Abstract
Background:
Laboratory-acquired infections (LAIs) with Plasmodium species are uncommon but represent a documented occupational hazard in insectaries, research laboratories, and clinical diagnostic settings. As malaria research expands, understanding historical and contemporary laboratory exposures is important for biosafety practice.
Methods:
We reviewed published reports of laboratory-acquired malaria, including a historical series summarized by Herwaldt (1920–1990) and confirmed cases identified through the ABSA International LAI Database and national surveillance reports (1968–2012). Cases were analyzed to assess the species involved, exposure mechanisms, clinical outcomes, and biosafety implications.
Results:
Approximately 38 laboratory-acquired malaria cases have been reported, although the exact number is difficult to determine due to overlapping reporting. Infections involved Plasmodium falciparum, P. vivax, and P. cynomolgi. Vector-borne transmission from experimentally infected Anopheles mosquitoes accounted for most cases; however, parenteral and non-intact skin exposures to parasitized blood also resulted in infection. All reported cases were symptomatic. A minority of P. falciparum infections were severe, although no fatalities were documented in the reviewed series. The median incubation period following nonvector exposure was ∼12.5 days.
Conclusions:
Laboratory-acquired malaria remains a preventable occupational risk. Effective mitigation requires integrated vector containment, sharps safety, appropriate personal protective equipment, engineering controls, medical surveillance, and a strong institutional biosafety culture in both insectary and in vitro research environments.
Introduction
Biosafety is an important component of responsible laboratory practice, especially in research that can pose serious risks to human health. Effective biosafety programs protect laboratory staff, prevent accidental pathogen release, and maintain public trust in diagnostic processes and biomedical research.1,2 Vector-borne diseases, such as malaria, tend to be more common among individuals whose occupations place them in contact with or in close proximity to disease vectors outside their home environment. 3 Although malaria is mainly transmitted through the bite of infected mosquitoes in community settings, work with Plasmodium species in the laboratory presents unique risks, including exposure to infected vectors and parasitized blood.4,5 The occurrence of malaria arising from laboratory-acquired infections (LAIs) underscores the importance of strict biosafety and biocontainment protocols, adherence to standard operating procedures (SOPs), the use of appropriate personal protective equipment (PPE), and medical surveillance.6,7 As malaria research covers areas such as routine diagnostics and research into vector biology, drug resistance, and in vitro parasite culture, applying stringent biosafety principles in laboratory activities is essential to safeguard staff.
Documented Malaria LAI Cases and Exposure Mechanisms
Laboratory-acquired malaria infections have been documented for decades, involving both vector-borne and blood-stage exposures. 5 A comprehensive review summarized 34 cases of malaria LAIs reported between the 1920 and the 1990. 5 The cases included 15 of P. falciparum, 10 of P. cynomolgi, which is primarily associated with nonhuman primate research, and 9 of P. vivax. 5 Additional historical reports and surveillance summaries further support the occurrence of laboratory-acquired malaria in both research and diagnostic settings. These cases were documented across the United States, Europe, New Zealand, and Asia, with vector-borne transmission in 55.9%, parenteral exposure in 29.4%, and exposure through nonintact skin in 14.7%. 5 All 34 cases were symptomatic, with two P. falciparum infections classified as severe, showing signs consistent with cerebral malaria, although no fatalities were reported. The median incubation period for nonvector exposures was ∼12.5 days (range = 4–17 days), highlighting that both mosquito-mediated and direct blood-stage exposures can cause clinically significant infections in laboratory settings. 5
Building on this historical overview, recent case reports and surveillance summaries, including data from the ABSA International LAI Database (https://my.absa.org/LAI) and national reports, document eight confirmed malaria LAI cases in the UK and the United States from 1968 to 2012, involving P. falciparum and P. vivax, which most likely overlaps some of the cases reported in the 2001 review due to a lack of LAI case detail. Druilhe et al. 8 described two accidental human infections with Plasmodium cynomolgi bastianelli, linked to primate malaria research, highlighting the zoonotic risks of experimental work involving nonhuman primate Plasmodium species. Surveillance summaries from the United States also documented laboratory-associated malaria cases during the 1990s, including reports of an entomologist infected on two separate occasions over a 2-year period through insectary-associated exposures.9,10 An unusual transmission event involving P. falciparum was also reported in Bordeaux, France, 11 emphasizing that atypical occupational or laboratory-associated exposures can occur even in non-endemic settings.
