Chapter 23 – Infections of the Blood & Lymph

Lyme Disease

  • Causative Agent: Borrelia burgdorferi (Gram-negative spirochete)
  • Disease Signs & Symptoms:
    • 1st Stage: Erythema migrans (bull’s-eye rash), flu-like symptoms
    • 2nd Stage: Heart irregularities, CNS symptoms
    • 3rd Stage: Arthritis, headaches, fatigue, depression
  • Disease Pathogenesis:
    • Early infection: Dissemination via bloodstream
    • Late infection: Tissue penetration; infection of heart, joints, skin
    • Evades immune system via surface proteins
  • Disease Epidemiology:
    • Leading vector-borne disease in U.S.
    • Found in Northeast, Midwest, Pacific West
    • Reservoirs: Field mice, squirrels, deer
    • Transmission: Bite of Ixodes tick
    • High-risk: Farmers, landscapers
  • Prevention & Treatment:
    • Early treatment with Doxycycline
    • Prevention: LYMErix vaccine (Recombinant OspA), DEET use, prompt tick removal
  • Diagnosis & other notes:
    • Clinical diagnosis based on signs, patient history
    • Chronic arthritis, facial palsy, long-term neurological symptoms

Toxoplasmosis

  • Causative Agent: Toxoplasma gondii (protozoan parasite)
  • Disease Signs & Symptoms:
    • Often asymptomatic
    • Congenital infection: Mental disabilities, blindness, deafness, stillbirth
    • In AIDS patients: Encephalitis
  • Disease Pathogenesis:
    • Oocysts ingested \rightarrow parasites distributed by macrophages \rightarrow lodge in organs like liver, brain, retina
    • Forms cysts
    • Capable of vertical transmission
  • Disease Epidemiology:
    • Reservoirs: Cats (Felidae family), cattle, pigs, rodents, humans
    • Highly prevalent in Central America (up to 95%)
    • Transmission: Vertical, fecal-oral (kitty litter, soil), undercooked meat
  • Prevention & Treatment:
    • Treatment: Sulfonamide + Trimethoprim; Spiramycin (early pregnancy)
    • Prevention: Hand washing, limit cat hunting, avoid raw/undercooked meat, pregnant women avoid litter boxes
  • Diagnosis & other notes:
    • Blood smear or CSF sample
    • Congenital defects (mental disabilities, blindness)
    • Encephalitis in AIDS patients
    • Potential link to mental disorders (e.g., schizophrenia)

Schistosomiasis

  • Causative Agent: Schistosoma spp. (S. mansoni, S. japonicum, S. haematobium)
  • Disease Signs & Symptoms:
    • Fever and rash
    • Blood in urine or stool
    • Enlarged liver or spleen (splenomegaly)
    • Possible CNS involvement
  • Disease Pathogenesis:
    • Cercariae penetrate skin \rightarrow adults mature in blood \rightarrow eggs deposited in vessels \rightarrow inflammation
    • Eggs shed in urine or feces
  • Disease Epidemiology:
    • Hundreds of millions infected annually
    • High prevalence in sub-Saharan Africa
    • Reservoirs: Wild animals (monkeys), humans
    • Transmission: Larvae penetrate skin in fresh water via snails (vector)
  • Prevention & Treatment:
    • Treatment: Praziquantel (causes muscle spasms and paralysis of worms)
    • Prevention: Avoid snail-infested water, proper sanitation, control snail populations
  • Diagnosis & other notes:
    • Diagnosis by detecting eggs in urine or stool
    • Granulomas in bladder \rightarrow bladder cancer
    • Liver damage
    • Infertility
    • Colon cancer

Gas Gangrene

  • Causative Agent: Clostridium perfringens (Gram-positive, obligate anaerobe)
  • Disease Signs & Symptoms:
    • Severe pain and swelling at wound site
    • Necrosis (death of tissue)
    • Gas production in wounds
  • Disease Pathogenesis:
    • Damage to blood supply \rightarrow necrosis \rightarrow anaerobic environment
    • Alpha toxin: Breaks down cell membranes, triggers blood clots
    • Theta toxin: Forms pores in cell membranes
    • Fermentation produces gas in tissues
  • Disease Epidemiology:
    • Common in war and surgical wounds, miscarriages, intestinal injuries, diabetic injuries, frostbite
    • Reservoirs: Human GI tract, soil, aquatic environments
    • Transmission: Wound contamination
  • Prevention & Treatment:
    • Treatment: Surgery (debridement), hyperbaric oxygen therapy, antibiotics
    • Prevention: Proper wound care, prophylactic antibiotics before surgeries
  • Diagnosis & other notes:
    • Fluid culture from wound site
    • Rapid spread
    • Death from sepsis if untreated