Microbiology Case Study: A 34 Year Old Female with Nausea, Vomiting, Diarrhea and Tender Extremities

Case History

A 34 year old female presented to the emergency department with a chief complaint of nausea, vomiting and diarrhea as well as tenderness in her extremities. These symptoms had been present for the previous 4 days with multiple episodes of diarrhea, associated low grade fevers & chills and she had poor oral intake as a result. Her past medical history was significant for human immunodeficiency virus (HIV) and chronic kidney disease. She has not be compliant with her anti-retroviral therapy and infectious disease prophylactic medications. Her vitals were within normal range and her physical exam elicited tenderness to palpation of her extremities and torso. No rashes and no erythema are seen. Routine laboratory tests as well as infectious disease work up, which included blood, stool & urine cultures, C. difficile and ova & parasite exam, were ordered. Notable findings included a slightly elevated white blood count (11.3 TH/cm2), creatinine of 7.1 mg/dL, HIV RNA viral load of 671 VC/mL and an absolute CD4 count of 7 cells/cm2. Two days after collection, her blood cultures were signaled as positive by the automated instrument.

Laboratory Identification

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Image 1. Gram stain from the blood culture bottles showed Gram negative cocci arranged in pairs (1000x oil immersion).
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Image 2. Small, whitish glistening colonies grew on blood and chocolate agars after 48 hours incubation in a 35°C incubator with 5% CO2.

The pathogen of interest grew from two sets of blood cultures and the direct Gram stain showed Gram negative cocci arranged in pairs (Image 1). After 48 hours incubation, small, whitish colonies were observed on blood and chocolate agars. No growth was seen on the MacConkey plate (Image 2). The isolate was positive for both catalase and oxidase. It was identified as Neisseria gonorrhoeae by both MALDI-TOF MS and a Vitek NH card.

Discussion

N. gonorrhoeae is the second most common sexually transmitted infection (STI) in the United States, only surpassed by Chlamydia trachomatis and they are often acquired together as a co-infection. Uncomplicated infections with N. gonorrhoeae typically present as acute urethritis with discharge. Asymptomatic infection occurs in 10% of males and upwards of 50% of females. As a result, females are at risk for the development of ascending infections and pelvic inflammatory disease leading to further reproductive issues. Disseminated gonococcal infection is uncommon (less than 1% of all gonococcal infections) but can occur and manifests as purulent arthritis with or without an accompanying dermatitis. In the case of our patient, her tenderness to palpation of the extremities could be a symptom of this disseminated septic arthritis.

In the laboratory, N. gonorrhoeae can be fastidious and requires special media such as chocolate, Martin-Lewis, modified Thayer-Martin or New York City agars as well as an enhanced CO2 environment in order to grow. The Gram stain of N. gonorrhoeae is described as Gram negative cocci with adjacent flattened sides and helpful biochemicals include catalase and oxidase (both positive).  Traditionally, in order to further speciate members of the Neisseria genus, sugar fermentation was necessary. N. gonorrhoeae only ferments glucose, while another notable member, N. meningitides, ferments both glucose and maltose.  Additionally, N. lactamica ferments glucose, maltose and lactose. Currently, commonly used methods of identification include API NH strips and automated instruments such as Vitek and MALDI-TOF MS.

Susceptibility testing for N. gonorrhoeae is usually limited to testing for beta-lactamase activity, although CLSI guidelines are available if deemed necessary. Current therapeutic guidelines recommend empiric treatment of uncomplicated infections with intramuscular ceftriaxone and oral azithromycin.

 

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-Kristen Adams, MD, is a fourth year Anatomic and Clinical Pathology resident at the University of Mississippi Medical Center. 

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-Lisa Stempak, MD, is an Assistant Professor of Pathology at the University of Mississippi Medical Center in Jackson, MS. She is certified by the American Board of Pathology in Anatomic and Clinical Pathology as well as Medical Microbiology. She is the director of the Microbiology and Serology Laboratories.  Her interests include infectious disease histology, process and quality improvement and resident education. 

