Arthropod borne infectious
disease
Arthropods that Transmit Disease
• Ticks, mosquitoes, fleas and biting flies
– Transmission usually by biting or ingestion
Infections
• Bacterial
– Ricketsia ricketsii, Borrelia burgdorferi, Yersinia
pestis, Francisella tularensis
• Viral (arboviruses)
– Dengue, West Nile, Encephalitic viruses
• Parasites
– Malaria, Dracunculiasis, tape worms
Rocky Mountain Spotted Fever
• Caused by obligate intracellular bacterium
Rickettsia rickettsii
• Tick borne disease
Fever, nausea, severe headaches, muscle pain and rash
Rocky Mt. spotted fever
Lyme Disease
• Borrelia burgdorferi
• Spirochete
• Obligate Intracellular pathogen
Borrelia burgdorferi
• 1.5Mbp
• Strange genomic layout
– Linear chromosome (900 kb)
– Has over 20 circular AND linear plasmids
• Genome decay in obligate intracellular bacteria
• Loses many biosynthesis pathways (why make it if
you can get it from the host)
Epidemiology
• Transmitted by ticks (mainly deer ticks)
– Most often by nymphal ticks
• Mammalian reservoirs: mice and deer
• Prevalent in northeast and midwest but
spreading and increasing occurrence
Lyme disease
Lyme disease
Compare to life cycle
Deer tick eating
Lyme disease symptoms
1st stage: first few days
erythema migrans (outwardly expanding rash)
Therefore gets a bullseye appearance. Not always occurs
(most of the time though)
Flu-like symptoms too (fever, headache, muscle soreness,
malaise)
Best treatable stage!
Lyme disease rash
Lyme disease symptoms
• 2nd stage: Dissemination: days to weeks
– spreads to bloodstream and may have bullseye
rash appear at other sites of the body
• Also pain in muscles joints and tendons, heart
palpitations, strong headaches
Lyme disease symptoms
• 3rd Stage: Persistent infections (months later)
• Brain, nerves, eyes, heart, joints
• Cognitive impairment, weakness, pain in joints
(especially the knees), fatigue
• Can end up with permanent damage
Transmission
• Bacteria normally live in gut epithelium of tick
• Must migrate to salivary glands to be secreted
to host
Vaccine LYMErix
• Recombinant Outer surface
protien A (OspA)
– Your body doesn’t make
antibodies to OspA normally
– OspA only expressed in unfed
ticks, not in fed ticks or host
• Temperature is the trigger to
stop OspA and start making
OspC
– other triggers for making
virulence proteins are pH and
Fe starvation
How the vaccine works
• Bacterial migration from midgut to salivary glands is
inhibited when ticks feed on OspA (and also in OspC)
immunized mice
• So immune serum appears to kill the bugs in the tick
or prevent migration
West Nile
• +RNA Flavivirus
• transmitted by mosquitoes that usually infects birds
• Many human infections are avirulent
West Nile
Severity of infections:
– Avirulent
– Mild fever (West Nile Fever)
– Serious meningitis or
encephalitis
Yersinia pestis
• Plague
– Bubonic
– Pneumonic
– Septicemic
• Transmitted by fleas
Plague
• Symptoms: Mostly
general
– pain, fever, malaise,
headaches
– Bubos
Molecular mechanisms
• Plasmids and pathogenicity island
– Specialized Type 3 Secretion system
– Yop (Yersinia outer proteins) for evading immune
system
This includes preventing phagocytosis, adhesion,
and inducing macrophage death
Francisella tularensis
• Facultative intracellular pathogen causing tularemia
or “rabbit fever”
• Often by ticks, also from mosquitoes and biting flies
Tularemia
• All feasible routes of infection
• Infects >250 species animals
• Infects all cell types tested