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