Host stress hormones alter vector feeding preferences, success, and productivity.

Stress hormones might represent a key link between individual-level infection outcome, population-level parasite transmission, and zoonotic disease risk. Although the effects of stress on immunity are well known, stress hormones could also affect host-vector interactions via modification of host behaviours or vector-feeding patterns and subsequent reproductive success. Here, we experimentally manipulated songbird stress hormones and examined subsequent feeding preferences, feeding success, and productivity of mosquito vectors in addition to defensive behaviours of hosts. Despite being more defensive, birds with elevated stress hormone concentrations were approximately twice as likely to be fed on by mosquitoes compared to control birds. Moreover, stress hormones altered the relationship between the timing of laying and clutch size in blood-fed mosquitoes. Our results suggest that host stress could affect the transmission dynamics of vector-borne parasites via multiple pathways.

Vector Competence and Capacity of Culex erraticus (Diptera: Culicidae) for Eastern Equine Encephalitis Virus in the Southeastern United States.

Field studies of the ecology of eastern equine encephalitis virus (EEEV; family Togaviridae, genus Alphavirus) in the southeastern United States have demonstrated that Culex erraticus (Dyar and Knab) is the most common mosquito at many enzootic sites and is often infected with the virus. However, the competence of Cx. erraticus for EEEV has not been explored in detail. Culex erraticus females were collected from the field and fed upon EEEV-infected chicks. The infected mosquitoes were provided honey for nutrition and to monitor for time to infectiveness. Of the mosquitoes that survived the 14-d postfeeding period, 89% were infected and 84% had evidence of a disseminated infection, though titers were generally low. EEEV was first detected in honey 6 d postinfection and was detected in samples collected from 94% of the mosquitoes with a disseminated infection overall. These data and others were then employed to estimate the relative vectorial capacity of Cx. erraticus at an EEEV enzootic site in Alabama. The vectorial capacity of Cx. erraticus at this site was 44% of Culiseta melanura (Coquillett), the accepted enzootic vector, suggesting Cx. erraticus may play a role in transmitting EEEV in areas where it is abundant and Cs. melanura rare.

Isolation of Onchocerca lupi in Dogs and Black Flies, California, USA.

In southern California, ocular infections caused by Onchocerca lupi were diagnosed in 3 dogs (1 in 2006, 2 in 2012). The infectious agent was confirmed through morphologic analysis of fixed parasites in tissues and by PCR and sequencing of amplicons derived from 2 mitochondrially encoded genes and 1 nuclear-encoded gene. A nested PCR based on the sequence of the cytochrome oxidase subunit 1 gene of the parasite was developed and used to screen Simulium black flies collected from southern California for O. lupi DNA. Six (2.8%; 95% CI 0.6%-5.0%) of 213 black flies contained O. lupi DNA. Partial mitochondrial16S rRNA gene sequences from the infected flies matched sequences derived from black fly larvae cytotaxonomically identified as Simulium tribulatum. These data implicate S. tribulatum flies as a putative vector for O. lupi in southern California.

Optimized strategy for real-time qPCR detection of Onchocerca volvulus DNA in pooled Simulium sp. blackfly vectors.

BACKGROUND: Onchocerca volvulus is a filarial parasite that is a major cause of dermatitis and blindness in endemic regions primarily in sub-Saharan Africa. Widespread efforts to control the disease caused by O. volvulus infection (onchocerciasis) began in 1974 and in recent years, following successful elimination of transmission in much of the Americas, the focus of efforts in Africa has moved from control to the more challenging goal of elimination of transmission in all endemic countries. Mass drug administration (MDA) with ivermectin has reached more than 150 million people and elimination of transmission has been confirmed in four South American countries, with at least two African countries having now stopped MDA as they approach verification of elimination. It is essential that accurate data for active transmission are used to assist in making the critical decision to stop MDA, since missing low levels of transmission and infection can lead to continued spread or recrudescence of the disease. METHODOLOGY/PRINCIPAL FINDINGS: Current World Health Organization guidelines for MDA stopping decisions and post-treatment surveillance include screening pools of the Simulium blackfly vector for the presence of O. volvulus larvae using a PCR-ELISA-based molecular technique. In this study, we address the potential of an updated, practical, standardized molecular diagnostic tool with increased sensitivity and species-specificity by comparing several candidate qPCR assays. When paired with heat-stable reagents, a qPCR assay with a mitochondrial DNA target (OvND5) was found to be more sensitive and species-specific than an O150 qPCR, which targets a non-protein coding repetitive DNA sequence. The OvND5 assay detected 19/20 pools of 100 blackfly heads spiked with a single L3, compared to 16/20 for the O150 qPCR assay. CONCLUSIONS/SIGNIFICANCE: Given the improved sensitivity, species-specificity and resistance to PCR inhibitors, we identified OvND5 as the optimal target for field sample detection. All reagents for this assay can be shipped at room temperature with no loss of activity. The qPCR protocol we propose is also simpler, faster, and more cost-effective than the current end-point molecular assays.

