New World Screwworm (NWS), or Cochliomyia hominivorax, is a potentially fatal disease due to severe larvae infestation and tissue destruction. A resurgence has been reported. This narrative review provides a focused overview of NWS for the emergency clinician, including the epidemiology, presentation, diagnosis, and management of the disease. NWS is endemic to tropical and subtropical America. While previously eradicated in the U.S., several human cases have been recently reported. This insect primarily infests livestock but may also affect humans. Female flies are attracted to mucosal surfaces and wounds and lay hundreds of eggs. Once hatching, larvae burrow into these surfaces and cause extensive damage by ingesting live tissue. Humans at risk include those with significant immunocompromise, open wounds, and those around animals. Infested patients present with severe swelling, bleeding, pain, and open, malodorous wounds. Larvae are usually visible in the wound. Bacterial superinfections may also occur. Suspected cases should be reported to the local or state public health department and the Centers for Disease Control and Prevention. Diagnosis includes morphologic identification of larvae removed from a wound. Larvae should be placed in a leak-proof container with 70% ethanol. Serum laboratory testing may also be needed in patients with evidence of bacterial superinfection and sepsis. Treatment includes removal of all larvae and often extensive debridement. Reevaluation of the wound within 48 h is recommended. Antibiotics are necessary for those with bacterial superinfection. Emergency clinicians should be aware of the presentation, diagnosis, evaluation, and management of NWS to ensure optimal outcomes.
The reinfestation of New World screwworm (Cochliomyia hominivorax [Coquerel]) (Diptera: Calliphoridae) in North America has prompted a broad effort to identify new management tools. In this study, the larval parasitoid Tachinaephagus zealandicus (Ashmead) (Hymenoptera: Encyrtidae) was evaluated as a potential biocontrol using the congeneric secondary screwworm Cochliomyia macellaria (Fab.) (Diptera: Calliphoridae) as a proxy host. When host:parasitoid ratios were varied from 5:1 to 40:1, female parasitoids killed up to 18 hosts (at 40:1) and produced 66 adult wasp progeny per female over 24 h. Parasitized pupae produced from 5.6 to 11.7 adult parasitoids per pupa at host:parasitoid ratios of 40:1 and 5:1, respectively. Parasitoids showed no preference for larvae of C. macellaria or Sarcophaga bullata Parker (Diptera: Sarcophagidae). Kill rates and successful parasitism was twice as high in moist (15% moisture) as in dry sandy loam soil. Addition of a layer of leaf litter to the soil surface had no effect on the ability of parasitoids to locate hosts. Parasitism in moist clay soil was similar to that in moist sandy soil, but higher parasitism was observed in dry clay than on dry sandy soil. Placing faux rocks as potential larval refuge on the pupation substrate surface provided larvae with some protection from parasitism in dry substrates. When larvae were given a 2-h head start before adding parasitoids, there was no effect on host mortality or parasitism in dry soil. Results are encouraging for possible use of T. zealandicus as a supplemental management tool for calliphorid pests.
Infestations of Cochliomyia hominivorax, the New World Screwworm (NWS), has become a reemerging veterinary concern in the United States due to the recent northward expansion of fly detections as far as northern Mexico. Rapid, accurate and validated detection pipelines need to be developed in the case of an incursion into the United States. Confirmatory cases are evaluated by morphological identification with no paired test to verify identifications. With the frequency of submissions of non-ideal samples, particularly from fly traps, a molecular tool would be necessary for species identification. In this manuscript, we develop and assess a pipeline including three real-time PCR assays targeting the ribosomal RNA and five sets of Sanger primers targeting the mitochondrial genome that would be used as a paired tool with morphological identification. Two of the assessed real-time PCR assays are highly specific, sensitive and repeatable requiring < 1 copy per reaction for detection. Four of the five Sanger primer sets were assessed, optimized and results evaluated for potential use in preliminary geographic analysis of specimens. This workflow will expedite screening of samples, provide a method to verify results using different tools and help understand genetic variations within the mitochondria for NWS outbreaks.
