1. 1
Classification & Visualization
of Infective Agents
Rumala Morel
Department of Parasitology

2. INFECTION MODULE 1 – Y2S2
SYSTEMATIC STUDY
OF
INFECTIVE AGENTS

3. 3
Infective Agents
Viruses
Bacteria
Fungi
Protozoa
Helminths
(Prions) – Infective proteins
Arthropods
Ectoparasites & vectors of disease
Spongiform
encephalopathy

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Visualizing microorganisms
• Different stains
• Microscopy - Light Microscopy
bright field
phase contrast
dark ground
fluorescent
Electron Microscopy

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1. CONDENSER lens
focuses light on the
specimen
2. Light then passes
through OCULAR &
OBJECTIVE lenses
Magnified Image
Bright field Microscope

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Dark ground
microscopy

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Phase contrast
microscopy
Dark ground
microscopy

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Visualization of Parasites
• Hand lens /magnifying glass
– helminth adults, arthopods
• Light Microscopy
– Low power x10 – helminth eggs
– High power x40 – protozoan cysts &
trophozoites
– Oil immersion x100 – protozoa eg. malaria
Technique depends on the degree of
magnification needed.
SIZE OF THE PARASITE

10. 10
Biological classification
Carolus Linnaeus – 18th century
(Systema naturae - 1735)
Grouped species according to
shared physical characteristics.
Introduced
Binominal classification:
Genus & species
eg. Homo sapiens

11. 11
First sorted into large groups and thereafter
subdivided to contain fewer and fewer organism
but sharing more and more common features
Biological classification - by Linnaeus - 18th century
Kingdom
Phylum
Family
Class
Order
Genus
species
Genus species
Binomial system
Plasmodium falciparum
Naming organism
Scientific names
italicize OR underline

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PROKARYOTE
Eg. bacteria
EUKARYOTE
Eg. protozoa

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Virus = an infectious
agent, consisting of genetic
material DNA or RNA wrapped up
in a protein coat.
100 x smaller than bacteria
Invades living cells and uses
them to keep itself alive and to
replicate itself.
Some viruses can cause life-
long and chronic infections
eg. Herpes viruses
Viruses

14. Viral classification
• DNA or RNA
• Size and Morphology
• Susceptibility to physical & chemical agents
• Symptoms
• Pathology
• Host and tissue tropism
• Transmission
• Immunological properties

15. VIRUSES

17. DNA RNA
• Parvoviridae
• Papovaviridae
• Adenoviridae
• Herpesviridae
• Poxviridae
• Hepadnaviridae
• Picornaviridae
• Reoviridae
• Togaviridae
• Arenaviridae
• Coronaviridae
• Retroviridae
• Bunyaviridae
• Orthomyxoviridae
• Paramyxoviridae
• Rhabdoviridae
VIRUSES

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SHAPE
Bacteria
Classification
is based on SHAPE

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Bacteria
Gram POSITIVE Cocci Gram NEGATIVE Bacilli
Gram POSITIVE Bacilli Gram NEGATIVE Cocci
in clusters in chains

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Fungi
Yeasts & Moulds

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Yeast
Cryptococcus
Yeast-like
Candida
Moulds
Dermatophytes
Dimorphic fungi
Histoplasma

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Parasites
Sporozoa Amoebae
Flagellates
Microsporidia
Roundworms Flatworms
Cestodes Trematodes
Nematodes
Ciliates
HelminthsProtozoa
Arthropods

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• Unicellular
• Animal like cells - heterotrophic nutrition -
require preformed organic substances
• Classified according to method of
locomotion
• Trophozoites - actively feed and multiply
• Cysts - resistant walls
• Most free-living
Protozoa
Binary division

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Protista (protozoans – unicellular, eukaryotic)
(1)AMOEBAE
Trophozoites & Cyst
(growing stage)
pseudopodia
(false feet)
(3) CILIATES
Balantidium coli- cilia(2) FLAGELLATES
Giardia lamblia
flagella

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(4).Apicomplexa
= SPOROZOA
No organelle for
motility
(5). MICROSPORIDIA
spore-forming
Plasmodium Coccidia

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PARASITIC PROTOZOA
1.Sporozoa
2.Amoebae
3.Flagellates
5. Microsporidia
Toxoplasma gondii – toxoplasmosis
Cryptospordium spp. - diarrhoea
Entamoeba histolytica – amoebiasis
Giardia intestinalis – diarrhoea
Trichomonas vaginalis – trichomoniasis
Leishmania spp. – leishmaniasis
Trypanosoma spp. - trypanosomiasis
4. Ciliates Balantidium coli - balantidiasis
Plasmodium spp.- malaria
Babesia - babesiosis
b).Coccidia
a).others