Winter severity predicts the timing of host shifts in the mosquito Culex erraticus.

In temperate regions, seasonal epidemics of many mosquito-borne viruses are triggered when mosquito populations shift from feeding on avian to mammalian hosts. We investigated effects of temperature on the timing of bird-to-mammal shifts using an 8 year dataset of blood-meals from a mosquito (Culex erraticus) in Alabama, USA. As expected, Cx. erraticus shifted from avian to mammalian hosts each year. The timing of the shift, however, varied considerably among years. Harshness of the preceding winter (chill accumulation) explained 93 per cent of the variation in the timing of bird-to-mammal shifts, with shifts occurring later in years following harsher winters. We hypothesize that winter temperatures drive the timing of bird-to-mammal shifts through effects on host reproductive phenology. Because mosquitoes target birds during the nesting season, and bird nesting occurs later in years following colder winters, later nesting dates result in a concomitant delay in the timing of bird-to-mammal host shifts. Global increases in winter temperatures could cause significant changes in the timing of seasonal host shifts by mosquitoes, with prolonged periods of epidemic transmission of mosquito-borne diseases.

Vertebrate hosts of Aedes aegypti and Aedes mediovittatus (Diptera: Culicidae) in rural Puerto Rico.

The distribution of Aedes (Stegomyia) aegypti (L.), the main vector of dengue viruses (DENV) worldwide, overlaps with Aedes (Gymnometopa) mediovittatus (Coquillett), the Caribbean treehole mosquito, in urban, suburban, and rural areas. Ae. mediovittatus is a competent vector of DENV with high rates of vertical DENV transmission in the laboratory. This study determined whether Ae. mediovittatus feeds on humans and compared its feeding patterns with co-occurring Ae. aegypti in two rural communities of Puerto Rico. Adult mosquitoes were captured for three consecutive days every week from July 2009 to May 2010 using BG-Sentinel traps with skin lures that were placed in the front yard of houses in both communities. Three methods were used to identify the 756 bloodmeals obtained in this study: a multiplex polymerase chain reaction (PCR) for humans and dogs targeting cytochrome b; a PCR targeting the 16S rRNA; and a nested PCR targeting cytochrome b. Ae. mediovittatus fed mostly on humans (45-52%) and dogs (28-32%) but also on cats, cows, horses, rats, pigs, goats, sheep, and chickens. Ae. aegypti fed mostly on humans (76-79%) and dogs (18-21%) but also on cats, horses, and chickens. Our results indicate that Ae. mediovittatus may have a relatively high rate of vector-human contact, which might facilitate virus transmission or harborage in rural areas of Puerto Rico.

Developing models for the forage ratios of Culiseta melanura and Culex erraticus using species characteristics for avian hosts.

Studies of mosquito preferences for avian hosts have found that some bird species are at greater risk than others of being fed upon by mosquitoes. The ecological factors that determine this interspecific variation in avian host use by mosquitoes have been little studied, despite the possibility that such variation may influence spatial and temporal patterns of the occurrence of mosquito-borne pathogens. Our objective was to identify ecological variables associated with the avian host forage ratios estimated from a previous study of mosquito feeding patterns in Tuskegee National Forest, AL. We used species' characteristics derived from the literature to develop multiple linear regression models for the forage ratios of Culiseta melanura (Coquillett) and Culex erraticus (Dyar & Knab) for avian hosts. We found that habitat-edge association and body mass of avian host species were the best predictors of forage ratios of Cx. erraticus for avian hosts. Although no avian host traits were inferred to be strong predictors of forage ratios of Cs. melanura, body mass had the greatest importance weight among those considered. Our results suggest that characteristics of avian hosts may predict their levels of use by some mosquito species.

