Summary of medical parasitology

A summary of medical parasitology
Types of parasites
According to dependence on host
Obligatory Facultative Accidental/Incidental Opportunistic
Can’t exist
without a
host.
Can exist independently
of their host, leading a
free living life.
enter accidentally
and can live in a host
different from their
normal
Having low pathogenicity 
become highly pathogenic
in
patients with a defective
immune system
According to habitat
 Endoparasites: live inside their host causing infection
 Ectoparasites: which are found attached to the skin of their host or its superficial tissue
causing infestation
Types of Hosts
Definitive Intermediate Reservoir Paratenic/transport Arthropod
Vector
Where adults
live or sexual
reproduction
takes place
Immature
larval stage
is found or
asexual
reproduction
Wide range of
animals as definitive
hosts besides man
where they can
continue their cycles
Larval stage exists but
with no development
but remains alive and
can be infective to
another host
transmits
parasites
from one host
to another
Host-parasite interrelationships
 Symbiosis: close association between two different organisms
 Mutualism: association where both the host and the parasites are so dependant on each
other that one cannot live without the other
 Commensalism: only the parasite derives benefit without causing injury to the host
 Parasitism: benefit + harm to host
 Super-infection = is reinfection with the same species of parasite

 Auto-infection is the case when an infected person is his own source of reexposure
internally or externally
Life cycle
It’s the cycle of development from the definitive host back to the same or another definitive
host.
 Direct: When a parasite requires only one specific species of host in which it completes its
life cycle
 Indirect: When two or more species of hosts are required the life cycle is  requires the
presence of one or two intermediate hosts.
Sources of parasitic infection or infestation
Soil – water – food – animals – infected persons – arthropods (vectors) – iatrogenic –
nosocomial – placenta - milk
 Zoonosis is the term given to the diseases of animals which are transmissible to man.
 Iatrogenic: through contaminated syringes as in transfusion malaria, or amongst drug
addicts.
 Nosocomial: parasitic infection acquired in hospital and was not present at the time of
Portal of entry into the body
Mouth (Most Important) – Skin – Respiratory tract – Placenta – genital tract
Development of infection
 Entrance migration to its final habitat maturation to the adult stage
 Clinical incubation period = Time between entry and appearance of the first signs and
symptoms
 The pre-patent or parasitological incubation period = interval between exposure to
infection and the earliest demonstration of the parasites or their products in feces, blood,
urine... etc.
Portal of exit
For life cycle continuation the parasite must have a portal of exit from the host via faeces
as eggs of most helminths and cysts of intestinal protozoa urine, sputum, blood or genital tract.
Pathogenesis of parasitic infection

Mechanical
Obstruction of a normal passage causing intestinal obstruction or
bile duct obstruction or appendicitis
Traumatic
 External: when the parasite invades the skin as in scabies or
myiasis
 Internal: when the parasites attach themselves by their buccal
capsule to the intestinal mucosa producing ulcers.
Toxic
Circulation of certain toxic by-products of parasites produces
generalized manifestations
Necrosis Enzymes elaborated by the parasite produce necrosis of tissues
Host immune
response
stimulation
Parasitic antigens stimulate both a humoral and cellular immune
response provoking tissue reactions consisting of cellular
proliferation and infiltration at the site of parasites’ antigens, or
deposition of circulating immune complexes in the tissues or fibrous
capsulation
Cellular
destruction
Destruction of red blood corpuscles , reticuloendothelial cells and
other tissue cells
Allergic
Manifestations
With insect bites
Neoplastic
Formation
Diagnosis of parasitic infections
Clinical diagnosis depends on characteristic signs & symptoms related to parasitic infection.
Laboratory diagnosis can be achieved by:
Direct Methods Indirect methods Molecular biological methods
Microscopical
examination of the
excreta, blood,
tissues or smears +
Culture and animal
inoculations
 Detection of antigens or
antibodies in the patients’
serum
 Mainly resorted to when
parasites are present in
tissues, or in cases of
i) DNA Probes: The DNA
hybridization probe technique is
based on the assumption that
each organism possesses a unique
nucleic acid sequence.
ii) Polymerase Chain Reaction (PCR):

