Abstract
We evaluated the safety, optimal dose, and preliminary effectiveness of a new-approach Africanized honeybee (Apis mellifera) Antivenom (AAV) in a phase I/II, multicenter, non-randomized, single-arm clinical trial involving 20 participants with multiple stings. Participants received 2 to 10 vials of AAV depending on the number of stings they suffered, or a predefined adjuvant, symptomatic, and complementary treatment. The primary safety endpoint was the occurrence of early adverse reactions within the first 24 h of treatment. Preliminary efficacy based on clinical evolution, including laboratory findings, was assessed at baseline and at various time points over the four following weeks. ELISA assays and mass spectrometry were used to estimate venom pharmacokinetics before, during, and after treatment. Twenty adult participants, i.e., 13 (65%) men and 7 (35%) women, with a median age of 44 years and a mean body surface area of 1.92 m2 (median = 1.93 m2) were recruited. The number of stings ranged from 7 to > 2,000, with a median of 52.5. Symptoms of envenoming were classified as mild, moderate, or severe in 80% (16), 15% (3), and 5% (1) of patients, respectively; patients with mild, moderate, or severe envenoming received 2, 6, and 10 vials of AAV as per the protocol. None of the patients had late reactions (serum sickness) within 30 d of treatment. There was no discontinuation of the protocol due to adverse events, and there were no serious adverse events. One patient had a moderate adverse event, transient itchy skin, and erythroderma. All participants completed the intravenous antivenom infusion within 2 h, and there was no loss to follow-up after discharge. ELISA assays showed venom (melittin and PLA2) concentrations varying between 0.25 and 1.479 ng/mL prior to treatment. Venom levels decreased in all patients during the hospitalization period. Surprisingly, in nine cases (45%), despite clinical recovery and the absence of symptoms, venom levels increased again during outpatient care 10 d after discharge. Mass spectrometry showed melittin in eight participants, 30 d after treatment. Considering the promising safety results for this investigational product in the treatment of massive Africanized honeybee attack, and its efficacy, reflected in the clinical improvements and corresponding immediate decrease in blood venom levels, the AAV has shown to be safe for human use. Clinical Trial Registration: UTN: U1111-1160-7011, identifier [RBR-3fthf8].
Introduction
In 1956, African honeybees of the subspecies, Apis mellifera scutellata, were introduced from Tanganyika and South Africa to Brazil because they were more productive and resistant to pests (). They incidentally escaped and crossed with the existing European bees of the subspecies, Apis mellifera mellifera, resulting in an Africanized hybrid. These presented marked defensive and swarming capacities, and easily adapted to different climates and environments. In addition, these capacities made it possible for them to expand throughout Brazil and several other countries in the Western Hemisphere, including the United States (–). When threatened, these honeybees massively attack the target; consequently, the number of accidents involving humans and animals has increased (, , ).
Bee venom is composed of a complex mixture of biogenic amines, proteins, enzymes, and peptides. Among these are proteins of low allergenic importance and intense pharmacological action such as melittin, phospholipase A2, apamine, hyaluronidase, and several low molecular weight peptides, which constitute approximately 50–60%, 11–12%, 3%, 1–2%, and 1% of the gross weight, respectively, and water, and mineral salts.
Melittin and phospholipase A2 are the two most toxic components of the bee venom and may act synergistically to induce a variety of pathophysiological effects (–).
Envenoming by venomous snakes is a serious public health problem in tropical countries and is one of the most neglected health problems according to the World Health Organization’s (WHO) classification (, ). Health effects become more serious when the envenoming is caused by the injection of fairly large amounts of venom, such as that caused by the bites of adult specimens of Bothrops jararaca. Similarly, A. mellifera attacks massively, and thousands of bees can inject up to half a gram of venom. The expansion of Africanized honeybees (AHB) throughout the Americas (, , 13), and consequently, the severity of the accidents they provoke, led health authorities to classify such accidents as objects of health surveillance in Brazil (Figure 1) ().
