A systematic review of published literature on mosquito control action thresholds across the world.

BACKGROUND: Despite the use of numerous methods of control measures, mosquito populations and mosquito-borne diseases are still increasing globally. Evidence-based action thresholds to initiate or intensify control activities have been identified as essential in reducing mosquito populations to required levels at the correct/optimal time. This systematic review was conducted to identify different mosquito control action thresholds existing across the world and associated surveillance and implementation characteristics. METHODOLOGY/PRINCIPAL FINDINGS: Searches for literature published from 2010 up to 2021 were performed using two search engines, Google Scholar and PubMed Central, according to PRISMA guidelines. A set of inclusion/exclusion criteria were identified and of the 1,485 initial selections, only 87 were included in the final review. Thirty inclusions reported originally generated thresholds. Thirteen inclusions were with statistical models that seemed intended to be continuously utilized to test the exceedance of thresholds in a specific region. There was another set of 44 inclusions that solely mentioned previously generated thresholds. The inclusions with "epidemiological thresholds" outnumbered those with "entomological thresholds". Most of the inclusions came from Asia and those thresholds were targeted toward Aedes and dengue control. Overall, mosquito counts (adult and larval) and climatic variables (temperature and rainfall) were the most used parameters in thresholds. The associated surveillance and implementation characteristics of the identified thresholds are discussed here. CONCLUSIONS/SIGNIFICANCE: The review identified 87 publications with different mosquito control thresholds developed across the world and published during the last decade. Associated surveillance and implementation characteristics will help organize surveillance systems targeting the development and implementation of action thresholds, as well as direct awareness towards already existing thresholds for those with programs lacking available resources for comprehensive surveillance systems. The findings of the review highlight data gaps and areas of focus to fill in the action threshold compartment of the IVM toolbox.

Efficacy Evaluation of Medium-Chain Fatty Acids as Skin and Spatial Repellents Against Aedes aegypti (Diptera:Culicidae) Mosquitoes.

Fatty acids derived from natural oils are considered as perspective products for adoption as repellents. Fatty acids derived from coconut oil have shown promise as repellents. This study consisted of an olfactometer evaluation of new formulations containing medium-chain fatty acids for spatial repellency and an in laboratory arm-in cage study for contact repellency against Aedes aegypti L. mosquitoes. Six formulations each of capric acid and lauric acid were evaluated for spatial repellency. These formulations contained 0.28-10% of either capric acid or lauric acid as the active ingredients in a consumer friendly skin care formulation. Base formula without fatty acids was evaluated as control in spatial repellency evaluation. For the arm-in cage evaluations, six formulations of capric acid, one base formulation, and a 7% N,N-diethyl-m-toluamide (DEET) product were tested for contact repellency. For contact repellency, United States Department of Agriculture (USDA) standard repellent test cages were used to determine the complete protection time (CPT) of the different formulated repellents. Among all capric acid formulations tested, the concentration of 2.25% (wt) indicated the best level of spatial repellency, but not significantly different from other concentrations. None of the lauric acid concentrations showed any level of spatial repellency. In the arm-in-cage evaluations, the highest contact repellency resulted from 4.5% capric acid, which was significantly higher than 7% DEET and base formula.

Molecular Surveillance of West Nile Virus in Mosquitoes and Sentinel Chickens.

Arboviral surveillance is a critical step in any effective mosquito control program. Surveillance aids in the early detection of pathogen transmission as well as establishes a baseline of transmission activity. Two of the most practical forms of arboviral surveillance is through the use of testing mosquito pools for the presence of pathogen and screening sentinel chickens for pathogen exposure. This chapter describes the process for each of these methods for West Nile virus.

Status of Vector Control Capabilities and Capacities in Florida and Texas, and its Potential Public Health Consequences.

It has been reported that roughly 80% of vector control organizations throughout the southern USA lack critical capabilities to properly address potential vector populations and vector-borne diseases within their jurisdictions. This study further investigated current vector control capabilities and capacity within the states of Florida and Texas. It was reported that only 26% of jurisdictions in Florida and 14% in Texas reported that they were "fully capable." Both states are among the top 4 states relative to the number of human cases of mosquito-borne diseases, and both states have had local transmission of Zika virus. Respondents from Florida indicated that 88% of jurisdictions have vector control capabilities to some degree, with 65% of those reporting they had sufficient capabilities. Respondents from Texas indicated that 89% of jurisdictions have vector control capabilities to some degree, with 67% of those reporting they had sufficient capabilities. As the prioritization of resource commitment for vector control capabilities varies throughout the USA, it is imperative that each state evaluates their specific needs and current capabilities and capacity to best ensure the public health needs of their constituents.