Approximately 38 laboratory-acquired or occupationally acquired malaria infections have been reported in the literature, although the precise total remains uncertain because several historical reviews and surveillance summaries likely contain overlapping cases. Most of these cases were associated with insectary activities and handling of experimentally infected Anopheles mosquitoes (vector-borne transmission). Fewer cases resulted from percutaneous or other blood exposures, such as a documented sharps injury during blood-film preparation (Table 1). All documented cases resulted in clinical illness consistent with malaria but were successfully treated. Therapeutic regimens included chloroquine, primaquine for P. vivax hypnozoites, and mefloquine for P. falciparum, including multidrug-resistant strains.1,14 No fatalities were reported among the identified cases (Table 1). In several instances, molecular confirmation demonstrated that the infecting strain was identical to the strain under study.16,17 No documented cases were identified for laboratories performing in vitro Plasmodium culture. The main exposure mechanisms identified across reported malaria LAI cases are summarized in Table 2.
Summary of documented laboratory-acquired malaria infections
Identified exposure mechanisms in laboratory-acquired malaria cases
Risk Factors and Risk Mitigation Strategies in Insectary Settings
Risk Factors Associated with Insectory Settings
Laboratory-acquired malaria risk is influenced by a combination of engineering, procedural, and organizational factors, which are summarized in Table 3. Engineering controls and facility design are central to mitigating the risk of malaria LAI; however, gaps in structural barriers, suboptimal containment infrastructure, or inconsistent implementation of arthropod containment measures (e.g., screened insectaries, double-door entry systems, or ultraviolet/light traps) may permit mosquito escape and uncontrolled exposure.2,18 Operational risks are further amplified by routine insectary procedures, including handling and dissection of infected mosquitoes, membrane blood feeding, cage transfer, and the movement of mosquitoes between feeding, incubation, and dissection containers, all of which increase the opportunities for unnoticed exposure.5,14 Additional vulnerabilities arise during storage of infected mosquitoes, particularly for small species, which can escape through fine mesh or inadequately sealed containers, as well as during disposal, transport, and shipment of infectious materials. These risks are compounded by limitations in laboratory practices, including inadequate technical proficiency, poor hazard awareness, inconsistent use of PPE, unrestricted access, lack of biohazard signage, and insufficient traceability of activities, all of which increase the likelihood of procedural errors and unrecognized exposure.2,7 Although less frequent, percutaneous injuries during diagnostic procedures represent a direct route for blood-stage infection. 13 In addition, insufficient decontamination and waste management practices may allow persistence of infectious material, indirectly contributing to exposure risk. Organizational factors, including limited occupational health surveillance, low awareness of malaria symptoms, and absence of structured reporting pathways, may delay diagnosis and contribute to underrecognition of LAIs. 2 Finally, the continuous presence of infected mosquito colonies represents a persistent source of exposure, and inadequate emergency preparedness and response systems may delay or limit effective containment following breaches. The relative likelihood and severity of these exposure pathways are summarized in Table 4.
Contributing risk factors associated with malaria insectary activities
PPE, personal protective equipment.
Relative risk characterization of laboratory-acquired malaria
Likelihood reflects relative frequency in reported laboratory-acquired infection cases.
Recommended Control Measures for Insectory Settings
Insectary primary and secondary biocontainment
Key control measures for mitigating laboratory-acquired malaria risk are summarized in Table 5 and align with six core elements of laboratory worker protection identified across historical LAI cases: vector containment, sharps safety, PPE, engineering controls, medical surveillance, and biosafety culture. Insectaries housing Anopheles mosquitoes infected with human Plasmodium species require stringent arthropod-containment measures to prevent accidental mosquito escapes and protect laboratory personnel. These facilities typically operate under Arthropod Containment Level 2 (ACL-2) or enhanced ACL-2 conditions18,19 (Table 6), depending on the institutional and local risk assessments. Core engineering controls include secure double-door entry systems, sealed penetrations, insect-proof screening, and controlled access. Unlike arboviral work, aerosol transmission is not relevant for malaria; therefore, containment measures focus on preventing infected mosquitoes from escaping. Experimentally infected mosquito colonies should be physically segregated from noninfected colonies, with dedicated containment areas where feasible. All cages, containers, and handling systems must be clearly labeled and identifiable to ensure that the infection status of any escaped vectors can be rapidly determined, supporting timely risk assessment and response.
