Microbiology Case Study: A 44 Year Old Male Finds a Tick on His Leg

Case History A 44 year old male pulled this (image 1) off of his leg after dragging brush out of a tree line in Vermont.

Image 1. Ixodes scapularis under a microscope. Characteristic features such as eight black legs, dorsal shield, and dark red color can be appreciated.

Ixodes scapularis

Ixodes scapularis, also known as the blacklegged tick or deer tick, is commonly found in the eastern and northern Midwest regions of the United States as well as southeastern Canada. This species of tick is approximately 3 mm in length. Morphologically, females have a black head and a dorsal shield with a dark red abdomen, while males are entirely black or dark brown. Both sexes have eight black legs and a characteristic anal opening, appearing within a horseshoe-shaped ridge on the ventral lower abdomen. Unlike other tick species, Ixodes scapularis does not have ridges on the edge of the lower abdomen. Ixodes scapularis can live up to 2 years in the wild and die after reproduction.1

Life Cycle, Transmission, and Infection

Ixodes scapularis is a three-host tick with a different host at each stage of development. Their life cycle lasts approximately 2 years, where they undergo 4 distinct developmental/life stages: egg, six-legged larva, eight-legged nymph, and adult. After hatching from the egg, it should have a blood meal at every developmental stage to survive. Ixodes scapularis is known to parasitize and feed from mammals, birds, reptiles, and amphibians, and its best-known host is the white-tailed deer. This species is unable to fly or jump so it usually waits for a host while resting in the tips of grass or shrubs. Depending on the developmental stage, preparation for feeding can take between 10 minutes to 2 hours.2 Once the tick finds a feeding spot on the host, it grasps onto the skin and cuts into the surface inserting its feeding tube, which can have barbs and can secrete a cement-like surface for better attachment. Moreover, the tick can also secrete small amounts of saliva with anesthetic properties to remain undetected during the blood meal. If attached to a sheltered spot, the tick can remain unnoticed for long periods. Ixodes scapularis will attach to its host and suck on the blood for a few days. The lengthy feeding process makes them good at transmitting infection. If the host has a bloodborne infection (e.g., Lyme disease), the tick may ingest the pathogen and become infected. If the tick feeds on a human later, that human can become infected with the same pathogen if it is a prolonged blood meal. However, if the tick is removed quickly (~ 24 hours), the risk of acquiring disease is reduced.2 The longer the tick is attached, the greater the risk of becoming infected. The risk of human infection is greater during the spring and summer.

Ixodes scapularis as a Disease Vector

Babesiosis

The causative agent of babesiosis are Basebesia microti and other Babesia species. These parasites preferentially infect red blood cells. In the United States, most cases are caused by Babesia microti.3 Babesiosis is most frequently reported in the upper midwestern and northeastern regions of the United States, where Babesia microti is endemic. Although this parasite is generally transmitted by Ixodes scapularis, Babesia parasites can also be transmitted via blood transfusions and, in some cases, congenitally. Babesiosis can range from asymptomatic to life-threatening. Some of the common signs and symptoms include fever, chills, sweats, general malaise or fatigue, myalgia, arthralgia, headaches, anorexia, nausea, and dark urine. Less common symptoms include cough, sore throat, emotional lability, depression, photophobia, conjunctival infection.3 Not all infected persons are symptomatic or febrile. Clinical presentation usually manifests within several weeks after exposure, but may develop or recur months after infection. The incubation period for Babesia species parasites is approximately 1-9+ weeks. Laboratory findings associated with babesiosis include decreased hematocrit due to hemolytic anemia, thrombocytopenia, elevated serum creatinine and blood urea nitrogen values, and mildly elevated hepatic transaminase values.3 To diagnose babesiosis in the laboratory, identification of intraerythrocytic Babesia parasites by light-microscopic examination of a blood smear, positive Babesia (or Babesia microti) PCR analysis, or isolation of Babesia parasites from a whole blood specimen by animal inoculation in a reference lab are recommended procedures. Additionally, demonstration of a Babesia-specific antibody titer by indirect fluorescent antibody testing for IgG can be used as supportive laboratory criteria—although it is not enough evidence to support a diagnosis of an active infection.3 Treatment for babesia usually lasts 7-10 days with a combination of two drugs: atovaquone plus azithromycin or clindamycin plus quinine, with the latter being the standard of care for severely ill patients.

