Skin Parasites Guide

Part One
SKIN PARASITES
Parasites of Skin-I. Dr.

Learning objectives
 Classify human parasites based on morphology into their FOUR main groups, with
examples of main parasites of medical importance for each group.
 List names, and the major structural features, pathogenic mechanisms, clinical
significance and laboratory diagnosis of the main parasites that cause infection of
the musculoskeletal & integumentary systems.
 Describe the properties, life cycle, pathogenesis, clinical significance and
laboratory diagnosis of the following parasites as causative agents of MSIS
infections:
 Leishmania tropica
 Onchocerca volvulus
 Sarcoptes scabiei
 Pediculus humanus
 Phthirus pubis

 Human parasites are animal species belong to a variety
of taxonomic groups:
1. Protozoa: single-celled parasites: there are four phyla of
this group:
 Sarcodina (amoeba): move by pesudopodia: Ex. Entamoeba
histolytica (causes dysentery)
 Mastigophora (flagellate): Move by flagella: Ex. Giardia
lamblia (causes giardiasis), Leishmania, Trypanosoma,
Trichomonas
 Ciliophora (cilliate): move by cillia: Ex. Blantidium coli
(cause blantidial dysetery)
 Sporozoa: did not possess organell for motility, commit
sexual reproduction: Ex. Plasmodium species (cause
malaria), Toxoplasma gondii.

2. Nematoda (round worms): multicellular (metazoa)
animals with round cylindrical cuticular body with
well developed systems (digested, reproductive, and
excretory systems).
 Nematodes of medical importance can be classified into:
 Intestinal (Ascaris lumbricoides). (Enterobius vermicularis –
pinworm), hookworms
 Tissue nematodes: (Onchocerca volvulus), (Trichinella
spiralis).
 Lymphatic nematodes: (Wuchereria bancrofti, Loa lao,
Brugia)

3. Platyhelminthes(flat warms): dorso-laterally
flattened, no body cavity, less developed systems,
mostly hermaphroditic. Flat worms of man fall
into two classes:
 Cestodes (tape worms): segmented body:
 Teania solium, T. saginata
 Trematodes (flukes): unsegmented body
 Schistosma species.

4. Arthropods (joint legs): are invertebrate animals,
with segmented skeleton and jointed appendages
that include three groups:
 Insects: mosquito, flies, lice,, bee, ….
 Arachnids: Spiders, scorpion, ticks, mites, …
 Crustacean: crabs, lobster, shrimps, …

Protozoa:
Flagellate
Nematode: Ascaris
lumbrecoides
B
A
Platyhelminthes:
A: Cestodes (tape worms)
B: Trematodes (flukes)
A B
Arthropods:
A: Insects (mosquito) B: Arachnids
(ticks)

•Leishmania tropica
•Onchocerca volvulus
•Sarcoptes scabiei
•Pediculus humanus
•Phthirus pubis

 Leishmaniasis is a vector-borne disease that is transmitted by
sandflies and caused by intracellular protozoa of the
genus Leishmania.
 Human infection is caused by about 21 of 30 species that infect
mammals.They cause:
 Cutaneous Leishmaniasis
 Visceral leishmaniaisis
 Mucosal and Muco-cutaneous
 The different species are morphologically indistinguishable, but
they can be differentiated by isoenzyme analysis, molecular
methods, or monoclonal antibodies.

 Human acquires the infection through the infective
bite of sandfly containing the infective stage
(Promastigote)
 The promastigote injected into the skin and being
phagocytosed by histeocytes (skin MQs)
 Inside the MQs, promastigote changed to amastigote,
which can live and multiply inside the MQs
 Sandfly takes the amastigote within a blood meal.
Inside the sandfly, amastigote changes into
promastigote, which multiplies and collected in the
mouthpart of the fly for new infection.