Laboratory Evaluation of Bigshot Maxim Against Three Species of Larval and Adult Mosquitoes, Aedes aegypti, Culex quinquefasciatus, and Anopheles quadrimaculatus.

The use of synthetic insecticides has been the main approach in mosquito control programs (MCPs) to prevent or reduce mosquito populations. The global problem of insecticide resistance and the concern of environmental impacts of synthetic insecticides have resulted in the interest of botanicals as an alternative. In this study, the botanical product BigShot Maxim, which contains cedarwood oil (14%), thyme oil (0.53%), and cinnamon oil (0.23%) as active ingredients, was examined in adulticide and larvicide bioassays against Aedes aegypti, Culex quinquefasciatus, and Anopheles quadrimaculatus. In the adulticide bioassay, 100% mortality was reached at a dilution of 1:10 after 4 h of exposure for all 3 species. In the larvicide bioassay, at the highest tested concentration (30 ppm by volume) the greatest mortality was 96.44 ± 1.44% SE for Ae. aegypti, 92.44 ± 2.07% SE for Cx. quinquefasciatus, and 33.33 ± 3.61% for An. quadrimaculatus, respectively. Insecticidal properties presented in all the experiments indicate that BigShot Maxim could be a viable alternative to some synthetic insecticides used in MCPs.

Initial Survey of Mosquito Control Programs with Set Action Thresholds and Associated Surveillance Characteristics.

The establishment of action thresholds is becoming critical in mosquito control management to implement effective proactive control measures using limited available resources. As a part of a large-scale study to identify different mosquito control action thresholds used in different geographical regions, we conducted an initial survey to identify mosquito control programs that claim to have set action thresholds and to investigate their associated program characteristics. We identified 68% (USA), 60% (mainland Australia), 78% (Asia), 35% (Africa), and 50% (US military units) of the responding programs, which perform mosquito control, have set mosquito control action thresholds. More than 50% of the programs that have not set mosquito control action thresholds already collect basic surveillance information as do the programs with thresholds. Further investigations with the selected mosquito control programs from this initial survey will help develop guidelines on establishing action thresholds by identifying different types of actual action thresholds used by programs in different geographical settings and other related information.

Prevalence of Neospora caninum Exposure in Wild Pigs (Sus scrofa) from Oklahoma with Implications of Testing Method on Detection.

Neospora caninum is a protozoan parasite, reported as a leading cause of cattle abortions and reproductive failure worldwide, costing the cattle industry approximately $1.3 billion annually. With wild pig (Sus scrofa) populations estimated at over six million in the United States, contact between wild pigs and livestock is inevitable, mainly because of the widespread geographic co-occurrence of the two species. As a known reservoir for numerous fungal, bacterial, viral and parasitic diseases, wild pigs are of particular importance for human and veterinary health relative to the prevention of infectious diseases. The seroprevalence of N. caninum in wild pig populations was previously documented in the United States, raising the question as to their exposure point of prevalence. This research screened 116 individual wild pigs for N. caninum using a variety of available assays. Using two different commercially available ELISA test kits, seroprevalence ranged from 12.5% to 67.8%. The Indirect Fluorescent Antibody Test resulted in our highest percent seroprevalence for these samples, at 84.1%. However, none of our samples showed any presence of N. caninum or associated pathologies via histological evaluation of representative tissues. Importantly, the assays used in this study were not congruent with all duplicate samples or between the test types used. The implications of these non-congruent results demonstrates that currently available testing assays produce variable results, underscoring the need for more reliable testing kits and a standardized methodology when assessing disease prevalence in wildlife, particularly for N. caninum in wild pigs, which impacts prevalence and comparability across studies.

Consideration of Vector-Borne and Zoonotic Diseases during Differential Diagnosis.