closed chronic infection
 Depend on the detection of
specific antigens or
antibodies in patient’s
serum
The principle of this technique
depends on the ability of
replicating a single target piece of
DNA of the parasite in the
presence of polymerase enzyme.
Medical helminthology (Worms)
Multi-cellular, bilaterally, symmetrical elongated, flat or rounded animals
Flat worms (Phylum Platyhelminths)
 Dorsoventrally flattened, leaf -like or ribbon-like
 Alimentary tract is rudimentary or completely absent and they have no body cavity.
Most of them are hermaphrodites
 Include Trematoda and Cestoidea include human parasites.
Class trematoda (flukes) Class cestoidea (Tapeworms)
General
Morphology
 Leaf-like, pear-shaped or
elongate worms
 Covered externally by a cuticle
which may be smooth, spiny or
tuberculated
 Beneath the cuticle are three
layers of muscle fibres and the
bulk of the body consists of a
spongy tissue in which the
internal organs are embedded.
 Adults are flat, ribbon like and
segmented.
 Length varies from few millimeters to
several meters
 The body is divided into head or
scolex, neck and several proglottids or
segments
 The chain of proglottids is called
strobila.
 The neck is the region of growth.
 The proglottids or segments are
differentiated into immature, mature
and gravid segments.
Suckers At least two suckers on their cuticle The scolex is provided with bothria (i.e.
grooves) or suckers as organs for
attachment, with or without rostellum

and hooks.
Excretory
system
 Definite number of excretory cells
 Waste products pass from the cell
to the excretory tubules, excretory
duct then into an excretory
bladder which discharges its
contents through a pore situated
at the posterior end of the fluke.
Flame cells and collecting ventral and
dorsal tubules running laterally,
emptying through a bladder in the
terminal proglottid
Nervous
system
Simple, consists of a ring of nerve
ganglia, around the pharynx,
in the scolex
Reproductive
system
Almost all the parasitic trematodes
are hermaphrodites except bilharzia
worms
 Hermaphrodites having both male
and female genital systems in each
mature segment.
 Reproduction is by self-fertilization in
the same segment or by cross
fertilization between different
segments.
Digestive
system
Starts by mouth opening at the
bottom of the oral sucker leads to
a pharynx, then a short oesophagus
which bifurcates into two long blind
intestinal caeca.
 Have neither a body cavity nor an
alimentary tract
 Nutrients are absorbed through their
cuticle or tegument which has also a
protective function by secreting
substances that inactivate the host
digestive enzymes.
Nutrition &
Respiration
Essentially anaerobic they feed on
blood, intestinal contents, biliary
secretions and tissue juices
depending on their habitat.
Life Cycle of
Trematodes
 Called digenetic trematodes
because they undergo two
different modes of reproduction
o Sexual in definitive host
o Asexual in intermediate
host (mainly a snail)
 Adults are parasites of small intestine
of man or animals
 Require one or two intermediate hosts
with the exception of Hymenolepis
nana which has one host only acting
both as intermediate and definitive

 With the exception of bilharzia
worms, all trematodes lay
operculated eggs which may or
may not contain a fully developed
embryo or miracidium when
freshly evacuated in the hosts
excreta.
 In water, eggs hatch liberating the
miracidia which are attracted to
their specific snail.
 After snail penetration, the
miracidia transform into
sporocysts. They give a second
generation of sporocysts or rediae.
 Cercariae finally leave the snail in
batches of hundreds at a time,
they are highly developed larval
forms
 A typical cercaria has a body and
a tail. The body resembles in its
organization the adult fluke
 The tail of the cercariae may be:
o Simple (leptocercous)
o Forked at its end
(furcocercous)
o Provided with a fin or
membrane
(pleurolophocercous)
 Cercariae do not feed in water,
they swim freely for few days
after which they either penetrate
the skin of the definitive host or
encyst in a 2nd
intermediate host
host
 Gravid segments or eggs of cestodes
are passed in the faeces of their
definitive hosts
 Cestodes that infect man belong to
two orders Pseudophyllidea and
Cyclophyllidea
In the Pseudophyllidea,
o Eggs are immature and
operculated resembling those of
trematodes
o They must reach fresh water to
become embryonated, and then hatch
liberating the coracidium
o These are ingested by Cyclops,
which is the first intermediate host
and develop into first stage larvae,
the procercoid larvae
o When the cyclops is ingested by
fish (the second intermediate host)
they develop into plerocercoid larvae
o Man and fish-eating mammals
become infected by eating
imperfectly cooked fish containing
the plerocercoid larva i.e. second
larval stage.
In the Cyclophyllidea,
o Eggs are mature when passed in
the stools
o After their ingestion by the
intermediate host, the hexacanth
embryos or oncospheres are
liberated from the egg shell,

