Key Points
Question
What lesions from yellow-legged hornets, other than stings, have been reported to French poison control centers in France?
Findings
A retrospective series of 29 cases of yellow-legged hornet ocular exposure, excluding stings in the eye, from French poison control centers found that the exposure was reported to be likely associated with the projection of a liquid by the hornet. Most patients reported a favorable outcome; 2 developed keratitis and another 2 presented with neuropathic pain, presumably associated with the projection of the hornet's liquid.
Meaning
These findings suggest liquid projections from yellow-legged hornets can cause eye damage, warranting attempts at prevention.
This case series describes ocular lesions occurring after exposure to a liquid projection emitted by a hornet (excluding stings in the eye).
Abstract
Importance
Since the accidental introduction of the yellow-legged hornet (Vespa velutina nigrithorax) in France in 2004, there have been reports of this insect unexpectedly projecting a liquid toward the human face, but ocular morbidity associated with this is unknown, to our knowledge.
Objective
To describe a case series of ocular lesions after exposure to a liquid projection emitted by a hornet.
Design, Setting, and Participants
This was an analysis of all cases of ocular exposure to a projection by a yellow-legged hornet (excluding stings in the eye) collected by French poison control centers between January 1, 2004, and December 31, 2019.
Main Outcomes and Measures
Symptoms were evaluated, and a fluorescein eye stain test was used.
Results
Twenty-nine cases were recorded (24 in male and 5 in female patients; median age, 40 [interquartile range, 11] years); the first occurred in 2009. Most cases (20 [80%]) were occupational exposure among professionals dealing with hornet nests (eg, firefighters, wasp exterminators). Symptoms consistent with conjunctivitis often resolved quickly after ocular decontamination, but 5 patients developed a periorbital edema, 2 experienced radiating neuropathic pain, and 2 experienced keratitis.
Conclusions and Relevance
These findings suggest that the projection of a liquid into the eyes by the yellow-legged hornet presents a new risk to human health, but its precise nature remains to be determined. Ocular lesions had a favorable outcome. For professionals who deal with these insects, adaptation of the usual protections designed for native hymenopterans may be warranted.
Introduction
Ocular injuries from hymenopterans (bees, wasps, ants, and sawflies) are usually associated with corneal stings. Complications threaten sight via different mechanisms (eg, venom toxicity, foreign-body reaction, infection, immunological reaction).1 To date, liquid projection from any hymenopterous insect is not a known cause of ocular injury.
Commonly referred to as the Asian hornet, the yellow-legged hornet Vespa velutina nigrithorax (eFigure 1 in the Supplement) was introduced from China to southwestern France around 2004.2 It is not very aggressive toward humans and attacks only when it feels threatened.3 Similar to the European hornet (Vespa crabro), it may be responsible for severe medical complications, but typically only in cases of multiple stings or anaphylaxis.4,5
Over the past decade, French poison control centers (PCCs) have received several unusual calls about patients experiencing ocular symptoms associated with the yellow-legged hornet without having been stung. To our knowledge, this particular behavior of V velutina and its clinical consequences have not yet been reported. This study aimed to describe the characteristics and outcomes of yellow-legged hornet ocular projections recorded by French PCCs.
Methods
All cases of exposure to xenobiotics collected by France’s 8 PCCs are registered anonymously in the French National Database of Poisonings (FNDP; French Ministry of Health). The FNDP’s use in this study was authorized by the French data protection authorities. Considering the anonymity of exposure cases registered in the FNDP, the patients’ informed consent was waived in agreement with French law.
We carried out a retrospective study to analyze all ocular exposure cases caused by the yellow-legged hornet (excluding stings in the eyes) collected in the FNDP between January 1, 2004 (the estimated year the yellow-legged hornet appeared in France), and December 31, 2019. V velutina was identified based on the affected individual’s description during a telephone call to the PCC.3 A clinical toxicologist (H.L.-C.) reviewed all cases and collected data. This investigation was designed in 2019, and data collection and analyses were conducted between January 2020 and May 2020. Excel version 2016 (Microsoft) was used for all analyses.
Results
The FNDP presented 29 ocular exposure cases (in 24 male and 5 female individuals; median age, 40 [interquartile range, 11] years) reported to be likely associated with a yellow-legged hornet, excluding stings in the eye (Table). These cases represent 5.6% of all accidental exposure to the yellow-legged hornet cases recorded in the FNDP during the same period (516 cases). There was 1 case per year in 2009, 2010, 2012, and 2013, 3 to 4 cases per year between 2014 and 2017, 8 in 2018, and 2 in 2019 (eFigures 2 and 3 in the Supplement).