OBJECTIVE: Recognition and reporting of vector-borne and zoonotic disease (VBZD) cases is largely dependent upon the consideration of such diseases by healthcare practitioners during the initial diagnosis and ordering of specific confirmative diagnostic tests. This study was conducted to assess the general knowledge and understanding of VBZD transmission and clinical presentation. METHODS: Healthcare practitioners were surveyed to determine the extent of training and educational experiences they received relative to VBZDs, and their likelihood to consider such diseases during differential diagnoses. In addition, an assessment of their knowledge of arthropod species that may transmit VBZD pathogens was conducted. RESULTS: Having postprofessional school training relevant to VBZDs significantly influenced diagnostic accuracy for such disease cases based on the presented clinical signs and symptoms. CONCLUSIONS: The prevalence of VBZDs in the United States likely is significantly underestimated. The authors suggest the enhancement of VBZD-focused education as an important initiative that would significantly improve timely diagnosis, treatment, and, ultimately, prevention of these diseases.

Evaluation of Lotions of Botanical-Based Repellents Against Aedes aegypti (Diptera: Culicidae).

Thirteen botanical product repellent compounds such as 2-undecanone, capric, lauric, coconut fatty acids (and their methyl ester derivatives), and catnip oil were formulated in either Coppertone or Aroma Land lotions and evaluated against laboratory-reared Aedes aegypti L. (Diptera: Culicidae) mosquitoes. These formulations contained 7-15 wt/wt of the botanical repellent as the major active ingredient either pure or as mixtures. USDA standard repellent test cages were used to determine the complete protection time (CPT) of the different formulated repellents. Two of the evaluated formulations, a 7% capric acid in Coppertone (CPT 2.7 ± 0.6 h) and 7% coconut fatty acids containing carrylic acid, capric acid, and lauric acid in Coppertone (CPT 2.3 ± 2.0 h), provided strong repellency against mosquitoes up to 3 h, which was equivalent to the (N,N-diethyl-m-toluamide) DEET control (CPT 2.7 ± 0.6 h). This work suggests future potential for these botanical product-based repellents as alternatives to commercial DEET-containing products.

The Influence of New Surveillance Data on Predictive Species Distribution Modeling of Aedes aegypti and Aedes albopictus in the United States.

The recent emergence or reemergence of various vector-borne diseases makes the knowledge of disease vectors' presence and distribution of paramount concern for protecting national human and animal health. While several studies have modeled Aedes aegypti or Aedes albopictus distributions in the past five years, studies at a large scale can miss the complexities that contribute to a species' distribution. Many localities in the United States have lacked or had sporadic surveillance conducted for these two species. To address these gaps in the current knowledge of Ae. aegypti and Ae. albopictus distributions in the United States, surveillance was focused on areas in Texas at the margins of their known ranges and in localities that had little or no surveillance conducted in the past. This information was used with a global database of occurrence records to create a predictive model of these two species' distributions in the United States. Additionally, the surveillance data from Texas was used to determine the influence of new data from the margins of a species' known range on predicted species' suitability maps. This information is critical in determining where to focus resources for the future and continued surveillance for these two species of medical concern.

Predictive Modeling for West Nile Virus and Mosquito Surveillance in Lubbock, Texas.

West Nile virus (WNV) was first detected in North America during 1999, and has since spread throughout the contiguous USA. West Nile virus causes West Nile fever and the more severe West Nile neuroinvasive disease. As part of a WNV vector surveillance program, we collected mosquitoes in Lubbock, Texas, using CO2-baited encephalitic vector survey (EVS) traps. During 219 wk from 2009 through 2017, EVS traps were operated for 1,748 trap nights, resulting in more than 101,000 mosquitoes captured. Weekly, selected female mosquito specimens were pooled by species and trap site, and screened for WNV using reverse transcription-polymerase chain reaction assay. Mosquitoes positive for WNV were detected during 16.9% (37/219) of the weeks. Using this information, we constructed a statistical model to predict the probability of detecting an infection within a mosquito pool as a factor of weather variables. The final model indicated that detection of WNV in mosquitoes was negatively associated with the week of year squared and average wind from 3 wk prior to sampling, and was positively associated with week of year, average visibility, average humidity from 2 wk prior to sampling, and average dew point from 4 wk prior to sampling. The model developed in this study may aid public health and vector control programs in swift and effective decision making relative to city-wide mosquito control efforts by predicting when the chances of mosquitoes having WNV are at their greatest.

Aflatoxin contamination in corn sold for wildlife feed in texas.