or on water vegetations penetrate the intestinal wall by aid
of the hooks and develop in
various organs into cystic larval
stages e.g. cysticercus -
cysticercoid - hydatid or coenurus
cysts
o When these larval stages are
ingested by the definitive hosts
they develop into adults in their
small intestines.
Examples Liver flukes: Fasciola hepatica /
gigantica
Intestinal flukes: Heterophyes
heterophyes
Blood flukes: Schistosoma mansoni/
haematobium
Pseudophyllidean Tapeworms:
o Diphyllobothrium latum
o Spirometra mansoni
Cyclophyllidean Tapeworms:
o Taenia solium / saginata
o Echinococcus granulosus
o Hymenolepis nana
o Dipylidium caninum
Round worms (Phylum Nematoda)Most are free living in soil or in water.
o Cylindrical worms, tapering at both ends, Unsegmented, bilaterally symmetrical
o Body covered by scleroprotein cuticle to resist digestive juices and enzymes of the
host may be smooth or marked with various thickenings or expansions
o Within the body cavity lie the digestive, reproductive and parts of the excretory and
nervous systems of the nematode.
o The digestive system is a patent tube starting with the mouth opening anteriorly and
ending posteriorly by an anus in females and a cloacal opening in males
o The mouth leads to the oesophagus which has a chitnized lumen shape and size are
useful for the identification of the nematode  may be cylindrical or “filariform”, club
shaped, double bulbed, rhabditiform and stichosome or “cellular”
o The nervous system consists of a nerve ring surrounding the oesophagus from which
nerve trunks extend anteriorly, posteriorly and laterally
o Some have a pair of chemoreceptors on minute papillae behind the anus (phasmids)

o The excretory system is composed of two lateral longitudinal canals connected by a
transverse tube which opens in the cervical region.
o Separate sexes males are always smaller than females
o Reproductive system in both sexes = a series of long tubules coiled around the intestine
o Female worms lay eggs (oviparous) or give birth to larvae (larviparous or viviparous).
o Nematodes can be classified according to their habitat into intestinal and tissue
nematodes or by the presence or absence of Phasmids:
Class Adenophorea (aphasmidea) Class Secernentea ( phasmidea)
devoid of phasmids and caudal papillae provided with phasmids and caudal papillae
The anterior part of the body is usually
very thin and contains the oesophagus
which is of the stichosome type
Females possess a single set of genitalia Females have a double set of genitalia
Eggs when laid are usually with polar
plugs
eggs laid are devoid of polar plugs
o Trichuris trichiura
o Capillaria philippinensis
o Trichinella spiralis.
Includes majority of parasitic nematodes
o Ascaris lumbricoides
o Strongyloides stercolaris
o Toxocara spp.
o Enterobius vemicularis
o Dracunculus medinensis
o Ancylostoma duodenale
o Filarial worms
Medical protozoology
Vast collection of unicellular microorganisms that are either free living or parasitic
General characteristic features of protozoa
Vital functions of protozoa are performed by the protoplasm which is differentiated into:

 Cytoplasm: Consists of
Ectoplasm Endoplasm
Outer layer of the cytoplasm Inner layer of cytoplasm
Viscid and finely granular Less viscid than the ectoplasm and more granular
Concerned mainly with
movement, ingestion of food,
excretion, secretion, respiration,
and protection
 Concerned with the digestion and reproduction of the
protozoon
 It contains the nucleus, food vacuoles, and stored food
material in the form of glycogen
 It may also contain contractile vacuoles for regulation
of osmotic pressure as in ciliates & free living amoeba
Function Done by:
Movement Pseudopodia, cilia or flagella
Food ingestion Pseudopodia, peristome (ciliates) or diffusion through cell membrane
Excretion of
metabolic
waste products
 Contractile vacuoles (ciliates)
 Diffusion through ectoplasm (flagellates)
 In malaria the metabolic by-products are deposited as pigment granules
in endoplasm.
Secretion  Entamoeba histolytica can secrete histiolytic enzymes to aid in its
penetration of tissues
 Antigenic materials
 Some protozoa secrete a cyst wall, as a means of protection and a means
of transmission to a new host.
Respiration anaerobic as in amoeba or aerobically as the malaria parasites.
Reproduction sexual or asexual.
 Nucleus: nuclear membrane surrounding the nucleoplasm may be compact or vesicular
They are divided into four phyla: Sarcomastigophora, Apicomplexa, Microspora & Ciliophora
Sarcomastigophora Move with the aid of pseudopodia, flagella or both and include two
subphyla Sarcodina and Mastigophora
Sarcodina Mastigophora
 Trophozoites move with the
aid of pseudopodia (flagella
 Trophozoites move with the aid
of one or more flagella

restricted to a developmental
stage)
 Asexual reproduction is by
binary fission
 E.g. Entamoeba histolytica
 Asexual reproduction is mainly
by longitudinal binary fission
 E.g. Leishmania, Giardia
lamblia & Trichomonas
vaginalis
Apicomplexa  Possess an apical complex which can be seen by EM
 Both sexual (sporogony) and asexual reproduction (schizogony)
 There are no definite organs of locomotion
 The secretion of microemes and rhoptries facilitate the entry of the
parasite into the host.
 Complicated life cycle involving sexual and asexual multiplication.
These cycles can occur in the same host or in two different hosts
 Members of Apicomplexa are; Plasmodia spp. Toxoplasma gondii
Isospora belli Cryptosporidia
Ciliophora
conjugation.
les e.g. Balantidium coli.
Medical entomology
Classification:
I- Class Crustacea : crabs, prawns and copepodes.
II- Class Arachnida : scorpions, spiders, ticks and mites.
III- Class Insecta or Hexapoda : fleas, lice, bugs, mosquitoes and flies.
I- Crustacea (copepods)

 Microscopically small, simple aquatic organisms
 The free living species are elongated, more or less convex on the dorsum, pyriform through
the cephalic and thoracic regions, narrowed in the abdominal portion and have two caudal
rami.
 The genera Diaptomas and Cyclops are medically important.
 Species of copepods inhabit both fresh and salt water bodies including lakes, ponds and
temporary pools, throughout the world, but they are more commonly found in still water
than in running streams.
II- Class Insecta
 The largest and most important class of arthropods
 The insects' body is distinctly divided into three parts: head, thorax and abdomen.
 General morphological characters of this class:
o The head carries mouth parts adapted for blood sucking or lapping
o A pair of long or short antennae.
 The class insecta contains four orders of medical importance
o 1. Order Anoplura (Lice)
o 2. Order hemiptera (Bugs)
o 3. Order Siphonaptera (Fleas)
o 4. Order Diptera (Flies and Mosquitoes)
III- Arachnid
 Two orders: Scorpionida & acarina
 Acarina = Superfamily Ixodoidea (Ticks) + Superfamily: Sarcoptoidea (Mites}
 Although these two superfamilies are basically similar, they have distinct differences.
Ticks Mites
Size Large Small
Cuticle Thick and leathery Thin and membranous
Body hairs Absent Present

Mouth parts Strong, well developed Poorly developed
Hypostome Teeth exposed and large Unarmed, hidden, small
Sarcoptes scabiei (The itch mite)
Morphology: Microscopic arthropod of ovoid contour covered with a greyish white
transversely striated cuticle pierced by some bristles and scales.
Development and Life Cycle
 Mites live in cutaneous burrows several mm to a few cm in length, these are always
selected in the thin delicate parts of the skin
 The fertilized female usually develops 1 – 2 eggs at a time within her body and is always
found at the blind end of the tunnel with her oviposited eggs behind her
 Within 3 - 5 days the eggs hatch and six legged larvae emerge
 The larvae migrate to the skin surface and then pass through the nymphal stage, reaching
adulthood a week after hatching larvae
 Mating takes place and both sexes burrow back into the skin.
Arthropods as disease transmitters
 Arthropods as Vectors of Pathogens (Disease Transmitters)
 In their role as transmitters or vectors of various pathogens to man, arthropods vary in the
intimacy of their association with the disease producing organism
 They may act either as mechanical vectors of the etiologic agent or as biological vectors
requiring a period of incubation or development in the host.
I- Mechanical Transmission

