Venom Anaphylaxis: Management in NZ

Allergy or hypersensitivity to insect stings is quite common in New Zealand and in some cases, especially asthmatics, is life threatening. For those people who are, or think they are allergic to stinging insects, a bee or a wasp sting is perceived as a serious and often a terrifying event. For them their allergy is a very serious problem and in extreme cases can present as a phobia. Reported deaths due to anaphylaxis caused by insect stings are rare (between 40 and 50 deaths per year in the USA — statistically this correlates to about 1 death every 3 years in NZ). However, allergic patients often suffer profound anxiety and many suffer major disruptions of their lifestyle in the effort to avoid contact with bees and wasps.

Bee and wasp stings are intended for defence of the colony and hence the venom is formulated to cause severe pain to intruders. Honeybee venom in particular has been analysed extensively; it contains many non-allergenic components as well as the two major allergens – phospholipase A2 and hyaluronidase. Why some people become sensitive to venom proteins while others who are similarly exposed do not is still a mystery to immunologists and a great deal of research is ongoing.

In 1979 pure Hymenoptera venoms were approved by the FDA for use in the diagnosis and treatment of insect sting allergy. Both honeybee and wasp (Polistes and Vespula) venoms have been available in New Zealand since that time and many patients have been desensitised successfully in this country. Desensitisation, or more correctly hyposensitisation is recommended by WHO for all individuals who have experienced severe anaphylactic reactions to insect stings and who are likely to be stung again (1) Obviously most New Zealanders and in particular allergic bee keepers and bee keepers’ family members, staff or neighbours who are allergic to venom fall into this category.

Severe local reactions are not regarded as an indication for hyposensitisation, although distinction from systemic (anaphylactic) reactions may be difficult with stings to the head and neck. In some patients with severe local reactions stings become successively more severe and such cases should be monitored carefully as a true anaphylactic reaction may occur at any time. Conversely, in other cases successive stings become less severe; to date there is no test to predict increasing sensitivity.

The following procedure is recommended for assessment and treatment of patients sensitive to insect stings:

When a severe systemic reaction to an insect sting is reported the patient should be referred to a pathology laboratory for skin tests approximately 6 weeks after the sting occurred. Skin testing with pure insect venoms is used to demonstrate the presence of specific IgE antibodies which are involved in the allergic reaction and will identify the offending insect when the patient is unsure whether he or she was stung by a bee or a wasp. The >a href="diagnosis_allergies.aspx#intrader">intradermal>/a> skin test is the most reliable test for venom allergy.

Many people especially young children are unable to identify the stinging culprit accurately and it is critical that the correct venom be used for hyposensitisation. Where >a href="diagnosis_allergies.aspx#skinpric">skin tests>/a> are not available or the results questionable, blood samples for >a href="diagnosis_allergies.aspx#rast">RAST>/a> (radio-allergosorbent test) or EAST (enzyme allergosorbent test) may be sent to hospital laboratories in the main centres. These tests measure the levels of venom-specific IgE in serum.

Although venom sensitivity differs between individuals and the dosage schedule may have to be adjusted to suit the individual patient the majority of patients follow a standard program which consists of a series of 12-15 weekly subcutaneous injections of increasing amounts of pure venom administered on an out-patient basis. Then at monthly intervals a dose equivalent to two bee stings is given as a "maintenance" dose. For patients who live out of town there are several "rush protocols" that can be used to get them up to maintenance in a much shorter period of time. The mechanism by which the hyposensitised individual becomes able to tolerate these increasing amounts of venom is still not fully understood.

However, it seems that lymphocytes begin to produce antibodies that block the IgE mediated allergic reaction. The monthly maintenance doses act as "boosters" to the immune system somehow "reminding" the lymphocytes to continue to produce the blocking antibodies.

Occasionally allergic reactions do occur during the initial phases of >a href="desensitisation.aspx"> hyposensitisation >/a> so patients are required to wait in the doctor’s surgery for about an hour after administration of venom products. As delayed reactions have been reported albeit rarely patients should be instructed in the use of and have available an emergency anaphylaxis kit for the self-administration of adrenaline during the initial treatment phase.

The recommended maintenance dose of 100ug of venom is considered about equivalent to two stings and protection against field stings is well documented. Hyposensitisation has been shown to be effective in 98% of the patients and the remainder suffer much milder reactions than they experienced before treatment >sup>(2)>/sup>. Monthly maintenance doses for five years are necessary for continued protection. The decision to discontinue maintenance therapy after five years is a clinical one to be made with due consideration of the patients’ lifestyle and the results of current sensitivity tests >sup>(3)>/sup>.

There is no evidence of any adverse effects of long-term immunotherapy with insect venom.

In New Zealand bee and wasp venoms are available on a Special Authority Pharmaceutical Benefit from the Ministry of Health; a specialist must apply for this on behalf of the patient who may then be referred back to his own GP for treatment. The venom is available from hospital pharmacies, the usual prescription charges apply but there is no charge for the actual venom products.

Although there is a relatively small population at risk of an allergic reaction following a sting with the passing of the Health and Safety in Employment Act in 1992 more attention will need to be paid to the management of allergic reactions to insect stings in the work place. To cope with emergencies beekeepers should consider having adrenaline on hand at all times if they or staff members are known to be allergic to insect stings.

References:

  1. WHO. The lancet; Feb. 4:259-261. 1989
  2. Hunt et al, N. Eng J Med; 299:157-161. 1978
  3. Sutherland D. Patient Management. Oct 1993

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