Tracking human New World screwworm in the Americas: burden, spread, and knowledge gaps

ABSTRACT

Objectives.

To map the available evidence on human cases of New World screwworm across the Americas and identify guidance relevant to surveillance and management.

Methods.

Searches were conducted in bibliographic databases (PubMed/MEDLINE, EMBASE, LILACS, Epistemonikos, Google Scholar, La Referencia, and OpenAlex), gray literature sources, and clinical trial registries. Searches were made in English, Spanish, and Portuguese. Eligible sources included peer-reviewed articles, case reports, case series, observational studies, reviews, guidelines, and technical documents addressing human infestation in the Americas

Results.

From 2 332 records identified, 75 studies met the inclusion criteria and were included in the review. Clinical presentations varied and included oral and maxillofacial, cutaneous and wound-associated, otic, nasal, orbital, and cervicofacial infestations. Management generally relied on prompt mechanical larval removal, wound care, and, when required, surgical debridement. Ivermectin was the most used antiparasitic treatment, although no robust comparative evidence was identified. National guidance documents broadly agreed on the importance of larval extraction, case notification, and intersectoral coordination, but differed in their clinical recommendations and the role of ivermectin.

Conclusions.

The available evidence is sparse, fragmented, and predominantly descriptive. The findings describe patterns in the published literature and should not be interpreted as estimates of population-level frequency or risk. Nevertheless, recurrent clinical patterns, vulnerable populations, and key public health priorities emerged and can support preparedness, surveillance, and the harmonization of guidance across the region.

Myiasis caused by Cochliomyia hominivorax, commonly known as the New World screwworm, is a parasitic condition affecting warm-blooded animals. It occurs mainly in livestock and wildlife, but may also infest humans, making it of clear public health relevance (1–3). The larval stages are obligate parasites that feed on living tissue, producing deep and painful lesions that may lead to extensive tissue destruction, secondary bacterial infection, and sepsis. In severe cases, New World screwworm can be fatal if not promptly recognized and treated (1, 4–6).

New World screwworm is endemic to tropical and subtropical regions of the Americas and the Caribbean (1, 2). A large-scale eradication campaign based on the sterile insect technique, which started in 1957, successfully eliminated New World screwworm from the United States, Mexico, and Central America, with Panama declared New World screwworm-free in 2006. This effort established a long-standing biological barrier at the Darién Gap through the Panama–United States Commission for the Eradication and Prevention of Screwworm, which for decades limited northward spread from South America (7, 8). However, beginning in 2022 and intensifying in 2023, a marked increase in cases in Panama signaled disruption of this containment. This was followed by persistent northward spread into Central America (1, 9). By the end of 2025, transmission had been confirmed in Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico and Nicaragua, indicating that previously effective control measures were no longer able to maintain the barrier south of the Darién Gap (1, 9).

Evidence suggests that the unregulated movement of livestock is a substantially greater risk for reintroduction and dissemination of New World screwworm than human travel and has likely played a central role in the recent geographic expansion (9, 10). Nevertheless, human cases have also emerged in the context of the current resurgence, including travel-associated cases identified in the United States and Canada in 2025 in people returning from newly affected outbreak countries (1, 10). These events highlight that the re-emergence of New World screwworm is not only a veterinary and agricultural problem, but also a growing public health concern.

The renewed spread of New World screwworm has major consequences for livestock production systems in Mexico and Central America, and broader economic and operational implications for trade, surveillance, and regional response capacity (9, 10). At the same time, how best to respond for human health relies on sparse and fragmented evidence, composed mostly of case reports, small case series, technical documents, and heterogeneous national guidance. This New World screwworm outbreak underscores the need for stronger One Health coordination across public health, animal health, and environmental sectors, as well as for harmonized approaches to surveillance and information-sharing, diagnosis, clinical management, and reporting of human and animal cases (2, 4, 6).

From a public health perspective, several countries currently at risk OF NSW are revising or developing technical documents for the detection, confirmation, clinical management and prevention of, and response to human myiasis caused by New World screwworm (6, 10). The present scoping review was undertaken to map the available human-focused evidence on New World screwworm across the Americas, synthesize the main clinical and public health patterns described in the literature, and identify existing national and regional guidance relevant to surveillance and management of human cases. The review aimed to inform public health authorities in Central America and Mexico as they update and harmonize their national public health guidelines.