Figure 1
These accidents show different magnitudes of clinical manifestation depending mainly on the number of stings and the individual’s sensitivity. The most frequent accident is that involving individuals not sensitized to the venom, affected by a few stings. In these cases, the clinical presentation is limited to a local inflammatory reaction, which manifests as erythematous papules, pain, and heat. In most cases, this situation is resolved without medical intervention. Another clinical form is that involving individuals sensitized to one or more components of the venom; they exhibit an immediate type I hypersensitivity reaction, as defined by Coombs and Gell (
The third presentation is that caused by multiple stings occurring when an individual is attacked by a swarm of honeybees. Here, a large amount of venom is inoculated, usually caused by hundreds or thousands of honeybees (
Laboratory findings change rapidly and the blood cell count may show leukocytosis with neutrophilia and a staggered leftward shift, and type I urinalysis usually reveals proteinuria, glycosuria, and the presence of heme pigments. Serum urea and creatinine levels may increase due to kidney damage. Levels of CK and aspartate aminotransferase (AST) are usually elevated due to severe rhabdomyolysis. Alanine aminotransferase (ALT) levels may increase over time, indicating liver failure. Finally, levels of acute-phase proteins, including the C-reactive protein (CRP) and fibrinogen, are usually altered, indicating a severe systemic inflammatory response syndrome (
Until recently, the treatment of patients who suffered from both smaller and larger numbers of stings was symptomatic and relied on antihistamines, corticosteroids, and even epinephrine in case of anaphylactic shock. The search for a specific treatment based on heterologous antivenoms has been a challenge for many researchers (
This clinical study was performed to assess the safety, establish the optimal minimum dose, and evaluate the preliminary effectiveness of the novel Apilic Antivenom (AAV).
Patients and Methods
Ethical Approval and Consent to Participate
The clinical protocol was approved by the Brazilian National Commission on Ethics in Research (CONEP, Certificate of Presentation of Ethical Appreciation No. 19006813.4.1001.5411, v7, approved on 06/07/2016), and the Brazilian National Health Surveillance Agency (ANVISA), which approved the Apis Study on 02/05/2016; No. 0907532142; Proc. No. 25361611582201493. This trial RBR-3FTHF8 was registered in 2015 in the Brazilian Clinical Trials Registry (ReBEC) (
Study Design
This was a phase I/II, multicenter, non-randomized, single-arm clinical trial study, involving 20 AHB multiple-sting participants treated with the new Apilic Antivenom “batch 155804 R” (Figure 2), performed from 08/22/2016 to 07/27/2018, in which 1 mL of AAV neutralized 1.25 mg of whole honeybee venom (
Figure 2

New Apilic Antivenom.
Outcomes
The primary endpoints were to assess the safety of AAV, based on the occurrence of adverse events, in participants exposed to multiple Africanized honeybees’ stings, and to estimate the proportion of participants showing improvements with respect to their initial clinical state, by monitoring symptoms and laboratory test results.
The secondary endpoint was to determine the correlation between the number of stings and the severity of the initial clinical presentation using the AHB score, adapted for this envenoming, based on APACHE II (
In addition, an exploratory endpoint was included in the study to estimate the pharmacokinetic profile of the AHB venom using ELISA tests carried out on blood samples collected at different time points (before AVV administration and 2, 6, 12, and 24 h after AAV administration). Furthermore, we aimed to assess the acute-phase reaction profile of AAV, by monitoring variations in C-reactive protein (CRP) and fibrinogen levels.
Inclusion, Exclusion, and Discontinuation Criteria
All participants who presenting with AHB stings were screened for eligibility by the clinical staff (Table 1). People aged over 18 years were eligible to receive AAV with respect to the number of stings, as described below. Each participant or his/her relative signed the FICF. Supplementary Video 1 - Stringer Video shows the procedure for removing the sting of Africanized bees in one of the patients.
Table 1
| Inclusion | Exclusion | Discontinuation |
|---|---|---|
| Participants over 18 years of age of both sexes | Participants who had a previous adverse reaction to heterologous serum produced in horses. | Developing anaphylactic shock resistant to the management protocol for reactions of acute hypersensitivities. |
| Participants admitted to the hospital after an accident with AHB | Participants who are pregnant or nursing | Withdrawing from the terms of free and informed consent form (FICF) |
| Participants or a responsible relative who signs informed consent (FICF) to receive the antivenom. | – | – |
Inclusion, exclusion, and discontinuation criteria.
Antivenom Doses and Adjuvant Treatments
Before treatment, height in centimeters (cm), body weight in kilograms (kg), body mass index in Kg/m2; and body surface area in square meters (m2) were measured, as described by Madden and Smith (
Up to 5 stings: Specific treatment with AAV was not indicated. Here, only adjuvant, symptomatic, and complementary treatments were administered.
Between 5 and 200 stings: Two vials (20 mL) of AAV;
Between 201 and 600 stings: Six vials (60 mL) of AAV;
Above 600 stings: Ten vials (100 mL) of AAV.
