Pamela L. Phillips

One Health approach to identify research needs in bovine and human babesioses: workshop report

BackgroundBabesia are emerging health threats to humans and animals in the United States. A collaborative effort of multiple disciplines to attain optimal health for people, animals and our environment, otherwise known as the One Health concept, was taken during a research workshop held in April 2009 to identify gaps in scientific knowledge regarding babesioses. The impetus for this analysis was the increased risk for outbreaks of bovine babesiosis, also known as Texas cattle fever, associated with the re-infestation of the U.S. by cattle fever ticks.ResultsThe involvement of wildlife in the ecology of cattle fever ticks jeopardizes the ability of state and federal agencies to keep the national herd free of Texas cattle fever. Similarly, there has been a progressive increase in the number of cases of human babesiosis over the past 25 years due to an increase in the white-tailed deer population. Human babesiosis due to cattle-associated Babesia divergens and Babesia divergens-like organisms have begun to appear in residents of the United States. Research needs for human and bovine babesioses were identified and are presented herein.ConclusionsThe translation of this research is expected to provide veterinary and public health systems with the tools to mitigate the impact of bovine and human babesioses. However, economic, political, and social commitments are urgently required, including increased national funding for animal and human Babesia research, to prevent the re-establishment of cattle fever ticks and the increasing problem of human babesiosis in the United States.

Seasonal and Spatial Distributions of Adult Screwworms (Diptera: Calliphoridae) in the Panama Canal Area, Republic of Panama

Abstract The distribution of screwworms, Cochliomyia hominivorax, (Coquerel) was studied in a seasonally moist lowland tropical forest in the Republic of Panama using a combination of field collections and satellite imagery. We found that different forest types could be distinguished and mapped using remotely sensed data. To determine the temporal and spatial distribution of flies, we collected flies coming to rotted liver at 82 sites in ten vegetation types (open areas, edge forest, dry scrub forest, forest successional stage 1, forest successional stage 2, forest successional stage 3, forest successional stage 4, forest successional stage 5, mature forests, palm swamp forest, and forest along streams) over three seasons (dry, transitional, wet). Nine of the vegetation types (excluding dry scrub forest) were identified and mapped using SPOT XS and Landsat 5 TM satellite data. Screwworm flies were most abundant during the transition from wet to dry season. Fly numbers were consistently higher in forest habitats, particularly those with trees 20–30 m in height and a fairly open canopy composed of many deciduous species that shed their leaves during the dry season. Screwworm numbers were also high in palm swamp forest, edge forest, and mature growth forest. Traps sampled in open areas had fewer flies and were unrelated to proximity to cattle. Females accounted for 88% of the total fly counts. This study further substantiates the importance of forests in the ecology and behavior of screwworm flies and demonstrates that remotely sensed data can be used to construct the spatial distribution of these flies in a tropical landscape. We discuss implications of this information to the screwworm eradication program.

Review of research advances in the screwworm eradication program over the past 25 years

New World screwworms, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae: Chrysomyinae), are devastating pests of warm‐blooded animals that cause significant economic damage to livestock. The successful campaign to eradicate screwworms from continental North America, led by the US Department of Agriculture and using the sterile insect technique, continues to receive research support that has resulted in improved technologies for all aspects of the program. The process and ingredients for mass‐rearing screwworms is more efficient and sustainable, and there is now a standardized protocol for developing new strains used in mass rearing. Cryopreservation of screwworm embryos allows strains to be preserved and recovered if necessary and also reduces rearing requirements for backup and research strains. Sterile fly release procedures and equipment have been updated leading to optimized sterile fly release rates. Surveillance for screwworm infestations and outbreaks have incorporated new trap designs, habitat analysis, and molecular genetic techniques that enhance monitoring the progress of the program as well as early detection and response to outbreaks. Genetic analyses of screwworm populations across their current range have increased the understanding of genetic differentiation, which may aide in developing new strains and determining the geographic origin of screwworms causing outbreaks when they occur. The ability to release only sterile males, which has been a goal of the program for over 60 years, has recently been accomplished through the development of transgenic sexing strains. The strains carry a conditional female lethal gene and are comparable to the wild‐type strain for several biological parameters that are important for mass production and performance in the field. The strains should improve efficiency of population suppression of the current and future eradication and prevention programs against screwworms. These research advances as well as future considerations are presented.

Artificial diets used in mass production of the New World screwworm, Cochliomyia hominivorax

The New World screwworm, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae), has been eradicated from North and Central America using the sterile insect technique. This success has been based on mass production of high‐quality screwworms using artificial diets since 1958. Many diet formulations for both larvae and adults have been developed, mainly driven by cost efficiency and material supply. However, only four larval and two adult diet formulations have been applied in the six sterile fly mass production plants in the USA, Mexico and Panama. Herein, we briefly review the history of screwworm diet research and development, introduce the diet formulations used in mass rearing and discuss their advantages and disadvantages in terms of plant application. Finally, we propose future research on screwworm nutrition, potential protein sources, feeding stimulants, further optimization of screwworm formulations and possible methods to reduce the negative qualities of waste generated during the mass production.