METHODS

This scoping review follows the methodological framework proposed by Arksey and O’Malley (11). Reporting followed the PRISMA Extension for Scoping Reviews (12). The review was designed to systematically map the available human-focused evidence on New World screwworm myiasis in the Americas, including published studies involving human cases, clinical guidelines, technical documents, surveillance protocols, and records from clinical trial registries. In addition, the review sought to identify the principal public health, academic, and surveillance institutions involved in the prevention, detection, and management of human New World screwworm myiasis in Mexico and Central America. Eligible sources included peer-reviewed case reports, case series, observational studies, reviews, clinical trial protocols, national and international guidelines, technical reports, theses, dissertations, and other forms of grey literature addressing human New World screwworm myiasis or its surveillance and management. Publications in English, Spanish, and Portuguese were considered. The geographical scope covered North, Central, and South America, as well as the Caribbean. Single case reports and case series were eligible and were retained when they described human myiasis caused by or attributed to C. hominivorax. We excluded publications not related to the Americas, animal-only studies unrelated to human or zoonotic surveillance, and ineligible publication types such as editorials, commentaries, or other documents that did not provide extractable human clinical, epidemiological, surveillance, or management data (11, 12).

We developed a multi-layered and topic-specific search strategy to ensure comprehensive coverage of the literature. The full search strategies, search dates, and number of retrieved records for each source are provided as supplementary material. For guidelines, protocols, and technical documents, we searched PubMed/MEDLINE, EMBASE, LILACS, Epistemonikos, Google Scholar, La Referencia, and OpenAlex. We used combinations of controlled vocabulary and free-text terms in English, Spanish, and Portuguese related to screwworm myiasis, including Cochliomyia hominivorax, Cochliomyia americana, Callitroga americana, gusano barrenador, mosca barrenadora, bicheira, and miíase, together with terms such as guideline, protocol, manejo, lineamiento, recommendation, and consensus. For human clinical and epidemiological evidence, we made complementary searches in the same databases using screwworm- and myiasis-related terms combined with pharmacological and therapeutic keywords, including ivermectin, doramectin, nitrofurazone, antiparasitic agents, larvicides, as well as surgery, case series, and clinical trials. Clinical trial registries, including the ICTRP Search Portal, ClinicalTrials.gov, ReBEC, and the EU Clinical Trials Register, were also consulted, although no relevant ongoing or completed studies were identified. All searches were conducted between September 10 2025 and February 19 2026.

All records were imported into Rayyan, a web-based systematic review management platform, for title and abstract screening; duplicates were removed before screening. Two reviewers independently screened titles and abstracts, retrieved full texts for potentially eligible reports, and resolved disagreements by consensus or, when necessary, consultation with a third reviewer. No automation tools were used to determine study eligibility or to automatically exclude records during the screening process. Data were charted using a standardized and piloted extraction form. Extracted variables included year of publication, country, study design, population, interventions or thematic focus, main findings, issuing institution, funding source, and institutional affiliation. For guidelines and protocols, the scope, target population, issuing authority, and main recommendations were recorded; for registered trials, the sponsor, status, sample size, and intervention were extracted. For grey literature, metadata were extracted and standardized when available from the source record or institutional website, including title, issuing institution, publication year or date, document type, country or region, and URL.

We conducted descriptive analyses to characterize publication trends, geographic distribution, study characteristics, and institutional involvement. In parallel, we carried out a structured mapping of public health agencies, academic institutions, veterinary and parasitology laboratories, and surveillance networks relevant to screwworm myiasis. We extracted funding sources and collaborative networks from acknowledgements, funding statements, and institutional reports. Findings were synthesized narratively, with descriptive statistics used to summarize study characteristics, institutional involvement, and bibliometric indicators. Tables and figures were prepared to summarize the results, and particular attention was given to evidence published in Spanish and Portuguese because of its relevance in endemic settings. Gaps and uncertainties, including the scarcity of clinical trials and the limited availability of standardized clinical guidelines, were explicitly noted. Given the predominantly descriptive nature of the evidence base, the review was intended to map reported patterns rather than estimate incidence, prevalence, or population-level risk.

