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GSU BIOL 1103K - Insect Notes 2

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SEM photos ofArgasidaeNote:mammillae in flexible exoskeleton,mouthparts attached between legs, not visible from aboveLife cycle (Ixodidae): egg-larva-nymph-adultLarvae have 3 pairs of legs, nymphs and adults 4 pairsAdult females feed once, lay single large batch of eggsArgasid tick life cycleCan be quite variable between species, but note:Multiple nymphal stages (as many as 8 in some species, usually less)Adults take many small blood meals (15-30 minutes)Many reproductive cycles in female’s lifetimeSexes can be distinguished in ixodid ticks by presence/absence of a scutumArgasid ticks lack a scutum, so determining sex harderMating:Soft ticks: occurs off the hostHard ticks: occurs on the host, except for Ixodes wheremating occurs both on and off the hostIxodid (hard) ticks locate hosts by questingIxodes holocephalus Engorged femaleVolume increases >10x; water is extracted and returned to host, so blood volume consumed 3+mlsIxodid tick adult females attach, feed for 10-14 daysIxodes eggsFemale adults (ixodid ticks) take one large blood meal, convert entire meal to 600-1000+ eggsLarvae sometimes called “seed ticks” due to small sizeNote 3 pairs of legsIxodes scapularis (Deer tick, Blacklegged tick)Three-host tick: (most ixodid ticks)Two-host tick (eg. Haemiphysalis)One-host tick (eg. Boophilus microplus)The point is to discuss opportunities for horizontal transmission, picking up pathogens from onehost, transferring to a different host later. Often larvae, nymphs use small hosts eg rodents, adultslarge hosts. A couple of adult ticks would kill a rodent.Implications of tick life cyclesThree host ticks:Usually exploit small hosts (eg rodents, rabbits, etc) as larvae, nymphs, larger hosts (deer, cattle)as adultsRelated to blood meal volume (one adult could kill a rodent, less blood = less eggs)Switching between hosts, host species increases opportunities for horizontal transfer ofpathogensTwo host ticks:Same host exploited as larva, nymphOnly one opportunity for horizontal transmission, unless vertical transmission also occursOne host tick:Same host exploited by all life stages (larva, nymph do not drop off host to molt)How can these ticks be disease vectors if all blood meals are taken from the same individual?Routes for transmission of pathogensSaliva, Regurgitation, Coxal Gland, and RectumDiseases associated with argasid ticks (Ornithodoros (pajahuella tick))Bite of pajahuella tick (Ornithodoros)Bite causes swelling, itch/pain in sensitized patientsSelf-resolvingTick Borne Relapsing Fever (TBRF)Western USA:Pathogen: Borrelia hermsi, B. parkeri, B. turicataVector: Ornithodoros hermsi, O. parkeri, O. turicataAfrica: mainly B. duttoni vectored by O. moubata complexOther species and vectors in AsiaIntrinsic incubation period 2-18 daysInitially high fever (up to 106o F), chills, headache, muscle and joint pain, nausea, dizziness,vomiting, increase over 4-6 days,Subsequent “flush” phase: temp falls, profuse sweating, blood pressure may fall dangerously;then symptoms resolveSymptoms return, each cycle 7-14 daysMortality 1-8%; locally infection rate can be high (up to 38% in 1-year-olds; may beneurological complicationsDuring the years 1990-2011, 483 cases of TBRF were reported in the western U.S., withinfections being transmitted most frequently in California, Washington, and Colorado.More common in AfricaTreatment: tetracycline type antibiotics eg doxycyclineOrnithodoros hermsi tends to be found at higher altitudes (1500 to 8000 feet) where it isassociated primarily with ground or tree squirrels and chipmunks.Ornithodoros parkeri occurs at lower altitudes, where they inhabit caves and the burrows ofground squirrels and prairie dogs, as well as those of burrowing owls.Ornithodoros turicata occurs in caves and ground squirrel or prairie dog burrows in the plainsregions of the Southwest, feeding off these animals and occasionally burrowing owls or otherburrow- or cave-dwelling animals.Why do symptoms relapse? Antigenic variationBorrelia expresses an antigenic glycoprotein on it’s surface. About a dozen open reading frames(ORFs) for such proteins are in genome, but only one promotor, so only ORF linked to promotoris expressed.Borrelia proliferate, leading to onset and increase in symptomsHost develops immune response, begins to kill bacteria, symptoms abateA few Borrelia undergo genetic rearrangement (different ORF linked to promotor), begin toexpress a different surface antigen.Host immune system initially doesn’t recognize new antigen, so bacterial population increases,symptoms returnHost immune system begins to recognize new antigen, cycle repeats (7-14 days/cycle) (up to 10cycles in untreated patients)Cycles continue until bacteria repeat old antigens for which host already has antibodies; at thatpoint immune system can eliminate infectionContrast with Trypanosoma brucei gambiense & T. b. rhodesiensis (causative agents of Africansleeping sickness): also use antigenic variation, but have vastly larger repertoire of genes (severalthousand) plus recombination results in supply of new antigens that never run out.Diseases caused by or vectored by hard ticks:Tick paralysisLyme disease and related diseasesRocky Mountain Spotted FeverMonocytic EhrlichiosisGranulocytic EhrlichiosisBabesiosis- Powassan and other virusesDeer ear heavily infested with Amblyomma americanumSevere infestations can lead to anemia, reduced resistanceto disease. Ticks tend to aggregate. Why?Why? 1. only certain areas of exposed skin, so ticks accumulate there, and2. Some ticks, esp. Amblomma americanum, secrete aggregation pheromone, attract more ticksto feed. Why? Saliva inhibits hemostasis, immune responses. More ticks feeding in 1 spot =better blood flow, better suppression of immune responseTick ParalysisAscending flaccid paralysisCaused by neurotoxin in tick salivaUSA: mainly Dermacentor andersoni, D. variabilisOften not diagnosed correctly; can be can be confused with Guillain-Barre syndrome, botulism,and myasthenia gravisMortality rate up to 10% if untreated; occasional cause of significant mortality in livestockBigger issue in Australia: “Paralysis tick” Ixodes holocephalusResolves in hours following tick removalLyme diseaseNamed for Old Lyme, Connecticut; described in 1975Causative agent Borrelia burgdorferi described in 19822-30 days after bite, rash termed Erythema migrans usually appearsnot seen by 40-60% of patientsIf untreated, progresses to muscle pain (myalgia),


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