Development of a Spatially Targeted Field Sampling Technique for the Southern Cattle Tick, Rhipicephalus microplus, by Mapping Whitetailed Deer, Odocoileus virginianus, Habitat in South Texas

Abstract The objective of our study was to determine whether satellite remote sensed data could be used to identify white-tailed deer, Odocoileus virginianus (Zimmerman) (Artiodactyla: Cervidae), habitat and target locations for sampling free-living larvae of the southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini) (Ixodida: Ixodidae) in South Texas. Two methods for mapping white-tailed deer habitat were used, an object-oriented method to identify closed canopies and waterways for deer movement and two vegetation indices: the Normalized Difference Vegetation Index and the Modified Soil Adjusted Vegetation Index to identify forage for deer. These two data sets of favorable white-tailed deer habitat were combined within a geographic information system to identify locations for sampling ticks. Larvae of R. (B.) microplus , were sampled in Zapata County, Texas, by walking transects with attached flannel panels to jeans. Although the data set and sampling period were limited, data analysis demonstrated that sampling of free-living larvae of R. (B.) microplus can be conducted in South Texas, and larvae were most abundant in areas that harbored O. virginianus . Spatial analysis of satellite imagery to classify white-tailed deer/southern cattle tick habitat proved efficacious and may be useful in directing sampling activities in the field.

Distribution and Persistence of Sterile Screwworms (Diptera: Calliphoridae) Released at the Panama–Colombia Border

Abstract The sterile insect technique is used by the Comisión Panamá – Estados Unidos para la Erradicación y Prevención del Gusano Barrenador del Ganado (COPEG) to maintain a barrier at the border of Panama and Colombia to prevent screwworms, Cochliomyia hominivorax (Coquerel), from South America reinfesting North America. Before studying the distribution and persistence of sterilized, mass-produced screwworms released in the barrier zone, the utility of applying fluorescent dust (∼1.0 mg/fly) to pupae and to newly emerged adults was evaluated to determine the potential effect on fly survival. The flight ability of flies collected from two adult emergence/collection systems (enclosed towers and open chambers) and treated with low (∼0.20 mg/fly) or high (∼1.0 mg/fly) amounts of fluorescent powder was compared. The distribution and persistence of sterile screwworms marked with fluorescent powder (∼0.20 mg/fly), after collection from the same two adult emergence/collection systems, was compared after their release in the barrier zone. The results demonstrated that: 1) fluorescent dust did not negatively affect sterile screwworm longevity or flight ability; 2) no differences were detected between sterile flies collected from the two emergence systems; and 3) sterile screwworms distributed evenly in the barrier zone and persisted for > 6 d. This information was useful in implementing the use of a new sterile fly emergence/collection system and deploying a new strain by COPEG for the barrier zone maintenance program; it will be valuable for evaluating alternative release strategies of sterile screwworms by the eradication and barrier maintenance program.

Screwworm (Diptera: Calliphoridae) in the United States: Response to and Elimination of the 2016–2017 Outbreak in Florida

Abstract Eradicating screwworm, Cochliomyia hominivorax (Coquerel), from continental North American via the sterile insect technique has provided huge economic benefit to livestock producers by eliminating screwworm myiasis. After confirmatory identification of fly samples from infested deer by the USDA National Veterinary Services Laboratory on September 30, 2016, an alert was issued that screwworm myiasis was discovered in the Florida Keys. Personnel from USDA Animal and Plant Health Inspection Service, Agricultural Research Service, the State of Florida, U.S. Fish and Wildlife Service and local officials responded to the outbreak focus on Big Pine Key. After witnessing infested Key deer (Odocoileus virginianus clavium Barboyr & Allen), screwworm adult sampling was initiated at 0930 h on October 5, 2016 using nets to collect flies arriving at putrid liver, with the first female collected within 1 h. Larval samples were collected from infested animals for DNA analyses and to develop a “Florida outbreak” colony to test mating compatibility with the mass-produced strain used for sterile fly releases. Ground release chambers for sterile screwworm releases were placed in favorable habitats based on satellite image analyses. Sterile pupae were first placed in the chambers on October 11, 2016. Further liver trapping showed that 13 Keys were infested. One case, presumably through animal movement, occurred near Homestead on the Florida mainland. Ultimately there were 35 sterile fly release stations, including 4 located around Homestead, but no further cases were identified. About 188 million sterile flies were released until successful eradication was declared on March 23, 2017. Containing the outbreak prevented economic losses to livestock producers and other wildlife on the mainland and kept eradication costs to a minimum.