The Topic of This Month Vol.18 No.8(No.210)
The subjects of the Topic of This Month of IASR have so far been such infectious diseases that the Infectious Diseases Surveillance Program deals with, but on the occasion of the renaming and partial reorganization of this Institute in April 1997, other important diseases that this Institute is concerned will also be taken up. As the Topic of This Month, the editorial board of IASR have agreed to take up hymenopteran stings, which are not infectious diseases but dealt with by the Department of Medical Entomology of this Institute.
1. The present status of hymenopteran stings
In this country, Hymenoptera provoking stings involves 16 species of hornets and yellow-jackets, 11 species of paper wasps, two species of honeybees, and 14 species of bumblebees. Thus, much more species of Hymenoptera are inhabiting in this country than in USA or any other European country. This causes the existence of so many kinds of hymenopterous venoms, complicating the problem of hymenopterous venom allergy.
According to the statistics of mortality from hymenopteran stings having been reported to the Ministry of Health and Welfare (MHW), there have been 30 to 40 victims every year, though some yearly variations are seen. There were as many as 73 victims in 1984, being the largest number in the statistics in the past (Table 1). There were 44 fatalities in 1994, being far outnumbering the deaths from venomous snakebites (10.7 fatal cases per annum, the average of the past three years). According to the report by Saku General Hospital in Nagano Prefecture, having summarized the monthly incidence of hymenopteran stings, cases seeing doctors have peaked in August and about 90% of cases have concentrated in summer from July to September. During this period, the sizes of nests of hornets, yellow-jackets and paper wasps become the maximum and the activity of worker hymenoptera to defend their nests is being heightened. According to the statistics complied by MHW based on the reports from each prefecture, claims and requests for extermination of hymenoptera outnumbered those of lice, ticks and rats and have been the largest in number during the past three years, being nine times as many as that 10 years ago (Fig. 1). Such a tendency of sudden increase in the claims may have been due to such various factors as (1) the human residential areas becoming adjoined or coming into the habitats of hornets, yellow-jackets and paper wasps in the suburbs of large cities, (2) human outdoor sports activities becoming more popular than before, and (3) Vespa mandarinia, an important natural enemy of small and medium-sized hornets, has recently decreased in number in suburban areas and vicinities.
2. Under what circumstances would hymenopteran stings occur ?
All fatal cases from hymenopteran stings are reported on a national scale in Japan. Some examples are shown below: A person was stung by several paper wasps (Polistes jadwigae) while he was trimming the garden trees resulting in shock symptoms and death. Another man was stung by hornets at several tens of sites during mushrooming, became unconscious and died. Another engaged in forestry was suddenly attacked by hornets when investigating for the yields, became unconscious, fell into a state of cardiac arrest when sent to a hospital, and died. The deaths of most cases were not due to envenomation of an amount larger than the lethal dose, but perhaps due to type I allergy involving IgE antibody. Such incidents are tragical because healthy persons are suddenly driven to death within tens of minutes or few hours. It is characteristic that most of death cases occur among middle-aged and elderly groups over 40 years old when they are in mountain areas where no ambulance is available. There have been three times more males than females of fatal cases (Table 2).
Some examples of not lethal but serious cases: A man was stung suddenly by hornets (Vespa xanthoptera) at 14 sites in a mountain and become unconscious for about 20 minutes. A truck driver was stung by a paper wasp (Parapolybia varia) at a site on his arm when he was leaving home for work and 10 minutes later he fell into coma when he was driving, resulting in a head-on collision with a bus. Another man was stung at three sites on his back by yellow-jackets (Vespa lewisi), developed generalized urticaria and difficulty in breathing, and was treated at an emergency clinic. Another man was stung on the scruff of his neck by a paper wasp flying in through the car window when he was driving, developed edema on his whole neck and difficulty in breathing. Analyses of these cases show that hymenopteran stings could occur ordinarily in our lives. It is understandable that agricultural and forestry workers are at high risk.
3. Hymenopterous venom allergy and its therapy and countermeasures
Three distinct components of hymenopterous venoms are known; enzymes, peptides, and low molecular weight substances (Table 3). It is known that these components evoke destruction of connective tissues, hypotension, permeability increase, pain, smooth muscle contraction, etc. and that upon envenomation by hymenopteran sting, these substances work together inducing various serious symptoms. Many patients of type I allergy have often been stung by worker hymenoptera of the same or related species. Since the enzymes in the venom have amino acid sequences partially identical to those common to other species of Hymenoptera, those who possess IgE antibody against a certain venom component should be careful about occurrence of anaphylaxis against hymenopterous venoms of multiple species.
For therapy of hymenopteran stings, steroid ointments containing antihistamines and cold compresses should be applied to the stings. When systemic symptoms are severe, an antihistaminic or steroid medicine should be given orally. If any shock symptom is found, 0.3-1.0 mg of epinephrine should be injected subcutaneously to ensure the airway and blood pressure, and it is important to administer a bronchodilator and steroid medicine and to take a countermeasure against arrhythmia. At some medical institutions, applied is hyposensitization therapy to those who have an anamnesis of hymenopterous venom allergy, but only as a clinical trial since the immunotherapy allergens have not yet been licensed in this country. In USA, as many as about 1-3% of the total population are said to be allergic to hymenopterous venoms. If the tendency of increasing in the hornet, yellow-jacket, and paper wasp population in suburban areas in this country is considered, it will be necessary to establish diagnosis and therapy of hymenopterous venom allergy.
For preventive measures, when one is unexpectedly coming upon with nests of hornets, yellow-jackets, and paper wasps during activities out in fields and being threatened or attacked by watchers of those hymenoptera, it is strictly prohibited to shout loudly or to try to drive them away with the arms. It is important to get away in a stoop posture as swiftly as possible from the nest.