By Cat Troiano
With summer just around the corner, outdoor recreation beckons. While sun, surf and communing with nature provide enjoyment throughout the warmer months, the season also presents ticks, which pose serious health risks that can compromise quality of life. When we think about diseases that are spread via bites from ticks, Lyme disease typically comes to mind. While Lyme disease is the most commonly diagnosed tick-borne illness, these parasitic arachnids transmit a lengthy list of other maladies as well. Many of these illnesses present with similar signs and symptoms, which is why testing is important for attaining a diagnosis.
How Are Tick-Borne Illnesses Spread?
Once hosts, such as mice, deer, dogs and sheep, become infected, they harbor the disease pathogens. Depending on which tick-borne disease is infecting the host, such pathogens may be viral, bacterial or protozoan in nature. Some tick-borne diseases are rickettsial, meaning that they are caused by rickettsia, which are microorganisms that possess qualities of both viruses and bacteria. Rickettsia cannot thrive and reproduce outside of living cells.
Ticks are parasitic organisms. Once a tick feeds off of the blood from an infected host, the tick becomes a vector. The contracted pathogen is then carried by the tick and transferred into the next host off which it feeds.
What Are the Most Common Tick-Borne Illnesses?
According to the Centers for Disease Control and Prevention, the number of confirmed and probable cases of Lyme disease exceeded 42,000 in 2017 and remains the most frequently reported tick-borne illness in the United States. Lyme disease is transmitted by the black-legged leg, which is commonly known as the deer tick, throughout the northeast, northern Midwest and mid-Atlantic states. It is also transmitted by the western black-legged tick in northern California and up the Pacific coast. You can read more about Lyme disease and its test interpretations here. Additional tick-borne illnesses, their vectors and geographic prevalence include:
- Anaplasmosis, transmitted by the black-legged tick in the northeastern and northern midwestern regions and by the Western black-legged tick in northern California and along the Pacific coast
- Ehrlichiosis, transmitted by the Lone Star tick throughout the eastern states and by the American dog tick along the Pacific coast and in areas east of the Rocky Mountains.
- Rocky Mountain spotted fever, transmitted by the American dog tick east of the Rocky Mountains and along the Pacific coast
- Rickettsia parkeri rickettsiosis, transmitted by the Rocky Mountain wood tick throughout the Rocky Mountain region
- Babesiosis, transmitted by the black-legged tick in the northeastern and northern midwestern regions and by the Western black-legged tick in northern California and along the Pacific coast
- Tularemia, transmitted by the Lone Star tick throughout the eastern states, by the Rocky Mountain wood tick throughout the Rocky Mountain region and by the American dog tick along the Pacific coast and in areas east of the Rocky Mountains
- Powassan virus, transmitted by the black-legged tick in the northeast as well as in the states of Virginia and Wisconsin
- Borrelia miyamotoi disease, transmitted by the black-legged tick in the northeastern and northern midwestern regions and by the Western black-legged tick in northern California and along the Pacific coast
- Tick-borne relapsing fever, transmitted by the orinthodoros soft tick in the western states
- Colorado tick fever, transmitted by the Rocky Mountain wood tick throughout the Rocky Mountain region
- Heartland virus, transmitted by the Lone Star tick in midwestern and southern states
Some ticks can harbor multiple diseases, and coinfection from one tick bite is a possibility. It is also important to note that some of these illnesses can be contracted internationally, and a number of additional tick-borne diseases have been identified in other nations. Novel tick-borne illnesses can also emerge, such as the recently identified Long Island tick rhabdovirus, which is transmitted by the ambloyomma americanum tick, and 364D rickettsiosis, transmitted by the Pacific Coast tick and recently discovered in the state of California.
Signs of Tick-Borne Illnesses
The signs and symptoms of many tick-borne illnesses are not unique to these illnesses, and they present with most of the tick-borne diseases. These influenza-like symptoms typically include:
- Muscle aches
- Joint pain
- General malaise
Some illnesses may progress with the presentation of symptoms of serious complications, such as neurological deficits, kidney or liver failure, or compromised cardiorespiratory function. Some diseases, such as Lyme disease, may present with a characteristic rash, but it is crucial to note that these rashes do not emerge on all infected patients.
On the rise in recent years is the incidence of red meat allergies caused by the bite of the Lone Star tick. Galactose is a monosaccharide, a simple sugar that is found in some foods, often in combination with glucose to form the disaccharide lactose. However, the Lone Star tick produces another galactose compound known as galactose-alpha-1,3-1 galactose, or alpha-gal, in its gastrointestinal tract. When the tick bites its host, this sugar is injected, and it renders the host allergic to red meats. This condition is known as alpha-gal syndrome. Some affected individuals will suffer from anaphylactic shock after consuming beef, pork, lamb and other red meats, and the reaction may occur three to six hours after they have eaten the red meat.
