Faculty of Allied
Medical Science
Parasitology
(MLPR-201)
fall 2013/2014
Arthropods as Vectors of the
Etiologic Agent of Diseases
Dr. Hamdy Badie M. El-Wakil
Prof. of Parasitology & Public Health .
Faculty of Allied Medical Sciences.
Pharos University In Alexandria,Egypt
Learning Outcomes
• By the end of this lecture the student should
understand Arthropods as Vectors of the
Etiologic Agent of Diseases.
INTRODUCTION
Members of the phylum Arthropods are the most abundant and widely
distributed of all animal groups. They may be found in every part of the world
and in every type of environment. Many, particularly those within classes
Insecta and Arachanida, live close association with humans; others, while
primarily parasites of animals, will readily attach or feed upon humans and
some may be specificity adapted as human parasites. They may be of medical
significance simply because of their physical attack and blood- sucking habits,
or they may be of considerable importance as distributors of organisms that
cause disease.
Phylum : Arthropoda
Class : Insecta
Class : Arachnida
Class : Crustacea
(Insects)
Sucking lice
Ticks
True bugs
Mites
Flies
Scorpiones
Fleas
Spiders
Beetles
Bees
Ants
Wasps
Moths
Butter flies
Cyclops
A- Arthropods as vectors of pathogens (Disease
transmitters):
• They may act as mechanical vectors either of the etiologic
agent or as biological vectors requiring a period of incubation
or development in the host through the following methods:• I- Mechanical Transmission:
• Arthropods transport the various pathogens in or on their
body and drop them on human food, drinks or tissues without
any biological changes for them , e.g. when house fly play a
role in the transmission of enteric pathogenic, cysts of
protozoa and eggs of helminthes.
•
• II- Biological Transmission:
• It occurs when the arthropod takes an active
role in the transmission of the pathogenic
organism through any of the following ways:
• 1- Propagative:
• The organism in the arthropod simply
multiplies in the vector without any cyclical
development like in a culture tube e.g.
Multiplication of Yersinia pestis in the fleas.
• 2-Cyclodevelopment: The organism
undergoes development or morphological
changes only without multiplication in the
arthropod e.g. development of microfilaria
within Culex sp. mosquito.
• 3- Cyclopropagative:
• Organisms undergo both developmental
changes and multiplication in the arthropod
e.g. Malaria in the female anopheles.
• III- Arthropods can also convey the organisms
to man by different methods:• 1- Vomit-drop: Non-blood sucking flies may deposit a vomit
drop containing the pathogens on human food or drink e.g.
Shigella bacilli and cysts of E. histolytica. Others arthropod
species may obtain the parasitic organisms in blood meal from
an infected person and deposit them in a vomit drop in the
puncture wound made in the skin of an uninfected person e.g.
Yersina of plague or in faecal pellets near the puncture wound
e.g. Rickettsia of epidemic and endemic Typhus.
• 2- Crushing: Contamination from the infected
haemolymph may occur when the arthropod is
crushed on the skin e.g. epidemic typhus.
• 3- Coxal fluid: during the act of feeding, soft ticks
produce infective fluids from the coxal glands that
contaminate the bite wound on skin.
• 4- Salivary secretion: Pathogens such as malaria and
viruses are discharged through the hypopharynx in
minute droplets of salivary secretion at time
arthropod takes a blood meal.
• IV- Sources of pathogens transmitted by arthropods:
• 1- Human being: as in case of malaria infection.
• 2- Rodents: they are considering as a source of infection for
fleas living on them by Yersinia pestis (the causative agent of
Plague).
• 3- Monkeys and birds: are sources for numerous viral
infections. In some cases, organisms have been so long and so
well adjusted to the arthropod that they produce no obvious
injury to the vector, to the extent they are transovarially
transmitted to their offspring e.g. Rickettsii and Borcellia
duttoni in ticks and R. tsutsugamuchi in mites.
B- Arthropods as etiological agent of diseases:
• In addition to their importance in the transmission of
pathogens to man, arthropods themselves play a significant
part as disease producing:
• 1- Specific parasites: Certain arthropods produce lesions in
the human tissue e.g. Myiasis producing flies, and itch mite
Sarcoptes scabies producing tunnels in the skin of man.
• 2- Through toxin and venom: Certain ticks produce fatal
paralysis in some individuals presumably due to toxins in their
secretions. Venoms introduced into the skin by bite of the
"black widow" spider, or the sting of a scorpion or bee may at
times produce both local reactions and profound systemic
shock.
• 3- Allergic reactions: These may be provoked by minute
blood sucking flies when depositing droplets of saliva on
the skin. House dust mites may cause rhinitis or asthma
by serving directly as allergens or by concentrating highly
antigenic material.
• 4- Entomophobia: the fear of arthropods acaroentomophobia can extremely important as a sever
neurosis.
• 5- Annoyance and blood loss.
• 6- Accidental injury to sense organs.
• 7- Dermatosis.
C - General Characters of Arthropods:
• All arthropods, while varying considerably in size and
shape, have certain features in common. They are all
bilaterally symmetrical and metamerically segmented.
They have externally a hard chitinous exoskeleton,
sometimes sclerotized or calcified, inside which a hollow
blood cavity is containing a clear fluid haemolymph.
Arthropods have an excretory system, but a few of them
consist of the malpighian tubules (2 or more), which lie in
the hemocele and open into the hindgut near its junction
with the midgut. They discharge the liquid wastes into
the hindgut.
• Respiration may be achieved by a variety of
methods e.g. via gills, lung books, gaseous
exchange, through the cuticle or by means of
spiracles. Circulatory system consisting of heart,
aorta, and sometimes-paired blood vessels that
opens into the hemocele, which extends into all
parts of the body. The blood consists of plasma
and amoeboid white cells; respiratory pigment is
hemocyanin in the plasma rather than
hemoglobin in the case of gill routing and book
lung-breathing.
• The forth system, called central nervous system which consists
of a dorsally situated composed of dorsal and ventral fused
cephalic ganglia "Brain" connected by circumesophageal
commissures to the media ventral paired nerve trunk, and to
twinned ganglia of each post-cephalic body system. Nerve
fibers extend from the central nervous system to all important
organs and tissues. Either in many groups, there are lightsensitive organs in the head individual eyespots (ocelli) or
compound eyes composed of ommatidia. All arthropods have
jointed appendages, which may take the form of legs,
antennae, mouthparts or cerci. The sexes are always
separates and morphologically distinguishable.
Two different types of development take place:
• 1- Incomplete metamorphosis: Hatched
larvae resemble the adults but are smaller and
gradually increase in size by successive
molting e.g. Ticks.
• 2- Complete metamorphosis: Hatched larvae
are completely different morphologically from
the adults. They may be worm like, transform
to the inactive pupal stage from which finally
the adults emerge , e.g. House fly.
D-Arthropods of medical importance:
• They are Included in the Following Classes:
• i- Class Insecta or Hexapoda e.g. house fly, fleas, lice, bugs,
mosquitoes and flies (venomous, biological and mechanical
vectors, intermediate hosts, and parasitic.
• ii- Class Archanida e.g. scorpion, spiders, ticks and mites.
• iii- Class Crustacea e.g. crabs, prawns and copepods.
• iv. Class Chilopoda e.g. censpodes (venomous).
• v. Class Pentatomida e.g. tongue worms (Endoparasitic).
Assignment
• Cimexlectularis