Ticks & Mites

Useful for MBBS, MD & M Sc students.

1. Ticks & Mites Dr Adil Raza

2. Belongs to class Arachnida and order Acarina . Ticks are large mites where body is covered with leathery integument. They have a pair of spiracles on either side, behind last pair of legs. Last segment shows circular pit with sensory hairs called the “Haller’s organ” Life span varies from 2 to 20 years . Males die after fertilizing females.

3. Order Acarina has two families: IXODIDAE : Hard tick ARGASIDAE: Soft tick

4. HARD TICK ( Ixodidae ) Around 700 species in 20 genera. Sac like body varying size from 2-10 mm when unfed and almost double when fed. Dorsoventarlly flattened.

5. HARD TICK ( Ixodidae ) The male have chitinized shield (SCUTUM). The capitulum or false head projects from the body and is visible from above differentiating these hard ticks from soft ticks. In female only anterior dorsal surface is chitinized which allows accommodating of large blood meal.

6. Genital opening of both sexes is close to the base of mouthparts on ventral surface. Gravid females often lays around 20000 eggs and dies. Egg hatch within few days giving rise to 6 legged larvae. It waits for the host. Once on the host it crawls to the soft areas like ear and axillary region. It takes blood meal and maults to form Nymphs.

7. The species that leave the host at each stage of molting (Larva-Nymph & Nymph -Adult) are called 3 host Ticks because they parasitize three hosts as adult, larva and nymph eg I.ricinus & Dermacentor andersoni . Some ticks remain on the same host after first molting ie from larva to nymph but change host from nymph to adult are called 2 host ticks. Eg Hyalomma & Rhipicephalus . Ticks that do not leave the host at the end of adult life are called single host ticks or one host tick eg Boophilus spp.

8. PEARLS First vector borne disease in World reported was tick borne disease & it was “ Texas cattle fever ” in 1893. It is caused by Protozoa Babesia bigemia & vector is cattle tick. Secretions from ovaries and salivary glands may produce anaphylaxis or tick paralysis. Tick paralysis is ascending motor paralysis and caused by Dermacentor andersoni and D. variabalis . Tick paralysis is endemic in USA, Canada, Australia, Africa. The tick toxin blocks the neuromuscular junction and some of the synapses of spinal cord, which results in failure to release of acetylcholine.

9. Diseases caused by ticks Disease Causative agent Vector T ularemia (Rabbit fever) Francisella tularensis Dermacentor variabilis , D. andersoni I ndian Tick Typhus Rickettsia conori Rhipicephalus sanguineus (Dog tick) C olarado tick fever Coltivirus ( Reoviridae ) Dermacentor andersoni K yasanur Forest disease KFD virus ( Flaviviridae ) Haemophysalis spinigera (Rabbit Tick) L yme Disease Borrelia burgdoferi Ixodes dammini

10. Diseases caused by ticks E hrlichiosis Ehrlichia chaffeensis Ixodes scapularis (Blacklegged tick) Amblyomma americanum T ick Paralysis Dermacentor , Ixodes , Haemophysalis H emorrhagic fever (Crimean congo hemorrhagic fever ) Nairovirus ( Bunyaviridae ) Hyalomma marginaum , Dermacentor marginatus E ncephalitis (Russian spring summer encephalitis) Flavivirus Ixodes persculatuis , Haemophysalis concinna B abesiosis (Red water fever )   Babesia microti Ixodes dammini

11. SOFT TICKS ( Argasidae )

12. They lack hard dorsal chitin shield ( Scutum ) Integument is soft and leathery and is round in shape.

13. Important species: Ornithodorus moubata It is vector of tick borne relapsing fever caused by Borrelia duttoni . In India relapsing fever is transmitted by O. tholozani , O.lahorensis .

14. MITES ( Sarcoptidae )

15. Important species Sarcoptes scabies var hominis : Itch mite Hair follicle mite: Demodex follicurum Trombiculid mite Leptotrombidium deliense   L. akamushi

16. Morphologically they are similar to ticks having a sac like body. They differ from the ticks in sizes (350-500 µM). Males are smaller than females. Body is more hairy.

17. Mites cause allergies Scrub Typhus is transmitted by trombiculid mite. Hair follicle mite infects eyebrows and face. It can also inhabits sebaceous glands of hair follicles.

18. Gravid Scabies mite burrows sub- cutaneously , lays eggs and defecate at regular intervals. These debris act as foreign bodies and cause severe itching due to allergic reactions called SCABIES

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