Control measures for mitigation of laboratory-acquired malaria risk
SOPs, standard operating procedures.
Table adapted from Kim Le and Blacksell. 20
Administrative controls
Administrative controls reinforce engineering safeguards. Facilities should implement comprehensive SOPs and ensure staff proficiency for mosquito handling, cage transfers, and the manipulation of infected vectors. Routine containment inspections and documented maintenance schedules are critical. Clear incident response procedures should be established and rehearsed. Structured medical surveillance programs and rapid referral pathways should be in place to ensure timely evaluation of potentially exposed personnel. Regular staff training on recognizing malaria symptoms and expectations for reporting is essential to reduce diagnostic delays. Accordingly, personnel must adhere to strict operational protocols, including the use of appropriate PPE, compliance with cage-transfer procedures, and documentation of escape-response plans. Effective waste management and decontamination practices are also essential components of insectary biosafety (Table 5).
Incident management
Immediate assessment of febrile illness in personnel working with infected mosquitoes should be standard practice. Facilities should ensure access to swift diagnostic testing and suitable antimalarial treatment. In certain high-risk situations, chemoprophylaxis may be considered in line with institutional policy and occupational health advice. In the event of suspected or confirmed mosquito escape, immediate containment measures should include active recapture or killing of escaped mosquitoes (e.g., using aspirators or approved insecticides), prompt notification of all personnel in the vicinity, and implementation of bystander awareness and medical surveillance procedures, including symptom monitoring and rapid access to diagnostic evaluation for potentially exposed individuals.
Personal protective equipment
Insufficient PPE, especially exposed skin, provides opportunities for unnoticed mosquito bites. Appropriate PPE acts as an additional barrier against vector exposure. Long-sleeve clothing and closed footwear should be standard in insectary environments housing infected mosquitoes. Gloves are advised, with consideration for double-gloving during dissections or high-risk procedures. Head coverings may be suitable depending on the facility’s risk assessment. In certain settings, insect-bite-resistant garments could be considered to further reduce exposure risk.
Percutaneous Transmission of Plasmodium
Percutaneous transmission was documented in at least one case, 13 where a clinical laboratory worker sustained a sharps injury while preparing a blood film from a sample later confirmed positive for P. falciparum.
Risk Factors Associated with Percutaneous Transmission of Plasmodium
This case highlights the potential risk of direct erythrocytic-stage cells during diagnostic procedures. Unlike mosquito-borne infection, percutaneous inoculation introduces blood-stage parasites rather than sporozoites and therefore does not initiate hepatic-stage infection or hypnozoite formation in P. vivax or P. ovale. 21 This distinction has important implications for post-exposure management and relapse risk, as hypnozoites arise exclusively following sporozoite-mediated liver invasion.
In Vitro Cultivation of Plasmodium
In addition to insectary-based research, significant laboratory work on malaria relies on the in vitro cultivation of Plasmodium parasites, particularly the continuous culture of P. falciparum. Short-term culture of other species, including P. vivax, is also conducted in specialized laboratories. This has been fundamental to studies of parasite biology, drug susceptibility, and resistance mechanisms since continuous culture methods were developed in the 1970. 22 Contemporary malaria research programs, including those at the Mahidol Oxford Tropical Medicine Research Unit (MORU) in Bangkok, have advanced the use of in vitro culture systems to study antimalarial pharmacodynamics, parasite clearance, host–parasite interactions, and emerging drug resistance. MORU researchers have made significant contributions to laboratory and translational studies examining parasite growth features, in vitro susceptibility testing, and the link between laboratory phenotypes and clinical outcomes in malaria. These activities involve handling parasitized human erythrocytes, often at varying parasitemia levels and in large volumes, thereby exposing workers to infectious blood-stage parasites. Although these culture systems are vital for scientific progress, they involve routine handling of parasitized human erythrocytes and therefore demand strict adherence to blood-handling precautions, sharps safety, biocontainment practices, and occupational health protocols to reduce the risk of LAIs.
Risk Factors Associated with In Vitro Plasmodium Culture
Risk factors associated with in vitro Plasmodium culture include handling high-parasitemia samples, manipulating large volumes of infected blood, performing slide preparations or injection procedures with sharps, and working without adequate splash protection. Although Plasmodium species are not classified as bloodborne pathogens (e.g., HIV or hepatitis viruses), the mechanics of occupational exposure are similar. Preventive measures should follow similar principles of blood containment and sharps safety. Clinical illness from blood-stage laboratory exposure may develop within days to weeks, especially in infections caused by P. falciparum, which poses a risk of severe disease if left untreated. However, prompt recognition and appropriate antimalarial treatment are highly effective, and documented cases have shown favorable outcomes when diagnosis is timely.