RESULTS

The scoping review identified a predominantly descriptive body of literature. Overall, 2 332 records were identified through database searches. After removal of 319 duplicate records, 2 013 records were screened by title and abstract, of which 1 882 were excluded. Of 131 reports sought for retrieval, all were assessed for full-text eligibility. Of these, 56 were excluded: 18 were not related to C. hominivorax, six were animal studies, and 32 were ineligible publications or study types, including editorials, commentaries, or other non-eligible documents. Thus, 75 studies were included in the review. The study-selection process is shown in Figure 1.

FIGURE 1. Identification of new studies via databases and registers.

Source: Prepared by authors based search results.

The available evidence on New World screwworm myiasis in humans consisted mainly of case reports and small case series, with fewer retrospective or observational datasets and limited review-based evidence. The largest registry-based dataset was from Ecuador and reported 2 187 registered cases, while the largest hospital-based or observational series included 84 pediatric patients in Ecuador, 83 patients in Paraguay, 63 hospitalized children in Uruguay, and 24 patients treated in public hospitals in Recife, Brazil (13–20). The 75 included studies were published between 1979 and 2024, with only a small number of reports published before 2000. This time distribution should be interpreted in light of the search strategy, which relied primarily on electronically indexed records and may therefore have captured more recent publications. Across studies, the evidence base was methodologically heterogeneous and mostly descriptive. We therefore did not estimate the total number of unique patients across all publications, because overlap among case reports, case series, observational studies, and reviews could not be excluded (13–20). Instead, we summarized the time distribution of the published evidence and the main clinical and epidemiological patterns reported in the studies.

Published reports originated mostly from Latin America, including Argentina, Brazil, Chile, Colombia, Costa Rica, Ecuador, Mexico, Paraguay, Peru, Uruguay, and Venezuela (Bolivarian Republic of), as well as French Guiana. This distribution reflects the geographic origin of the available published literature and should not be interpreted as a measure of disease frequency or geographic burden (14–16, 21–52). Identified reports frequently involved socially and clinically vulnerable individuals, including children, older adults, neurologically impaired or bedridden patients, individuals with poor hygiene or social abandonment, and patients with chronic wounds, malignancy, tracheostomies, or prolonged immobilization (16–20, 23, 26, 28, 31, 37, 43, 53–56). Rarely, health-care-associated exposure was described, including infestation of a tracheostomy wound in a comatose hospitalized patient; in that report, oviposition was attributed to flies entering through open, unscreened hospital windows (53). More broadly, dependence on caregivers, impaired self-care, and prolonged exposure of wounds or body cavities were recurrent circumstances associated with infestation. However, in reports involving institutional settings it was often not clear if the infestation was present before admission or if exposure occurred within the health-care environment (16–19, 23, 26, 28, 53, 54, 56).

Clinical involvement was differed anatomically. Oral and maxillofacial disease was among the most frequently described type, while cutaneous and wound-associated disease was also common. Otic, nasal, orbital, ophthalmic, rhino-orbital, and cervical presentations were repeatedly documented. Less frequent but clinically relevant localizations included vulvar, uterine, and intestinal involvement (20–25, 28, 30–32, 35, 36, 39–41, 44–46, 49, 50, 54–68). Clinical and social conditions recurrently described across reports included neurological impairment, intellectual disability, cerebral palsy, chronic hypoxic brain injury, stroke-related dependency, poor caregiver support, poverty, poor hygiene, homelessness, abandonment, chronic dermatoses, pediculosis, diabetes, vascular insufficiency, malignancy, tracheostomy, and traumatic or postsurgical wounds (14, 16–20, 22, 23, 27, 31, 33, 35, 37, 42, 43, 46, 54–56, 58, 63, 64, 69–71). The main anatomical sites, vulnerability contexts, and management patterns identified in the literature are summarized in Table 1.

TABLE 1. Human myiasis caused by Cochliomyia hominivorax: anatomical sites, vulnerability contexts, and management patterns.

