Tick killing in situ before removal to prevent allergic and anaphylactic reactions in humans: a cross-sectional study

The Australasian Society of Clinical Immunology and Allergy (ASCIA) recommends killing ticks in situ with an ether-containing spray and allowing them to drop off. The rationale is that this helps prevent allergy or anaphylaxis, since removal by other means might squeeze intra-abdominal contents and introduce more allergens.

One would think such a recommendation is based on high-quality evidence. It turns out this paper is probably the best evidence we have to inform practice. Oh great! Let’s have a look.

Just a word of warning, this ride is about to get bumpy.

Let’s start with the paper’s conclusion. It states, “[Our] results support killing ticks in situ before careful removal by mouthparts to reduce allergic/anaphylactic reactions…”

This wording suggests the researchers prospectively compared freezing with other methods of removal. But they didn’t. I am not joking.

The authors report their experience essentially using one method of tick removal and conclude it worked well. Once again, they did not properly compare it with anything else.

They do mention that anaphylaxis still occurred in some patients after ticks were frozen. Is it possible that the brief act of freezing a tick causes it to regurgitate more allergenic contents compared with careful removal using fine tipped forceps? The honest answer is that we simply do not know. There is clear clinical equipoise here and a proper comparative trial would be entirely ethical.

Unfortunately, there has now been a considerable amount of confidently expressed advice from ASCIA and others telling people that ticks must be killed before removal and that you should “freeze it and don’t squeeze it.” The certainty of these recommendations is not justified based on the evidence available.

One might ask, what is the harm in freezing before removal? Well, putting aside the possibility that we do not actually know whether freezing could worsen allergic reactions, the sprays themselves come with some cost. I checked my local pharmacy and they were about $25. The recommendation may also encourage people to present to busy emergency departments and wait hours before removal. Even worse, some people may become reluctant to remove ticks at all, despite prolonged attachment being associated with tick paralysis and tick-borne infections.

Oh, and not to be pedantic, but the title of the paper describes it as a cross-sectional study. It isn’t. It’s a prospective case series, or at best a prospective cohort study without a comparator group.

This is not a rant. It is simply pointing out the obvious. There is currently no good quality evidence supporting the recommendation to kill ticks in situ before removal. For all we know, it may even make things worse.

The emperor has no clothes!

 

Covering:

Taylor BWP, Ratchford A, Nunen S, et al. Tick killing in situ before removal to prevent allergic and anaphylactic reactions in humans: a cross-sectional study (although it’s not). Asia Pac Allergy. 2019;9(2):e15. [Link to full text of paper]