lone star ticks: alpha-gal anaphylaxis from eating red meat
The spread of the lone star tick as a result of climate
change/warmer weather has led to the northward spread of some tick-borne
illnesses. A prior blog highlighted the spread of the
potentially fatal Heartland virus, associated with the lone star tick (http://gmodestmedblogs.blogspot.com/2023/03/climate-change-tick-disease-spreads.html); this blog includes a picture of the tick as well as
more general observations of the effects of climate change on the spread of
infectious diseases. And, now the alpha-gal syndrome (AGS)
Details:
-- the lone star tick bites have been associated with the
alpha-gal syndrome, AGS (also called the red meat allergy or tick bite meat
allergy), a potentially life-threatening allergic condition
--
it seems that AGS is primarily associated with lone star tick bites, though
other ticks may also be involved (one suspect is Ixodes spp: the culprit also in anaplasmosis, Lyme
disease, babesiosis, Borrelia miyamotoi disease, Powassan virus disease, and
ehrlichiosis).
-- AGS has been found in areas where lone star ticks have not
been found, further suggesting a role for other tick species
-- AGS occurs because the oligosaccharide galactose-α- 1,3 galactose (aka, alpha-gal) is not found in humans, or in
fish, reptiles, or birds. And sensitization to this sugar in humans can lead to
subsequent severe hypersensitivity reactions
-- but alpha-gal is
found in meat (beef, pork, rabbit, lamb, venison) as well as products from these
animals (cow's milk or any milk products). of note, certain medications can
also have alpha-gal,
including gelatin derived from pork or beef and used in meds (eg some gelcaps,
such as acetaminophen; gelatin-containing vaccines, heparin and antivenoms)
-- it appears that lone star tick bites can initiate this allergic
response if one subsequently eats one of the foods above.
-- the current accepted model per the CDC is that
AGS is an IgE-mediated hypersensitivity reaction to ingesting alpha-gal, though
symptoms are often delayed by 2-6 hours or more after eating a food with
alpha-gal, and this can happen after years of eating these foods without prior
hypersensitivity symptoms
-- there are lots of unanswered
questions, including:
-- what is the exact role
of ticks: how do they initiate this IgE response to subsequent ingestion of
foods with galactose-α- 1,3 galactose, yet just eating those foods seems okay.
--
alpha-gal moieties have been found in black tick saliva (Ixodes scapularis,
a black-legged "deer tick" found in eastern US, related to Ixodes pacificus
in the west), as well as in the lone star tick: all of this suggesting a link
between the tick bites and subsequent AGS.
-- why do some people get AGS but others do
not (what is the specific immunologic mechanism that leads to these rather
different responses to those foods)
-- epidemiologic information is
spotty:
-- https://www.cdc.gov/ticks/alpha-gal/index.html :
the CDC estimates that between 2010 and 2022 there have been >110,000
suspected cases of AGS after people are exposed to red meat or other products
containing alpha-gal (some estimates are between 96,000 and 450,000 getting AGS
in the US since 2010)
-- unfortunately, AGS is not a notifiable condition to the
CDC, so prevalence data are not likely very accurate.
