A: Landscape use changes:1800s, early 1900s: most of the land used for pasture, hay production, crops such as cotton etc.As automobiles replaced horses, much less land needed for pasture, hay fieldsland reverts to forest, good deer habitat due to lots of forest margin, plants to browseB: Elimination of predators (wolves, screw-worm flies)More food (A) + less predation (B) = Deer pop’ns ~12 x pre-European colonization levelsMore deer = more Ixodes ticks (remember deer are not reservoirs for Borria burgdorferi though)C: Human pop’n distribution: suburbs farther from city, more rural, more contact with vectorsMore reservoirs + more deer + more rural “lifestyle” = more diseaseUnit 3 (PPT 3)Rocky Mountain Spotted FeverPathogen Rickettsia rickettsiiVectors Dermacentor andersoni (West), D. variabilis (East)Vectors also serve as reservoirs-efficient transovarialtransmissionAmplification through a variety of vertebrates, especiallychipmunks, microtine rodentsWidely distributed through Central America, South AmericaFormerly in Rocky Mountain states, but now more prevalentin Appalachian states (esp. North Carolina, Tennessee, GAabout 5th or 6th on the list); local “hot spots” eg Long IslandBoth vertical transmission (mother to egg/larva) and horizontal transmission to amplifying hosts(chipmunks, other rodents) maintains the pathogen in Nature.Dermacentor variabilisRocky Mountain Spotted Fever Symptoms:occur 2-14 days post-biteInitially non-specific signs such as fever, myalgia, headache, nauseaOften gastrointestinal involvement which may become severeTypically (88-92% of cases) a petecial rash develops between 3rd and 5th day. [Petecial rash =spotted rash, see photos].Some cases have delayed rash or rash never developsSerious illness, fatal in 4-8% of cases (historically 20-80% ) if untreatedResponds to tetracyclines (doxycycline) and chloramphenicolRMSF RashNote: each rash spot reflects site where blood vessel is hemorrhaging. You can see this on theskin, but it is also occurring internally including in the gut, causing the gastrointestinal tractsymptoms. Eventually excessive damage to blood vessels impairs circulation, and can causeorgan failure and impaired circulation to extremities, sometimes leading to life-threateninggangrene.RMSF incidence 1993-2010: another emerging tick-borne diseaseEhrlichiosis/AnaplasmosisObligate intracellular pathogens, in membrane-bound vacuolesOccur in grape-like clusters termed morulaeTwo species infect humans:Ehrlichia chaffeensis: Human Monocytic EhrlichiosisAnaplasma phagocytophila Human Granulocytic EhrlichiosisDogs: Ehrlichia canis, E. ewingiiHorses: E. equi, A. phagocytophilaE. ewingii will occasionally infect humansNote: some species formerly included in Ehrlichia have beenmoved to other generaEg Ehrlichia phagocytophila now included in AnaplasmaHuman Monocytic Ehrlichiosis (HME)Vector of HME: Amblyomma americanumReservoir: white-tailed deerPathogen: Ehrlichia chaffeensis- Ehrlichia chaffeensis morulae- immunofluorescence assay (IFA)Note: no need to memorize any numbers on this slide. The point is just that symptoms aregeneral and there is no unique diagnostic sign, unlike Lyme (bulls-eye rash) or RMSF (petechialrash).Monocytic ehrlichiosis is an emerging disease in the US.Human granulocytic AnaplasmosisVector: Ixodes scapularisPathogen: Anaplasma phagocytophilaReservoir: white-footed mouseSame ecology as Lyme disease, however much less prevalent. Why? White-footed mice are ableto infect vectors for only 5-10 days before their immune system contains the infection, so fewticks can be infected per reservoir host. Mice infected with Lyme are able to infect vectors forthe rest of their life (immune system does not eliminate Borrelia infection) so many ticks canfeed/become
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