Microbiology Case Study: A 50 Year Old Male with Fever and Diarrhea

Case History

A 50 year old male initially presented with cold symptoms. He was seen and evaluated at urgent care, with suspicion for bronchitis, but with no improvement with albuterol. Physical exam raised a suspicion for bacterial sinusitis. The patient was treated with amoxicillin/clavulanic acid with little improvement, and he was admitted to the hospital a week later for fever and diarrhea. Blood cultures were obtained. He was initially treated with cefepime prior to the speciation of the culture, and then switched to erythromycin for a 7 day course.

Laboratory Identification

Blood cultures were positive for gram negative curved/spiral rods. Gram stain and colony morphology were consistent with Campylobacter which was confirmed as C. jejuni by MALDI-TOF.

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Image 1. Gram stain showing gram negative curved/spiral rods.

Discussion

C. jejuni are gram negative curved or spiral rods. Campy CVA agar is used for stool cultures because it is selective for Campylobacter and contains cefoperazone, vancomycin, and amphotericin B (CVA) which inhibit normal fecal flora. The media is incubated at 42°C under microaerophilic conditions, supporting the growth of Campylobacter jejuni and C. coli. C. jejuni is thermophilic, with growth on blood agar at 37°C and 42°C. Growth does not occur at 25°C. The colonies on blood agar are non-hemolytic, gray and smooth. Our isolate grew, albeit not happily, on blood and chocolate at 37°C with 5-10% CO2.

Infection is often transmitted by contaminated foods such as undercooked chicken. C. jejuni are most commonly associated with human infections however, C. coli have also been implicated. Guillain-Barre syndrome has been associated with patients following an infection with C. jejuni. It is not known how our patient was exposed. Macrolides are effective treatment modalities for C. jejuni, as well as fluoroquinolones, however, resistance to fluoroquinolones is increasing.

 

-Mustafa Mohammad, MD is a 3rd year anatomic and clinical pathology resident at the University of Vermont Medical Center.

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-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.

Microbiology Case Study: An 18 Year Old with Vaginal Discharge

Case Presentation

An 18 year old girl presents to her pediatrician with her mother for her pre-college check-up. She has no past medical history. After her mother leaves the room for the social history component, the girl admits to having sex with her boyfriend for the first time two weeks ago and complains of a yellow green malodorous vaginal discharge that started a week ago. She endorses mild pelvic pain. A pelvic exam is performed and mild cervical tenderness is noted. The cervix is pink, nulliparous, inflamed and is covered by small red punctate spots. A thin yellow green frothy discharge of fishy odor is also detected. A wet prep is made and reveals squamous cells and numerous motile organisms.

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Figure 1.  Trichomonas vaginalis in a Pap test. The protozoa are often found next to squamous cells. (ThinPrep)

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Figure 2.  Collection of Trichomonas vaginalis parasites eating at a squamous cell in a Pap (ThinPrep)

Discussion

Our patient was diagnosed with Trichomonas vaginalis (TV). TV is a flagellated parasitic protozoan for which humans are the only known host. It is 10-20 um long and 2-14 um wide with multiple flagella projecting from the anterior and posterior sides. It has a single trophozoite stage and does not survive well outside of its host. TV is a predatory obligate parasite that eats bacteria, vaginal epithelial cells, and red blood cells. It uses fermentative metabolism to produce the carbohydrates needed for fuel. TV is a sexually transmitted disease; however, because it is not reportable to local health departments, the true epidemiologic incidence rate is unknown. Its prevalence is highly variable by population and location. For example, some studies cite a prevalence of 3.1% of American pre-menopausal women (2.3% of adolescents) [1], while in certain high-risk populations the rate might be as high as 47% [2]. Most affected patients are asymptomatic; about a third of females become symptomatic within six months of infection. Symptoms for females include vulvar and vaginal irritation and itching, pain with urination and a diffuse, malodorous, yellow-green vaginal discharge. The cervix becomes reddened in a punctuated fashion causing the well-known strawberry cervix seen on colposcopy. In males, urethritis can develop. TV is often diagnosed via wet mount microscopy, where the protozoa can be seen moving around (Video 1). However, the sensitivity is relatively low, especially among males. Detection by nucleic acid probe from urine, endocervical, and vaginal swabs are considered more sensitive. TV can also be incidentally discovered on Pap tests (Figures 1 and 2). Treatment typically consists of a single dose of metronidazole [1,2]. It is critical that partners be treated as well, because otherwise reinfection may occur.

