Parasitology Lecture for MSKL
Parasitology Unit
Learning Objectives
( 1 ) To understand the main parasites that cause infection of the integumentary and
musculoskeletal systems , as regard their names and clinical significance
( 2 ) To understand the following parasites as pathogens of the integumentary and
musculoskeletal systems , as regard description of their structure , life cycle,
pathogenesis, and laboratory diagnosis
( A ) Leishmania tropica
( B ) Onchocerca volvulus
( C ) Trichinella spiralis
( D ) Sarcocystis
( 3 ) To understand the following parasites as skin pathogens, as regard outline of
their structure, life cycle, pathogenesis, and laboratory diagnosis
( A ) Sarcoptes scabiei
( B ) Pediculus humanus
( C ) 1Phthirus pubis
Main parasites  infection of Skin , Muscle , Bone
( 1 ) Leishmania tropica
Clinical Significance : Skin ulcer ( Cutaneous Leishmaniasis )
( 2 ) Dermatobia hominis larva
Clinical Significance : Skin ulcer ( Cutaneous Myiasis )
( 3 ) Onchocerca volvulus
Clinical Significance : Skin nodules
( 4 ) Trichinella spiralis
Clinical Significance : Muscle pain
( 5 ) Sarcoptes scabiei
Clinical Significance : Skin rash and itch
( 6 ) Pediculus humanus
Clinical Significance : Skin itch
( 7 ) Phthirus pubis
Clinical Significance : Skin itch
( 8 ) Echinococcus ( Hydatid Cyst )
Clinical Significance : Bone hydatid cyst  bone pain
2
Leishmania tropica
Structure : ( Amastigote stage ) Size : 3 um Shape : Oval
Life Cycle : When Sand Fly bites man it injects promastigote stage into skin
( this stage is found only in the Sand Fly and in the Culture Medium . It is
not found in skin lesion of man )  macrophage takes promastigote 
develop into amastigote stage which multiply  macrophage rupture 
release amastigotes  taken by Sand Fly  bite other man to complete
the life cycle
Pathogenesis : Multiplication of amastigotes inside macrophages is followed by
rupture and release of numerous amastigotes in subcutaneous tissue . The body
inflammatory reactions around amastigotes  granuloma  ischaemic ulcer
Laboratory diagnosis : ( 1 ) Microscopy Method ( sample is smear from skin
ulcer , examined for amastigote stage )
( 2 ) Culture
Method ( 3 ) Serology Method ( 4 ) Molecular Method
3
Right Upper : Leishmania skin ulcers Right Lower : Amastigote ( small oval bodies )
Left Upper : Animal host
Left Lower : Sand Fly environment
Copyright : Dr M Al Sagayer , Riyadh , KSA
4
Onchocerca
volvulus
Structure : ( Microfilaria stage ) Size : 300 um long Shape : round , no sheath
Life cycle : Black Fly injects microfilaria into skin  develop to male and
female adult worms  produce more microfilaria in subcutaneous tissue
 taken by Black Fly  bite other man to complete the life cycle
Pathogenesis : Microfilaria migrate in subcutaneous tissue  Body
inflammatory reactions around microfilaria & adult worms  nodule
formation
Laboratory Diagnosis : (1) Microscopy Method ( sample is skin snip
examined for microfilaria stage )
5
Onchocerca skin nodule ( From : www.medicine.mcgill.ca )
Onchocerca microfilaria ( From : www.pediatriatropical.com )
6
Trichinella spiralis , Sarcocystis
Trichinella spiralis
Structure : ( encysted larva ) Size : 0.1 mm Shape : round , like coil
Life cycle : Encysted larva in pig muscle  taken by man or animal  adult in
intestine  produce more larva  via blood  muscles
Pathogenesis : migrating larva cause allergic reactions and oedema , encysted larva in
muscle causes allergic reactions and pain
Laboratory diagnosis ( 1 ) Microscopy Method ( 2 ) Serology Method
Sarcocystis
This is a rare parasitic muscle infection in humans. Sarcocystis infection occur mainly in
animals eg sheep , pigs . Man is an accidental intermediate host . Sarcocystis
infection in man may cause myositis .
7
Right photograph : Dermatobia hominis larva
Left photograph :
Cutaneous myiasis ulcer
Copyright : Akhtar J , Qadri M , Abdelmageed Imam .
Saudi Medical Journal , 2000 , Volume 21 ( 7 ) , Pages 689 – 691
8
Sarcoptes scabiei , Pediculus humanus , Phthirus pubis
Sarcoptes scabiei
Structure : ( adult stage ) Size : 0.3 mm Shape : oval
Life cycle : Egg  hatch larva  develop to adult ( cycle is completed under the skin )
Pathogenesis : Female adult burrow into skin  lay eggs  itch
Laboratory diagnosis : Microscopy method
Pediculus humanus
Structure : ( adult stage ) Size : 2 mm Shape : oval
Life cycle : Egg  hatch nymph  develop to adult
Pathogenesis : Adult bite  itch
Laboratory diagnosis : Microscopy method
Phthirus pubis
Structure : ( adult stage ) Size : 1 mm Shape : oval
Pathogenesis : Adult bite  itch
Laboratory
diagnosis : Microscopy method
9
Sarcoptes skin rash ( From : www.skinsight.com )
Sarcoptes parasite ( From : www.en.academic.ru )
10
Good Parasitology References
( 1 ) Tropical Medicine & Parasitology
W Peters & G Pasvol , 5th edition , 2005
Mosby Publishers , US .
Note : 7 copies of this reference are
available in Qassim University
Library .
( 2 ) Parasitic Diseases Division , CDC ( US )
www.cdc.gov/nczved/divisions/dpd
11