Molecular characterization of the 2016 new world screwworm fly outbreak in the Florida Keys

Authors: DUPUIS, JULIAN - University Of Hawaii; Guerrero, Felicito; Skoda, Steven; Phillips, Pamela; WELCH, JOHN - Animal And Plant Health Inspection Service (APHIS); SCHLATER, JACK - Animal And Plant Health Inspection Service (APHIS); AZEREDO-ESPIN, ANA MARIA - Universidade De Campinas (UNICAMP); Perez De Leon, Adalberto - Beto; Geib, Scott

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2018
Publication Date: 7/1/2018
Citation: Dupuis, J.R., Guerrero, F., Skoda, S.R., Phillips, P.L., Welch, J.B., Schlater, J.L., Azeredo-Espin, A.L., Perez De Leon, A.A., Geib, S.M. 2018. Molecular characterization of the 2016 new world screwworm fly outbreak in the Florida Keys. Journal of Medical Entomology. 55(4):938-946.

Interpretive Summary: The New World screwworm (NWS) is a livestock pest that was eradicated from the U.S. through the successful application of the sterile insect technique. The immature stages, or screwworms, feed on the live flesh of livestock, humans, and wildlife. NWS is now regarded as a high-consequence foreign animal pest because if reintroduced, it poses a severe threat to U.S. animal health, the agricultural economy, and could impact human health as well. A NWS outbreak occurred in Florida in 2016, which represented the first detection of this high-consequence pest in the U.S. more than 30 years after its eradication was accomplished. Quarantine and rapid reactivation of the sterile insect technique eradicated the NWS from Florida by early 2017. However, the geographic source of this infestation remains unknown. Here, we report genetics research to analyze samples from all confirmed cases of NWS from the Florida outbreak. The results were compared to data from NWS collected before. Our investigation addressed these research questions: 1) is this infestation the result of a single invasion from one source, or multiple independent invasions from different sources?; 2) what is the geographic origin of this invasion? We found virtually no sequence variation between NWS samples collected during the Florida outbreak, which is consistent with a single source of introduction. Nevertheless, we also found very little geographic resolution in any of the datasets, which precludes identification of the source of this NWS outbreak. These findings highlight the need for more fine-scale genetic and molecular assessments of NWS population structure, which would enhance agricultural biosecurity preparedness to determine the source of NWS should future outbreaks occur in the U.S.

Technical Abstract: New World screwworm (NWS), Cochliomyia hominivorax, is a myiasis-causing fly that can be a serious threat to the health of livestock, wildlife, and humans. The eradication of this species from North and Central America is an excellent example of successful integrated pest management using sterile insect technique; from the 1950s to the 2000s it was progressively eradicated from the southern USA, Mexico, and Central America, as well as from several islands of the Caribbean. In late 2016 and early 2017, autochthonous NWS were detected in the Florida Keys and nearby Homestead, Florida, which represents the first invasion in the USA by this species in more than 30 years. Rapid use of the sterile insect technique, implemented as part of a quarantine and eradication effort, was successful in eliminating the infestation by early 2017, however, the geographic source of this infestation remains unknown. Here, we use targeted amplicon sequencing to generate mitochondrial and nuclear sequence data for samples from all confirmed cases of NWS from this infestation, and compare these sequences to preexisting datasets sampling the native distribution of NWS. We ask two questions regarding the Florida Keys outbreak. First, is this infestation the result of a single invasion from one source, or multiple independent invasions from different sources? And second, what is the geographic origin of this invasion? We found virtually no sequence variation between specimens collected from the Florida Keys outbreak, which is consistent with a single source of introduction. However, we also found very little geographic resolution in any of the datasets, which precludes identification of the source of this outbreak. Our lack of success in answering our second question speaks to the need for more fine-scale genetic or genomic assessments of NWS population structure, which would facilitate source determination of potential future outbreaks.