The New World screwworm, Cochliomyia hominivorax (Coquerel, 1858; Diptera: Calliphoridae), was eradicated from North and Central America through the first application of the sterile insect technique. The sterile screwworm adult fly releases were mixed sex, but releasing only males could be much more effective. Here, we describe screwworm transgenic sexing strains (TSSs) with expected embryo lethality. Strains were developed with a Tetracycline-off (Tet-off) system utilizing either the Lucilia cuprina (Wiedemann, 1830) nullo (DR6) or Cochliomyia macellaria (Fabricius, 1755) CG14427 (DR7) gene promoter and a tTA-activated effector to promote female lethality. The promoter activity was highest in 2 to 3 h embryos and low in larvae and adults. However, these strains also had unexpected high expression in pupae. Evaluation on two doxycycline (Dox) suppression regimens found that inclusion of Dox in the last larval feeding rescued females of the subsequent generation, likely by maternal transfer of Dox. All TSSs produced only males on a reduced Dox feeding regimen, but the female lethal period for the DR6 TSS was too late in development to reduce diet costs. Production parameters were met by all strains in colony, but strains had lower male fly survival than current production strains after removing Dox. In noncompetitive mating success trials, DR6 strains performed poorly, but DR7 performed equally to production strain males. However, males from all TSSs fared poorly in mating competition tests against production males. Our study highlights the importance of tightly regulated gene promoters and stage-specific antibiotic feeding schemes for the development and evaluation of TSSs based on the Tet-off system.
New World screwworm, Cochliomyia hominivorax (Coquerel), is an obligate parasite of warm-blooded animals and a serious threat to livestock, wild animals, and humans. The sterile insect technique (SIT) was used to eradicate screwworm from North and Central America during the mid-1900s to the early-2000s. Traps are an important tool for screwworm control programs, where they are used for surveillance, evaluation of production strains, and to estimate the ratio of wild to sterile flies following aerial and ground releases. Here, we tested two trap designs for capturing New World screwworm. The vertical sticky trap, the trap currently used, is a triangle-shaped trap with 1,710 cm2 surface area coated with insect adhesive. The cylinder sticky trap is a cylinder-shaped trap with 1,700 cm2 surface area coated with the same insect adhesive. Both traps were baited with swormlure-4 as an attractant. We used a release-recapture study with a randomized block design to test the efficacy of the two trap designs. The cylinder sticky trap captured significantly more C. hominivorax than the vertical sticky trap, likely due to an increase in the ability of the flies to land on the surface of the cylinder-shaped trap.
Myiasis is the infestation of humans and other warm-blooded animals with dipterous larvae. In the current study, a total of 40 maggots were collected from the cutaneous lesions of the Chinese Milu (Elaphurus davidianus) in China. Based on morphological identification, the third-instar larvae were classified as Chrysomya bezziana. To accurately identify this species, genomic DNA from the larvae was analyzed using the mitochondrial cytochrome c oxidase subunit I (COI) gene. The findings indicated that the examined larvae were unequivocally consistent with the Old World screwworm fly, C. bezziana. This study firstly documented the cases of cutaneous myiasis caused by C. bezziana in Chinese Milu, and provided effective strategies for the prevention and control of myiasis.
Filth flies pose a health risk because of the microbes they carry outside and inside of their bodies to humans and animals. Mostly synthetic chemical insecticides are used for fly control. Alternative approaches with a different mode of action are needed because of increasing fly resistance to pesticides. We used a modified World Health Organization cone test to determine the efficacy of the minerals produced by diatoms (diatomaceous earth) as a mechanical insecticide against adults of the house fly, Musca domestica, the secondary screwworm, Cochliomyia macellaria, and the grey flesh fly, Sarcophaga bullata, under low and high humidity. The use of mechanical insecticides as an alternative to kill filth flies has received minimal consideration. However, recent research showed that expanded perlite, a new mechanical insecticide made from volcanic rock, was highly efficacious against mosquitoes and flies. Mortality for diatomaceous earth in this paper at 30°C and 50% relative humidity was observed as early as 2 h after exposure with 50% and 90% mortality observed at 3.5 and 4.6 h (the LT50 and LT90, respectively) in M. domestica. The LT50 and LT90 increased as the size of the fly species increased (M. domestica to C. macellaria to S. bullata) and increased for all three species when the relative humidity increased from 50 to 70%. These results suggest dehydration was the mode of action. Scanning electron micrographs of C. macellaria adults 2 h after diatomaceous earth exposure, showed the flies were evenly self-covered with the mineral with no obvious damage to the cuticle. Proof of concept was demonstrated that diatomaceous earth as a residual surface treatment could be used as an alternative for filth fly control.