Recommended Control Measures for In Vitro Culture of Plasmodium
Primary containment
Specific biosafety guidance for laboratory work with Plasmodium remains limited; however, Payne 4 provided early recommendations for in vivo and in vitro malaria research. All manipulations involving parasitized blood should be conducted within a certified Class II biological safety cabinet to minimize splashes and environmental contamination. 23 In the event of a spill inside the cabinet, the area should remain undisturbed to allow aerosols to settle before applying a disinfectant, followed by careful surface decontamination using absorbent material and appropriate chemical agents. 23 Centrifuge buckets and sealed rotors should also be routinely disinfected after use, particularly if tube breakage is suspected.
Safety-engineered sharps, sealed centrifuge systems, and clear standard operating procedures for blood handling and disposal are essential.
PPE and administrative controls
Appropriate PPE, such as laboratory coats or gowns, gloves (considering double-gloving during higher-risk procedures), and eye or face protection during splash-prone tasks, provides additional barriers against exposure. Administrative measures should include structured protocols for exposure reporting, pathways for occupational health consultation, and staff training on bloodborne exposure precautions.
Decontamination and Disinfection for Plasmodium in Laboratory and Insectary Settings
Effective decontamination and disinfection procedures are crucial parts of biosafety practice in laboratories working with Plasmodium species, whether in insectary settings or during in vitro cultivation of blood-stage parasites. Although Plasmodium parasites are relatively fragile outside their natural host, strict adherence to validated decontamination protocols is necessary to reduce the risk of occupational exposure from contaminated surfaces, sharps, or laboratory equipment. General laboratory biosafety guidance recommends that organisms transmitted through blood exposure be handled using standard chemical disinfection and sterilization procedures suitable for bloodborne pathogens.2,4,23
Chemical Disinfection
Blood-stage Plasmodium parasites maintained within human erythrocytes are readily inactivated by commonly used hospital-grade disinfectants. Freshly prepared sodium hypochlorite solutions (typically 0.1–0.5% available chlorine) are widely recommended for surface decontamination following spills of parasitized blood, with a minimum contact time of ∼10 min to ensure efficacy.2,4,23 Higher concentrations (e.g., 0.5–1%) may be used for gross contamination involving visible blood. Alcohol-based disinfectants (e.g., 70% ethanol) are effective on small, clean surfaces. Still, they are less suitable for large-volume blood spills, where the protein load may reduce disinfectant activity. 24 Phenolic compounds and other hospital-grade disinfectants are appropriate when used in accordance with manufacturer instructions and established biosafety guidance.2,4,24 Liquid waste containing parasitized blood should be chemically disinfected before disposal in accordance with institutional and local regulatory guidelines.
In insectary settings, additional decontamination considerations apply. While Plasmodium parasites do not persist in the environment without a vertebrate host, infected mosquito carcasses, dissected tissues, and associated materials should be treated as potentially infectious waste and autoclaved or chemically disinfected before disposal. There is also a risk that live infected mosquitoes may be inadvertently retained in containers (e.g., cups or holding vessels) and escape during handling or disposal if not carefully checked. Work surfaces used for mosquito dissections should be cleaned with an appropriate disinfectant after each session, consistent with general laboratory biosafety recommendations. 2
Autoclaving
Autoclaving (121°C, 15 psi, ≥15–30 min depending on load size) remains the preferred method for decontamination of solid waste contaminated with Plasmodium, including culture materials, disposable plasticware, and sharps containers.2,4,23
Discussion
Laboratory-acquired malaria remains a rare but well-documented and preventable occupational hazard in both insectary and in vitro research settings. The documented cases over more than four decades show that even well-equipped facilities with a multicomponent biocontainment framework are not immune to risk. Furthermore, the potential introduction of vectors capable of sustaining local transmission is also an important consideration. As malaria research expands, particularly in areas such as vector biology, drug resistance, and parasite culture, biosafety protocols must continue to evolve. Continuous vigilance, ongoing training, effective engineering controls, strict adherence to procedural standards, and proactive occupational health monitoring are vital to reduce exposure.
