Interrupted blood-feeding by Culiseta melanura (Diptera: Culicidae) on European starlings

Human-Mosquito Contact: A Missing Link in Our Understanding of Mosquito-Borne Disease Transmission Dynamics

Despite the critical role that contact between hosts and vectors, through vector bites, plays in driving vector-borne disease (VBD) transmission, transmission risk is primarily studied through the lens of vector density and overlooks host-vector contact dynamics. This review article synthesizes current knowledge of host-vector contact with an emphasis on mosquito bites. It provides a framework including biological and mathematical definitions of host-mosquito contact rate, blood-feeding rate, and per capita biting rates. We describe how contact rates vary and how this variation is influenced by mosquito and vertebrate factors. Our framework challenges a classic assumption that mosquitoes bite at a fixed rate determined by the duration of their gonotrophic cycle. We explore alternative ecological assumptions based on the functional response, blood index, forage ratio, and ideal free distribution within a mechanistic host-vector contact model. We highlight that host-vector contact is a critical parameter that integrates many factors driving disease transmission. A renewed focus on contact dynamics between hosts and vectors will contribute new insights into the mechanisms behind VBD spread and emergence that are sorely lacking. Given the framework for including contact rates as an explicit component of mathematical models of VBD, as well as different methods to study contact rates empirically to move the field forward, researchers should explicitly test contact rate models with empirical studies. Such integrative studies promise to enhance understanding of extrinsic and intrinsic factors affecting host-vector contact rates and thus are critical to understand both the mechanisms driving VBD emergence and guiding their prevention and control.

Understanding host utilization by mosquitoes: determinants, challenges and future directions

Mosquito host utilization is a key factor in the transmission of vector-borne pathogens given that it greatly influences host-vector contact rates. Blood-feeding patterns of mosquitoes are not random, as some mosquitoes feed on particular species and/or individuals more than expected by chance. Mosquitoes use a number of cues including visual, olfactory, acoustic, and thermal stimuli emitted by vertebrate hosts to locate and identify their blood meal sources. Thus, differences in the quality/intensity of the released cues may drive host selection by mosquitoes at both inter- and intra-specific levels. Such patterns of host selection by mosquitoes in space and time can be structured by factors related to mosquitoes (e.g. innate host preference, behavioural plasticity), to hosts (e.g. emission of host-seeking cues, host availability) or to both (e.g. pathogen infection). In this study, we review current evidence, from phenomena to mechanisms, of how these factors influence host utilization by mosquitoes. We also review the methodologies commonly used in this research field and identify the major challenges for future studies. To bridge the knowledge gaps, we propose improvements to strengthen traditional approaches and the use of a functional trait-based approach to infer mosquito host utilization in natural communities.

Variation in Tick Load Among Bird Body Parts: Implications for Studying the Role of Birds in the Ecology and Epidemiology of Tick-Borne Diseases

Wild birds play important roles in the maintenance and dispersal of tick populations and tick-borne pathogens, yet in field studies of tick-borne disease ecology and epidemiology there is limited standardization of how birds are searched for ticks. We conducted a qualitative literature review of 100 field studies where birds were searched for ticks to characterize which parts of a bird's anatomy are typically sampled. To increase understanding of potential biases associated with different sampling approaches, we described variation in tick loads among bird body parts using field-collected data from 459 wild-caught birds that were searched across the entire body. The literature review illustrated a lack of clarity and consistency in tick-searching protocols: 57% of studies did not explicitly report whether entire birds or only particular body parts were searched, 34% reported concentrating searches on certain body parts (most frequently the head only), and only 9% explicitly reported searching the entire bird. Based on field-collected data, only 22% of ticks were found on the head, indicating that studies focusing on the head likely miss a large proportion of ticks. We provide tentative evidence that feeding locations may vary among tick species; 89% of Amblyomma americanum, 73% of Ambloyomma maculatum, and 56% of Haemaphysalis leporispalustris were on body parts other than the head. Our findings indicate a need for clear reporting and increased standardization of tick searching methodologies, including sampling the entire bird body, to provide an unbiased understanding of the role of birds in the maintenance and emergence of tick-borne pathogens.

Climate change projections of West Nile virus infections in Europe: implications for blood safety practices

BACKGROUND

West Nile virus (WNV) is transmitted by mosquitoes in both urban as well as in rural environments and can be pathogenic in birds, horses and humans. Extrinsic factors such as temperature and land use are determinants of WNV outbreaks in Europe, along with intrinsic factors of the vector and virus.

