Human Pests: Lice and Bed Bugs (Pt. 2)

Epidemic Typhus, Epidemic Typhus, and Louse-borne relapsing fever

What is Rickettsia prowazekii?

responsible for epidemic typhus

Basic Information about Rickettsia prowazekii

• Gram-negative

• Obligate intracellular & parasitic

• Aerobic Bacillus bacteria

• Etiologic agent of epidemic typhus

Define Etiologic

causing or contributing to the development of a disease or condition

What is Epidemic Typhus?

a disease of cold months when heavy clothing and poor sanitary conditions are conducive to lice proliferation

Who named the genus Rickettsia?

• Henrique de Rocha Lima

  • given to the intracellular microorganisms found in lice

Taxonomy of Rickettsia

• Two families: (1) Anaplasmataceae and (2) Rickettsiaceae

• The latter family comprises the genera Rickettsia and Orientia

• Two distinct groups are found within the Rickettsia genus, including the spotted fever group and the typhus group

What two species of the typhus group are pathogenic for humans?

1. Rickettsia typhi

2. Rickettsia prowazekii

How is Rickettsia prowazekii transmitted?

• Transmitted in the feces of lice

  • Transmitted when it poops = right after feeding

• Spread the infection when scratching or rubbing skin

• One of its relatives (ancestor) precipitated some of the greatest plagues to afflict the human race

  • NOTE: Epidemic typhus often confused with typhoid fever

Mitochondrial Evolution Paradox

Transmission of Epidemic Typhus

• The transmission does not directly occur by bites but by the contamination of bite sites

• Do the pathogens have a negative effect on the vector?

  • For many vectors, it is unclear.

  • Here, the vector (lice) is harmed by the pathogen

    • multiplies in the lower gut epithelium

    • released on the rupture of infected epithelial cells

    • Blood enters the louse body cavity as a result of loss of the epithelial lining, the louse becomes red, and infected red lice die within 1 week

Clinical Symptoms and Signs of Epidemic Typhus

• Many organisms of the Rickettsiaceae family cause important human diseases with a broad range of clinical manifestations

• Most human rickettsioses are diagnosed by careful clinical examination and epidemiological investigation of patients

• Patients usually have 1–3 days of malaise before the abrupt onset of severe headaches and fever

• Other symptoms include severe myalgias, arthralgias, rashes, and non-specific constitutional symptoms (ie, malaise, anorexia, chills);

Other Clinical Symptoms and Signs of Epidemic Typhus

• CNS manifestations (eg, delirium, coma, and seizures) can occur in up to 80% of cases.

• Skin lesions are distributed mostly on the trunk, starting in the axilla, and may spread centrifugally to involve the extremities

  • Occasionally, they are found on the soft palate and conjunctiva, but not on the face, palms, and soles

• Eschars are absent

• Brill-Zinsser disease

Diagnosis and Treatment of Epidemic Typhus

• Doxycycline = a tetracycline antibiotic