Surveillance and diagnostics are critical for the early detection, containment and eradication of exotic pests. For the screwworm fly, this is usually via targeted surveillance and exclusion testing of trap-caught flies, as well as the identification of larvae associated with myiasis wounds. We present a specific and sensitive real-time polymerase chain reaction (PCR) assay for the detection of the New World screwworm fly, Cochliomyia hominivorax Coquerel (Diptera: Calliphoridae). The assay targets the cytochrome oxidase subunit 1 (cox1) gene from adult flies or larvae and retains high analytical sensitivity when multiplexed with an existing assay for the Old World screwworm fly, Chrysomya bezziana Villeneuve (Diptera: Calliphoridae), achieving a limit of detection of less than 1 copy per microlitre of reaction. To assess its utility for surveillance and diagnostics, a novel non-destructive DNA extraction method was performed on spiked trap catches of field-caught flies, and on boiled and unboiled specimens of larval instars. The multiplexed assay detected 95% of spiked flies, and all screwworm flies from positive samples were retrieved and morphologically identified. Results from larval instars confirmed that the assay can be used for larvae, with higher sensitivity observed for unboiled larval instars. This molecular assay enables the simultaneous detection of Co. hominivorax and Ch. bezziana, offering a reliable alternative to existing single-target and destructive methods of bulk fly testing. It also holds potential for broader application in the identification of larval stages.
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The New World screwworm, Cochliomyia hominivorax, is an obligate parasite of warm-blooded animals and a major pest of livestock and wildlife in the Americas. The first genome assembly for C. hominivorax enabled substantial progress in key areas including gene expression related to fly behavior and physiology and gene editing technologies. However, the first genome was sequenced prior to several technological advances that result in fewer errors and better genome annotations. Here, we used the trio-binning approach to produce haplotype-resolved genome assemblies of C. hominivorax. A single male progeny from the cross of a Panama line male with a production strain female was sequenced using PacBio HiFi and scaffolded using Hi-C chromatin conformation, while Illumina NextSeq 2000 was used for short-read sequencing of both parents to facilitate trio-binning. We produced a linear haploid reference assembly by transferring a copy of the X chromosome and mitochondrial genome to the paternal haplotype. This assembly is comprised of 5 autosomes, 2 sex chromosomes, the mitogenome, and 75 unplaced scaffolds spanning 455.6 Mb, which is closer to the predicted size based on flow cytometry (443.8 Mb) than the previous assembly of 534.4 Mb. NCBI's external Eukaryotic Genome Annotation Pipeline (EGAPx) was used to annotate the protein-coding and non-coding genes in the linear haploid reference and the maternal haplotype assemblies. Due to the better resolution of the sex chromosomes and updated genome annotations, these improved assemblies will advance future experiments aimed at understanding sex determination, gene expression, and the evolution of parasitism in the Calliphoridae.
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We describe New World screwworm (Cochliomyia hominivorax) infestation in 2 injured mountain tapirs (Tapirus pinchaque) from a protected area in the Central Andes, Colombia. Screwworms were not a known threat to mountain tapirs. Community outreach is needed to raise awareness on effects of this parasite on humans, domestic animals, and wildlife.
Oral myiasis is a rare medical condition in which soft tissues of the oral cavity are invaded by the larvae (maggots) of several flies. We report a fatal case in a 75-year-old man from a subtropical rural region of Ecuador who presented to a public health center with respiratory distress, peripheral cyanosis, dyspnea, and a Glasgow Coma Scale score of 9 of 15. The oral cavity emitted a fetid odor and contained bloody secretions with extensive larval invasion affecting the gingiva, lower lip, tongue, and soft palate. More than 300 larvae were manually extracted and morphologically identified as third-instar Cochliomyia hominivorax. The patient had a known history of epilepsy managed with carbamazepine (400 mg/day). Despite supportive management, including oxygen therapy and fluid resuscitation, the patient died approximately 8 hours after admission. The rapid deterioration was probably owing to airway compromise caused by larval migration toward the oropharynx. This case underscores the importance of prompt diagnosis and aggressive management of oral myiasis in vulnerable elderly individuals.
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The New World Screwworm (Cochliomyia hominivorax) has reemerged in Central America, posing risks to livestock and public health. Recent outbreaks highlight its northward spread, raising concerns about its potential reintroduction into Mexico. This study uses linear regression models to examine the role of animal movement in the parasite's spread, with a particular focus on human-mediated factors. Our analysis determined a spread rate of 1.2-1.9 km/day for screwworm outbreaks. Furthermore, consecutive outbreak events occurring more than 50 km apart suggest a strong association with animal movements rather than natural dispersal mechanisms. Based on these findings, we identified potential routes for its reintroduction into Mexico. To mitigate further outbreaks, enhanced control measures, active surveillance, and regional cooperation are urgently required.
