Mosquito Species Composition at a Zoological Park in South Carolina,USA,August–December 2023

Introduction

Zoological parks are vital societal resources that provide conservation education, cultural value, and economic benefits. Beyond this, zoos offer unique opportunities for scientific research. In the context of infectious disease, they house both native and exotic animal species and employ specialized care teams that often triage injured wildlife. Animals in zoos can act as disease sentinels for humans, wildlife, and domestic animals during outbreaks, such as the West Nile virus outbreak at the Bronx Zoo in New York in 1999 (Robinette et al., 2017). Despite this, public zoos are rarely integrated into infectious disease surveillance networks. Limited collaboration between academic programs, wildlife centers, and zoological facilities represents a missed opportunity to explore the intersection of endemic vectors, pathogens, and nonnative animal species.

Columbia is the state capital of South Carolina with a humid, subtropical climate favorable to multiple vectors of human and animal pathogens (CDC, 2025). Riverbanks Zoo & Garden spans 170 acres along the Saluda River in the downtown metroplex and welcomes approximately one million visitors annually (Riverbanks, 2025). Despite the diverse range of exotic and native animals and significant visitor attendance, no targeted mosquito surveillance efforts at the zoo are ongoing, and previous reports at the Riverbanks Zoo & Garden were conducted >10 years prior (Nelder et al., 2009; Tuten et al., 2012). To address this gap, this study established baseline surveillance to identify mosquitoes of medical or veterinary relevance and report pathogen infection rates.

Materials and Methods

Eight CDC light traps (model number 512, John W Hock Co., Gainesville, FL) baited with 0.9 kg of dry ice in a perforated cooler were hung overnight on fence lines 1.5 meters off the ground and 36.5 meters apart 1 night per week between August 15 and December 1, 2023. Traps were set adjacent to enclosures that included exotic wildlife, native animals, and human-only areas (Supplementary Fig. S1). No pest control methods were performed within a .25-mile radius of traps. Trap location was determined in collaboration with zoo staff to collect in the areas they perceived as highest risk of concern for mosquitos. Temperature (average, minimum, and maximum) and rainfall (cumulative precipitation) data were collected from the National Weather Service’s NOAA Online Weather Data (NOWData). After collections, all collected mosquitos were immediately stored at −80°C before morphological identification to species using a standard dichotomous key (Darsie, 1981). Pathogen testing was performed on three species: Culex quinquefasciatus, Culex tarsalis, and Culex territans. Maintaining the cold chain using a chill table, mosquitoes were pooled by species in pool sizes up to five mosquitoes per pool. Pools were tested for West Nile virus using the RAMP^® WNV assay and reader instrument (Azelis, Shreveport, LA). The RAMP^® WNV assay was selected to be in parallel with local vector control agency methods so data could be shared with this public health agency.

Results

A total of 597 mosquitoes representing 17 distinct species were collected during the 4-month period—approximately 40 mosquitoes per trap night (Table 1). Culex spp. were the most collected (70.7%), with about half of this genus identified as Culex coronator. Several medically relevant species were collected, including Aedes vexans (18%), Aedes albopictus (2.2%), Psorophora ferox (1.8%), Anopheles punctipennis (1.5%), Aedes triseriatus (1.0%), Culex quinquefasciatus (0.8%), and Culex tarsalis (0.5%). Most mosquitoes originated from two traps (65.7%), with 127 mosquitoes collected from trap #6 and 262 mosquitoes collected from trap #8. These traps were located adjacent to exotic animal enclosures; trap #6 was between the zebra and ostrich enclosures, and trap #8 was adjacent to the giraffe enclosure.

OPEN IN VIEWER

Table 1.

Mosquito Species Collected by Trap Number, August–December 2023

		Trap number
	N (%)	#1	#2	#3	#4	#5	#6	#7	#8
Genus and species	597	N = 7	N = 82	N = 28	N = 13	N = 39	N = 127	N = 39	N = 262
Aedes	132 (22.1)	1 (20.0)	21 (25.6)	7 (25.0)	2 (15.4)	15 (38.5)	25 (19.7)	14 (5.9)	47 (17.9)
albopictus	13 (2.2)	—	4	—	—	—	3	—	6
atlanticus	1 (0.2)	—	—	—	—	—	—	—	1
canadensis	1 (0.2)	—	—	—	—	—	—	—	1
triseriatus	6 (1.0)	—	—	1	—	—	3	—	3
vexans	109 (18.3)	1	17	6	2	13	19	14	37
species unknown	2 (0.3)	—	—	—	—	2	—	—	—
Anopheles	11 (1.8)	0	3 (5.5)	1 (3.6)	0	1 (2.6)	2 (1.6)	1 (2.6)	3 (1.1)
quadrimaculatus	1 (0.2)	—	1	—	—	—	—	—	—
perplexens	1 (0.2)	—	—	—	—	—	1	—	—
punctipennis	9 (1.5)	—	2	1	—	1	1	1	3
Culex	422 (70.7)	5 (71.4)	55 (67.1)	19 (67.9)	11 (84.6)	23 (59.0)	96 (75.6)	22 (56.4)	191 (72.9)
coronator	341 (57.1)	3	36	17	7	14	86	21	157
erraticus	19 (3.2)	—	10	1	1	2	1	1	3
nigripalpus	11 (1.8)	2	2	—	—	—	3	—	4
pipiens/quinquefasciatus	5 (0.8)	—	2	—	—	2	—	—	1
salinarius	2 (0.3)	—	1	—	—	—	1	—	—
tarsalis	3 (0.5)	—	1		1	1	—	—	—
territans	1 (0.2)	—	—	—	—	—	—	—	1
species unknown	40 (6.7)	—	3	1	2	4	5	—	25
Ochlerotatus hendersoni	1 (0.2)	0	1 (1.2)	0	0	0	0	0	0
Psorophora	16 (2.7)	1 (20.0)	2 (2.4)	1 (3.6)	0	0	3 (2.4)	1 (2.6)	8 (3.1)
ferox	11 (1.8)	1	1	1	—	—	3	—	5
species unknown	5 (0.8)	—	1	—	—	—	—	1	3
Unknown (genus)	15 (2.5)	0	0	0	0	0	1 (0.8)	1 (2.6)	13 (5.0)

Mosquito collections peaked in abundance in mid-September (Supplementary Fig. S2), with higher abundance following heavy precipitation and temperatures in the 24–26°C range. A total of nine mosquitoes were tested for WNV by species: five Culex quinquefasciatus, three Culex tarsalis, and one Culex territans. The first cassette, pooled with Culex quinquefasciatus species, obtained a low signal reading determined as equivocal. All additional cassettes, containing Culex tarsalis and Culex territans, yielded negative WNV test results.

Discussion

This low-cost pilot study was conducted at South Carolina’s largest zoo and helped us define contemporary mosquito-borne disease risk in a region endemic for West Nile virus, St. Louis encephalitis virus, and Eastern equine encephalitis virus. A large diversity of mosquito species was collected, including 15 medically relevant mosquito species. The most productive traps were adjacent to the zebra and giraffe enclosures, highlighting potential ongoing contact between native animals, arthropods, and exotic animals, likely due to varying enclosure habitats.

An unusually diverse amount of mosquito vectors was collected in this surveillance effort, perhaps as a reflection of the varied habitats and potential hosts. Culex coronator and Aedes vexans were two frequently collected species of mosquitoes known for their potential role in the transmission of neurotropic viruses, including St. Louis encephalitis virus and West Nile virus. They can also transmit transplacental viruses, such as Zika virus, or parasites that cause endocarditis, such as Dirofilaria immitis. However, their role as alternative vectors in the transmission cycle of these pathogens is still unclear, and unfortunately, testing them was outside the project’s scope. Collectively, these aspects warrant further research, particularly for exotic animal species (Gendernalik et al., 2017; Turell et al., 2005). Three medically relevant West Nile virus vector species were collected, but all tested negative. The low overall vector count, combined with a traditionally low rate of infected mosquitoes in circulation annually (Vincent et al., 2020), could explain the lack of arboviral-positive mosquitoes from the zoo. The most collected mosquito, Culex coronator, has been found and reported infected with WNV and SLEV; however, this mosquito is not considered a primary vector for human infection. Expanded research to test insecticide resistance and additional mosquito-borne pathogens would add another critical layer to understanding the unique disease transmission dynamics found in zoo environments.

A few limitations in this study are worth noting. This preliminary study did not include the full peak of mosquito activity in central South Carolina. This academic public collaboration temporally correlated to the fall semester, and future studies should be performed throughout the 12-month calendar year. We were unable to incorporate gravid traps due to the scope of the project; however, given that we found Culex mosquitoes future, studies should employ gravid traps, which are better tailored to this genus. Similarly, we were unable to test Culex coronator or Aedes vexans, two potential bridge or alternative arboviral species, and future studies would ideally encompass all potential mosquito vectors, not just the primary species. Lastly, future studies should incorporate blood meal analysis to verify potential ecological interactions in zoo settings where you have both native and nonnative mammalian species.

Conclusions

In closing, this pilot study highlights zoological parks as overlooked yet valuable sites for research at the human–animal interface, aligning with a One Health approach to vector-borne and zoonotic disease detection and prevention. Zoos represent a unique setting for such efforts: they provide seminatural environments that support both animal health research and public health preparedness. The absence of arboviral detection should not be viewed as a limitation; rather, it adds essential data for constructing a comprehensive assessment of vector-borne disease risk, especially in settings with substantial human–animal interaction. Continued, interdisciplinary partnership with consistent surveillance in these and similar environments is critical to generating timely, actionable data to better monitor and address emerging threats to human and animal health.

Authors’ Contributions

K.B.: Conceptualization, data collection, writing—original draft, writing—review and editing. E.O.P.: Conceptualization, data collection, writing—review and editing. S.S.: Data collection, writing—review and editing. L.G.-G.: Writing—review and editing. K.D.-B.: Writing—review and editing. M.W.: Conceptualization, writing—review and editing. M.S.N.: Funding acquisition, supervision, conceptualization, writing—review and editing.