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21.1: Case Study: Threats to Our Health

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    Case Study: What's Lurking in the Woods

    Nineteen-year-old Ximena spent a relaxing week of summer vacation visiting her grandparents in New Jersey. She particularly enjoyed taking their dog on long walks in the woods near their home, occasionally spotting deer on the overgrown paths. About a week after she returned home to California, Ximena came down with what she thought was the flu. She had a fever, chills, fatigue, headache, and body aches. But in the shower one morning, she noticed an unusual rash on her calf. It looked like a bulls-eye on a target, with a central circle surrounded by a ring, similar to the rash in Figure \(\PageIndex{1}\).

    Erythema migrans-erythematous rash in Lyme disease
    Figure \(\PageIndex{1}\): This is erythematous bulls-eye rash because of the concentric rings.

    The rash caused Ximena to become concerned that she might have something other than the flu. She went to her doctor, who examined her and asked if she had taken any trips lately. Surprised, Ximena said yes, and told him about her trip to New Jersey. He told her that a bulls-eye rash combined with flu-like symptoms are often indications of Lyme disease. Lyme disease can occur in California, but it is much more prevalent in the northeastern United States, including New York and New Jersey (Figure \(\PageIndex{2}\)).

    U.S. map showing reported cases of Lyme Disease at a county-wide level for 2017
    Figure \(\PageIndex{2}\): Map of cases of Lyme disease reported to the Centers for Disease Control and Prevention (CDC) in 2017, based on the county of residence of the infected person. This does not mean the person was actually infected in that location since people travel, but there are vastly more cases of Lyme disease reported in the Northeast and Upper Midwest than in the rest of the U.S.

    Lyme disease is caused by bacteria that are spread to people through tick bites. In the northeastern U.S., it is spread by the black-legged tick or deer tick. These ticks are commonly found in wooded areas, such as the paths Ximena walked on during her trip. So those relaxing walks in the woods might have caused Ximena to pick up an unwanted souvenir—a disease that was making her feel awful.

    Although flu-like symptoms can indicate any number of diseases, a bulls-eye rash is a distinctive characteristic of Lyme disease. Therefore, based on Ximena’s symptoms and the fact that she was in an area likely to harbor Lyme disease, her doctor immediately starts her on medication to treat Lyme disease. To confirm the diagnosis, he also takes a blood sample to test for the disease. He tells Ximena that she may not test positive yet, even if she does have Lyme disease, because it can take a few weeks after infection for evidence to show up in the blood. In the meantime, the medication he prescribed should start helping her feel better soon if she does have Lyme disease.

    In this chapter, you will learn about some of the major types of human diseases. These include infectious diseases, such as HIV, as well as noninfectious diseases, such as most cancers. You will learn about the causes of these diseases, the effects they have on the body, and the types of treatment. You will also learn about the ways in which infectious diseases are transmitted, and steps you can take to prevent infection. At the end of the chapter, you will learn more about how Lyme disease is transmitted, its effects on the body, how it is treated, Ximena’s path to recovery, and how you can protect yourself from this relatively common infectious disease.

    Chapter Overview: Disease

    In this chapter, you will learn about human diseases. Specifically, you will learn about:

    • How problems in regulating homeostasis can result in disease.
    • The differences between infectious and noninfectious diseases, and acute and chronic diseases.
    • Epidemics, pandemics, endemic diseases, and emerging diseases.
    • The science of epidemiology and how it is used to improve public health.
    • The different types of pathogens that cause infectious diseases, how they are transmitted, and how they can be prevented and treated.
    • Sexually transmitted diseases, such as genital herpes, human papillomavirus (HPV), and human immunodeficiency virus (HIV), and their effects on the body; how they can be prevented and treated; and their impact on public health.
    • Noninfectious diseases such as diabetes, cardiovascular disease, cystic fibrosis, and cancer, and their mechanisms, risk factors, diagnosis, and treatments.
    • Ways to prevent noninfectious disease through healthy lifestyle choices.

    As you read the chapter, think about the following questions:

    1. What kind of medication do you think Ximena’s doctor gave her to treat Lyme disease?
    2. What type of pathogen transmission is involved in Lyme disease? What is another disease that is transmitted in a similar way?
    3. Why, specifically, might Ximena’s blood test not be positive for Lyme disease for a few weeks, even if she does have the disease?
    4. How do you think the term “endemic” relates to Lyme disease?


    1. Erythematous rash by CDC/ James Gathany, public domain
    2. Reported Cases of Lyme Disease – the United States, 2018; Centers for Disease Control (CDC), public domain
    3. Text is adapted from Human Biology by CK-12 licensed CC BY-NC 3.0

    This page titled 21.1: Case Study: Threats to Our Health is shared under a CK-12 license and was authored, remixed, and/or curated by Suzanne Wakim & Mandeep Grewal via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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