Anaplasmosis

Anaplasmosis, formerly known as Human Granulocytic Ehrlichiosis, is caused by Anaplasma phagocytophilum. Anaplasmosis is commonly reported in the upper Midwest and northeastern regions of the United States. The incubation period for Anaplasma phagocytophilum is 5-14 days.3 Some of the common signs and symptoms of anaplasmosis include fever, chills, rigors, severe headaches, malaise, myalgia, gastrointestinal symptoms such as nausea, vomiting, diarrhea, and anorexia, and, in some cases, rash. The general laboratory findings for anaplasmosis during the first week of clinical disease include mild anemia, thrombocytopenia, leukopenia, and mild to moderate elevations in hepatic transaminases.3 Under the microscope, the visualization of morulae in the cytoplasm of granulocytes during examination of blood smears is indicative of diagnosis. However, to definitely determine diagnosis in the laboratory, detection of DNA by PCR of whole blood is recommended during the first week of illness. Additionally, demonstration of a four-fold change in IgG specific antibody titer by indirect immunofluorescence antibody assay in paired serum samples is recommended. The first serum sample should be taken during the first week of illness and the second serum sample should be taken 2-4 weeks after. Moreover, immunohistochemical staining of the organism from the skin, tissue, or bone marrow biopsies is also recommended for diagnosis.3 Anaplasmosis is treated with doxycycline. Treatment should be started once there is a clinical suspicion of disease, as delaying treatment may result in severe illness or in death.

Lyme Disease

The causative agents for Lyme disease include Borrelia burgdorferi and Borrelia mayonii. Lyme disease is most frequently reported in the Upper Midwestern and northeastern regions of the United States with some cases being reported in northern California, Oregon, and Washington. Data from 2015 shows that 95% of Lyme disease cases were reported in the following 14 states: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, and Wisconsin.3 The incubation period for Borrelia parasites is usually 3-30 days.3 Some of the early (3-30 days after a tick bite) signs and symptoms of Lyme disease include fever, chills, headache, fatigue, muscle and joint aches, and swollen lymph nodes may occur with an absence of rash. Erythema migrans is a characteristic rash of Lyme disease and it occurs in 70%-80% of infected people.4 This rash starts at the site of a tick bite after an average of 3-30 days (average is 7 days) and it gradually expands over several days reaching up to 30 cm across.4 As it enlarges, it can result in the characteristic “bulls-eye” appearance; it may feel warm to the touch and it is rarely itchy or painful. Some of the later (days to months after a tick bite) signs and symptoms include severe headache and neck stiffness, additional erythema migrans rashes in other areas of the body, facial palsy, arthritis with severe joint pain and swelling—especially in the knees, intermittent pain in the tendons, muscles, joints, and bones. It may also lead to heart palpitations or Lyme carditis, episodes of dizziness or shortness of breath, inflammation of the brain and spinal cord, nerve pain, and shooting pains, numbness, or tingling of the hands and feet.4 Laboratory diagnosis for Lyme disease includes the demonstration of IgM or IgG antibodies in serum and a two-step testing protocol is highly recommended.5 Moreover, isolation of an organism from a clinical specimen is also recommended. Treatment for Lyme disease includes antibiotics such as doxycycline, cefuroxime axetil, or amoxicillin.

When assessing a patient for any tick-borne diseases, the clinical presentation should be considered alongside the likelihood that the patient has been exposed to an infected Ixodes scapularis tick, or any other tick. Moreover, if a tick is found, engorgement of the tick should be considered when assessing for the possibility of disease transmission.

References

  1. Thevanayagam S. Ixodes scapularis [Internet]. 2012. Available from: https://animaldiversity.org/accounts/Ixodes_scapularis/.
  2. Centers for Disease Control and Prevention. Lifecycle of Blacklegged Ticks [Internet]. 2011 [updated November 15, 2011]. Available from: https://www.cdc.gov/lyme/transmission/blacklegged.html.
  3. Centers for Disease Control and Prevention. Tickborne Diseases of the United States: A Reference Manual for Healthcare Providers [Internet]2018. Available from: https://www.cdc.gov/ticks/tickbornediseases/TickborneDiseases-P.pdf.
  4. Centers for Disease Control and Prevention. Lyme Disease – Signs and Symtoms [Internet]. 2021. Available from: https://www.cdc.gov/lyme/signs_symptoms/index.html.
  5. Mead P, Petersen J, Hinckley A. Updated CDC Recommendation for Serologic Diagnosis of Lyme Disease. MMWR Morb Mortal Wkly Rep. 2019;68(32):703. Epub 2019/08/16. doi: 10.15585/mmwr.mm6832a4. PubMed PMID: 31415492; PubMed Central PMCID: PMCPMC6818702 potential conflicts of interest. No potential conflicts of interest were disclosed.

Amelia Lamberty is a Master’s student in the Pathology Master’s Program.

-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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