METHODS

With a multivariate model for WNV transmission we computed the probability of WNV infection in 2014, with July 2014 temperature anomalies. We applied the July temperature anomalies under the balanced A1B climate change scenario (mix of all energy sources, fossil and non-fossil) for 2025 and 2050 to model and project the risk of WNV infection in the future. Since asymptomatic infections are common in humans (which can result in the contamination of the donated blood) we estimated the predictive prevalence of WNV infections in the blood donor population.

RESULTS

External validation of the probability model with 2014 cases indicated good prediction, based on an Area Under Curve (AUC) of 0.871 (SD = 0.032), on the Receiver Operating Characteristic Curve (ROC). The climate change projections for 2025 reveal a higher probability of WNV infection particularly at the edges of the current transmission areas (for example in Eastern Croatia, Northeastern and Northwestern Turkey) and an even further expansion in 2050. The prevalence of infection in (blood donor) populations in the outbreak-affected districts is expected to expand in the future.

CONCLUSIONS

Predictive modelling of environmental and climatic drivers of WNV can be a valuable tool for public health practice. It can help delineate districts at risk for future transmission. These areas can be subjected to integrated disease and vector surveillance, outreach to the public and health care providers, implementation of personal protective measures, screening of blood donors, and vector abatement activities.

Cascade of ecological consequences for West Nile virus transmission when aquatic macrophytes invade stormwater habitats

Artificial aquatic habitats are ubiquitous in anthropogenic landscapes and highly susceptible to colonization by invasive plant species. Recent research into the ecology of infectious diseases indicates that the establishment of invasive plant species can trigger ecological cascades which alter the transmission dynamics of vector-borne pathogens that imperil human health. Here, we examined whether the presence or management of two invasive, emergent plants, cattails (Typha spp.) and phragmites (Phragmites australis), in stormwater dry detention basins (DDBs) alter the local distribution of vectors, avian hosts, or West Nile virus (WNV) transmission risk in an urban residential setting. Mosquitoes and birds were surveyed at 14 DDBs and paired adjacent residential sites. During the study period, emergent vegetation was mowed by site managers in three DDBs. In the absence of vegetation management, the overall abundance and species composition of both adult vectors and avian hosts differed between residential and DDB habitats; however, WNV entomological risk indices were equivalent. Communal bird roosts composed primarily of three species, European Starlings (Sturnus vulgaris), Red-winged Blackbirds (Agelaius phoeniceus), and Common Grackles (Quiscalus quiscula), representing a broad range of WNV reservoir competence, were observed at half (three out of six) of the DDBs containing unmanaged stands of phragmites; however, their presence was associated with a lower seasonal increase in vector infection rate. Conversely, mowing of emergent vegetation resulted in a significant and sustained increase in the abundance of WNV-infected vectors in DDBs and the increase in risk extended to adjacent residential sites. These findings indicate that management of invasive plants in DDBs during the growing season can increase, while presence of communal bird roosts can decrease, WNV transmission risk.

Reduced West Nile Virus Transmission Around Communal Roosts of Great-Tailed Grackle (Quiscalus mexicanus)

West Nile virus has caused several outbreaks among humans in the Phoenix metropolitan area (Arizona, southwest USA) within the last decade. Recent ecologic studies have implicated Culex quinquefasciatus and Culex tarsalis as the mosquito vectors and identified three abundant passerine birds-great-tailed grackle (Quiscalus mexicanus), house sparrow (Passer domesticus), and house finch (Haemorhous mexicanus)-as key amplifiers among vertebrates. Nocturnal congregations of certain species have been suggested as critical for late summer West Nile virus amplification. We evaluated the hypothesis that house sparrow (P. domesticus) and/or great-tailed grackle (Q. mexicanus) communal roost sites (n = 22 and n = 5, respectively) in a primarily suburban environment were spatially associated with West Nile virus transmission indices during the 2010 outbreak of human neurological disease in metropolitan Phoenix. Spatial associations between human case residences and communal roosts were non-significant for house sparrows, and were negative for great-tailed grackle. Several theories that explain these observations are discussed, including the possibility that grackle communal roosts are protective.