 

References

  1. Kissinger P. Trichomonas vaginalis: a review of epidemiologic, clinical and treatment issues. BMC Infectious Diseases. 2015; 15(307): 1-8.
  2. Meites E et al. A review of evidence-based care of symptomatic trichomoniasis and asymptomatic Trichomonas vaginalis infections. Clinical Infectious Diseases. 2015; 61(S8): S837-48.

 

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-Amanda Strickland, MD, is a 2nd year Anatomic and Clinical Pathology Resident at UT Southwestern Medical Center.

Erin McElvania TeKippe, PhD, D(ABMM), is the Director of Clinical Microbiology at Children’s Medical Center in Dallas Texas and an Assistant Professor of Pathology and Pediatrics at University of Texas Southwestern Medical Center.

 

Microbiology Case Study: A 58 Year Old Female with Lung Nodules

Case History

A 58 year old female with past medical history significant for Type II diabetes, hypertension, hyperlipidemia, chronic diastolic heart failure, and hypothyroidism was hospitalized for following a fall and was found to have compression fractures. The hospitalization was complicated by flash pulmonary edema requiring intubation. CT chest obtained during this hospitalization demonstrated lung nodules, which were biopsied and cultured.

Laboratory Identification

The bacterial and mycobacterial cultures grew gram positive bacilli which were positive on Modified Kinyoun stain. They were negative for Auramine/Rhodamine. The organism grew on several media, including 7H11, Chocolate, and Buffered Charcoal Yeast Extract (BCYE). They formed chalky, white-pink colonies. The organism was confirmed as Nocardia nova by a reference laboratory.

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Image 1. Modified acid fast bacilli on Modified Kinyoun stain.

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Image 2. Chalky white-pink colonies on BCYE agar.

Discussion

Nocardia nova is a weakly acid fast, aerobic filamentous, beaded, gram positive bacilli with right-angled branching. It is identified by a Modified Kinyoun stain. Nocardia grows best on BCYE agar; however it also can grow within 3-5 days on blood and chocolate agar. It forms chalky white-pink colonies. Molecular testing is performed to speciate Nocardia, primarily 16S ribosomal RNA gene sequencing, as well as mass spectrometry. Most infections can be treated with sulfonamides for 6-12 months, however, the CDC recommends performing speciation and susceptibility testing on every isolate due to specific susceptibility profiles and drug resistant strains. Our patient was treated with high dose sulfamethoxazole/trimethoprim and meropenem.

Nocardia nova is commonly found in soil and is one of several pathogenic Nocardia species. Nocardia is often inhaled and presents as a chronic pulmonary infection with cough, shortness of breath, and fever. Nocardia can also cause pleural effusions, empyema, pericarditis, abscesses, or dissemination to deep organs, especially the brain. Nocardia can also be contracted though trauma, causing cutaneous diseases such as a mycetoma or cellulitis. Because of its low virulence, Nocardia generally affects immunocompromised patients, however those with preexisting pulmonary disease can also be susceptible to infection.

 

-Mustafa Mohammad, MD is a 3rd year anatomic and clinical pathology resident at the University of Vermont Medical Center.

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-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.

Hematopathology Case Study: A 69 Year Old Female with Persistent Monocytosis

Case History

A 69 year old female with a past medical history significant for endometrial adenocarcinoma, traumatic brain injury, atrial fibrillation, hypertension, hyperlipidemia, and persistent monocytosis (absolute monocyte count ranging from 1.6-3.7 K/uL) who had an indeterminate lesion identified in the T5 vertebra, read as “hemangioma, although surrounding edema is worrisome for malignancy” upon staging imaging for history of endometrial carcinoma.