Domain/categorya	Number of studies (study design)	Main clinical context	Main management approaches reported	References
Anatomical distribution
Oral and upper aerodigestive tract involvement (oral cavity, gingivomaxillary region, palate, sublingual area, oropharynx, mixed oronasal presentations)	1. (CR 10, CS 3, mixed 1)	Reported in patients with neurological impairment, prolonged mouth opening, poor oral hygiene, dependence on caregivers, trauma, or tracheostomy	Mechanical larval extraction, saline or antiseptic irrigation, surgical debridement when required, and adjunct ivermectin (oral or subcutaneous in selected cases); antibiotics added when super-infection suspected	20. 23, 28, 31, 32, 40, 46, 51, 55, 56, 58, 62, 65, 72
Cutaneous and wound-associated disease (scalp, limbs, feet, abdominal wounds, breast, umbilicus, chronic or traumatic wounds)	1. (CR 12; CS 2; Obs 2)	Reported in patients with poor hygiene, chronic wounds, dermatoses, pediculosis, diabetes, vascular disease, malignancy, or social neglect	Mechanical removal, local cleaning, occlusive or asphyxiating measures in selected cases, surgical wound debridement, oral ivermectin in some reports, and systemic antibiotics when bacterial superinfection or extensive tissue injury present	18. 19, 22, 27, 37, 38, 42, 43, 54, 70, 71, 73–77
Otic, nasal, orbital, and cervicofacial cavity involvement	1. (CR 10; CS 1; mixed 1)	Clinically important because of the reported risk of deep extension, tissue destruction, secondary infection, and functional loss	Manual extraction, irrigation or topical/local antiparasitic measures, debridement, and oral or topical ivermectin; enucleation or more extensive surgery occasionally required for severe orbital or rhino-orbital disease	21. 24, 25, 30, 36, 39, 41, 44, 57, 59, 64, 66
Genitourinary and other uncommon sites (vulvar, penile, intestinal)	3 (CR 3)	Reported in patients with neglected local conditions or severe comorbidity	Mechanical extraction, local cleaning, ivermectin in selected cases, antibiotics when indicated, and definitive surgery in advanced genitourinary disease	45. 63, 76
Vulnerability contexts
Neurological impairment, disability, dependency, or frailty	1. (CR 7; Obs 2; mixed 1)	Reported in patients with intellectual disability, cerebral palsy, chronic hypoxic brain injury, stroke-related dependency, senility, and poor caregiver support	Management was site-specific and included larval extraction and local wound care; reports also emphasized caregiver support, hygiene, and prevention of prolonged wound exposure or delayed recognition	14. 16, 19, 23, 27, 31, 35, 46, 56, 58
Poverty, social neglect, poor hygiene, and rural exposure	1. (CR 6; CS 1; Obs 3)	Reported background conditions included poverty, social neglect, poor hygiene, rural exposure, delayed access to care, and chronic wound neglect	Prevention-oriented measures, wound care, hygiene support, and early recognition	16. 17, 19, 33, 42, 54, 55, 58, 63, 71
Chronic wounds and underlying medical disease	1. (CR 5; CS 4; Obs 3; mixed 1)	Chronic dermatoses, pediculosis, diabetes, vascular insufficiency, malignancy, tracheostomy, and traumatic or postsurgical wounds	Management often combined extraction, debridement, antimicrobial therapy, and adjunct ivermectin depending on site and severity	16–18, 20, 22, 27, 33, 37, 43, 54, 64, 69, 70
Management patterns
Mechanical extraction and local wound care	2. (CR 15; CS 4; Obs 5; mixed 2)	Reported across multiple anatomical sites	Removal with forceps, irrigation with saline or antiseptic solutions, cleaning, and wound reassessment	14–25, 28, 31, 37, 43, 46, 47, 51, 54, 59, 62–64, 74, 78
Ivermectin as adjunct antiparasitic therapy	1. (CR 8; CS 5; Obs 4; mixed 2)	Reported in oral, cutaneous, nasal, orbital, otic, and complex wound disease	Reported ivermectin routes included oral, topical, subcutaneous, and local administration; ivermectin usually used in addition to extraction rather than as isolated therapy	14–16, 18–21, 24, 25, 28, 37, 40, 46, 47, 53, 64, 65, 78, 79
Surgical debridement or major procedures in severe disease	7 (CR 4; CS 2; Obs 1)	Reported in deep cavitary disease, malignant wounds, orbital/rhinoorbital involvement, or necrotic lesions	Surgical debridement, endoscopic extraction, enucleation, and, in extreme cases, amputation in advanced presentations	17. 25, 59, 63, 64, 74, 78
Antibiotic therapy for superinfection or extensive tissue injury	1. (CR 8; CS 5; Obs 4)	Co-administered when bacterial superinfection, necrosis, postoperative contamination, or malignant wounds present	Clindamycin, gentamicin, amoxicillin/clavulanate, ceftriaxone, oxacillin, cefazolin, levofloxacin, ciprofloxacin, and metronidazole	15–18, 23, 24, 28, 33, 37, 43, 46, 54, 58, 63, 64, 69, 78

