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RESEARCH Causes of ant sting anaphylaxis in Australia: the Australian Ant Venom Allergy Study Simon G A Brown, Pauline van Eeden, Michael D Wiese, Raymond J Mullins, Graham O Solley, Robert Puy, Robert W Taylor and Robert J Heddle he prevalence of systemic allergy to ABSTRACT native ant stings in Australia is as high as 3% in areas where these Objective: To determine the Australian native ant species associated with ant sting T anaphylaxis, geographical distribution of allergic reactions, and feasibility of diagnostic insects are commonly encountered, such as Tasmania and regional Victoria.1,2 In one venom-specific IgE (sIgE) testing. large Tasmanian emergency department Design, setting and participants: Descriptive clinical, entomological and study, ant sting allergy was the most com- immunological study of Australians with a history of ant sting anaphylaxis, recruited in mon cause of anaphylaxis (30%), exceeding 2006–2007 through media exposure and referrals from allergy practices and emergency cases attributed to bees, wasps, antibiotics physicians nationwide. We interviewed participants, collected entomological or food.3 specimens, prepared reference venom extracts, and conducted serum sIgE testing Myrmecia pilosula (jack jumper ant [JJA]) against ant venom panels relevant to the species found in each geographical region. is theThe major Medical cause Journal of ant ofsting Australia anaphylaxis ISSN: Main outcome measures: Reaction causation attributed using a combination of ant 2 in Tasmania.0025-729X A 18double-blind, July 2011 195 randomised 2 69-73 identification and sIgE testing. placebo-controlled©The Medical Journaltrial has of Australiademonstrated 2011 Results: 376 participants reported 735 systemic reactions. Of 299 participants for whom the effectivenesswww.mja.com.au of JJA venom immuno- a cause was determined, 265 (89%; 95% CI, 84%–92%) had reacted clinically to Myrmecia therapyResearch (VIT) to reduce the risk of sting species and 34 (11%; 95% CI, 8%–16%) to green-head ant (Rhytidoponera metallica). Of anaphylaxis, and an ongoing treatment and those with reactions to Myrmecia species, 176 reacted to jack jumper ant (Myrmecia research program has been established.4,5 pilosula species complex), 18 to other jumper ants (15 to Myrmecia nigrocincta, three to Access to treatment outside Tasmania is Myrmecia ludlowi) and 56 to a variety of bulldog ants, with some participants reacting to limited by inadequate knowledge of the more than one type of bulldog ant. Variable serological cross-reactivity between bulldog causative species in other regions and the ant species was observed, and sera from patients with bulldog ant allergy were all absence of diagnostic tests for other ant positive to one or more venoms extracted from Myrmecia forficata, Myrmecia pyriformis species. Accurate diagnosis is further com- and Myrmecia nigriceps. plicated because the JJA is a “species com- Conclusion: Four main groups of Australian ants cause anaphylaxis. Serum sIgE testing plex”, comprising seven closely related enhances the accuracy of diagnosis and is a prerequisite for administering species- species with almost identical morphology. specific venom immunotherapy. These were first recognised by chromo- somal differences but can now be distin- MJA 2011; 195: 69–73 guished using subtle differences in morphological characteristics.6 The objectives of the Australian Ant study home page, to encourage people with implicated by circumstance (eg, seen Venom Allergy Study were to determine the ant sting allergy to contact us directly. nearby), and a reaction severity grade of geographical distribution of the major ant Inclusion criteria were a history of a gen- mild (skin only), moderate (involvement of species associated with anaphylaxis eralised systemic allergic reaction to an iden- additional organ systems) or severe (hypo- throughout Australia, and to examine the tified or suspected ant sting. Cases were tension or hypoxaemia).3 Serum samples feasibility of newly developed diagnostic excluded if investigation indicated that a were obtained and stored at − 80° C until testing to confirm the diagnosis of allergy to systemic reaction did not occur or that an analysis. non-JJA ant species. ant sting was not the cause. The human research ethics committees of each investi- Entomological specimens, collection gator’s institution granted ethics approval. METHODS and identification Participants gave written informed consent. With the assistance of participants’ non-ant- Study population allergic family or friends, 2–4 specimens of In 2006 and 2007, we requested case refer- Clinical data ant(s) were provided from each location rals from Australian doctors with allergy Participants identified the responsible