Another tick-borne condition is tick paralysis, a rare phenomenon that primarily affects children. Tick paralysis is transmitted by various tick species, including the American dog tick, and it results when a biting tick deposits a neurotoxin into its host. Signs of tick paralysis include flaccid weakness, changes in voice, respiratory difficulty and neurological symptoms of paralysis ascend up the body from the lower extremities. Unlike other tick-borne illnesses, the condition typically resolves rapidly and completely once the infected tick is extricated from the host, but if the tick is not discovered and the condition continues to progress, respiratory failure and death can result.
So many diseases and symptoms! How are physicians to make specific diagnoses under these conditions? Laboratory tests are available for detecting antibodies for several of the most common tick-borne illnesses.
Laboratory testing to identify a particular tick-borne disease should be pursued for any patient who presents with these symptoms and meets any one of the following criteria that increases his or her risk for exposure:
- The patient found a tick attached on their body.
- The patient resides in a geographic location in which any tick-borne disease(s) is prevalent.
- The patient has recently traveled to a geographic location where tick-borne illnesses are prevalent.
- The patient has recently spent time in an area where ticks are endemic – i.e. camping in a wooded area.
Abnormal laboratory findings on a complete blood count in a patient with tick-borne illness may include low hematocrit, platelet and white blood cell counts and an elevated reticulocyte count. Abnormal findings on a metabolic profile may include elevated liver enzymes and elevated renal values, which include creatinine and blood urea nitrogen levels. Elevated protein may be detected on a urinalysis.
In addition to ordering a complete blood count and metabolic profile, there are numerous individual laboratory tests available to diagnose particular suspected tick-borne diseases. Depending on the test that is selected, diagnosis is achieved through the following various methods:
- Microscopic visualization and identification of the pathogen in blood cells
- Enzyme-linked immunosorbent assay (ELISA) to detect specific antibodies
- Immunofluorescent assay (IFA) to detect particular IgG or IgM antibodies
- Polymerase chain reaction to identify pathogen DNA
- Immunoblot technique, such as the Western blot test
- Culture to identify bacterial pathogens
The newest addition to the arsenal of tests for diagnosing tick-borne diseases is the TBD Serochip, which is a real-time polymerase chain reaction method screening. The advantage of this particular test is that it evaluates one blood sample to detect antibodies of eight of the most common tick-borne pathogens found in the United States. This alone makes this test valuable in that it can pinpoint a specific infection when generalized symptoms might otherwise require multiple individual tests, and it also has the capability to identify coinfections. The eight diseases that can be diagnosed with this test include Lyme disease, anaplasmosis, babesiosis, ehrlichiosis, Rocky Mountain spotted fever, Heartland virus, Powassan virus and borrelia miyamotoi.
An alpha-gal IgE test is available for determining if a patient who has suffered an allergic reaction after consuming red meat has contracted alpha-gal syndrome.
There is no laboratory test for tick paralysis. However, if a patient presents with symptoms, physicians should seek out a tick that is attached on the patient as well as order testing to rule out Guillain-Barre syndrome, an autoimmune disorder that presents with similar signs, including paralysis.
Treatment and Prevention
Tick-borne diseases, some of which can progress rapidly, should be treated as early as possible in symptomatic patients, which often means administering treatment even before test results become available. Most tick-borne diseases are treated with antibiotic therapy, typically with doxycycline or tetracycline.
There is no treatment for alpha-gal syndrome, and patients are strongly advised to avoid all red meat and food products containing meat-based ingredients. In some cases, allergy symptoms can abate over time if the patient does not sustain another bite from a tick that injects alpha-gal.
To reduce the risk of contracting tick-borne diseases, patients should be advised to take preventative measures, which includes adopting the following practices:
- When venturing outdoors where there is an inherent risk of exposure to ticks, don light-colored clothing so that ticks are easy to spot, and wear long sleeves and pants. Tucking the bottoms of the pant legs into white socks will help to prevent ticks from migrating to the legs, and they will be easy to find on white socks.
- Apply a tick repellent spray that contains DEET to both outer clothing and exposed skin.
- Campers should spray the outer surfaces of tents and other gear with insecticidal products that contain permethrin.
- When hiking, remain on cleared trails, and avoid straying off course into areas with tall grasses, brush and weeds.
- Pet owners should apply topical tick preventative products as prescribed by their veterinarians to dogs and to cats that go outdoors.
- Clothing should be stripped immediately upon returning indoors and placed directly into the dryer for 10 minutes to kill any ticks that were missed when inspecting the apparel. Patients should then shower and wash their hair, and conduct a thorough inspection of their skin from head to toe, removing any ticks immediately.
- Outdoor home property should be maintained and kept free of all brush and debris to eliminate areas that small wild animals, the primary hosts for ticks, may find hospitable. Trees, lawns and shrubs should be sprayed regularly with insecticide products.
To help physicians to rule out some of the tick-borne disease possibilities, patients should be advised to deposit any ticks that they extricate from their bodies into a sealed jar or a Ziploc bag. If symptoms of illness develop, bringing the tick along to the doctor’s appointment can facilitate a visual identification of the tick, which helps to guide in antibiotic and test selection for more timely success with treatment.