CR, single-case report; CS, case series or multiple-case report; Obs, observational or retrospective study; mixed, case report or case series with literature review.

^aCategories are not mutually exclusive, and individual publications may contribute to more than one domain.

Source: Prepared by authors based on study findings.

Management was centered on prompt mechanical extraction of larvae and local wound care, with escalation to surgical treatment when deeper anatomical extension, tissue necrosis, or involvement of critical structures was present (14–25, 28, 31, 37, 43, 46, 47, 51, 54, 59, 62–64, 74, 78). Ivermectin was the most frequently reported antiparasitic agent used (through oral, topical or subcutaneous, administration), generally as an adjunct rather than a stand-alone intervention (14–16, 18–21, 24, 25, 28, 37, 40, 43, 46, 47, 53, 64–65, 78, 79). No robust comparative treatment studies were identified (14–25, 28, 31, 33, 37, 40, 43, 46, 47, 51, 53, 54, 58, 62–65, 69, 74, 78, 79). Antibiotics were commonly co-administered when bacterial superinfection, extensive tissue injury, malignant wounds, or postoperative contamination were suspected (15–18, 23, 24, 28, 33, 37, 43, 46, 54, 58, 63, 64, 69, 78). The search of national ministries, regional agencies, and international organizations identified a heterogeneous set of normative and technical documents related to New World screwworm in humans (67, 80–89). Only a limited number of open-access national guidance documents were retrieved that directly addressed human surveillance and/or clinical management, notably those from Costa Rica, El Salvador, Honduras, and Mexico (84–88). Across these documents, there was broad agreement on larval extraction, notification, and intersectoral coordination, but less consistency in therapeutic recommendations. Honduras explicitly recommended oral ivermectin for human cases, Mexico mentioned ivermectin as an optional adjunct in selected cases while emphasizing limited evidence and off-label use, and El Salvador did not include ivermectin in its human treatment recommendations (85, 86, 88). Belize required notification of suspected human cases but did not provide clinical management recommendations, while Argentina and Brazil had broader regulatory, laboratory, veterinary, or institutional resources rather than open-access national clinical guidelines specifically focused on human New World screwworm myiasis (84–88). The main national and regional guidance documents, institutional actors, and operational content identified in the review are summarized in Table 2.

TABLE 2. National and regional guidance, institutional actors, and operational content related to Cochliomyia hominivorax.