Avian roosting behavior influences vector-host interactions for West Nile virus hosts

BACKGROUND

Extensive work has shown that vectors almost never feed at random. Often, a subset of individual hosts and host species are fed on much more frequently than expected from their abundance and this can amplify pathogen transmission. However, the drivers of variation in contact patterns between vectors and their hosts are not well understood, even in relatively well-studied systems such as West Nile virus (WNV).

METHODS

We compared roosting height and roost aggregation size of seven avian host species of WNV with patterns of host-seeking mosquito (Culex pipiens) abundance at communal and non-communal roost sites.

RESULTS

First, host-seeking mosquito abundance increased with height and paralleled increased mosquito feeding preferences on species roosting higher in the tree canopy. Second, there were several hundred-fold fewer mosquitoes per bird trapped at American robin (Turdus migratorius) communal roosts compared to non-communal roost sites, which could reduce transmission from and to this key amplifying host species. Third, seasonal changes in communal roost formation may partly explain observed seasonal changes in mosquito feeding patterns, including a decrease in feeding on communal roosting robins.

CONCLUSIONS

These results illustrate how variation in habitat use by hosts and vectors and social aggregation by hosts influence vector-host interactions and link the behavioral ecology of birds and the transmission of vector-borne diseases to humans.

Vector-host interactions and epizootiology of eastern equine encephalitis virus in Massachusetts

Eastern equine encephalitis (EEE) virus is a highly pathogenic mosquito-borne zoonosis that is responsible for outbreaks of severe disease in humans and equines, resulting in high mortality or severe neurological impairment in most survivors. In the northeastern United States, EEE virus is maintained in an enzootic cycle involving the ornithophilic mosquito, Culiseta melanura (Coquillett) and passerine birds in freshwater swamp habitats. To evaluate the role of Cs. melanura and Culiseta morsitans (Theobald) in recent episodes of EEE virus activity in Massachusetts, we collected blood-fed mosquitoes between June, 2007, and October, 2008, from virus foci in 6 counties, and identified the source of blood meals by PCR amplification of mitochondrial cytochrome b gene and sequencing. Analysis of 529 Cs. melanura and 25 Cs. morsitans revealed that nearly 99% and 96% of mosquitoes, respectively, acquired blood meals solely from avian hosts. American Robin, Turdus migratorius Linnaeus was identified as the most common vertebrate host for Cs. melanura (21.7%, n=115), followed by Tufted Titmouse, Baeolophus bicolor (L.) (8.7%, n=46), Black-capped Chickadee, Poecile atricapillus (L.) (8.5%, n=45), Scarlet Tanager, Piranga olivacea (Gmelin) (6.8%, n=36), Field Sparrow, Spizella pusilla (Wilson) (6.2%, n=33), Northern Cardinal, Cardinalis cardinalis (L.) (5.7%, n=30), and other mostly Passeriformes birds. Mammalian-derived blood meals were identified as white-tailed deer, Odocoileus virginianus Zimmermann, domestic cow, Bos taurus L., and human, Homo sapiens L. There were 4 isolations of EEE virus, West Nile virus, and Highland J virus from Cs. melanura. Our results in conjunction with other lines of evidence, including reservoir competency, prevalence of antibody, and infection in nature, suggest that the American Robin, Tufted Titmouse, Black-capped Chickadee, and a few other passerine birds may play key roles in supporting EEE virus transmission in Massachusetts. Infrequent blood feeding of Cs. melanura on mammalian hosts, including humans, also indicates that this mosquito may occasionally contribute to epidemic/epizootic transmission of EEE virus in this region.

The fitness of African malaria vectors in the presence and limitation of host behaviour

Background

Host responses are important sources of selection upon the host species range of ectoparasites and phytophagous insects. However little is known about the role of host responses in defining the host species range of malaria vectors. This study aimed to estimate the relative importance of host behaviour to the feeding success and fitness of African malaria vectors, and assess its ability to predict their known host species preferences in nature.

Methods

Paired evaluations of the feeding success and fitness of African vectors Anopheles arabiensis and Anopheles gambiae sensu stricto in the presence and limitation of host behaviour were conducted in a semi-field system (SFS) at Ifakara Health Institute, Tanzania. In one set of trials, mosquitoes were released within the SFS and allowed to forage overnight on a host that was free to exhibit a natural behaviour in response to insect biting. In the other, mosquitoes were allowed to feed directly on from the skin surface of immobile hosts. The feeding success and subsequent fitness of vectors under these conditions were investigated on six host types (humans, calves, chickens, cows, dogs and goats) to assess whether physical movements of preferred host species (cattle for An. arabiensis, humans for An. gambiae s.s.) were less effective at preventing mosquito bites than those of common alternatives.

