Rickettsiae

CASE 1

• A 38 year old man complained of fever and “flu” 5 days after returning from a business trip to South Africa. He was part of a team of 6 West African engineers who visited a dam construction site in South Africa. As the fever began, he also noticed 4-5 new, crusty spots on his legs and buttocks (see below). They were not painful or tender. He could not account for them.

• One other member of the visiting team, a Nigerian, had also experienced fever after the trip.

• P.E. Temp= 39.0, HR=100/min, BP=125/85. There were 5 eschars (3-5 mm in size) on the lower body. Otherwise unremarkable.

• The patient was given oral doxycycline 100mg twice daily for 3 days, and his fever resolved promptly. Three weeks later, a serology to Rickettsia africae was positive at 1:1250.

Questions:

1. How was this infection acquired?
2. What is the usual outcome of this infection when untreated? When treated?
3. R. africae belongs to which group of Rickettsial pathogens? How is it related to Rickettsia rickettsii, the agent of Rocky Mountain Spotted Fever? What other agents belong in this group?
4. Which cells of the body are primarily infected by this group of pathogens?
5. How do Rickettsiae evade the humoral immune response? (hint: How do they move from cell-to-cell?)
6. Can you isolate the infecting pathogen from this patient? If so, what would be required?

CASE 2

• A 35 year old Ghanaian military physician joins a UN-sponsored mission to support the medical facilities at a refugee camp in Chad, east of Darfur. The occupants of the camp are underfed, and there have been severe water shortages limiting washing of clothes and personal hygiene. Shortly after the physician arrives, an outbreak of fever begins in the camp. Within two weeks, the camp facility records over 60 episodes of a non-specific, malarial-smear-negative fever with 18 associated deaths.

• Most of the patients have developed punctate hemorrhages (petechiae) on the skin, spreading from the trunk to the distal extremities. Some have large black, bruise-like lesions in the skin (ecchymoses). A photograph of an afffected individual is shown below. Death is associated with hypotension and shock. Most of the ill patients are also noted to have body lice.

• On suspicion of epidemic typhus, all patients with undifferentiated fever are treated promptly with doxycycline, and the additional deaths are averted.

Questions:

1. How is this disease transmitted from lice to humans? Specifically, what is indicated by the blue arrow in the photo of a louse below?



2. What is the name of the pathogen that causes louse-borne (epidemic) typhus?
3. To what group of Rickettsiae does this pathogen belong? What are the other members and the diseases that they cause
4. Where is epidemic typhus most likely to occur?
5. What is the usual reservoir for louse-borne typhus?
6. How can this outbreak best be controlled in the refugee camp?