The adjuvant, symptomatic, and complementary treatments were described and published in detail by Barbosa et al. (
Criteria for Measuring the Severity and Clinical Outcomes in the Participants
An AHB score was assigned based on APACHE II, which is a validated system for classifying disease severity (
AHB Score Proposed for Clinical and Laboratory Assessments
-Age > 60 years: Score 1
-Body mass index > 30 kg/m2: Score 1
-Time elapsed between the accident and medical care (over 24 hours): Score 1
-Number of stings
5–200 stings: Score 1
201–600 stings: Score 2
More than 600 stings: Score 3
-Hemodynamic disorders (tachycardia, arterial hypotension, shock): Score 1
-Respiratory disorders (bradypnea, bronchospasm, wheezing, and/or dyspnea): Score 1
-Neurological disorders (mental confusion and/or intense headache): Score 1
-Acute kidney injury (anuria and/or oliguria): Score 1
-Increased CK levels: Score 1
-Increased ALT levels: Score 1
-Increased creatinine levels: Score 1
-Increased CRP levels: Score 1
-Increased fibrinogen levels: Score 1
-Increased leukocyte levels: Score 1
-Decreased platelet count: Score 1
Subsidiary and Strategic Laboratory Tests
Laboratory tests (CK, ALT, creatinine, CRP, fibrinogen, leukocytes, and platelets) were used to assess safety parameters before treatment (hospital admission), on the day of discharge, and at follow-up (10, 20, and 30 d after discharge from the hospital). All procedures and protocols for laboratory tests are presented in Data Sheet 1-Tables-1-2 (
Classification of Early and Late Adverse Reactions to Antivenom
Adverse reactions to AAV were defined as mild, moderate, or severe based on the international classification of anaphylactic reactions described in Table 2 (
Table 2
| Mild | Moderate | Severe |
|---|---|---|
| Facial edema | Abdominal pain | Drowsiness or altered consciousness |
| Pruritus | Nausea | Systolic BP < 80 mm Hg |
| Urticaria | Vomiting | Cyanosis |
| Fever | Bronchospasm | Confusion |
| Rigor | Stridor | Shock |
Classification of acute adverse reactions to antivenoms (
ELISA Assays for the Estimation of Venom Pharmacokinetics
F(ab’)2-type immunoglobulin fractions prepared from the blood of hyperimmunized horses against melittin and PLA2, found in the venom of A. mellifera [Anti-melittin F(ab’)2, and Anti-PLA2 F(ab’)2], were obtained from the AAV using a modified version of the single affinity chromatographic step described by Chávez-Olórtegui et al. (
Crude venom (32 mg) from A. mellifera was immobilized with 3 g of CNBr-Sepharose resin and prepared according to the manufacturer’s instructions (Cytiva GE Healthcare Life Sciences - USA) for the aforementioned affinity chromatography assay. Anti-melittin F(ab’)2 and Anti-PLA2 F(ab’)2 were conjugated to peroxidase (HRP - Sigma) according to the method described by Nakane and Kawoi (
Then, an ELISA assay was performed to quantify the melittin and PLA2 fractions in the blood of participants by the method described by Bucaretchi et al. (
Mass Spectrometry Analyses
The participants’ sera (50 µL) were added to 5% DMSO, 0.1% acetic acid (50 µL), and vortexed for 30 min. Then, the solution was centrifuged for 3 min at 3000 × g. The supernatant was collected for further processing. Purified melittin from crude A. mellifera venom (
Samples were analyzed by liquid chromatography-tandem mass spectrometry in an ESI-IT-TOF instrument coupled to a UFLC 20A Prominence (Shimadzu, Kyoto, Japan). Samples (15 μL) were injected into a C18 column (Kinetex C18 2.6 µm 100 Å, 100 × 4.6 mm), and analyzed using a binary gradient, employing the following solvents: (A) water:DMSO:acetic acid (949:50:1) and (B) ACN:DMSO:water:acetic acid (850:50:99:1). Optimal detection conditions for melittin were achieved at an elution gradient of 25–50% B for 20 min at a constant flow of 0.7 mL.min-1, after initial isocratic elution for 5 min. Eluates were monitored using a Shimadzu SPD-M20A PDA detector (Shimadzu, Kyoto, Japan) before being injected into the mass spectrometer.
The interface was maintained at 4.5 kV and 275°C. The detection voltage was 1.95 kV, and fragmentation was induced using argon collision, with 55 ‘energy’ parameters. MS spectra were acquired in positive mode in the 700–730 m/z range, and MS/MS spectra were obtained in the 50–1400 m/z range, according to the previous optimization with purified melittin. The m/z ion, 712.15 (M+4H+), was selected for fragmentation, and the [y13]2+ ion (811.95, the tallest peak) was monitored at MS2 (Data Sheet 2 - Figures 1-5).
