Fleas & Plague
Announcements
• Should have Chap 9 read by today
• Presentation today by Jonathan Rogers
• On Deck for Thursday Philip Crain,
Gordon Chaney. Subject will be: Black
flies, sand flies, biting midges and their
diseases
• Read Chaps 10, 11, 12, 13
• Will review for hour exam on Thursday
• Note “In the News” on the website
Quiz Review
• Question 1 – B, A, D. Note: Because of typo: E,A, D also was
acceptable. Grading – 2 out of 3 = full credit, 1 right = 1 point.
• Question 2. Grading – 4/5 = full credit, 2 or 3/5 = 1 point
X Allergies
X Psychological Stress
__ Trench Fever & Relapsing Fever
X Intermediate Hosts of Animal Parasites
__ or X Food Contamination
• Question 3. Grading – 4/5 = full credit, 2 or 3/5 = 1 point.
__ or X Lice are solenophages
__ Bed bugs are laterally flattened
X All bugs are adapted to feeding on liquids
X Bed bugs are in the same order as Kissing Bugs
__ Bed bugs are actually more closely related to lice than to Conenose bugs
Quiz Review
• Question 4. Best Answer in Class
“It is indirectly transmitted through the feces
of the bug when the host scratches it into
the biting wound or site or into mucus [sic]
membranes.”
Class Quiz Scores
Number of Students
12
10
8
6
4
2
0
6
7
8
9
Points Out of 10 Possible
10
Disease pathology
• Pathogen replicates mainly within vascular
endothelial cells.
• Infected cells proliferate and degenerate, results
in vascular occlusion.
• Occlusion induces a focal ulcer followed by
hematogenous dissemination of the pathogen
systemically.
• Abrupt onset of clinical disease after ~4 weeks:
headache, fever, and often a hemorrhagic rash.
• Ocular lesions sometimes occur as with all of the
diseases produced by Rickettsiae.
Louse-borne Relapsing Fever
• Spirochete bacterium, Borrelia recurrentis
• Pathogen infects the louse blood stream,
is transmitted when the louse is crushed &
rubbed in to the skin.
• Few thousand/year, 95% of cases are in
Ethiopia.
Trench Fever
• Bacterial disease, Bartonella quintana
• A form of “Bartonellosis”. We’ll see
another one later.
• Like typhus, transmitted in louse feces.
• Often asymptomatic in healthy hosts. May
express nonspecifically in stressed hosts.
• Increased association of stress & urban
environments leads to term: “Urban
Trench Fever”.
Fleas
• Order Siphonaptera with 15 families & about 2,500 spp.
• All spp. are ectoparasites of vertebrates, almost all (94%)
target mammals.
• Closest living relatives are the Boreidae (snow
scorpionflies) in the Order Mecoptera (scorpionflies)
Boreid example
“sensilium”
=
“pygidium”
“ctenidium” = “comb”, e.g. “genal
comb” = “genal ctenidium”
Flea Identification
• Identification is based on external morphology
• Usually difficult on “raw” specimens but easy on “cleared”
specimens
• Several pictorial keys that are easy to use.
• Here is a good one from CDC
Uncleared Specimen
Cleared Specimen
Flea Identification: What is this flea?
Flea Identification: What is this flea?
Flea Identification: What is this flea?
Flea Identification: What is this flea?
Note the location of the ocular bristle
Flea Identification: What is this flea?
Medical/Public Health Significance
• Allergies
• Tungiasis – infestation by chigoe fleas
• Others (rickettsia, helminths, Q-fever, other
pathogens).
• Murine (endemic) Typhus
• Plague: 3 forms
– Bubonic is from the flea
– Pneumonic from aerial dispersal
– Septicemic from high-titer injection
Murine Typhus
• Also called “endemic typhus” or “flea-borne
typhus”, see book for other names
• Rickettsial: Rickettsia typhii (different species
than epidemic typhus, R. powazekii)
• Flea acquires pathogen from rats, passes it in
feces, feces get scratched into skin.
• No obvious negative effect on flea (unlike R.
powazekii which kills the louse).
• Patients present with mild – high fever,
prostration, sometimes rash. Debilitation can be
a couple of months, low fatality rate.
Plague
• Bacterial disease, Yersinia pestis
• Primarily a rodent pathogen, humans are
accidental hosts
• When ingested, bacterium multiplies in
flea gut, blocks it. Future attempts at
feeding result in regurgitation of
contaminated blood.
Manifestation
• Following injection into the new host, initial replication is inside
tissue macrophages.
• Macrophages rupture, releasing larger numbers of bacteria into the
blood stream.
• Many attack the draining lymph nodes, which become hot, swollen,
tender, and hemorrhagic, giving rise to the characteristic black
buboes responsible for the name of this disease.
• Within hours of the initial flea bite, the infection spills out into the
bloodstream, leading to substantial involvement of the liver, spleen,
and lungs.
• Patient develops a severe bacterial pneumonia, exhaling large
numbers of viable organisms into the air during coughing fits
representing a highly contagious health hazard to caregivers.
• Incubation period is 1 – 6 days (depending on form) and patient
remains infectious for 3 weeks or death.
• Once infected/contaminated, most rodents & fleas remain infectious
for life.
Spread of the Black Death
Historical Impact Example: The
Horse Plague
Historical Impact Example: The
Horse Plague
Historical Impact Example: The
Horse Plague
Horse Plague Impact
• Spain ceased active colonization from
Spain. Essentially froze Spanish
influence.
• Italy never colonized the Americas
• French colonial aspirations were restricted
in their infancy.
• In the absence of competition from Spain,
Portugal, Italy, & France – England
developed a blue-water navy.
Why the periodic pandemics?
• Three biotypes (“biovars”) of Y. pestis:
– biovar ‘Antiqua’ – Justinian’s Plague (541)
– biovar ‘Medievalis’ – Black Death (1347)
– biovar ‘Orientalis’ – Chinese Plague (1894)
• At least some pandemics were more
related to the vector than to the pathogen.
– E.g. Horse Plague (1512) was probably driven
by the human flea, Pulex irritans rather than
the Oriental Rat Flea, Xenopsylla cheopis
Current Status of Plague
•Between 1998 and
2008, nearly 24,000
cases have been
reported, including about
2,000 deaths
•In 2003, 9 countries
reported 2118 cases and
182 deaths.
•98.7% of those cases
and 98.9% of those
deaths were reported
from Africa.
•Most serious current
epidemic is in the Congo
(FKA Zaire).
• August, 2009, outbreak
in Qinghai, China
US Human
Cases
1970 - 1997
US normally has 10 – 20
cases/year