Table. Characteristics of Ocular Lesion Cases Following a Yellow-Legged Hornet (Vespa velutina nigrithorax) Projectiona.
| No. | Exposure date, mo and y | Region of France | Age, decades | Circumstancesb | Medical consultation | Fluorescein eye stain test result | Symptoms | Outcome |
|---|---|---|---|---|---|---|---|---|
| 1 | October 2009 | SW | 50s | Professional | Yes | NA | ERP | Recovery in 48 h |
| 2 | October 2010 | SW | 50s | Professional | Yes | Normal | ERP | Recovery in 24 h |
| 3 | July 2012 | SW | 50s | Nonprofessional | No | NA | ERP | Recovery in a few h |
| 4 | August 2013 | SW | 20s | Professional | Yes | Normal | ERP | Lost to follow-up |
| 5 | July 2014 | SW | 50s | Nonprofessional | Yes | NA | ERP and PE | Lost to follow-up |
| 6 | November 2014 | SW | 40s | Professional | Yes | Normal | ERP | Recovery on day 7 |
| 7 | November 2014 | SW | 20s | Professional | Yes | NA | ERP | Recovery in 18 h |
| 8 | November 2014 | W | 40s | Nonprofessional | No | NA | ERP | Recovery in 5 h |
| 9 | June 2015 | CNE | Adult | Nonprofessional | No | NA | ERP and rhinitis | Recovery in 48 h |
| 10 | July 2015 | W | 50s | Professional | Yes | NA | ERP and PE | Persistent periorbital edema on day 6 |
| 11 | October 2015 | W | 30s | Professional | Yes | Normal | ERP | Improvement of symptoms in 48 h |
| 12 | November 2015 | W | 20s | Professional | Yes | Normal | ERP and PE | Recovery on day 7 |
| 13 | October 2016 | SW | 40s | Professional | Yes | Corneal lesions | ERP and BV | Recovery in 24 h |
| 14 | October 2016 | SW | 30s | Professional | Yes | Normal | ERP and radiating pain | Recovery in 17 h |
| 15 | October 2016 | SE | 40s | Professional | NA | NA | ERP | Lost to follow-up |
| 16 | September 2017 | W | 30s | Professional | Yes | Normal | ERP | Improvement of symptoms in 24 h |
| 17 | October 2017 | CNE | Adult | Professional | NA | NA | ERP and BV | Lost to follow-up |
| 18 | October 2017 | SW | 30s | Professional | NA | NA | ERP and PE | Lost to follow-up |
| 19 | October 2017 | SW | 50s | Professional | Yes | Corneal lesions | ERP and BV | Recovery on day 3 |
| 20 | July 2018 | W | 40s | Professional | No | NA | ERP | Improvement of symptoms after 90 min |
| 21 | August 2018 | CNE | Adolescent | Nonprofessional | Yes | Normal | ERP and PE | Recovery on day 5 |
| 22 | August 2018 | CNE | 20s | Professional | Yes | Normal | ERP | Recovery in 24 h |
| 23 | September 2018 | CNE | 40s | Nonprofessional | Yes | NA | ERP | Recovery in 12 h |
| 24 | September 2018 | SE | 30s | Nonprofessional | NA | NA | ERP | Lost to follow-up |
| 25 | September 2018 | SE | 40s | Professional | NA | NA | ERP | Lost to follow-up |
| 26 | September 2018 | SW | 40s | Professional | No | NA | ERP | Recovery after decontamination |
| 27 | October 2018 | SE | 30s | Professional | Yes | Normal | ERP | Lost to follow-up |
| 28 | April 2019 | CNE | 30s | Nonprofessional | Yes | Normal | ERP and radiating pain | Hemicranial pain for 20 d |
| 29 | August 2019 | W | 30s | Nonprofessional | Yes | NA | ERP | Recovery after decontamination |
Abbreviations: BV, blurred vision; CNE, center, north, and east; ERP, eye redness and pain; NA, not applicable; PE, periorbital edema; SE, southeast; SW, southwest; W, west.
The cohort included 24 male and 5 female individuals.
Professional exposures occurred in 11 firefighters, 5 wasp exterminators, 2 communal employees, and 2 others in unspecified employment. Nonprofessional exposures included 3 in a garden, 3 in a house, and 3 in unspecified locations.
Circumstances of Exposure
About two-thirds of cases (n = 20) involved professionals dealing with nests, mostly firefighters and wasp exterminators, who were wearing the usual protective clothing, including a woven mesh in front of the face. The remaining individuals (n = 9) were exposed while they were trying to squash and/or succeeding in squashing a yellow-legged hornet, resting outdoors, or gardening. Two patients wore eyeglasses (to improve visual acuity) that had slipped because of head movements.