Supplemental feeding with corn to attract and manage deer is a common practice throughout Texas. Other species, including northern bobwhites (Colinus virginianus), are commonly seen feeding around supplemental deer feeders. In many cases, supplemental feeding continues year-round so feed supply stores always have supplemental corn in stock. Fluctuating weather and improper storage of corn can lead to and/or amplify aflatoxin contamination. Due to the recent decline of bobwhites throughout the Rolling Plains ecoregion of Texas, there has been interest in finding factors such as toxins that could be linked to their decline. In this study, we purchased and sampled supplemental corn from 19 locations throughout this ecoregion to determine if aflatoxin contamination was present in individual bags prior to being dispersed to wildlife. Of the 57 bags sampled, 33 bags (approximately 58%) contained aflatoxin with a bag range between 0.0-19.91 parts per billion (ppb). Additionally, three metal and three polypropylene supplemental feeders were each filled with 45.4 kg of triple cleaned corn and placed in an open field to study long-term aflatoxin buildup. Feeders were sampled every 3 months from November 2013-November 2014. Average concentration of aflatoxin over the year was 4.08 ± 2.53 ppb (±SE) in metal feeders, and 1.43 ± 0.89 ppb (±SE) in polypropylene feeders. The concentration of aflatoxins is not affected by the type of feeder (metal vs polypropylene), the season corn was sampled, and the location in the feeder (top, middle, bottom) where corn is sampled. It is unlikely that corn used in supplemental feeders is contributing to the bobwhite decline due to the low levels of aflatoxin found in purchased corn and long-term storage of corn used in supplemental feeders.

A Quantitative PCR Protocol for Detection of Oxyspirura petrowi in Northern Bobwhites (Colinus virginianus).

Oxyspirura petrowi is a parasitic nematode that infects wild birds. This parasite has a broad host range, but has recently been reported in high prevalences from native Galliformes species in the United States. In order to better understand the impact O. petrowi has on wild bird populations, we developed a quantitative PCR protocol to detect infections in wild northern bobwhites (Colinus virginianus). We used paired fecal and cloacal swab samples from wild caught and experimentally infected northern bobwhites and matching fecal float data from experimentally infected birds to validate our assay. Overall we detected more positive birds from fecal samples than the paired cloacal swabs and there was strong agreement between the qPCR results from fecal samples and from fecal flotation (84%; κ = 0.69 [0.53-0.84 95% CI]). We also detected O. petrowi DNA in ten replicates of samples spiked with one O. petrowi egg. This qPCR assay is an effective assay to detect O. petrowi infections in wild birds. Our results suggest that fecal samples are the most appropriate sample for detecting infections; although, cloacal swabs can be useful for determining if O. petrowi is circulating in a population.

A survey of neonicotinoid use and potential exposure to northern bobwhite (Colinus virginianus) and scaled quail (Callipepla squamata) in the Rolling Plains of Texas and Oklahoma.

Northern bobwhite (quail) (Colinus virginianus) and scaled quail (Callipepla squamata) populations have declined dramatically in the Rolling Plains ecoregion of Texas and Oklahoma (USA). There is rising concern about potential toxicity of neonicotinoids to birds. To investigate this concern, the authors examined crops of 81 northern bobwhite and 17 scaled quail to determine the presence or absence of seeds treated with 3 neonicotinoids (clothianidin, imidacloprid, and thiamethoxam). No treated seeds were found in the 98 crops examined. Liver samples from all 98 quail were collected and analyzed for neonicotinoid residues. Analysis revealed very low concentrations of neonicotinoids within the quail liver samples. The results suggest there is little to no risk of direct toxicity to quail from neonicotinoids. Environ Toxicol Chem 2016;35:1511-1515. © 2015 SETAC.

Low Titers of Canine Distemper Virus Antibody in Wild Fishers (Martes pennanti) in the Eastern USA.

Canine distemper virus (CDV) infects species in the order Carnivora. Members of the family Mustelidae are among the species most susceptible to CDV and have a high mortality rate after infection. Assessing an animal's pathogen or disease load prior to any reintroduction project is important to help protect the animal being reintroduced, as well as the wildlife and livestock in the area of relocation. We screened 58 fishers for CDV antibody prior to their release into Pennsylvania, US, as part of a reintroduction program. Five of the 58 (9%) fishers had a weak-positive reaction for CDV antibody at a dilution of 1:16. None of the fishers exhibited any clinical sign of canine distemper while being held prior to release.

Utility of two modified-live virus canine distemper vaccines in wild-caught fishers (Martes pennanti).