CBC at the time was: WBC 9.8; HGB 12.9; HCT 37.6; PLT 154; MCV 92 fL; MCH 31.7.

Automated differential showed: 43.0 Neutrophils; 34.8 Lymphocytes; 20.0 Monocytes; 1.4 Eosinophils; 0.2 Basophils; 0.6 Immature granulocytes.

Absolute monocyte count was 1.95 K/uL.

This lesion was biopsied and given the findings, a subsequent bone marrow biopsy was performed on 5/4/2017. The bone marrow core biopsy contained multiple compact aggregates of spindle shaped cells with hypogranular cytoplasm, morphologically compatible with atypical mast cells. Within these aggregates, numerous eosinophils are present. By immunohistochemistry, the mast cells are brightly positive for CD117 and mast cell tryptase. Concurrent bone marrow aspirate flow cytometry demonstrated a small population of mast cells that co-expressed CD2 and CD25.

Of note, the patient was found to have a persistent absolute monocytosis. Flow cytometry revealed an abnormal population of monocytes that displayed aberrant phenotypic expression of CD2 and CD56 (subset).

Next-generation sequencing revealed two truncation mutations in the TET2 gene (K988* in 34.6% of the reads and Q1138* in 36.4% of the reads). Cytogenetic analysis revealed a normal female karyotype (46,XX).

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Overall, an immunophenotypically abnormal population of mast cells and monocytes are present in the context of a long-standing absolute monocytosis and the presence of two TET2 truncating mutations, supporting a diagnosis of systemic mastocytosis with an associated hematologic non-mast cell lineage disorder (best classified as chronic myelomonocytic leukemia).

Discussion

A diagnosis of systemic mastocytosis is a combination of clinical, morphologic, immunophenotypic, and molecular analyses, as required by the World Health Organization (WHO 2008). By current consensus guidelines, SM variants are partly distinguished by clinicopathologic criteria referred collectively as B and C findings. B findings include: >30% of bone marrow mast cells (MC) on biopsy and/or serum tryptase levels >200 ng/mL; increased marrow cellularity/dysplasia without meeting diagnostic criteria for another myeloid neoplasm; or enlargement of liver, spleen, or lymph nodes without evidence of organ damage. C findings include: evidence of organ damage caused by a local MC infiltrate, such as abnormal liver function and/or ascites, hypersplenism, cytopenias, large osteolytic lesions/fractures, and malabsorption with weight loss caused by MC infiltrate in the gastrointestinal tract.

Systemic mastocytosis commonly occurs in two types with different clinical courses based upon the aforementioned findings. Indolent SM (ISM) is defined by the absence of C findings. Smoldering SM is a subtype of ISM that displays 2 or more B findings. ISM may become more aggressive and a descriptive term of advanced SM refers to a category including aggressive SM (ASM), mast cell leukemia (MCL), and “SM with an associated myeloid neoplasm.” The latter entity comprises more than 90% of cases that have previously been referred to as SM with an associated hematologic non-mast cell lineage disorder (SH-AHNMD).

ASM and MCL are characterized by organ damage and histologic characteristics. ASM often exhibits multifocal bone marrow infiltration of atypical mast cells that are often spindled in shape with hypogranular or immature morphology. Marked fibrosis often accompanies the infiltrate as well as a KIT D816V mutation. MCL is codified by more than 20% of the marrow aspirate nucleated cells represent by mast cells and on core biopsy, a compact infiltrate is often identified with usually low level fibrosis. In MCL, circulating mast cells are greater than 10% of nucleated cells but according to Gotlib et al., the aleukemic MCL (less than 10% circulating mast cells) is more common.

In the context of our patient, myeloid neoplasms associated with SM are often represented by MDS, MPN, or MDS/MPN overlap disorders, and occasionally AML.

Associated lymphoid or plasma cell neoplasms have been described, but in a much lower frequency.

