The document discusses the class Arachnida and focuses on three medically important orders: Parasitiforms (ticks), Acarina (mites), and Araneida (spiders). It provides details on tick morphology, life cycles, the many diseases they vector like Lyme disease, and their medical significance. It also describes mites, covering types like house dust and scabies mites, mite morphology, life cycles, and diseases they cause like allergies. Scabies is characterized by burrowing female scabies mites causing skin lesions.

1. Class Arachnida
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Arachnida:
• Contains 3 orders of medical importance:
1. Parasitiforms (Ticks)
2. Acarina (Mites)
3. Araneida (Spiders)
Characteristics:
 Body is divided into cephalothorax & abdomen,
 Adults have 4 pairs of legs,
 Wingless, Antennae absent,
 Undergo incomplete metamorphosis,

2. Arachnida . . .
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Order Parasitiforms & Suborder Ixodida,
• Includes three families:
1. Ixodidae (hard ticks),
2. Argasidae (soft ticks),
• There are an estimated 820 species of ticks
in the world, of which over 90 occur in the
continental U.S.
• About 80 species are in the family Ixodidae,
known as “hard ticks,” and
• About 10 species are in the family
Argasidae, known as “soft ticks."
How Many Kinds of Ticks Are There?

3. Arachnida . . .
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• Ticks are chelicerates with 4 pairs of legs,
 Palps & mouth parts form the chelicera,
• Body is divided into two functional units:
 Gnathosoma (Capitulum), which carries
the chelicera, palps & mouth,
 Idiosoma, includes legs, brain, digestive
and reproductive structures,
Morphology

4. Arachnida . . .
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Biological features:
• Obligate parasites where all active instars are blood feeders.
• Non permanent parasites; find a new host every time they feed.
• Many species live for 2-4 years or >10 years,
• Unfed ticks may survive for more than a year; off-host.
• Wide host range with passive host searching strategy,
i.e. waiting, climbing on, attaching and feeding,
Ticks . . .

5. Arachnida . . .
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Biological features . . .
• Life cycle passes through Egg larva  nymph adult stages,
• Deposit eggs in a large batch (# 23,000/female), then female dies,
• Larva search's for a host, climbs, attaches & feeds for 3-7 days,
• The engorged larva drops off & eventually molts to a nymph,
• Nymph searches for a new host and at engorgement drops off;
and then molts to an adult stage,
Ticks . . .

6. Medical & veterinary significance
Direct effects of tick feeding:
• External parasites of humans & almost all other animals,
• Painful bite, general malaise, headaches, etc.
• Allergic nature of materials in saliva & cement,
• Ticks secrete powerful toxins that cause tick paralysis to hosts,
• Tick paralysis ascends from limbs to upper body parts,
 May lead to death from respiratory failure,
• Removing the tick results in a dramatic resolution of paralysis,
Arachnida . . .
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Ticks . . .

7. 1. Forest encephalitis (viral disease),
2. Xinjiang hemorrhagic fever (spirochaetal disease)
3. Lyme disease (spirochaetal disease)
4. Tick-borne relapsing fever(spirochaetal disease)
5. Q-fever (rickettsial disease)
6. North Asia tick-borne typhus (rickettsia disease)
7. Other bacterial diseases (plague, tularemia, etc.)
Arachnida . . .
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Medical & veterinary significance
Ticks as vectors of disease
The indirect impairment:

8. Arachnida . . .
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• Are 2nd only to mosquitoes in the no of diseases vectored,
• Disease transmission by transstadial & transovarial,
• All active instars are vectors of disease,
• Using d/t hosts in d/t instars increasing vectorial capability,
• Great longevity of ticks makes them good reservoir hosts,
• Intracellular digestion easies pathogen entry to the tissue,
Ticks as vectors . . .

9. 9
• Human babesiosis & theileriosis are a tick born diseases,
• Human infections are mostly by B. microti & B. bovis,
• Babesia Species invade RBCs causing human babesiosis,
• Theileria species invade T- cells & B- cells causing theileriosis,
 Theileriosis is a disease that displays malaria like symptoms
but without periodicity,
Ticks as vectors of intra-erythrocytic protozoa parasites
Arachnida . . .