Statistical Analysis
Statistical analyses, and the choice comparison tests used among the research participants, were carried out with respect to presuppositions determined by the results, characteristics, and course of the variables in the study. Binomial variables were compared using the chi-squared and Fisher’s exact tests. Numerical values were compared using the Student’s t-test or the Mann–Whitney U test. Statistical analyses of the pharmacokinetic assays were performed using the GraphPad Prism software version 8.3.0, with differences considered to be statistically significant when p < 0.05. The results obtained were compared using the ANOVA test for repeated measures, followed by Tukey’s test. The data are represented as the mean ± standard error of the mean (
Results
Description of Participants
Twenty participants were included, i.e., 13 males (65%) and 7 females (35%). Participants’ ages varied between 22 and 77 years, with a median age of 44 years. Nineteen patients were white-skinned, and one was brown-skinned. Sixteen of them were from the Botucatu region (SP) and four from Tubarão (SC). The number of stings varied from 7 to more than 2,000. The number of vials of AAV administered, based on the clinical protocol, was as follows: mild cases (two vials), 16 participants; moderate cases (six vials), 3 participants; and severe cases (10 vials), 1 participant. The time elapsed between the accident and the clinical care varied as follows: less than 24 h, 5 cases; 1 d, 5 cases; and between 2 and 6 d, 8 cases. One participant was attended 10 and another 19 days after the accident (Table 3).
Table 3
| Protocol number | Age | Sex | Clinical care location | Occupation | Estimated number of stings | Number of antivenom vials | Time between accident and clinical care |
|---|---|---|---|---|---|---|---|
| 00101 | 32 | F | Botucatu | B | 400 | 6 | 3 |
| 00102 | 32 | M | Botucatu | B | 40 | 2 | 10 |
| 00103 | 38 | M | Botucatu | A | 10 | 2 | 0 |
| 00105 | 23 | M | Botucatu | A | 16 | 2 | 0 |
| 00106 | 30 | F | Botucatu | A | 10 | 2 | 2 |
| 00107 | 54 | F | Botucatu | A | 150 | 2 | 1 |
| 00108 | 52 | M | Botucatu | A | 500 | 6 | 19 |
| 00109 | 49 | M | Botucatu | A | 55 | 2 | 2 |
| 00110 | 46 | M | Botucatu | A | 165 | 2 | 2 |
| 00111 | 30 | F | Botucatu | A | 10 | 2 | 4 |
| 00112 | 50 | F | Botucatu | B | 30 | 2 | 4 |
| 00113 | 42 | F | Botucatu | B | 50 | 2 | 4 |
| 00114 | 36 | M | Botucatu | A | 500 | 6 | 1 |
| 00115 | 61 | M | Botucatu | B | 100 | 2 | 1 |
| 00116 | 34 | M | Botucatu | A | 180 | 2 | 1 |
| 00117 | 46 | M | Botucatu | A | 2000 | 10 | 6 |
| 00301 | 61 | M | Tubarão | A | 20 | 2 | 0 |
| 00302 | 77 | M | Tubarão | A | 150 | 2 | 0 |
| 00303 | 22 | M | Tubarão | A | 7 | 2 | 1 |
| 00304 | 66 | F | Tubarão | A | 50 | 2 | 0 |
Description of participants; study protocol number, age, sex, clinical care location, occupation, the estimated number of stings, number of AVV vials administered, and the time elapsed between the accident and medical care in days.
M, male; F, female; HCFMB, Hospital of Clinics at Botucatu Medical School (UNESP). HNSC, Nossa Senhora da Conceição Hospital at Southern Santa Catarina University (UNISUL), Tubarão (SC); Occupation: A – occupation not related to agricultural or wilderness activities; B – occupation related to agricultural or wilderness activities; Colors: white – mild cases; yellow – moderate cases; orange – severe case.
As shown in Table 4, height varied between 151 and 190 cm, body mass index (BMI) ranged from 19.3 to 32.8 kg/m2 (mean: 26.4; median: 26.1), and body surface area (BSA) varied from 1.54 to 2.30 m2 (mean: 1.92 m2; median: 1.93 m2).
Table 4
| Protocolnumber | Height in centimeters(cm) | Weight in kilograms(Kg) | Body mass index | Body surface area | Estimated number of stings |
|---|---|---|---|---|---|
| 00101 | 176 | 65 | 21.0 | 1.78 | 400 |
| 00102 | 175 | 80 | 26.1 | 1.97 | 40 |
| 00103 | 178 | 94 | 29.7 | 2.16 | 10 |
| 00105 | 190 | 100 | 27.7 | 2.30 | 16 |
| 00106 | 157 | 62,8 | 25.5 | 1.66 | 10 |
| 00107 | 165 | 81 | 29.8 | 1.93 | 150 |
| 00108 | 175 | 77 | 25.1 | 1.93 | 500 |
| 00109 | 179 | 77 | 24.0 | 1.96 | 55 |
| 00110 | 165 | 52,5 | 19.3 | 1.54 | 165 |
| 00111 | 168 | 70 | 24.8 | 1.81 | 10 |
| 00112 | 161 | 67 | 25.8 | 1.73 | 30 |
| 00113 | 175 | 88 | 28.7 | 2.07 | 50 |
| 00114 | 188 | 98,1 | 27.8 | 2.26 | 500 |
| 00115 | 167 | 74 | 26.5 | 1.85 | 100 |
| 00116 | 182 | 78 | 23.5 | 1.99 | 180 |
| 00117 | 173 | 89 | 29.7 | 2.07 | 2000 |
| 00301 | 198 | – | – | – | 20 |
| 00302 | 168 | 70 | 24.8 | 1.81 | 150 |
| 00303 | 167 | 91,5 | 32.8 | 2.05 | 7 |
| 00304 | 151 | 68 | 29.8 | 1.69 | 50 |
Description of participants; study protocol number, height in centimeters (cm), weight in kilograms (Kg), body mass index in Kg/m2, body surface area (m2), and estimated number of stings.