Theoretical potential of passerine filariasis to enhance the enzootic transmission of West Nile virus.

Vertebrate reservoirs of arboviruses are often infected with microfilariae (MF). Laboratory studies have shown that MF can enhance the infectivity of arboviruses to mosquitoes. Soon after being ingested, MF penetrate the mosquito midgut. If the host blood also contains virus (i.e., vertebrate is dually infected), penetrating MF may introduce virus into the hemocoel. This can transform otherwise virus-incompetent mosquito species into virus-competent species and simultaneously accelerate viral development, allowing mosquitoes to transmit virus sooner than normal. This phenomenon is termed microfilarial enhancement of arboviral transmission. The prevalence of MF is very high in many passerine populations in North America. Therefore, we investigated if microfilarial enhancement could have facilitated the establishment and rapid spread of West Nile virus (WNV) across the mid-western United States. Our investigations revealed that mosquitoes, WNV, and passerine MF do interact in nature because; 1) 17% of 54 common grackles (Quiscalus quiscula L.), 8% of 26 American robins (Turdus migratorius L.), and 33% of three eastern kingbirds (Tyrannus tyrannus L.) were concurrently microfilaremic and seropositive to WNV; 2) feeding activities of mosquitoes overlapped temporally with the appearance of MF in the blood of common grackles; 3) mosquitoes fed on common grackles and American robins in nature; and 4) mosquito ingestion of two taxonomically distant species of passerine MF (i.e., Chandlerella quiscali and Eufilaria spp.) resulted in penetration of mosquito midguts. To estimate the theoretical effect that MF enhancement could have on WNV transmission in areas of high MF prevalence, vectorial capacity values were calculated for Culex mosquitoes feeding on common grackles, whereby MF enhancement was either invoked or ignored. For Cx. pipiens, vectorial capacity increased over three-fold when potential effects of MF were included in the calculations. For Cx. tarsalis, the effect was less (i.e., 1.4-fold increase). Closer attention should be paid to the potential of MF to enhance mosquito transmission of arboviruses.

Use of Ov16-Based Serology for Post-Elimination Surveillance of Onchocerciasis in Ecuador.

Onchocerciasis is a blinding disease caused by the filarial parasite Onchocerca volvulus, with a worldwide distribution. Onchocerciasis has been targeted for regional elimination based on annual and semiannual mass drug administration (MDA) with ivermectin in endemic communities over several years. This strategy in Ecuador led to the interruption of transmission and suspension of ivermectin MDA in 2009 with certification of elimination in 2014. In the present study, we analyzed sera collected in 2018 from 123 children aged 5-9 years from formerly hyperendemic communities in the Esmeraldas focus, Ecuador, for the presence of antibodies to Ov16 antigen. All samples were negative, indicating no evidence of transmission since MDA was stopped. Ov16-based serology offers an economic and practical alternative for measuring vector infectivity for post-certification surveillance in formerly endemic countries where expertise and capacity to reliably measure fly infectivity rates are costly to maintain.

Evidence for suppression of Onchocerca volvulus transmission in the Oaxaca focus in Mexico.

Entomologic and serologic surveys were performed in four sentinel communities in the Oaxaca focus in southern Mexico to assess the level of transmission and exposure incidence to Onchocerca volvulus. All communities have been receiving ivermectin mass treatment twice per year since 1997. In one community, parasite DNA was detected by polymerase chain reaction-enzyme-linked immunosorbent assay in 2004 in one pool of 50 vector heads of 170 such pools (8,500 flies) examined, which indicated an estimated transmission potential of 6.7 third-stage larvae/person/year. No evidence for transmission was found in the three other communities in 13,650 flies examined. All persons in a cohort consisting of 117 children in the four communities remained serologically negative for antibodies recognizing a cocktail of recombinant antigens over a four-year period from 2001 to 2004, which indicated an exposure incidence of 0%. Taken together, these data suggest that transmission has been suppressed in the four communities.