In accordance with the diagnostic implications, KIT D816V mutational analysis is important therapeutically. Most patients with SM harbor the KIT D816V mutation (>80% in one clinical series; 90-100% in research studies using purified MCs), which is a considered imatinib-resistant mutation. Midostaurin (a second generation TKI) may provide some disease response while nilotinib or dasatinib are usually less likely to lead to a durable response. The rare patients who have a juxtamembrane domain KIT mutation are much more likely to respond to imatinib or masitinib.

For disease response, criteria were first published in 2003 by Valent, et al. In a reiterated version published in 2007, the evaluation of clinical evidence of organ damage (C findings), was the foundation for determining appropriate response. Another facet to determining response was in relation to BM MC burden, serum tryptase level, and organomegaly, which further subcategorized the levels of major response (MR). MR was defined as normalization of 1 or more C findings. In turn, MR was divided into 3 categories:

  1. Complete remission (resolution of MC infiltrates in organs, serum tryptase less than 20 ng/mL, and disappearance of SM-associated organomegaly)
  2. Incomplete remission (decrease in MC infiltrates in organs and/or serum tryptase levels and/or visible regression of organomegaly by >50%)
  3. Pure clinical response (without decrease in MC infiltrates, serum tryptase levels, or organomegaly)

Partial response (PR) is defined as incomplete regression of 1 or more C findings and include good partial response (GPR; >50% regression of 1 or more C findings) and minor response (<50% regression).

Lastly, the Mayo Clinic published revised response criteria in 2010 which established minimal baseline laboratory abnormalities for organ damage to be evaluated in order to allow for more accurate assessment of response to therapy that is clinically more relevant.

Overall, systemic mastocytosis is a rare entity that displays a range of presentations that can be described as indolent up to an aggressive (advanced) phenotype. The hallmarks for diagnosis include histologic, immunophenotypic, molecular, and clinical findings.

 

References

  1. Gotlib, J et al. “International Working Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) & European Competence Network on Mastocytosis (ECNM) consensus response criteria in advanced systemic mastocytosis,” Blood, 2012.
  2. Horny HP et al. “Mastocytosis,” In: Swerdlow S et al. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. Lyon: IARC Press; 2008:53-63
  3. Valent P et al. “Aggressive systemic mastocytosis and related mast cell disorders: current treatment options and proposed response criteria.” Leuk Res. 2003;27(7):635-641.
  4. Pardanani A, et al. “A critical reappraisal of treatment response criteria in systemic mastocytosis and a proposal for revisions. Eur J Haematol. 2010;84(5):371-378.

 

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-Phillip Michaels, MD is a board certified anatomic and clinical pathologist who is a current hematopathology fellow at Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA. His research interests include molecular profiling of diffuse large B-cell lymphoma as well as pathology resident education, especially in hematopathology and molecular genetic pathology.

Microbiology Case Study: A 60 Year Old Male with Longstanding Skin Lesions

Case History

A 60 year old male from Louisiana presents to his family doctor with a chief complaint of longstanding skin lesions for approximately the last two years. On physical exam, there are several sharply defined reddish-brown plaques on his upper back and extremities. He reports sensory loss involving his chest, back and upper extremities. The lesions have not responded to conventional topical anti-fungal treatments. Punch biopsies along the margin of the most active lesion were obtained and sent to the Microbiology laboratory for bacterial, fungal and mycobacterial cultures and to the Pathology Department for histologic diagnosis.

Tissue sections

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Image 1. Section from the right upper extremity skin punch biopsy demonstrates a normal basket-weave stratum corneum and normal epidermis with nodular superficial and deep granulomatous inflammatory infiltrate. A Grenz zone, a narrow layer beneath the epidermis that is not infiltrated or involved in the same way as are the lower layers of the dermis, is noted (H&E, 40x).
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Image 2. Inflammation engulfing eccrine glands in the deep portion of the dermis (H&E, 100x).
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Image 3. Portion of punch biopsy demonstrating perineural inflammation consisting predominantly of mononuclear cells (H&E, 400x).
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Image 4. Fite stain highlighting numerous acid fast bacilli within macrophages surrounding the eccrine glands (1000x oil immersion).

