Chapter 12 Flashcards
Ticks (family)
Ixodidae, Argasidae, Nuttalliellidae
Mites (Family)
Trombidiforme & Sarcoptiforme
The Ixodida contain three extant families:
the
Ixodidae, Argasidae, and Nuttalliellidae
What are the two families
of ticks that are important in medicine?
Ixodidae
(hard ticks) and Argasidae (soft ticks)
Ticks (Acari) – Nuttalliellidae
- Nuttalliella Namaqua is a tick found in Southern
Africa from Tanzania to Namibia and South Africa,
which is placed in its own family, Nuttalliellidae
Females possess features of hard and soft ticks
and have been designated as the “missing link”
between the main tick families
Ticks (Acari) - Morphologies
- The major external regions of ticks are the
capitulum (gnathosoma), idiosoma, and the legs - The capitulum consists of the basis capituli, which
articulates with the body; the segmented palps, the
chelicerae, and the toothed hypostome.
Ixodid Life Cycle
Immature and adult ticks each take a bloodmeal,
except for the nonfeeding males of some species
(especially members of the genus Ixodes). Following
contact with the host, a tick uses its chelicerae to
puncture the skin and its hypostome to securely anchor
itself. In many species, attachment is known to be
reinforced by secretion of cementing substances with
the saliva into and around the wound site.
* Females feed only once. Following mating, females
ingest blood rapidly (24-48 h) and swell enormously.
Replete, mated females drop from their hosts, find a
sheltered location, and subsequently oviposit hundreds
to thousands of eggs
Males swell only slightly during feeding. They
usually remain on their hosts, feed repeatedly, and
inseminate several females. Mating typically occurs
on the host. Certain species of Ixodes, however,
mate on their hosts, in nests, or in vegetation.
Many Ixodes males have vestigial hypostomes, and
these species invariably mate off the host.
* Except for Ixodes species, males and females
require a bloodmeal to stimulate oogenesis and
spermatogenesis.
Ticks (Acari) – Medical Importance
In humans, thousands of cases of tick-borne diseases
caused by these agents occur annually, and the
incidence of human disease is increasing globally.
* In addition, the bites of ticks can cause toxic reactions,
allergic responses, and even fatal paralysis, while the
wounds that they produce can create entry sites for
secondary microbial infections and diminish the value
of livestock by damaging their hides.
* Tick-borne diseases such as babesiosis, anaplasmosis,
theileriosis, heartwater, etc
Medically important hard ticks include Ixodes,
Dermacentor, Amblyomma, Haemaphysalis,
Rhipicephalus, and Hyalomma
* Hard ticks are vectors of typhuses such as Rocky
Mountain spotted fever (Rickettsia rickettsii) and
Meditteranean spotted fever (R. connorii), Lyme
disease (Borrelia burgdorferi), and Q fever (Coxiella
burnetii)
* Many arboviruses, including tick-borne encephalitis,
Omsk haemorrhagic fever, Kyasanur Forest disease,
Crimean-Congo haemorrhagic fever and Colorado tick
fever, are transmitted by hard ticks. Furthermore, they
also transmit tularaemia (Francisella tularensis), and
cause tick paralysis.
Mites (Acari)
Order Trombidiformes
Order Trombidiformes
* Chiggers (Order Trombidiformes): Chiggers are the
immature stage of certain mites belonging to the family
Trombiculidae. The medically most important species
include Leptotrombidium deliense, L. akamushi, and L.
fletcheri, which are vectors of scrub typhus (Orientia
tsutsugamushi). This infection is found in Asia, the Pacific
regions and Australia
*
* Other trombiculid mites cause itching and a form of
dermatitis known as scrub itch. For example, the larvae of
Neotrombicula autumnalis and Eutrombicula alfreddugesi
commonly attack people and cause considerable discomfort
Order Sarcoptiformes
Dust mites (Order Sarcoptiformes): Typically they may be 300 mites per gram of
house dust. Densities above 100 mites per gram are considered a risk factor for
sensitization to allergies such as bronchial asthma, rhinitis, conjuctivitis, and
sometimes atopic eczema, while 500 mites per gram is a major risk factor in the
development of acute asthma to those allergic to house dust mites
* In Malaysia, the most common and densely populated species was Blomia
tropicalis with an average density of 8,934 mites/g of dust. Dermatophagoides
pteronyssinus was the next in abundance, followed by Malayoglyphus
intermedius
* Sarcoptes scabiei or the itch mite is a parasitic mite (an arthropod) that burrows
into skin and causes scabies
Mites (Acari) - Morphologies
The body is divided into two major regions, the anterior
gnathosoma, bearing the pedipalps and chelicerae, and the
idiosoma, the remainder of the body bearing the legs and
eyes (when present).
* The mouthparts consist primarily of a pair of chelicerae,
each of which is typically three-segmented and terminates
in a chela, or pincer.
* The chela is composed of a fixed digit and a movable digit
designed for seizing or grasping. In the case of certain
parasitic mites, the chelicerae are highly modified as long,
slender structures for piercing skin to feed on blood and
other host tissues.
- Mites typically have four pairs of legs as nymphs and adults
but only three pairs as larvae. - The legs are divided into the following segments: coxa,
trochanter, femur, genu, tibia, tarsus, and pretarsus. - The pretarsus commonly bears a pair of claws, a single
median empodium, and in certain groups a membranous
pulvillus. - These structures are highly variable among different groups
of mites and aid in movement or clinging to various
surfaces, including hosts.
Mites (Acari) – Life Cycle
The basic developmental stages in the life history of
mites are the egg, prelarva, larva, protonymph,
deutonymph, tritonymph, and adult.
* Depending on the taxonomic group, one or more
stages may be suppressed, resulting in a wide range
of life-history patterns (e.g., chiggers)
Eggs may be deposited externally or retained in the
uterus until hatching. The prelarva is a nonfeeding,
quiescent stage that may or may not have legs,
mouthparts, or other distinct external features. The
larva is typically an active form that molts to
produce a nymph.
* The nymphs usually resemble the adults of a given
taxon except for their smaller size, pattern of
sclerotization, and pattern of setae.
The deutonymph of certain astigmatid mites is noteworthy
in that it is highly modified morphologically as a nonfeeding
stage adapted for surviving adverse environmental
conditions.
* They often have specialized clasping structures such as anal
or ventral suckers that enable them to adhere to phoretic
hosts, which aid in carrying them to more favorable sites
where they can continue their development.
* Certain of these deutonymphs may become parasites in hair
follicles or subcutaneous tissues of mammals and birds.
Scabies Mites – Life Cycle
Scabies mites mate on the hosts’ skin and the
fertilized female burrows into the skin forming
tortuous tunnel
* The female lays eggs in the tunnels, which hatch
into larvae within 3-8 days. The larvae develop into
nymphs and adults
* Males do not burrow into skin but remain on the
surface, along with larvae and nymphs
* The life cycle takes 2–3 weeks
Mites (Acari) – Medical Importance
There are many types of problems that mites can
cause:
* Temporary irritation of the skin due to bites
* Persistent dermatitis due to mites invading skin or hair follicles
* mite-induced allergies
* Transmission of pathogenic microbial agents
* Intermediate host of tapeworms
* Invading respiratory passages, ear canals and internal organs
* Fear of mites is called acarophobia, or delusory acariosis, convinced
infestation of oneself by mites when none are present.
