Modifying the Biogents Sentinel Trap to Increase the Longevity of Captured Aedes aegypti

A modified BG-Sentinel trap equipped with FTA card as a novel tool for mosquito-borne disease surveillance: a field test for flavivirus detection

Early detection of pathogens in vectors is important in preventing the spread of arboviral diseases, providing a timely indicator of pathogen circulation before outbreaks occur. However, entomological surveillance may face logistical constraints, such as maintaining the cold chain, and resource limitations, such as the field and laboratory workload of mosquito processing. We propose an FTA card-based trapping system that aims to simplify both field and laboratory phases of arbovirus surveillance. We modified a BG-Sentinel trap to include a mosquito collection chamber and a sugar feeding source through an FTA card soaked in a long-lasting viscous solution of honey and hydroxy-cellulose hydrogel. The FTA card ensures environmental preservation of nucleic acids, allowing continuous collection and feeding activity of specimens for several days and reducing the effort required for viral detection. We tested the trap prototype during two field seasons (2019 and 2021) in North-eastern Italy and compared it to CDC-CO2 trapping applied in West Nile and Usutu virus regional surveillance. Collections by the BG-FTA approach detected high species diversity, including Culex pipiens, Aedes albopictus, Culex modestus, Anopheles maculipennis sensu lato and Ochlerotatus caspius. When used for two-days sampling, the BG-FTA trap performed equally to CDC also for the WNV-major vector Cx. pipiens. The FTA cards detected both WNV and USUV, confirming the reliability of this novel approach to detect viral circulation in infectious mosquitoes. We recommend this surveillance approach as a particularly useful alternative in multi-target surveillance, for sampling in remote areas and in contexts characterized by high mosquito densities and diversity.

Analysis of trapped mosquito excreta as a noninvasive method to reveal biodiversity and arbovirus circulation

Emerging and endemic mosquito-borne viruses can be difficult to detect and monitor because they often cause asymptomatic infections in human or vertebrate animals or cause nonspecific febrile illness with a short recovery waiting period. Some of these pathogens circulate into complex cryptic cycles involving several animal species as reservoir or amplifying hosts. Detection of cases in vertebrate hosts can be complemented by entomological surveillance, but this method is not adapted to low infection rates in mosquito populations that typically occur in low or nonendemic areas. We identified West Nile virus circulation in Camargue, a wetland area in South of France, using a cost-effective xenomonitoring method based on the molecular detection of virus in excreta from trapped mosquitoes. We also succeeded at identifying the mosquito species community on several sampling sites, together with the vertebrate hosts on which they fed prior to being captured using amplicon-based metabarcoding on mosquito excreta without processing any mosquitoes. Mosquito excreta-based virus surveillance can complement standard surveillance methods because it is cost-effective and does not require personnel with a strong background in entomology. This strategy can also be used to noninvasively explore the ecological network underlying arbovirus circulation.

Attraction Versus Capture: Efficiency of BG-Sentinel Trap Under Semi-Field Conditions and Characterizing Response Behaviors for Female Aedes aegypti (Diptera: Culicidae)

Aedes aegypti (L.) is an important vector of viruses causing dengue, Zika, chikungunya, and yellow fever and as such is a threat to public health worldwide. Effective trapping methods are essential for surveillance of both the mosquito species and disease presence. The BG-Sentinel (BGS) is a widely used to trap Ae. aegypti but little is known of its efficiency, i.e., what proportion of the mosquitoes encountering the trap are captured. The first version of the BGS trap was predominantly white, and the current version is mostly navy blue. While this trap is often deployed without any olfactory lure, it can also be deployed with CO2 and/or a human skin odor mimic lure to increase capture rates. We tested the efficiency of capturing Ae. aegypti under semi-field conditions for the original white version without lures as well the blue version with and without various lure combinations. None of the configurations tested here captured 100% of the mosquitoes that encountered the trap. A navy-blue trap emitting CO2 and a skin odor mimic produced the highest capture (14% of the total insects in the semi-field cage), but its capture efficiency was just 5% (of mosquitoes encountering the trap). Mosquitoes often had multiple encounters with a trap that did not result in capture; they crossed over the trap entrance without being captured or landed on the sides of the trap. Understanding these behaviors and the factors that induce them has the potential to suggest improvement in trap design and therefore capture efficiency.

A LAMP-based colorimetric assay to expedite field surveillance of the invasive mosquito species Aedes aegypti and Aedes albopictus

BACKGROUND

Yellow fever, dengue, chikungunya and Zika viruses are responsible for considerable morbidity and mortality in humans. Aedes aegypti and Aedes albopictus are the most important mosquito vectors involved in their transmission. Accurate identification of these species is essential for the implementation of control programs to limit arbovirus transmission, during suspected detections at ports of first entry, to delimit incursions or during presence/absence surveillance programs in regions vulnerable to invasion. We developed and evaluated simple and rapid colorimetric isothermal tests to detect these two mosquito species based on loop-mediated isothermal amplification (LAMP) targeting the ribosomal RNA internal transcribed spacer 1 (ITS1).

METHODOLOGY/PRINCIPAL FINDINGS

Samples were prepared by homogenizing and heating at 99 oC for 10 min before an aliquot was added to the LAMP reaction. After 40 min incubation at 65 oC, a colour change indicated a positive result. The tests were 100% sensitive and species-specific, and demonstrated a limit of detection comparable with PCR-based detection (TaqMan chemistry). The LAMP assays were able to detect target species for various life stages tested (adult, 1st instar larva, 4th instar larva and pupa), and body components, such as legs, wings and pupal exuviae. Importantly, the LAMP assays could detect Ae. aegypti DNA in mosquitoes stored in Biogents Sentinel traps deployed in the field for 14 d. A single 1st instar Ae. aegypti larva could also be detected in a pool of 1,000 non-target 1st instar Aedes notoscriptus, thus expediting processing of ovitrap collections obtained during presence/absence surveys. A simple syringe-sponge protocol facilitated the concentration and collection of larvae from the ovitrap water post-hatch.

CONCLUSIONS/SIGNIFICANCE

We describe the development of LAMP assays for species identification and demonstrate their direct application for surveillance in different field contexts. The LAMP assays described herein are useful adjuncts to laboratory diagnostic testing or could be employed as standalone tests. Their speed, ease-of-use, low cost and need for minimal equipment and training make the LAMP assays ideal for adoption in low-resource settings without the need to access diagnostic laboratory services.

Temperature is a common climatic descriptor of lachryphagous activity period in Phortica variegata (Diptera: Drosophilidae) from multiple geographical locations

Background

The drosophilid Phortica variegata is known as vector of Thelazia callipaeda, the oriental eyeworm native to Asia that has become an emergent zoonotic agent in several European regions. Unlike almost all other arthropod vectors of pathogens, only P. variegata males feed of lachrymal secretions of animals, ingesting first-stage larvae (L1) of the worm living in the orbital cavities of the host, and allowing with the same behaviour the introduction of infective L3. Despite the increased detection of T. callipaeda in many European countries, information about the length of the lachryphagous activity period of P. variegata and a deep knowledge of the environmental and climatic variables involved are still limited.

Methods

We herein present the results of a multicentre study involving five sites from four different countries (Italy, Spain, UK and USA) where canine thelaziosis is endemic and/or where it has already been ascertained the presence of P. variegata. Field data have been obtained on a fortnightly basis from mid-April to the end of November 2018 from a contemporary standardized sampling (same sampling effort and time of collection in all sites) of lachryphagous flies collected around the eyes of a human bait using an entomological net. These data have been associated to data collection of local climatic variables (day length, temperature, wind speed, barometric pressure and relative humidity).

Results

Overall, a total of 4862 P. variegata flies (4637 males and 224 females) were collected, with high differences in densities among the different sampling sites. Significant positive correlations were found between P. variegata male density and temperature and wind speed, while negative correlations were observed for barometric pressure and relative humidity. However, the above significant differences are confirmed in each sampling site separately only for the temperature.

Conclusions

This multicentre study highlights that temperature is the major common environmental driver in describing the lachryphagous activity of P. variegata in Europe and USA and, therefore, the transmission risk of thelaziosis.