 

On histologic examination of the skin biopsy, nodular, superficial and deep granulomatous inflammation was noted surrounding eccrine glands and engulfing nerves (Images 1-3). Fite staining illustrated numerous acid fast bacilli (Image 4) and, given the geographic location of the patient and clinical symptoms, was felt to be highly suggestive of Mycobacterium leprae. The case was sent for confirmatory testing by polymerase chain reaction (PCR). All cultures collected were negative.

Discussion

Mycobacterium leprae is a chronic, granulomatous disease which presents as anesthetic skin lesions and peripheral neuropathy with nerve thickening. While rare in the United States (US) today, historically it was one of most prominent pathogens in Mycobacterium genus apart from M. tuberculosis. In the past, leprosy (also known as Hansen’s disease) was prevalent throughout Europe, but due to systematic control programs aimed at underserved and rural locations, the number of cases drastically decreased and countries with the majority of recent cases include India, Brazil and Indonesia. According to National Hansen’s Disease Registry, a total of 178 cases were reported in the US in 2015. Of these, 72% (129) of cases were reported in Arkansas, California, Florida, Hawaii, Louisiana, New York and Texas. Transmission to those who are in prolonged and close contact with an infected person is thought to occur via shedding from the nose. While humans are the only known reservoir of leprosy, infections with organisms indistinguishable from M. leprae have been detected among wild armadillos in parts of the southern US.

The diagnosis of M. leprae is largely a clinical one as the organism is not able to be grown on artificial media, but histology and confirmatory PCR are useful adjuncts. Skin biopsies should be full thickness and include the deep dermis. Ideally, the most active edge of the most active lesion should be biopsied. There is a spectrum of M. leprae which ranges from few lesions and a paucity of bacilli (tuberculoid leprosy) to widespread skin involvement with numerous bacilli (lepromatous leprosy).  Histologically, there are granulomatous aggregates of epithelioid cells, multinucleate giant cells and lymphocytes and inflammation often engulfs sweat glands and nerves. Small lesions that have poorly defined borders and are found on the elbows, knees or ears are where bacilli tend to be located. A Fite stain is useful to highlight the acid fast bacilli located in the macrophages within the inflammatory nodules. M. leprae PCR can also be performed on blood, urine, nasal cavity specimens and skin biopsies as a sensitive diagnostic technique. PCR can also be used to detect certain genes that confer resistance to common treatment drugs such as rifampin, ofloxacin and dapsone.

As with other mycobacterial diseases, the treatment for M. leprae infections consists of a long term multidrug regimen. The six most commonly used medications include rifampin, dapsone, clofazimine, minocycline, ofloxacin, and clarithromycin.

 

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-Katie Tumminello, MD, is a fourth year Anatomic and Clinical Pathology resident at the University of Mississippi Medical Center. 

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-Lisa Stempak, MD, is an Assistant Professor of Pathology at the University of Mississippi Medical Center in Jackson, MS. She is certified by the American Board of Pathology in Anatomic and Clinical Pathology as well as Medical Microbiology. She is the director of the Microbiology and Serology Laboratories.  Her interests include infectious disease histology, process and quality improvement and resident education. 

Microbiology Case Study: A 51-Year-Old Woman with a Tick Bite

Case History

A 51-year-old female with a past medical history of chronic lower back pain, depression, and anxiety presented to an outpatient dermatology clinic for a lesion on her left cheek that was present for years but has recently grown and become irritated.  Additionally, she reported a “skin taggy thing” that she first noticed on her posterior neck about two days ago.  Upon physical examination, a tick was observed latched onto the right posterior neck.  After being alerted to the presence of a tick, the patient did disclose that she was in the woods three days prior.  The bite site was locally anaesthetized and the tick was removed and sent to the laboratory for arthropod identification.  Furthermore, the patient received a single prophylactic dose of doxycycline 200 mg.

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Image 1. Ixodes scapularis, adult female, dorsal surface: an anterior capitulum (A) that contains mouth parts (paired palpi (B) and a median (partially intact) hypostome (C)) and the basis capituli (D) with two porose areas (E). The scutum (F) is inornate. 
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Image 2. Ixodes scapularis, adult female, ventral surface: eight coxa (G) of paired legs I-IV, a genital aperture (H), two spiracular plates (I), and an anal groove (J) that is anterior to the anus (K).