Country or region	Guidelines or protocols identified (human unless stated)	Key guidance content on human disease	Institutions and agencies	Networks and initiatives
Belize	Agricultural health regulations addressing screwworm myiasis, 2024 (84)	Regulatory and notification-focused; mandatory reporting of suspected human cases; no clinical management recommendations on human disease identified; no ivermectin guidance	Belize Agricultural Health Authority	Regional co-ordination (OIRSA; SE-COMISCA)
Honduras	National guidelines for epidemiological surveillance, clinical management, and prevention of human myiasis caused by screwworm, 2024 (85)	Human surveillance and clinical management; case definition provided; mandatory notification; manual extraction and debridement recommended; wound care, tetanus assessment, and antibiotics when indicated; oral ivermectin explicitly recommended	Ministry of Health; SAG–SENASA; IHIMV	FETP-FL-OH; SE-COMISCA; OIRSA
El Salva-dor	Technical guideline for comprehensive care of myiasis in humans, 2025 (86)	Human clinical care and epidemiological investigation; case definition provided; mandatory notification; complete manual/surgical removal recommended; antisepsis, topical/systemic antibiotics, tetanus assessment, and follow-up measures included; ivermectin not included in human treatment recommendations.	Ministry of Health	SE-COMISCA; SICA
Costa Ri-ca	National surveillance guideline for myiasis in humans, 2024 (87)	Primarily surveillance-oriented; human case detection and notification emphasized; limited clinical treatment detail; no clear ivermectin recommendation identified	Ministry of Health	SE-COMISCA; OIRSA; FETP
Mexico	Standard operating procedures for epidemiological surveillance of human myiasis due to C. hominivorax, 2024–2025 (88, 89)	Human surveillance plus clinical management elements; case definition provided; mandatory notification; manual/surgical extraction, irrigation, antisepsis, debridement, and antibiotics addressed; ivermectin mentioned as an optional adjunct in selected cases, with explicit caution about limited evidence and off-label use	Ministry of Health; CENETEC; SENASICA; COFEPRIS	Regional co-ordination; IAEA and FAO sterile insect technique
Argentina	Technical and regulatory resources available; no single openaccess national clinical guideline dedicated to C. hominivorax	No open-access disease-specific human clinical guideline identified	Ministry of Health; SENASA; ANLIS–Malbrán; ANMAT	REDSUR (South American Field Epidemiology Training Program Network); regional cooperation
Brazil	Practical dermatology guidance including myiasis management, 2024 (90); no single open-access national human clinical guideline specifically dedicated to C. hominivorax identified.	General myiasis/dermatology guidance and procedural management available, but no open-access national human guideline specifically dedicated to C. hominivorax identified	Ministry of Health; ANVISA; MAPA; LACEN; SBMT; universities	National public health laboratory network (LACEN); regional initiatives
Panama–USA	Binational operational framework for eradication and prevention through sterile insect technique (80)	Population control and eradication framework; not a human clinical management guideline.	Ministry of Health (Panama); USDA/APHIS	COPEG (sterile fly production, release, and barrier maintenance)
Guatemala	National clinical management guideline for human myiasis caused by screwworm 2025 (91)	Human clinical management and ministerial communication addressing human cases; specific therapeutic recommendations were not summarized because the full text of both documents was not available for verification in the materials reviewed.	Ministry of Public Health and Social Assistance	SE-COMISCA; OIRSA
Nicaragua, Dominican Republic	No open-access national human guidelines identified	No open-access human-focused guidance identified	National ministries of health	SE-COMISCA; OIRSA
Regional (Central America)	No regional human clinical guideline; coordination or technical resources availa-ble	Coordination, surveillance support and technical exchange; no unified regional human clinical management guideline identified	SE-COMISCA; OIRSA; PAHO	Regional webinars; FETP and RedSURFETP; IAEA sterile insect technique
Global (WOAH, IAEA, FAO)	WOAH notification standards; IAEA sterile insect technique technical documentation; FAO coordination frameworks	Animal health notification, vector control, and technical cooperation; no human clinical treatment guidelines.	WOAH; IAEA; FAO; USDA/APHIS	International surveillance; sterile insect technique programs

ANLIS–Malbrán, Administración Nacional de Laboratorios e Institutos de Salud “Dr. Carlos G. Malbrán”; ANMAT, Administración Nacional de Medicamentos, Alimentos y Tecnología Médica; ANVISA, Agência Nacional de Vigilância Sanitária; CDC, Centers for Disease Control and Prevention; CENETEC, Centro Nacional de Excelencia Tecnológica en Salud; COFEPRIS, Comisión Federal para la Pro-tección contra Riesgos Sanitarios; COPEG, Comisión Panamá–Estados Unidos para la Erradicación y Prevención del Gusano Barrenador del Ganado; FAO, Food and Agriculture Organization of the United Nations; FETP, Field Epidemiology Training Program; FETP-FL-OH, Frontline Field Epidemiology Training Pro-gram–One Health; IAEA, International Atomic Energy Agency; IICA, Inter-American Institute for Cooperation on Agriculture; IHIMV, Instituto Hondureño de Investigaciones Médico Veterinarias; LACEN, Laboratórios Centrais de Saúde Pública; MAPA, Ministério da Agricultura e Pecuária; OIRSA, Organismo Internacional Regional de Sanidad Agropecuaria; PAHO, Pan American Health Organization; SAG–SENASA, Secretaría de Agricultura y Ganadería–Servicio Nacional de Sanidad e Inocuidad Agroalimentaria; SBMT, Sociedade Brasileira de Medicina Tropical; SE-COMISCA, Secretaría Ejecutiva del Consejo de Ministros de Salud de Centroamérica y República Dominicana; SENASA, Servicio Nacional de Sanidad y Calidad Agroalimentaria; SENASICA, Servicio Nacional de Sanidad, Inocuidad y Calidad Agroalimentaria; SICA, Sistema de la Integración Centroamericana; USDA/APHIS, United States Department of Agriculture/Animal and Plant Health Inspection Service; WOAH, World Organisation for Animal Health.