Sand fly
Promastigote
Skin
Amastigote

 According to geographical distribution:
 Old world
▪ Species caused old world leishmaniasis:
▪ L. tropica (LCL)
▪ L. major (LCL)
▪ L. aethiopica (DCL)
 New world:
▪ Species caused old world leishmaniasis:
▪ L. mexicana complex

 Leishmania tropica:
 Found in middle east
 Causes LCL, also known as dry-urban oriental sore
▪ Aleppo ulcer, Baghdad ulcer, Kabul ulcer,Tehran, …
 Dry, painless ulcer with raised edges
 Round (~5cm), few in number
 Found in face (children), lower limps (adults)
 Healed spontaneously within 4-6 months leaving
characteristic depressed and smooth bottom scar

 Specimen:
 Scraping from new formed ulcer or nodule
 Skin punch near the ulcer
 techniques:
1- from the scraped material)
 Make smear, stain with Geimsa, examine under microscope;
result:
▪ Intracellular amastigote
 Inoculate in 3N culture medium, incubate at 27°C for 3 days;
result:
▪ Extracellular promastigote
2- From skin punch: Histopathology

 Leishmanin skin test:
 Intradermal injection of parasite antigen
 Testing the presence of cellular immunity
 Monitor the reaction within 72 hours
 Result:
▪ No skin change (negative)
▪ Signs of inflamation (redness and swelling - > 5mm)
(positive)

Onchocerciasis
River blindness
PARASITES OF SKIN-I. DR.

• Onchocerciasis is a parasitic disease caused by
the filarial worm Onchocerca volvulus.
• It is transmitted through the bites of infected
blackflies, which carry immature larval forms of
the parasite from human to human.
• In the human body, the larvae form nodules in
the subcutaneous tissue, where they mature to
adult worms.
• After mating, the female adult worm can release
up to 1000 embryos (microfilariae) a day.

• These move through the body, and when they die
they cause a variety of conditions, including
blindness, skin rashes, lesions, intense itching and
skin depigmentation.
• Onchocerciasis is often called “river blindness”
because the blackfly which transmits the disease
abounds in fertile riverside areas, that frequently
remain uninhabited for fear of infection.
• O. volvulus is almost exclusively a parasite of man.

Pathogenecity
• Symptoms are caused by the microfilariae, which
move around the human body in the
subcutaneous tissue and induce intense
inflammatory responses, especially when they
die.
• Infected people may show symptoms such as
severe itching and various skin lesions.
• In most cases, nodules develop under the skin.
• Some infected people develop eye lesions which
can lead to visual impairment and permanent
blindness.

Clinical presentation
• Onchocercasis is associated with many skin
conditions:
• Papular rash
• Subcutaneous nodules (containing adults with
fibrotic tissue)
• Hypopigmentation (leopard skin)
• Rough, fibrotic extended skin

Papular rash
Hypopigmentation
Subcutaneous nodules (containing adults with fibrotic tissue)

Diagnosis
• Specimens:
1- Skin snip
• Apply in microscopic glass slide, or emerge in test
tube
• Examine under the microscope, result:
• Motile, unsheathed thread-like microfilarea
• For confirmation: stain with Geimsa’s stain
2- Skin punch:
• Histopathology preparation, H&E staining

A
B
O. volvulus microfilaria
A: Unstained
B: Stained
Kin snip technique
O. volvulus microfilaria in
tissue preparation

Scabies (Sarcoptic mange) ‫الجرب‬

Sarcoptes scabiei (Mites)
 The human itch mite, is in the arthropod class
Arachnida, subclass Acari, family Sarcoptidae.
 The mites burrow into the upper layer of the skin but
never below the stratum corneum.
 The burrows appear as tiny raised serpentine lines
that are grayish or skin-colored and can be a
centimeter or more in length.
 It should be noted that races of mites found on other
animals may cause a self-limited infestation in
humans with temporary itching due to dermatitis;
however they do not multiply on the human host.

