Chapter 64: Infectious Disorders

Infectious mononucleosis, predominantly caused by Epstein-Barr virus, presents with the classic triad of fever, pharyngitis, and cervical lymphadenopathy, often accompanied by splenomegaly and atypical lymphocytosis. Diagnosis relies on heterophile antibody testing, and management is primarily supportive with emphasis on activity restriction to prevent splenic rupture. Lyme disease, transmitted by Ixodes scapularis ticks infected with Borrelia burgdorferi spirochetes, manifests in three clinical stages: early localized disease marked by erythema migrans rash, early disseminated disease with secondary skin lesions and neurological manifestations such as facial palsy, and late disease characterized by arthritis and encephalopathy. Two-step serological testing confirms diagnosis when clinical presentation is unclear, and doxycycline remains the standard antimicrobial treatment. HIV infection progressively destroys CD4+ T cells through reverse transcriptase-mediated integration into host DNA, with transmission occurring via sexual contact, blood exposure, or perinatal routes. The CDC recommends universal screening using fourth-generation antigen-antibody assays, and modern management involves initiating antiretroviral therapy regardless of CD4 count to achieve viral suppression and prevent transmission. AIDS develops when CD4+ counts decline below 200 cells per microliter or opportunistic infections emerge, including Pneumocystis jiroveci pneumonia, Mycobacterium avium complex, toxoplasmosis, and candidiasis. Prophylaxis protocols for opportunistic infections and regular monitoring of viral load and CD4 counts are essential components of care, alongside preventive immunizations and management of comorbid conditions in this chronically managed population.