-- And, many health care providers are unaware of this
syndrome, further decreasing accuracy of reporting: the CDC has found that 42% of health care
providers were not aware of AGS and another 35% were not confident on their
ability to diagnose or manage AGS patients (https://pubmed.ncbi.nlm.nih.gov/37498792/ )
-- one commercial lab tested 105,674 people between 2010 and 2018
and found 32% were positive for galactose-α- 1,3 galactose IgE
-- based on the limited data available, one estimate suggests
that 20%-78% of AGS cases are undiagnosed
-- for the CDC
reporting form for AGS cases: https://www.cdc.gov/ticks/alpha-gal/pdfs/328065-A_NCEZID_FRM_Alpha_gal_CRF_508_2.pdf
--- typical symptoms of AGS include abdominal cramping, urticaria
and anaphylaxis, though the full list includes nausea, diarrhea, vomiting,
heartburn, itching, swelling of lips/tongue/throat/face/eyelids, shortness of
breath, cough, wheezing, acute episodes of hypotension. Attributing these
symptoms to AGS also requires the absence of a clear alternative diagnosis
(though the absence of a clear cause for urticaria is really common in clinical
practice, especially an issue since about 20% of people have hives at some
point in their lives. i have a patient with chronic recurrent hives who was
found to have H Pylori stool antigen on routine testing, this was treated, and,
unexpectedly, the hives have not recurred now for several years)
-- though AGS symptoms may be as mild as a rash or
GI upset
-- case definitions of AGS (see https://cdn.ymaws.com/www.cste.org/resource/resmgr/ps/ps2021/21-ID-07_Alpha_Gal_Syndrome.pdf )
-- laboratory confirmation: IgE specific to alpha-gal > 0.1
IU/mL or >= 0.1 kU/L
-- presumptive lab evidence: allergy skin test being
positive to one or more of pork, beef, lamb, or other mammalian-derived
products
-- confirmed care: meets clinical criteria and confirmatory lab
test
-- probable case: meets clinical criteria and presumptive lab test
-- suspected case: meets confirmatory lab test but no clinical
information available
-- treatment: antihistamines, epinephrine and the elimination
of products with galactose-α- 1,3 galactose. Other meds used include omalizumab
-- an epi-pen should also be prescribed, given the ubiquity of
foods/products that might (unknowingly) include alpha-gal and the potentially
lethal effects of the hypersensitivity reaction
Commentary:
-- The Boston Globe had an article on the AGS, "Here’s some red
meat for all the tick haters": https://edition.pagesuite.com/popovers/dynamic_article_popover.aspx?artguid=92bf6a80-ac85-4392-ac42-05972c99caca ,
making several of the points above, and highlighting several cases:
-- a woman who
developed hives and difficulty breathing after a tick bite, then a few weeks
later had a bowl of beef chili but attributed this to "panicking"
-- another woman
who had an intense allergic reaction after taking "Tylenol gelcaps and
candy corn", both of which could lead to AGS after a sensitizing tick bite
-- there has been
wide-spread invasion of the lone star tick locally: "in Rhode Island and
probably the Cape and Islands, (researchers) saw a 300% increase between
2019-2022 when compared to 2014-2018"
-- this alpha-gal
allergy seems to disappear after 3-5 years if no subsequent tick bite [this is
not so surprising: data on severe penicillin allergy also show dramatic
decreases on allergy testing years later: http://gmodestmedblogs.blogspot.com/2017/03/penicillin-allergy.html]
-- as a personal
anecdote, we have a small house in very rural Vermont. Over the past 3 years,
there has been a huge increase in ticks (mostly the blacklegged ones, though
lone star ticks have occasionally been found in southern Vermont), such that
for a couple of months in the summer, just walking outside to the car led to
4-6 ticks crawling up one's body; and more prolonged exposure to 10-20
ticks.... eg see https://www.healthvermont.gov/disease-control/tickborne-diseases/information-ticks-vermont
-- here is the current spread of the lone star tick in the
US, from its meager beginnings in the South:
so, what does this all mean:
-- health care workers need to be familiar with AGS as a potential
source of severe allergic reactions
-- many people may be unaware of having had a tick bite,
especially with some of the smaller ticks or ticks in hard to see locations
-- if no source of the allergic reaction can be identified, we
should consider getting specific IgE testing (best test) or allergy testing to
see if likely to be AGS
-- patients should have epi-pens
-- patients with AGS should avoid potential foods that might lead
to the allergic reaction (seems like vegans are doing it right....)
-- and, and, and: this is yet another of the very many reasons
that there needs to be a global concerted effort to decrease the use of fossil
fuels and try to bend the curve against continued climate change
geoff
-----------------------------------
If you would like to be on the regular email list
for upcoming blogs, please contact me at gmodest@bidmc.harvard.edu
to get access to all of the blogs:
go to http://gmodestmedblogs.blogspot.com/ to see the blogs in reverse chronological
order
-- click on 3 parallel lines top left, if you want to
see blogs by category, then click on "labels" and choose a category
-- or you can just click on the magnifying glass on
top right, then type in a name in the search box and get all the blogs with
that name in them
if you would like to see the articles in this
blog, please email me.
please feel free to circulate this to others.
also, if you send me their emails (gmodest@bidmc.harvard.edu),
i can add them to the list
Comments
Post a Comment
if you would like to receive the near-daily emails regularly, please email me at gmodest@uphams.org