A cryptic species of Onchocerca (Nematoda: Onchocercidae) in blackflies (Simulium spp.) from southern California, USA.

BACKGROUND: Entomological surveillance for pathogens based on molecular screening of putative arthropod vectors such as blackflies (Diptera: Simuliidae) is becoming increasingly important. Surveillance provides a means to understand host and geographical patterns of underestimated biodiversity among North American species of Onchocerca and a pathway to identify and track expanding emergence of the zoonotic Onchocerca lupi. Herein, we have screened two blackfly species, Simulium tescorum and Simulium vittatum (s.l.), from Los Angeles County, southern California, USA for DNA of filarioid nematodes to better understand species richness and limits within the genus Onchocerca. METHODS: A total of 1056 and 378 female blackflies was collected using CO2-baited mosquito traps from March to November of 2015 and 2016, respectively. All blackflies during 2015 were individually processed for DNA extraction and PCR targeting of the cytochrome c oxidase subunit 1 (cox1) of the mitochondrial DNA (mtDNA). Specimens of S. tescorum collected in 2016 were processed individually with heads and bodies extracted separately, whereas those of S. vittatum (s.l.) were processed in pooled samples with heads and bodies extracted separately. A subset of filarioid-positive samples from 2015 and all samples from 2016 were screened using a PCR targeting the NADH dehydrogenase subunit 5 (nad5) gene (mtDNA). RESULTS: In 2015, 356 S. tescorum (33.7%) and 683 S. vittatum (s.l.) (64.7%) were collected, and an additional 17 specimens were not assessed morphologically. In 2016, a total of 378 blackflies was collected. Of these, 43 (11.6%) were S. tescorum and 327 (88.4%) were S. vittatum (s.l.), and an additional 8 specimens were not assessed morphologically. In 2015, Onchocerca sequences were detected in 4.8% (n = 17) of S. tescorum samples, and only one S. vittatum (0.15%). In 2016, only a single S. vittatum pool was positive for the same cryptic Onchocerca species. In phylogenetic comparisons based on nad5, the Onchocerca sequences from California formed a clade with those isolates in white-tailed deer from upstate New York, suggesting these belong to a single widespread cryptic species. CONCLUSIONS: An uncharacterized species of Onchocerca associated with cervid hosts was found in blackflies from southern California. Sequence data demonstrated it is likely conspecific with an unnamed species of Onchocerca previously found in white-tailed deer from upstate New York. Current data support recognition of a broad geographical distribution across North America for an apparently cryptic species of Onchocerca that is discrete from O. cervipedis, considered to be a typical filarioid among cervids. Our data suggest that this cryptic species of Onchocerca may infect subspecies of white-tailed deer (Odocoileus virginianus), and mule and black-tailed deer (Odocoileus hemionus) at temporal latitudes. The blackflies Simulium tescorum and S. vittatum (s.l.) (presumably, S. tribulatum) are putative vectors. Discovery of a cryptic complex indicates that species diversity and putative associations for definitive hosts and vectors of Onchocerca species in North America must be reassessed.

Host choice and West Nile virus infection rates in blood-fed mosquitoes, including members of the Culex pipiens complex, from Memphis and Shelby County, Tennessee, 2002-2003.

The source of bloodmeals in 2,082 blood-fed mosquitoes collected from February 2002 through December 2003 in Memphis and surrounding areas of Shelby County, Tennessee were determined. Members of the genus Culex and Anopheles quadrimaculatus predominated in the collections. Members of the Cx. pipiens complex and Cx. restuans were found to feed predominately upon avian hosts, though mammalian hosts made up a substantial proportion of the bloodmeals in these species. No significant difference was seen in the host class of bloodmeals in mosquitoes identified as Cx. pipiens pipiens, Cx. p. quinquefasciatus, or hybrids between these two taxa. Anopheles quadrimaculatus and Cx. erraticus fed primarily upon mammalian hosts. Three avian species (the American Robin, the Common Grackle, and the Northern Cardinal) made up the majority of avian-derived bloodmeals, with the American Robin representing the most frequently fed upon avian host. An analysis of these host feeding data using a modification of a transmission model for Eastern Equine encephalitis virus suggested that the American Robin and Common Grackle represented the most important reservoir hosts for West Nile virus. A temporal analysis of the feeding patterns of the dominant Culex species did not support a shift in feeding behavior away from robins to mammals late in the summer. However, a significant degree of temporal variation was noted in the proportion of robin-derived bloodmeals when the data were analyzed by semi-monthly periods throughout the summers of 2002 and 2003. This pattern was consistent with the hypothesis that the mosquitoes were preferentially feeding upon nesting birds.

