Parasitology pt 2

• Order: Ixodida


  This order includes all ticks
• Taxonomy: Three families recognized


  • Ixodidae
  • Argasidae
  • Nuttallidae
• Ixodidae


  • 13G
  • 650 spp.
• Argasidae


  • 5G
  • 150 spp.
• Nuttallidae


  • 1G
• Family: Ixodidae


  • Referred to as hard ticks; presence of a dorsal scutum
  • Sexual dimorphism: the scutum is small in females and almost covers the whole of the dorsal surface in males
  • Head or capitulum is terminal and always visible from the dorsal view

  
• Family: Argasidae


  • Referred to as soft ticks
  • There is no dorsal scutum
  • They are tough, leathery ticks with little differentiation between sexes
  • The capitulum is not visible from the dorsal aspect

  
• Differences in Biology


  • Ixodidae: A single nymphal stage, Adult female engorges lays large batch of eggs then dies
  • Argasidae: Several nymphal stages, Female feeds several times lays several batches of eggs

  
• Classification of Tick Life Cycles (according to number of hosts)

  • One host ticks
  • Two host ticks
  • Three host ticks

  
• One Host Ticks


  All the three instars engorge on the same host and the two moults take place there

  
• Two Host Ticks


  The larva engorges and moults on the first host and the nymph drops off after engorgement, The nymph moults on the ground and the adult finds a second host

  
• Three Host Ticks


  These require a different host for every instar, They drop and moult on to the ground after every engorgement

  
• Tick Life Cycles


  • 3-host
  • 2-host
  • 1-host

  
• Two or three host ticks transmit diseases trans-stadially, Infects tick vector as a larva, The infection is maintained when it molts to nymph then adult

  
• One host ticks transmit diseases trans-ovarially, The infectious agent is transmitted from female to offspring via ovaries

  
• Factors Affecting Tick Life Cycles

  • Intrinsic: Number of Hosts, Nature of Hosts, Location on Hosts
  • Extrinsic (Ecological): Temperature, Relative Humidity, Seasonal changes
• Monotropic Cycle


  Immatures parasitize the same hosts as adults
• Ditropic Cycle


  Immatures parasitize small mammals, reptiles and birds, while adults are only found on large mammals
• Teleotropic Cycle


  Immatures engorge on the available land vertebrates and adults on large mammals only
• Location on the Host


  The tick's location on the host is linked to the possibility of penetration by the hypostome, On ungulates, ticks with a short hypostome are found on the head, margin of the anus and under the tail, Long hypostome species attach to parts of the body where the skin is thicker

  
• Temperature


  Each species has a particular temperature threshold below which diapause occurs
• Relative Humidity


  This is a microclimate
• Seasonal Variations


  Within the tropics, peaks of activity at the beginning and in the middle of the rain season
• Pathogenic Role of Ticks

  • Direct: Injuries through bites, Sucking blood, Tick paralysis, General toxicoses
  • Indirect: Disease transmission
• Injuries through bites


  Secondary bacterial infections, primary myiasis, screw-worm myiasis
• Tick paralysis


  A condition which occurs in animals and man if infested by certain species of ticks, The ticks release a toxin in their saliva which causes a progressive, ascending symmetrical paralysis beginning with the hind legs followed by the fore legs
• General toxicosis


  Some tick toxins have a general immunosuppressive effect which could occasionally re-activate chronic infections
• The aim of a tick control programme is not to control all ticks simultaneously, but a definite species because of its particular importance. This is what is referred to as a target species.
• Campaign Plan Factors


  • Target species
  • Campaign temporary or regular
  • Target location
• Control Methods


  • Modification of plant cover
  • Burning pastures
  • Elimination of wild ungulates
  • Pasture rotation
  • Use of acaricides
• Amblyomma spp.


  • A. ovale, A. cajennense, A. variegatum
  • Found mainly in tropical areas and Africa
  • Located in head and neck region
  • Three-host ticks

  
• Diagnosis


  Long mouthparts are important features, Scutum is usually ornamented
• Clinical importance


  Inflict painful bites, Wound caused by tick is susceptible to secondary bacterial infection, Economic loss - damaged hides, Transmit a number of tick-borne diseases (Rocky Mountain Spotted Fever, Ehrlichia ruminantium (heartwater or cowdriosis))
• Rhipicephalus spp.


  • Brown dog tick/kennel tick: R. sanguineus
  • Found worldwide
  • Hosts: dogs, mammals and birds
  • Often located in ears and between toes (adults), Immatures prefer neck region

  
• Life Cycle


  This is a three-host tick, Mating occurs on the host, The female feeds for ~14 days before dropping off host, She lays ~4000 eggs in a sheltered spot (cracks, crevices), The entire life cycle could occur in ~2months with favourable conditions, An unfed adult can live up to 19 months

  
• Pathogenesis


  R. sanguineus is responsible for transmitting Babesia canis, Ehrlichia canis, Causing tick paralysis, Many other protozoal, viral and rickettsial infections of animals and man, Can take only one infected tick

  
• Diagnosis


  Rhipicephalus spp have a hexagonally shaped basis capitulum
• MITES


  This group includes both parasitic and free living forms, The parasitic mites are small, less than 0.3mm long, They are in prolonged contact with the skin of the host, causing various forms of a condition known as mange or scabies, Most mites spend their entire life cycles on the host. In this case transmission is by contact

  
• Taxonomy


  • Burrowing mites: Sarcoptidae, Demodicidae, Laminosioptidae
  • Non-burrowing mites: Psoroptidae, Cheyletidae, Dermanyssidae
• Oribatid Mites: These are free-living non-parasitic mites found in leaf litter, soil and in some cases commercial animal feed. They act as intermediate hosts of some tapeworm such as Moniezia.