Results

Anopheles arabiensis generally had greater feeding success when applied directly to host skin than when foraging on unrestricted hosts (in five of six host species). However, An. gambiae s.s. obtained blood meals from free and restrained hosts with similar success from most host types (four out of six). Overall, the blood meal size, oviposition rate, fecundity and post-feeding survival of mosquito vectors were significantly higher after feeding on hosts free to exhibit behaviour, than those who were immobilized during feeding trials.

Conclusions

Allowing hosts to move freely during exposure to mosquitoes was associated with moderate reductions in mosquito feeding success, but no detrimental impact to the subsequent fitness of mosquitoes that were able to feed upon them. This suggests that physical defensive behaviours exhibited by common host species including humans do not impose substantial fitness costs on African malaria vectors.

How effective is preening against mobile ectoparasites? An experimental test with pigeons and hippoboscid flies

Birds combat ectoparasites with many defences but the first line of defence is grooming behaviour, which includes preening with the bill and scratching with the feet. Preening has been shown to be very effective against ectoparasites. However, most tests have been with feather lice, which are relatively slow moving. Less is known about the effectiveness of preening as a defence against more mobile and evasive ectoparasites such as hippoboscid flies. Hippoboscids, which feed on blood, have direct effects on the host such asanaemia, as well as indirect effects as vectors of pathogens. Hence, effective defence against hippoboscid flies is important. We used captive Rock Pigeons (Columba livia) to test whether preening behaviour helps to control pigeon flies (Pseudolynchia canariensis). We found that pigeons responded to fly infestation by preening twice as much as pigeons without flies. Preening birds killed twice as many flies over the course of our week-long experiment as birds with impaired preening; however, preening did not kill all of the flies. We also tested the role of the bill overhang, which is critical for effective preening against feather lice, by experimentally removing the overhang and re-measuring the effectiveness of preening against flies. Birds without overhangs were as effective at controlling flies as were birds with overhangs. Overall, we found that preening is effective against mobile hippoboscid flies, yet it does not eliminate them. We discuss the potential impact of preening on the transmission dynamics of blood parasites vectored by hippoboscid flies.

Further observations on in vitro hybridization of hemosporidian parasites: patterns of ookinete development in Haemoproteus spp

Increasingly frequent outbreaks of zoonotic infections call for studies of wildlife parasites to reach a better understanding of the mechanisms of host switch, leading to the evolution of new diseases. However, speciation processes have been insufficiently addressed in experimental parasitology studies, primarily due to difficulties in determining and measuring mate-recognition signals in parasites. We investigated patterns of sexual process and ookinete development in avian Haemoproteus (Parahaemoproteus) spp. (Haemosporida, Haemoproteidae) using in vitro experiments on between-lineage hybridization. Eleven mitochondrial cytochrome b (cyt b) lineages belonging to 9 species of hemoproteid were isolated from naturally infected passerine birds. The parasites were identified to species on the basis of morphology of their gametocytes and polymerase chain reaction amplification of segments of the cyt b gene. Sexual process and ookinete development were initiated in vitro by mixing blood containing mature gametocytes with a 3.7% solution of sodium citrate and exposing the mixture to air. Ookinetes of all lineages except Haemoproteus payevskyi (lineage hRW1) and Haemoproteus nucleocondensus (hGRW1) developed; the 2 latter species did not exflagellate. Between-lineage hybridization was initiated by mixing blood containing mature gametocytes of 2 different parasites; the following experiments were performed: (1) Haemoproteus pallidus (lineage hPFC1) × Haemoproteus minutus (lineage hTURDUS2); (2) H. pallidus (hPFC1) × Haemoproteus tartakovskyi (hSISKIN1); (3) Haemoproteus belopolskyi (hHIICT3) × Haemoproteus lanii (hRB1); (4) Haemoproteus balmorali (hSFC1) × H. pallidus (hPFC1); (5) H. belopolskyi (hHIICT1) × Haemoproteus parabelopolskyi (hSYBOR1); (6) H. tartakovskyi (hHAWF1) × H. tartakovskyi (hSISKIN1); (7) H. pallidus (hPFC1) × H. lanii (hRB1); (8) H. tartakovskyi (hHAWF1) × H. parabelopolskyi (hSYBOR1). We report 4 patterns of between-lineage interactions that seem to be common and might prevent mixing lineages during simultaneous sexual process in wildlife: (1) the blockage of ookinete development of both parasites; (2) the development of ookinetes of 1 parasite and blockage of ookinete development of the other; (3) selective within-lineage mating resulting in ookinete development of both parent species and absence of hybrid organisms; (4) absence of selective within-lineage mating resulting in presence of ookinetes of both parents and also development of hybrid organisms with unclear potential for further sporogony. The present study indicates directions for collection of source material in the investigation of mechanisms of reproductive isolation leading to speciation in these parasites. The next steps in these studies should be the development of nuclear markers for distinguishing hemosporidian hybrid organisms and the experimental observation of further development of hybrid ookinetes in vectors.