West Nile virus infection in mosquitoes in the mid-south USA, 2002-2005.

West Nile virus (family Flaviviridae, genus Flavivirus, WNV) was first detected in the Tennessee Valley and in Alabama in August 2001. In summer 2002, intensive viral activity was seen, but in subsequent years, viral activity settled into an enzootic pattern. Here, we report an analysis of viral activity in the mosquito fauna in the Mid-South from 2002 (the first year viral activity was detected in mosquitoes) through 2005. Eight mosquito species were infected with WNV during 2002. However, viral activity was only detected in four species--Culex salinarius Coquillett, Culex erraticus Dyar & Knab, Coquillettidia perturbans Walker, and Aedes vexans Meigen--in multiple years. The greatest number of positive pools was in Cx. erraticus and Cx. salinarius. Despite being specifically targeted for collection, Aedes albopictus Skuse was only found to be infected during the epiornitic year (2002), suggesting that under enzootic transmission conditions its role as a bridge vector in the region may not be significant. Virus-positive pools of Cx. erraticus were identified from winter-resting and early season dry ice-baited trap collections in 2005, implicating this species in WNV overwintering in Alabama. Molecular analysis of individuals initially identified as members of the Culex pipiens L. complex suggested that alleles characteristic of Cx. pipiens predominated in mosquitoes collected in Huntsville, AL, whereas alleles in the Auburn, AL, population were predominately characteristic of Culex quinquefaciatus Say. The southern boundary of the overlap zone of the two species seems to be located primarily between Huntsville and Auburn, a distance of 350 km.

Associations between two mosquito populations and West Nile virus in Harris County, Texas, 2003-06.

Associations between Culex quinquefasciatus, Aedes albopictus and West Nile virus (WNV) activity, temperature, and rainfall in Harris County, Texas 2003-06 are discussed. Human cases were highly correlated to Cx. quinquefasciatus (r = 0.87) and Ae. albopictus (r = 0.78) pools, blue jays (r = 0.83), and Ae. albopictus collected (r = 0.71), but not Cx. quinquefasciatus collected (r = 0.45). Human cases were associated with temperature (r = 0.71), not rainfall (r = 0.29), whereas temperature correlated with Ae. albopictus and Cx. quinquefasciatus collections (r = 0.88 and 0.70, respectively) and Cx. quinqueftsciatus pools (r = 0.75), but not Ae. albopictus pools (r = 0.55). Both species (collections and pools) and blue jays were weakly correlated (r 5 0.41) with rainfall, but blue jays were better correlated with Cx. quinquefasciatus pools (r = 0.87), compared with Ae. albopictus pools (r = 0.67), Ae. albopictus collections (r = 0.69), and Cx. quinquefasciatus collections (r = 0.46). Peak minimum infection rate for Cx. quinquefasciatus (4.55), and Ae. albopictus (4.41) was in August with highest human cases (17.87), blue jays (55.58), and temperature (29.01 degrees C). Between both species, blood meal analysis indicated 68.18% of Cx. quinquefasciatus mammalian hosts were dog, while 22.72% were human, whereas Ae. albopictus had higher human (44.44%) but fewer dog hosts (22.22%). Ten bird species were identified as hosts for Cx. quinquefasciatus, with northern cardinal and blue jay representing 26.66% and 20.00%, respectively. No bird feeding activity was observed in Ae. albopictus. The earliest and latest human blood meal occurred in May (Ae. albopictus) and November (Cx. quinquefasciatus); 66.66% of human host identifications between both species occurred in October-November, after the seasonal human case peak. Based upon our data, WNV activity in both mosquito species warrants further investigation of their individual roles in WNV ecology within this region.