 

Discussion

Ixodes scapularis (black-legged ticks), also known as deer ticks (their preferred hosts are white-tailed deer), are small arachnids.  As obligate ectoparasites of vertebral hosts, I. scapularis are also willing to feed on humans.  Importantly, infected arthropods can be vectors of multiple pathogens including: the spirochete, Borrelia burgdorferi, that causes Lyme disease; the intracellular gram-negative bacterium, Anaplasma phagocytophilum, that causes human granulocytic anaplasmosis; the Apicomplexan parasites, Babesia spp, that cause babesiosis; and the flavivirus, Powassan virus, that causes encephalitis.

The I. scapularis life cycle, ranging from one to two years in length, is composed of four developmental stages: egg, larva, nymph, and sexually dimorphic adult.  Compared to nymphs and adults that have eight legs, larvae are smaller and have six legs.  The term “three-host cycle” implies that during each of the three motile stages, I. scapularis takes a blood meal from a different host animal, at which time the tick’s saliva is injected and transmission of pathogens can occur.

Hard ticks possess an anterior capitulum (Image 1, A) whereas soft ticks lack a capitulum.  The capitulum is made up of mouth parts that are attached to the basis capituli.  The mouth parts refer to paired appendages called palpi (Image 1, B) that are parallel to a median hypostome (Image 1, C).  The hypostome holds teeth-like structures, called denticles, arranged in a specific formula useful for identification.  The mouth parts (palpi and hypostome) are longer than the width of the basis capituli (Image 1, D) and this ratio is also useful in identification.  The dorsal surface of the basis capituli has two porose areas (Image 1, E) in adult females that secrete wax to waterproof eggs.  The dorsal shield, called a scutum (Image 1, F), is absent in soft ticks and inornate compared to other hard ticks.  In adult males, the scutum covers nearly the entire dorsum.  Other hard ticks have eyes (lateral markings on the scutum) and festoons (grooved bulges on the posterior margin) that are both absent in I. scapularis.  The ventral surface demonstrates coxa (Image 2, G) that are the basal segments of paired legs, numbered I-IV from anterior to posterior.  Posterior to coxa IV are paired spiracular plates (Image 2, I), external openings of the respiratory system.  A median genital aperture (Image 2, H) is present in adults.  The distinct anal groove (Image 2, J) is an inverted U-shaped curve located anterior to the anus (Image 2, K) in all Ixodes species, as opposed to posterior or indistinct anal grooves of other genera of hard ticks.

Following arthropod identification in parasitology, microbiology laboratory reports include: the genus (Ixodes), species (scapularis), developmental stage (adult female), level of engorgement (unengorged), and status of mouth parts (partially intact).  The genus and species are of medical importance because of their characteristic associations with various human pathogens.  Of the developmental stages, nymphs and adults are most frequently associated with human transmission of A. phagocytophilum.  Also, larvae are unable to transmit B. burgdorferi because the spirochete is not transmitted vertically to eggs; as such, a blood meal from a reservoir host is required.  Nymphs, being smaller in size than adults, are more likely to complete feeding undetected and thereby transmit B. burgdorferi.  Feeding is necessary for adult females to achieve fertility; therefore males are less likely to be discovered on hosts.  The level of engorgement, an estimate of feeding time, is relevant because approximately 36 hours are required for B. burgdorferi to multiply in the tick’s midgut and migrate to salivary glands for transmission to a host, by which time ticks are visibly engorged.  Lastly, if the mouth parts (palpi and hypostome) are intact, this suggests that there was only brief host contact and it is less likely that pathogen transmission occurred.

Reference

-Patterson FC and Winn WC. Practical identification of hard ticks in the parasitology laboratory. Pathology Case Reviews 2003; 8(4):187-198.

 

-Adina Bodolan, MD is a 1st year anatomic and clinical pathology resident at the University of Vermont Medical Center.

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-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.