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