Louse- and flea-borne diseases

Louse- and flea-borne diseases are caused by pathogens that are transmitted by lice or fleas. The most dangerous flea-borne diseases are plague and murine typhus.

Epidemic typhus is a louse-borne disease that is described separately in “Typhus.”

Trench fever (five-day fever)

• Epidemiology: most commonly affects people who are at risk of body louse infestation (e.g., homeless)
• Etiology: Bartonella quintana
• Transmission: : feces of infected body louse (vector)
• Clinical features
  • Recurrent fever episodes that last ∼ 5 days
  • Nonspecific, flu-like symptoms (malaise, headache, nausea, vomiting)
  • Bone pain, splenomegaly, and maculopapular rash of the trunk may occur
• Diagnostics: isolation of Bartonella confirms the diagnosis
  • Bartonella is difficult to grow on culture
  • Serology testing or PCR are often necessary
• Treatment: doxycycline PLUS gentamicin

Louse-borne relapsing fever

• Epidemiology: most common in areas affected by overcrowding, war, refugee camps
• Pathogen: Borrelia recurrentis
• Transmission: : feces of infected body louse (vector)
• Clinical features
  • Recurring episodes of high fever (39–43°C) lasting 3–6 days followed by an afebrile period of 7 days
  • Other symptoms include headache, arthralgia, nausea, confusion, macular rash
• Diagnostics
  • Confirmatory test: detection of B. recurrentis in peripheral blood smear, bone marrow, or CSF with Wright or Giemsa stain
  • Culture is difficult
  • Laboratory studies: normocytic anemia, thrombocytopenia , ↑ ESR
• Treatment
  • Doxycycline OR ceftriaxone
  • Children and pregnant woman: amoxicillin and cefuroxime

Borrelia recurentis causes a recurrent (relapsing) fever.

Murine typhus is described separately in “Typhus.” Dipylidiasis is described separately in "Helminth infections."

Plague

Epidemiology ^[1]

• Endemic in the Western US as sporadic cases in rural areas
• Certain foci in Asia (e.g., India), South America, and sub-Saharan Africa (e.g., Madagascar)

Etiology ^[1][2]

• Pathogen: Yersinia pestis
• Reservoir: : prairie dogs, squirrels, rodents
• Transmission
  • Bites by infected fleas (most common)
  • Rarely: contact with tissue or respiratory droplets from an infected animal or human ^[2]

Y. pestis is considered a pathogen of the highest concern because of its potential use as a bioweapon. ^[2]

Clinical features ^[1][2]

The signs and symptoms of plague depend on the clinical form of the disease.

• Incubation period: 1–8 days ^[1][2]
• Bubonic plague (most common)
  • Symptoms of bubonic plague include sudden onset of fever, headache, myalgias, chills, and painful swollen lymph nodes (buboes)
  • May progress to sepsis, pneumonia, and meningitis
• Pneumonic plague
  • Symptoms of pneumonic plague overlap with symptoms of pneumonia (e.g., fever, dyspnea, productive cough) ^[2]
  • Rapid progression with possible respiratory failure and shock if untreated
• Septicemic plague: clinical features of sepsis, possible shock, gastrointestinal symptoms (e.g., abdominal pain, diarrhea), acral gangrene, without localizing signs ^[1][2]
• Rare forms: meningeal , pharyngeal ^[2]

Diagnosis of plague ^[1][3]

Suspect plague in patients with concerning clinical features who report recent travel to endemic areas or contact with rodents or other vectors. Diagnosis is confirmed if Y. pestis is detected on microscopy or culture or the F1 antigen of Y. pestis is detected on serology.

• Microbiology
  • Bacterial cultures from blood, sputum, CSF, or bubo aspirate depending on the presentation
  • Direct visualization and staining on microscopy
    • Wayson stain: bipolar staining of bacteria (“closed safety pin” appearance)
    • Gram stain: small gram-negative coccobacilli
• Serology: detects antibodies to F1 antigen of Y. pestis ^[3]
• Rapid tests: detect F1 antigen; highly sensitive and can be used to support diagnosis in remote areas ^[4][5]

Plague is a nationally notifiable disease. ^[1]

Treatment of plague ^[2]

Immediately start antibiotic therapy for 10–14 days. ^[2]

• Bubonic or pharyngeal plague
  • First-line: fluoroquinolones, e.g., ciprofloxacin (off-label) , doxycycline , or aminoglycosides, e.g., gentamicin (off-label) ^[2]
  • Second-line: chloramphenicol (off-label) ^[2]
• Pneumonic or septicemic plague
  • First-line: fluoroquinolones, e.g., ciprofloxacin , or aminoglycosides, e.g., gentamicin (off-label) ^[2]
  • Second-line: tetracyclines, e.g., doxycycline ^[2]
• Plague meningitis: chloramphenicol (off-label) or fluoroquinolones, e.g., levofloxacin ^[2]

Do not delay treatment for diagnostics. ^[3]

Prevention of plague ^[1][2]

• Infection control: Implement droplet precautions for patients with pneumonic plague.
• Postexposure prophylaxis: Consider for individuals who have had direct contact with a person with pneumonic plague, an infected animal, or infectious materials.
  • Doxycycline (off-label) ^[2]
  • OR a fluoroquinolone, e.g., ciprofloxacin ^[2]
• Vaccination is not currently available in the US.