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• 200 million cases of malaria annually
• Killed more humans than any other disease.
• 1 million deaths /year. 90% in sub-Saharan
Africa, an African child dies of malaria every 30
sec.
• Over half the world's
population live in
malarious areas
Malaria
Finger prick screening for
MP = Malarial Parasite

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• Main causative organism - Entamoeba histolytica
• Other causes – Balantidium coli, Trichiuris trichiura
• Invade colonic mucosa ulcers
Parasitic diarrhoea – Blood & mucous
Blood & mucous
diarrhoea
=
Amoebic dysenteryPortal vein (blood)
Liver Amoebic hepatitis
Amoebic liver abscess
Entamoeba trohpozoiteEntamoeba cyst

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Parasitic watery diarrhoea
Giardia duodenalis
causes giardiasis
Cryptosporidium
spp. causes
cryptosporidiosis
Persistent diarrhea in
AIDS,
other
immunosuppressed
CystTrophozoite

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Toxoplasma
encephalitis –in
AIDS
Congenital
Toxoplasmosis
Microcephaly

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3 types
• Visceral – Mediterranean, India
• Mucocutaneous (Espundia)
– South America
• Cutaneous – skin ulcers
Leishmaniasis
Leishmania donovani
In Sri Lanka
Visceral,
Cutaneous
& Mucocutaneous

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Helminths
ROUNDWORMS
=
NEMATODES
FLATWORMS
TREMATODESCESTODES

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NEMATODES
 Cylindrical
 Sexes separate- male smaller
 Muscular outer wall - organs are suspended in a
false body cavity (pseudo coelom)
 4 moults in Life Cycle
 INTESTINAL
 TISSUE
cuticle
muscle layer
body
cavity

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Enterobius vermicularis
(kiri panuwa)
Transmitted from
person to person
GEOHELMINTHS
(soil transmitted worms)
Ascaris lumbricoides
Trichuris triciura
Strongyloides stercoralis
Hookworms–
Necator americanus (In SL)
Ancylostoma duodenale
Commonest helminthiases (worm infections) in SL
Nematodes

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Whipworm = Trichuris trichiura
Soil transmission similar to Ascaris
+ direct feco -oral
Trichiuris eggs Trichiuris adults Ascaris adults

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Hookworms
Pallor/Anaemia
due to blood loss
Adult – 1 cm
Sucking blood in
intestine

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Larva currens –
Cutaneous Larva
Migrans = CLM
Disseminated disease in immunosuppressed
NO EGGS in stool
Only rhabditiform larva in stools
Strongyloidiasis
Strongyloides stercoralis

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Phylum- PLATYHELMINTHES
Flatworms
• Class- Cestodes/
Tapeworms
• Class- Trematodes/
Flukes

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Features common to Cestodes 1
• Morphology: Flat, ribbon like.
• Location: Adults in intestinal tract of
vertebrates.
• Size
Echinococcus granulosus
Taenia
few milimeters 10 metres

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• Head: “Scolex”/ “Hold-fast” organ - attach to host’s
intestine
• Scolex: sucking grooves, hooks or suckers
• Hermaphrodite: segments have both testes &
ovaries (male & female together)
• No alimentary tract: absorption through body wall.
Features common to Cestodes 2

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Trematodes- flat & leaflike,
sexes not separate
(except in blood flukes)
• Water borne
[Schistosomes = blood flukes]
• Food borne
[tissue flukes]

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Class- Trematodes
• Blood Flukes• Tissue Flukes
Tissue flukes
hermaphroditic
Schistosomes
2 sexes are
separate

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ARTHROPODS 1
1. Mosquitos- transmit most important vector borne
diseases in Sri Lanka
2. Lice - Head louse & body louse
- Pubic louse
transmit Louse-borne relapsing fever, Epidemic typhus,
Trench fever
3. Fleas - transmit plague, murine typhus
4. Flies - sand fly – transmit leishmaniasis
CLASS INSECTA

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Mosquito borne diseases

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Mosquito borne diseases
• Arboviruses
– Yellow fever
– Dengue
– Japanese
encephalitis [JE]
– Chikungunya
• Protozoa – Malaria
• Helminth - Filariasis
Anopheles
Malaria
Aedes - Dengue
Culex – filariasis
- JE
Control – find
mosquito larva
& eliminate
breeding places

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ARTHROPODS 2
Mites - Scabies mite = Sarcoptes scabieii
-Trombiculid mite larvae – transmit
scrub typhus
CLASS ARACHNIDA
Ticks - transmit tick-borne viral encephalitis,
rickettsiae
&

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Fleas are vectors of
PLAGUE
Scabies spread
by
scabies mite
Ticks spread
rickettsial &
viral
disease