BACKGROUND: Canine distemper virus (CDV) infects families in the order Carnivora. As a preventive measure, vaccinations against CDV are frequently given to mustelids in captive environments. OBJECTIVES: Our objectives were to compare the utility between two modified-live virus canine distemper vaccines (MLV CDV's), Fervac-D® (no longer manufactured) and Galaxy-D® (now manufactured by MSD Animal Health as part of a multivalent vaccine), in developing an immune response in wild-caught fishers. ANIMALS AND METHODS: The Pennsylvania Fisher Reintroduction Project (PFRP) used 14 wild-caught fishers during one year of the project to evaluate the utility of vaccinations against CDV as part of any reintroduction project. Fishers were injected subcutaneously in the nape of the neck with their designated vaccine. RESULTS: Fervac-D® did not effectively stimulate development of a serologic antibody response, whereas Galaxy-D® had adequate seroconversion or rise of titer levels to suggest that the general use of MLV CDV may be suitable in fishers pending further studies. CONCLUSION: We recommend that future studies be conducted, evaluating the use of currently produced vaccines in fishers. Future research should also focus on the length of days required between administration of primary and booster vaccines to achieve sufficient immune response. CLINICAL IMPORTANCE: If only primary doses are required, then hard-release reintroduction projects for fishers could be recommended. If primary and booster vaccines are required then soft-release reintroduction projects should be recommended that include captive management periods, allowing for appropriate vaccination intervals needed to maximize the probability of protection against CDV.

Efficacy of two canine distemper vaccines in wild Nearctic river otters (Lontra canadensis).

Canine distemper virus (CDV), a contagious morbillivirus, infects families in the order Carnivora, including Nearctic river otters (Lontra canadensis). As a preventative measure, vaccinations against CDV are frequently given to mustelids in captive environments. The Pennsylvania River Otter Reintroduction Project (PRORP) used wild-caught river otters to evaluate the efficacy and need for vaccinations against CDV as part of any reintroduction project. The objectives of this study were to: 1) evaluate the prevalence of exposure to CDV in wild river otters, 2) determine the immunologic response of river otters (i.e., seroconversion) after vaccination with a single (primary) vaccine dose compared to a second (booster) dose of Galaxy-D, a modified live-virus canine distemper (CD) vaccine (MLV CDV), and 3) determine the immunologic response after being vaccinated with a primary vaccination compared to a booster dose of Fervac-D, an MLV CDV. River otters were injected subcutaneously in the nape of the neck with their designated vaccine. Timeframes for collection of blood samples and/or injection of booster vaccines varied depending on the parameters of PRORP. Ten of the 22 river otters had positive prevaccination titer levels to CD. Both vaccines, Galaxy-D and Fervac-D, produced sufficient seroconversion or rise of titer levels (86% and 57%, respectively) to recommend the use of vaccines in wild river otters. Future studies are recommended to evaluate currently produced CD vaccines. Future research should also focus on the number of days required between administration of primary and booster vaccines to achieve sufficient immune response. If only a primary dose is required, then hard-release reintroduction projects for river otters could be recommended. If primary and booster vaccines are required then soft-release reintroduction projects should be recommended. Soft-release projects should include captive management periods that allow for appropriate vaccination intervals and boosters needed to maximize the probability of protection against CDV.

The parasitic eyeworm Oxyspirura petrowi as a possible cause of decline in the threatened lesser prairie-chicken (Tympanuchus pallidicinctus).

Lesser prairie-chickens (Tympanuchus pallidicinctus) have been declining range wide since the early 1900's despite efforts to establish conservation and improve their habitat. In early 2014, the lesser prairie-chicken was listed as a threatened species under the U.S Endangered Species Act and the need to find out why they are declining is more important than ever. Nine hunter shot lesser prairie-chickens were donated and sampled for the presence or absence of the eyeworm Oxyspirura petrowi, a known parasite that can cause damage to the eye of its host, and common environmental contaminants. Eyeworm infection was found in 7 of 9 birds (78% infection rate) with an infection range between 0-16 O. petrowi per bird. Breast, liver, and fat tissue samples from the lesser prairie-chickens were analyzed for the frequency of 20 organochlorine pesticides. Femurs and livers were also tested on these birds for metal contaminants. Pesticides were found in several samples above the detection limits but were still in the low ng/g range. Notable was the ubiquitous presence of endrin aldehyde across all tissues. One femur showed 5.66 µg/g of lead (Pb) but this is still relatively low. No liver samples had elevated mercury (Hg) above detection limits. The presence of these organochlorines is consistent with the historic use of pesticides in this region. With pesticide and metals found in such low levels and parasitic nematode infections at rather high levels, it is recommended that these parasites be further evaluated as a contributing factor to the decline of the lesser prairie-chicken.