Source: Prepared by authors based on study findings.

The institutional bodies relevant to New World screwworm in the Americas included ministries of health, animal health authorities, laboratory networks, regulatory agencies, regional coordination bodies, and academic institutions. At the national level, Costa Rica, El Salvador, Honduras, and Mexico have guidance on human New World screwworm myiasis or operational documents, while Argentina and Brazil have primarily laboratory, regulatory, and institutional structures. At the regional level, the Executive Secretariat of the Council of Ministers of Health of Central America and the Dominican Republic (SE-COMISCA), the Regional International Organization for Plant and Animal Health (OIRSA), the Panama-United States Commission for the Eradication and Prevention of Screw-worm (COPEG), the Pan American Health Organization (PAHO), the Field Epidemiology Training Program (FETP) networks, and the International Atomic Energy Agency (IAEA) technical cooperation had visible roles in surveillance, cross-border coordination, or vector control activities (67, 80–89).

DISCUSSION

Response to the re-emergence and northward spread of New World screwworm across the Americas, particularly in Central America and Mexico, is difficult because evidence on the human disease is sparse, fragmented, and mostly descriptive. Although the current outbreak has revived attention to the public health relevance of human infestation, the literature identified in this review consisted mainly of case reports, small case series, and a limited number of observational datasets, with substantial heterogeneity in design, reporting, and clinical detail. This limits direct comparison across settings and estimation of the true burden of disease, and reduces confidence in inferences about management and outcomes (13–20). As shown in Figure 1, only 75 studies met the eligibility criteria for inclusion, underscoring the lack of human-focused evidence when contrasted with the scale of the current regional resurgence of the human disease.

Despite these limitations, several recurrent patterns were identified in the literature. Reports frequently included socially and medically vulnerable individuals, including children, older adults, neurologically impaired or bedridden patients, and people with chronic wounds, tracheostomies, malignancy, poor hygiene, or limited caregiver support. However, because the underlying source populations and appropriate comparison groups were generally unavailable, these findings cannot establish that these groups are at increased population-level risk. Their apparent overrepresentation may also reflect publication, referral, or health-care-access biases. Nevertheless, the recurrence of these contexts across reports highlights their relevance for clinical recognition, wound assessment, and surveillance (Table 1) (16–25, 28, 30–32, 35–37, 39–46, 49–50, 53–68, 71, 74, 76).

The literature on treatment was similarly limited in methodological strength but consistent in general approach. Across reports, management centered on prompt mechanical extraction of larvae, local cleaning or irrigation, and surgical debridement when deeper invasion, necrosis, or involvement of critical structures was present. Ivermectin was the most frequently reported antiparasitic agent and was administered by multiple routes, usually as an adjunct rather than stand-alone therapy. Antibiotics were commonly added when bacterial superinfection or extensive tissue injury was suspected. However, no robust comparative studies were identified and the apparent effectiveness of ivermectin should therefore be interpreted as practice-based and descriptive rather than as comparative evidence of efficacy (14–25, 28, 31, 33, 37, 40, 43, 46–47, 51, 53, 54, 58, 62–65, 69, 74, 78, 79). This distinction is particularly important because some national documents mention pharmacologic therapy, yet the underlying evidence in humans remains observational and heterogeneous.