ant where systemic reactions had occurred. Ants practices by emailing all members of the (where possible) from colour illustrations of were not collected from the Northern Terri- Australasian Society of Clinical Immunology common species and completed a question- tory, northern Queensland or northern and Allergy, and from emergency medicine naire, followed by a structured telephone or Western Australia because few participants specialists by emailing all Fellows of the face-to-face interview. We recorded partici- came from these areas, nor from Tasmania, Australasian College for Emergency Medi- pants’ age and sex, the geographical location as ants in that region are already well char- cine. We also used press releases and stories where each reaction occurred, reaction fea- acterised. Wherever possible, the investiga- in regional newspapers and on radio and tures, a description of the insect and tors made field trips to collect additional television, and web search indexing with a whether it was clearly seen to sting or specimens for identification and whole ant MJA • Volume 195 Number 2 • 18 July 2011 69 RESEARCH nests (colonies) for venom extraction from reference venoms for use in sIgE assays, only positive sIgE result allowed us to confirm a areas where stings had occurred. Ant colo- after both formal entomological identifica- clear ant description or, if there was some nies were transported on dry ice, then stored tion and confirmation of the presence of uncertainty about the ant(s) described, at − 80° C until venom sac dissection and identical bands on polyacrylamide gel elec- allowed us to decide between several possi- processing, as previously described.4,7,8 trophoresis in venom samples from each ble causes. However, multiple positive sIgE Specimens were identified by one of us component colony. results (representing either cross-reactivity (RW T) and deposited in the Common- or multiple sensitisations) required a high wealth Scientific and Industrial Research Venom-specific IgE assays and degree of clinical certainty (visual identifi- Organisation (CSIRO) Australian National determining reaction causation cation) before attributing causation. Insect Collection. A time-resolved fluorescence method, disso- ciation-enhanced lanthanide fluoroimmu- Statistical analysis Venom extracts noassay (DELFIA; Wallac, Turku, Proportions were calculated with 95% confi- After morphological identification, venoms Finland),10 was used to detect sIgE against a dence intervals (binomial exact) (Stata, release extracted from different sibling species of panel of ant venoms relevant to each geo- 11; StataCorp, College Station, Tex, USA). the JJA species complex were analysed by graphical region where sting reactions had polyacrylamide gel electrophoresis accord- occurred. Venom panels for sIgE testing RESULTS ing to our previously established methods.9 were chosen for each region based on our Once homology of venoms from sibling collected specimens and known distribu- Three hundred and seventy-six participants species was confirmed, we used a standard- tions.11,12 We were unable to include species reported 735 systemic reactions. Basic ised JJA extract produced by the Tasmanian if they were rarely encountered and we demographic and reaction data are shown in Jack Jumper Allergy Program for our could not obtain sufficient venom. Box 2. We identified 283 specimens of venom-specific IgE (sIgE) assays.7 The cause of each reaction was attributed stinging ants collected from locations where For all other species, venom extracts from using a combination of ant identification and reactions had occurred (Box 3). There were the same species were pooled to create sIgE testing, as outlined in Box 1. A single four dominant ant species or groups, each with characteristic morphology: (i) JJA spe- cies complex; (ii) other jumper ants 1 Determining reaction causation in 376 participants with ant stings (Myrmecia nigrocincta in New South Wales and Queensland, Myrmecia ludlowi in WA); (iii) bulldog ants (BDA) of the Myrmecia gulosa species group; and (iv) Rhytidoponera metallica (green-head ant [GHA]) (Box 4). Venom-specific IgE results and reaction causation Venoms used for sIgE testing for each region are shown in Box 3. Serum samples from 325 participants (86%; 95% CI, 83%–90%) were sIgE-positive to one or more venoms relevant to the geographical regions where the stings occurred. Reaction causes were 2 Participant demographics and reaction characteristics Characteristic Number of participants 376 Age in years, median (IQR) 46 (33–64) Male 158 (42%) Age in years at first reaction, 46 (19–58) median (IQR) Years since last reaction, 1.7 (0.4–5.0) median (IQR) Severity of worst reaction Mild 22 (6%) Moderate 150 (40%) Severe 204 (54%) DELFIA = dissociation-enhanced