Mosquitoes and Ticks
Jen Hand
Mosquitoes and ticks are more than just pesky pests: Their bites can lead to infections, the transmission of diseases, and allergic reactions. Rising temperatures and extreme weather have not only led to longer breeding seasons but also the expansion of the geographic ranges where insects and arachnids can survive.
In particular, there is a growing public health concern surrounding the mosquito-caused West Nile virus and the less familiar a-gal syndrome, an allergy to red meat that may develop after a tick bite.
According to a JAMA review article published online on July 7, 2025, West Nile virus is the leading cause of mosquito-borne illness in the United States. CDC, meanwhile, notes that the actual number of a-gal syndrome cases is not yet known but has increased in the past several years. They estimate that as many as 450,000 people may be affected.
Currently no vaccines or specific treatments exist for either illness. Therefore, pharmacists can focus on prevention measures, education on symptoms, and supportive care for their patients.
West Nile virus
When this year’s peak transmission season of West Nile virus arrived in mid-August, reported cases were increasing and expected to rise further, according to CDC. First discovered in the United States in 1999, West Nile virus, a neurotropic flavivirus spread by Culex species mosquitoes, has infected millions of people.
About 80% of cases are asymptomatic, 20% cause a febrile illness, and less than 1% of infected people develop neuroinvasive West Nile virus disease (e.g., meningitis, encephalitis, or acute flaccid myelitis). Among the 20% of symptomatic patients, most develop non-neuroinvasive disease often involving fever, fatigue, headache, myalgia, rash, vomiting, and/or diarrhea, according to the review in JAMA.
“Each year, about 2,000 people get sick, including more than 1,200 severe, life-threatening illnesses and more than 120 deaths,” said Lyle Petersen, MD, who authored the JAMA review.
Mosquitoes live throughout the United States, according to CDC, and about 12 types spread germs through bites. Humans are dead-end hosts for West Nile virus, meaning it will not spread to another person or to another mosquito via a post-infection bite.
Petersen noted that people with certain chronic conditions such as cancer, diabetes, hypertension, or kidney disease, and those over 65 years old are at higher risk of severe illness. In addition, individuals with a weakened immune system, including those who take certain medications, are at high risk.
“For example, rituximab, ocrelizumab, or similar medications, used to treat cancers, autoimmune diseases, and inflammatory conditions or prevent rejection of transplanted organs weaken the immune system,” said Petersen.
The JAMA review researchers found that the mortality rate of patients with neuroinvasive disease is 10% overall, but 20% in patients 70 years or older and 30% to 40% in patients with hematologic malignancies, solid organ transplants, and those receiving B-cell depleting monoclonal antibodies.
“For patients with fever or neurologic symptoms during summer and fall months, [West Nile virus] should be considered,” wrote the study authors.
People who live in or travel to an area where West Nile virus circulates are at risk of infection, as are those who spend a lot of time outdoors or who cannot keep mosquitoes out of their residence between dawn and dusk.
“Ninety percent of mosquito control is getting rid of their breeding grounds,” said Joseph Diclaro, PhD, from the Anastasia Mosquito Control District of St. Johns County, FL.
This includes regularly inspecting and eliminating standing water.
Tick talk, clocking in on a-gal syndrome
Discovered in the mid-aughts when researchers connected allergic reactions to the cancer drug cetuximab in patients from a group of southeastern states with a mysterious red meat allergy popping up in the same places, a-gal syndrome is a serious and potentially life-threatening immunoglobulin E (IgE)–based delayed allergic condition characterized by a hypersensitivity to the oligosaccharide galactose-a-1,3-galactose (a-gal).
a-gal syndrome is found in most mammals and products derived from them and the saliva of certain ticks, mainly the lone star tick (Amblyomma americanum), but it is also found in other species.
“A classic pattern of [a-gal syndrome] is being in contact with a-gal during dinner and waking up in the middle of the night with hives, anaphylaxis, or other allergic symptoms,” said Petersen, who is also director of CDC’s Division of Vector-Borne Diseases.
Not all those who are bitten by a lone star tick will get a-gal syndrome, however, and while it can take weeks or months to develop symptoms, onset typically occurs 2 to 6 hours after exposure. The delayed reactions distinguish a-gal syndrome from other more immediate food allergies and can present challenges in correctly diagnosing and reporting it.
Cases of a-gal syndrome are not nationally notifiable to CDC. However, this summer both Virginia and Tennessee implemented laws requiring physicians to report cases to their state departments of health. A diagnosis requires a positive blood test and a clinical exam including a detailed patient history. CDC acknowledges that some people may not get tested, so the number of cases is likely far greater.
People with a-gal syndrome may experience urticaria, angioedema, wheezing, GI upset, diarrhea, or anaphylaxis after consumption of or exposure to products containing a-gal. These include red meat (e.g., beef, pork, venison, lamb, and other meat from mammals), dairy products, carrageenan, gelatin, and/or some medications, vaccines, or other medical or personal care products.
Petersen noted that health care providers and patients need to work together to manage symptoms, identify a-gal containing products to avoid, and discuss ways to prevent future bites. To increase awareness of a-gal syndrome and help to quickly diagnose patients, CDC’s website offers a new online training module for health care providers.
“The training includes opportunities for free continuing education in seven professional categories, including continuing pharmacy education,“ said Petersen. ■
The bug stops here
Taking precautions to mitigate mosquito and tick bites starts before going outside. Pharmacists are frequently a patient’s first contact for health information and may be asked to help navigate the myriads of available insect repellents.
To avoid tick bites, CDC suggests wearing loose-fitting long sleeves and pants, avoiding woody and brushy areas with high grass and leaf litter, walking in the center of marked trails, and understanding personal risk factors like spending high amounts of time outside or hunting. Performing tick checks—do not forget pets and children—showering shortly after being outdoors, and correctly removing embedded ticks lessens the risk of infection from a bite.
CDC recommends use of products containing EPA–registered active ingredients. This ensures the product has been evaluated and approved for human safety and effectiveness when applied according to the label’s instructions. Topical products with DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE, plant derived) or para-menthane-diol PMD (the synthesized version of OLE), and 2-undecanone (plant derived) are active ingredients that provide reasonably long-lasting protection.
Generally, higher concentrations of active ingredients provide longer duration of protection, so products with less than 10% active ingredients might offer only 1 to 2 hours of protection.
CDC says that insect repellent should not be applied under clothing, and if also using sunscreen, apply it first and the repellent second. The effectiveness of non–EPA-registered repellents, including some botanical or natural ones, is unknown. Using the insecticide permethrin for treating clothes and other gear is also recommended to repel and kill ticks and mosquitoes. ■