Invasive apex predators have profound impacts on natural communities, yet the consequences of these impacts on the transmission of zoonotic pathogens are unexplored. Collapse of large- and medium-sized mammal populations in the Florida Everglades has been linked to the invasive Burmese python, Kuhl. We used historic and current data to investigate potential impacts of these community effects on contact between the reservoir hosts (certain rodents) and vectors of Everglades virus, a zoonotic mosquito-borne pathogen that circulates in southern Florida. The percentage of blood meals taken from the primary reservoir host, the hispid cotton rat, Say and Ord, increased dramatically (422.2%) from 1979 (14.7%) to 2016 (76.8%), while blood meals from deer, raccoons and opossums decreased by 98.2%, reflecting precipitous declines in relative abundance of these larger mammals, attributed to python predation. Overall species diversity of hosts detected in blood meals from the Everglades declined by 40.2% over the same period ((1979) = 1.68, (2016) = 1.01). Predictions based upon the dilution effect theory suggest that increased relative feedings upon reservoir hosts translate into increased abundance of infectious vectors, and a corresponding upsurge of Everglades virus occurrence and risk of human exposure, although this was not tested in the current study. This work constitutes the first indication that an invasive predator can increase contact between vectors and reservoirs of a human pathogen and highlights unrecognized indirect impacts of invasive predators.

Background Epizootic hemorrhagic disease virus (EHDV) is an Orbivirus of veterinary importance which is transmitted by biting midges of the genus Culicoides (Diptera: Ceratopogonidae) to ruminants. Culicoides sonorensis Wirth & Jones, the only confirmed vector of EHDV in the USA, is rare in the southeastern states where transmission persists, suggesting that other Culicoides species transmit EHDV in this region. The present study aimed to determine which Culicoides species transmitted EHDV in Florida and Alabama, two states in the southeastern USA. Viral RNA was detected in field-collected midges using molecular methods. These data are presented alongside data on Culicoides blood meal analysis, white-tailed deer ( Odocoileus virginianus ) aspiration, and seasonality to demonstrate an interaction between potential vector species and EHDV hosts. Results Out of 661 pools tested, 20 pools were positive for EHDV viral RNA, including six pools from Culicoides stellifer (Coquillett) and 14 pools from Culicoides venustus Hoffman. The overall infection rate was 0.06% for C. stellifer and 2.18% for C. venustus . No positive pools were identified for a further 17 species. Serotypes identified in Culicoides included EHDV-2, EHDV-6, and coinfections of EHDV-2 and EHDV-6 and were identified in similar proportions to serotypes in deer at 3 of 4 deer farms. Viral detections conducted in Alabama also identified one positive pool of C. venustus . Blood meal analysis revealed that both Culicoides species fed on white-tailed deer (verified through aspiration), fallow deer, and elk, species for which EHDV viremia has been documented. Seasonality data indicated that both species were present throughout the period in which viral transmission occurred to EHDV hosts in 2016 in addition to the 2017 epizootic. Conclusions Our finding of EHDV positive pools of field-collected C. stellifer and C. venustus and an interaction between these species and EHDV hosts satisfy two of the four criteria for vector incrimination as set by the World Health Organization. Determining the vectors of EHDV is an important step towards developing sound strategies for the control of vector Culicoides and management of EHDV in the southeastern USA.

Everglades virus (EVEV), subtype II within the Venezuelan equine encephalitis (VEE) virus complex, is a mosquitoborne zoonotic pathogen endemic to south Florida, USA. EVEV infection in humans is considered rare, probably because of the sylvatic nature of the vector, the Culex ( Melanoconion ) cedecei mosquito. The introduction of Cx. panocossa , a tropical vector mosquito of VEE virus subtypes that inhabits urban areas, may increase human EVEV exposure. Field studies investigating spatial and temporal patterns of abundance, host use, and EVEV infection of Cx. cedecei mosquitoes in Everglades National Park found that vector abundance was dynamic across season and region. Rodents, particularly Sigmodon hispidus rats , were primary vertebrate hosts, constituting 77%–100% of Cx. cedecei blood meals. Humans were fed upon at several locations. We detected EVEV infection in Cx. cedecei mosquitoes in lower and upper regions of Everglades National Park only during the wet season, despite an abundance of Cx. cedecei mosquitoes at other sampling times.

BackgroundUnderstanding mechanisms that contribute to viral dissemination in mosquito vectors will contribute to our ability to interfere with the transmission of viral pathogens that impact public health. The expression of genes in two Culex pipiens quinquefasciatus populations from Florida with known differences in vector competence to West Nile virus (WNV) were compared using high throughput sequencing.ResultsA total of 15,176 transcripts were combined for comparison of expression differences between the two populations and 118 transcripts were differentially expressed (p < 0.05). The fold change in expression of the differentially expressed genes ranged from -7.5 – 6.13. The more competent population for WNV (Gainesville) over expressed 77 genes and down regulated 44 genes, compared with the less competent population for WNV (Vero Beach). Also, splicing analysis identified 3 transcripts with significantly different splice forms between the two populations. The functional analysis showed that the largest proportion of transcripts was included in the catalytic activity and transporter activity groups except for those in the unknown group. Interestingly, the up- regulated gene set contained most of the catalytic activity function and the down- regulated gene set had a notable proportion of transcripts with transporter activity function. Immune response category was shown in only the down regulated gene set, although those represent a relatively small portion of the function. Several different vitellogenin genes were expressed differentially. Based on the RNAseq data analysis, ovary development was compared across the populations and following WNV infection. There were significant differences among the compared groups.ConclusionsThis study suggests that ovary development is correlated to vector competence in two Culex populations in Florida. Both populations control energy allocations to reproduction as a response to WNV. This result provides novel insight into the defense mechanism used by Culex spp. mosquitoes against WNV.

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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, CO-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. CO-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.

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.