When arthropods transport pathogens in or on their body and drop them unchanged on
human food, drinks or tissues  role of house fly in the transmission of enteric pathogens,
cysts of protozoa and eggs of helminths.
II- Biological Transmission
This type of transmission occurs when the arthropod takes an active role in the transmission
of the organism.
i- 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
ii- Cyclodevelopmental: The organism undergoes developmental or morphological changes
only without multiplication in the arthropod. E.g. Development of microfilaria within
Culex mosquito.
iii- Cyclopropagative: Organisms undergo both developmental changes and multiplication
in the arthropod. E.g. Malaria in the female anopheles.
 Arthropods can also convey the organisms to man by different methods: Vomit drop,
Crushing, Coxal Fluid & Salivary Secretion
Crustacea Cyclops  Dracanculus & Diphyllobothrium latum
Hard ticks
Disease Type Organism Mode
Rocky Mountain Spotted
Fever
Rickettsial
Rickettsia rickettsia Bite, Faeces,
crushing &
transovarialQ Fever
Rickettsia diaporica
(+soft)
Undulant Fever Bacterial Brucella Bite or

(Brucellosis) crushing
Lyme Disease Spirochaetal Borrelia burgdoferi Bite
- Russian Spring
Summer Encephalitis
- Colorado Tick Fever
- Western
Encephalomyelitis
Viral
Bite or
crushing
Babesiosis Protozoan
Babesia microti and
Babesia divergens:
Splenectomized ppl
 haemolytic anemia
Bite or
Crushing
Soft ticks
Q fever and relapsing fevers
1. Endemic Relapsing Fever 2. Persian Type of Relapsing Fever
Borrelia duttoni Borrelia persica
 Bite of infected ticks or coxal fluid
 The spirochetes may either enter
the puncture wound or penetrate
the unbroken skin
 Endemic in Iran and Middle East
as well as India
 Mode of Infection: Bite and
coxal fluid of the tick.
Lice
Rickesttsial Dieases Bacterial Diseases
Epidemic or Louse Borne Typhus Epidemic Relapsing Fever
Rickettesia prowazeki Borrelia recurrentis
 Faeces of infected lice containing
the rickettsia contaminate skin
abrasions, conjunctiva and mucous
membranes.
Occurs only through crushing the
louse because the organisms pass from
the intestines to the haemocoele where
they are distributed throughout the

 Inhalation of dried faeces carrying
the organism.
 Crushing of insects on the skin.
body of the louse and are present in
the haemolymph.
Winged
bug
Chagas's disease: Trypanosoma cruzi
Fleas
1. Plague  Essentially a disease of rodents from which it is contracted
to humans through the bites of fleas
 The flea vector responsible for transmission of plague is
Xenopsylla cheopis. It is a good vector because:
1. It becomes easily blocked.
2. Feeds on both infected rodents and humans.
3. Abundant near human habitations.
2. Murine
Endemic
Typhus
3. Helmenthic
Parasites
 Ctenocephalides canis, and C. felis and Pulex irritans are
intermediate hosts for Dipylidium caninum
 Nosopsyllus fasciatus and Xenopsylla cheopis can serve as
vectors for Hymenolepis diminuta.
Anopheles
mosquitoes
1. Malaria
 30 of 200 anophelines are responsible for the transmission of malaria
 In order to be an efficient malaria vector the female anopheles must possess
four characteristics:
a) Must feed frequently on human blood (anthropophilic).
b) Must be moderately susceptible to gametocytes i.e. development of the
parasite can occur in it.
c) Must live long enough for Plasmodium parasite to complete its
development.

