with incomplete coverage evidence suggests that mosquitoes are diverted from households that use repellent to those that do not. Therefore, if repellents are to be considered for vector control, strategies to maximise coverage are required

Environmental Impacts on life history in container breeding mosquitoes

In this dissertation I explore different ways that the environment impacts life history in mosquitoes in ways that may alter vectorial capacity. In chapter I, I tested if short-term sugar deprivation experienced after exposure to La Crosse virus altered infection rates in Aedes albopictus and if sugar treatment and virus infection status altered blood feeding behavior and fecundity. I found no evidence that sugar deprivation impacted infection rates or fecundity. Sugar deprivation did increase blood feeding. There was no effect of infection status on blood feeding or fecundity. In chapter II, I tested for effects of seasonal cues (temperature and photoperiod) experienced during larval development on Aedes triseriatus. I found reduced larval survivorship, reduced development rate, and smaller sizes when larvae were reared under warmer conditions with a shorter photoperiod. I found no effect of seasonal rearing temperatures on adult longevity and a significant size and treatment interaction for fecundity. In chapter III, I tested the effects of larval habitat age and prior habitat exploitation by a previous non-overlapping cohort of larvae on female larval survivorship, development rate, size and adult longevity. I found that larvae reared in older habitats had increased survivorship, reduced development rate, and resulting adults had increased longevity. Prior exploitation significantly increased development rate only. In chapter IV, I investigated the impacts of larval habitat size and habitat drying on mosquito communities. I found that larval densities differed over time only in the smallest containers and that two weeks was sufficient for these communities to rebound to densities observed in stable volume habitats after they were completely dried and refilled. Predatory species density was not affected by habitat size or drying. Predator density did not affect prey density but did significantly decrease adult longevity which indicates negative trait-mediated effects of predation on prey species