1-Body mass index in Kg/m2 (BMI), estimated body surface area (BSA) in m2. Colors: White – mild cases; Yellow – moderate cases; orange – severe cases.
Participant 302, aged 77, received 150 stings and was attended to at the hospital in Tubarão (SC) 1 h after the accident. Figure 3A shows a bee inside the ocular conjunctiva of the participant, demonstrating the aggressiveness of this accident. Figure 3B shows an Africanized honeybee.
Figure 3

(A) Participant 302 with A. mellifera Africanized honeybee inside the ocular conjunctiva. (B)Apis mellifera Africanized honeybee.
Clinical Outcomes
Adverse Events Not Related to the Investigational Product
Participant 103 developed an abscess on the lower-left flank (hypogastric region); participant 105 had inflammation of the right eye; participant 115 had strong-smelling urine, and pain in the testicular and lumbar regions (kidney); participant 113 had tachycardia and edema in the lower limbs (chronic hypertensive patient), and participant 111 had bronchospasms.
At follow-up visits, especially 10 d after treatment, all four participants, with moderate to severe cases, complained of intense itching in the lesions. This complaint was also mentioned by one of the participants who suffered a mild accident.
Adverse Events Related to the Investigational Product
During the AAV infusion, participant 110 presented with numb lips and itchy head; and participant 117 had pruritus and urticarial reactions. All AEs related to the product were adequately treated, and AAV infusion was completed. All adverse events, whether related or unrelated to the study, are described in Data Sheet 3 - Clinical aspects.
Clinical and Laboratory Outcomes
According to Table 1 from Data Sheet 4 Tables-1-21, from a clinical perspective, only one patient had hemodynamic alterations, whereas two presented with respiratory disorders. From a laboratory perspective, 15 had elevated CK levels, nine showed increased CRP levels, eight had leukocytosis, seven showed increased fibrinogen levels, and four showed increased ALT levels. All laboratory findings for CK, CRP, ALT, and complete blood count, including platelets count, fibrinogen, and creatinine levels, are available in the Supplementary Materials in Data Sheet 5 -Laboratory exams.
The AHB scores assigned to the participants before the administration of AVV were 7, 6, and 5 or below 5, for 2, 5, and 13 participants, respectively (Table 2, Data Sheet 4 -table 1-21). The participant with the most severe case had a score of 7, and the 3 participants whose cases were considered to be of moderate severity had scores of 7 and 6, for 1 and 2 of them, respectively. All 16 participants whose cases were considered to be of mild severity had a score of 5 or less.
Laboratory tests showed an increase in CK, CRP, leukocytosis, fibrinogen, and ALT levels in 15, 9, 8, 7, and 4 participants, respectively. The biological AHB score, excluding clinical parameters, assigned to participants before the administration of AVV, was 5 in one, 4 in two, 3 in six, and score 2 or 1 in 11 participants respectively (Table 6, Data Sheet 4 -Tables-1-21).
As shown in Table 18 of the Data Sheet 4 -Tables-1-21, none of the participants showed clinical alterations 30 d after the administration of AAV. However, CRP, fibrinogen, CK, and ALT and leukocytosis, were altered in 4, 3, 2, and 1 of them, respectively.
As shown in Table 21 of the Data Sheet 4 -Tables-1-21, eight participants still had changes in the laboratory AHB score 30 d after AAV administration, with 1, 2, and 5 participants at scores 3, 2, and 1, respectively. Four participants, including 3 considered to have moderate cases and 1 considered to have a severe case, presented a laboratory AHB score of zero. Finally, Table 5 shows the comparison between AHB scores before and 30 d after AAV treatment.