d) Plasmodia parasites must be present in adequate numbers to maintain
transmission.
 Infected female Anopheles mosquitoes transmit malaria by pushing their
proboscis stylets into the blood capillaries injecting with their salivary
secretions the sporozoites.
2. Filarial Worms
When the infected mosquito bites man, the larvae of Wuchereria bancrofti, and
Brugia malayi are attracted by the warmth of his body, break through Dutton’s
membrane (part of insect’s mouth), move out on the skin which they enter
through the puncture wound made by the bite.
3. Arboviruses ( arthropod born viruses): Via Salivary Secretions
Sand flies 1. Leishmania
2. Viral Diseae: Phlebotomus Fever (Sandfly Fever): Acute infectious viral disease
trasmitted transovarially by the bite of the sandfly
Musca
domestica
1. Accidental myiasis
2. Mechanical transmission of organisms on its hairs, mouth parts, pulvilli,
vomitus and faeces
a) Parasitic diseases: Cysts of protozoa e.g. E. histolytica, G. lamblia and eggs
of helminths, A. lumbricoides, T.trichiura, H.nana, E. vermicularis.
b) Bacterial diseases: typhoid, cholera, dysentery, pyogenic cocci.....etc.
c) Viruses: Enteroviruses, poliomyelitis,infective hepatitis....etc.

Arthropods as causative agents to disease: by
1. Some produce lesions in the human tissue
a. Myiasis producing flies,
b. The itch mite Sarcoptes scabie producing tunnels in the skin of man.
2. Toxins and Venom
3. Allergic Reactions
4. Entomophobia
Hard Ticks
a. Anaemia: Blood loss in heavy infestation can be considerable.
b. Dermatosis
 Any species of tick that attaches itself to human skin produces trauma by the insertion of
its mouth parts into the skin layers
 The feeding activity provokes an inflammatory infiltration of the tissues producing
hyperaemia, oedema and haemorrhage
 Additional damage is caused by attempting to pull out the tick from its anchorage thus
detached mouth parts remain in tissues causing foreign body reactions that may be severe.
c. Tick Paralysis
 May develop from the tick implanted on any part of the body
 The most serious when the tick injects its toxin on the back of the neck or along the spinal
column
 The syndrome is that of a generalized toxaemia, with rise of temperature and rapid
ascending flaccid paralysis, difficulty in swallowing and in respiration and death
 The cause of the disease is a toxin in the salivary secretions that prevent the nerve impulse
from traversing terminal motor nerve fibers
Scorpion
 Scorpions produce an immediate intense aching pain, with burning sensation radiating
from the site of bite
 Lymphadenitis and systemic symptoms that frequently include generalized numbness,
throbbing and twitching especially of fingers, toes, ear lobes and tip of the nose and chin

 Profuse sweating, excess salivation, glossopharyngeal involvement so that the speech and
swallowing become difficult together with vomiting, muscle spasm of the abdomen and
convulsions.
 Mental disturbances and hallucination.
Diagnosis
 Clinically the patient presents with an aching throbbing pain radiating from the site of the
inflamed indurated sting
 Lymphadenitis and systemic symptoms of ascending motor paralysis may be present.
Treatment
Local General
 Ligate the limb with a tourniquet above
the site of the sting and incise freely until
the blood washes the toxin
 cover the wound with potassium
permanganate
 Local pain is relieved by a local anaesthetic
administered topically or injected
i- Suitable oral or potential analgesic.
ii- General supportive treatment.
iii-Maintenance of airway, to assist
respiration and maintenance of blood
pressure by intravenous infusion and
hydro-cortisone.
iv-Antivenin should be given
intramuscularly.
The following systemic therapy is recommended:
 5 - 10% glucose in normal saline solution by intravenous infusion
 Followed by injection of insulin if there is hyperglycaemia
 Treatment of shock with IV hydrocortisone
 Administration of atropine or barbiturate or diazepam for convulsions and as a sedative.