Lifecycle
 Human acquires scabies by direct contact with infested individual, or
through clothing, …
 This form molts into slightly larger nymphs before molting into adults.
 Larvae and nymphs may often be found in molting pouches or in hair
follicles and look similar to adults, only smaller.
 Adults are round, sac-like eyeless mites.
 Females are 0.30 to 0.45 mm long and 0.25 to 0.35 mm wide, and
males are slightly more than half that size.
 Mating occurs after the active male penetrates the molting pouch of
the adult female

Clinical presentation
 If a person has had scabies before, they become
sensitized to mites and symptoms generally occur
much sooner, within 1 to 4 days.
 Mites burrowing under the skin cause a rash, which
is most frequently found on the hands, particularly
the webbing between the fingers; the folds of the
wrist, elbow or knee; the penis; the breast; and/or the
shoulder blades.
 Burrows and mites may be as few as 10-15 in
number and can be difficult to find.

 Severe itching, especially at night and frequently over
much of the body, including areas where mites are
undetectable, is the most-common symptom of scabies.
 A more severe form of scabies that is more common
among persons who are immunocompromised, elderly, or
institutionalized is called crusted (Norwegian) scabies and
is characterized by vesicles and formation of thick crusts
over the skin, accompanied by abundant mites but only
slight itching.
 Complications due to infestation are usually caused by
secondary bacterial infections

Nodular scabies
Crusted (Norwegian) scabies

Diagnosis
 Most diagnoses of scabies infestation are made based upon the
appearance and distribution of the rash and the presence of
burrows.
 Whenever possible scabies should be confirmed by isolating
the mites, ova or feces in a skin scraping.
 Scrapings should be made at the burrows, especially on the
hands between the fingers and the folds of the wrist.
 Alternatively, mites can be extracted from a burrow by gently
pricking open the burrow with a needle and working it toward
the end where the mite is living.
 The extracted mite then can be identified by microscopy.

Scabies burrows
Adult female
Eggs

Adult mite in burrow in the stratum corneum

Pediculus humanus capitis
The Head Louse (
‫الشعر‬ ‫قمل‬
)
 The head louse is an ectoparasite insect whose only host are
humans.
 The resides close to the scalp to maintain its body temperature.
 The adult louse is about the size of a sesame seed, has 6 legs (each
with claws), and is tan to grayish-white
 In persons with dark hair, the adult louse will appear darker.
 Females are usually larger than males and can lay up to 8 nits per
day. Adult lice can live up to 30 days on a person’s head.
 To live, adult lice need to feed on blood several times daily. Without
blood meals, the louse will die within 1 to 2 days off the host.

 The majority of infestations are asymptomatic.
 When symptoms are noted they may include a tickling feeling of
something moving in the hair, itching, caused by the an allergic
reaction to louse saliva, and irritability.
 Secondary bacterial infection may be a complication.
 The diagnosis of pediculosis is best made by finding a live
nymph or adult louse on the scalp or in the hair of a person.
 Finding numerous nits within 6 mm of the scalp is highly
suggestive of active infestation.
 Finding nits only more than 6 mm from the scalp is only
indicative of previous infestation.

Phthirus pubis,
the pubic or crab louse (
‫العانة‬ ‫قمل‬
)
 The majority of infestations are asymptomatic.
 When symptoms are noted they may include a tickling feeling of
something moving in the hair, itching, caused by the an allergic
reaction to louse saliva, and irritability.
 Pruritis caused by the bites of pubic lice may be very intense,
and discoloration of the skin may occur if the infestation is left
untreated for an extended length of time.
 The diagnosis of phthiriasis is best made by finding a live
nymph, adult louse, or a nit on the hair of a person, usually in
the pubic or perianal area, although they may also be found on
armpit, moustache and chest hairs.

• What is the name of Leishmania parasite stage
that is found in human
• What is the vector and infective stage of
Leishmania parasite
• What are the clinical characteristics of L. tropica
ulcer.
• Mention three of skin lesions that are caused by
O. volvulus
• What is the causative agent of scabie?
• Why there is itching during lice infestation?

Skin Parasites Guide

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