An important contribution of this review is the identification of a fragmented but active normative and institutional landscape for dealing with human New World screwworm in the region. As summarized in Table 2, only a limited number of open-access national documents directly addressed human case surveillance and/or clinical management, notably those from Costa Rica, El Salvador, Honduras, and Mexico, while documents from Belize focused on notification and regulatory control and those from Argentina and Brazil contributed broader regulatory, veterinary, laboratory, or institutional resources rather than disease-specific open-access clinical guidance for the human disease (84–88). Across the available national documents, there was broad convergence on immediate larval extraction, notification, and intersectoral coordination. However, there was less consistency in clinical detail and especially in recommendations on ivermectin. Honduras’ guidance explicitly recommended oral ivermectin, Mexico’s guidance mentioned it as an optional adjunct in selected cases while highlighting the limited evidence and off-label nature of its use, and El Salvador’s guidance did not include ivermectin in its treatment recommendations for humans (85, 86, 88). Case definitions, reporting pathways, and therapeutic detail were also not fully standardized across countries. Taken together, these findings suggest that the region already has the institutional basis for response, but not yet a harmonized public health framework for management of human New World screwworm.

These findings have important public health implications. Under conditions of renewed spread, delayed recognition or underreporting of human infestation may persist if case definitions are inconsistent, notification pathways remain unclear, or frontline clinicians have limited familiarity with the condition. The regional picture supports prioritizing interoperable surveillance and notification systems, clearer reporting responsibilities, and stronger coordination between clinical services, laboratories, animal health authorities, wildlife management authorities, and public health institutions. Within the One Health framework, existing structures such as the Panama-United States Commission for the Eradication and Prevention of Screw-worm (COPEG), the Executive Secretariat of the Council of Ministers of Health of Central America and the Dominican Republic (SE-COMISCA), the Regional International Organization for Plant and Animal Health (OIRSA), and the Field Epidemiology Training Program (FETP) networks, and PAHO technical cooperation provide a practical foundation for harmonization and preparedness rather than requiring the creation of entirely new parallel mechanisms (67, 80–89).

Several gaps should shape the research agenda. The absence of standardized outcome definitions, the scarcity of multicenter prospective human studies, and the lack of comparative therapeutic evaluations remain major limitations. Diagnostic research should assess integrated morphological and molecular approaches, as well as remote and digital tools that may help accelerate recognition and reporting in settings with limited entomologic expertise (6). A pragmatic next step would be the development of multicenter human case registries using a minimum common dataset, including a standard case definition, demographic characteristics, occupation, relevant risk factors, anatomical site of infestation, management, and outcomes. Such registries could produce analyzable cohorts and provide a more reliable basis for future comparative or interventional research (1, 2, 6–8).

This review has several strengths. It used a multilingual search strategy, including peer-reviewed and grey literature, and integrated clinical evidence with mapping of national guidance, institutional actors, and regional operational structures. At the same time, it has important limitations. The underlying evidence was overwhelmingly descriptive, reporting was inconsistent across studies, duplication of patients across reports could not be excluded, and the epidemiological and normative context is evolving rapidly. In addition, the absence of population denominators and comparison groups prevented estimation of incidence, prevalence, or relative risk, and the prominence of unusual or severe cases in the literature may have introduced publication and referral bias. Because the search was based on electronic bibliographic databases, trial registries, and electronically accessible grey-literature sources, older publications, locally archived reports, or non-indexed documents not available online may have been underrepresented. These limitations do not weaken the importance of the findings; rather, they highlight that decisions are currently being made with incomplete and uneven evidence, making transparent synthesis and regional coordination especially important.

Overall, the current evidence related to human disease supports a coordinated One Health response centered on earlier recognition, standardized notification, integrated surveillance across animal and human health sectors, and harmonization of public health guidance across affected and at-risk countries. The available literature does not yet support high-certainty conclusions on adjunct pharmacological treatment, but it does identify recurrent clinical patterns, vulnerable populations, and operational priorities that can inform preparedness and response while the human evidence base continues to mature.

Data availability:

Data available upon request from Fernando Tortosa (tortosafer@paho.org).

Declaration of artificial intelligence (AI) use:

During preparation of the revised manuscript, the authors used ChatGPT (OpenAI) to support English-language editing. The tool was not used to generate data, conduct statistical analyses, interpret results, or draw scientific conclusions. All AI-assisted outputs were reviewed, edited, and approved by the authors, who take full responsibility for the content of the manuscript.

Disclaimer:

The authors hold sole responsibility for the views expressed in the manuscript, which may not necessarily reflect the opinion or policy of the Revista Panamericana de Salud Pública / Pan American Journal of Public Health and/or those of the Pan American Health Organization and the World Health Organization.