Group size and nest spacing affect Buggy Creek virus (Togaviridae: Alphavirus) infection in nestling house sparrows

The transmission of parasites and pathogens among vertebrates often depends on host population size, host species diversity, and the extent of crowding among potential hosts, but little is known about how these variables apply to most vector-borne pathogens such as the arboviruses (arthropod-borne viruses). Buggy Creek virus (BCRV; Togaviridae: Alphavirus) is an RNA arbovirus transmitted by the swallow bug (Oeciacus vicarius) to the cliff swallow (Petrochelidon pyrrhonota) and the introduced house sparrow (Passer domesticus) that has recently invaded swallow nesting colonies. The virus has little impact on cliff swallows, but house sparrows are seriously affected by BCRV. For house sparrows occupying swallow nesting colonies in western Nebraska, USA, the prevalence of BCRV in nestling sparrows increased with sparrow colony size at a site but decreased with the number of cliff swallows present. If one nestling in a nest was infected with the virus, there was a greater likelihood that one or more of its nest-mates would also be infected than nestlings chosen at random. The closer a nest was to another nest containing infected nestlings, the greater the likelihood that some of the nestlings in the focal nest would be BCRV-positive. These results illustrate that BCRV represents a cost of coloniality for a vertebrate host (the house sparrow), perhaps the first such demonstration for an arbovirus, and that virus infection is spatially clustered within nests and within colonies. The decreased incidence of BCRV in sparrows as cliff swallows at a site increased reflects the "dilution effect," in which virus transmission is reduced when a vector switches to feeding on a less competent vertebrate host.

Blood feeding position increases success of recalcitrant mosquitoes

Aedes aegypti and Aedes albopictus are competent natural and laboratory vectors for numerous arthropod-borne viruses (arboviruses), many of which pose global public health concerns. Efficiently imbibing a blood meal from an artificial membrane feeder, Ae. aegypti is an easy feeder: ∼ 96% success. Alternatively, Ae. albopictus is known to be a difficult feeder imbibing poorly: ∼ 20% success. Adult female mosquitoes were grouped in cohorts of 50, proffered a bovine blood meal, and challenged with experimental variables, and feeding success was documented. Controls included Ae. aegypti and the artificial glass membrane feeder: topside presentation (upside-down feeding position only). Variables included lambskin versus bovine collagen sausage membranes, presence or absence of gentle motion, filial generations, and large or small blood packets positioned differently: horizontal presentation (right side-up or nose-up feeding position) and vertical presentation (nose-up feeding position only). Both species preferred sausage casings, and ultrastructural analysis revealed that sausage casings had a textured gripping surface not observed on lambskin membranes. Neither filial generations nor gentle motion improved feeding; however, a 32%-46% increase in blood feeding was observed when Ae. albopictus fed on large horizontal and large or small vertical blood packets. Upside-down feeding of Ae. albopictus with a blood suspension of Sindbis virus heat resistant (SVHR) and the original isolate (AR339) resulted in virus dissemination of 10% and 50%, respectively. Use of bovine collagen sausage membranes in a vertical feeding position will increase the number of engorged females, thereby substantially increasing the number of arbovirus-exposed organisms in the laboratory. Differences in blooding success in response to feeding position further separates the behavior attributes of two Aedine species. Blood meal presentation facilitates gravity and we suggest this is a deciding factor in the feeding success of Ae. albopictus.