Table 5
| Number of participants/AHB Scores | 101 | 102 | 103 | 105 | 106 | 107 | 108 | 109 | 110 | 111 | 112 | 113 | 114 | 115 | 116 | 117 | 301 | 302 | 303 | 304 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| AHB Scores before AAV treatment (*) | 6 | 3 | 2 | 2 | 7 | 5 | 7 | 6 | 4 | 6 | 3 | 4 | 6 | 5 | 5 | 7 | 4 | 6 | 5 | 4 |
| AHB Scores before AAV treatment (**) | 3 | 1 | 1 | 1 | 5 | 3 | 4 | 4 | 2 | 2 | 1 | 2 | 3 | 2 | 3 | 3 | 2 | 3 | 2 | 2 |
| AHB Scores 30 d after AAV treatment (***) | 0 | 0 | 2 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 3 | 1 | 2 |
Comparison between AHB scores before and 30 days after AAV treatment.
Colors: White – mild cases; Yellow – moderate cases; orange – severe cases.
(*) AHB Scores before AAV treatment, including clinical parameters.
(**) AHB Scores before AAV treatment, excluding clinical parameters.
(***) AHB scores 30 d after AAV treatment, excluding clinical parameters.
Melittin and Phospholipase A2 Pharmacokinetics—ELISA Assays
All participants were monitored at 0, 2, 6, 12, 24, and 48 h of hospitalization, and at 10, 20, and 30 d of outpatient follow-up. Of the 20 participants, 6 had missed at least one of the scheduled sample collection sessions, and the ELISA test was not performed for 2 participants (301 and 303).
Fourteen participants had a complete follow-up, and all their blood samples for the different collection periods were obtained. Concentrations of melittin + phospholipase A2 varied between 0.03 ng/mL and 587.35 ng/mL during the hospitalization and follow-up period; despite the excellent clinical states of all the participants, melittin + phospholipase A2 concentrations ranged between 0 and 1.479 ng/mL.
Figure 4 shows the time-course of melittin + phospholipase A2 levels in eighteen participants at admission, 2, 6, 12, 24, and 48 h after admission, and at 10, 20, and 30 d during the outpatient follow-up period. It is possible to observe that the blood concentration of melittin and PLA2 rises again especially after 10 days of admission, but without any clinical symptoms.
Figure 4

Time-course of melittin + phospholipase A2 levels (ng/mL) by ELISA test in eighteen participants at admission, 2, 6, 12, 24, and 48 h after admission and AAV administration, and at 10, 20, and 30 d during the outpatient follow-up period.
All the results of the ELISA assays are available in Data Sheet 6-Elisa assays.
Mass Spectrometry
Analyses of the TIC chromatograms (Figures 5A, B) indicated that the 712.15 ion [M+4H4+], as well as the MS2 profiles, particularly that of the [y13]2+ fragment, made it possible to determine the presence and relative levels of melittin in the participants, as shown in Table 6. The relative quantity of melittin in the serum was determined based on the graphical interpretation of the spectra, as presented in the Supplementary Materials, in Data Sheet 2 –Figures-1–5.
Figure 5

Representative mass spectrometry profile for the qualitative assessment of the presence of melittin in the serum of participant 115, considered positive (+++): (A) Melittin [M+4H]4+ MS profile and (B) MS2 interpreted profile, annotated for the larger b and y ions, as well as internal fragments (*).
Table 6
| No. of participants | 00101 | 00102 | 00103 | 00105 | 00106 | 00107 | 00108 | 00109 | 00110 | 00111 |
|---|---|---|---|---|---|---|---|---|---|---|
| Estimated number of stings | 400 | 40 | 10 | 16 | 10 | 150 | 500 | 55 | 165 | 10 |
| Number of antivenom vials | 6 | 2 | 2 | 2 | 2 | 2 | 6 | 2 | 2 | 2 |
| Presence of melittin | (+) | - | - | - | (+) | - | (*) | (+) | - | (++) |
| No. of participants | 00112 | 00113 | 00114 | 00115 | 00116 | 00117 | 00301 | 00302 | 00303 | 00304 |
| Estimated number of stings | 30 | 50 | 500 | 100 | 180 | 2.000 | 20 | 150 | 7 | 50 |
| Number of antivenom vials | 2 | 2 | 6 | 2 | 2 | 10 | 2 | 2 | 2 | 2 |
| Presence of melittin | - | - | (+) | (+++) | - | (+) | - | - | - | (++) |
Qualitative melittin detection in 19 participants 30 days after the AAV treatment.
* (not evaluated) Colors: White – mild cases; Yellow – moderate cases; orange – severe cases.