Environmental Drivers of Seasonal Patterns of Host Utilization by Culiseta melanura (Diptera: Culicidae) in Florida.

Field studies were carried out in four Florida counties to investigate winter and spring ecology of host use by Culiseta melanura (Coquillet), the primary vector of eastern equine encephalomyelitis virus (EEEV) in North America. Bloodmeal analysis by PCR was used to identify 233 host bloodmeals, which mainly originated from birds (78.5%) and reptiles (17.2%), primarily Anolis spp. lizards. Across counties, the percentage of bloodmeals from reptiles (7-37% depending upon county) increased with increasing day length and temperature in the spring. Multiple logistic regression revealed that differences in reptile host use across collection sites were largely explained by differences in average day length and temperature on the day of collection, and is probably owing to environment-driven behavioral patterns of ectothermic animals. Although past studies have demonstrated reptile biting by epizootic vectors of EEEV, including Culex (Melanoconion) spp., this is the first study to demonstrate widespread and common feeding upon ectothermic hosts by Cs. melanura. This work suggests that reptiles, particularly anole lizards, play a role in the ecology of EEEV in Florida either as amplifying hosts or as noncompetent hosts which dilute vector feedings thereby suppressing transmission. Detailed laboratory studies investigating impacts of environmental variables (temperature and photoperiod) on EEEV competence of anoles are needed to assess whether these animals support virus amplification.

Molecular Identification of Onchocerca spp. Larvae in Simulium damnosum sensu lato Collected in Northern Uganda.

Previous studies have demonstrated that the presence of larvae of other filarial species in Simulium damnosum sensu lato can distort estimates of transmission potential for Onchocerca volvulus in West Africa. However, studies conducted in foci of onchocerciasis in West Central Uganda indicated that larvae other than O. volvulus were not common in vectors collected there. Recent data collected in Northern Uganda revealed a striking discordance between estimates of the prevalence of flies carrying O. volvulus infective larvae obtained from molecular pool screening and dissection methods. To resolve this discrepancy, sequences from three mitochondrially encoded genes were analyzed from the larvae collected by dissection. All larvae analyzed were Onchocerca ochengi v. Siisa, a parasite of cattle, or Onchocerca ramachandrini, a parasite of warthogs. These results suggest that nonhuman parasite larvae are common in vectors in Northern Uganda, underscoring the necessity for molecular identification methods to accurately estimate O. volvulus transmission.

Large-scale entomologic assessment of Onchocerca volvulus transmission by poolscreen PCR in Mexico.

To study the impact of mass Mectizan treatment on Onchocerca volvulus transmission in Mexico, entomological surveys were carried out in the endemic foci of Oaxaca, Southern Chiapas, and Northern Chiapas. Collected flies were screened by polymerase chain reaction (PCR) for O. volvulus parasites. The prevalence of infected and infective flies was estimated using the PoolScreen algorithm and with a novel probability-based method. O. volvulus infective larvae were not detected in flies from 6/13 communities. In 7/13 communities, infective flies were detected, with prevalences ranging from 1.6/10,000 to 29.0/10,000 and seasonal transmission potentials ranging from 0.4 to 3.3. Infected and infective flies were found in a community in Northern Chiapas, suggesting that, according to World Health Organization criteria, autochthonous transmission exists in this focus. These data suggest that O. volvulus transmission in Mexico has been suppressed or brought to a level that may be insufficient to sustain the parasite population.

Host-feeding patterns of Aedes albopictus (Diptera: Culicidae) in relation to availability of human and domestic animals in suburban landscapes of central North Carolina.