Symptoms
All patients experienced immediate unilateral eye redness and pain. In addition, rhinitis, blurred vision, and periorbital edema were reported in 1, 3, and 5 patients, respectively. Two patients reported having persistent radiating pains from the affected eye to the ipsilateral hemicranium although other ocular symptoms had resolved. Two patients had a history of anaphylaxis to the European hornet but developed no allergic manifestation during their call to the PCC (ie, after 60 minutes and 90 minutes in the 2 separate cases).
Outcome
Eight patients were lost to follow-up. Nineteen patients visited a physician. Among 13 fluorescein eye stain tests performed, 2 revealed corneal lesions. Ocular symptoms resolved quickly, usually within a few hours of decontamination with water or saline solution, or sometimes after a few days of usual symptomatic treatment. One patient reported a persistent periorbital edema on day 6, and 1 presented with hemicranial neuropathic pain for 20 days.
Discussion
French PCCs recorded a series of 29 cases of ocular symptoms presumably associated with the projection from a yellow-legged hornet, which were associated with minor injuries and favorable outcomes. After immediate ocular irritation characterized by eye redness and pain, symptoms normally resolved quickly. However, 2 patients experienced keratitis and 2 others experienced neuropathic pain. No allergic reaction was observed in this series.
The yellow-legged hornet has a surprising ability to project liquid,6 which was commonly thought to be venom; however, there are no scientific data on its nature or anatomic origin. Indeed, like all Vespidae species, the yellow-legged hornet attempts to sting or exude venom from its stinger if it feels threatened. Moreover, individuals can use sting venom volatiles as an alarm pheromone to attract multiple hornets for an attack.7 The venom’s composition could explain the symptoms observed in these cases. Nearly 300 putative toxins have been identified in V velutina venom, some of which could be involved as metalloproteases in corneal damage.8 Others are neurotoxins, which could explain the prolonged neuropathic pain observed in 2 patients in this cohort.4 However, because the venom gland’s volume is largely less than the volume of liquid projected (ie, the venom reservoir is about 1 mm in length),9 this liquid might originate from the intestinal tract, with or without venom.
Moreover, the projection mechanism is also unexplained; it may be voluntary or a reflex during flight. This phenomenon has also been observed in other hymenoptera species, such as ants,10 or coleoptera species, such as carabid beetles,11 which project a liquid containing formic acid. This projection occurs when the insect feels threatened. However, to our knowledge, this behavior has not been observed in Vespidae species. One hypothesis is that insects with a sting present venom without formic acid and use different behavior for defense (sting vs liquid projection). Our findings in V velutina could indicate defense behaviors, stinging, and liquid projection. In addition, in the domestic setting, exposures occurred mainly when killing the insect; in these cases, the projection could be a result of being threatened or a mechanical effect of abdomen compression from crushing the insect.
When dealing with a yellow-legged hornet nest, professionals appear to be at risk of being sprayed in the face; wearing a mesh over the face is insufficient protection. In fact, this risk could be increased by the mesh if hornets indeed release their venom when stinging the mesh. Wearing safety glasses is highly recommended. Our case series suggests that wearing eyeglasses is ineffective protection. Therefore, prompt ocular decontamination with water or saline solution is strongly suggested in cases of ocular exposure.
Limitations
Our data are limited by the retrospective design of the study. Data on matters, such as ophthalmological examination, treatments, and outcome, that are routinely documented in the database, are not exhaustive. Considering the voluntary report of cases to PCCs, selection bias prevented calculation of a risk estimate. Further studies are necessary to investigate this health concern and understand the risk. Confirmatory studies could consist of a prospective collection of cases treated in emergencies or by ophthalmologists in areas where V velutina is widespread.
Conclusions
This original case series suggests that the yellow-legged hornet V velutina can extrude and project an unidentified liquid in the eyes, causing ocular lesions. Periorbital edema, neuropathic pain, and keratitis were reported, which had favorable outcomes. This study highlights a new occupational risk for professionals dealing with yellow-legged hornet nests, warranting attempts at prevention.
eFigure 1. A Vespa velutina nigrithorax (Yellow-Legged Hornet).
eFigure 2. Geographic Evolution of the Cases.
eFigure 3. Temporal Evolution of the Cases
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
eFigure 1. A Vespa velutina nigrithorax (Yellow-Legged Hornet).
eFigure 2. Geographic Evolution of the Cases.
eFigure 3. Temporal Evolution of the Cases