Arthropod Containment Level 2 (ACL-2) and enhanced ACL-2 conditions provide a structured framework for working with infected mosquitoes, but they have inherent limitations when applied to malaria research involving Anopheles spp. ACL-2 provides a structured containment framework for arthropods infected with pathogens requiring containment beyond standard laboratory practices, with specific measures to determine through risk assessment. It relies heavily on physical barriers, procedural controls, and operator compliance rather than complete containment. Unlike high-containment laboratory systems, ACL-2 facilities do not require fully sealed environments or redundant containment layers, and effectiveness depends on the integrity of screening, door systems, and routine practices, all of which are vulnerable to small breaches, wear, or human error. Historical malaria LAI cases demonstrate that infections can occur despite the presence of established containment measures, often due to unnoticed mosquito escape or unrecognized bites during routine handling or dissection.5,17 Furthermore, ACL-2 guidance places substantial emphasis on administrative controls and training, yet variability in implementation, documentation, and enforcement across institutions can lead to inconsistent protection levels, particularly in resource-limited settings.2,25 Additional challenges arise from the biological characteristics of Anopheles mosquitoes, including their small size, flight capacity, and ability to escape through minor structural gaps or during routine cage manipulation, which are not fully mitigated by standard ACL-2 design features. Moreover, ACL-2 does not specifically address the cumulative risk associated with high-density infected mosquito colonies or frequent manipulation of vectors, which may increase exposure probability over time. These limitations highlight that, while ACL-2 provides an essential baseline for containment, it should be complemented by enhanced engineering controls, rigorous operational practices, and a strong biosafety culture to reduce the residual risk of malaria LAIs.2,5,18
However, distinguishing occupational (i.e., laboratory-acquired) from community-acquired malaria infection in high-transmission settings is inherently challenging, as background exposure to infected mosquitoes is common and often indistinguishable clinically from laboratory exposure. In such contexts, febrile illness among laboratory or insectary staff may be presumed to reflect community transmission unless there is a clear exposure incident or molecular linkage to a laboratory strain, potentially leading to underrecognition of LAIs. This contrasts with low-transmission or nonendemic settings, where malaria in laboratory personnel is more readily attributed to occupational exposure. The likelihood of exposure in endemic settings may be similar or even higher in laboratory environments due to concentrated handling of infected vectors or parasitized blood, yet biosafety practices and occupational surveillance may be variably implemented. A similar challenge has been described for tuberculosis, where distinguishing occupational from community transmission among health care and laboratory workers is difficult in high-burden settings, and underestimation of occupational risk is well recognized. These considerations suggest that malaria LAIs may be substantially underreported in endemic regions and highlight the importance of strengthening occupational health surveillance, molecular epidemiology, and systematic reporting frameworks to better define risk.2,26–29
Ultimately, preventing malaria LAIs depends on implementing a comprehensive and integrated biosafety framework built around six core elements of worker protection: effective vector containment, sharps safety, appropriate PPE, engineering controls, occupational health and medical surveillance, and a strong institutional biosafety culture. While each element independently reduces exposure risk, the reviewed cases demonstrate that failures in any single component may compromise overall protection. Accordingly, effective malaria biosafety programs require the coordinated application of these measures across both insectary and in vitro laboratory environments. Maintaining this integrated and proactive approach will be crucial to ensuring that progress in malaria research does not compromise laboratory worker safety.
Authors’ Contributions
S.D.B.: Conceptualization, methodology, supervision, writing—original draft, writing—review and editing, and funding acquisition. S.D.: Conceptualization, methodology, investigation, data curation, writing—original draft, and writing—review and editing. V.C.: Methodology and writing—review and editing. K.C.: Writing—review and editing. A.D.: Supervision and Writing—review and editing.
Footnotes
Acknowledgments
The authors would like to acknowledge the enduring influence of the late Prof. Sir Nicholas White, whose contributions to tropical medicine, in particular malaria, in Southeast Asia and beyond were profound. His research, mentorship, and unwavering commitment to advancing science in the region have shaped both the field and the many individuals who continue this work today.
Authors’ Disclosure Statement
The authors declare that the research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.
Funding Information
This research was funded in whole or in part by the Wellcome Trust (315982/Z/24/Z). For the purpose of open access, the author has applied a CC BY public copyright license to any Author Accepted Article version arising from this submission. The Shoklo Malaria Research Unit is part of the Mahidol-Oxford Tropical Medicine Research Unit, supported by Wellcome, UK.