10. Arachnida . . .
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• Tick-associated pathogens in Rickettsia group,
e.g., Ehrlichia
• The two main types of human ehrlichiosis:-
I. Human Monocytic Ehrlichiosis (HME),
 has a particular affinity to lymphocytes,
monocytes and macrophages,
II. Human Granulocytic Anaplasmosis (HGA),
 favors neutrophils, basophils & eosinophils,
Ticks as a vector of intracellular bacteria

11. Arachnida . . .
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• The spirochaete genus Borelia, e.g., B. burgdorferi,
 Lyme boreliosis is the most commonly reported,
• Causes human muscle pain or aching,
 Erythema migrans is a rash that appears in the early
stages of Lyme disease,
 Lyme arthritis as oligo-articular relapsing arthritis,
primarily affecting large joints,
 Transmitted through the bites of hard ticks.
Ticks as a vector of intracellular bacteria . . .

12. Arachnida . . .
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Erythema migrans is a rash that appears in the early stages of Lyme disease

13. Arachnida . . .
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Erythema migrans is a rash that appears in the early stages of Lyme disease

14. Arachnida . . .
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Arboviruses
The list of arboviral disease vectored by ticks:
• The Russian spring-summer encephalitis,
• Louping ill and Kyasanur forest disease,
• Crimean Congo hemorrhagic fever,
• Colorado tick fever produce a generalized
systemic infection,
Ticks as a vector of viruses. . .

15. Arachnida . . .
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16. Arachnida . . .
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Ticks have 3 d/t life cycles according to the no of hosts involved

17. Arachnida . . .
 Mites comprise a large group of small to tiny
arthropods,
• less than 1mm long,
 They cause disease themselves & vector disease,
 Important in resurgent & emergent diseases,
(e.g., various rickettsial infections)
 Two body regions an anterior gnathosoma &
posterior idiosoma,
 Idiosoma bears the legs, simple eyes and most
sensory inputs including sight, digestion, excretion
and reproduction,
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Acarina: The Mites

18. Arachnida . . .
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The life cycle of Mites

19. Arachnida . . .
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• Many parasitic mites feed only on body fluids,
• Digestion is external; predigested skin is sucked up,
• The house-dust mite bite off & swallow solid foods,
 Its fecal pellet is a primary source of allergens,
• Mite eggs may be laid singly on or off the host,
Mites . . .

20. Arachnida . . .
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• Human itch mites and scaly leg mites of birds lay their
eggs in the burrow created by the females in the skin.
• Mites have the following developmental stages:
 egg, pre-larvae, larva, protonymph, deutonymph, tritonyph & adult.
• Migration from host to host occurs as mated adult females or
as wandering adult males move,
Mites . . .

21. Arachnida . . .
• Two species of mites infect humans:
1. Demodex folliculorium, the hair follicle mite,
2. D. brevis, the subaceous gland mite,
• Mites are parasites that feed on human epithelial cells
and subaceous gland cells,
 leading to swelling and keratinization of skin,
• Mite infection is common on cheeks, eyelashes and
foreheads of men,
 Cases of scaly skin, granuloma of the eyelid,
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Mites and human disease

22. Arachnida . . .
• Live in our homes & feed on cast skin scales, hair, etc…
• More than 20 species of mites inhabit house dust,
• Affect 50-100 million people worldwide,
• Are the most important source of allergens in house dust,
 Severe allergies,
 Fever-like symptoms,
 Skin inflammation,
 Asthma,
• Mite feces are dry capsules with allergenic enzymes,
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House-Dust mites

23. Arachnida . . .
Scabies mite (Sarcoptes scabie)
The human itch mite & scabies:
 Clinical scabies is characterized
by lesions with burrowing adult
female,
 Scabies mite is the cause of
scabies and is distributed
worldwide.
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24. Arachnida . . .
• Clinical scabies is characterized by lesions with burrowing adult female
Sarcoptes scabiei, which is commonly called egg laying machines.
• Ovigerous females secrete lytic enzymes and dig their way into the skin,
• Transmission occurs when mated mites move from person to person,
• Most infestations are associated with the wrinkled areas of forearms,
hands, wrists & elbows or any susceptible areas that hands may touch.
• Secondary infections are common, and scabies-initiated streptococcal
infections in children may be associated chronic renal disease later in life.
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The human itch mite and scabies:

25. THANKS
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