Sarcoptes scabiei (Itch mite)
 It is a specific skin parasite causing scabies among the overcrowded poor population.
 Clinical Picture of Scabies
o The usual sites involved are the interdigital spaces, ulnar, aspect of the arm, elbows,
axillae, groin, breast, umbilicus shoulder, back and buttocks.
o The burrows are made in the epidermis with an external opening through the horny
layer
o As they feed on the tissues, the mites deposit minute faecal pellets believed to
provoke the characteristic vesiculations of the skin and the severe pruritis which is
intensified by warmth and perspiration of the affected area.
o Warmth is enhanced at night, this initiates an acidic secretion which intensifies the
irritation.
o Pustules, and secondary bacterial infection sometimes complicate the lesion.
 Diagnosis
o Characteristics nocturnal itching.
o Site of the lesions and its character.
o Recovery of the mite after scratching the tunnel with a sharp needle The scraped
material is cleared in 10% potassium hydroxide and examined microscopically to
detect the adults.
 Treatment
o Before treatment the infested part should be thoroughly scrubbed all over by soap
and lifa to open the tunnels for five successive days
o These sites are then rubbed with the acaricidal lotion such as Eurax (crotamiton)
which is an efficient acaricide and also inhibits the growth of bacteria
o The patients clothes and bed sheets should be sterilized by boiling during treatment.
Allergenic Mites in House Dust
 House dust often contains allergenic mites
 These are found in dust on the floors, furniture, mattresses and bedding
 The most common is "Dermatophagoides farinae". These contain dust allergens and also
produce allergic reactions in humans.

Lice (Pediculosis)
 Infestation with lice occurring most commonly in jails and groups of soldiers
 Body lice produce distinctive cutaneous lesions due to prolonged exposure to the salivary
secretion
 The patient is hypersensitive and the skin develops a peculiar form of dermatitis
characterized by bronzed pigmentation and pustular formation.
Treatment:
1. A synthetic pyrethroid (Licid) which has a direct knocking effect both on lice and nits.
2. Malathion (Quick) which is an anticholinesterase inhibitor and also acts on lice and nits.
 These compounds should be rubbed in the hair and scalp, left for two hours and then
shampooed.
 Care should be taken that they do not enter or come in contact with mucous
membranes or eyes.
PHTHIRUS PUBIS (Crab Louse)
 Found in pubic hair but occasionally adults migrate to the axilla, eye brows and eye lashes,
beards and other hairy parts causing severe itching.
 Treatment
1. Apply gammexane powder.
2. Boil the underwear.
3. Shave the pubic or axillary hair.
Bed bugs
 Mechanically transmit pathogenic micro-organisms to man
 Recent findings in West and South Africa indicate that they may be naturally infected with
hepatitis B virus.

Fleas
Tunga penetrans Flea Dermatitis
 The fertilized female invades the epidermis of
humans usually attacked are the soles of the feet,
the interdigital spaces and below the toe nails
 The gravid female burrows into the skin and
becomes engorged with blood
 It becomes as large as a pea.
 Secondary infected and may lead to extensive
ulceration, abscess formation or even gangrene.
 Human infestation is usually acquired from contact
with sand which is a favorite habitat for these fleas.
 Treatment: Surgical removal.
 Flea bites may cause considerable
discomfort, the skin lesion is
frequently, reddish, raised,
oedematous and indurated or
even pustular
 Local application of carbolated
petrolatum is usually palliative,
and benzyl benzoate
dimethylpthalate could be used as
a repellant.
Mosquitoes (Mosquito dermatitis)
The introduction of the salivary secretions by mosquito bites usually produces a local reaction
in highly susceptible individuals they may produce severe generalized allergic manifestations.
Flies (Myiasis producing flies)
 Myiasis: can be defined as the invasion of tissues or organs of live humans or other
vertebrate animals with larvae of higher diptera
 Myiasis can be classified according to:
A) The biological habits of the fly:
1. Specific or obligatory myiasis.
2. Semis-pecific or facultative myiasis.
3. Accidental myiasis.
B) The site of the tissue invaded:
I- Internal myiasis: Intestinal - Gastric -Urogenital
II- External myiasis: Cutaneous - Ocular - Oral - Nasopharyngeal.
Diagnosis: Recovery of larva of higher diptera with the H shape chephalopharyngeal skeleton
in the wound.
Treatment: surgical removal

Summary of medical parasitology

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Summary of medical parasitology