Developing GIS-based eastern equine encephalitis vector-host models in Tuskegee, Alabama

BACKGROUND

A site near Tuskegee, Alabama was examined for vector-host activities of eastern equine encephalomyelitis virus (EEEV). Land cover maps of the study site were created in ArcInfo 9.2 from QuickBird data encompassing visible and near-infrared (NIR) band information (0.45 to 0.72 microm) acquired July 15, 2008. Georeferenced mosquito and bird sampling sites, and their associated land cover attributes from the study site, were overlaid onto the satellite data. SAS 9.1.4 was used to explore univariate statistics and to generate regression models using the field and remote-sampled mosquito and bird data. Regression models indicated that Culex erracticus and Northern Cardinals were the most abundant mosquito and bird species, respectively. Spatial linear prediction models were then generated in Geostatistical Analyst Extension of ArcGIS 9.2. Additionally, a model of the study site was generated, based on a Digital Elevation Model (DEM), using ArcScene extension of ArcGIS 9.2.

RESULTS

For total mosquito count data, a first-order trend ordinary kriging process was fitted to the semivariogram at a partial sill of 5.041 km, nugget of 6.325 km, lag size of 7.076 km, and range of 31.43 km, using 12 lags. For total adult Cx. erracticus count, a first-order trend ordinary kriging process was fitted to the semivariogram at a partial sill of 5.764 km, nugget of 6.114 km, lag size of 7.472 km, and range of 32.62 km, using 12 lags. For the total bird count data, a first-order trend ordinary kriging process was fitted to the semivariogram at a partial sill of 4.998 km, nugget of 5.413 km, lag size of 7.549 km and range of 35.27 km, using 12 lags. For the Northern Cardinal count data, a first-order trend ordinary kriging process was fitted to the semivariogram at a partial sill of 6.387 km, nugget of 5.935 km, lag size of 8.549 km and a range of 41.38 km, using 12 lags. Results of the DEM analyses indicated a statistically significant inverse linear relationship between total sampled mosquito data and elevation (R2 = -.4262; p < .0001), with a standard deviation (SD) of 10.46, and total sampled bird data and elevation (R2 = -.5111; p < .0001), with a SD of 22.97. DEM statistics also indicated a significant inverse linear relationship between total sampled Cx. erracticus data and elevation (R2 = -.4711; p < .0001), with a SD of 11.16, and the total sampled Northern Cardinal data and elevation (R2 = -.5831; p < .0001), SD of 11.42.

CONCLUSION

These data demonstrate that GIS/remote sensing models and spatial statistics can capture space-varying functional relationships between field-sampled mosquito and bird parameters for determining risk for EEEV transmission.

Avian host-selection by Culex pipiens in experimental trials

Evidence from field studies suggests that Culex pipiens, the primary mosquito vector of West Nile virus (WNV) in the northeastern and north central United States, feeds preferentially on American robins (Turdus migratorius). To determine the contribution of innate preferences to observed preference patterns in the field, we conducted host preference trials with a known number of adult female C. pipiens in outdoor cages comparing the relative attractiveness of American robins with two common sympatric bird species, European starling, Sternus vulgaris and house sparrow, Passer domesticus. Host seeking C. pipiens were three times more likely to enter robin-baited traps when with the alternate host was a European starling (n = 4 trials; OR = 3.06; CI [1.42–6.46]) and almost twice more likely when the alternative was a house sparrow (n = 8 trials; OR = 1.80; CI = [1.22–2.90]). There was no difference in the probability of trap entry when two robins were offered (n = 8 trials). Logistic regression analysis determined that the age, sex and weight of the birds, the date of the trial, starting-time, temperature, humidity, wind-speed and age of the mosquitoes had no effect on the probability of a choosing a robin over an alternate bird. Findings indicate that preferential feeding by C. pipiens mosquitoes on certain avian hosts is likely to be inherent, and we discuss the implications innate host preferences may have on enzootic WNV transmission.

Mosquito landing rates on nesting American robins (Turdus migratorius)

We measured mosquito landing rates on adult and nestling American robins at nests with infrared cameras in Washington, D.C., and Maryland, United States. Mosquitoes landed on nesting robins almost exclusively between dusk and dawn. The mean number of mosquito landings per night was higher for adults (123.3 +/- SE 32.8) than nestlings (37.26 +/- 14.8). The fraction of mosquitoes landing at a nest on nestlings increased with decreases in adult brooding. Oral swabs from nestlings at these and 13 other robin, Gray catbird, and house finch nests were negative for West Nile virus (WNV). These results show that landing rates were higher on adults and that parental brooding reduces the landing rates of mosquitoes on nestlings.