Myiasis is the invasion of mammalian tissues by dipterous larvae. Cutaneous myiasis is the commonest type, and less commonly, internal tissues and organs are affected. Here, we report the first case of oro-nasopharyngeal myiasis caused by the third-instar larvae of Chrysomya bezziana (Old-World screwworm) in Sri Lanka. A retired 71-year-old female tea-plucker presented to the hospital with a 4-day history of nasal bleeding and neck discomfort. Except for well-controlled hypertension, she had no significant medical history. On examination, there was an ulcerated area in the posterior oro-nasopharynx filled with maggots. Hematological analysis showed a high C-reactive protein level (24 mg/dL) and white blood cell count (17.5 × 109/L) with 80% neutrophils. Computed tomography showed severe inflammation of the pharynx with no features of a neoplasm or parapharyngeal abscess. An examination was performed under anesthesia followed by manual removal of larvae, surgical debridement with biopsy, and treatment with antiparasitic medicines and antibiotics. Histopathology excluded neoplasm and only showed inflammatory changes. All extracted larvae were morphologically similar and identified as third-instar larvae of C. bezziana using a trinocular zoom stereomicroscope. The patient recovered and was discharged from the hospital on the 15th day and was well at 2 months follow-up.
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The screwworm fly, Cochliomyia hominivorax, is a significant pest in Brazil, posing threats to agriculture and public health. Laboratory rearing is crucial for developing control strategies like the sterile insect technique (SIT); but the effects of multi-generational rearing on the fly's biological parameters are not fully understood. This study investigated the impact of rearing C. hominivorax for 12 inbred generations on its morphometrics, reproductive capacity, and life expectancy. Specimens were collected at distinct developmental stages across 12 generations for morphometric analysis, and key viability traits were assessed through biological assays. Data were analyzed using linear mixed-effects models and Kaplan-Meier survival analysis. The results revealed that morphometric parameters and key reproductive traits (oviposition, egg weight, hatchability, and larval survival) remained stable across all generations (p > 0.05). However, a significant decline in adult life expectancy was observed (log-rank test, χ2 = 338.257, p < 0.001), becoming pronounced from the fifth generation onwards. Significant sexual dimorphism was also confirmed: males were larger and heavier (Mann-Whitney U = 9884.5, p < 0.001), while females exhibited significantly greater longevity (log-rank test, χ2 = 44.538, p < 0.001). Continuous laboratory rearing of C. hominivorax appears robust for maintaining physical and reproductive traits, but negatively impacts fitness-related traits like longevity, likely due to inbreeding. These findings provide a critical quantitative baseline for quality control in mass-rearing programs and highlight the need for strategies to manage genetic diversity in laboratory colonies to ensure their effectiveness for research and SIT applications.
The present study surveyed traumatic myiasis cases admitted to the governmental Veterinary hospitals (belonging to the Iraqi Ministry of Agriculture) distributed throughout Iraq, between 2019 and 2023, and highlights the epidemiological changes occurred in comparison to the previous situation. A total of 916 cases were detected in various animals from nine governorates, with an annual average of 183.2 cases/year, which is lower than the corresponding value estimated for the period 1996-2000 (23,510 cases/year) or for 2001-2018 (811.2 cases/year). Cases peaked during early summer, unlike the earlier surveys during winter, which assumes that the pupal development peaks during spring. Numbers and geographical distribution of the cases suggest emergent infestations in the northern region, persistent endemic infestations in the middle region, and cleared or lowered infestations in the southern region. Out of the 916 cases, sheep (610 cases) had the highest infestations, and the annual number of infested sheep was estimated at 54,000 animals, giving rise to a yearly economic loss mounts greatly over 1.5 million USD. Cattle (172 cases) was the second most frequently infested animal; however, cattle cases declined over years. Forty-four dog cases were detected, mostly in Diyala; nonetheless, dog myiasis is largely underreported in Iraq since millions of dogs live as strays. The Old World screwworm fly accounted for over 90% of the infestations, which underlines its historical role as the major contributor to traumatic myiasis in Iraq. In conclusion, significant changes in the epidemiology of animal traumatic myiasis in Iraq are strongly suggested. The Iraqi authorities should therefore consider these changes in updating various strategies established to effectively combat this economically important disease.