Discussion
Antivenom therapy was discovered in 1894 in France by Césaire Auguste Phisalix and Gabriel Bertrand (
Since the 2000s, CEVAP has initiated different strategies to develop new antivenoms and therapies named “next antivenom approach”, including the development of a new Apilic antivenom (AAV), based on the association between a robust clinical protocol and an antivenom that strategically neutralizes only toxic molecules, i.e., melittin and phospholipase A2 (
In 2017, the Brazilian National Health Surveillance Agency (ANVISA), through Resolution RDC N ° 187 of November 8, 2017, established the minimum requirements for the registration of hyperimmune sera, with the aim of guaranteeing the quality, safety, and efficacy of these products. It also established that the request for the registration of these immunobiological must include the results of clinical trial studies. This is because, until then, Brazilian antivenoms were not validated through clinical trials (
The certainty diagnosis of envenoming by Africanized honey bees was made by the signs, symptoms, and by the clinical history of the patients, such as walking near an apiary, beekeepers handling swarms without the personal protective equipment (PPE), and, accidentally, when the people walked or played sports on the field (
According to WHO guidelines (
As AAV was designed to specifically neutralize the two main toxic compounds of the venom, the clinical effects of low molecular mass proteins and peptides, that cause manifestation such as intense pruritus, flushing, hyperthermia, papules, urticarial plaques, hypotension, tachycardia, headache, nausea, vomiting, abdominal colic, bronchospasms, and psychomotor agitation, were neutralized by symptomatic medications such as antihistamines, corticosteroids, adrenaline (when the anaphylactic shock was suspected), and pethidine hydrochloride (for severe pain). In case of the occurrence of bronchospasms, oxygen (O2) catheters associated with β-2-agonist-type inhaled bronchodilators (salbutamol, fenoterol, or terbutaline) were used at the usual recommended doses (
Safety was assessed mainly through early adverse events, particularly, IgE-mediated anaphylactic reactions type I, non-IgE-mediated anaphylactic reactions, pyrogenic reactions (endotoxin contamination), and late adverse reactions (type III hypersensitivity, such as serum sickness) (
Regarding adverse events unrelated to the product, the persistence of itching the sting sites at the first follow-up outpatient, i.e., 10 d after AAV administration, was highlighted. This clinical manifestation and its persistence at the sting site or in the subcutaneous cellular tissue are related to envenoming (
Regarding the adverse events related to this product, only two participants (10%) experienced mild and early adverse reactions, such as numbness of the lips, itchy head, pruritus, and urticarial reactions. Recently, Mendonça-da-Silva et al. (
It should be emphasized that in the event of an accident involving AHB, classically described adverse reactions due to antivenoms may be confused with adverse events of the envenoming itself. Therefore, it becomes difficult to determine whether they are caused by the venom or AAV (
As concerns clinical and laboratory outcomes, the authors proposed a new AHB score to assess the severity of the participants’ cases at the time of the first visit, in addition to the evolutive outcome. The use of the AHB score proved to be simple and showed proportionality to the severity of the envenoming, and the normalization of clinical and biological signs. As it combines clinical and biological criteria, the score appears to be both sensitive and accurate, particularly with respect to biological variables, for the characterization of the severity and course of envenoming. This allowed us to confirm clinical remission in all participants 30 d after AAV administration. However, biological alterations persisted in some participants (8/20) even though they did not present with particularly severe envenomings. Surprisingly, the two participants with the most severe cases of envenoming, who received 500 and 2,000 stings, and were assigned an AHB score of 7, had a score of zero 30 d after AAV administration. In addition, all the 5 participants who had an AHB score of 6 at inclusion, had a score of zero 30 d after discharge; but one remained at 1 because of a CRP level slightly above the limit (1.1 mg/dL). It should also be emphasized that envenoming caused by venomous animals triggers a systemic inflammatory response syndrome described by several authors since the 1990s (
ELISA tests, standardized to assess the presence of melittin and phospholipase A2 in this study, showed the reappearance of these two fractions 10, 20, and 30 d after treatment in most participants.
In a study using an ovine model to evaluate the interactions between the venom produced by Micrurus fulvius and a F(ab’)2 antivenom administered intravenously, Paniagua et al. (
We hypothesize that, in consonance with the findings of Paniagua et al. (
Finally, qualitative mass spectrometry (
Conclusions
AAV proved to be safe, as related adverse events were observed in only two (10%) participants, corroborating reports on heterologous antivenom use. No late adverse events were observed on d 10, 20, or 30 during clinical surveillance. Preliminary efficacy was observed by clinical improvement in participants, a decrease in acute-phase-reaction markers, and a reduction in circulating melittin and phospholipase A2 levels, measured using ELISA. The doses recommended in the clinical protocol should be reassessed and increased, given that melittin was founding the blood of eight participants 30 d after the specific treatment, through mass spectrometry. It should be noted that these issues were expected, as accidents involving AHB are peculiar and different from all other venomous animal accidents described. A phase III clinical trial should be performed to confirm these observations, adjust the recommended doses, and assess the efficacy of the product.