Use and husbandry of captive European starlings (Sturnus vulgaris) in scientific research: a review of current practice

Summary

We reviewed the use of captive European starlings ( Sturnus vulgaris) in scientific research published between 2000 and 2004. We estimated the numbers of birds used and documented their origin and the range of husbandry regimes employed with the aim of comparing current practice with the new European guidelines for husbandry of laboratory animals. Over the five-year period, 106 primary articles report the use of an estimated total of 2490 captive starlings. The majority of birds were caught from the wild either as adults or fledglings, and only 3% were hand-reared from chicks. There was considerable variation in husbandry. In the majority of cases, standards fell below those currently recommended as best practice in the UK and cited in new European guidelines. The median volume of home cages employed was 0.42 m3 (0.13–5.1 m3, interquartile range), whereas current recommendations suggest a minimum of 1.0 m3 for a singly-housed bird. The median volume of space allowed per bird was 0.13 m3/bird (0.08–1.05 m3/bird, Q1–Q3), whereas current recommendations suggest a minimum of 0.33 m3/bird. Only 27% of the articles mentioned providing any form of environmental enrichment for birds in their home cages. We recommend that more research be conducted into the welfare of starlings to inform legislation and guidelines, and thus maximize the welfare of captive animals.

Does reservoir host mortality enhance transmission of West Nile virus?

Background

Since its 1999 emergence in New York City, West Nile virus (WNV) has become the most important and widespread cause of mosquito-transmitted disease in North America. Its sweeping spread from the Atlantic to the Pacific coast was accompanied by widespread mortality among wild birds, especially corvids. Only sporadic avian mortality had previously been associated with this infection in the Old World. Here, we examine the possibility that reservoir host mortality may intensify transmission, both by concentrating vector mosquitoes on remaining hosts and by preventing the accumulation of "herd immunity".

Results

Inspection of the Ross-Macdonald expression of the basic reproductive number (R₀) suggests that this quantity may increase with reservoir host mortality. Computer simulation confirms this finding and indicates that the level of virulence is positively associated with the numbers of infectious mosquitoes by the end of the epizootic. The presence of reservoir incompetent hosts in even moderate numbers largely eliminated the transmission-enhancing effect of host mortality. Local host die-off may prevent mosquitoes to "waste" infectious blood meals on immune host and may thus facilitate perpetuation and spread of transmission.

Conclusion

Under certain conditions, host mortality may enhance transmission of WNV and similarly maintained arboviruses and thus facilitate their emergence and spread. The validity of the assumptions upon which this argument is built need to be empirically examined.

A dynamic transmission model of eastern equine encephalitis virus

Eastern equine encephalitis virus (EEEV) is one of several arthropod-borne viruses (arboviruses) endemic to the United States. Interactions between arthropod (mosquito) vectors and avian amplification host populations play a significant role in the dynamics of arboviral transmission. Recent data have suggested the hypothesis that an increased rate of successful feeding on young-of-the-year (YOY) birds might play a role in the dynamics of EEEV transmission. To test this hypothesis, we developed a model to explore the effect of the interactions of the vectors and avian host populations on EEEV transmission. Sensitivity analyses conducted using this model revealed eleven parameters that were capable of disproportionately affecting the predicted level of EEEV infection in the vertebrate reservoir and vector populations. Of these, four parameters were related to the interaction of the vector with young-of-the-year birds. Furthermore, adult birds could not substitute for young-of-the-year in initiating and maintaining a predicted enzootic outbreak of EEEV. Taken together, the model predicted that young-of-the-year birds play a key role in establishing and maintaining enzootic outbreaks of EEEV.

Efficiency of rubidium marking in Aedes albopictus (Diptera: Culicidae): preliminary evaluation on persistence of egg labeling, survival, and fecundity of marked female

Rubidium chloride (RbCl) has been used for the study of vector biology and behavior, although the efficacy of marking, egg production, and survivorship of marked females have been poorly studied. Four concentrations of RbCl were tested, among which 0.025 M was the best for marking Aedes albopictus: more than 80% of egg batches of females fed once with blood containing RbCl were marked; Rb-marked egg batches, interspersed with non marked ones were recovered until 61 days after a blood meal containing RbCl followed by non marked meals; RbCl was essentially detected in the abdomen of marked females, whose egg production and survivorship did not differ from non marked ones, at least in the three weeks following the Rb-marked blood meal.