Aedes albopictus (Skuse) (Diptera: Culicidae) is a major nuisance mosquito and a potential arbovirus vector. The host-feeding patterns of Ae. albopictus were investigated during the 2002 and 2003 mosquito seasons in suburban neighborhoods in Wake County, Raleigh, NC. Hosts of blood-fed Ae. albopictus (n = 1,094) were identified with an indirect enzyme-linked immunosorbent assay, by using antisera made in New Zealand White rabbits to the sera of animals that would commonly occur in peridomestic habitats. Ae. albopictus fed predominantly on mammalian hosts (83%). Common mammalian hosts included humans (24%), cats (21%), and dogs (14%). However, a notable proportion (7%) of bloodmeals also was taken from avian hosts. Some bloodmeals taken from birds were identified to species by a polymerase chain reaction-heteroduplex assay (PCR-HDA). Ae. albopictus fed predominantly on chickens and a northern cardinal. PCR-HDA failed to produce detectable products for 29 (58%) of 50 bloodmeals for which DNA had been amplified, indicating that these mosquitoes took mixed bloodmeals from avian and nonavian hosts. Ae. albopictus preference for humans, dogs, and cats was determined by calculating host-feeding indices for the three host pairs based on the proportion of host specific blood-fed mosquitoes collected in relation to the number of specific hosts per residence as established by a door-to-door survey conducted in 2003. Estimates of the average amount of time that residents and their pets (cats and dogs) spent out of doors were obtained. Host-feeding indices based only on host abundance indicated that Ae. albopictus was more likely to feed on domestic animals. However, when feeding indices were time-weighted, Ae. albopictus fed preferentially upon humans. Ae. albopictus blood feeding on humans was investigated using a STR/PCR-DNA profiling technique that involved amplification of three short tandem repeats loci. Of 40 human bloodmeals, 32 (80%) were from a single human, whereas eight (20%) were multiple bloodmeals taken from more than one human host. We conclude that the blood-feeding preference of Ae. albopictus for mammals will limit acquisition of arboviruses by this species from infected avian amplification hosts. This feeding preference likely limits the vector potential of Ae. albopictus for North American arboviruses.

Evaluation of the Honey-Card Technique for Detection of Transmission of Arboviruses in Florida and Comparison With Sentinel Chicken Seroconversion.

Zoonotic mosquito-borne viruses, such as the West Nile virus (WNV) and eastern equine encephalitis virus (EEEV), are major public health threats in the United States. Early detection of virus transmission and targeted vector management are critical to protect humans against these pathogens. Sentinel chickens and pool screening of mosquitoes, the most widely used methods of arbovirus early detection, have technical time-lags that compromise their early-detection value. The exploitation of sugar-feeding by trapped mosquitoes for arbovirus surveillance may represent a viable alternative to other methods. Here we compared effectiveness of sugar-impregnated nucleic-acid preserving substrates (SIPS) and sentinel chicken program for detecting WNV, EEEV, and St. Louis encephalitis virus in gravid traps, CO2-baited light traps, and resting traps at 10 locations in two Florida counties. In St. Johns County, comparable numbers of EEEV detections were made by SIPS traps (18) and sentinel chickens (22), but fewer WNV detections were made using SIPS (1) than sentinel chickens (13). In Volusia County, seven arbovirus detections were made via the sentinel chicken program (one EEEV and six WNV), whereas only one arbovirus detection (WNV) was made using SIPS. CO2-baited light traps captured >90% of total mosquitoes, yet yielded <30% of arbovirus detections. Resting traps and gravid traps captured a fraction of total mosquitoes, yet yielded roughly equivalent numbers of arbovirus detections, as did light traps. Challenges to successful deployment of SIPS include optimization of traps for collecting all vector species, increasing sugar-feeding rates of trapped vectors, and developing tractable methods for arbovirus detection.

The First Confirmed Elimination of an Onchocerciasis Focus in Africa: Abu Hamed, Sudan.

Mass treatment with ivermectin for onchocerciasis was stopped in 2012 in Abu Hamed, an isolated focus on the River Nile in northern Sudan. A 3-year posttreatment surveillance (PTS) ensued, at the end of which an evaluation was conducted in 2015 following the current World Health Organization guidelines for verification of onchocerciasis elimination. Vector black flies were collected from sentinel breeding sites and finger-prick bloodspots were collected from children ≤ 10 years of age resident in 35 communities within the focus. Polymerase chain reaction (PCR) screening of 19,191 flies from four sites for the O-150 parasite-specific marker found no flies carrying Onchocerca volvulus larvae (0%, 95% upper confidence limit [UCL] = 0.16), and serological testing of 5,266 children identified only one Ov16 seropositive child (0.019%, 95% UCL = 0.074); whose skin snips were negative when tested by O-150 PCR assay. These results indicate that for the first time in Africa, onchocerciasis elimination has been verified after a successful PTS in Abu Hamed.