A 72 year old male presented to UVMMC in July, after being found unconscious and not breathing in his home. The patient presented with swelling of the throat and tongue, which had obstructed his airway. In addition to the swelling, the patient also presented with a hive-like rash along his upper torso and arms along with low blood pressure. The patient was successfully treated by an injection of epinephrine and asked about food allergies, as his clinical presentation was indicative of anaphylaxis. Having declared no food allergies, the patient was asked what he had eaten before the episode, noting that he had a beef burger for dinner hours earlier, which was not unusual for his diet. The attending physician noted the time between the man’s last meal and symptoms of anaphylaxis, which seemingly ruled out a food allergy. The patient was eventually discharged home, with recommendations to monitor his diet and return if symptoms resumed.
Two days later, the patient returned to UVMMC with coughing, shortness of breath, swelling of his tongue and throat, and heartburn. Once again, the patient was treated with injectable epinephrine, which alleviated his symptoms. When asked again about his diet, the man mentioned that hours earlier at dinner he had pork chops, which was also not unusual for his diet. Upon closer examination, a circular rash was observed on the patient’s right shoulder and the patient was tested for Lyme Disease. While awaiting the results of the test, the patient was asked about any exposures to ticks. Upon the mention of tick exposure, the man recalled seeing one a week prior crawling on his arm while he was watering his garden. Insisting that he did not feel a bite and quickly brushed the tick off of his arm, the man described the tick as being brown with a singular white dot on the center of its body. When the Lyme Disease test returned negative, the attending physician ordered a blood test, looking for specific antibodies to alpha-gal. The test returned positive, and the man was diagnosed with Alpha-Gal Syndrome (AGS) from exposure to a Lone Star Tick (Amblyomma americanum) bite. The patient was then referred to an allergist for symptom management.
Lone star ticks (Amblyomma americanum) are aggressive human-biting ticks that actively seek out potential hosts through the use of CO2 trails and vibrational movements.4 This strategy is a distinct behavior when compared to other tick species that commonly employ the ‘ambush strategy’ involving lying in wait for a potential host to pass by.4,5 A complete life cycle for a lone star tick involves three distinct stages, including a larval, nymph and adult stage.3 While the bite of a larval tick is considered less dangerous due to it feeding for the first time and being less likely to have exposure to infected hosts, there is a risk that certain pathogens can be passed from the mother tick to the larvae.4 All three stages of the Lone Star tick’s life cycle require a blood meal from three different hosts, and all stages will feed on humans along with other vertebrate animals.3 These ticks live primarily in areas of woodlands where there is plenty of undergrowth and tall grasses.5
Due to changes in the climate, such as shorter, milder winters and an increased abundance of preferred hosts, the Lone Star tick has increased in both abundance and distribution over the last several decades.3 Despite these concerning trends, these ticks are commonly found throughout the eastern, southeastern, and south-central regions of the United States.3 Because Lyme Disease places such a huge burden on public health populations, the Lone Star tick is often overshadowed in public health messaging by black-legged ticks such as “deer” ticks (Ixodes scapularis) due to their Lyme-carrying abilities.4 In contrast, the Lone Star tick is incapable of transmitting the spirochete that causes Lyme Disease (Borrelia burgdorferi)3, which is a reason why the patient’s blood test was negative for the pathogen in the current case.
Despite being incapable of carrying Lyme Disease, symptoms associated with a Lone Star tick bite may present similarly to that of Lyme Disease including the presence of a rash on the skin.3,4 While similar, this rash is considered distinct from the rash observed in Lyme Disease and has been termed Southern Tick-Associated Rash Illness (STARI).3 While the specific etiologic agent has not yet been identified, the rash is often accompanied by fatigue, headache, fever, and muscle pains and will usually present within seven days of a tick bite.3 While no diagnostic test is available to distinguish STARI from Lyme disease, diagnosis is usually based on symptoms, geographic location, possibility of a tick bite, and the presentation of the rash which is typically a red circle expanding to around 8cm in diameter.3
Lone Star ticks can transmit a variety of bacterial and viral pathogens, but they are most commonly associated with Alpha-Gal Syndrome (AGS).2,3,4,5 Alpha-Gal refers to the sugar molecule galactose-alpha 1,3-galactose, which is commonly found in most mammals except people, fish, reptiles, and birds.2 The sugar molecule is found in meats (pork, beef, rabbit, lamb, venison, etc.), as well as in mammalian products such as gelatin, cow’s milk, or milk products.2 Lone Star ticks transmit this sugar to humans by feeding on hosts and maintaining trace amounts of alpha-gal within their salivary glands, which is then injected into the next host.2,4 In humans, the immune system reacts to alpha-gal in the bloodstream similarly to a foreign invader, initiating an IgE-mediated allergic response.4 Symptoms will often vary between each individual but can include hives, nausea, vomiting, heartburn, dizziness or fainting, and anaphylaxis, among many other symptoms.2,4
It is estimated that between 2010 and 2022, more than 110,000 people were suspected of having AGS, and diagnosis is usually confirmed by blood tests which look for specific antibodies to the sugar.2 Interestingly, not every exposure to alpha-gal will result in an allergic reaction, and unlike food allergies where exposure can result in immediate reaction symptoms, it could take up to several hours after ingestion of an animal product containing alpha-gal for symptoms to appear in AGS patients.4 Unfortunately, there is no treatment for AGS, but patients are typically managed by an allergist with recommendations of carrying an injectable epinephrine device, avoiding foods containing alpha-gal, taking antihistamines as needed, and monitoring or adjusting other medications which may be manufactured using gelatin capsules.2,4
References
1 [Figure 1 Image]: ACP Internist. (n.d.). MKSAP Quiz: Evaluation for a Skin Eruption [website]. Accessed online on December 5th 2023 from, https://acpinternist.org/archives/2016/10/mksap.htm
2 CDC. (2023). Alpha-gal Syndrome [website]. Accessed online on November 17th 2023, from https://www.cdc.gov/ticks/alpha-gal/index.html
3 CDC. (2018). Lone star tick a concern, but not for Lyme disease [website]. Accessed online on November 17th, 2023 from https://www.cdc.gov/stari/disease/index.html
4 Kennedy, A. C., BCE1, & Marshall, E. (2021). Lone Star Ticks (Amblyomma americanum):: An Emerging Threat in Delaware. Delaware journal of public health, 7(1), 66–71. https://doi.org/10.32481/djph.2021.01.013
5 Vermont Department of Health. (2023). Information on Ticks in Vermont [website]. Accessed online on November 17th, 2023 from https://www.healthvermont.gov/disease-control/tickborne-diseases/information-ticks-vermont
-Maggie King is a Masters student in the Department of Pathology and Laboratory Medicine at the University of Vermont.
-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.
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