Funding
This study was supported by the National Council of Technological and Scientific Development (CNPq) under Grant No. 437089/2018-5 (LS), 563582/2010-3 (BB), and 401170/2013-6 (BB), and in part by grants from the Coordination for the Improvement of Higher Education Personnel (CAPES) [AUX-PE Toxinology Proc. No. 23,038.000823/201121]. RF is a CNPq PQ1C fellow researcher [303224/2018-5]. DP is a CNPq fellow researcher [301974/2019-5]. BB is a CNPq PQ-2 fellow researcher [306339/2020-0]. FAPESP Grant No. 2020/09819-6 and No. 2020/16747-1 (BM, LS, RF). PROPG/UNESP Edital 01/2021. DECIT/MS No. 841906/2016-SICONV and No.841904/2016- SICONV (RF).
Statements
Data availability statement
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.
Ethics statement
The clinical protocol has been previously approved by the Brazilian National Commission on Ethics in Research (CONEP, Certificate of Presentation of Ethical Appreciation No. 19006813.4.1001.5411, v7, approved in 06/07/2016) and the Brazilian National Health Surveillance Agency (ANVISA) whose Consent Record of Apis Study was approved on 02/05 2016 by No. 0907532142, Proc. No. 25361611582201493. This trial RBR-3FTHF8 was registered in 2015 in the Brazilian Clinical Trials Registry (ReBEC) (
Author contributions
AB, FS-T, and MM were the principal investigators. FC, BM, and LS standardized the ELISA assay. RF and LC produced and performed quality control on the Apilic Antivenom. JB, DT, NM, CC, MC, and AO recruited the participants. DP developed the mass spectrometry assay. RF, LB, J-PC, and BB discussed the proposal and corrected the manuscript. All authors contributed to the article and approved the submitted version.
Acknowledgments
We are grateful to the Center for the Study of Venoms and Venomous Animals (CEVAP) of the São Paulo State University (UNESP), Brazil; Pasqual Barretti, Rodrigo Bazan, Carlos Antonio Caramori, and Patricia Carvalho Garcia from the Botucatu Medical School, São Paulo State University (UNESP), Brazil; André Balbi and the emergency room team of the Botucatu Medical School Clinical Hospital (HCFMB), São Paulo, Brazil; Sergio Muller of the São Paulo State Department of Health; Camile Giaretta Sachetti, Patricia de Souza Boaventura, and Felipe Nunes Bonifácio from the Department of Science and Technology of the Brazilian Ministry of Health; and Ricardo de Oliveira Orsi from the Botucatu School of Veterinary Medicine and Zootechnics (UNESP), Brazil.
Conflict of interest
RF is a CNPq PQ1C fellow researcher, process number 303224/2018-5.
RF, BB, LC, and DP participated as authors in patent application BR10201502630. Deposit: 10/16/2015. PCT deposit number: 10201502630. PCT deposit date: 10/16/2015 “Process of obtaining anti-apilic equine serum and its uses” INPI: National Institute of Industrial Property, Brazil.
The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Supplementary material
The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fimmu.2021.653151/full#supplementary-material
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Summary
Keywords
antivenom, Apis mellifera (Africanized), clinical trial, safety assessment, enzyme-linked immunosorbent assay (ELISA)
Citation
Barbosa AN, Ferreira Jr RS, de Carvalho FCT, Schuelter-Trevisol F, Mendes MB, Mendonça BC, Batista JN, Trevisol DJ, Boyer L, Chippaux J-P, Medolago NB, Cassaro CV, Carneiro MTR, de Oliveira APP, Pimenta DC, da Cunha LER, Santos LD and Barraviera B (2021) Single-Arm, Multicenter Phase I/II Clinical Trial for the Treatment of Envenomings by Massive Africanized Honey Bee Stings Using the Unique Apilic Antivenom. Front. Immunol. 12:653151. doi: 10.3389/fimmu.2021.653151
Received
13 January 2021
Accepted
05 March 2021
Published
23 March 2021
Volume
12 - 2021
Edited by
Choo Hock Tan, University of Malaya, Malaysia
Reviewed by
José María Gutiérrez, University of Costa Rica, Costa Rica; Anjana Silva, Rajarata University of Sri Lanka, Sri Lanka
Updates

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Copyright
© 2021 Barbosa, Ferreira, de Carvalho, Schuelter-Trevisol, Mendes, Mendonça, Batista, Trevisol, Boyer, Chippaux, Medolago, Cassaro, Carneiro, de Oliveira, Pimenta, da Cunha, Santos and Barraviera.
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*Correspondence: Rui Seabra Ferreira Jr, rui.seabra@unesp.br
†These authors have contributed equally to this work and share first authorship
This article was submitted to Vaccines and Molecular Therapeutics, a section of the journal Frontiers in Immunology
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