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Lab 6 Appendix: The Arachnids

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Introduction

Adult arachnids are eight-legged arthropods with anterior body segments fused into a cephalothorax bearing walking legs, sensory structures and the feeding apparatus, which is capable only of fluid feeding. Arachnids develop by a pattern of punctuated growth and molting similar to simple metamorphosis in insects. A number of specialized forms have evolved a dependency on feeding upon vertebrate animal blood or tissue fluid and may be temporary or permanent inhabitants of the skin or other tissues in wild and domestic animals and humans. Such arachnids may act as transmitters of pathogens (eg. the Lyme disease agent), as agents of dermatosis (mange, scabies) and systemic disease (eg. tick paralysis) and as sources of blood loss and annoyance sufficient to impact production in food animals and the general welfare of companion animals and their owners.

Objectives Checklist

Be able to recognize a representative mite from each of the following 5 families:

  1. Dermanyssidae
  2. Psoroptidae
  3. Demodicidae
  4. Chyletidae
  5. Sarcoptidae

Be able to:

  1. Use the pictorial key to identify an unknown tick specimen to the genus level.
  2. Recognize Rhipicephalus, Ixodes, Dermacentor, Ambylomma ticks without using a key.


Lab Exercises

THE MITES

NON-BURROWING MITES

mesostigmated mite A "tick'like" mesostigmated mite

Family Dermanyssidae

These are tick-like mites with an ovoid body shape. They have a pair of spiracles between the third and fourth coxae. In life, they use their long legs to move about both on the host and in its nest or bedding.

Ornithonyssus sylviarum: northern fowl mite.

Pneumonyssus caninum: nasal cavity and sinuses of dogs

Dermanyssus gallinae: chicken mite (a.k.a. "red mite")

Family Chyletidae

This family has palptibial claws curved ventrally and usually greatly enlarged. Parasites of birds and small mammals

Cheyletiella parasitivorax: rabbits

Cheyletiella parasitivorax Cheyletiella parasitivorax
Note: The body has a "waist" and the large palps have pinchers on their ends.

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Family Psoroptidae

This family has long terminal setae on legs III and legs IV may be reduced, usually with claws; males with anal suckers. These are skin parasites of mammals.

Psoroptes ovis: sheep and cattle; causes "sheep scab" (Psoroptic mange)

Psoroptes ovis Psoroptes ovis Psoroptic mange Psoroptic mange ("sheep scab")

 

Psoroptes ovis life cycle Psoroptes ovis
   life cycle

Chorioptes bovis: sheep, cattle, goats and horses                                                                          Otodectes cyanotis: dogs and cats

Chorioptes bovis

Chorioptes bovis

 

Otodectes cyanotis

The red arrow points to
the epimeres of legs I and II,
which converge.

Otodectes cyanotis

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BURROWING MITES

Family Sarcoptidae

Mites in this family are rounded or sac-like with short legs.

Sarcoptes scabiei: all domestic animals and humans; causes sarcoptic mange (or "scabies" in humans).

Sarcoptes scabiei Sarcoptes scabiei

Note the pretarsi of legs I and II (arrows) are in the form of simple (unsegmented) stalked pedicels and suckers.

Sarcoptes scabiei skin scraping Sarcoptes scabiei

A skin scraping showing eggs (black arrows) and an adult (red arrow).

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Notoedres cati: cats
This mite is similar in appearance to Sarcoptes but is smaller.
(Sarcoptes is rare on cats.)

Knemidocoptes sp.: poultry (a.k.a. "scaly-leg" mite)
This mite also resembles Sarcoptes in shape but the legs have claw-like structures instead of suckers.
(Sarcoptes is not found on poultry.)

 

Notoedres cati

 

Notoedres cati

 

 

 

Knemidocoptes

Knemidocoptes

Family Demodicidae

Elongated, annulated, worm-like species found in hair follicles, and the surface glands and ducts of vertebrates.

Demodex canis: dogs

Demodex canis

Demodex canis

 

 

 

 

Section through skin of a dog with demodectic mange. While no mites are seen in this section note the pathology present.

Demodex canis pathology

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THE TICKS

Family Argasidae: The Soft Ticks

Ticks in this family have no scutum (hard shield-like plate on dorsal surface) but have a leathery cuticle. The mouthparts are not visible from the dorsal side.

soft ticks (Argasidae)

Soft Ticks

Argas is to the left and Otobius is to the right.

Family Ixodidae: The Hard Ticks

These ticks possess a rigid, chitinous scutum on their dorsal surface and their mouthparts appear at the anterior end of the body when viewed from the dorsal aspect.

Ixodes scapularis (a.k.a. deer tick and black-legged tick): vector of Borrelia burgdorferi  (Lyme disease agent)

To learn more about Lyme disease, check out the following Web sites: http://www.niaid.nih.gov/publications/lyme/niaid%20lymedisbookf2.pdf  and   http://www.cdc.gov/ncidod/dvbid/lyme/index.htm

Ixodes scapularis close up
Ixodes scapularis
Ixodes scapularis Ventral side of an engorged female.
Note the preanal groove (characteristic of genus).
Ixodes scapularis From left to right:
Nymph, adult female, and adult male.

Click here to link to the Ixodes scapularis life cycle.

Haemaphysalis sp.

Amblyomma americanum (a.k.a. Lone Star Tick)

Dermacentor variabilis (a.k.a. American Dog Tick) - rodents and other small mammals (larval and nymphal stages);
middle-sized to large mammals including dogs and humans (adults)

Dermacentor variabilis
Dermacentor variabilis laying eggs
Dermacentor variabilis From left to right:
Unengorged adult female, engorged adult female, and unengorged adult male.
Dermacentor variabilis female laying eggs.
Note the number of eggs laid by one tick.

Rhipicephalus sanguineus: (a.k.a. Brown Dog Tick) - dogs

Rhipicephalus sanguineus
Engorged adult female
Rhipicephalus sanguineus
Larval tick (left) and egg (upper right)
Rhipicephalus sanguineus
Note the short mouthparts.

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Copyright © 2008 - University of Pennsylvania School of Veterinary Medicine, All rights reserved.
Faculty: Dr. Thomas Nolan
Students: Takis Weekes V'11, Molly Church V'09, Diana Knight V'08, Douglas Gilson V'05, Chris Dykhouse V'04, Kimberly Mah V'00

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Comments or Questions contact Dr. Tom Nolan at: