Uptick in Ticks Equals More Tick-Borne Infections
Updated: Aug 25
“If you’re in an area where these [tick-borne] diseases are endemic, every year is a bad year for ticks.”
- Charles Beard, Ph.D., deputy director, Division of Vector-borne Diseases, Centers for Disease Control and Prevention
“Ticks are a formidable foe to public health. We are in desperate need of new tools to fight ticks and the pathogens they spread.”
- Jason Rasgon, Ph.D., professor of entomology and disease epidemiology, Pennsylvania State University
A dramatic “uptick in ticks” has occurred in many areas in the U.S. causing tick-borne infections to more than double since 2004. Global warming is the single biggest reason for this predicament; it prolongs the tick breeding season thereby creating new “hot spots” for tick encounters.
For all of us who venture into woods or fields, it is important to be familiar with several essential facts about ticks and tick-borne infections. In this Germ Gems post, I review these facts and highlight several new developments in the field.
A recap on what everyone needs to know about tickborne infections. Only a small fraction of the 899 known tick species in the world are vectors for human pathogens. In my April 14, 2021 Germ Gems post, “Tick Talk,” I highlighted four of the most important tick species that cause human suffering: the blacklegged tick (Ixodes scapularis), lone star tick (Amblyomma americanum), American dog tick (Dermacentor variabilis), and brown dog tick (Rhipicephalus sanguineus). In addition, I discussed the pathogens (bacteria, viruses, and parasites) these ticks transmit and the diseases they cause. Rather than repeat that information here, I refer the reader to my earlier post.
Different tick species inhabit different areas of the country. But, regardless of the species, there are three things you should know (and remember) about ticks: (1) how to prevent tick bites; (2) if you find a tick attached to your body, how to remove it; and (3) once it’s removed, how to identify the species.
Several outstanding Internet resources are available for guidance on prevention of tick bites, tick removal, species identification, and the pathogens transmitted by ticks. I found the following sites to be the most useful: Tick Encounters from the University of Rhode Island; Tick Identification-You Tube; Tick Removal-YouTube; and Mayo Clinic’s Guide to different tick species and diseases they carry (https://www.mayoclinic.org › tick-species › sls-20147911).
On the horizon for Lyme disease: a new diagnostic test and vaccine. Lyme disease, caused by the bacterium, Borrelia burgdorferi (carried by the blacklegged tick), is the most impactful of all the tickborne infections. (In the U.S., medical costs of $1 billion per year are ascribed to Lyme disease.) According to the Centers for Disease Control and Prevention, the number of cases of Lyme disease in the U.S. has climbed to approximately half a million a year. An August 3, 2022 article in FAIR Health, “Insurance Data Shows Big Rise in Lyme Disease in US,” reported the dramatic increase not only of acute Lyme disease but also of a poorly understood condition known as chronic Lyme disease.
There is a treatment for this tick-borne disease. If administered in a timely fashion, doxycycline, a safe and inexpensive antibiotic, remains effective in treatment of most cases of Lyme disease. Currently, a persistent shortcoming for timely administration of this antibiotic is the lack of a reliable diagnostic test for the disease. To address this need, researchers at Tufts University have developed a new test for Lyme disease which should be available soon.
To me, the most exciting news in the field of Lyme disease is the development of a vaccine to prevent the disease. Pfizer and the French drugmaker Valneva created VLA15, a vaccine that is in its final stage of a clinical trial. VLA15 aims to protect people as young as five from Lyme disease. (If the phase-three clinical trial is a success, the companies say they would likely seek official authorization in 2025).
Ticks on the move. Two tick species are on the move in the U.S. The Heartland virus (HRTV) was first detected in Missouri in 2009. The lone star tick, the vector for HRTV, has now spread to six states. Most people infected with HRTV experience fever, fatigue, decreased appetite, headache, nausea, diarrhea, and muscle or joint pain. Many are hospitalized but only rarely is the infection fatal (mainly in older adults).
Until it was first reported in the U.S. in 2017, the Asian longhorned tick was not found in the Western Hemisphere. Now this tick has been found in a number of animal species throughout the States. As of September 2021, Asian longhorned ticks were identified in animals in Arkansas, Connecticut, Delaware, Georgia, Kentucky, Maryland, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia, and West Virginia.
The Asian longhorned tick appears to be less attracted to human skin than our “native” ticks (such as the blacklegged tick, lone star tick, and American dog tick). Experimental studies have shown, however, that Asian longhorned ticks have the ability to carry the bacterium that causes Rocky Mountain Spotted fever, but human cases have yet to be identified.
Ticks to keep our eyes on. As we saw with the arrival of the Asian longhorned tick, ticks are capable of immigrating to the U.S. Two tick-borne infections that are not (yet) seen in the U.S. that we need to carefully watch for are tick-borne encephalitis (TBE) and Langya henipavirus (LayV) virus infection.
In certain parts of the world, TBE virus, a member of the family Flaviviridae, is an important cause of viral infection in the central nervous system. Fortunately, neither the virus nor the tick species that carry it (Ixodes ricinus and persulicatus), are currently found in the U.S. But in eastern, central, northern and increasingly western European countries, and in northern China, Mongolia, and the Russian Federation, TBE causes about 10,000-12,000 cases of encephalitis (brain infection) a year. (The FDA-approved vaccine, TicoVac, is available to protect U.S. adults and children (1 year or older) against the TBE virus when living in or visiting endemic areas.)
LayV, a new animal virus recently identified in eastern China, was first described in the New England Journal of Medicineon August 4, 2022. Carried by shrews, LayV is a zoonotic disease that causes respiratory tract infections which can be fatal. It is closely related to two other henipaviruses, Hendra virus and Nipah virus, and it shares a tick vector (tick species Haemaphysalis longcornis) with a bunyavirus that causes tick-borne severe fever with thrombocytopenia syndrome (SFTS)
In the U.S. the tick species Haemaphysalis longicornis exists but neither the SFTS virus nor LayV has been reported. It is essential, however, that the public health, veterinary medicine, and medical communities remain vigilant and alert us if these viruses get a foothold in ticks in the U.S.
Let’s hear it for acarology (the study of mites and ticks). In February 2022, it was announced that for the first time acarologists had edited genes of ticks using the genome editing tool CRISPR-Cas9. The goal of these researchers is to better understand the biology of ticks on a deeper, more molecular level, with an eye to applying their discoveries to methods for improving human and animal health. The value of this research, published in iScience, is increasingly obvious in an era when climate change is allowing ticks to rapidly invade new areas, putting even more people and animals at risk of disabling and sometime fatal tick-borne infections.